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Posts Tagged ‘Carnivora’

Of dogs and hyenas

I know I posted this video last year.  I find it extremely fascinating. So here it is again:

Source.

This lecture is a discussion of the parallel evolution of the bone-crushing jaws in hyenas and an extinct North American subfamily of canids called the Borophaginae.  Canidae (‘the dog family”) has historically had three subfamilies.  The earliest dogs were  Hesperocyoninae (“the dawn dogs”).  The earliest known dog species, which was in this subfamily, superficially resembled a ringtail. The Hesperocyoninae were generally smaller animals, and many of these animals were capable of climbing trees.

It is from these primitive dogs that the two other subfamilies evolved.  Most early canid evolution happened in North America, and it is here that all three subfamilies first evolved.

As this lecture discusses, the borophagine dogs evolved to eat bones from very large prey species. They became massive creatures, the largest dogs the world has ever seen.

They thrived in North America f0r 33 million years.

But the big borophagine dogs became hyperspecialized to living on large carcasses.

And as they became more specialized, they became much more vulnerable to extinction. All it would take is for the relative abundance of certain large prey species to drop a bit, and their populations could collapse.

The extant subfamily of Canidade, the Caninae, are much more generalist in their diet. Although Ethiopian wolves live almost exclusive on a species of mole-rat, they can effectively hunt other things, and the only extant dog species that has a truly specialized diet is the bat-eared fox, which lives almost exclusively harvester termites. All other dogs are capable of varying their diet quite a bit.

And that’s probably why there are about 35 species of Caninae in existence today.

And there are no large borophagine dogs left. Some of the smaller, less specialized Borophaginae might still be around, but these animals became extinct relatively early on, as did all the Hesperocyoninae.

Now, let’s make things really confusing.

Modern hyenas are a mere remnant of what was once a fairly diverse family of carnivorans.

They evolved for the same bone-crushing abilities as the Borophaginae.

And it is likely that their hyperspecialization resulted in their demise as well.

Today, there are only four species of hyena left. One of these (the aardwolf) is a termite-eating specialist– just like the bat-eared fox. Brown and striped hyenas are mostly scavengers. Only the spotted hyena, which just so happens to live on the only continent that has anything like megafauna left, is a major bone-crushing predator.

And just as there have been the parallel evolution of bone-crushing in both dogs and hyenas, there has also been an evolution of the cursorial “wolf avatars” in both families.

There were once dog-like hyenas and hyena-like dogs. Only a single species of dog-like hyena still exists. It is the aardwolf, the little termite-eating hyena that I mentioned earlier.

Chasmaporthetes, the hyena that Tseng mentions in this talk, was also a dog-like hyena. It is the only hyena to have ever made it into North America. It was also the most northerly distributed.

There are lots of questions about why this hyena made it in North America.

One hypothesis is that it actually had less of a hyena-like ecological niche, and therefore, it would not have had to compete with the borophagine dogs.

Tseng mentions that his research found that Chasmaporthetes had the ability to crush bones as well as a modern spotted hyena.

So maybe it wasn’t that different from the borophagine dogs.

Of course, the reasons why it thrived in North America are likely quite complex, and because it was a hyena trying to be a wolf in a continent filled with wolves trying to be hyenas, it still may have had very little competition after all.

So the story of dogs and hyenas is complex.

Now, it should be mentioned that dogs and hyenas are not closely related. The last time they shared a common ancestors was 43 million years ago, when their common ancestor would have been a Miacid.

Canids belong to the suborder Caniformia, which includes mustelids, skunks and stink badgers, bears, procyonids, the red panda, the earless seals, the eared seals, and the walrus.

Hyenas, despite their similarity to dogs living and extinct, are actually more closely related to cats. They are in the suborder Feliformia, which includes the cat family (Felidae) and then a whole bunch of other small carnivorans whose exact taxonomic position is still being worked out. Hyenas are most closely related to the civet family (Viverridae).Mongooses and meerkats are also relatives in the family Herpestidae, and closely related to them are the Malagasy carnivorans, which are all in the family Eupleridae. Several species of Malagasy carnivorans look like mongooses, and they are still referred to as mongooses. However, there are others, like the Malagasy civet and the fossa, that were classified in the civet family until recently. There are also African and Asiatic linsangs that were  also classified as civets, but recent genetic evidence has revealed that African linsangs are civets but the two Asiatic species are actually very primitive relatives of the cat family.

