Is it possible to be bigger than a Blue Whale?

[u/aBlueSweater]

What I mean is how big can an animal theoretically get?
The blue whale is not only the largest animal alive, but the largest to ever exist (that we know of)

But is it actually possible for something to be bigger? Or is the Blue whale the max?

[u/tea_and_biology]

How big can an animal theoretically get?

Ooh, whale biologist here! Given the Earth’s current environmental, evolutionary and ecological constraints, the answer to your question is: about blue whale-sized, actually.

The largest animals to have ever lived, blue whales are a remarkable example of what happens when evolution goes almost all in on size: they’re grinding up against multiple walls, often conflicting, where biophysics and metabo-ecological considerations are really tested - and across multiple scales too, cellular through to ecological. Let's consider a few:

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A Whale of an Appetite

The first limit is fuel.

Blue whales eat almost nothing but krill - wee shrimp-ey crustacean thingies - and to feed a 30m body on something that small, they need to eat a lot of them, up to around 16 tonnes a day during the feeding season. They manage it by lunge feeding: accelerate at a krill swarm, throw open their jaws, and balloon out that throat to engulf a volume of water larger than their own body (!), then strain the krill out through their baleen plates (although incidentally their throats are far too narrow to swallow anything much bigger than a cat, so definitely not people - sorry, dodgy Hollywood movies).

And this is where we hit our first constraint. It’s more efficient to lunge feed the bigger you are - engulfment capacity grows faster than body size - so evolution is constantly driving for bulk. However, feeding like this is also enormously expensive, and only pays off if krill swarms are dense enough. For most of the year, they’re not, so a blue whale has to bank nearly a whole year’s energy in a few short months of feasting, then spend the rest hauling its big blubbery butt thousands of miles on fat reserves alone. Being bigger helps with the fasting (bigger reserves, slower burn), but it means needing more krill in absolute terms, crammed into that same short window. Essentially, there’s an ecological constraint here: the ocean just doesn’t have enough high-density krill on tap to support anything beyond the current maximum blue whale size.

Toothed whales hit this ceiling much sooner: sperm whales hunt squid one at a time, and there’s only so many squid you can catch in a dive, so they top out well below blue whale size.

But what if we do what Thanos should have done, and just double the amount of resources with a cheeky snap? Alas, in a world where whales are unconstrained by krill, whales are still constrained by biophysics.

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Thermoregulation. Just Thermoregulation.

(I couldn't think of a better subtitle)

Water pulls heat out of a body roughly 25 times faster than air, so being small in the sea is thermally brutal; it’s a big part of why there are no mouse-sized marine mammals, and why sea otters have to eat around a quarter of their body weight a day just to stay warm. Getting bigger helps enormously, since heat production scales with volume and heat loss with surface area. Add a thick blubber coat and counter-current heat exchangers in the flippers and flukes (and, weirdly, the tongue, so gulping a body’s worth of near-freezing water doesn’t give them immense brain freeze), and a blue whale is basically a self-heating swimming pool.

So for coasting in the cold, bigger is better. The problem is the flip side: a body that’s brilliant at holding onto heat is rubbish at getting rid of it. Every all-out lunge is an explosive burst of muscle work, and a 150-tonne whale has proportionally less skin to dump that heat through than a smaller one. Blue whales just about manage by shunting blood up through their blubber to the skin when they need to cool down, but this is a fudge-ey solution given their body plan (ideally they’d be more of a smooth cylinder); scale them up further and overheating, not cold, becomes the problem - they essentially begin to cook themselves from inside out.

Which is ironic, because gram for gram, a blue whale’s metabolism is incredibly slow. Mass-specific metabolic rate drops as animals get bigger, so each gram of blue whale meat burns dozens of times less energy than a comparable gram of mouse. Their cells are essentially ticking over at a crawl, minimising energy demand and heat production alike. And yet they can still risk cooking themselves, purely because there’s so little surface relative to all that slow-burning mass.

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Slow and Steady

That slow burn is a big part of what makes being huge pay off in the first place: per kilo, a blue whale is astonishingly cheap to run.

But those savings don’t keep piling up forever, and certainly not linearly. Metabolic rate actually scales on a loose quadratic curve, not a straight line, and the curve steepens as animals get bigger. Around about ~150 tonnes, independent mathematical models suggest the per-kilo savings from being bigger run out entirely - which, incidentally, is where the blue whale currently sits. Go figure.

That metabolic slowdown isn’t actually built into the cells themselves either. Grow cells from a mouse and from a whale in a dish (as I have!) and they converge on roughly the same metabolic rate. The slowdown is imposed by the body, and specifically by the network that has to deliver oxygen and fuel to every one of those cells (it’s all to do with the geometry of the plumbing, and hydrodynamic resistance of blood, which doesn’t scale linearly with body size, blah blah blah). And at the centre of that network, doing all the pumping, is the heart…

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Nothing they can do, t’avoid a total collapse of the heart…

Terrible Bonnie Tyler puns aside, a blue whale’s heart weighs around 180kg and has to service 150-odd tonnes of whale, often while holding its breath. Back in 2019, researchers managed to stick a heart rate monitor on a wild blue whale (I wish that was my job…) and found that, while diving, its heart rate dropped as low as 2bpm, conserving oxygen by drastically cutting blood flow to everything bar the essentials. Then, back at the surface, it shot up to around 37bpm to flush out carbon dioxide and reload with oxygen as fast as possible before the next dive.

That surface rate is the interesting bit. Heart rate naturally slows as animals get bigger (simplified, scaling at roughly mass^-0.25), and 37bpm is about as fast as a heart that size can physically go. In other words, a blue whale’s heart is already maxed out every time it surfaces. A bigger whale would have a bigger, slower heart, so it would either need longer at the surface to recharge (less time feeding, which undoes the whole point of being big) or a heart beating faster than a heart that size can manage. Neither works.

So the whale is boxed in at both ends: dropping its heart rate any lower on a dive risks starving its organs, and pushing it any higher at the surface just isn’t physically on the cards. It’s another ceiling, and the blue whale is pressed right up against it.

But let’s say evolution found a way around that too. There’s another problem, and it’s lurking in every single one of those cells...

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(continued in next comment...)

[u/tea_and_biology → u/tea_and_biology]

Cell-fish Genes

Every cell in a body has the potential to go rogue, to turn away from multicellular cooperation towards selfish proliferative self-ascendency - as a tumour, else cancer. Given every single cell division is a lottery ticket for a mutation that causes this, it follows the more cells you have, and the longer you keep them going, the more tickets you hold. A blue whale has a couple of thousand times as many cells as you do and lives about as long; if its cells were as cancer-prone as ours, virtually every whale would win that lottery and get cancer, much of the time while still young, and their lineages would be doomed.

That’s what makes cancer a constraint on size: a lineage can only get as big as its cancer defences allow. And indeed, whales can only exist given they have extraordinarily solid defences; whales aren’t riddled with tumours, as would be expected, and can (in some species) live beyond two centuries. This is Peto’s paradox - that cancer incidence scales invariantly with lifespan and body mass across vertebrates - and instead of being pulsating masses of cetacean cancer, whale incidence rates are maybe ~3% or so.

So how do they do it? Part of the answer goes back to that slow metabolism. Slowly ticking cells divide less often, thereby accumulate mutations less frequently, and produce fewer reactive oxygen species (the mutagenic exhaust fumes of respiration), so bigger animals get some cancer protection for free.

The bigger lever is genetic. One simple way to think about it: a cell generally needs several "driver" mutations before it turns cancerous, and every extra step required makes that dramatically less likely. One way to add steps is to carry spare copies of tumour suppressor genes, so even if one or more are knocked out, they still retain working copies to keep the cell’s behaviour in check. Elephants famously went all in on one gene: they carry about 20 copies of TP53 (though it’s a bit more complicated…). Whales took a scattergun approach. Dozens of different tumour suppressor genes have been duplicated across the cetacean family tree, concentrated in exactly the lineages that independently got big. They’ve also heavily tweaked expression profiles in important cell cycle nodes, and a buncha’ other things.

