Heads up!

Dinosaurs are strange looking things aren't they? They resemble nothing that exists today. However, if we look closer, we can spot some similarities between them and living animals. In this post, we'll take a look a their skulls - what do they tell us about how dinosaurs lived?

First up is Prenocephale (Preen-o-sef-a-lee) (Sloped Head) (Maryanska and Osmolska, 1974). As can be seen in the picture, Prenocephale possesses a domed head. The function of the dome is a matter of much debate with ideas ranging from competition between males for mating (Colbert, 1955) to species or individual recognition (Goodwin and Horner, 2004).

Next is Troodon (Tro-o-don) (Wounding Tooth) (Leidy, 1856). The narrow, delicate jaw it possesses would indicate it is a carnivore. It has large, forward-facing eyes that helped it to gauge distances when hunting for prey. It's teeth, however, tells a more complicated story. To keep it short, there are two opposing views. That of Holtz et al. (1998), who believe Troodon to be omnivorous (based on the size and spacing of its denticles (small serrations on the tooth itself)) and Fiorillo (2008), who believes them to be entirely carnivorous (based on the large size of the teeth and their wear patterns). Now, you may have heard that Troodon is the most intelligent dinosaur based on its brain-to-body size ratio. We'll be looking at this claim in more detail later.

Next is Euoplocephalus (Yoo-Op-Low-Seff-A-Lus) (Well Armoured Head) (Lambe, 1910). Euoplocephalus has a wedge-shaped, squat head protected by spikes. It also has a short, wide mouth similar to a rhinoceros' with which it ate low-growing plants and shrubs. It's skull is very distinctive when compared to other ankylosaurs with relatively small, variably fluted teeth that lack a cingulum (a ridge at the base of the tooth), modified palpebrals (eyelids), shallow nostrils and the teeth of the upper jaw are curved towards the middle (Vickaryous and Russell, 2003). It also possessed bony eyelids, however, these are no longer regarded as being unique to Euoplocephalus (Coombs, 1972). However, despite this slew of defining characteristics it has recently been suggested that what we know of as Euoplocephalus is actually composed of four different genera namely: Euoplocephalus, Anodontosaurus (An-Oh-Dont-Oh-Saw-Us) (Toothless Lizard) (Sternberg, 1929), Scolosaurus (Sko-Low-Saw-Us) (Pointed Stake Lizard) (Nopcsa, 1928) and Dyoplosaurus (Die-Op-Low-Saw-Us) (Doubly-Armoured Lizard) (Parks, 1924). If this is the case, the distinguishing features of Euoplocephalus would become: absence of any ornamentation behind the eyes and, on the first armour ring of the neck, again no ornamentation and the osteoderms (bony scales) in the middle have a keel (in biology, ornamention is anything that serves as a display feature like spikes, horns, brightly-coloured feathers etc.) (Arbour and Currie, 2013). But we'll look in more detail on that later.

Finally, we have Styracosaurus (Stye-Rack-Oh-Saw-Us) (Spiked Lizard) (Lambe, 1913). Pretty impressive skull isn't it? There is a lot of variation amongst Styracosaurus individuals but they all seem to have had at least four large spikes on the frill. These spines could reach 50-55 cm long (Dodson, 1996). The large nasal horn, however, is probably not as big as depicted in this picture. The original specimen that Lambe used to described Styracosaurus had an incomplete horn. Lambe estimated that this horn was about 57 cm long. However, based on other material discovered since, the horn probably probably ended in a rounded tip about 20 cm long (Ryan et al., 2007). The function of the frill and horns has been debated about for decades. The ideas have been: attachment points for large jaw muscles (Lull, 1908); combat/defence (Farke et al., 2009); to regulate body temperature in a similar fashion to elephant's ears (Wheeler, 1978); and for sexual display (Farlow and Dodson, 1975).

So, as can be seen, dinosaur skulls are very varied and can provide us with a lot of information, even if there are still many unanswered questions. Next time, we'll take a look at another four dinosaur skulls. However, for the next post, we'll look at the process palaeontologists take to find, excavate and study fossils, starting with where they look for fossils.

