Two New Horned Dinosaur Discoveries Reveal A Striking Evolutionary Divide

Its certainly been a bumper day for new horned dinosaur discoveries: Two newly unveiled ceratopsids, one found in southern Utah and the other excavated in Montana, are showcasing how diverse this group of wandering herbivorous beasts truly were. Both lived in the Late Cretaceous period between 100 and 66 million years ago, and their discovery adds fresh detail to the story of the dinosaurs during their final geological chapter.

The first, analyzed by a team led by Ohio University, roamed the southern portion of the ancient North American continental land mass Laramidia around 77 million years ago. Named Machairoceratops cronusi, its fossilized fragmented skull revealed that it would have been 6 to 8 meters (19.7 to 26.2 feet) long, and would have weighed up to 1.81 tonnes (2 tons).

As detailed in the study in PLOS ONE, like other centrosaurine ceratopsids, it had a parrot-like beak, a huge nose, ornamented frills (neck shield), and a distinctive cranial horn arrangement. Notably, its neck shield was clearly very different in appearance from any of the other ceratopsids found across the entirety of Laramidia.

A reconstruction of the skull of Machairoceratops cronusi. Lund et al./PLOS ONE

Machairoceratops is unique in possessing two large, forward curving spikes off of the back of the neck shield, each of which is marked by a peculiar groove extending from the base of the spike to the tip, the function of which is currently unknown, Eric Lund, the studys lead author and Ohio University graduate student, said in a statement.

The skull, although unique, is more similar to the only other centosaurine ceratopsid yet discovered from southern Laramidia, Diabloceratops, than any found in the north of the long-gone hot and swampy island continent. This strongly suggests that there was an evolutionary divide between the ceratopsids on Laramidia, marked by a latitudinal boundary. The two groups were likely experiencing different sets of environmental pressures or dietary requirements, forcing them to evolve in different ways in order to survive.

An artists impression of Spiclypeus shipporum. Mike Skrepnick

Speaking of this divide, the second ceratopsid, as also described in the journal PLOS ONE in a separate study, was unearthed in northern Laramidia. The international research team, led by Dr. Jordan Mallon of the Canadian Museum of Nature, named it Spiclypeus shipporum. It lived 76 million years ago and possessed a spiked shield around its head, covered with triangular spikes.

Identified as an entirely new species by looking for novel features on its broken fossilized skull, legs, hips, and backbone, the researchers highlight that the horns over its eyes, which stick out sideways from its skull, are particularly unusual. In addition, the spikes on its cranial shield curve in multiple directions, which would have given it a very peculiar appearance.

Judith, as described by Jordan Mallon. Canadian Museum of Nature via YouTube

In this sense,Spiclypeusis transitional between more primitive forms in which all the spikes at the back of the frill radiate outward, and those such asKosmoceratopsin which they all curl forward, Mallon, the lead author of the paper, said in a statement.

Like many dinosaur species around the world, this one also has a nickname,Judith, named after the geological formation in which it was originally found. Sadly, Judith may have lived a life of pain: her upper arm bone show signs of both arthritis and serious bone infections.

It would have limped along for a good portion of its life, but researchers say that, despite this, it appeared to have lived to maturity. In any case, Judith is another wonderful example of how different the northern ceratopsids were compared to their southern counterparts.

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Read more: http://www.iflscience.com/plants-and-animals/two-new-horned-dinosaur-discoveries-reveal-striking-evolutionary-divide

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