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09.01.2016 19:08 - Largest prehistoric animals Vol.1 Vertebrates part5 Pterosaurs - Another contenders
Автор: valentint Категория: Забавление   
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Последна промяна: 05.12.2016 20:14


Yet another possible contender for the title is Ornithocheirus, which allegedly had a 12-meter (39-foot) wingspan. However, specimen of this size have not been formally described in the literature. Ornithocheirus is a pterosaurgenus known from fragmentary fossil remains uncovered from sediments in the UK.
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Several species have been referred to the genus, most of which are now considered as dubious species, or members of different genera, and the genus is now often considered to include only the type species, Ornithocheirus simus. Species have been referred to Ornithocheirus from the mid-Cretaceous period of both Europe and South America, but O. simus is known only from the UK. Because O. simus was originally named based on poorly preserved fossil material, the genus Ornithocheirus has suffered enduring problems of zoological nomenclature.

Fossil remains of 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, are sometimes classified as species of Ornithocheirus, but have also been placed in their own genera, most notably Tropeognathus.

The original material of Ornithocheirus simus, recovered from England, indicates a mid-sized species with a wing span of 2.5 m (8.2 ft). Referred specimens attributed to Ornithocheirus simus can reach 5 m (16.5 ft).

O. simus bore a distinctive convex "keeled" crest on its snout. Unlike the related Anhanguera and Coloborhynchus, which had an expanded rosette of teeth at the jaw tips, Ornithocheirus species (including O. simus) 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 Tropeognathus mesembrinus, making clear distinction between these two species impossible.

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.


Arambourgiania is a pterosaur from the Late Cretaceous (Maastrichtian) of Jordan. It was one of the largest members of this group.
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In the early forties, a railway worker during repairs on the Amman-Damascus railroad near Russeifa found a two foot long fossil bone. In 1943 this was acquired by the director of a nearby phosphate mine, Amin Kawar, who brought it to the attention of a British archeologist, Fielding, after the war. This generated some publicity — the bone was even shown to Abdullah I of Jordan — but more importantly, it made the scientific community aware of the find.

In 1953 the fossil was sent to Paris, where it was examined by Camille Arambourg of the Muséum national d'histoire naturelle. In 1954, he concluded the bone was the wing metacarpal of a giant pterosaur. In 1959, he named a new genus and species: Titanopteryx philadelphiae. The genus name meant "titan wing" in Greek; the specific name refers to the name of Amman in Antiquity: Philadelphia. Arambourg let a plaster cast be made and then sent the fossil back to the phosphate mine; this last aspect was later forgotten and the bone was assumed lost.

In 1975 Douglas A. Lawson, studying the related Quetzalcoatlus, concluded the bone was not a metacarpal but a cervical vertebra.

In the eighties, Russian paleontologist Lev Nesov was informed by an entomologist that the name Titanopteryx had already been given by Günther Enderlein to a fly from the Simulidae family in 1934. Therefore, in 1987 he renamed the genus into Arambourgiania, honouring Arambourg. However, the name "Titanopteryx" was informally kept in use in the West, partially because the new name was assumed by many to be a nomen dubium.

Early 1995, paleontologists David Martill and Eberhard Frey traveled to Jordan in an attempt to clarify matters. In a cupboard of the office of the Jordan Phosphate Mines Company they discovered some other pterosaur bones: a smaller vertebra and the proximal and distal extremities of a wing phalanx — but not the original find. However, after their departure to Europe engineer Rashdie Sadaqah of the mine investigated further and in 1996 established it had been bought from the company in 1969 by geologist Hani N. Khoury who had donated it in 1973 to the University of Jordan; it was still present in the collection of this institute and now could be restudied by Martill and Frey.

The holotype, VF 1, consists of a very elongated cervical vertebra, probably the fifth. Today the middle section is missing; the original find was about 62 centimetres long, but had been sawed into three parts. Most of the fossil consists of an internal infilling or mould; the thin bone walls are missing on most of the surface. The find had not presented the whole vertebra; a piece was absent from its posterior end as well. Frey and Martill estimated the total length to have been 78 centimetres, using for comparison the relative position of the smallest shaft diameter of the fifth cervical vertebra of Quetzalcoatlus. From this again the total neck length was extrapolated at about three metres. From the relatively slender vertebra the length dimension was then selected to be compared to that of Quetzalcoatlus, estimated at 66 centimeters long, resulting in a ratio of 1.18. Applying that ratio to the overall size, Frey and Martill in 1998 concluded that the wingspan of Arambourgiania had been twelve to thirteen metres, compared with the ten to eleven metres of Quetzalcoatlus, and that Arambourgiania was thus the largest pterosaur then known. Later estimates have been more moderate, sometimes as low as seven metres.

Frey and Martill rejected the suggestion that Arambourgiania was a nomen dubium or identical to Quetzalcoatlus and affirmed its validity in relation to "Titanopteryx".

Nesov in 1984 had placed the species within Azhdarchinae, part of the Pteranodontidae; the same year Kevin Padian placed it within Titanopterygidae. Both concepts have fallen into disuse now that such forms are commonly assigned to the Azhdarchidae.

Tropeognathus
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Tropeognathus was first named in 1987 after the description of a pterosaur skull that had been purchased from a fossil dealer. In 2002 a set of lower jaws was further attributed to the genus, and most recently at the time of writing a third specimen was added in 2013, and this was the first inclusion of post cranial remains. Today these specimens all represent members of the type species Tropeognathus mesembrinus which is held as valid, while a second species, Tropeognathus robustus which was also named in 1987 and based upon a more robust jaw, has a questionable validity.
Only two years after Tropeognathus was established, there was speculation that it might have actually been a specimen of Anhanguera (Kellner, 1989). Tropeognathus has also been considered a synonym to Coloborhynchus (Veldmeijer, 1998), Criorhynchus (Fastnacht, 2001) and Ornithocheirus (Unwin, 2001). With the addition of new post cranial remains in 2013 however, Tropeognathus has now gained a wider acceptance to its validity, and a 2013 taxonomic review by Rodrigues and Kellner supported the view that Tropeognathus is a valid genus.
Tropeognathus is easily amongst the largest known ornithocheirid pterosaurs, a kind that seem to have been best adapted for flying over bodies of water and snatching fish from the water. Also with the addition of new fossil material in 2013, Tropeognathus was the largest pterosaur from Gondwana, the amalgamation of the southern continents that were largely separated from the northern continents that are known as Laurasia. Only the largest azhdarchid pteroasurs such as Quetzalcoatlus from North America are known to have comfortably exceeded Tropeognathus in size. Like relative genera, Tropeognathus had a toothed beak, and large rounded growths which have been dubbed ‘keels’ rising from the tips of both upper and lower jaws.
The wings of Tropeognathus seem to be very long while at the same time thin, similar to some other types of pterosaurs such as pteranodonts. This may indicate that large ornithocheirds like Tropeognathus may have used a flight principal called dynamic soaring to conserve energy. This is where air current passing over ocean waves are exploited so that an individual can use them to pick up speed and lift without having to expend energy to continuously flap the wings. This idea of flight has also been proposed for the pterosaur Pteranodon, and can be seen in action by some modern sea birds such as the albatross which although has a different wing construction, has a roughly similar wing proportion. Glider pilots are also known to use this flight principal, though usually more often on a grander scale such as an air current rising over a mountain.














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