Thursday, December 3, 2009

Eocursor

I have a soft spot for the humble dinosaurs. The dinosaurs that didn't sport outlandish spines, crests, and claws. The dinosaurs who mainly interest paleoartists for their ability to fit in the mouths of larger theropods. If you were to time travel back to the Mesozoic with the intent of bringing back a pet, I think these guys would have been your best bet. Smallish herbivores like Hypsilophodon, Drinker, Othnielsaurus, Fruitadens, or the subject of today's post, dog-sized Eocursor.

Eocursor parvus by ArthurWeasley, via Wikimedia Commons

Eocursor parvus was discovered in South Africa in the early nineties and finally named and described by Richard Butler, Roger Smith, and David Norman in 2007 (Eocursor means "dawn runner," due to those long runner's legs it sports). Butler just published a fuller description of Eocursor's anatomy in the journal of the Linnaean Society.

By the Cretaceous period, the great limb of the dinosaur family tree known as the ornithischians had flowered into a diverse group which comprised the dominant herbivores in a variety of environments. They included the horned ceratopsians, the many flavors of duckbills, the spiked and armored ankylosaurs, and the dome-heads. Iguanodon, Stegosaurus, Triceratops, and Ankylosaurus were all ornithischians.

Of the precious few Triassic ornithischians paleontologists have found, Eocursor is the best known, and is as close as we've come to a shared ancestor for all of those important groups. All of the Triassic ornithischians are known from a pretty small area- they've all been found in Argentina and South Africa, which during the Triassic period were connected as part of the great southern continent called Gondwana. During the Jurassic and Cretaceous, they spread all over the globe. According to Butler, Eocursor's general similarity to ornithischians of the Early Jurassic period - primarily Lesothosaurus, Heterodontosaurus, and Scutellosaurus - lends support to the idea that the great diversification in the ornithischian family occured after the extinction event that ended the Triassic and began the Jurassic. As new ecological niches opened up, the ornithischians adapted to them. They developed new ways to get around and to eat. As predatory theropods likewise evolved to take advantage of the new prey species, the ornithischians evolved defensive mechanisms. It's an evolutionary cascade that would result in all of the wonderfully bizarre forms dinosaurs would take.

The Triassic is a mysterious time in the evolution of the dinosaurs, and as noted above, has not offered up the great bounties of fossils the Jurassic and Cretaceous have. But new discoveries have the potential to shed a lot of light on how the early dinosaurs split into the groups we know well. A great place to find out about new developments in Triassic paleontology - which includes plenty of interesting non-dinosaurs - is a blog called Chinleana.

UPDATED - Just saw that Zach Miller wrote about one of those cool non-dino Triassic critters at When Pigs Fly Returns!

UPDATED AGAIN - And Chinleana writes about the same critter, which is called Vancleavea. I love the artist's rendition. Very dragon-like.

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