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| Ornithocheirus spp. | |
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| Tweet Topic Started: Nov 24 2012, 05:56 AM (2,977 Views) | |
| Carcharadon | Nov 24 2012, 05:56 AM Post #1 |
Shark Toothed Reptile
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Ornithocheirus spp. Temporal range: Early-Late Cretaceous, 112–108 Ma Kingdom: Animalia Phylum: Chordata Order: †Pterosauria Suborder: †Pterodactyloidea Family: †Ornithocheiridae Subfamily: †Ornithocheirinae Seeley, 1870 Genus: †Ornithocheirus Seeley, 1869 Species
Ornithocheirus (from Greek "ορνις", meaning bird, and "χειρ", meaning hand) was a pterosaur from the Cretaceous period of Europe and South America. Based on poor fossil material, the genus has caused enduring problems of zoological nomenclature. Fossil remains currently classified as Ornithocheirus have been recovered mainly from the Cambridge Greensand of England, dating to the beginning of the Albian stage of the late Cretaceous period, about 110 million years ago. Additional fossils from the Santana Formation of Brazil, dating to 112-108 million years ago, have been classified as species of Ornithocheirus. Description The original material of Ornithocheirus simus, recovered from England, indicates a mid-sized species with a wing span of 2.5 m (8 ft). Referred specimens attributed to Ornithocheirus simus (alternately called Criorhynchus simus) can reach 5 m (16 ft). Tropeognathus mesembrinus is also usually considered a part of the Ornithocheirus genus as O. mesembrinus, and reached over 6 m (20 ft) in wingspan. Both O. simus and O. mesembrinus bore distinctive convex "keeled" crests on their snouts. The upper crests arose from the snout tip and extended back to the nostril. An additional, smaller crest projected down from the lower jaw at the symphysis ("chin" area). While many ornithocheirids had a small, rounded bony crest projecting from the back of the skull, this was particularly large and well-developed in Ornithocheirus. Unlike the related Anhanguera and Coloborhynchus, which had an expanded rosette of teeth at the jaw tips, Ornithocheirus had straight jaws that narrowed toward the tip. Also unlike related pterosaurs, the teeth of Ornithocheirus were mostly vertical, rather than set at an outward-pointing angle. They also had fewer teeth than related species. The type specimen of Ornithocheirus simus is represented only by a broken piece of the upper jaw tip. While it does preserve several characteristic features of Ornithocheirus, it is nearly identical to comparable bones in O. mesembrinus, making clear distinction between these two species impossible. Discovery and naming During the 19th century, in England many fragmentary pterosaur fossils were found in the Cambridge Greensand, a layer from the early Cretaceous, that had originated as a sandy seabed. Decomposing pterosaur cadavers, floating on the sea surface, had gradually lost individual bones that sank to the bottom of the sea. Water currents then moved the bones around, eroding and polishing them, until they were at last covered by more sand and fossilised. Even the largest of these remains were damaged and difficult to interpret. They had been assigned to the genus Pterodactylus, as was common for any pterosaur species described in the early and middle 19th century. Young researcher Harry Govier Seeley was commissioned to bring order to the pterosaur collection of the Sedgwick Museum in Cambridge. He soon concluded that it was best to create a new genus for the Cambridge Greensand material that he named Ornithocheirus, "bird hand", as he in this period still considered pterosaurs to be the direct ancestors of birds, and assumed the hand of the genus to represent a transitional stage in the evolution towards the bird hand. To distinguish the best pieces in the collection, and partly because they had already been described as species by other scientists, he in 1869 and 1870 each gave them a separate species name: O. simus, O. woodwardi, O. oxyrhinus, O. carteri, O. platyrhinus, O. sedgwickii, O. crassidens, O. capito, O. eurygnathus, O. reedi, O. cuvieri, O. scaphorhynchus, O. brachyrhinus, O. colorhinus, O. dentatus, O. denticulatus, O. enchorhynchus, O. xyphorhynchus, O. fittoni, O. nasutus, O. polyodon, O. compressirostris, O. tenuirostris, O. machaerorhynchus, O. platystomus, O. microdon, O. oweni and O. huxleyi, thus 28 in total. As yet Seeley did not designate a type species. When Seeley published his conclusions in his 1870 book The Ornithosauria, this provoked a reaction by the leading British paleontologist of his day, Richard Owen. Owen was not an evolutionist and he therefore considered the name Ornithocheirus to be inappropriate; he also thought it was possible to distinguish two main types within the material, based on differences in snout form and tooth position — the best fossils consisted of jaw fragments. He in 1874 created two new genera: Coloborhynchus and Criorhynchus. Coloborhynchus, "maimed beak", comprised a new species, Coloborhynchus clavirostris, the type species, and two species reassigned from Ornithocheirus: C. sedgwickii and C. cuvieri. Criorhynchus, "ram beak", consisted entirely of former Ornithocheirus species: