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Posts Tagged ‘evolution’

brush wolf

It cannot be overstated how much the discovery that coyotes are not as distantly related to wolves as we believed ultimately questions our entire understanding of the evolution of the Canis species.

The traditional understanding Canis species evolved from some form of Eucyon dog some six million years ago. Wang and Tedford, who wrote the most important book on the paleontology of the dog family, believe this was Eucyon davisi, which was the first of its genus to enter Eurasia. The genus Eucyon is where the common ancestor of the Canis dogs (including Lycaon and Cuon) and the South American wild dogs would be located. Eucyon dogs were small. Imagine them as being something like a black-backed jackal or a Hoary fox rather than a coyote.

Then, 5 million years later in the Southwestern US and northern Mexico, a coyote-like Canis evolved, which was called Canis lepophagus. This animal is sometimes considered the common ancestor of wolves and coyotes. It may be, but considering how close we now know wolves and coyotes are now, it’s not the most recent common ancestor. Canis lepophagus did migrate into Eurasia, where it either founded or is identical to Canis arnensis.

In Eurasia, several smaller jackal-to-coyote forms evolved. One of these was Canis estruscus,  which then evolved into Canis mosbachensis (which is called Canis variabilis in China).

Ron Nowak believed the red wolf was an offshoot of this wolf that wound up colonizing North America and then becoming isolated from the rest of Canis mobachensis when the ice sheets expanded. There was also a competing view that the red wolf was actually a remnant version of Canis edwardii or Canis priscolatrans (which were probably the same animal). This animal was roughly the size of a red wolf, but Nowak rejected it as a red wolf ancestor because it lived too early for what he thought were red wolf fossils.

The Eurasian wolf species evolved mosbachensis-variabilis, but the two forms of wolf shared habitat and likely exchanged genes, making it very difficult

The coyote’s evolution was never clear. It was thought to have evolved out of Canis lepophagus. It was thought that lepophagus evolved into edwardii, and then it began to become more gracile and smaller, eventually becoming the now coyote.  It’s now pretty clear that it evolved out of the Eurasian Canis lupus and not these endemic North American “wolves.”

It either evolved from the modern wolf, which evolved into roughly its current form 800,000 years ago, or it came from a late surviving mosbachensis-type wolves that were regularly crossing with modern wolves before they came into this continent. Maybe the remains that Nowak had been considering “red wolves,” were actually these ancestral wolves that were evolving into the modern coyote.

Maybe when this wave of wolves came back across from Eurasia, perhaps 50,000-100,000 years ago, it came into a world already dominated by a dire wolves, which already occupied the niche for large, pack hunting canids and this wave of Canis lupus evolved as the American jackal.  After all, the bobcat is just a diminutive Eurasian lynx that found itself in a very similar position when it came into this continent, and it evolved to be a smaller animal that generally hunts smaller quarry than its larger ancestor. Of course, the modern bobcat didn’t reach its current form until about 20,000 years ago, but it still was forced to adapt to a slightly different niche than its Eurasian ancestor.

In literature on the paleontology of Canis, there is a heated debate as to how these animals all fit. The conventional view is that the wolf evolved from Canis mosbachensis/variabilis through Canis etruscus, which may be the same thing as Canis edwardii/ Canis priscolatrans. Wang and Tedford contend that the coyote and wolf split from Eucyon.  The modern wolf evolved from Canis chihliensis, which was a large wolf-like canid. It spread into North America to found Canis armbrusteri, which then evolved into the dire wolf (Canis dirus) in North America and Canis gezi and Canis nehringi in South America.  In the Old World, another offshoot of chihliensis gave rise to Canis falconeri, which the supposedly gave rise to the Xencyon, which is supposed ancestor of the dhole and African wild dog. Another view holds that the Armbruster’s wolf (C armbrusteri) is descended from edwardii/priscolatrans (which may be the same as etruscus). This lineage then gave rise to the dire wolf and the two sister species in South America, thus descending solely from North America wolves.

All of these ideas come from paleontology, and they pretty much are done without looking very deeply into the studies that are examining the DNA of these species. It is pretty obvious from that literature that the notion that coyotes and wolves split at the time of the Eucyon ancestor is quite wrong. For that hypothesis to work, African of  wild dogs and dholes would have to be genetically closer to wolves than coyotes and golden jackals are. They aren’t.

But if the genome-wide analysis shows that coyotes are so much more closely related to wolves is true, then all these fossil and subfossil canids that are said to be the most recent common ancestor of wolves and coyotes simply aren’t.  Instead, all of these species that are classified in Canis are likely a mix of evolutionary dead ends, like the dire and Armbruster’s wolf, or could be hidden ancestors of extant canids that aren’t wolves or coyotes.

