Fruitadens

''Fruitadens'' is a genus of heterodontosaurid dinosaur. The name means "Fruita teeth", in reference to Fruita, Colorado (USA), where its fossils were first found. It is known from partial skulls and skeletons from at least four individuals of differing biological ages, found in Tithonian (Late Jurassic) rocks of the Morrison Formation in Colorado. ''Fruitadens'' is one of the smallest known ornithischian dinosaur, with young adults estimated at in length and in weight. It is interpreted as an omnivore and represents one of the latest-surviving heterodontosaurids.

History of discovery

''Fruitadens'' is known from fossils recovered under a valid paleontological permit in the 1970s and 1980s by teams led by George Callison, for the Natural History Museum of Los Angeles County (LACM). The discovery area, on lands managed by the Bureau of Land Management, is known as the Fruita Paleontological Area; the specimens were found there in sandstones of the Brushy Basin Member. Roughly equivalent beds have been dated to 150.3 ± 0.3 million years old and 150.2 ± 0.5 million years old, indicating an early Tithonian age.

The fossils now named ''Fruitadens'' were first thought to belong to a fabrosaurid similar to '' Echinodon'', a genus from the Early Cretaceous of England; Fabrosauridae at the time was considered a general group of primitive ornithopods, and ''Echinodon'' itself had not yet been reclassified as a heterodontosaurid. ''Fruitadens'', although not formally described for a number of years, was briefly described in several works, usually as a relative of ''Echinodon'' or a new species of the genus. Formal description came in January 2010, by Richard Butler and colleagues (though the paper was published online before print in late 2009). The type species is ''F. haagarorum'', in recognition of support provided by Paul Haaga Jr., Heather Haaga, Blythe Haaga, Paul Haaga III, and Catalina Haaga for the Natural History Museum of Los Angeles County.

Description

''Fruitadens'' is based on LACM 115747, consisting of incomplete jaws, a number of vertebrae, and partial hind limbs, of a nearly fully grown individual. At least three other individuals have been found. LACM 115727 is another nearly fully grown individual, known from vertebrae and hind limb bones. This individual was about the same size as LACM 115747, and was five years old at death. LACM 120478 consists of the upper arm and most of the left leg of a juvenile, in its second year. Finally, LACM 128258 includes partial jaws and vertebrae of another juvenile. The largest individuals are estimated to have been about long and in weight. This makes ''Fruitadens'' the smallest known ornithischian and comparable in size to the smallest known dinosaurs, outside of birds. Known material of '' Echinodon'' and '' Tianyulong'', related heterodontosaurids, comes from similar-sized individuals, but it is not known how old they were upon death.

''Fruitadens'' was similar to ''Heterodontosaurus'' in anatomy, with relatively short arms and long distal sections of the legs (feet and shins). The lower jaws had an enlarged canine-like tooth, with a corresponding gap in the upper jaw. Unlike ''Echinodon'', there wasn't an enlarged tooth in the upper jaw. Uniquely, a small peg-like tooth was present in front of the canine-like tooth. Replacement teeth were present in the jaws, unlike most other heterodontosaurids. The hind limb bones were hollow, like those of small theropod dinosaurs. ''Fruitadens'' seems to have been more closely related to ''Heterodontosaurus'' than ''Echinodon'', which was closer in time.

Classification

The cladogram below follows the analysis by Butler ''et al.'', 2011:

Paleoecology and paleobiology

The four individuals were found in localities at the base of the Morrison Formation's Brushy Basin Member, in crevasse splay sandstones deposited in floodplains. The Fruita localities preserved a contemporaneous fauna including snails, clams, crayfish, various insects (represented by trace fossils), the lungfish '' Ceratodus'', ray–finned fish, the turtle '' Glyptops'', rhynchocephalian reptiles '' Eilenodon'' and '' Opisthias'', several genera of lizards, a mesosuchian crocodylomorph, and the mammals ''Fruitafossor'', ''Glirodon'', and '' Priacodon''. Disarticulated dinosaur fossils are common in the area.

''Fruitadens'' was probably bipedal and cursorial, and is suggested to have been omnivorous. Like ''Echinodon'' and ''Tianyulong'', other late-surviving heterodontosaurids, ''Fruitadens'' had less specialized jaws than Early Jurassic heterodontosaurids like ''Heterodontosaurus'', and is interpreted as a generalist. A 2012 study of the skull suggested its diet was composed of select plant material and possibly insects or other invertebrates.

See also

* 2010 in paleontology
* Dinosaurs of the Morrison Formation

References

External links

'Tiny dinosaur species identified' BBC website page on ''Fruitadens haagarorum''.

{{Taxonbar, from=Q133058

Heterodontosauridae
Dinosaur genera
Tithonian dinosaurs
Morrison Formation
Taxa named by Peter Galton
Taxa named by Luis M. Chiappe
Fossil taxa described in 2010
Dinosaurs of the United States