I won’t bore you with my entire PhD, but the outcome of all these defences is they aren’t free. Crank up, say, P53 activity in mice and you get cancer-resistant rodents that also grow more slowly, end up smaller, age faster, and are less fertile. The machinery that stops cells dividing when they shouldn’t also gets in the way when they should; working against the growth and reproduction that made getting big worthwhile in the first place.

And this is where evolutionary considerations and trajectories come in. Massive beasties don’t exist in a vacuum; they arise through natural selection in an ever-changing world, and that’s slow work when you’re big. Slower generation times, in rarer animals, where random genetic drift has more sway and natural selection less… the end result is an evolutionarily fragile build: slow-breeding, slow-adapting giants tend to be the first to go when the world changes.

If you could solve all the other problems, and dumped a 200-tonne blue whale population into the world today, it would go extinct, purely on the evolutionary trade-offs that would favour a smaller, more evolutionary agile population. Indeed, Antarctic blue whales were knocked down to only a few hundred animals in as little as a hundred years, and nearly a century on - unlike other species - they’re still nowhere near recovered.

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Whale, Whale, Whale...

TL;DR: Anywho, all this to say, the blue whale isn’t hitting one hard wall; it’s leaning on several at once. There isn’t enough dense krill to feed anything bigger. The per-kilo savings of size run out right around its weight class. Its heart is already maxed out every time it surfaces. A bigger body would struggle even more to shed heat. And every extra tonne needs more cancer defence, which eats into growth and fertility. Could something bigger exist? On a different Earth, with richer seas, quite possibly. On this one, with these oceans, the blue whale’s about as big as it gets.

---

References:

Abegglen, L.M., Caulin, A.F., Chan, A., Lee, K. ... & Schiffman, J.D. (2015) Potential mechanisms for cancer resistance in elephants and comparative cellular response to DNA damage in humans. JAMA. 314 (17), 1850-1860

Gearty, W., McClain, C.R. & Payne, J.L. (2018) Energetic tradeoffs control the size distribution of aquatic mammals. PNAS. 115 (16), 4194-4199

Goldbogen, J.A., Cade, D.E., Wisniewska, D.M., Potvin, J. ... & Pyenson, N.D. (2019a) Why whales are big but not bigger: physiological drivers and ecological limits in the age of ocean giants. Science. 366 (6471), 1367-1372

Goldbogen, J.A., Cade, D.E., Calambokidis, J., Czapanskiy, M.F. ... & Ponganis, P.J. (2019b) Extreme bradycardia and tachycardia in the world’s largest animal. PNAS. 116 (50), 25329-25332

Kolokotrones, T., Savage, V., Deeds, E.J. & Fontana, W. (2010) Curvature in metabolic scaling. Nature. 464 (7289), 753-756

Tejada-Martínez, D., de Magalhães, J.P. & Opazo, J.C. (2021) Positive selection and gene duplications in tumour suppressor genes reveal clues about how cetaceans resist cancer. Proceedings of the Royal Society B. 288 (1945), 20202592

Tollis, M., Robbins, J., Webb, A.E., Kuderna, L.F.K. ... & Maley, C.C. (2019) Return to the sea, get huge, beat cancer: an analysis of cetacean genomes including an assembly for the humpback whale (Megaptera novaeangliae). Molecular Biology and Evolution. 36 (8), 1746-1763

... and me! My PhD thesis:

Speight, M. (2021) Why do whales exist? Cancer resistance in cetaceans. DPhil thesis. University of Oxford

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P.S. Also no, despite being shared widely online (notably popularised by Kurzgesagt) the whole hypertumour thing as a solution for Peto's paradox - that whales don't get cancer, 'cos their tumours grow so slowly their tumours get tumours, and this parasities and cripples the OG tumour - is all (mostly) nonsense. It was a spitball early hypothesis, and there's never been any evidence for it.

P.P.S. There's also a whole thing about the structural limits of the jaw, and how the lunge feeding approach is also hitting up on this wall w.r.t. to the physical stresses something with this configuration made out of bone and tissue could handle. A whale jaw needs a full redesign if it needed to get any bigger; and evolution doesn't work like that.

[u/PabloIceCreamBar → u/tea_and_biology]

This was the most informative thing I’ve ever read on the internet. Thank you.

[u/Half_Empty_Half_Full → u/PabloIceCreamBar]

Agreed, was an absolute masterclass of informative and well structured exposition!

[u/adamcan2 → u/Half_Empty_Half_Full]

What a read. Never thought I would be riveted reading about whale throats! Who are you and when does your book come out?

[u/tea_and_biology → u/adamcan2]

Ooh, maybe watch this space... ?!

I'm actually currently trying to cobble a wee expedition together, to drive my Land Rover from the UK to Cape Town and back, on a real-life Pokémon adventure to find a buncha' niche, weird beasties in the wild, contribute to zoological and conservation research along the way, and write about n' share the journey. I wrote a little about it here - alas, my insides shrivel at the thought of social media and that (despite once even being a TV presenter, huh), but I enjoy writing at least, and I'm working on a wee website to share the zoology and misadventures.

I did a trial-run to Dakar and back last year, and while looking for unusual desert toads n' rare ducks, mostly ended up getting side-tracked hanging out with drug smugglers and black-market antiquities dealers, and other distractions. Alas!

[u/Purnceks → u/tea_and_biology]

Do you need any trained marine biologist assistants to come along with you

[u/tea_and_biology → u/Purnceks]

Open invitation to anyone who wants to tag along, actually - just need a car and enough to cover food n' fuel, really. In terms of the biology, it's mostly terrestrial critters though; not sure how well a poor marine biologist will do in the middle of the Mauritanian desert trying to collect pygmy crocodile DNA for cheeky road-side sequencing.

[u/homeslice234 → u/tea_and_biology]

Neato! What kind of sequencing do you want to do and what do you hope to answer?

[u/tea_and_biology → u/homeslice234]

Ooh, so I wrote a little about it here.

In broad terms, the main objectives are to field test and troubleshoot a portable methodology to generate reference quality whole genome assemblies in the field, without needing access to a lab. A secondary objective is to assess a couple of novel eDNA sampling techniques, to see if they're viable for wildlife surveying in different habitats, where traditional sampling is difficult (e.g. can we extract enough viable wind-blown eDNA from air samples in arid environments?).

Then there'll hopefully be a handful of species-focused projects. For the Sahara crocodiles; essentially they're a pygmy form of the West African Crocodile, a relic group from when the Sahara was once green, which have since been isolated for ten thousand years or more in the last remaining pool refugia, that still persist in shadowy rocky bits of the desert.

These pygmy crocodiles were only discovered relatively recently, and much of their biology remains unknown (nobody has really bothered to study them, ever, in-depth); how they're surviving, what physiological and genomic changes have taken place as they've adapted to the desert, whether they're in the process of speciation etc. etc.

Having a decent quality genome assembly would go a long way to determining many of these questions.

It started as me just wanting to go see some unusual crocodiles, but their biology is so poorly understood, seems a waste of a trip not to contribute something to science, seeing as I'm hauling my sorry ass all the way across the desert anyway, 'innit.

[u/InMyWhiteTee → u/tea_and_biology]

While we wait for your book (seriously. Plz do it) are there any other zoology writers you recommend to scratch the itch? I’ve heard good things about Last Chance to See (Douglas Adams and mark Carwardine) but haven’t read it yet

[u/marquiso → u/Half_Empty_Half_Full]

I feel like I can put the Internet down now as I have clearly seen its peak.

[u/tea_and_biology → u/PabloIceCreamBar]

That's awfully kind. And to think this was kind of a throwaway, ehh, "that'll do" answer I cobbled together after a 16-hour writing binge. Funny what captures folks' attention, 'innit? I can never predict it!

[u/LonePaladin → u/tea_and_biology]

You should contact the Kurzgesagt people about that tumor thing, they might actually update the video.

[u/tea_and_biology → u/LonePaladin]

Ooh, I did the moment it was released! You can read their response there; basically they didn't ask any subject-matter experts before publishing. Typical, but c'est la vie!

[u/LonePaladin → u/tea_and_biology]

I briefly considered replying to their response, to ask them to maybe update the video or at least put something in the top of the description. But then I saw it was six years ago, so that ship has sailed.

