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[[File:OrnitocheiridsDB.jpg|thumb|''Cimolioptetus'' (right) stealing prey from a ''Lonchodectes'' (left), both were derived members of this group and possible fish [[Predator|hunters]]]]
[[File:OrnitocheiridsDB.jpg|thumb|''Cimolioptetus'' (right) stealing prey from a ''Lonchodectes'' (left), both were derived members of this group and possible fish [[Predator|hunters]]]]
Ornithocheirids like ''Tropeognathus'' and ''Coloborhynchus'' are considered to be fish-eaters, and had longer and sharper teeth compared to the more rounded teeth of ''Istiodactylus'', though this is still sometimes disputed.<ref>{{Cite web|url=https://gsa.confex.com/gsa/2017AM/webprogram/Paper305496.html|title=Abstract: DIET OF ORNITHOCHEIROID PTEROSAURS INFERRED FROM STABLE CARBON ISOTOPE ANALYSIS OF TOOTH ENAMEL (GSA Annual Meeting in Seattle, Washington, USA - 2017)|website=gsa.confex.com}}</ref> Another difference that can be seen in more primitive ornithocheiromorphs their eyes being proportionally smaller compared to the assumed predatory and more advanced ornithocheirids, this again adds to the fact that the more [[primitive (phylogenetics)|primitive]] groups (istiodactylids) were most likely scavengers, and later got more successful within the food chain, leading the later, more advanced groups (ornithocheirids and lonchodectids) to be the [[dominance (ecology)|dominant]] fish hunters during the early Late Cretaceous.<ref>{{Cite web|url=https://gsa.confex.com/gsa/2017AM/webprogram/Paper305496.html|title=Abstract: DIET OF ORNITHOCHEIROID PTEROSAURS INFERRED FROM STABLE CARBON ISOTOPE ANALYSIS OF TOOTH ENAMEL (GSA Annual Meeting in Seattle, Washington, USA - 2017)|website=gsa.confex.com}}</ref>
Ornithocheirids like ''Tropeognathus'' and ''Coloborhynchus'' are considered to be fish-eaters, and had longer and sharper teeth compared to the more rounded teeth of ''Istiodactylus'', though this is still sometimes disputed.<ref>{{Cite web|url=https://gsa.confex.com/gsa/2017AM/webprogram/Paper305496.html|title=Abstract: DIET OF ORNITHOCHEIROID PTEROSAURS INFERRED FROM STABLE CARBON ISOTOPE ANALYSIS OF TOOTH ENAMEL (GSA Annual Meeting in Seattle, Washington, USA - 2017)|website=gsa.confex.com}}</ref> Another difference that can be seen in more primitive ornithocheiromorphs their eyes being proportionally smaller compared to the assumed predatory and more advanced ornithocheirids, this again adds to the fact that the more [[primitive (phylogenetics)|primitive]] groups (istiodactylids) were most likely scavengers, and later got more successful within the food chain, leading the later, more advanced groups (ornithocheirids and lonchodectids) to be the [[dominance (ecology)|dominant]] fish hunters during the early Late Cretaceous.<ref>{{Cite web|url=https://gsa.confex.com/gsa/2017AM/webprogram/Paper305496.html|title=Abstract: DIET OF ORNITHOCHEIROID PTEROSAURS INFERRED FROM STABLE CARBON ISOTOPE ANALYSIS OF TOOTH ENAMEL (GSA Annual Meeting in Seattle, Washington, USA - 2017)|website=gsa.confex.com}}</ref>