For example, black-backed and side-striped jackals diverged from the rest of Canis and its allies at about the same time that Eucyon was diverging from Canis. It is possible that there are many relatives of these particular dogs that are hidden in this vast sea of Canis fossils.

The new discovery about the coyote’s split from the wolf also means that any remains of North American canid that are listed as coyote that date to 1 million years before present are not coyotes. What they actually were is a very good question.

We’ve spent a lot of time assuming that coyotes and wolves were quite divergent. We know now that they really aren’t, but when we look into the past at all the “wolves” and “coyotes” that came before, we see how this genus became so successful. It can easily evolve into big game-hunting forms, but the real success is in its ability to assume the size and shape of the generalist predator. Phenotypic plasticity is a wonderful thing for a lineage to possess.

But the real message of the new discovery about wolves and coyotes should be is a cautionary tale about paleontology. Paleontology is a wonderful science, and it makes amazing discoveries every day, but when its faced with a lineage of animals where phenotypic plasticity and tendencies toward parallel and convergent evolution are commonplace, it is bound to make errors. Paleontologists aren’t examining flesh and blood that can have its molecules tested for relationships. They are measuring anatomical characters and determining phylogenetic relationships based upon the similarities of these characters.

Which works well.

Until you get something like wolves and coyotes, where there are many ancient fossil and subfossil remains that look like they could be ancestors of either.

But the DNA says they aren’t.

And paleontology would have problem catching the inverse. There are many species that we’ve discovered only through DNA testing. African butterfly fish in the Congo and Niger basins look identical to each other, but they have been isolated from each other for 57 million years. I have yet to see this species split into two, but if they were mammals, you could bet they would be placed in distinct species in heartbeat.

Paleontology is missing some really important things we’ve since found out through molecular analyses.

And paleontologists know this.

They are working with the data they have, and by definition, it’s going to be more incomplete than genetic studies.

Science is provisional. Different disciplines and methodologies are going to come up with different answers. It’s pretty amazing that one genome-wide assay study can wipe out so much literature in paleontology.

These debates have been raging for years.

And it turns out that everyone was actually wrong.

Update 21 August 2016:  It turns out that I missed a paper that actually did some limited DNA analysis and found that Canis nehringi was pretty much a South American dire wolf, as in it was likely the same species as the North American dire wolf. Canis gezi, however, was  more closely related to the modern maned wolf and had been incorrectly identified as a wolf. So let this stand as a correction to the error above.

 

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Canis cedazoensis

Canis cedazoensis was an early species of the wolf-coyote-jackal tribe. It lived what is now the American Southwest and Northern Mexico until 300,000 years ago. It probably scavenged kills of bigger predators and lifted off the fawns of the various species of pronghorn.

Conventionally, we believed that the lineage from which this jackal-like canid gave rise to the wolf, the coyote, and the golden jackal. We based these assessments on comparative morphology from fossil and subfossil remains, and it all made sense.

These jackal-like forms entered Eurasia and Africa. They gave rise to the Xenocyon, the first wolf-like canid to evolve of this lineage.  The Xenocyon gave rise to the dhole and the African wild dog. Then the actual wolves evolved in Eurasia, and they walked back into North America to found the Armbruster’s wolf and the Dire wolf. They spread to South America, and endemic North American wolves, Canis edwardii and the putative red wolf evolved out of an unrelated jackal-like line.

The coyote descended from some sort of jackal-like canid in North America and a least a million years of evolution separates the coyote from the modern gray wolf.

The most recent study that examined full genomes of various wolves, dogs, and coyotes revealed that the separation between coyotes and gray wolves happened only 50,000 years ago. This finding pretty much destroys all this thinking.

We’ve conventionally thought of the lineage starting out with jackal-like forms that evolve into wolf-like forms, but the truth is we have a lineage that started out with jackal-like forms. Wolf-like forms evolved at least twice from this lineage, and jackal-like forms have evolved from wolf-like forms as well.

What we’ve missed that just as the Xenocyon and the dhole and African wild dog have evolved into wolf-like forms in parallel to actual wolves, the real story of Canis is that there has been a constant tension between selection for wolf-like traits and jackal-like traits. The coyote is a wolf that has re-adapted itself to the jackal-like form. To become a jackal is to become a generalist again. To evolve towards the wolf is become an apex predator and be forced to hunt for large game to survive.

