| Pelecanimimus | |
|---|---|
 | |
| Restoration ofP. polyodon | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | †Ornithomimosauria |
| Clade: | †Macrocheiriformes |
| Genus: | †Pelecanimimus Perez-Morenoet al.,1994 |
| Species: | †P. polyodon |
| Binomial name | |
| †Pelecanimimus polyodon Perez-Morenoet al., 1994 | |
Pelecanimimus (meaning "pelican mimic") is anextinctgenus ofbasal ("primitive")ornithomimosauriandinosaur from theEarly Cretaceous ofSpain. It is notable for possessing moreteeth than any other member of theOrnithomimosauria (or any othertheropod), most of which were toothless.
In July 1993Armando Díaz Romeral discovered a theropod skeleton at theLas Hoyas Unit 3 site. In 1994 this was named and described byBernardino Pérez Pérez-Moreno,José Luis Sanz,Angela Buscalioni,José Moratalla, Francisco Ortega andDiego Rasskin-Gutman as a new species:Pelecanimimus polyodon. The generic name is derived fromLatinpelecanus, "pelican", andmimus, "mimic", in reference to the long snout and throat pouch. Thespecific name is a reference to the large number of teeth possessed by this theropod and is derived from Greek πολύς (polys), "many" and ὀδούς (odous) "tooth".[1]
Theholotype specimen,LH 7777, part of the Las Hoyas Collection presently housed at theMuseo de Cuenca,Cuenca,Spain, ofPelecanimimus was recovered at theLa Hoyas locality in Cuenca Province, Spain, fromlagerstätte beds within theCalizas de La Huérguina Formation dating to the LowerBarremian.The only known specimen consists of the articulated front half of a skeleton and includes the skull, lower jaws, all the neck vertebrae and most of the back vertebrae, ribs,sternum, thepectoral girdle, a complete right forelimb and most of the left forelimb. Remains of the soft parts are visible at the back of the skull, around the neck and around the front limbs.[1]
Pelecanimimus was a small ornithomimosaur, at about 1.9–2.5 m (6.2–8.2 ft) and 17–30 kg (37–66 lb).[2][3] 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 sevenpremaxillary teeth, about thirtymaxillary, and seventy-five in thedentary. The teeth wereheterodont, 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. Interdental plates were lacking.[4]
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 inPelecanimimus, coupled with a lack of interdental space, was interpreted by Pérez-Morenoet al. as anadaptation for cutting and ripping, a "functional counterpart of the cutting edge of abeak," as well as anexaptation leading to the toothless cutting edge found in later ornithomimosaurs.[1] The arms and hands ofPelecanimimus were more typical of ornithomimosaurs, with theulna andradius bones in the lower arm tightly adhered to each other. The hand was hook-like and had fingers of equal length equipped with rather straight claws.[1]
Soft-tissue remains preserved by the exceptional preservational environment of the La Hoyas lagerstätte revealed the presence of a small skin or keratin crest on the back of the head, and agular pouch similar to the much larger pouches found in modern pelicans, from whichPelecanimimus 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 wrinkled skin, interpreted as lacking scales or feathers. Filament-like structures were also preserved; first interpreted as an integument, some of these were later seen as representing preserved muscle fibers.[5]Pelecanimimus was also the first ornithomimosaur discovered with a preservedhyoid apparatus (specialized tongue bones in the neck).[1]Gregory S. Paul has speculated thatPelecanimimus might have been capable offlight or be a recent descendant from a flying animal.[6] This is due to the presence of largesternal plates and uncinate processes, which imply flight musculature. These adaptations have been noted years later by the paleontologistMickey Mortimer.[7]
Pelecanimimus was by the describers assigned to the Ornithomimosauria, in the basalmost position.[1] A latercladistic analysis by Makovickyet al. (2005) confirmed thatPelecanimimus is the most basal member of the Ornithomimosauria, less derived even thanHarpymimus.[8] A study by Kobayashi and Lü in 2003 indicated that these two species formed a basal arrangement of steps leading towards the more advancedornithomimids (see cladogram below).[9] The discovery ofPelecanimimus has played an important and surprising role in understanding theevolution of the Ornithomimosauria. To quote Pérez-Morenoet 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 primitivetetanuran theropods have up to 80 teeth with tall blade-like crowns, and the primitive ornithomimosaurs have only a few small teeth. Thephylogenetic 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 placeddenticles (as introodontids) would be an adaptation for cutting and ripping. On the other hand, an excessive number of teeth with no interdental space (as inPelecanimimus) 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."[1]
Cladogram after Kobayashi and Lü, 2003:[9]
| Ornithomimosauria |
| ||||||
The Las Hoyas lagerstätte has produced numerous other exquisitely preserved species, including theenantiornithine birdsIberomesornis,Concornis, andEoalulavis, along with non-aviantheropod teeth,Concavenator remains, and a few fragmentarysauropod bones. Coarse sediments of the La Hoyas lagerstätte have produced bones of theornithopod dinosaurIguanodon. The lagerstätte beds have also yielded remains oflizards andsalamanders, as well as of the unique early mammalSpinolestes. Severalpterosaurs likeEuropejara andcrocodylomorphs are also known.[citation needed]
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