===Locomotion and flight===
[[File:IstiodactylusDB3.jpg|thumb|left|A flying restoration of ''Istiodactylus'', notice its high aspect ratio]]
Ornithocheiromorphs, like other pterosaurs, are considered to have been skilled fliers as well as swift at moving on the ground. Footprints from several species show that most pterosaurs did not sprawl their limbs to a large degree, as in modern reptiles, but rather held the limbs relatively erect when walking, like [[dinosaur]]s. While footprints are yet to be known, it is likely that ornithocheiromorphs also walked erect.<ref name=wittonhabib2010>{{cite journal | last1 = Witton | first1 = M.P. | last2 = Habib | first2 = M.B. | year = 2010 | title = On the Size and Flight Diversity of Giant Pterosaurs, the Use of Birds as Pterosaur Analogues and Comments on Pterosaur Flightlessness | url = http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013982 | journal = PLoS ONE | volume = 5 | issue = 11| page = e13982 | doi = 10.1371/journal.pone.0013982 | pmid=21085624 | pmc=2981443}}</ref> Compared to other earlier pterosaurs such as [[rhamphorhynchid]]s, ornithocheiromorphs had unusually uneven [[limb]] proportions, with the forelimbs resulting in a much longer
scale compared to the hind limbs. Their close relatives, the pteranodontids were also found with similar features, though they more likely flew like modern-day [[albatross]]es rather than anything else. Paleontologists also suggest that they most likely spend long stretches of time sea fishing, travelling very long distances without flapping while at the same time flying close the surface of the water with exploited wind speed, and without the necesity of [[thermal]]s.<ref name=padian1983>{{Cite journal | author = Padian, K. | year = 1983 | title = A functional analysis of flying and walking in pterosaurs | url = | journal = Paleobiology | volume = 9 | issue = 3| pages = 218–239| doi = 10.1017/S009483730000765X}}</ref> This would likely have required them to use unique modes of locomotion compared to other pterosaurs, this can already be seen in earlier evolutions such as ''Istiodactylus''<ref name=witton2012/> and ''[[Nurhachius]]''<ref name="Zhou2019">Zhou X., Pêgas R.V., Leal M.E.C. & Bonde N. 2019. ''Nurhachius luei'', a new istiodactylid pterosaur (Pterosauria, Pterodactyloidea) from the Early Cretaceous Jiufotang Formation of Chaoyang City, Liaoning Province (China) and comments on the Istiodactylidae". ''PeerJ'' '''7''':e7688</ref>
, with powerful musculature attachments and well-developed pectoral and upper arm bones. Like albatrosses, ornithocheiromorphs also had a high [[aspect ratio (aeronautics)|aspect ratio]] and low [[wing loading]]s. The wing remains of ''Nurhachius'' have been compared to those of modern [[soaring birds]], which fly with little flapping, and may have been ideal for low-energy soaring, which is necessary when searching for [[carrion]] (assuming istiodactylids were scavengers).<ref name="Zhou2019"/> The wings of istiodactylids also seem to have been shorter compared to the fish-eating ornithocherids, and unlike them, which were more suited for taking off and landing, istiodactylids may have preferred a more terrestrial setting. This is also seen in many inland soaring birds, which have a lower aspect ratio compared those that soar over the ocean. It is also possible that ornithocheiromorphs ran (but not walked) bipedally, or that they used a hopping gait.<ref name=wittonhabib2010/> Many pterosaur researchers like Mike Habib have noted that the limb proportions of some ornithocheiromorphs such as ''[[Anhanguera (pterosaur)|Anhanguera]]'' are consistent with hopping<ref name=habibblog>Habib, M. (2011). "[http://h2vp.blogspot.com/2011/09/dinosaur-revolution-anhanguera.html Dinosaur Revolution: ''Anhanguera''.]" ''H2VP: Paleobiomechanics''. Weblog entry, 20-SEP-2011. Accessed 28-SEP-2011: http://h2vp.blogspot.com/2011/09/dinosaur-revolution-anhanguera.html</ref>, though the scavenging istiodactylids are probably still the best examples of pterosaurs with a more terrestrial setting.


==Paleoecology==
==Paleoecology==

Revision as of 10:31, 12 May 2020

Ornithocheiromorphs
Temporal range: Early-Late Cretaceous, 140–94 Ma
Reconstructed skeleton of Tropeognathus in the National Museum of Brazil
Skeletal cast of Maaradactylus spielbergi in the Naturalis Biodiversity Center
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Order: †Pterosauria
Suborder: †Pterodactyloidea
Clade: †Pteranodontoidea
Clade: †Ornithocheiromorpha
Andres et al., 2014
Subgroups