What we know from the fossil record is the story of wolves and dogs and coyotes and their kin is that it began with “jackals.”  Paleontology says that North America is where this story got started, but the oldest species in this lineage of dogs lives in Africa.

I would love to know the full story.

Canis cedazoensis is a creature lost to time. If we could see one, maybe we know some answers. Maybe we would see something very much like a black-backed jackal. Maybe it would answer some questions.

And it would probably raise more.

Yet more of the mystery to which we should humble ourselves.

It began with jackals, and in the Anthropocene, it may end with them as well. The coyote and Eurasian jackal have continued to spread their range. The coyote is from from Alaska and Newfoundland to Panama– on its way to Colombia. The Eurasian jackal (the “golden jackal,” as it is normally called) spreads north and west through Europe. Both are generalists of the jackal type.

Phenotypic plasticity and convergent evolution have played quite a game with this part of the dog family.

Science is always provisional, and often takes just one profound discovery to turn over the apple cart.

And oh, has it been turned!

 

 

 

 

 

 

 

 

 

 

 

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velvet claw

If you probably couldn’t tell from reading this blog, carnivoran evolution and natural history is one of my passions.

Where did all of this get started? I’d say sometime in the mid-90s. I used to watch A&E’s old Wildlife Mysteries series on Thursday nights. These were mostly very high quality wildlife documentaries and a lot of them were BBC productions.

Some of these films were shown in a series called “Carnivores.” It was about the evolution of the order Carnivora, minus the pinnipeds. And I loved it.

The series was based upon the work of David MacDonald, a carnivoran specialist and conservation biologist at Oxford.

In the UK, it was shown as “The Velvet Claw,” which is one reason I’ve had a few problems finding even clips of it online.

And for a long time, all that we could see are short clips, but now, well, it’s been uploaded in full.  Here is the entire series on Youtube.

I don’t know how long it’s going to be up, so you’d better watch it soon.

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sumatran rhino

A few days ago, I had a discussion on Facebook with someone about Sumatran rhinoceroses and why they were still hairy. I had posted one of Frans de Waal’s photos of a Sumatra rhino calf, and as calves go, it was very shaggy.

The discussion got to a really interesting question, which I think points out to a misunderstanding of the mechanisms by which evolution happens. The discussion went something like this:

“Sumatran rhinos are hairy. Therefore, there must be some reason they are hairy. Otherwise, there would be selection against having lots of hair in jungles of Southeast Asia, Borneo, and Sumatra.”

The answer I had was that the Sumatran rhino is the closest living relative to the extinct woolly rhino. Woolly rhinos were quite well-furred out, and it’s possible even now for animals to retain primitive traits. You hear people talking all the time about living fossils, but there is usually no understanding that a 20 million-year-old shark that looks very similar to living species most likely is incapable of reproducing with that living species (if the two were made to live contemporaneously with each other.)

The error is in assuming that a trait an animal possesses is always a benefit to it. This is a corollary of thinking the evolutions happens through natural selection alone, when it is actually only one way that it happens. (And it’s actually not the main way).

The truth is the Sumatran rhino is nothing more– or less– than the last survivor a lineage of rhinos that retained their furry bodies of their tapir-like ancestors. (And Sumatran rhinos aren’t even that hairy!).

And it should be noted that there are plenty of mammals in the Sumatran rhino’s range that have much furrier bodies.

Evolution isn’t planned out. It can only work with what genetic material is available in the population. Assuming that Sumatran rhinos retain their excessive fur only because it has some advantage to them is putting the cart before the horse.

Now, there is a possibility that there is some advantage for these rhinos to retain the very furred up bodies. I’ve not seen any literature that explores this possibility, but the fact that this animal is so closely related to the woolly rhino kind of provides the best explanation. This animal retains a primitive trait solely because that’s what its ancestors were. It just can’t magically evolve a relatively hairless body.

So always be careful in assuming that a trait exists solely because there is some advantage to it. That’s a real problem in our popular understanding of evolution.

Be very careful of putting the cart before the horse. Sometimes a trait is advantageous. It’s often just neutral.

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Not dinosaurs and not lizards either.

Source.

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Does Senator Ron Johnson (R-WI) believe in evolution?

Source.

Senator Johnson has not yet issued an official response.

I bet he doesn’t because we learned from a “great Republican scientist” named Rafael Cruz that evolution was nothing more than a communist scheme.  Rafael’s son is the Canadian-born Senator from Texas who is the poster boy for everything that is wrong with right wing America.

Update: When I started writing this at 6:20 AM, there was no answer. At 6:30, there was. He does believe in evolution! There is hope after all!

 

 

 

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