Meet the two-horned cousin of triceratops

From I09: Meet the two-horned cousin of triceratops
(Also at: http://blogs.smithsonianmag.com/dinosaur/2011/10/new-mexicos-peculiar-two-horned-dinosaur/
Triceratops has captured the public imagination ever since the first fossils were discovered in 1887. But it's hardly the only horned dinosaur that once roamed the Earth. Meet the two-horned zuniceratops, oldest of the American relatives of triceratops.

Compared to its more famous cousin, zuniceratops was a tiny dinosaur. The fossil record indicates that triceratops could reach up to thirty feet in length, ten feet in height, and weight over 25,000 pounds. Zuniceratops, on the other hand, was a puny ten feet long and three feet tall, and a very mild 200 to 250 pounds. The creature is named for the Zuni people, a Native American tribe that lives in the area of New Mexico where the dinosaur was discovered in 1996.

Relative to other horned dinosaurs like it - known collectively as the ceratopsians - zuniceratops was both much smaller and much older, dating back at least 90 million years ago. That makes it much older than triceratops, which emerged a mere three million years before the final extinction of the dinosaurs. This two-horned little guy was the earliest known ceratopsian in North America, though he wasn't the grandfather of triceratops - their evolutionary relationship is more like distant cousins once or twice removed, though they do look very similar.

The remains of Zuniceratops exhibit a mosaic of features shared with both earlier ceratopsians (such as Protoceratops) and the later, more familiar ceratopsids (such as Triceratops). While the body of Zuniceratops appeared to retain a more archaic, lightly built form, the prominent brow horns, the arrangement of the teeth (set up like a pair of scissors to shear vertically through food), a curved part of the hip called the ischium, and other characteristics underlined a close relationship to the ceratopsid dinosaurs that would eventually become so common on the continent.

But Zuniceratops was not a “missing link” or an ancestor to any of the ceratopsid dinosaurs. Instead, it is a peculiar dinosaur with a suite of features that may help us understand the transition between the more archaic ceratopsians and the early ceratopsids. The arrangement of anatomical characters in Zuniceratops gives us a general picture of what was happening among the horned dinosaurs at the time. After all, the grand pattern of evolution is a wildly branching tree of life, and in technical terms, Zuniceratops falls on a branch just outside the ceratopsid group—a relatively close cousin—but it did not share some of the telltale characteristics of the famous dinosaur group. Hopefully, as more dinosaurs like Zuniceratops are found, paleontologists will gain a clearer picture of how the greatest of the horned dinosaurs evolved.

References:

Farke, A., Sampson, S., Forster, C., & Loewen, M. (2009). Turanoceratops tardabilis—sister taxon, but not a ceratopsid Naturwissenschaften, 96 (7), 869-870 DOI: 10.1007/s00114-009-0543-8

Wolfe, D.G. & Kirkland, J.I. (1998). “Zuniceratops christopheri n. gen. & n. sp., a ceratopsian dinosaur from the Moreno Hill Formation (Cretaceous, Turonian) of west-central New Mexico”. Lower and Middle Cretaceous Terrestrial Ecosystems, New Mexico Museum of Natural History and Science Bulletin 24: 307–317.

Wolfe, D. G. (2000). New information on the skull of Zuniceratops christopheri, a neoceratopsian dinosaur from the Cretaceous Moreno Hill Formation, New Mexico. pp. 93–94, in S. G. Lucas and A. B. Heckert, eds. Dinosaurs of New Mexico. New Mexico Museum of Natural History and Science Bulletin No. 17.