Ornithocheiromorpha (from Ancient Greek, meaning "bird hand form") is a group of pterosaurs within the suborder Pterodactyloidea. Fossil remains of this group date back from the Early to Late Cretaceous periods (Berriasian to Turonian stages). Ornithocheiromorphs were discovered worldwide, except Antarctica, though most genera were 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 better adapted and larger pterosaurs such the pteranodontids and azhdarchoids. The most diverse families of the group, the Ornithocheiridae and Anhangueridae (some authors consider them synonyms), survived until the early Late Cretaceous with Ferrodraco, Ornithocheirus, Cimoliopterus[1], Lonchodectes and Lonchodraco[2] being some of the last remaining. The Ornithocheiromorpha was defined in 2014 by Andres and colleagues. They made Ornithocheiromorpha the most inclusive clade containing Ornithocheirus but not Pteranodon.[3]

History of discovery

Early research

Associated and referred bones of P. giganteus, now known as Lonchodraco

The first specimens of ornithocheiromorphs were unearthed at a chalk pit in Burham near Maidstone, Kent. Bowerbank (1846) named and described the remains found as a new species of Pterodactylus: P. giganteus[4], though in 2013, Taissa Rodrigues and Alexander Kellner assigned this species to a Lonchodectes, and created a Lonchodectes giganteus. But it was then considered a nomen dubium and therefore, they created a new genus called Lonchodraco, resulting in a Lonchodraco giganteus. In the same chalk pit where P. giganteus was found, there were also unearthed remains of two other pterosaur species, one of which was named in 1851, also by Bowerbank, as Pterodactylus cuvieri[1]; in honour to George Cuvier, and the second species was described by Richard Owen, also in 1851, as Pterodactylus compressirostris, although it is currently known as the type species of Lonchodectes.

P. cuvieri holotype and lost tooth

In 1861, fossil remains found yet again in the UK, were also referred as new Pterodactylus species and Richard Owen described it as P. simus, but in the same year, Harry Govier Seeley created a new genus named Ornithocheirus, "bird hand", as paleontologists in this period still considered pterosaurs to be the direct ancestors of birds. In 1869, Seeley renamed Pterodactylus cuvieri into Ptenodactylus cuvieri[5], but in 1870, Seeley had realised that the generic name Ptenodactylus had been preoccupied, and thus renamed the species into Ornithocheirus cuvieri. Between 1869 and 1870, Seeley renamed various species of pterosaurs, including P. cuvieri into newly named species of Ornithocheirus, therefore 28 in total. Though Seeley didn't designate a type species.

Richard Owen wasn't pleased when Seeley published his conclusions in his 1870 book The Ornithosauria[6], and he therefore considered the name Ornithocheirus to be inappropriate. In 1874, Owen created two new genera, Coloborhynchus, meaning "maimed beak" and Criorhynchus, meaning "ram beak". While Coloborhynchus consisted in a totally new type species, C. clavirostris[7] as well as two species reassigned from Ornithocheirus, Criorhynchus consisted entirely of former Ornithocheirus species, including the type species, O. simus, which was later renamed by Owen as Criorhynchus simus, as well as 5 other species. In the same year, Owen also renamed O. cuvieri into Coloborhynchus cuvieri.[8]

Holotype specimen of O. simus and referred specimen (holotype of the junior synonym O. platyrhinus)

Seeley later disagreed and didn't accept Owen's position, and therefore he assigned Ornithocheirus simus as the type species of Ornithocheirus and also named a new separate species, O. bunzeli. Edward Newton (1888) then reassigned several existing species, including Coloborhynchus clavirostris into Ornithocheirus.

In 1914, Reginald Walter Hooley kept the name Ornithocheirus, but created two new genera: Lonchodectes, meaning "lance biter", and Amblydectes, meaning "blunt biter". Both consisted of 3 species. Though this classification was rarely applied at the time. Pterodactylus compressirostris was formerly transferred to Ornithocheirus in 1870 by Seeley,[6] before becoming the type species of Lonchodectes in Hooley's 1914 review of Ornithocheirus.[9] Confusingly, this species was also long regarded, incorrectly, as the type species of Ornithocheirus.[10]

Skull fragments of Ornithodesmus latidens, which is currently known as Istiodactylus latidens

In 1887, Seeley 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.[11] John Whitaker Hulke suggested later that year that Ornithodesmus was a pterosaur, finding it similar to fossils that he had seen before, but Seeley disagreed.[12] Seeley also reported another specimen found on the same site, which was then acquired in the British Museum in 1882. The specimen had been assigned to Ornithocheirus nobilis by Richard Lydekker in 1888, but Seeley considered it another species of Ornithodesmus, which he now considered a species pterosaur instead of a bird. Seeley (1901) named this new species O. latidens, which means "wide tooth".