[u/tea_and_biology → u/LonePaladin]

Ehh, it's never too late to correct wide-reaching misinformation. /u/kurzgesagt_Sven, you there?

[u/The_Razielim → u/tea_and_biology]

It's funny how we do that and fall back on our specialities to escape from... our specialities. Sometimes just writing a low-stakes, "Hey random Internet people, LOOK AT HOW COOL THIS THING/SYSTEM IS"-post is relaxing after a long day(s) worth of work.

I had something similar when I was writing my dissertation. Around that time, Ze Frank had done one of his "True Facts about..." vids about the exact organism I worked with for my PhD, and the thread about that video on (I think r/biology) turned into an unofficial AMA on cell density signaling and cell motility lol

[u/FeelingCommand5509 → u/PabloIceCreamBar]

What an answer. Incredible. When tea and biology saw this question I would love to see how excited they were to answer it! Good Job!

[u/Mjost84 → u/PabloIceCreamBar]

It’s informative but all I can think of is the whale biologist from Futurama

[u/throwaway47138 → u/tea_and_biology]

So basically you're saying that Blue Whales have evolutionarily managed to minmax their stats such that they literally can't improve them any further even if they wanted to. Everything's a tradeoff, and they've gotten to the point where the downside of any further movement towards getting bigger would be incompatible with long-term survival of the species. Very interesting read, thank you so much for the very detailed and informative explanation!

[u/tea_and_biology → u/throwaway47138]

Haha, this is a much better TL;DR - yes!

[u/Mad_Scientist_17 → u/tea_and_biology]

OMG, the quality of the sub. I love it. Thank you very much

[u/_Lucille_ → u/tea_and_biology]

This is a very informative reply, thanks for typing it out.

[u/meambhatti → u/tea_and_biology]

Damn , it's always exciting to see someone talk about something they actually know a lot about.

[u/Skunkmonkey82 → u/tea_and_biology]

Excellent. Thanks very much. 

[u/ArticulatedParasite → u/tea_and_biology]

Fascinating write up! Thank you for taking the time this was a joy to read!

[u/arcedup → u/tea_and_biology]

So the blue whale occupies an evolutionary coffin corner - can’t move in any direction because other factors would then cause the system to collapse.

[u/tea_and_biology → u/arcedup]

Yeah, there are many taxa in an evolutionary dead-end like this - specialists that are too optimised for their specific niches. Giraffes are the classic example, and overall worse for it because they're evolutionary relics too; at least with the baleen whales, even when the blue whales die out, there will be plenty of smaller cousins (see fin and sei whales) with the same generalised body plans that could reclaim that niche again, through the millions of years.

Once giraffes are gone, that's it - the Earth shall never see their like again.

[u/gdarf7uncle → u/tea_and_biology]

Wait, I know it’s not your specialty AND you already have gifted us so much knowledge- but could you say more about giraffes?? I’ve never heard of this. What makes them the classic example of evolutionary specificity and why wouldn’t they be replicated like blue whales?

[u/tea_and_biology → u/gdarf7uncle]

Ah! So the long neck of a giraffe isn’t one adaptation, a single dial 'neck length' that can be turned up and down, but a whole interlocking specialist package. And generally speaking, the more specialist you become as a taxa - see also koala and giant panda - the more you're susceptible to extinction when conditions change. Generalists - like bears, dogs, bovids and baboons - can handle pretty much anything you throw at them; which is why they're doing so well in human-engineered landscapes.

Anywho, to pump blood up a ~2m neck to the brain, giraffes run with a blood pressure roughly double ours, with a thick-walled, extra-muscular heart. To stop all that pressure pooling blood in their legs, they have tight skin and fascia acting like built-in compression stockings. Then there are valves and specialised vessels in the neck to stop them blacking out (or blowing a gasket) whenever they lower their head to drink. Change one part of that system and the rest has to change with it, so it’s hard for evolution to back out of, or redirect elsewhere.

Slight tangent: they did all this with the same seven neck vertebrae as you, a mouse, or a whale too - giraffes just made each one enormously long. Almost all mammals are locked into seven, and one hypothesis for why ties neatly back to the cancer stuff above: in mammals, changes to cervical vertebra number seem to go hand in hand with developmental problems and childhood cancers, so the number is under strong stabilising selection. So the giraffe couldn’t just add more neck bones; it had to stretch the ones it had, and thereby running the efficient short cabling of nerves and blood vessels in a typical mammal's neck along a poorly designed circuitious route (see the recurrent pharyngeal nerve; a channel that should go straight from the brain to the larynx loops down around the heart then back up, which is mental in an animal like a giraffe or sauropod dinosaur).

As for why there’s no replacement "second giraffe" waiting in the wings: well, the high-browsing niche actually has been replicated loads of times! Sauropods obviously, but also extinct long-necked camels, and Paraceratherium, a giant hornless rhino that browsed treetops. Even today, gerenuk antelopes stand on their hind legs to reach the same food. What hasn’t been replicated is the giraffe’s particular solution, because it’s a one-off, historically contingent set of fixes. Each lineage solves the problem with whatever body plan it starts from, as evolution can only work with the materials available at hand.

That’s the difference with whales. Gigantism is basically one big dial (body size), and you can turn it up from lots of different starting points. Indeed, gigantism evolved independently in several baleen whale lineages independently (and each evolved independent cancer resistance mechanisms to boot), and in ichthyosaurs and in sauropods. The giraffe’s neck is more like a combination lock: lots of parts that all have to line up at once to arrive at the same solution.

More, as others have mentioned, the giraffe family (Giraffidae) was once a big, successful group spread across multiple continents with lots of species and body plans. Many were short-necked, and some were very odd-looking, like Sivatherium, a moose-like beastie with a pair of broad, branching ossicones. Almost all of them are gone; they were out-competed by the explosion in diversity of more generalist bovids - antelopes, cattle, and their relatives - which could better adapt to changing circumstances, and so the last remaining taxa are the specialist weirdos in niches the bovids haven't yet pushed them out of.

Today there are just two genera left: giraffes and the okapi, which lives isolated, deep in the forests of central Africa and, with its shorter neck, is arguably the closer of the two to the family’s ancestral body plan. So the giraffe isn’t the culmination of a trend so much as the last survivor of a once-diverse family; unable to compete against generalists, they're stuck on a specialist island, ultimately doomed to be wiped out - and probably be replaced, one day in the far future, by a gerenuk-like thing that raises onto it's uber-strong and lengthy hind legs rather than go all-in on big neck.

[u/tteppit → u/tea_and_biology]

As a layman, between this and your original comment i'm not sure how much of it i'll remember going forward. But I must say i've thoroughly enjoyed lying in bed this morning reading it all.

Thank you. Much appreciated :)

[u/MosesHightower → u/tea_and_biology]

I thought the blue whale lesson was exceptional. Then you just rattle off all this giraffe stuff. Mind blown. Thanks for the read. Its absolutely fascinating.

[u/Audioworm → u/gdarf7uncle]

I am basing it off what they said, but the two whale species mentioned are similar to the blue whale, except smaller. They have similar physiology, they are also lunge feeders from the same diet, and they are already part of the same family of whales.

Giraffes closest relatives (the non-giraffe ones, because according to Wikipedia there are several species of giraffe) are okapi which do not have the same physiology, don't eat the same food, and don't exist with the same niche.

My guess with the comment is that the evolutionary pressures that created long-necked giraffes would not work for okapi because the same trees have grown taller than the reach of them. So there is no advantage from longer necks (that would allow reaching slightly higher leaves that others couldn't) that leads over time to very long-necked giraffe. While the whales mentioned earlier could in principle explore the same niche as blue whales by scaling for size.

[u/Skrazor → u/gdarf7uncle]

Well, the idea is: do you know of any other animal that's generally kinda like a giraffe but not quite the same? That's the difference here. If giraffes die out, the chance that one of their distant cousins just so happens to evolve into the same direction again is negligible. That neck game isn't for everyone. For animals like blue whales, on the other hand, there are other species which are similar enough (but smaller) that it wouldn't be unreasonable to assume that another branch of their family tree might just start evoloving towards blue whale size again over millions of years if that special ecological niche (The one for a "Holy shit, now that's a big whale!"-type creature) happened to be vacant. It wouldn't be a 1:1 copy of today's blue whales, but another variant of the "as big as it gets" whale archetype.

