GEOL 104 Dinosaurs: A Natural History

Fall Semester 2017
Through the Eyes of a Dinosaur: Dinosaur Brains & Senses

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

Key Points:
•Cladistics (phylogenetic systematics) is a method for approximating the evolutionary relationships among taxa.
•Cladistics works by trying to reconstruct the pattern of common ancestry rather than finding direct ancestor-descendant relationships.
•Not all traits are equally useful for reconstructing phylogenetic relationships: only shared evolutionary transformations help us determine phylogenetic patterns.
•Phylogenetic information can be used as a basis for taxonomy; as a means of inferring missing and ancestral information; and for determining the time of divergence between lineages.

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: 6 July 2017

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