Posts Tagged ‘Canis armbrusteri’

The Enigmatic Small Wolf Species of the Early-Mid Pleistocene of North America

August 6, 2017

There were at least 5 species of wolf-sized canids living in North America from about ~1.8 million years BP-~300,000 years BP.  Edward’s wolf (Canis edwardii) was a medium-sized canid, averaging about 75 pounds, that apparently occurred from coast to coast.  It’s the same species formerly known as Canis priscolatrans, and it was an evolutionary dead end–its extinction occurred about 300,000 years ago.  Armbruster’s wolf (Canis armbrusteri) co-occurred with Edward’s wolf but was a larger species, weighing on average 125 pounds.  Armbruster’s wolf is thought to be the evolutionary ancestor of the famous dire wolf (Canis dirus) which became extinct about 11,000 years ago.  Troxell’s dog (Protocyon texanus) was related to African hunting dogs.  Fossil evidence of this species has been found in Texas, the Yukon, and Alaska; and it probably had a wider range than the fossil record indicates.  Perhaps it lived in low numbers in geographic regions where processes of preservation were rare. The timber wolf (Canis lupus) was apparently confined to Alaska and Eurasia during the mid-Pleistocene and didn’t colonize North America until the late Pleistocene.  Finally, a mystery species nearly identical to the present day coyote (Canis latrans) left fossil evidence at sites in Nebraska, Colorado, California, Arkansas, Pennsylvania, Maryland, and West Virginia.  Some of the fossils at these sites are estimated to be 1 million years old.  Paleontologists identified these specimens as Canis latrans, though they cautiously also referred to them as coyote-like.  However, a recent study of wolf, coyote, and dog genetics determined the coyote is a recently evolved species no older than 50,000 years when it first diverged from timber wolves.  This result suggests the mid-Pleistocene species identified as Canis latrans may be an extinct mystery species.

In addition to the fossil record scientists can use a molecular clock to determine when 2 or more species diverged from a common ancestor.  A species has a fixed mutation rate, and scientists add up generations of mutational changes to determine the time of divergence from its closest related species.  (This is a vastly oversimplified explanation but will suffice for the purpose of this blog article.)  There are problems with using molecular clocks.  Different species have different rates of mutation, and the mutation rate can change over time.  Scientists try to calibrate the molecular clock with the fossil record by using various statistical methods.  An early study of wolf and coyote genetics determined the 2 species diverged about 1 million years ago, and this result is consistent with the fossil record, but the results of the newer study mentioned above totally contradict the fossil evidence.  There are 2 explanations for this discrepancy.  a) The new study is wrong.  Maybe the scientists used too many assumptions and dodgy statistics and just came up with the wrong number.  or b) The new study is right, and the mid-Pleistocene species identified as Canis latrans was an evolutionary dead end that went extinct.  The similarity between this mystery species and Canis latrans is just a remarkable example of convergent evolution. c) The new study is right and is not inconsistent with the fossil record.  Perhaps the common ancestor of the coyote and timber wolf was coyote-like.  Ice Age glaciers caused the divergence.  Populations north of the Cordilleran ice sheet evolved into timber wolves but populations south of it remained coyote-like.

Below are images of mid-Pleistocene  skull and jaw specimens identified as Canis latrans along with the skull and jaw of a present day coyote.  I can’t tell the difference, so I favor explanation a.  Even in a case of convergent evolution, there would have to be some notable anatomical differences between 2 different species.

Image result for irvingtonian Canis latrans skull

Genetic evidence from 1 study suggests coyotes diverged from gray wolves about 50,000 years ago.  However, this skull, assigned to Canis latrans (coyote) from Maryland dates to >300,000 years ago.  Is the genetic evidence incorrect or was there a species then so similar to modern coyotes it deceived paleontologists? Image from the below referenced paper by Tedford et. al.

Image result for Canis latrans skull

Present day skulls of Canis latrans.

Some zoologists think coyotes and dogs should now be classified as subspecies of timber wolf based on the data from the newer genetics study.  I don’t agree.  The behavioral characteristics of wolves, dogs, and coyotes are too dissimilar; and they don’t normally interbreed in natural conditions.  Humans can easily eradicate wolves from a region, but they can not eliminate coyotes because the latter are so much better adapted for living close to people.  Wolves and coyotes can survive in the wilderness, but they make terrible pets.  Most dogs make excellent companions for people but can’t survive in the wild.  In my opinion wolves, coyotes, and dogs are closely related but definitely different species.

References:

Tedford, Richard; X. Wang, and B. Taylor

“Phylogenetic Systematics of the North American Fossil Caninae”

Bulletin of the American Museum of Natural History  2009

Von Holdt, Bridgett; et. al.

“Whole Genome Sequence Analysis Shows that Two Endemic Species of North American Wolf are Admixtures of Coyote and Gray Wolf”

Science Advances (27) July 2016

Wilson, Paul; et. al.

“DNA Profile of Eastern Canadian Wolf and Red Wolf Provide Evidence for a Common Evolutionary History Independent of the Gray Wolf”

Canadian Journal of Zoology 2000

 

 

 

Advertisements