What is the largest an animal can be?

Factual Questions
21

Huh. Ignorance fought. Though that’s one study, versus (AIUI) several dozen which have concluded that oxygen levels were much higher in the past (particularly during the Carboniferous period).

Your education is not deficient. I meant that animals which draw oxygen from water (i.e., fish, squid, etc.) presumably could not conceivably grow larger than blue whales do because of oceanic oxygen levels. Looking at my post again it was quite unclear, and the obvious reading is that I meant whales are constrained by oceanic oxygen. :smack:

22

Most of those giant insects were long gone before the dinosaurs came into the picture.

23

I think Enola was referring to Cretaceous/Jurassic/Tertiary marine reptiles rather than dinosaurs per se. “Sea dinosaurs” suggests that s/he thinks that plesiosaurs and the like were marine dinosaurs.

Given that the dozen largest extant animals are aquatic, it’s not unreasonable to conclude that there may have been aquatic creatures (whether fish or reptiles) larger than any dinosaur. Given that the largest known extinct marine reptiles (Kronosaurus and the like) were not even close to the size of modern whales, we may just be missing large parts of the fossil record.

Plus, while there are lots of areas of the Earth which were once covered in water and no longer are, AIUI there are vast tracts of the Pacific which have always been ocean. Also, much of the ancient Atlantic seafloor that once harbored fossils would have been destroyed by subduction.

24

The fossil record of species is by no means complete, doubtless there were far more species of aquatic reptiles like Plesiosaurs, Mosasaurs, Ichthyosaurs,etc (not technically dinosaurs but often lumped in with them) that we have the remains of . However, none of these got to Blue whale weight so it’s doubtful.

wiki:
Pliosauroids (Pliosauroidea)[edit source]
There is much controversy over the largest known of these reptiles. Fossil remains of a pliosaur nicknamed as Predator X have been discovered and excavated from Norway in 2008. This pliosaur has been estimated at 15 metres (49 ft) in length and 45 metric tons (50 short tons) in weight.[65][66] However, in 2002, a team of paleontologists in Mexico discovered the remains of a pliosaur nicknamed as Monster of Aramberri, which is also estimated at 15 metres (49 ft) in length.[67] This specimen is however claimed to be a juvenile and has been attacked by a larger pliosaur.[68] Some media sources claimed that Monster of Aramberri was a Liopleurodon but its species is unconfirmed thus far.[67] Another very large pliosaur was Pliosaurus macromerus, known from a single 2.8 m long incomplete mandible. It may have reached 18 metres (59 ft), assuming the skull was about 17% of the total body length.[69]

Here are some of the biggest:

25

Ahh, thanks. I’m reading up on that era now! Fascinating.

26

The largest modern marine animals, including baleen whales and large sharks, are suspension-feeders on plankton. Although the plankton includes animals like krill, this is essentially a “grazing” lifestyle. Relying on a food source that can’t flee could be the reason they are able to reach such large sizes, like large dinosaur and mammalian herbivores. Active predators have to expend energy in pursuing their prey, which may limit their size. Sperm whales are close to the largest active marine predators known.

There are no known suspension feeders among Mesozoic marine reptiles, which may explain why they did not get as big as baleen whales.

I don’t think that “incomplete fossil record” is an adequate explanation for the lack of Blue Whale sized marine reptiles.

27

Remember that there are also other constraining factors on size besides gravity, such as food availability. A species can’t stably consist of only a few individuals–for long-term stability, it probably has to be at least in the thousands. Get big enough, and the Earth isn’t a big enough place to feed a stable population. Also likely a constraint is the length that a sensory or motor neuron can grow to reach all the way from the brain to the extremities of the animal.

28

Sure, a T. rex is the same order of magnitude as an elephant, but I’m not sure that an elephant is the right comparison for a T. rex. The largest land herbivores ever (which may well have had a lifestyle and niche similar to that of elephants) were ten times as big as elephants, which is significant. But the largest land carnivores ever were twenty times as big as modern land carnivores, and that’s even more significant.