The British paleontologist Reginald Hooley described two more specimens of O. latidens in 1913[13], which were collected in 1904 from the sea after a rockfall near Atherfield Point on the Isle of Wight. The first of the specimens was collected, and consisted of a skull, neck and trunk vertebrae, a shoulder blade, an ischium, and parts of the forelimbs. The second specimen was collected in just one block, and it includes parts of the forelimbs and pectoral girdle. These two specimens represent the most complete remains of Cretaceous pterosaurs found in England. Hooley also discussed O. latidens in detail, which led Ornithodesmus to be placed within its own family, Ornithodesmidae. But then his article ended with a discussion wherein it was noted that the palaeontologist Charles William Andrews had expressed doubts as to whether O. latidens belonged in the genus Ornithodesmus, as the vertebrae of the specimen that genus was based on differed markedly from those of Hooley's specimen. The American palaeontologist Samuel W. Williston subsequently reviewed Hooley's article, disagreeing with some of his conclusions about the anatomy and classification of the animal.[14] After Hooley's monograph, little was written about the animal for the rest of the 20th century, and no similar pterosaurs were found for decades.[15]

In 1993 however, the British palaeontologists 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 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. Now as a definite species of pterosaur, "O." latidens thus required a new genus name.[16] Howse, Milner, and David Martill in 2001, moved "O." latidens to a new genus called Istiodactylus. The generic name means "sail finger", which refers to the wings of large pterosaurs. After moving "O." latidens into Istiodactylus, they had also named a new family called Istiodactylidae, with Istiodactylus as the only member.[17]

Discoveries outside Europe

Fossil skull of Tropeognathus
Comparison between the holotypes of Tropeognathus mesembrinus and Ornithocheirus simus

Other important ornithocheiromorph discoveries include the ornithocheirids Tropeognathus[18] and Anhanguera[19] from the Romualdo Formation in Brazil. Tropeognathus was described with its type species, T. mesembrinus in 1987 by Peter Wellnhofer[20], but then led to an enormous taxonomic confusion. In 1989, Alexander Kellner considered it an Anhanguera mesembrinus, then a Coloborhynchus mesembrinus by Veldmeijer in 1998, and then a Criorhynchus mesembrinus in 2001 by Michael Fastnacht. T. mesembrinus was then considered a junior synonym of Ornithocheirus simus by David Unwin[21], but he then proposed an Ornithocheirus mesembrinus in 2003[22]. In 2013 however, Taissa Rodrigues and Alexander Kellner concluded that Tropeognathus would be valid again, and containing only T. mesembrinus, the type species.[23]

The discovery of Anhanguera in 1985 made some authors assign several species of Ornithocheirus to the new genus, this is due to the similarities of Anhanguera and Ornithocheirus. One of which was Ornithocheirus cuvieri, formerly known as Pterodactylus cuvieri, was renamed by David Unwin in 2001 as Anhanguera cuvieri, though in 2013, Rodrigues and Kellner created a separate genus: Cimoliopterus. The generic name means "chalk wing", in reference to the Chalk Formation. The type species still remains as Pterodactylus cuvieri, and the resulting new combination name is Cimiliopterus cuvieri.[23] Other species include A. piscator, which is known from a nearly-complete skeleton, and was once proposed to belong to the genus Coloborhynchus,[24] but it has recently been placed back into Anhanguera by Andres and Myers (2013).[25] Another species which is also known from a complete skeleton is A. spielbergi, which was also originally considered as a species of Coloborhynchus in 2003,[26] though it has been reassigned to Maaradactylus, specifically to its own species, M. spielbergi.[27]

Skull of Hamipterus tianshanensis

Another 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. The site represented a nesting colony that storm floods had covered with mud. Dozens of individuals could be secured to run into the many hundreds.[28] 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.[28] These findings represented the largest known concentration of pterosaur fossils in Asia, with the exception of the Pterodaustro nesting colonies of Argentina.