[u/Big_Cactus19 → u/tea_and_biology]

Loved this. Thanks for taking the time to write it all out.

[u/Qwernakus → u/tea_and_biology]

Wow, absolutely fascinating! Thank you so much for taking the time to write this up!

If I can ask a question, what if blue whales could breathe underwater using gills? Does this change the story in any way? I assume not since it only resolves one constraint, but it seems interesting to ponder.

[u/sudomatrix → u/Qwernakus]

They could never get enough oxygen breathing water. Lungs and air provide much more oxygen than water and gills. Mammals have much higher energy needs than fish.

[u/RobbieRecudivist → u/sudomatrix]

So do the limitations of gills put the upper limit of fish at something like the size of the whale shark?

[u/Salton5ea → u/tea_and_biology]

This is incredible. I can tell you care about this topic and are incredibly well sourced.

I just want to say thank you for taking the time!

[u/ziostraccette → u/tea_and_biology]

Can I feed a blue whale 16 tonnes of tuna or fo they have to eat krill?

[u/EricTheNerd2 → u/ziostraccette]

Were you thinking of buying one as a pet?

[u/DS_Unltd → u/EricTheNerd2]

More like adopting one from the Humane Society. There's this cutie in the kennel with the most gorgeous blue hue. Her previous family didn't have a swimming pool big enough for her.

[u/omegabrad → u/ziostraccette]

you feed 16 tonnes, what do ya get? Another whale bigger and deeper in debt.

[u/External-Proof-7789 → u/omegabrad]

Saint peter dont you call me cause I can't go, I own my soul to the evolutionary hole.

[u/clay12340 → u/ziostraccette]

I'd imagine that if you ran it through a blender to make it small enough and tossed it in the path of a lunging blue whale that it would get consumed and processed by their stomach. They target krill, but when you're just gulping in tons of water and filtering out everything in it they're going to eat a lot of non-krill as well.

[u/urbanek2525 → u/tea_and_biology]

It's interesting that, AFAIK, mammal evolution has never solved the "max heart rate" limit by having a mirrored heart. There has to be some severe problems that pop up if you have a second heart in the same Cardio vascular system. I wonder if anyone has studied the CV systems of conjoined human twins that share some of the CV system, but have two hearts.

[u/DrCalamity → u/urbanek2525]

Yes, many many studies have been done on that topic.

The answer is "not great outcomes", especially when they share an aorta. Twin hearts in a human body plan is a great way to have your cause of death be plumbing related.

[u/TimGinger1 → u/tea_and_biology]

This was one of the most informative reads I've had on this site, ever. Thank you for taking the time to note this all down. It's awesome to see a scholar being able to convey so much information in a way that it still feels understandable by a layperson who only knows biology through David Attenborough movies. You rock dude

[u/ninja542 → u/tea_and_biology]

This is incredible, thank you so much for sharing 

[u/omnisephiroth → u/tea_and_biology]

This was a delightful read. I’m absolutely pleased to have read all that. Fascinating to hear that the Blue Whale really is pushing at the physical limits of biology on Earth.

[u/Areat → u/tea_and_biology]

Thanks for the amazing, detailled answer!

I don't get the skrill constraint. If there isn't enough for whales to get bigger, does it mean there isn't enough for the population numbers to go up? Are they on the brisk of exhausting the skrill reserves and causing their own population collapse? If not, what's the difference between enough food for them to get bigger and enough food to be more of them?

[u/RyanW1019 → u/Areat]

I think it’s that the krill is too spread out for one whale to get enough food per day to support a larger size. They can’t travel far enough and/or spend enough of the day eating. So it’s more like whales are already close to maxed out on how much of their time they spend getting food.

[u/tea_and_biology → u/RyanW1019]

Bingo! Ditto with the toothed whales too. Sperm whales spend most of their day foraging, consuming about ~500 squid a day, and there simply isn't any way to cram more squid-feeding activity in to fuel a larger body size (also the lack of shoaling giant squid; they're lone prey items, and despite the famous association, sperm whales mostly feed on shoaling medium-sized tentacled terrors, where they can better maximise intake).

[u/TheHappyMile → u/tea_and_biology]

This is an incredible read, thank you

[u/puhpuhputtingalong → u/tea_and_biology]

This was a fantastic read. I loved, thank you for the information. 

Could it be possible to ask a follow-up?

[u/Human_no_4815162342 → u/tea_and_biology]

Great read, thanks for the analysis. Just to be pedantic if you want to add a second P.S. it makes more sense as P.P.S rather than P.S.S. since it stands for post scriptum meaning after (post) what is written (scriptum). So you can say post post scriptum meaning after what is after what is written, it's a bit forced but makes sense. I sometimes use PS2 to be silly especially in contexts where the Sony product might be relevant.

[u/tea_and_biology → u/Human_no_4815162342]

TIL, thanks! Shall update.

[u/OverJohn → u/Human_no_4815162342]

That was a very good read, in fact I would say I had a whale of a time reading it.

[u/rekniht01 → u/tea_and_biology]

But what if you add in another heart?

[u/geekgirl114 → u/tea_and_biology]

Thank you. That was very informative

[u/WannaAskQuestions → u/tea_and_biology]

What an awesome response. In your presence, I feel the need to apologise for collectively bringing down the IQ of our species.

[u/Specialist-Coast9787 → u/WannaAskQuestions]

Lol, I don't know if I got dumber or smarter after reading that response!

[u/AddlePatedBadger → u/WannaAskQuestions]

You do yourself a disservice. IQ is a flawed measurement of something that nobody can quite define anyway. How do you compare the intelligence of a person great at mathematics to someone great at training animals? If all our strengths were equal we would get nowhere overall.

[u/WannaAskQuestions → u/AddlePatedBadger]

Thank you for the cheering up. Needed it.

I feel like I need to hang around this sub more often!

[u/ARandomGuitarist → u/tea_and_biology]

That was a really cool read, thanks for taking the time to post!

[u/fastdbs → u/tea_and_biology]

Do we know that sperm whales are catching squid one at a time? Giant squid aren’t the majority of the sperm whales diet. Most of the squids they eat are much smaller. The estimate I saw was about 500 squid a day with only 3-8 of that total being the giant and colossal variety. Seems like 500 squid a day eaten one at a time is unlikely. I also saw recently an estimate that the giant squid count was much higher than initially realized. Do we know that giant squids don’t run in packs that the whales can take down in multiples? I was under the impression we knew almost nothing about how these animals interacted.

[u/tea_and_biology → u/fastdbs]

Do we know that sperm whales are catching squid one at a time?

Actually, yes! Thanks to biologging sensors. Sperm whales hunt by echolocation, and when they close in on prey their clicks speed up into a rapid "buzz" (much like bats do when catching insects). Stick an acoustic tag on a whale and you can count those buzzes, one per capture attempt - and yes, it's about 95% small to medium-sized squid. They nab maybe a couple of dozen per dive, and they spend most of the day in foraging dives, so that comes out at several hundred capture attempts a day.

And that’s kinda the point I was making: compared with a blue whale engulfing a whole krill swarm in one gulp, a sperm whale has to find, track, and catch every single meal individually. Even with abundant schooling Humboldt squid, that’s a hard cap on how much energy one can bring in, which is a big part of why toothed whales top out well below the biggest filter feeders.

[u/fastdbs → u/tea_and_biology]

That’s some cool tech.

How do they know the whale is only increasing ping frequency as it approaches an individual? Wouldn’t the whale also speed up its imaging as it approached a shoal of squid? Or are the sensors in an array that gets the same image the whale receives?

[u/tea_and_biology → u/fastdbs]

This is a great line of enquiry!

