Reconstruction of Prenocephale prenes, showing different types of speculative behavior and hypothetic presence of filamentous integumentary structures in pachycephalosaurs. This is my first entry for “All Your Yesterdays” contest - [link].

Prenocephale prenes is pachycephalosaurid ornithischian from the Nemegt formation (Mongolia). It was about 2.4 meters long and lived during the late Campanian, or early Maastricthian times (~ 72 million years ago). It was herbivorous animal. Here, it’s shown hiding from big predator, the theropod Alioramus remotus.

The filamentous integumentary structures depicted here are speculative, but similar integumentary structures, made of beta-keratin and located mostly in the dorsal part of the torso, are found in the ceratopsian Psittacosaurus (Ceratosauria is a sister clade of Pachycephalosauria), and in the heterodontosaur Tianyulong. Both of them being ornithischian dinosaurs (former being more derived, and the latter more basal ornithischian), leave open the possibility that such structures could have been more distributed among the members of the group, and even homologous to the feathers in theropods. Reconstructing Prenocephale with filaments is my way to support the idea (it’s only idea for now given the fossil material at hand and the lack of studies testing this hypothesis) that the presence of filamentous integumentary structures is a basal trait for Dinosauria.

Here, the filaments are located in between the scales, as similar arrangement of feathers and scales is known in some modern birds. This can be explained by Prum’s model for feathers evolution, in which feathers (or protofeather filaments) are homologous in the embryonic stage of animal’s development, and later form different types of integument, which sometimes can coexist.

The majority of the body is covered with scales, following the model seen in Triceratops – subrectangular scales on the ventral side of the body, and finer scales above them. Some of the scales are bigger, with oval form, and are circled by smaller scales, forming rosette-like pattern.

It’s known that at least some dinosaurs (Oryctodromeus and possibly its closest relatives) had an adaptations of digging and were able to live in dens. Similar adaptations are not known for pachycephalosaurids (as far as my knowledge goes), but many digging/denning animals have no obvious adaptations for such behavior/life style. Here, Prenocephale is using a den to hide from a predator. I won’t go as far as stating the burrow was made by the dinosaur, it may just use already existing one.

But denning is not its only protection. If some pachycephalosaurs really were able hide underground from time to time, then they could have gone even further by using mimicry. Because of the specific shape of their head - the dome structure, some of them could have used it to mimic the rocks around, thus increasing their chance to not be noticed by the predator.

References:

Mayr, G., D. S. Peters, G. Plodowski, O. Vogel. 2002. Bristle-like integumentary structures at the tail of the horned dinosaur Psittacosaurus.- Naturwissenschaften, 89, 361-365.

Paul, G. S. 2010. The Princeton field guide to dinosaurs.- Princeton University Press (for Prenocephale skeletal drawing; as obviously seen, neither his style, nor the pose of his skeletal drawing were used in any form in my artwork).

Prum, R. O. 2003. Are current critics of the theropod origin of birds science? Rebuttal to Feduccia (2002).- The Auk, 120, 2, 550-561.

Varricchio, D. J., A. J. Martin, Y. Katsura. 2007. First trace and body fossil evidence of a burrowing, denning dinosaur.- Proceedings of Royal Society Biological Sciences, 274, 1361-1368.

Xu, X., X. Zheng, H. You. 2009. A new feather type in a nonavian theropod and the early evolution of feathers.- Proc. Natl. Acad. Sci., 106, 3, 832-834.