So just as hyenas are not dogs, mongooses are not weasels.

Carnivoran evolution is a bit confusing at times.

It’s very hard to keep the relationships between families straight.

Caniforms are more diverse than feliforms, which with the exception of cats and hyenas, have tended to remain small and to be found almost exclusively on the African and Asia mainland. Caniforms vary from the tiny least weasel that weighs only 2 or 3 ounces to the southern elephant seal that can weigh 8,800 pounds.

I hope this clear up some misconceptions about hyenas and dogs and of carnivoran taxonomy in general.

Most people can tell the difference between a cat and a dog.

But when someone tells you fisher cats, polecats, and ring-tailed cats are not cats and hyenas aren’t dogs, it is difficult to understand.

Evolution makes for strange convergences.

It’s one of the weird and marvelous things about it.

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Also check out the Caniformia video to see how the whole order Carnivora evolved from common ancestors that looked like genets or genet/fox hybrids.

He mislabels a few species- snow leopards, clouded leopards, and the ocelot.

And at least one Pantherine cat has hybridized with a “small” cat. The cougar and leopard have produced “pumapards.” Also, modern cheetahs evolved in the Old World, but they do share common ancestry with cougars and jaguarundis. The ancestral cheetah entered the Old World, but it was more like a cougar than a cheetah. However, there were North American cheetahs, but they were more closely related modern cougars and jaguarundis than Old World cheetahs.  The cougar cats have evolved cheetah-like characteristics twice: once in the Old World and once in the New World. The New World “cheetahs” evolved first, but they are not ancestral to the Old World cheetah species.

Despite these little quibbles, this is an excellent video, and it should be watched with the Caniformia video to really understand how dogs, cats, and other Carnivora species evolved.

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He takes down Ray Comfort’s nonsense.  Comfort has no clue.

He also argues that Lycaon pictus ought to be in the genus Canis, for exactly the same reason I feel it should be. It and the dhole are more closely related to the other species of the genus Canis than the black-backed jackal and side-striped jackal are. Xenocyon lycoanoides, the extinct ancestor of the African wild dog, should also be part of this very important genus in the dog family.  (See the dog phylogenetic tree).

He is a little off on the origins of the dog. The East Asian theory of dog origins seems to have been falsified through the genome-wide study that utilitized SNP chip technology found that dogs had greater genetic similarity with Middle Eastern wolves, which suggests that the Middle Eastern wolves, not the East Asian wolves, are the main ancestors of domestic dogs.

Epicyon and the Amphicyonids make an appearance in this video, as to the “dog-bears” (Hemicyonids).

The Caniformia suborder of Carnivora has the most diverse species. Not only does it have domestic dogs, which have greater diversity in head morphology than the whole order Carnivora combined, it includes the smallest member of the order (the least weasel) and the largest (the southern elephant seal). Yes, Carnivora includes the seals, walruses, and seal lions, which are now classified within the Caniformia suborder.

Red pandas are fascinating because of their status as a “living fossil.’

And giant pandas are bears with fused chromosomes.  The two animals evolved their bamboo diet and their very similar s specialized wrist that acts like a thumb in parallel with with each other. Their common ancestor in the basal Caniformia didn’t have that thumb wrist or the specialized bamboo diet. Because both of these animals are derived from meat-eating Carnivora ancestors, they have not developed the ability to digest cellulose, so they have to eat tons of bamboo to survive. If these animals had been designed, one would think the designer would have put in some digestive bacteria in them to help them digest cellulose.

Please note that hyenas are missing from the Caniform cladistics video. Simple reason:  Hyenas are not in Caniformia. They are in the other big suborder of Carnivora, Feliformia.  Yes. Hyenas have a closer common ancestor with cats than with dogs.