See also:
More dinosaurs
More dinosaur anatomy
Even more dinosaur anatomy

References

Arbour, V. and Currie, P. (2013) 'Euoplocephalus tutus and the Diversity of Ankylosaurid Dinosaurs in the Late Cretaceous of Alberta, Canada, and Montana, USA', PLoS One, http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062421

Colbert, E. (1955) Evolution of the Vertebrates, New York: John Wiley

Coombs, W. (1972) 'The Bony Eyelid of Euoplocephalus (Reptilia, Ornithischia)', Journal of Paleontology, 46 (5), pp. 637-650

Dodson, P. (1996) The Horned Dinosaurs: A Natural History, Princeton: Princeton University Press

Farke, A., Wolf, E., Tanke, D. and Sereno, P. (2009) 'Evidence of combat in Triceratops', PLoS One, http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0004252

Farlow, J. and Dodson, P. (1975) 'The behavioral significance of frill and horn morphology in ceratopsian dinosaurs', Evolution, 29 (2), pp. 353-361

Fiorillo, A. (2008) 'On the Occurrence of Exceptionally Large Teeth of Troodon (Dinosauria: Saurischia) from the Late Cretaceous of Northern Alaska', Palaios, 23 (5), pp. 322-328

Goodwin, M. and Horner, J. (2004) 'Cranial histology of pachycephalosaurs (Ornithischia: Marginocephalia) reveals transitory structures inconsistent with head-butting behavior', Paleobiology, 30 (2), pp. 253-267

Holtz, T., Brinkman, D. and Chandler, C. (1998) 'Denticle morphometrics and a possibly omnivorous feeding habit for the theropod dinosaur Troodon', Gaia, 15, pp. 159-166

Lambe, L. (1910) 'Note on the parietal crest of Centrosaurus apertus, and a proprosed new generic name for Stereocephalus tutus' Ottawa Naturalist, 24, pp. 149-151

Lambe, L. (1913) 'A new genus and species of Ceratopsia from the Belly River Formation of Alberta', Ottawa Naturalist, 27, pp. 109-116

Leidy, J. (1856) 'Notice of remains of extinct reptiles and fishes, discovered by Dr. F. V. Hayden in the badlands of the Judith River, Nebraska Territory', Proceedings of the Academy of Natural Sciences of Philadelphia, 8, pp. 72-73

Lull, R. (1908) 'The cranial musculature and the origin of the frill in the ceratopsian dinosaurs', American Journal of Science, 4 (25), pp. 387-399

Maryanska, T. and Osmolska, H. (1974) 'Pachycephalosauria, a new sub-order of ornithischian dinosaurs', Paleontologia Polonica, 30 (3), pp. 45-102

Nopcsa, F. (1928) 'Dinosaurierreste aus Siebenbuergen' Geological Hungarica Series Palaeontologica, 4, pp. 1-76

Parks, W. (1924) 'Dyoplosaurus acutosquameus, a new genus and species of armored dinosaur; with notes on a skeleton of Prosaurolophus maximus', University of Toronto Studies Geological Series, 18, pp. 1-35

Ryan, M., Holmes, R. and Russell, A. (2007) 'A revision of the late Campanian centrosaurine ceratopsid genus Styracosaurus from the Western Interior of North America', Journal of Vertebrate Paleontology, 27 (4), pp. 944-962

Sternberg, C. (1929) 'A toothless armored dinosaur from the Upper Cretaceous of Alberta', Bulletin of the National Museum of Canada, 54 (49), pp. 28-33

Vickaryous, M. and Russell, A. (2003) 'A redescription of the skull of Euoplocephalus tutus (Archosauria: Ornithischia): a foundation for comparative and systematic studies of ankylosaurian dinosaurs', Zoological Journal of the Linnean Society, 137 (1), pp. 157-186

Wheeler, P. (1978) 'Elaborate CNS cooling structures in large dinosaurs' Nature, 275 (5679), pp. 441-443