Kosmodraco is a genus of large bodied choristodere from the Paleocene of North America. Originally described as a species of the closely related Simoedosaurus, it was found to represent a distinct genus in 2022. Multiple fossil skulls show a relatively short and robust snout and a skull that is considerably wider behind the eyes. Two species are currently recognized, K. dakotensis and K. magnicornis.
History and naming The first specimen now known to belong to Kosmodraco was discovered in 1964 and 1968 in the Polecat Bench Formation (Wyoming). These two skulls, alongside others from Montana's Bear Creek, were reported on briefly by Sigogneau-Russell and Donald in 1978, who regarded them as evidence for the presence of the Eurasian genus Simoedosaurus in North America. However, at the time, these four specimens, although thought to be diagnostic at a genus level, were still unprepared and not assigned to a species. They were subsequently stored in the collection of the Princeton University. It wasn't until a fifth specimen from North Dakota was prepared that the North American remains were named, with Bruce R. Erickson creating the new species Simoedosaurus dakotensis in 1987 and assigning the Princeton material and two additional specimens to it. Erickson, however, did realize there were differences in the specimens, noting that the North Dakota specimen was not just older (mid Tiffanian) than the Princeton fossils (late Tiffanian to Clarkforkian) but also larger, which he initially attributed to differences between growth stages. Later, in 2022, Chase Doran Brownstein reexamined the American Simoedosaurus material, finding that it differed enough to be described as its own genus. Brownstein further considered that the two best preserved Princeton specimens, YPM VPPU 19168 and YPM VPPU 18724, weren't juveniles but should instead be considered a second species. Subsequently, the genus Kosmodraco was erected with K. dakotensis as the type species and a second species in the form of K. magnicornis. The name Kosmodraco translates to "ornamented dragon" from the Greek κοσμος and Latin draco. The type species was named after the state of North Dakota, while K. magnicornis was named for its large squamosal spikes, derived from the Latin magnum (large) and cornum (horn).
Description
Unlike the well known Champsosaurus, Kosmodraco had an exceptionally brevirostrine skull with the blunt muzzle only making up approximately one third of the total skull length. The posterior region, mostly made up of the squamosal bone, is exaggeratedly broad, giving the skull an overall triangular form. Additionally, all of the skulls show that the cranium of Kosmodraco was exceptionally flat and covered by ridges and furrows along the dorsal and lateral surface. To add to this, four transverse bumps are present on the prefrontals before and between the eyes. The external nares make up around half the width of the bulbous premaxilla and are partly divided by the fused nasal bone. The nasal further extends into the nares through an internasal bar. The premaxilla is only slightly longer than wide and followed by a marked constriction where they meet the maxillae. Four premaxillary teeth of somewhat similar size are followed by forty-five maxillary teeth. In the holotype specimen, the anterior areas of the maxilla show an alternating patter between erupted teeth and empty alveoli, with the second maxilla showing the opposite distribution. Following the 16th tooth, this alternating pattern stops in favor of more continuous tooth rows. Tooth rows are additionally present on the vomers and palatines with small and blunt dentition. The paired prefrontals are anteriorly bifurcated by the nasal and reach to almost the exact halfway point between the orbits where they meet the rectangular frontal bones. The orbits are subangular and directed dorsolaterally, in spite of the flattening of the skull. The shape of the orbits is owed to the fact that the skull roof overhangs large portions of them. Almost the entire medial border of the supratemporal fenestrae consists of the parietal bones, which display a long suture along the center of the skull. The central portion where the two parietals meet is located in a shallow through while the posterior elements of the bones are raised as a crest before meeting the squamosals. The squamosal bones themselves display prominent nodes towards the rear of the skull. The infratemporal and supratemporal fenestrae are similar in size and the maximum distance between the squamosals is only slightly larger than the width of the skull table.
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