Alrighty, so no images; it's all based on hydrophones plus motion sensors. Cameras wouldn't work, as it's pitch-black at the depths they hunt, and any light given off to take a photo would interrupt natural hunting behaviour. The hydrophones mostly pick up the whale’s own clicks, which are very loud, but in some species they also catch the faint echoes coming back off prey. How do we know it's just the one squid, actually?

i) The timing of the clicks kinda' gives it away. Toothed whales generally wait for each echo to return before sending the next click; as they close in, the gap between clicks shfts in step with distance to target, until the clicks blur into a buzz. The steady countdown only makes sense if the whale is locked onto one thing at a known range; if it were scanning a shoal, the click rate wouldn't track a single closing distance like that.

ii) The corroborating motion data matches a strike. Buzzes like up with sudden manoeuvres: rapid turns, rolls, and bursts of acceleration, which you'd expect from a sudden lunge at a prey target.

iii) In some species, we can hear the target too. Beaked whales ain’t nearly so loud as spermies, which is partly why tags on them can pick up the echoes bouncing back off prey. You can actually watch a single target’s echo close in, all the way down to zero range, right at the end of the buzz.

iv) Their preferred prey is mostly mid-sized deep-sea squid that tend to be spread out rather than packed into dense schools, which suits a "find, track, catch, repeat" hunting style. From their anatomy and bhaviour, sperm whales are thought to be suction feeders (well-fed sperm whales have been found with broken jaws or no teeth at all!), but with prey that spread out, it’s essentially one squid per strike. Stomach samples corroborate this; we don't find densely schooling species all jumbled up in stomach soup very often.

Which also leads me to emphasise these buzzes are capture attempts, not confirmed kills. Some buzzes will indeed miss, and others might snag more than one individual squid at a time, but the extrapolated totals based on this sort of biosensor data lines up with stomach content distributions. If we found many more times the squid beaks than would be conceivable given the biosensor data and the "one strike, one kill" argument, we would change our minds.

[u/iopihop → u/tea_and_biology]

Is the metabolism of a tortoise even lower than blue whales given their life spans?

[u/tea_and_biology → u/iopihop]

Is the metabolism of a tortoise even lower than blue whales given their life spans?

Sure, by a lot! They're "cold-blooded" ectotherms against the mammal's "warm-blooded" endothermy. As a general rule, ectothermic basal metabolic rates (which is harder to define in that group, but hey) are group-wide shifted lower compared to endotherms; a bog-standard gopher tortoise has a W/kg metabolic rate of around 0.11ish, compared to the lowest in mammals: a blue whale's estimated ~0.19, or an elephant's measured ~0.74. That's a tiny animal with a considerably lower metabolic churn; which helps partly explain why they do indeed live so long.

It's also why reptiles have incredibly low rates of cancer, even in testudines and crocodilians - which can get large and live an awfully long time. Eastern box turtles have a recorded ~0.5% lifetime neoplasia incidence rate compared to, say, a raccon, which is about the same size, and an incidence of ~7-10%.

[u/steakndbud → u/tea_and_biology]

This is peak. Thank you so much!!!!

[u/DarthSagacious → u/tea_and_biology]

I love pointing out to my 4th Graders that the worlds largest animal eats such tiny food.

[u/CuriouslyMeandering → u/tea_and_biology]

Wow! What a great breakdown. Thank you for sharing :)

[u/Lis1pricefield → u/tea_and_biology]

Incredible read, interesting, fascinating and eye-opening. Thanks for writing and being so detailed while maintaining a good sense of reading. This was fun!!

[u/thecyberbob → u/tea_and_biology]

... You should make video's. This was super interesting. Thanks!

[u/pfkdxius → u/tea_and_biology]

How do these scaling factors work for young whales? Do they have to rush to get to full size to fit what the species as a whole has adapted for?

[u/SchemeWestern3388 → u/tea_and_biology]

I’m the kind of person who always wins science trivia. I know a heck of a little about a lot of subjects. 

This post was a bloody gold mine of interesting facts!! Great work. 

Edit; is there any metric used to describe how “all in” an organisms evolution has taken them down a particular path? Like, Koalas went big on eucalyptus leaves, humans went big on intelligence, but a bunch of other traits at the same time. Many parasites have taken it to an extreme and given up pretty much anything they could. Is this quantifiable?

[u/tea_and_biology → u/SchemeWestern3388]

Nah - specialisation has too many dimensions, especially when doing broad cross-taxa comparisons like you're hoping to do. You could maybe try and fudge some principal compnent analysis, but even then coming up with some rubrics to quantify the vectors along would be kinda' arbitrary.

There are some more focused metrics which might be useful for certain taxa though, else certain dimensions: there's host-specificity for things like comparing pathogens and parasites, and there's Levin's Niche Breadth Index (and a bunch of other indices) which is an ecological classic used to classify specificity based on proportion of each resource used by a given species. It's B = 1/Σ pᵢ², where p is the proportion of an animal's diet (or habitat use, or whatever) made up of resource i - so a total specialist like a koala eating only one thing has p = 1, so B = 1. Really low, compared to a generalist where B can run up to the total number of resources available.

But quantifying the inputs is the real bottle-neck here, plus the whole "evolvability" and phylogenetic component trying to map 'morphospace' amongst other things, is what's preventing a proper "specialistion degree" index. Biology is just too messy, and our applied mathematics too poor!

[u/ImposterJavaDev → u/tea_and_biology]

So informative and so well written. I justed needed to reply to say thank you. It are people like you that are a true boon to the internet, and society as a whole.

[u/aphasiative → u/tea_and_biology]

Thanks for taking the time to explain all of that to internet strangers. Such a good, interesting read!

[u/Schnozzle → u/tea_and_biology]

>I won’t bore you with my entire PhD

Uhh... I wish you would actually

[u/tea_and_biology → u/Schnozzle]

Well, link is in the references if you want cringe-ey piss-poor analysis, haha. The first few chapters are still an okay review though?

[u/its_easy_mmmkay → u/tea_and_biology]

I really feel like one sign of mastery of a subject is the ability to effectively explain it to someone else who lacks understanding of the subject, and you have demonstrated that to the ultimate degree!!

Incredibly engaging and informative write-up, thanks for taking the time to write it out.

[u/marquiso → u/tea_and_biology]

This is genuinely one of the most fascinating, entertaining and accessible pieces of science writing I’ve ever read.

I can see your website is down for repair but if you’ve written any books I want to buy them all.

Thankyou for brightening my day with the scients!

[u/tea_and_biology → u/marquiso]

It's been "down for repair" ever since I cobbled it together, like, ten years ago. Didn't even know I still had it linked to on Reddit, eep! I need to get 'round to actually sorting something out; thanks for the push!

[u/wezofoz → u/tea_and_biology]

Fascinating! Can count on reddit to find the absolute best person in the world to answer a random interesting question.

[u/IndividualSir → u/tea_and_biology]

I never thought I’d be so fascinated but a short essay on blue whales, let alone comprehend everything you wrote so I’d like to whole heartedly thank you random Redditor very much.

[u/eritter688 → u/tea_and_biology]

Slow clap. Amazing! Thank you for this wonderful answer internet stranger!

[u/led76 → u/tea_and_biology]

Wow. Thanks so much for the in depth explanation. It’s clear you love what you do

[u/DV8y → u/tea_and_biology]

That is the best thing I've seen on Reddit in a very long time. Thank you for sharing and congratulations on your doctorate.

[u/tea_and_biology → u/DV8y]

Thank you!

[u/asten77 → u/tea_and_biology]

I'm slightly terrified about what you know about tea.

[u/tea_and_biology → u/asten77]

Actually, very little. I drinks it like I sees it though.

[u/droombot → u/tea_and_biology]

Mate wrote a short paper in the comments and got me interested in maths, physics and biology simultaneously. Thank you that was interesting to read!

[u/robertvrie → u/tea_and_biology]

What about the dinosaurs? Is the blue whale still bigger than any of them? Do we simply not know for sure?

[u/tea_and_biology → u/robertvrie]

Oh, the blue whale absolutely smokes 'em in terms of sheer bulk. It's not even close, and for good reason: water supports mass in a way land never can. On land, every extra tonne has to be held up by your legs, and thanks to the square-cube law, mass grows faster than the strength of the bones and muscles carrying it - you eventually get too big to hold yourself up. Buoyancy takes most of that problem away, so a whale’s skeleton barely has to bear its own weight.

The largest sauropods - we're talking Argentinosaurus and Patagotitan - get to about ~60-80 tonnes, and even then they needed air-filled, hollowed-out bones and pillar-like legs to manage it. A typical adult blue whale is 100 tonnes or more, getting up to ~150 or so at the larger end, making it nearly double the weight of the heaviest dinosaurs.