This is a very good video.

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A baby pangolin of some sort.

I asked the question yesterday about which animals were most closely related to pangolins.

Originally they were lumped with the sloths, the anteaters, and the armadillos to form the order Edentata. This order also included the aardvark (more about that animal this evening).

Today the sloths, the anteaters, and the armadillos are all in the order Xenarthra. (If you watch any Jeff Corwin shows, this is one of his favorite words to use.)

The aardvark isn’t related to Xenarthra. Calling them “earth pigs,” as their name means in Afrikaans, isn’t really all that far off the mark. I’ll discuss aardvarks a little later.

Pangolins, though, are actually not closely related to either aardvarks or the New World anteaters and armadillos.

They certainly look like they would. I mean a silky anteater does look a bit like a pangolin with the scales, right?

Well, it turns out that pangolins aren’t that closely related to any of these animals.

Their closest relatives are in the order Carnivora.

Yes. Pangolins are more closely related to puppies than they are to anteaters and aardvarks.

Analysis of their DNA finds that the order for the pangolins, Pholidota, is closely related to Carnivora. The two orders are now grouped in a single clade called Ferae. Ferae also included an extinct order of carnivorous mammals known as Creodonts.

Now, this sounds a bit strange. Carnivores are known for their teeth. In fact, one of their distinguishing features is their impressive carnassials. Pangolins are toothless.

No Carnivore has armor plates.

But if you look at the video of the spotted skunk from the earlier post and compare it to the video of the pangolin, can you see a family resemblance?

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The closest relative to Ferae are the Perissodactyla.

Those are the odd-toed ungulates: tapirs, rhinos, and the horse family.

These same studies have fond that horses are more closely related to dogs and cats than they are to cows.

But cows are more closely related to dolphins.

And we primates are most closely related to colugos (“flying lemurs”), tree shrews (which aren’t shrews), and then rodents and lagomorphs.

So we’re more closely related to rats than we are to dogs.

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It’s a Northern elephant seal skull.

This is what they look like alive:

Source.

Northern elephant seals are the second largest members of the order Carnivora. The largest is the Southern elephant seal.

This may have been a bit confusing for some of you because seals, sea lions, and walruses were once classified in their own order called Pinnipedia. This order is no longer considered valid.

Seals, sea lions, and the walrus are derived from the same common ancestor as bears.

That puts these marine mammals with in the suborder Caniformia. This suborder includes dogs, bears,  the red panda, mustelids, skunks and stink badgers, and procyonids.

The smallest member of the order Carnivora is the least weasel. It is a mustelid, and it is also a member of the suborder Caniformia. The largest fully terrestrial member of the order Carnivora is the Kodiak subspecies of the brown bear, but the largest bear is the polar bear, which could be classified as a marine mammal.

The other suborder in Carnivora is Feliformia, which isn’t quite as spectacularly diverse in shapes, but it does include hyenas, which is why hyenas are more closely related to cats than they are to dogs.

I should point out that Southern elephant seals are significantly larger than Northern elephant seals. The biggest bull Northern elephant seals weigh about 5,000 pounds. On average, the biggest Southern elephant seals weigh over 8,000 pounds. The biggest on record was nearly 11,000 pounds in weight.

In case you’re curious, the walrus is a close third behind the northern elephant seal when it comes to size. The biggest bull walruses weigh over 4,00o pounds.  The fourth largest is the Steller’s sea lion, which gets up to around 2,500 pounds.

All of these are much larger than Kodiak and polar bears. The biggest wild Kodiak bears weigh over 1,400 pounds, and the heaviest polar bear on record supposedly weighed over 2,000 pounds (I’m skeptical). One should remember that polar bears are actually a modified brown bear that can utilize marine and polar ice environments.

Northern elephant seals experienced a rapid population drop when whalers augmented their stores of train with their blubber. The population is believed to have dropped to as low as 100 individuals. There are currently 100,000 of  them on the Pacific Coast of North America. These animals have very low genetic diversity, and although they appear fine right now in terms of their productivity, the species could be fragile.

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