GEOL 104 Dinosaurs: A Natural History

Fall Semester 2018
Through the Eyes of a Dinosaur: Dinosaur Brains & Senses

Close-up of the face of the ceratopsid Styracosaurus by John Conway

Key Points:
•Although brains and sense organs do not fossilize, there are some approaches that allow us to approximate the sensory abilities of extinct dinosaurs.
•The relative size of different portions of the dinosaurian brain allow us to interpret which functions were emphasized and which reduced in any given group of dinosaur.
•Non-avian dinosaur brain size is smaller than those of birds or mammals, but typically larger than those of crocodilians, lepidosaurs, and turtles.
•Dinosaur olfaction and vision seem to have been fairly well-developed, as was their sense of balance.

We can use biomechanics for understanding the sensory world of the dinosaurs.

One of the most important tools is the CT scanner. CT scans have given considerable new help in figuring out how dinosaurs lived and operated. For example, they help reveal the development of different lobes of the brain, as recorded in the endocast (the void left over when the brain decays:

From this, the relative sizes of the olfactory (smelling), optic (sight), and other lobes can be examined.

Additionally, CT scans allow su to assess the relative size of the various semicircular canals (organs of balance in the ears).

Dinosaur hearing has been approximated using the size of the preserved inner ear spaces. Preliminary research shows that giant dinosaurs like Giraffatitan have have heard sounds best about 1 octave below the preferred hearing frequencies of humans.

Dinosaur vision has been estimated by combining phylogenetic distributions of traits in living taxa and in some measurements from bones. Living diapsids typically have 4-to-5 types of color receptors (compared to 3 in us and other related primates, and only 2 in most placental mammals), with ranges slightly higher into the ultraviolet than we see. Thus, almost certainly extinct diapsids (including non-avian dinosaurs) had "bird-like" vision: more ability to divide up visible light into various colors than we do.

Looking at the position of the orbits, we can approximate the degree to which vision overlapped in the species, and thus the ability to which they could potentially have binocular vision (and thus better depth perception). Most dinosaurs had fairly limited binocular vision, but a great range of vision around them. Certain theropod groups (in particular tyrannosaurids and deinonychosaurs) had quite good overlap, however.

By measuring the size of the aperture of the eyes (the space inside the bony sclerotic ring) versus the outside edge of the sclerotic ring, you can attempt to see if the dinosaur or other species was mostly diurnal (active during the daytime), nocturnal (active at night), or cathemeral (active in both: a very common behavior for large-bodied animals). Preliminary studies show most Mesozoic dinosaurs as cathemeral, with a few (such as Velociraptor, Microraptor, Megapnosaurus, and the juvenile small theropod Juravenator) as nocturnal, and Archaeopteryx, basal avialians, and the small ornithischian Agilisaurus as diurnal.

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Last modified: 13 August 2018

The Late Cretaceous abelisaurid Majungasaurus (left) and the Late Jurassic carnosaur Allosaurus (right), showing the endocranium (brain cavity), from Witmer & Ridgely (2009) doi: 10.1002/ar.20983