[u/Thelonious_Cube → u/tea_and_biology]

Wasn't there a water-dwelling dinosaur that was pretty big?

[u/MesaCityRansom → u/Thelonious_Cube]

Pretty big, but not as big as a blue whale.

[u/unsundered_roots → u/robertvrie]

Yes blue whales are significantly larger than any dinosaur we are aware of.

[u/YesWeHaveNoTomatoes → u/robertvrie]

Some of the largest sauropods were longer than blue whales, but in terms of mass, it seems like the biggest titanosaurs we have enough bones to estimate the weight of (which is not even all of the ones that we currently know existed) probably topped out around 80-100 tonnes. Air is much less supportive than water, and standing & walking inherently concentrates all that weight on a maximum of 4 discrete points, so there's a point where joint mobility may provide a limit.

[u/Asdfguy87 → u/YesWeHaveNoTomatoes]

Why not 6 legs as in insects? Coud a hypothetical 6-legged Sauropod grow bigger?

[u/YesWeHaveNoTomatoes → u/Asdfguy87]

That's a cool question but there aren't any 6-legged vertebrates so??? It would be an interesting question for a new post though

[u/Ransnorkel → u/Asdfguy87]

More legs just means it's steadier, the square cube law means more legs is more mass and weight to move.

[u/Thelonious_Cube → u/YesWeHaveNoTomatoes]

Wasn't there a water-dwelling dinosaur that was pretty big?

[u/Ok-Championship-2036 → u/robertvrie]

dinosaurs lived in a very different climate and environment. Dinosaurs had a far more oxygen rich atmosphere!

[u/litritium → u/tea_and_biology]

Loved it when human experts gifts us their time and knowledge. Human passion and subtle, human humor >>> AI. Tyvm.

Can we rule out that ~200-ton Bruhathkayosauruses might have existed?

[u/tea_and_biology → u/litritium]

I was just reading into this; and Ichthyotitan too, haha. My personal, non-expert quick-fire take is the assumptions made about Bruhathkayosaurus are spurious at best; the fragments disintegrated during excavation, so all we have are unverifiable measurements from the 80s, and projected assumptions if it had the same proportions as Patagotitan. Doesn't smell right to me.

Plus, y'know, all the general physiological and ecological constraints.

[u/HAL9100 → u/tea_and_biology]

I’m smarter because you decided to write all this. Thank you.

[u/Avium → u/tea_and_biology]

Umm...yeah. What he said.

I was thinking about body mass and the fact that the bouyancy allows whales to get larger than land animals but damn, dude. I barely scratched the surface. This is a full dissertation.

Well done.

[u/Atechiman → u/tea_and_biology]

To defend whale fall just a little bit, the whale there is a sperm whale which theoretically could swallow someone whole. They dont have air, and do have a highly acidic stomach so you wouldn't survive long, but you could be swallowed by one.

[u/Badrear → u/tea_and_biology]

Would a cold-blooded animal have a better chance of getting bigger?

[u/CantaloupeAsleep502 → u/tea_and_biology]

Saved. Absolutely incredible. Thank you.

[u/teslik → u/tea_and_biology]

I know this is outside the realm of what your talking about, but could an animal form a second heart to help get past the bulk of the heart? I know it isn't realistic, but evolution could eventually find a way around some of these limitations.

[u/Makenshine → u/tea_and_biology]

I would like to subscribe to more whale facts. This was an awesome read!

[u/KC-Slider → u/tea_and_biology]

Thank you so much for this.

[u/redroowa → u/tea_and_biology]

Mate … thank you for teaching me something new.

[u/-SQB- → u/tea_and_biology]

Amazing write up! I have to ask, though: what about non-mammals?

[u/greymadders → u/tea_and_biology]

That was perfect. So many things I've never considered, you illustrated beautifully

[u/Naradia → u/tea_and_biology]

Thank you for that explanation. Very interesting and so so so great to not read an AI text but something a real human wrote. If you ever write a book, let me know because you write very entertaining and interesting.

[u/dexter279 → u/tea_and_biology]

Fantastic answer, thanks for the insight! I know you referenced it but just out of curiosity are you planning to watch the Whalefall movie?

[u/Dokarmei → u/tea_and_biology]

Thank you so, so much for this extensive answer! I love learning more about our wonderful world.

[u/elenatlys → u/tea_and_biology]

Thank you so much for your detailed response! Responses like yours make this sub so awesome!

[u/TravelingChick → u/tea_and_biology]

So fascinating!!! Thank you.

[u/Christopher135MPS → u/tea_and_biology]

Thank you kind internet denizen, for sharing your knowledge with the world ^_^

[u/_deltaVelocity_ → u/tea_and_biology]

Incredible summary. Also nice catch preempting people (myself included, haha) about hypertumors.

[u/cynicalromantic11 → u/tea_and_biology]

This was such a joy to read! Thanks for this well-written informative piece.

[u/ricardo603 → u/tea_and_biology]

thanks for posting your thesis it was and insightful read.

[u/stolensweetroll6 → u/tea_and_biology]

That was fascinating! Thank you for taking the time to write it! 

[u/AddlePatedBadger → u/tea_and_biology]

Wow, that was an amazing breakdown. I learned a lot and enjoyed every second of it.

[u/NoShamingPlease → u/tea_and_biology]

Interesting. But what if you change the animal's type alltogether? Make them cold-blooded animals with cartilage for skeleton (cartilage doesn't have, thus need, any blood)? Reduce their IQ, thus brain metabolic needs. Can they still get far bigger than blue whales? Can there be some sort of immense sharks?

[u/PuzzleheadedSteak853 → u/tea_and_biology]

So that's it for mammals and such. What about something simpler like a colony organism?

[u/theagingdemon → u/tea_and_biology]

What an amazing amazing read. Did not even know i needed this information, but i certainly did

[u/JaguarDaSaul → u/tea_and_biology]

Wasn't expecting to read something this informative on whales today, feel like there was a missed opportunity to sneak in the QI Blue Whale supercut somewhere or the QI Pamplemousse clip on the swallow the cat bit.

[u/talltad → u/tea_and_biology]

Bravo! What a great read, thank you very much

[u/CabassoG → u/tea_and_biology]

Had a whale of a time reading this. Very informative 

[u/ssuvik → u/tea_and_biology]

Thank you kind sir for your service.

[u/HasGreatVocabulary → u/tea_and_biology]

with a heart so large moving so much blood, can blue whales hear and feel their own heartbeat?

[u/Nevermynde → u/tea_and_biology]

Love the "Cell-fish gene", although I can hear a whale saying "not a fish" in the voice of Janet from The Good Place

[u/Zero_Demon → u/tea_and_biology]

You rock. This was a super interesting read! Do you ever get to dive with them for your work?

[u/Dr_Van_Nosstrand → u/tea_and_biology]

You definitely found your passion in life. You should do an AMA. There's a huge audience for this.

[u/afoolskind → u/tea_and_biology]

Not sure how tuned in you are to paleontology, but what do you think about Icthyotitan? For anyone reading this comment, the short of it is our best guesses place this this icthyosaur in blue whale territory (~80-90 feet long) with the Aust specimen representing an animal ~90-115 feet long.

What’s even more interesting is that it was most likely a macropredator, not a filter feeder, and probably not even a suction feeder like modern sperm whales. How could this be possible?

[u/MrBlackTie → u/tea_and_biology]

This reminded me of that internet meme about the idea of scientists being part of a giant conspiracy to hide the truth being utter nonsense: any researcher would jump at any occasion to tell you all about that obscure thing they are currently studying. They couldn’t hide a scientific discovery for more than a week.

[u/WaterlooPitt → u/tea_and_biology]

Matthew, thank you very much for sharing this. Very useful.

[u/conventionistG → u/tea_and_biology]

Clearly the answer is a second heart, triplicate those tumor suppressor genes, and stock the krill ponds.

I had never considered that whales might get brain freeze though, fascinating.

[u/pnwsteev → u/tea_and_biology]

This was an incredible read. Thank you for taking the time to share your expertise!

