Ornithocheiromorpha
Ornithocheiromorpha is a group of pterosaurs within the suborder Pterodactyloidea. Fossil remains of this group date back from the Early to Late Cretaceous periods, around 140 to 92.5 million years ago. Ornithocheiromorphs have been discovered worldwide except Antarctica, though most genera have been recovered in Europe, Asia and South America. They were the most diverse and successful pterosaurs during the Early Cretaceous, but throughout the Late Cretaceous they were replaced by pteranodontians and azhdarchoids. The Ornithocheiromorpha was defined in 2014 by Andres and colleagues, and they made Ornithocheiromorpha the most inclusive clade containing Ornithocheirus, but not Pteranodon.
Ornithocheiromorphs are considered to be some of the largest animals to have ever flown. Members of this group are also regarded to have some of the largest pterosaur wingspans, such as the one estimated for the huge Tropeognathus, though still not as large as those estimated for the azhdarchids, which may have reached up to. When ornithocheiromorphs first appeared, they were initially scavengers, consisting in a more terrestrial setting, but their success had made them the top predators of the skies, as well as the most common type of fish-eating pterosaur throughout the early Late Cretaceous. Some paleontologists also consider ornithocheiromorphs an earlier step of evolution to the pteranodontians, this is due to the similar flying techniques and flight locomotions, as well as their diet, which mainly consisted of fish, and therefore also hunted very similarly. Ornithocheiromorphs also flew like soaring birds, keeping their wings stretched and rarely flapping.
History of research
Early discoveries
The first specimens of ornithocheiromorphs were unearthed at a chalk pit near Burham in Kent, England. In 1846, British paleontologist James Scott Bowerbank named and described the remains found as Pterodactylus giganteus, as it was common at that time to assign any new described pterosaur species to Pterodactylus. In the same chalk pit as P. giganteus, two other pterosaur species were discovered. The first was named in 1851 by Bowerbank as Pterodactylus cuvieri, in honor of the prominent German naturalist and zoologist Georges Cuvier, while the second was described in the same year by British paleontologist Sir Richard Owen as Pterodactylus compressirostris. P. compressirostris later became the type species of a newly created genus called Lonchodectes in a review by English paleontologist Reginald Walter Hooley in 1914. Confusingly, this species was also long regarded, incorrectly, as the type species of Ornithocheirus.In 1861, further pterosaur specimens were found in the UK, and were given the new species Pterodactylus simus by Owen. British paleontologist Harry Govier Seeley then created the new genus Ornithocheirus for the new species in the same year, the generic name translating as "bird hand" is due to the notion of the time that pterosaurs were the ancestors of modern birds. In 1870, Seeley reassigned the species Pterodactylus cuvieri as Ornithocheirus cuvieri. In 1874, Richard Owen proposed two new genera, Coloborhynchus, meaning "maimed beak", and Criorhynchus, meaning "ram beak". While Coloborhynchus consisted in a totally new type species, C. clavirostris, as well as two other species reassigned from Ornithocheirus, Criorhynchus consisted entirely of former Ornithocheirus species, including O. simus, which was later reassigned by Owen as Criorhynchus simus.
File:PZSL1851PlateReptilia04.png|thumb|Holotype of Pterodactylus cuvieri, now known as Cimoliopterus
In 2013, Brazilian paleontologists Taissa Rodrigues & Alexander Kellner made a deeper analysis on the species Pterodactylus cuvieri. In the analysis, they stated that it needed a separate genus, and assigning it to Ornithocheirus was inappropriate, therefore, they created the new genus called Cimoliopterus, with the new resulting combination Cimoliopterus cuvieri. In the same study, Rodrigues & Kellner also reviewed the species Pterodactylus giganteus, and reassigned it to a newly created genus called Lonchodraco, this resulted in a new combination called Lonchodraco giganteus.
In 1887, Seeley had described new fossil remains from the Isle of Wight, an island off the coast of southern England. He thought it belonged to some kind of bird-like creature, which he named it Ornithodesmus cluniculus. Seeley also reported another specimen found on the same site. He then considered it another species of Ornithodesmus. In 1901, Seeley named this new species as O. latidens, meaning "wide tooth". Later, Reginald Hooley discussed O. latidens in detail, based on specimens he had found, which led Ornithodesmus to be placed within a new family called Ornithodesmidae. Paleontologist Charles William Andrews however, had expressed doubts as to whether O. latidens belonged in the genus Ornithodesmus, as the vertebrae of the specimen of that genus was based on differed markedly from those of Hooley's specimen.
In 1993, the British paleontologists Stafford C. Howse and Andrew C. Milner concluded that the holotype sacrum and only specimen of O. cluniculus didn't belong to a pterosaur, but instead to a maniraptoran theropod dinosaur. They also pointed out that no detailed attempts had been made to compare the sacrum of O. cluniculus with those of pterosaurs, and that O. latidens had in effect been treated as the type species of the genus Ornithodesmus. Howse, Milner, and David Martill in 2001, moved "O." latidens to a new genus called Istiodactylus. They had also named a new family called Istiodactylidae, with Istiodactylus as the only member.
