Pelecanimimus

Taxobox
name = "Pelecanimimus"
status = fossil
fossil_range = Early Cretaceous


image_width = 200px
image_caption =
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Theropoda
infraordo = Ornithomimosauria
genus = "Pelecanimimus"
species = "P. polyodon"
binomial = "Pelecanimimus polyodon"
binomial_authority = Perez-Moreno "et al.", 1994

"Pelecanimimus" (meaning "pelican mimic") is a genus of primitive (basal) ornithomimosaur from the Early Cretaceous of Spain. It is notable for possessing more teeth than any other member of the Ornithomimosauria, most of which were toothless. The only known specimen consists of the articulated front half of a skeleton and includes the skull, all the neck vertebrae and most of the back vertebrae, ribs, sternum, the pectoral girdle, a complete right forelimb and most of the left forelimb. The species, "P. polydon", is named for the large number of teeth possessed by this theropod (Greek "polys" = "many" + Greek "odus" = teeth).

Description

"Pelecanimimus" was a small ornithomimosaur, at about 2-2.5 m long (6.5 - 8 ft). Its skull was unusually long and narrow, with a maximum length of about 4.5 times its maximum height. It was highly unusual among ornithomimosaurs in its large number of teeth: it had about 220 very small teeth in total, with 7 premaxillary, about 30 maxillary, and 75 in the dentary. The teeth were heterodont, showing two different basic forms. The teeth in the front of the upper jaw were broad and D-shaped in cross section, while those further back were blade-like, and on the whole the teeth in the upper jaw were larger than those in the lower. All of its teeth were unserrated, and had a constricted "waist" between the crown and the root.Kobayashi, Y., and Barsbold, R. (2005). "Anatomy of "Harpymimus okladnikovi" Barsbold and Perle 1984 (Dinosauria; Theropoda) of Mongolia." in "The Carnivorous Dinosaurs" ed. Carpenter, K. 2005. Indiana University Press:97-126.]

Only one other ornithomimosaur is known to possess teeth, "Harpymimus", which had far fewer (eleven total, and only in the lower jaw). The presence of such a large number of teeth in "Pelecanimimus", coupled with a lack of interdental space, was interpreted by Perez-Moreno "et al." as an adaptation for cutting and ripping, a "functional counterpart of the cutting edge of a beak," as well as an exaptation leading to the toothless cutting edge found in later ornithomimosaurs.

The arms and hands of "Pelecanimimus" were more typical of ornithomimosaurs, with the ulna and radius bones in the lower arm tightly adhered close to the hand, which were hook-like and had fingers of equal length.

Soft-tissue impressions preserved by the exceptional preservational environment of the La Hoyas lagerstätten revealed the presence of a small skin or keratin crest on the back of the head, and a gular pouch similar to the much larger pouches found in modern pelicans, from which "Pelecanimimus" took its name. "Pelecanimimus" might have been much like a modern day crane, wading out in lakes or ponds using its claws and teeth to capture fish and then storing them in its skin flap. Some parts of the impressions revealed a smooth, skin-like surface, initially interpreted as lacking any ornamentation or feathers. "Pelecanimimus" was also the first ornithomimosaur discovered with a preserved hyoid apparatus (specialized bones in the neck).Perez-Moreno, B. P., Sanz, J. L., Buscalioni, A. D., Moratalla, J. J., Ortega, F., and Raskin-Gutman, D. (1994). "A unique multitoothed ornithomimosaur from the Lower Cretaceous of Spain." "Nature", 30: 363-367.]

Phylogeny and Evolution

A cladistic analyses by Makovicky "et al." (2005) indicated that "Pelecanimimus" is the basalmost member of the Ornithomimosauria, less derived even than "Harpymimus".Makovicky, P., Kobayashi, Y. and Currie, P. J. (2004). "Ornithomimosauria." pp. 137-150 in D. B. Weishampel, P. Dodson, et H. Osmólska (eds.), "The Dinosauria". 2nd ed. University of California Press, Berkeley.] A study by Kobayashi and Lü in 2003 indicated that these two species formed a basal arrangement of steps leading towards the more advanced ornithomimids (see cladogram below).Kobayashi, Y., and Lü, J.-C. (2003). "A new ornithomimid dinosaur with gregarious habits from the Late Cretaceous of China." "Acta Palaeontologica Polonica" 48:235-259.] The discovery of "Pelecanimimus" has played an important and surprising role in understanding the evolution of the Ornithomimosauria. To quote Pérez-Moreno "et al.", "The phylogenetic hypothesis...supports an unexpected approach, involving exaptation, which might explain the evolutionary process towards the toothless condition in Ornithomimosauria. Until now, a progressive reduction in the number of teeth has been considered as the most likely explanation: the primitive tetanurine theropods have up to 80 teeth with tall blade-like crowns, and the primitive ornithomimosaurs have only a few small teeth. The phylogenetic hypothesis suggests an alternative evolutionary process based on a functional analysis of increasing numbers of teeth. A high number of teeth with enough interdental space and properly placed denticles (as in troodontids) would be an adaptation for cutting and ripping. On the other hand, an excessive number of teeth with no interdental space (as in "Pelecanimimus") would be a functional counterpart of the cutting edge of a beak. Thus, increasing the number of teeth would be an adaptation for cutting and ripping, as long as the space between adjacent teeth was preserved...while it would have the effect of working as a beak if spaces were filled with more teeth. The adaption to a cut-and-rip function therefore becomes an exaptation with a slicing effect, eventually leading to the cutting edge seen in most ornithomimosaurs."

Cladogram after Kobayashi and Lü, 2003:

Ornithomimosauria
--"Pelecanimimus" `--o
--"Harpymimus" `--o
--"Garudimimus" `--Ornithomimidae

Provenance

The holotype specimen (LH 777, Museo de Cuenca, Cuenca, Spain) of "Pelicanimimus" was recovered at the famous La Hoyas locality in Cuenca Province, Spain, from lagerstätte beds within the Calizas de La Huérguina Formation (Lower Barremian). This same lagerstätte has produced numerous other exquisitely preserved species, including the enantiornithine birds "Iberomesornis", "Concornis", and "Eoalulavis", along with non-avian theropod teeth and a few fragmentary sauropod bones. Coarse sediments of the La Hoyas lagerstätte have produced bones of the ornithopod dinosaur "Iguanodon". The lagerstätte beds have also yielded remains of lizards and salamanders.

In popular culture

"Pelecanimimus" was featured in the 2002 video game "Dino Island", published by Monte Cristo.

References