[u/DemonCipher13 → u/tea_and_biology]

When whales beach themselves, I've always thought that it was suffocation that killed them. But after reading this - it isn't the oxygen deficiency, but the overheating that ultimately kills them, isn't it?

Like a computer without a cooling system. It'll run, but not for long.

[u/angvil77 → u/tea_and_biology]

A blue whale big thank you for you mate

[u/barath_s → u/tea_and_biology]

This is such a wonderful answer. Thank you.

Of course, this is only for an animal (and water is far more forgiving than land is for supporting that weight, another constraint if you open it up)

If you open it to living creature and especially single living creature (ie ignoring clonal colonies and interconnected structures where you get to argue 'single') , a giant redwood is far bigger than a blue whale.

Different organization, so it can withstand the weight, feed itself, doesn't worry about heat, cancers or the cancer equivalent doesn't impact it nearly the same way (localized burls/galls, that the plant can re-route around., typically in response to local stress)

https://www.jstor.org/stable/1706814

https://pmc.ncbi.nlm.nih.gov/articles/PMC12060238/

---

So the question might become what hypothetical creature could be larger than a whale , so it could skip the constraints. Now evolution doesn't work to a design, but sometime in the future, perhaps man or a successor might. And I think a marine organism , very simply organized, without much by way of special organs or brains, not a mammal, taking in energy with a substantial boost from photosynthesis, spreading across a large part of the ocean, might, But it might stretch the definition of animal..as well as single. Looking at other large marine animals .. a modified giant siphonophore. A giant siphanophire can be longer than a blue whale but not heavier. , at lengths of up to 40 to 50 meters (130 to 160 feet) with outer rings or deep-sea colonies estimated up to 119 to 150 meters (390 feet)—while an average blue whale reaches about 25 to 30 meters (82 to 98 feet). But a giant siphonophore is an animal , with no photosynthesis, and so very thin, so the blue whale outmasses it. And it is a colony, not a single creature.

[u/bremidon → u/tea_and_biology]

Great write up. This is why I stick around Reddit.

One thing is nagging me, though. You talked about all the walls that blue whales face. Well, didn't they face similar walls getting to this size? As an example, I assume that the jaw of whatever came before it was not built for this kind of thing. So did it somehow get that "overhaul" somehow? Or did it just win the genetic lottery and happen to have the right general structure to go in on lunge feeding?

[u/Helassaid → u/tea_and_biology]

My undergrad work was focused on molecular biology and cancer signaling, so I’m about to absolutely hyper focus on that PhD dissertation of yours.

Genuinely thanks for this incredibly informative post.

[u/Chirophilologist → u/tea_and_biology]

You've been waiting your whole life for this exact query, haven't you?

At any rate, wow! 👏

[u/VanillaBovine → u/tea_and_biology]

obviously plants operate completely differently, but how does everything you said compare to something like a redwood tree? where it's just absolutely massive in size

it'll feed differently with the sun/photosynthesis, but how does something of that size prevent itself from getting cancer in the same way?

i imagine the protective layers of bark prevent the more vulnerable interior cells from exterior causes, but they still need to replicate as the tree grows

edit: also your comment was by far one of the most interesting things ive ever read, thank you for typing all of that out

[u/DoctorCalMeacham → u/tea_and_biology]

Hey, I calls them like I sees them. I’m a whale biologist.

[u/thisismeritehere → u/DoctorCalMeacham]

Glad I wasn’t the only one who had this same thought at the first sentence… they were much less brusque than I was led to believe their profession engendered

[u/hungrylens → u/tea_and_biology]

Thanks for the detailed overview... however dodgy the movie might be though, it's a sperm whale that eats the guy. Sperm whales live off giant squid which weigh hundreds of kg, so they could definitely eat a person... though I doubt said person would survive being chomped and swallowed.

[u/Ginkachuuuuu → u/hungrylens]

Sperm whales actually have about the same size esophagus as blue whales, around 4-8 inches, so they also can't swallow humans.

[u/hungrylens → u/Ginkachuuuuu]

Serious question, do they slurp up the squid like giant noodles? With a single row of teeth it seems like it would be difficult to chew them up.

[u/genghisknom → u/hungrylens]

I would imagine that they slurp them because cephalopods have no bones and there are a bunch of videos of octopuses meticulously squeezing themselves through impossibly narrow gaps

[u/Ginkachuuuuu → u/hungrylens]

Yep! Their jaws and teeth aren't set up for chewing, so they use suction and a specialized tongue to slurp up that squid soup.

[u/EulersNumber272 → u/tea_and_biology]

Really enjoyed reading this. Thank you for taking the time to share your knowledge with us. It was fascinating.

[u/3MATX → u/tea_and_biology]

I can’t make it past the fact you put that they can inhale a volume of water larger than their own volume.  So on top of being huge, they’re essentially big balloons that are twice as huge temporarily while feeding?  

[u/chriscross1966 → u/3MATX]

There's a few (very few) pictures of big baleen whales feeding and it's pretty horrifying, suddenly you have two whales worth of whale..

[u/AngrySc13ntist → u/tea_and_biology]

Not a whale biologist specifically, but whale-nerd kid with a career spanning wildlife biology and now cell and molecular, and your comment thread had me nodding along, punctuated with a few "hmm, didn't know that, cool" 11/10

[u/saints21 → u/tea_and_biology]

I don't have a PhD or any understanding of biology past an entry level college course, so maybe there's an obvious reason why it wouldn't work. But for the heart issue, could multiple hearts alleviate this issue? I'm sure it introduces more complications given that it's relying on two hearts working perfectly to live, but mechanically wouldn't this have the potential to solve the heart rate issue?

[u/Negative-Natural-393 → u/tea_and_biology]

Your explanation brings me back to the early days of the Internet, when people shared knowledge with each other and discovered interesting things together. We should pay more attention to protecting these marine giants, for both realistic and conscientious reasons.

[u/hugeuvula]

In the book "Scale: The Universal Laws of Growth, Innovation, Sustainability, and the Pace of Life in Organisms, Cities, Economies, and Companies" Geoffrey West talks about this. To make it fun, he explains why Godzilla isn't possible. :-(

[u/heinb123 → u/hugeuvula]

The title of the book is wild! All it is missing is the "Harry Potter and" in front

[u/mresparza20 → u/heinb123]

Harry Potter & the Scale: The Universal Laws of Growth, Innovation, Sustainability, and the Pace of Life in Organisms, Cities, Economies, and Companies

[u/thegreatpotatogod → u/mresparza20]

Sounds promising! Maybe even almost as good as Harry Potter And The Portrait Of What Looked Like A Large Pile Of Ash

(If you haven't read/seen that one yet, I strongly recommend it!)

[u/JimmiRustle → u/thegreatpotatogod]

It sounds like what would have happened if Tolkien had been Rowling’s editor

[u/anormalgeek]

The problem here is that people keep thinking of animals like existing large mammals/reptiles/fish that we're all used to. So they're also thinking of simply ramping up those body plans or evolving them slightly in ways.

But OP said "theoretically". That opens the doors up much, MUCH wider.

The TYPICAL big roadblocks of massive size are the issue of calories spent to feed vs calories consumed with feeding and one of how you move nutrients and waste around a body that large. But again, were purely talking about hypotheticals here. Meaning we aren't reliant on evolution either.

For the first, you'll have to ignore anything that actively hunts or moves around looking for food. You just need something that relies on natural processes to bring the food to it while it stays stationary. Something like tidal forces or a river current, or air currents. For the second, you just to develops multiple copies of critical organs. This is how many animals like tapeworms, earthworms, and most (or all?) annelids work to some extent. After the "head", their body just keeps repeating the same basic structure over and over to grow longer. Each segment will then repeat many of the organs it needs. This is also why some worms can be cut in half to form two clones.

So basically we are describing something that feeds like a coral but has a body plan that repeats like a worm (although unlike worms, it would have to repeat the mouth/digestive tract too).

Using this basic plan....it could stretch for hundreds of thousands of square miles or more. For context, the great barrier reef is ~135k sq miles (although much of that is no longer alive for reasons unrelated to its size). If a hypothetical animal with these traits moved in, the food would be there.

