| Name: Fruitadens haagarorum Etymology: From the Fruita locality in Colorado), and Latin "dens" (tooth); and from the surname Haaga Distribution: Late Jurassic (early Tithonian) of North America Type Specimen: Jaw, vertebrae and limb bones of a near-adult individual Estimated size: 65 - 75 cm body length |  |
Interesting Fact: Not all dinosaurs were giants!
It's really not surprising that small (relative to humans) dinosaurs existed: they were a dominant group, spread across the whole globe, persisting for ~200 million years, who filled most ecological niches (habitats with specific resources such as different food types). However, up until 2010, the only small dinosaurs described were theropods. Then along came the smallest known ornithischian, Fruitadens haagarorum.
Remember how I mentioned niches before? Basically, in any given environment, there are different food types to consume. If an animal can eat a variety of food types, it can occupy a variety of niches. The teeth of F. haagarorum, along with other heterodontosaurids, suggest they were omnivorous (eating both plants and animals). It is possible that this omnivory, and resulting occupation of many niches, was the reason for the 100 million year success of the heterodontosaurids.
It's really not surprising that small (relative to humans) dinosaurs existed: they were a dominant group, spread across the whole globe, persisting for ~200 million years, who filled most ecological niches (habitats with specific resources such as different food types). However, up until 2010, the only small dinosaurs described were theropods. Then along came the smallest known ornithischian, Fruitadens haagarorum.
Remember how I mentioned niches before? Basically, in any given environment, there are different food types to consume. If an animal can eat a variety of food types, it can occupy a variety of niches. The teeth of F. haagarorum, along with other heterodontosaurids, suggest they were omnivorous (eating both plants and animals). It is possible that this omnivory, and resulting occupation of many niches, was the reason for the 100 million year success of the heterodontosaurids.
Figure showing F. haagarorum jaws and teeth. The teeth aren't as tightly packed as you would expect in a herbivore, and along with a lack of tooth-on-tooth wear on the teeth, this suggests its diet didn't consist solely of plant material. Scalebars, (a,c,d) 5mm; (e) 10mm; (f) 0.15mm. From Butler et al., 2010.
Simplified cladogram of all dinosaurs. F. haagarorum was a heterodontosaurid, within ornithischia.
References:
Butler, R., Galton, P., Porro, L., Chiappe, L., Henderson, D. and Erickson, G., 2010. Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic heterodontosaurid from North America. Proc. Royal Soc. B 277: 375 - 381.
Butler, R., Porro, L., Galton, P., Chiappe, L., 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.
Butler, R., Galton, P., Porro, L., Chiappe, L., Henderson, D. and Erickson, G., 2010. Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic heterodontosaurid from North America. Proc. Royal Soc. B 277: 375 - 381.
Butler, R., Porro, L., Galton, P., Chiappe, L., 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.