Discoveries outside Europe
Other important ornithocheiromorph discoveries include the anhanguerids Tropeognathus and Anhanguera from the Romualdo Formation in Brazil. Tropeognathus was described with its type species, T. mesembrinus in 1987 by German paleontologist Peter Wellnhofer. The generic name is derived from Greek τρόπις, tropis, meaning "keel", and γνάθος, gnathos, meaning "jaw". The specific name is derived from Koine mesembrinos, "of the noontide", simplified as "southern", in reference to the provenance from the Southern Hemisphere. The description then led to an enormous taxonomic confusion. In 1989, Brazilian paleontologist Alexander Kellner considered it an Anhanguera mesembrinus, then a Coloborhynchus mesembrinus by Veldmeijer in 1998, and then a Criorhynchus mesembrinus in 2001 by German paleontologist Michael Fastnacht. T. mesembrinus was then considered a junior synonym of Ornithocheirus simus by British paleontologist David Unwin in 2001, but he then proposed an Ornithocheirus mesembrinus in 2003. In 2013 however, Taissa Rodrigues and Alexander Kellner concluded that Tropeognathus would be valid again, and containing only T. mesembrinus, the type species.A discovery in Asia, specifically northwestern China, was reported in 2006. The lake sediments allowed an exceptional preservation of fossils, and therefore paleontologists Qiu Zhanxiang and Wang Banyue started official excavations. Part of the findings consisted of dense concentrations of pterosaur bones, associated with soft tissues and eggs. In 2014, a new species was named and described: Hamipterus tianshanensis. It was named by Wang Xiaolin, Alexander Kellner, Jiang Shunxing, Wang Qiang, Ma Yingxia, Yahefujiang Paidoula, Cheng Xin, Taissa Rodrigues, Meng Xi, Zhang Jialiang, Li Ning, and Zhou Zhonghe. The generic name Hamipterus combines that of the Hami region, with the word pteron, meaning "wing", and the specific name refers to the provenance from the Tian Shan, a mountain range.
Description
Size
Ornithocheiromorphs were large pterosaurs, with wingspans normally ranging between. Istiodactylus for example, had a wingspan ranging from, with the most complete known skull estimated to have been about in length, based on a long-lost fragment of its jaw reported in 2012. Though its jaws measured only, which was less than 80 percent of the skull's length. Anhanguerids and were typically larger than others of the group and were more successful within the food chain rather than other ornithocheiromorphs, one reason is because of their large size, for example, Tropeognathus mesembrinus, had a normal wingspan of about, and as the maximum estimate. Another species which was impressively large is Coloborhynchus capito, with a total skull length that could have been up to, leading to an estimated wingspan of. However, this species may belong to a different genus called Nicorhynchus.Skull and crests
Most anhanguerids bore distinctive convex "keeled" crests on their snout and underside of their mandible, this was well developed in several genera such as Tropeognathus. The similar Anhanguera possessed jaws that were tapered in width, but expanded into a broad, spoon-shaped rosette at the tip. The jaws are distinguished from its relatives by several differences in the crest and teeth: unlike its close relatives Coloborhynchus and Ornithocheirus, the crest on the upper jaw of Anhanguera didn't begin at the tip of the snout, therefore, it was set farther back on the skull.Other anhanguerids like Cearadactylus had its first preparations with many serious mistakes: the front of the snout and the lower jaws were confused leading to a reconstruction in which the anterior part of the head was upside down. Some of the teeth were extensively restored and enlarged until the wider front of the jaws showed very large and robust teeth projecting outward. With this arrangement, the maxilla was kinked, and its interlocking teeth suggested that Cearadactylus had a piscivourous diet, allowing the animal to keep hold of slippery fish. Another smaller genus similar to Cearadactylus is Guidraco. Its holotype skull has a length of, which makes it smaller than other genera. The skull is very elongated however, and a hollow profile is seen, but not very pointed, as the upper edge and the line of the jaw run nearly parallel over most of their length.
Even though most ornithocheiromorphs didn't have a cranial crest like the closely related pteranodontids, there were some exceptions, this included Caulkicephalus and Ludodactylus. Caulkicephalus had a rounded snout, very similar to that of Ornithocheirus and Anhanguera, and therefore it is placed within either Anhangueridae or Ornithocheiridae, depending on the author. Caulkicephalus was also a large pterosaur, with wingspan estimates of around.
Ornithocheiriform teeth were heterodont, and they have sufficient differences that individual teeth can be distinguished between whether they belonged to the rostral, medial, or the posterior portion of the tooth row. The rostral teeth had a subcircular cross-section and their crowns curved more lingually than distally. The medial teeth shared the curvature of the anterior teeth but were more elliptical in cross-section. The posterior teeth were oval in cross-section and curved more distally than lingually.