Make no mistake, canids are a homegrown North American phenomenon. And like many things American, canids were exported across the globe and took firm root in every continent. A lot of attention has been focused recently upon the origin of domestic dogs. No one doubts they came from wolves, but where exactly did wolves come from, and who are their immediate fossil relatives? These were the questions swirling in my head when I dragged my pappasan chair onto the back deck, settled in, and read “Dogs: Their fossil relatives and evolutionary history” over the course of two afternoons. (Probably could have read it in one day if I hadn’t spent so much time taking notes.) It was written by Xiaoming Wang and Richard Tedford, and illustrated by Mauricio Anton.
To be fair, this is not an easy read unless you like learning about extinct species, ancient climates and environments and don’t mind piecing together relationships in your head. It’s not entirely angled at an academic audience, but it’s also not entirely angled at a lay audience; it’s more like a hybrid approach that aims a few notches down from scientific journal writing and a few notches above what you might read in Discovery magazine. You might get the impression that this is a book about “dogs,” as in Fido, Rusty and Old Yeller. But not so. Only a few pages are devoted to modern dogs and their origins, versus the bulk of the book which is devoted to making sense of the now extinct dog-like and wolf-like prototype species that came first. And what a family tree it is! The manuscript traces the evolution of the three sub-families within the family Canidae: Hesperocyinae, Borophaginae, and Caninidae.
It’s the last of these sub-families that gave rise to modern dogs. The first two sub-families are all now extinct, known only from fossil bones and teeth. But by understanding them, and their relationships to each other, modern canid relationships make more sense. The author’s description of what defines a true canid begins with a close look at the anatomy of the auditory bulla and carnassial teeth, and a close look at some of the earliest mammalian carnivore families to display these features. For example, the weasel-sized Miacids which lived in the late Paleocene to early Eocene 50 to 60 million years ago, and which harbored the first “true” pairs of carnassial teeth, according to the authors. They propose that all modern families comprising the order Carnivora may have stemmed from Miacids — including true canids of the Canidae family.
Trying to trace the canid family tree in this book is a bit like trying to trace family trees in a bad soap opera. The authors jump around alot, and just when you think you’ve got it, they pull out a distant cousin you never knew existed. But the picture I gleaned over many pages was that the earliest member of Canidae was a sub-family named Prohesperocyon in the late Eocene, about 40 million years ago. Prohesperocyon gave rise to the sub-family Hesperocyon which included a genus of the same name (dated to about 37 million years ago in the late Eocene). And it was this genus to which all living canids owe their excellent hearing. Apparently, Hesperocyon hit the evolutionary jackpot by being the first to evolve a bony auditory bulla trait that was later aquired by almost all living carnivorans and which conferred better hearing. It was also the sub-family Hersperocyon which gave rise to the Leptocyon sub-family in what we now call the southwestern U.S. And this group had one heck of an impact on our continent because they are thought to be the original stock of all true canids. However, when the early, smallish, generalized Leptocyon lived 23 million years ago, they were dwarfed by the larger dog-like genera within the sub-families Hesperocyonines and Borophagines — the latter of which included the most awesome and gruesome bone-crushing dogs. (Borophagines hailed from the Archaecyon genus, which is also traced back to Hesperocyon.)
And yes, I confess, I have to constantly look back at my notes to write this because there is no way I’m memorizing this stuff. **
From the Leptocyons, things get really interesting for canids in North America. According to the authors, the various sub-families tended to develop larger body sizes, but larger dogs tended to constrain the body sizes of other dogs they competed with. And so it was not until the large and severely imposing Borophagines went extinct that the lineage leading to what we now know of as coyotes, wolves and dogs was able to diversify and grow larger. The authors attempt to integrate this adaptive radiation of canids with paleoclimactic and paleoenvironmental changes such as extensive contintental glaciation events and the conversion of large parts of North America from forest to open grasslands.
Perhaps the most interesting part to me was the discussion from pages 133 to about 148, which discusses the importance of canids leaving North America for China and further adaptations that took place in Eurasia, Europe and Africa. Species of Canis, Vulpes and Eucyon left north America for Eurasia about 4 to 5 million years ago, as well as Nyctereutes, the raccoon dog. I thought for sure at this point they were making this animal up, but then I found pictures of this still-living creature! Yes, Asia still has a raccoon dog, though the original stock went extinct in North America a long time ago (and modern clothing companies are trying to ensure that this animal dies a horrific death to be made into fur lining for our coats). As is expected when a species cracks open a new environmental niche, Canis experienced an adaptive radiation in their new Eurasian digs. There was a sudden expansion of Canis at the beginning of Pleistocene, about 1.8 million years ago, associated with the origin of the mammoth steppe biome.
Canis lupus arose in Europe about 0.8 million years ago, probably from Canis arnensis, the authors imply. Then, about 0.1 million years ago, Canis lupus re-invaded North America, the land its ancestors had left. And yet, it was not the first wolf to trot across the N.A. continent. An older species of wolf was already there, having evolved from the stock canids that had remained in North America and that had not left across the land bridge. And on this point, I was severely disappointed with the authors. Their section on the red wolf relied on outdated interpretations of the animal’s origins, and failed utterly to bring in a current understanding of the animal’s evolution. (Why do paleontologists so hate genetics?) But I’ll have to save my thoughts on this point for my book…
As you’ve probably concluded by now, “Dogs” is one long chart of who begot who begot who and what went where and when. It really is dense, what can I say? The only thing that kept it from getting too boring was my constant attention to tracing where wolves came from. (And yes, you need pen and paper and a slide rule to do so with this text, because there is no simple phylogenetic tree to refer to on this point, despite the book’s title.)
The one element that makes this book sing is the art, however. Anton created scientific illustrations of the fossil bones as well as reconstructions of what the animals would have looked like while living. And while there is some degree of artistic license in these, it is amazing to see the extrapolation process from bones to muscles (estimated based on the size of the muscle insertion points evident in the bones) to skin and fur. Having the illustrations to peer at makes the often dry writing of the text so much more enjoyable. It truly would not be the same reading experience without the art. If you read cinematically, as I do, then you’ll probably amuse yourself with paleo-scenes, but there is no “story” in the book; it’s more like a string of facts culled straight from the fossil record.
Overall, I found this book intriguing because it relates to a subject close to my heart — wolf evolution — but I’d have to classify it on the reference side of things, rather than within a popular science book category — no matter how snazzy the book jacket appears. I’d recommend it to people interested in the fossil canid lineage and familiar with evolution and paleontology, but less so for people who want to learn where their boxer Buster came from.
(** I read this book weeks ago and wrote this post based on my notes… If I’ve erred in family, sub-family, or genus name, please let me know. If you’re not satisfied with my ultra-condensed version of canid evolution as presented here… gimme a break and go read the book!)