Description

Size

Size comparison of Istiodactylus latidens

Ornithocheiromorphs were large pterosaurs, with wingspans normally ranging between 3 to 6 metres (9.8 to 19.7 ft). Istiodactylus for example, had a wingspan ranging from 4.3 to 5 metres (14 to 16 ft), with the most complete known skull estimated to have been about 45 centimetres (18 in) in length, based on a long-lost fragment of its jaw reported in 2012.[29] Though its jaws measured only 28.5 centimetres (11.2 in), which was less than 80 percent of the skull's length.[15] Ornithocheirids 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, Ornithocheirus itself had a wingspan measuring 4.5 to 6.1 metres (15 to 20 ft). Other ornithocheirids were also regarded with similar wingspans, though the largest is probably Tropeognathus mesembrinus, with a wingspan measuring more than 7 metres (23 ft) and 8.2 metres (27 ft) as the maximum estimate. Another genus which was impresively large is Coloborhynchus, with a total skull length that could have been up to 75 centimetres (30 in), leading to an estimated wingspan of 7 metres (23 ft).[30] However, this species may belong to a different genus.[23] One of the smaller genera includes the boreopterid Boreopterus, which is estimated to have a wingspan of around 1.45 metres (4.8 ft), but some paleontologists consider it a synonym of Zhenyuanopterus, in this case measuring around 3.5 to 4 metres (11 to 13 ft) in length.

Skeletal diagram of Zhenyuanopterus longirostris

Distinguishing traits

Restoration of Ornithocheirus, notice its narrow snout

Most pterosaurs of this group had extensive wing-membranes, which were distended by a long wing-finger and would have been covered in hair-like pycnofibres.[31] Some ornithocheiromorphs, like the basal Lonchodectes, had long jaws with many short teeth, and the jaws were compressed vertically. Ornithocheirus simus had a relatively narrower jaw tip compared to related genera like Coloborhynchus and Anhanguera. Most ornithocheirids bore distinctive convex "keeled" crests on their snouts and underside of the lower jaws, and this was well developed in several genera such as Tropeognathus.[32] T. mesembrinus also had the first five dorsal vertebrae fused into a notarium, with five sacral vertebrae fused into a synsacrum. The third and fourth sacral vertebrae are keeled, with the front blade of the ilium being strongly directed upwards. The similar Anhanguera possesed 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.[33]

Some basal anhanguerians 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.[34] Some of the teeth were extensively restored and enlarged until the wider front of the jaws showed very large and robust teeth projecting outwards. With this arrangement the upper jaw was kinked, and its interlocking teeth suggested that Cearadactylus had a piscivourous diet, allowing the animal to keep hold of slippery fish. Cearadactylus was somewhat similar to ornithocheirids like Coloborhynchus, but it lacked the "keeled" crest on its snout, and therefore it was a more basal ornithocheiromorph.

Life restoration of Caulkicephalus trimicrodon, with a head crest similar to that of Pteranodon

Even though most ornithocheiromorphs didn't have head crests like their close relatives, the pteranodontids, there were some exceptions, this included Caulkicephalus and Ludodactylus.[35] While Ludodactylus is suggested to be a more basal member of the group, Caulkicephalus is more similar to ornithocheirids. This is due to its rounded snout, very similar to that of Ornithocheirus and therefore it was placed within Ornithocheiridae. Caulkicephalus was also a large pterosaur, with wingspan estimates of around 5 metres (16 ft).

Classification

Below is a cladogram showing the results of a phylogenetic analysis presented by Andres & Myers, 2014.[3]

 Pteranodontoidea 

Paleobiology

Diet and feeding

A hypothetical recreation of a group of Istiodactylus feeding on a carcass of a stegosaur

