In paleontology, the fossil is the basic data point for any research, regardless of the amount of technology used. Consequently, descriptions of a fossil’s anatomy are critical for scientists answering a variety of questions. What species is this animal? Look to the fossil. What did it eat? Look at the teeth. Where does the animal fit on the evolutionary tree? Compare its fossil with other fossils. Detailed documentation and description of a specimen isn’t particularly glamorous, but absolutely necessary.
The tiny plant-eating dinosaur Fruitadens scurried through the underbrush of Colorado around 150 million years ago, long before the rise of the Rocky Mountains. First named in a brief article in 2010, Fruitadens made a splash for its diminutive length of less than 1 meter and estimated body mass of under 1 kilogram. Unfortunately, the original publication did not have space for more than a general anatomical description as well as confirmation that Fruitadens’ small size wasn’t because it was “just” a baby of a larger species. Thus, a new paper in PLoS ONE by Richard Butler, Laura Porro, Peter Galton, and Luis Chiappe fills in many of the essential details.
Fruitadens belonged to an unusual, widespread, and rare group of dinosaurs called heterodontosaurids. They first appeared around 200 million years ago in South Africa, and persisted until around 140 million years ago in England. Heterodontosaurids were small (no more than 2 meters in maximum body length) and characterized by unusual fangs at the front of their jaws. Fruitadens was no exception—although its lower jaw is incomplete, the preserved portion of the teeth shows that it too probaby had fangs. The rest of the teeth are more conventional, similar to those seen in other small plant-eating dinosaurs.
So, how did Fruitadens and other heterodontosaurids use their tiny, fanged jaws? The researchers developed simple two-dimensional models of the jaws in heterodontosaurids, reconstructing the movements associated with the bones and muscles. A basic difference between early and late-surviving heterodontosaurids (including Fruitadens) was identified. Specifically, Fruitadens and its close relatives had simpler jaw anatomy than their ancestors, suggestive of a switch to simpler, weaker, and more rapid jaw movements. Although much more work remains, Butler and colleagues suggest that Fruitadens may have been an ecological generalist subsisting on a variety of plants, insects, and other small organisms. This contrasts with the diet of its ancestors, subsisting primarily on plants.
Because they are so small, heterodontosaurid fossil are pretty scarce, and details of their evolutionary relationships are sketchy. Butler and colleagues carefully documented all of the relevant anatomical details in Fruitadens through photographs, CT scans, and text. In the process, the researchers identify some previously unrecognized features that characterize heterodontosaurids as a whole, and other formerly recognized features that do not. Although much work remains—particularly through the collection and description of new fossils—this new paper is an important step towards better understanding Fruitadens and its enigmatic kin.
Butler RJ, Galton PM, Porro LB, Chiappe LM, Henderson DM, Erickson GM (2010) Lower limits of ornithischian dinosaur body size inferred from a diminutive new Upper Jurassic heterodontosaurid from North America. Proc Roy Soc B 277: 375–381.
Butler RJ, Porro LB, Galton PM, Chiappe LM (2012) Anatomy and cranial functional morphology of the small-bodied dinosaur Fruitadens haagarorum from the Upper Jurassic of the USA. PLoS ONE 7(4): e31556. doi:10.1371/journal.pone.0031556
Top image from http://en.wikipedia.org/wiki/File:Fruitadens.jpg, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.
Bottom image from Butler et al. 2012, Figure 1.
About the Author: Dr. Andrew Farke is a vertebrate paleontologist and an academic editor at PLoS ONE. He handled the manuscript described in this post. Andy also has a blog, The Open Source Paleontologist and can be followed via Twitter @andyfarke.