We have several  large feline species but no corresponding large canine species. I mean, if you look at a lion or a tiger, you have a really large cat. Even smaller cats like leopards, cheetahs, etc. are still really big cats. But, the largest existing canines are wolves which are really not a lot bigger than a large sheppard.

So, the question: why did large cats survive to the modern world where large canines did not?

Thank you

Good question.

I suspect the answer is that in dogs almost all of the differences in size are down to polymorphisms in the IGF-1 gene (one of the major growth factors for mammals). We know from humans with pituitary tumours that secrete growth hormone (which acts via IGF-1) that these people although tall and large are actually very weak and unwell (despite the ways jaws was portrayed in the James Bond films). As such a very large dog would be at a disadvantage from a survival point of view. In contrast I would guess that large cats are dependent upon much larger numbers of gene differences and thus have evolved to maximise the survival advantages they confer.


I'll be interested to see what others on the site think.

It could jsut be chance - wolves and dholes are actually pretty big and among the cats, only lions and tigers are really bigger. So there's simply just 2 cats that are bigger than the biggest dogs - not much of a trend really...

I think what Ron wants to know is why cats have evolved much larger body sizes than dogs. For instance, in the extant felids alone, all Panthera species (snow leopard, leopard, jaguar, tiger and lion) all exceed 50 kg on average (mean body mass). Even the cheetah weighs close to 50 kg and the puma weighing more than 50 kg. That's three (or maybe two) instances of independent size increase in the extant cats.

If you add the fossil ones, then you get the North American jaguar (P. onca augusta) at around 35~100kg, the American cave lion (P. atrox) at around 350 kg, among others for the crown clade. But there's also the very large sabretoothed cats with Smilodon at around 200~300 kg (depending on the mass estimation) and Xenosmilus also around that weight.

In contrast, the largest modern canid is the grey wolf at around 35 kg, and even in the fossil record you rarely see dogs exceeding 50 kg (the Dire wolf is 50~80 kg or so). While it has been reported that Epicyon (a borophagine taxon) can be up to 170 kg (Sorkin, 2008 LETHAIA 41: 333-347), all estimates from that study are rather large (Smilodon at 470 kg), so sticking with the Paleobiology Database, Epicyon would be around 85 kg. So nothing in the order of the largest fossil large cat as far as I am aware.

So perhaps it is genetic like David W suggests?

Ah right, I think I'd missread the question. Still, it could be a chance issue in the sense that early in their evolution cats adopted a body form or lifestyle that great facilitated an increase to large size that dogs did not. Basal forms of both are pretty small and in that sense cats may have got 'lucky' in ending up with a bauplan that allowed them to get large.

Maybe so Dave but the "mechanism" that allowed the body plan to enlarge in cats will still be genetic.

Well of course, it has to be. But going back to the original quesiton as to "why" the cats did better at big sizes, it could simply be serendipity.

humm!

Is there such a thing as serendipity with regard to evolutionary pressures on a phenotype or genes? Surely in this case the reason cats enlarged was because there was a niche that an increase in size allowed them to fill. I find it difficult to envisage how a "chance" increase in size would have been maintained if there was no survival advantage for it to continue - noting that an increase in size requires more food to maintain it.

I'm not suggesting the increase in size was down to chance, merely the fact that they were able to exploit it may have been chance. Evolution doesn't plan in advance, so they had no way of knowing that niches for large size would excist or would ever exist. The fact that they (potentially, I am hypothesising) happened to have a bodyplan / genetic predispoition / whatever that could facilitate them getting big that was better than their rivals (i.e. dogs) was purely chance.

Compare that to say the bauplan of a jerboa and a rat. Neither plans to get to the size of a horse say, but the fundamental layout of the rat is likely to be better at that then a somewaht bipedal jerboa. Kill off all the world's big mammals and free up the big niches and see what happens and we might see lots of giant rats and no giant jerboas. Alternatively, the jerboas might have gens already that allow rapid grather and a qucik mutation might allow them to reach big size faster and occupy the niches for big herbivores. But it's not about anything particually special about either group that we can point a finger at. That's what I'm getting at.

At some level of course it'll be genetically controlled (pretty much everyhting is) but in terms of saying 'this was the thing' that let cats get big and more specifically 'this is why cats had that thing', it simply could be luck (i.e. not controlled for, or selected for, but soemthing like a founder effect, or they happened to have certain traits that don't require adaptation if they scale isometrically, or already had more genes for growth, or happened to get big-growth genes first).

Ahha yes now see what you mean with regard to chance/serendipity - took me a while to catchup but there now! Thanks David

Well i probably didn't explain it too well!

"Kill off all the world's big mammals and free up the big niches and see what happens."

Nice experimental protocol, but you'll never get ethical approval.

My two cents for an adaptive hypothesis...(just speculation!)

Most cats are solitary(ish) and hunt by stalking and ambush. Many canids are social and hunt in packs by running down prey. Assuming these "lifestyles" are ancestral then perhaps variation in prey species size presents a greater diversity of niches for cats than dogs. So small cats can hunt insects/mice while you'd need to be a really big cat to ambush a moose by yourself. In contrast group hunting may mean you can tackle a wide range of prey sizes, including large animals, without having to be large.

So you think lions might be secondarily social?

Uh ... and I guess leopards would be secondarily antisocial?

Yep - with the BIG caveat of course this is me speculating and I'm not an expert on lions! However, in general the social evolution field would argue that sociality is derrived from ancestral non-sociality. That this is the case in feline (and specifically lion) evolution would seem to be the view Craig Packer takes and his group probably knows more about (African) lions than anyone else.

http://www.cbs.umn.edu/research/labs/li … oup-living

There are some interesting ideas in here too about cooperative hunting not being as important for lions as is widely believed. If so then the evolution of the social/group living lion lifestyle may have been driven by other benefits entirely.

No idea about leopards.. but I think lions are the only social panthera and may even be the only social felid so not sure we need to invoke a loss of sociality in leopard ancestry  - or maybe I'm misunderstanding!