Ornithocheiromorphs were originally regarded as piscivorous creatures, feeding mainly on small and mid-sized fish.[36] Some paleontologists even suggested details on how these pterosaurs caught fish, some of which included dipping their beaks close to the water for prey. Hooley for example, found that the beak of the well known Istiodactylus was similar to those of birds such as herons, storks, and skimmers, and suggested that Istiodactylus probably fed on fish, this was mainly based on his 1913 jaw reconstruction of the animal. Peter Wellnhofer (1991), compared the jaw endings of Istiodactylus with those of a duck, but he then noticed that it wasn't a "duck-billed pterosaur" or anything similar, even though it was popularly called that way.[37] Other diet suggestions for Istiodactylus were mostly based on the broad snout remains, as well as the very distinctive teeth; leading to the thought of a more terrestrial life and hunting methods. This conclusion was later followed by Howse and colleagues suggesting that the strong, yet bizarre teeth of Istiodactylus were more suited for scavenging carcasses rather than catching fish, this led the idea of a different feeding technique, which consisted in bitting and twisting the skull to remove large chunks out of the carcass. These methods of scavenging are similar that of modern-day scavengers such as vultures and marabou storks.[17] In 2010, Attila Ősi agreed that Istiodactylus was able to cut meat with its teeth and jaws, but also mentioned that it wouldn't have been able to process the food properly.[38] Witton in 2012 found that the teeth of Istiodactylus were unlike the recurved and enlarged teeth seen in the more derived ornithocheirids, he instead pointed out that it was more "razor-edged".[29] The German paleontogist Michael Fastnacht made an unpublished thesis about how Istiodactylus fed, showing that some biomechanical calculations predicted a filter-feeding method similar to ducks, and very unique within this group pterosaurs. Witton then discussed it with Fastnacht, and found out that the skull was incorrectly reconstructed, including making the rostrum too broad, and the jaws too long; this then led to the misunderstanding of a duck-like beak.

Between 2012 and 2013, Witton concluded that Istiodactylus shared some chacarteristics with modern-day scavenging birds, and therefore found out that it had strong jaw muscles and thus also had a powerful bite. The skull was also deep, resulting in an easier way of tearing chunks of flesh; though some individual skull remains showed narrower and more slender parts, as well as a shorter toothrow compared to the more advanced ornithocheirids and anhanguerids. Other ornithocheiromorphs, specifically the istiodactylids, possesed similar features, but fossil remains are still poor, so its hard to compare the differences and similarities. One genus though, which is Liaoxipterus, is known for a skull with several unique traits, including numerous peg-like teeth. The shape of its teeth indicated that Liaoxipterus was a possible insect eater[39], and compared to Istiodactylus and other ornithocheiromorphs, Liaoxipterus was also smaller in size, this is perhaps an indication that the more primitive members of this group (istiodactylids in this case) were smaller compared to more derived and families such as the lonchodectids, ornithocheirids and targaryendraconians. This can also seen in the size comparison between ornithocheirids and istiodactylids, with the wingspan of Tropeognathus for example, which measured almost double that of Istiodactylus.

Cimolioptetus (right) stealing prey from a Lonchodectes (left), both were derived members of this group and possible fish hunters

Ornithocheirids like Tropeognathus and Coloborhynchus are considered to be fish-eaters, and had longer and sharper teeth compared to the more rounded teeth of Istiodactylus, though this is still sometimes disputed.[40] Another difference that can be seen in more primitive ornithocheiromorphs their eyes being proportionally smaller compared to the assumed predatory and more advanced ornithocheirids, this again adds to the fact that the more primitive groups (istiodactylids) were most likely scavengers, and later got more successful within the food chain, leading the later, more advanced groups (ornithocheirids and lonchodectids) to be the dominant fish hunters during the early Late Cretaceous.[41]

