PLOS Paleo Top 10 OA Fossil Vertebrates #9: Spiclypeus shipporum

Next up on the list of Top 10 Open Access Fossil Vertebrates, as voted by the paleontology community, is Spiclypeus shipporum, a new chasmosaurine ceratopsian dinosaur that was described earlier this year and published in PLOS ONE. The holotype specimen, nicknamed “Judith” after the Judith River Formation from which it was discovered, is about 76 million years old. It is now housed at the Canadian Museum of Nature where lead author, Dr. Jordan C. Mallon, is based.

map
A) Location in Montana where Spiclypeus is found. B) Stratigraphic position of Spiclypeus in the Judith River Fm. C) Quarry map by J. Small. From Mallon et al (2016) CC-BY

The discovery of Judith was made over a decade ago by Dr. Bill Shipp, a retired nuclear physicist and fossil enthusiast. Shipp stumbled across the fossil remains while exploring his newly acquired property in Montana in 2005. “Little did I know that the first time I went fossil hunting I would stumble on a new species,” Shipp said.

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The dig site in Montana where Spiclypeus was recovered. 76 million years ago, this area was a lowland floodplain with braided and meandering stream systems. Photo courtesy Joe Small.

The Canadian Museum of Nature purchased the fossil in 2015 from Shipp, and also aided in collecting the specimen from Shipp’s property. To honor Shipp and his family for their fantastic contribution to science, the author’s of the paper gave the specific epithet shipporum.

judith
Skull reconstruction of Spiclypeus shipporum (CMN 57081). The missing parts of the skull are shown faded. From Mallon et al. (2016) CC-BY

Spiclypeus‘s generic name means “spiked shield,” referring to the impressive display of spikes on its frill. Though the skull is approximately 50% complete, Mallon and colleagues were able to recognize several distinguishing characteristics that separate Spiclypeus from other ceratopsians, including the laterally-directed postorbital horns and the unique arrangement of spikes on the frill. Some of these spikes curl forward while others project outward from the frill.

“In this sense, Spiclypeus is transitional between more primitive forms in which all the spikes at the back of the frill radiate outward, and those such as Kosmoceratops in which they all curl forward,” says Mallon.

In the study’s phylogenetic analysis of evolutionary relationships, Spiclypeus was recovered within the Chasmosaurinae clade, sister to Kosmosceratops Vagaceratops. This study also casts doubt on the taxonomic validity of some other species of ceratopsians, namely the first described ceratopsian, Ceratops montanus, a taxon long-considered nomen dubium. The original specimen of Ceratops was known only from postorbital horns and a parietal occiput, and was discovered approximately 53 kilometers away from where Spiclypeus was discovered. The know material of Ceratops shows great similarity to both SpiclypeusThis study suggests that Ceratops could possibly belong to the same species as Spiclypeus. However, the evidence for this relationship is vague, and the authors, not wanting to draw this conclusion based on such little evidence, chose to erect new genus Spiclypeus instead.

Based on pathological evidence gained from Judith’s remains, it is easy to interpret that Judith had a hard life, and was in poor health when it died. Bone remodeling in the skull suggests possible infections post-combat or from some other blow to the skull.

Additionally, the humerus shows signs of arthritis and infection, according to an analysis conducted by Dr. Edward Iuliano, a radiologist at the Kadlec Regional Medical Center in Richland, Washington.

“If you look near the elbow, you can see great openings that developed to drain and infection. We don’t know how the bone became infected, but we can be sure that it caused the animal great pain for years and probably made its left forelimb useless for walking,” explains Mallon.

humerus
The disease-riddled left humerus of Judith. The large opening near the elbow (red arrow, inset) served to drain a nasty bone infection. Image: Scott Rufolo © Canadian Museum of Nature

Despite Judith’s injuries, however, growth rings in the bones suggest that Judith was at least 10 years old when it died.

Spiclypeus is one of nine recognized dinosaur species from the Judith River Formation in Montana, much lower in number than its contemporaries (Belly River Group of Alberta has yielded around 55 distinct species, and the Kaiparowits Formation of Utah has yielded approximately 15 recognized species). But species like Spiclypeus are unique to the Judith River Formation in Montana, and not shared with the neighboring faunal assemblages. Mallon suggests that dinosaur species at this time were highly localized, possible due to dietary specializations. Discoveries like Spiclypeus demonstrate that, for as much as we now know about dinosaurs of the Cretaceous, we still have much to learn.

The Canadian Museum of Nature has produced some great online material regarding Spiclypeus, and I recommend you check them out!

Reference:

Mallon JC, Ott CJ, Larson PL, Iuliano EM, Evans DC (2016) Spiclypeus shipporum gen. et sp. nov., a Boldly Audacious New Chasmosaurine Ceratopsid (Dinosauria: Ornithischia) from the Judith River Formation (Upper Cretaceous: Campanian) of Montana, USA. PLoS ONE 11(5): e0154218. doi:10.1371/journal.pone.0154218

This post contains materials provided by the Canadian Museum of Nature.

Featured image: Reconstruction of Judith, hold diseased front arm aloft. Artwork by Mike Skrepnick.

Published by Sarah Z. Gibson

Dr. Sarah Z. Gibson is a paleontologist and science communicator based in Minnesota. Her research focuses on the evolutionary history of ray-finned fishes from the Early Mesozoic. https://orcid.org/0000-0002-6784-3980

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