Wednesday, December 19, 2007

Pakicetus' Vegetarian Ancestry

Well, it turns out that pakicetids, known to you and I as the earliest known whale ancestors, had vegetarian ancestors of their own. This week's Nature has an article about Indohyus, a new deer-like terrestrial whale from India. The creature can be identified as a whale based on the structure of its middle ear. Surprisingly, it is herbivorous. Pakicetus, Ambulocetus, and all the other whales are carnivorous, so one would expect that whales came from a carnivorous ancestor. Such, it seems, is not the case.

More surprisingly, this is the first time in MY experience that an herbivorous animal has gone back to being carnivorous. The evolution of herbivory requires several changes in the body, including the gut, dentition, behavior, and metabolism. To go BACK to carnivory seems like a waste of all that effort. Indohyus supposedly fed on water-based vegetation. Why did whales so quickly turn to meat? Are there not enough plants underwater?

And then, of course, there's some exciting marsupial news: It turns out that kangaroos didn't always hop. Early versions galloped. Nambaroo gillespieae is a virtually complete early kangaroo that ran on all fours, may have had an arboreal streak, and had "fangs." Despite the fearsome dentition, Nambaroo was still a vegetarian at heart.

Indohyus is in this week's Nature, and Nambaroo is in the Journal of Paleontology. If any of you out there in Readerland have access to these journals, I would greatly appreciate the PDF.

4 comments:

Christopher Taylor said...

Actually, some kangaroos (the propleopines) are widely accepted as at least partially carnivorous (and the recent Hypsiprymnodon is partially insectivorous). You can go here for a picture and discussion of the skull of the best known propleopine, Ekaltadeta.

Thylacoleo is an even better example of a carnivorous marsupial with herbivorous ancestors.

Neil said...

Homo is another herbivore -> carnivore (or at least omnivore) taxon.

Christopher Taylor said...

It's probably also a significant point that basal artiodactyls are more omnivores than exclusive herbivores. Pigs and hippos will both happily eat meat when available (I'm not sure about peccaries) - remember Brian Switek's bit about carnivory in hippos? It's not until we reach the camelids and ruminants that we get fairly exclusive herbivory, but even antelope have been known to down birds when hankering for a bit of extra protein.

Zach Miller said...

Good point, guys. Thanks for correcting me. I don't often take omnivory into account when writing about mammalian diets...