Homalocephale vs. Dryosaurus


Time Period & Environment: Late Cretaceous Nemegt Formation of Mongolia, araucarian conifer forest

Written By: Caitlin Lindblad

It is an usually hot, muggy afternoon during the wet season, late Cretaceous of Mongolia 70 million years ago. The araucarian conifer forest canopy provides relief from the sun, though only aquatic residents can escape the heaviness hanging the air. Dark clouds soon begin tumbling across the sky, forewarning a thunderstorm fuelled by the high temperatures and humidity.

For a lone male Dryosaurus that mysteriously appeared here few days ago, this nothing strange. This new environment doesn’t seem particularly parched, though the heavy downpour is welcome nonetheless. In his home of late Jurassic American West these torrential rains bring fresh growth and an end to the dry season (Demko and Parrish 1998, Engelmann et al. 2004). Instinctively, he heads for shelter.

Under a nearby patch of forest cover, the flat head of a female Homalocephale pokes above the undergrowth. Visibility is significantly reduced, though she doesn’t seem concerned as her smaller stature helps her hide in vegetation. Besides, many predators are probably taking shelter themselves, unable to hunt successfully with their senses dampened.

The Homalocephale is struck on her right flank, suddenly pinned by the body of another dinosaur. She nips the attacker with her beak-like mouth, causing them to leap to their feet.

It is the Dryosaurus. Drawn to the foggy silhouette of this shelter he tripped over her, unable to see it was already taken. Shaken but not stirred, Homalocephale rights herself. To her, he looks very similar to one of her neighbours Prenocephale, which sports a round domed head instead of her flat one (Evans et al 2018).

Dome or no dome, it makes no difference. The strike to her side is an invitation to a territorial scuffle, something she has had plenty experience in. Dryosaurus has also chased off other small dinosaurs over dry scraps of food back home, but this is a new confusing context. The little dinosaur, its face just visible above the drenched ferns seems itching for a fight. Homalocephale charges, grazing the side of the Dryosaurus. He startles, not expecting the jolt and begins turning around.

Homalocephale however, is not finished and returns for round two. This time she catches the back of his thigh, buckling it in the process. The Dryosaurus takes the hint and trots off, snorting in discomfort. It is better to deal with being soaked than an angry roommate.

Homalocephale advances!!!


Demko, T.M., Parrish, J.T., 1998. Paleoclimatic setting of the Upper Jurassic Morrison. In: Carpenter, K., Chure, D.J., Kirkland, J. (Eds.), The Upper Jurassic Morrison Formation: An Interdisciplinary Study. Modern Geology, vol. 22, pp. 283 – 296.

Engelmann G. F; Chure D.J; Fiorillo A.R. 2004.. The implications of a dry climate for the paleoecology of the fauna of the Upper Jurassic Morrison Formation. , 167(3-4), 297–308. doi:10.1016/j.sedgeo.2004.01.008

Evans D.C, Hayashi S., Chiba K., Watabe M., Ryan M. J, Lee Y.N., Currie P.J., Tsogtbaatar K., Barsbold R.. 2018. Morphology and histology of new cranial specimens of Pachycephalosauridae (Dinosauria: Ornithischia) from the Nemegt Formation, Mongolia. Palaeogeography, Palaeoclimatology, Palaeoecology 494: 121–134

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