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Posts Tagged ‘Borophaginae’

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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Aelurodon ferox

Aelurodon ferox was a species of wild dog that lived in North America between 10 and 16 million years ago.

It was about the size of a wolf– weighing between 88 and 100 pounds.

It was not a wolf at all.

It was sort of a wolf before there were wolves.

You see, North America, there was a subfamily of the dog family that was solely endemic to North America.

They were called the Borophaginae (technically, “the bone eaters” but are more popularly known as the bone crushers).

Some of these dogs had quite powerful jaws– much more so than those of  a modern Northern big-game hunting wolf– and rather large size.

These dogs are often popularly referred to as “hyena dogs,” which makes things even more wonderfully confusing. African wild dogs were sometimes given exactly the same name.

The largest Borophagine dogs were in the genus Epicyon, and these dogs were very much like large hyenas. They had very powerful jaws and robust teeth that allowed them break large bones in much the same way modern hyenas do. (Wikipedia says that there was a species of Aelurodon that was as large as a tiger. I can’t find the reference. Wikipedia is probably wrong.)

This image of Aelurodon ferox comes from Dogs: Their Fossil Relatives and Evolutionary History (2010) by Xiaoming Wang and Richard Tedford.

You’ll note that the image of Aelurodon ferox shows a dewclaw on the hind legs. All Borophagine dogs had dewclaws on their hind legs. No modern wild dogs have this feature, except domestic dogs and wild dogs that inherited this trait through crossbreeding with domestic dogs with this trait.  (These dewclaws on the hind legs have been a great diagnostic feature for determining if Italian wolves have dog ancestry.)

Dogs derive from ancestors that had five digits on each toe.  Bears and raccoons have five digits on each foot, as did the ancestors of dogs, bears, and raccoons.

However, dogs have evolved to be long distance runners, and as they have developed into runners, they have evolved specialized running feet.  These feet are digitigrade, which means they walk on their toes.  Having one less toe on the ground allows for more efficient movement, so the fifth toe on the inside has moved away from the bottom of the foot and up the leg.  The fifth toe in most modern dogs is found only on the front legs. African wild dogs have actually lost the fifth toe on the front legs, but it is found on all other dog species.

Borophagine dogs evolved from ancestors with five digits on each foot. They were capable of running long and hard, like wolves and other modern dogs, but they had not yet lost the dewclaw on the hind legs.

So there were once wolves that were not wolves and dogs that had hyena features living in North America, and these animals had dewclaws on their hind legs.

 

 

 

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Jess got the closest to getting this creature’s identity correct.

It is supposed to Amphicyon ingens, a species of “bear dog” (family Amphicyonidae) that lived in North America 13.6 million years ago.

Contrary to what this depiction suggests, this animal did not look like a lion with a dog’s head slapped on it.

The larger species of bear dog had features we would associate with modern bears, dogs, and, yes, big cats.

I note that one important bear-like feature is missing from this depiction– the plantigrade foot anatomy.

This depiction does a much better job of showing this feature:

This particular depiction of a member of the genus Amphicyon looks like a hybrid between a lion and a black bear. However, the muzzle of Amphicyon ingens was much longer than either a bear’s or a big cat’s, a trait we associate with modern dogs.

This depiction of a bear dog comes closest to Amphicyon ingens– because it is an actual attempt reconstruct this species:

With an estimated weight in excess of 1300 pounds, Amphicyon ingens was the largest of bear dog family. They evolved from wolf-like ancestors into bear-like creatures. The wolf body-type is actually a primitive carnivore body-type. Even the early hyenas, which are feliform Carnivores, looked more like wolves than hyenas. It has traditionally been suggested that bear dogs were close relatives of bears, but because the early ones looked so much like wolves, it has been suggested that they are actually derived from early caniforms,  the suborder that includes both modern dogs and bears.

These animals had to have been ambush hunters, much like the big cats.  The prey in those days was big and slow. When pack-hunting Borophaginae came into North America (such as Epicyon), it is thought that they outcompeted Amphicyon.

It is an interesting theory. We do know that modern wolves tend to dominate cougars. A cougar can kill a wolf on its own, but it cannot withstand competition from a pack of wolves. Wolves are better able to use a wider array of prey sources and take up all the best hunting grounds, leaving the cougar, a deer and elk hunting specialist, to eke out an existence on the margins.

Perhaps the same thing happened in North America when Epicyon showed up. Amphicyon ingens may have been able to kill a pack of Epicyon, but because they were pack hunters, they were better able to compete in the same area. (It is possible that the same thing happened when the dingo showed up on the Australian mainland and outcompeted the solitary mainland thylacine.)

Whatever the reasons for its extinction, Amphicyon ingens was a spectacular predator. It was not a lion with a dog’s head photo-shopped onto it.  That particular depiction reminds me of creationist Kirk Cameron’s bogus examples of transitional forms, the most famous of which is the crocoduck.

It’s a bad depiction. End of story.

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Epicyon

The mystery extinct canid is Epicyon (“near dog.”) This genus of large canids lived in North America until about 5 million year ago.

It was a Borophagine (“bone crushing dog” or “hyena-like dog.”) The  Borophaginae were a subfamily of early canids that lived exclusively in North America. Although the larger members of this subfamily clearly had bone crushing capabilities, many of the smaller members were actually more like raccoons.

The bigger members of this subfamily include the Epicyon dogs, which were quite hyena-like and were about twice the size of a large wolf;  the Borophagus dogs that were a quite bit smaller but possessed more powerful jaws; and the Aelurodon dogs, which were massive pack hunters with similarly strong jaws.

The largest dog ever to exist was Aelurdon taxoides. The biggest specimens of that species were about the same size as a tiger.

One of my favorite cryptozoological explorations is the Shuka warakin.  A supposed specimen of this animal was collected in 1886.  This creature was taxidermied and then lost for over a century.

It was recently found, and a few cryptozoologists have suggested that it was a Borophagus. (This article incorrectly calls Borophagus a hyena. It was not a hyena. It was a dog that had hyena features and lived like a hyena.)

My guess is that was some kind of abnormal wolf or wolf hybrid.

However, because it had a sloping back, I wonder if it could have been an early form of show German shepherd.

Someone is trying to breed a German shepherd-type dog so that it looks like a dire wolf.

Maybe that’s what they are trying to do to the German shepherd dog.

It’s supposed to be a Bor0phagus!

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