the type species Criorhynchus simus and furthermore C. eurygnathus, C. capito, C. platystomus, C. crassidens and C. reedi. Seeley did not accept Owen's position. In 1881 he designated O. simus the type species of Ornithocheirus and named a new species O. bunzeli. In 1888 Edward Newton renamed several existing species names into: Ornithocheirus clavirostris, O. daviesii, O. sagittirostris, O. validus and O. giganteus; as new species he created: O. clifti, O. diomedeus, O. nobilis and O. curtus. Others had already named an O. umbrosus, O. harpyia, O. macrorhinus and O. hilsensis and would create an O. hlavaci, O. wiedenrothi and O. mesembrinus. In 1914 Reginald Walter Hooley made a new attempt to structure the large number of species. Keeping the name Ornithocheirus, he added to it Owen's Criorhynchus, in which however Coloborhynchus was sunk, and to allow for a greater differentiation created two new genera, again based on jaw form: Lonchodectes and Amblydectes. Lonchodectes, "lance biter", comprised L. compressirostris, L. giganteus and L. daviesii. Amblydectes, "blunt biter", consisted of A. platystomus, A. crassidens and A. eurygnathus. However, Hooley's classification was rarely applied later in the century, when it became common to subsume all the poorly preserved and confusing material under the name Ornithocheirus. In 1978 Peter Wellnhofer, assuming no type species had been designated, made Ornithocheirus compressirostris the type. From the seventies onwards many new pterosaur fossils were found in Brazil, from formations about the same age as the Cambridge Greensand, 110 million years old. Contrary to the English material, these new finds included some of the best preserved large pterosaur skeletons and several new genera names were given to them, such as Anhanguera. This situation caused a renewed interest in the Ornithocheirus material and the validity of the several names based on it, for it might be possible that it could by more detailed studies be established that the Brazilian pterosaurs were actually junior synonyms of the European types. Several European researchers concluded that this was indeed the case. Unwin revived Coloborhynchus and Michael Fastnacht Criorhynchus, each author ascribing Brazilian species to these genera. However, in 2000 Unwin stated that Criorhynchus could not be valid. Referring to Seeley's designation of 1881 he considered Ornithocheirus simus, holotype CAMSM B.54428, to be the type species. This also made it possible to revive Lonchodectes, using as type the former O. compressirostris, which then became L. compressirostris. This position has not universally been accepted. Brazilian workers also typically reject the identification of their genera with European types. Unwin, and this caused no controversy, reaffirmed that most Ornithocheirus species are nomina dubia, names that are invalid because the fossils they refer to lack sufficient diagnostic features. As a result, though over forty species have been named in the genus Ornithocheirus over the years, not a single one of them, not even O. simus, is currently recognized as valid by all pterosaur researchers. Often, there is a total lack of consensus; e.g. Tropeognathus mesembrinus named by Peter Wellnhofer in 1987 has afterwards been considered Ornithocheirus mesembrinus by David Unwin in 2003 (making Tropeognathus a junior synonym), but as Anhanguera mesembrinus by Alexander Kellner in 1989, Coloborhynchus mesembrinus by André Veldmeijer in 1998 and Criorhynchus mesembrinus by Michael Fastnacht in 2001. Even earlier, in 2001, Unwin had referred the "Tropeognathus" material to O. simus in which he was followed by Veldmeijer; however the latter denied that O. simus is the type species in favor of O. compressirostris (alternately Lonchodectes), and used the names Criorhynchus simus and Cr. mesembrinus. Kellner in 2000 again recognized Tropeognathus as a valid genus. Species currently or possibly assigned to Ornithocheirus:
Cimoliornis, Cretornis, and Palaeornis, misidentified as birds, have been assigned to Ornithocheirus, but they may instead be separate genera, a position held by David Unwin. Cimoliornis may be closer to azhdarchoidea, and Palaeornis was shown to be a lonchodectid in 2009. In popular culture Ornithocheirus was the subject of an entire episode of the award-winning BBC television program Walking with Dinosaurs. In Walking with Dinosaurs: A Natural History, a companion book to the series, it was claimed that several large bone fragments from the Santana Formation of Brazil indicated that Ornithocheirus may have had a wingspan reaching almost 12 metres and a weight of a hundred kilogrammes, making it one of the largest known pterosaurs. However, the largest definite Ornithocheirus specimens known measure 6 metres in wingspan. The specimens which the producers of the program used to justify such a large size estimate are currently undescribed, and are being studied by Dave Martill and Heinz Peter Bredow. Bredow stated that he does not believe this highest estimate is likely, and that the producers likely chose the highest possible estimate because it was more "spectacular."    
Edited by Taipan, Nov 25 2012, 08:49 PM.
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