Brains of Omnivorous Dinosaurs Show Traces of Predatory Ancestry

Therizinosaurs were among the strangest of all dinosaurs. Evolution drastically modified these descendants of carnivorous coelurosaurs into feathered, long-necked, tubby omnivores. And, thanks to a new PLoS One study by Stephen Lautenschlager and coauthors, we now know that these peculiar dinosaurs had finely-tuned senses of smell and hearing.

Dinosaur brains rotted away long ago. But the endocranial cavity of a dinosaur skull preserves the shape of the animal’s brain, providing paleontologists with an outline of the creature’s neuroanatomy. In the new study, Lautenschlager and collaborators CT-scanned the skull of Erlikosaurus andrewsi and partial braincases of Falcarius utahensis and Nothronychus mckinleyi to investigate how therizinosaurs sensed the Cretaceous world.

Contrary to what the researchers expected, Erlikosaurus apparently had a well-developed sense of smell. Previous research on dinosaur olfaction suggested that less finely-tuned scenting abilities accompanied shifts to omnivory and herbivory among lineages like the ostrich-ish ornithomimosaurs and unusual oviraptorsaurs. Since therizinosaurs are thought to be omnivores or herbivores, these dinosaurs either retained a refined sense of smell from their ancestors or evolved the ability as part of their foraging behavior. In fact, the authors suggest, therizinosaurs might have retained a good sense of smell so that they could track down the “highly odoriferous” flowers and fruiting plants that proliferated during the Cretaceous.

The therizinosaurs examined in the study also had relatively well-developed senses of hearing, and, despite lacking the visual acuity of their predatory relatives, apparently had brain specializations which indicate that Erlikosaurus and Nothronychus “were capable of keeping their gaze focused on a target during rapid head and neck movement.” This skill might have been useful in interactions between therizinosaurs during confrontations or courtship, the authors propose.

Altogether, the mix of unexpected brain features hint that therizinosaurs co-opted the brain anatomy of their ancestors. While the bodies of therizinosaurs underwent major changes as they became better adapted to a mixed diet of flesh and forage, their brains still retained hallmarks of their hypercarnivorous ancestry.

Reference:

Lautenschlager, S., Rayfield, E., Altangerel, P., Zanno, L., Witmer, L. 2012. The endocranial anatomy of the Therizinosauria and its implications for sensory and cognitive function. PLoS ONE 7, 12: e52289. doi:10.1371/journal.pone.0052289