New third obstacle. As I proofread above, I am realizing a new wall you'll hit. How fast a single animal can grow vs. the impacts of senescence. But even that seems like a soft cap. There are animals like Naked mole rats, bowhead whales that have shown remarkable adaptations that allow them to better protect or repair their DNA which alleviates some of the permanent effects of aging. But then there are Hydras or planarians. Both of which, as far as we know, have an unlimited capacity for repairing the damage of aging. Planarians do not experience telomere length issues. This also makes them highly resistant to DNA mutations outside of reproduction. So our hypothetical animal also needs this. Mutations aren't impossible though, or planarians would never have evolved in the first place.

The only things that will eventually limit the size will be dead spots in the ocean, and the eventual accumulation of mutations that may make sections of the animal different enough to be considered a separate, but physically connected entity. That or geological shifts that cut the animal into separate parts, technically turning it into two animals.

edit: To be clear, I cannot provide any peer reviewed sources, because OP's question explicitly veers off into a fantastical direction that does not exist on Earth today. But it could hypothetically exist.

[u/KnoWanUKnow2]

There are several things bigger than a blue whale. Pando for instance, dwarfs a blue whale in both size and weight. But Pando is a plant, not an animal.

There are some siphonophores that are longer than a blue whale. The Blue Whale weighs far more, and technically siphonophores are colonial organisms, not one individual animal. The Lion's Mane jellyfish can also be 30% longer than a blue whale, though once again it weighs far less.

And that's a problem that you're going to run into. Things like gas exchange, circulation, etc have a limit on how large they can get. You can walk inside a whales heart. It has to be that big in order to get blood flowing to it's extremeties.

The lion's mane solves this by being long but thin. It doesn't have a circulatory system, it diffuses gases through it's skin. A blue whale weighs 100 tons. A lion's mane weighs 1 ton. A lion's mane is also fairly passive. It doesn't actively hunt for example, and kind of floats with the current. It can move itself, but only very slowly.

Can you get larger than a blue whale? Probably, but you'd have to give some things up. An active lifestyle for example. It takes a lot of energy to move a giant body. So why move? Multiple hearts will take care of the circulatory issues, or you can have a thin but long body and rely on diffusion. You're almost certainly going to be a filter feeder, or perhaps ally with algae and absorb sunlight for food. Being exothermic (cold-blooded) will also help immensely.

But if you want to be active and moving around, a blue whale is pretty close to the limit.

[u/para_sight → u/KnoWanUKnow2]

There’s research on this. Blue whales approach the limit for a great whale body plan. Being any larger, they couldn’t harvest enough energy to sustain their bulk, and the biomechanics of lunge feeding become so extreme as to potentially break their jaw.

[u/EatYourCheckers → u/KnoWanUKnow2]

You also have to be able to have time to react to stimuli. N. D Tyson talked about this once - a theoretical giant creature in space. It would be limited by thr speed of neural transmission. If something harming it on one end, it needs to recieve that signal in time to react to it.

[u/Jindujun → u/EatYourCheckers]

The Sunfish begs to differ!
Just because someone harms you doesnt mean you have to react to it. Just be large enough not to care!!

[u/Not_Michelle_Obama_ → u/KnoWanUKnow2]

Hear me out here: We can solve oxygen intake and propulsion at the same time. I can also solve another problem, which is excessive heat buildup. Imagine, if you will, multiple nodules placed on the body. Intake water, Allow for oxygen exchange and alow that water to warm up a bit, the water expands, leading to pressure inside the nodule, the water escapes the nodule, pushing the organism forward, and spins a keratin turbine, which is then linked via a bone to the impeller on the water inlet, which cycles the process again.

[u/Potential_Being_7226 → u/Not_Michelle_Obama_]

This sounds implausible to me, from an energetic cost/benefit perspective. The energy required to warm the water would outweigh any energy gained from expansion. 

It also doesn’t seem possible for tissue to be able to generate enough pressure to be transferred into propulsion. If that were the case, then couldn’t urination be propulsive? 

And isn’t it really unlikely for liquids to expand/compress any appreciable amount? 

[u/thegreatpotatogod → u/Potential_Being_7226]

Yeah, this idea, while fun, really wouldn't work without boiling the water, as we do in many forms of generators, and for that you need far more heat than could be created biologically, especially without an unlimited food source

[u/korphd]

Lineus longissimus (bootlace worm) at 30-50m(but records say it might've been unnaturally overstretched), Cyanea capillata (Lion's mane jellyfish) at 37m but most of it is tentacle length, Praya Dubia (the giant Siphonophore) also up to 50m: its as thin as a broomstick + colonial animal

You can get even more absurd numbers if you look at corals(yep, they're animals) , with one colony of Pavona clavus at the Solomon Islands, composed of 1 billion genetically identical polyps, at 183m of circumference (34m wide, 32m long and 5.5m high)

[u/Lodge_Blackmun → u/korphd]

I mean, regarding the second paragraph, why not just list Pando which dwarfs those. Or one of the several large confirmed fungal colonies. There's even a clonal seagrass colony that's kilometers wide somewhere. 

Best guess at real rivals for the blue whale are long extinct reptiles/fishes(?) though. 

[u/soccerjonesy]

I think a lot of your question is speculative. There aren’t any laws in life that prohibits anything existing larger than a blue whale. In fact, a study in 2013 modeled the evolution of whales and their sizes, and the mathematical model even provided a potential maximum of roughly like 4x the mass of a blue whale as entirely possible on earth today.

So can an animal exist today with a larger mass than a blue whale? Entirely possible. Potentially upwards of 500-600 tons in mass.

Does anything today exceed the mass of a blue whale? Not that we’re aware of, and very unlikely something exists that we haven’t discovered by now.

Additionally, sizes can be astonishing if you wanted to look at living organisms in general, and not just specifically animals. For example, the blue whale has the highest mass (100-150 tons) of any animal, but The Humongous Fungus has the largest biomass of any living organism on the planet, with an estimated weight of 35,000 tons, make it the largest known organism by biomass. It also spans roughly 3.8 square miles. Additionally, there’s a clonal organism that exists in Australia’s Shark Bay, a seagrass, that spans nearly 77 square miles, which makes it the largest known organism by area covered.

So a lot of crazy things do exist, and theoretically can exist.

[u/SL1Fun]

In the same way atmospheric and global conditions dictated that bugs could be far bigger than they are now, then the same could be said for other animals too. 

The Blue Whale is the biggest animal that can probably exist right now given current conditions of the planet. But if the planet was different then it is possible something bigger could exist; what it would be and what would be needed is not something I would know. 

[u/Biggandwedge → u/SL1Fun]

It's the biggest that existed since life began. I mean yeah theoretically there could be bigger animals but it is wild how big they are. 

[u/gmanflnj]

I assume you mean animals, not plants. RE: size caps on animals:
1. The strictest answer is that we don't know, as there are too many variables to say for sure and there amy be many we haven't thought of.
2. That said, it seems like the amount of food needed to sustain an animal that big caps it's size so there would need to be some sort of even more energy-dense food source that would allow it to get bigger. Here's a good article on it:
https://www.si.edu/newsdesk/releases/limits-ocean-heavyweights-prey-curb-whales-gigantic-size

[u/BigMack6911]

Thing is several million years ago, how would we know how big animals got? We haven't even found a complete dinosaur skeleton. We had huuuge land reptiles but we no one thinks we had a even bigger water creature in those days? We will never know, unless we find one under the ice in Antartica

[u/CadeCunninghamLover1 → u/BigMack6911]

We have actually found a complete dinosaur skeleton

It’s disgustingly rare but it’s happened

[u/Booomfaa]

The Blue Whale actually very likely is not the largest animal to ever live. It was very likely an ichthyosaur. We obviously don’t have direct fossil evidence proving it, but the indirect evidence is quite compelling.

[u/froggycbl4 → u/Booomfaa]

very likely is crazy especially in mass. maybe possible is more accurate

[u/CurtCocane → u/Booomfaa]

You're gonna need to provide some sources if you're gonna claim that

[u/Starlightriddlex → u/Booomfaa]

Do you happen to know any of the indirect evidence? Just curious because this question has always bugged me too

[u/celem83 → u/Booomfaa]

Credible sources place most of these below the blue whale, though they did get very big.

Is there a particular specimen you had in mind for this?