http://www.facebook.com/l.php?u=http%3A%2F%2Fwww.plosone.org%2Farticle%2Finfo%3Adoi%2F10.1371%2Fjournal.pone.0012292&h=eb74c Two brand-spanking new chasmosaurine ceratopsids from Utah:
Utahceratops and
Kosmosaurus. The former is a sister taxon to
Pentaceratops while the latter is a sister taxon to
Vagaceratops.
Utahceratops is unique in having a teardrop-shaped nasal horn that sits almost entirely behind the nasal opening. This gives it a very long snout. Also strangely, the brow horns are small and laterally-directed rather than pointing forward. The frill is similar to
Anchiceratops and
Pentaceratops. It is a large chasmosaurine, and much of the post-cranial skeleton is known.
Kosmoceratops is smaller than
Utahceratops but unbelievably wierd. It has a short, blunted nasal horn and it also has laterally-directed brow horns that actually grow in arcs along their lengths! The frill is very short for a chasmosaurine, and the parietal fenestrae are small. Most amazingly, eight finger-like projections overlay the dorsal margin of the frill (like bangs), and a large hook-like spike originates at each upper corner of the frill
. Kosmoceratops has the most decorative head of any dinosaur ever!
Almost more importantly, the two genera add to an increasingly clear picture of ceratopsid radiation and evolution in North America. During the Late Cretaceous, a giant shallow sea--the Sundance or Western Interior Seaway--split North America into two distinct landmasses. The western half was basically just a ribbon of land with young mountain ranges on the western coast and beachfront property on the east cost. Most of North America's dinosaurs, including all known ceratopsids (with one Chinese exception) roamed this strip of land.
But what's especially odd is that this strip of land was about a third the square footage of Africa, and probably smaller at times. And yet we have multiple large herbivores living at any one time, all of which were about the mass of an elephant, being pursued by large carnivores. Each distinct time period seems to be marked by a unique community of herbivores: two kinds of duckbills, two kinds of ceratopsids, and an ankylosaur or two. Each species is replaced, possibly through anagenesis, over millions of years. No species lived much longer than a million years, and there are very few cases of overlap between communities.
It's very strange, especially when you take home ranges and plant resources into consideration. It implies that these herbivorous dinosaurs had lower metabolic demands than modern herbivores, or the plant life was more sustainable and lush, or both.
Even better? The southern and northern communities of this strip of land are quite different, and there is no overlap. That is, you don't find any
Pentaceratops in the north AND the south. This division persists until the latest Cretaceous, when
Torosaurus pops up in Utah and Montana. Theoretically, that means there was some kind of environmental or geographic barrier preventing faunal exchange between the north and the south, but we don't know what that is yet. It's possible that a persistent river system or an expansion of the Sundance Sea divided that strip of land, but there isn't evidence for it...yet.
Download that paper (it's free) and give it a read. Fascinating stuff!