Perhaps. But by that definition, is a sea slug (which eats by everting its stomach) an animal? How about a Venus flytrap, which closes up its digestive apparatus around its meal? Does motility matter? Just how much difference is there, practically speaking, between a fungus and a sponge? Does motility matter? Because a tumbleweed is more mobile than a sponge. And that’s just with Earth life: Alien lifeforms could and probably would be even harder to categorize. You might well end up with three organisms, one a macroscopic motile heterotroph with a fully-contained digestive system and sensory apparatus tied to motor response via rapid reflexes, one a microscopic autotroph with none of those capabilities, and one superficially in between those two on all counts… and yet the first two might be more closely related to each other than to the third. Heck, maybe the first two are even two different life stages of the same species: What do we call that?

29

My point was that you can come up with a definition of “animal” that could include alien life forms. Of course I recognize that there might be some that couldn’t be easily categorized, which is what I said in my post.

30

Any theories on what limits the size of whales? Would a 50-meter-long Blue Whale violate any laws of physics or biology?

31

Ok, so what animal could be larger than a blue whale?

100 feet long and 173 tons.

It is just possible, tho very unlikely that some long necked and long tailed pliosaur may exceed that length.

(shark)Megalodon got over 50’ log, maybe 60’ even, and maybe 60 tons. Whale sized, sure, but not bigger. And we have many, many shark teeth, so it’s unlikely there is some extinct shark a lot bigger.

But other than that, I dont think any vertebrate could get bigger.

Now, sure, colonial animals could have been large. It is not impossible that some early sponge like colonial creature might have covered acres. Maybe even a whole sea bottom. But then, what defines a single animal there? So, let’s skip those.

At the top of the invertebrate pile is the the colossal squid (Mesonychoteuthis hamiltoni), maybe 50 feet long, but not even a ton. Not impossible for some extinct squid to get over 100’ long including tentacles (little fossil record of those without shells, altho they might have been big) . But weight- not even close.

Jellies? Well, the largest known has a bell about a meter across with 10 meter/40feet long “arms”. There’s no reason at all one of these in the long past couldnt have "tentacles’ more that 100’ long. But again, weight would be smallish in comparison with a whale.

So, pretty much the Blue Whale is the winner.

32

FWIW, the largest known bony fish is the extinct Leedsichthys, which was a filter-feeder.

33

In as much as they are considered animals, I suppose certain types of sponges could hypothetically grow to proportions that exceed the size of a blue whale.

So far the largest discovered sponge is described as the size of a minivan. The same reports notes that some shallow water sponges could live to 2300 years, thought dating them is difficult. Perhaps a deep water sponge located where a current provides a steady flow of water and nutrients could grow just as long and even bigger?

34

Yes, even covering acres maybe, why not? But then, what is “one animal” here?

35

There have been fungi and stands of trees covering acres all determined to be one organism as a single genetic identity is determined to exist. Why not for sponges?

36

Yes, they can grow bigger!

It seems like the extremely large animals ( which can also be trees ) do not hunt and eat meat, as this would require large prey and a food chain to support the large prey.

In the water, larger animals such as Blue Whale can be supported.

When you get very big, gravity can be the enemy. Things weigh a lot less in water.

However, if you want to talk theory, it is possible to have bigger ( but perhaps not more massive in weight ) type of floating animal that is lighter than say a thick/dense form of gas on a planet or moon’s atmosphere.

In other words, the animal would " float " and use wings, or paddle like expenditures to move around. This type of animal would most likely eat the abundant smaller lifeforms that wade aimlessly in the gas.

An even further out example would be a very large aminal capable of living in deep space that gets it nutrition from asteroids and such.

37

True. But unknown =/= impossible. After all, there are plenty of marine “grazers” that aren’t quite as developed as baleen whales, like the whale shark and basking shark.

38

Sure, why not? But otoh- why? If we found evidence of some Cambrian sponge that covered a acre, it would still be a footnote. And so far, no evidence of such.

39

I wouldn’t conciser an individual made up of many discrete polyps to be a single animal (any more than I conciser an ant colony an individual animal.) So “no” to sponges and corals. But I’d give bryozoans the benefit of the doubt, since they are interconnected. Tunicate pyrosomes are an edge case (and while not especially massive, can be pretty darn long.)

40

I agree, and there’s no reason one of them couldn’t be longer than a a blue whale.