Locomotion and flight

A flying restoration of Istiodactylus, notice its high aspect ratio

Ornithocheiromorphs, like other pterosaurs, are considered to have been skilled fliers as well as swift at moving on the ground. Footprints from several species show that most pterosaurs did not sprawl their limbs to a large degree, as in modern reptiles, but rather held the limbs relatively erect when walking, like dinosaurs. While footprints are yet to be known, it is likely that ornithocheiromorphs also walked erect.[42] Compared to other earlier pterosaurs such as rhamphorhynchids, ornithocheiromorphs had unusually uneven limb proportions, with the forelimbs resulting in a much longer scale compared to the hind limbs. Their close relatives, the pteranodontids were also found with similar features, though they more likely flew like modern-day albatrosses rather than anything else. Paleontologists also suggest that they most likely spend long stretches of time sea fishing, travelling very long distances without flapping while at the same time flying close the surface of the water with exploited wind speed, and without the necesity of thermals.[43] This would likely have required them to use unique modes of locomotion compared to other pterosaurs, this can already be seen in earlier evolutions such as Istiodactylus[29] and Nurhachius[44] , with powerful musculature attachments and well-developed pectoral and upper arm bones. Like albatrosses, ornithocheiromorphs also had a high aspect ratio and low wing loadings. The wing remains of Nurhachius have been compared to those of modern soaring birds, which fly with little flapping, and may have been ideal for low-energy soaring, which is necessary when searching for carrion (assuming istiodactylids were scavengers).[44] The wings of istiodactylids also seem to have been shorter compared to the fish-eating ornithocherids, and unlike them, which were more suited for taking off and landing, istiodactylids may have preferred a more terrestrial setting. This is also seen in many inland soaring birds, which have a lower aspect ratio compared those that soar over the ocean. It is also possible that ornithocheiromorphs ran (but not walked) bipedally, or that they used a hopping gait.[42] Many pterosaur researchers like Mike Habib have noted that the limb proportions of some ornithocheiromorphs such as Anhanguera are consistent with hopping[45], though the scavenging istiodactylids are probably still the best examples of pterosaurs with a more terrestrial setting.

Paleoecology

Restoration of Irritator walking down a coastline in the Romualdo Formation environment, with a pair of ornithocheirids, a Thalassodromeus and the compsognathid Mirischia in the background

The ornithocheiromorphs were distributed around the world, but most of them were concentrated in specific places. One specific fossil site containing an impresive number of pterosaurs is the Romualdo Formation in Brazil, where many ornithocheiromorphs were uncovered. The formation includes many species of Anhanguera[33], several fossil remains of basal members, including Brasileodactylus, Cearadactylus and Unwindia, as well as Tropeognathus[18], Coloborhynchus, Maaradactylus, Araripesaurus and Barbosania. These pterosaur genera were just some of the many recovered from the site, which also includes the thalassodromids Tupuxuara and Thalassodromeus, as well as the tapejarid[46] Tapejara, the basal pteranodontoid Santanadactylus and the dubious Araripedactylus. Some other creatures from the formation include the theropods Irritator, Mirischia and Santanaraptor, the crocodylomorph Araripesuchus and even turtle remains were found, with some specimens referring to Santanachelys, Cearachelys and Araripemys.

Reconstructed skeleton of the spinosaurid Irritator holding a possible anhanguerid pterosaur in its jaws

Another important fossil site is the Wessex Formation in the Isle of Wight near the coast England. The formation doesn't contain many fossil remains of pterosaurs compared to the Romualdo Formation, but it is still a very important site. It mainly contains remains of the istiodactylid Istiodactylus[29], the ornithocheirid Caulkicephalus, and Wightia, a tapejarid. The formation is also known for several theropods, including the spinosaurid Baryonyx[47], the tyrannosauroid Eotyrannus, the dromaeosaurid Ornithodesmus, the compsognathid Aristosuchus as well as the allosauroid Neovenator. Other animals of the formation include many differents types of herbivorous dinosaurs like Iguanodon, Polacanthus, Ornithopsis, Mantellisaurus and Hypsilophodon as well as the neosuchian Bernissartia and turtle remains of Helochelydra.

Life restoration of Australovenator feeding on the carcass of a Diamantinasaurus in the Winton Formation environment

A few fossils reported from the Toolebuc Formation and Winton Formation are believed to be from some of the most derived ornithocheiromorphs, due to the age of the fossil remains, which dated back to the Albian and Cenomanian stages of the Cretaceous, and even some are believed to belong from the Turonian stage. The Toolebuc Formation includes several remains of ornithocheiromorphs which are now referred to the genera Aussiedraco[48] and Mythunga[49]. The formation also includes some other animals such as herbivorous dinosaurs like the ornithopod Muttaburrasaurus[50] and the ankylosaur Kunbarrasaurus.[51], as well as marine animals including the ichthyosaur Platypterygius, the pliosaurid Kronosaurus and the elasmosaurid Eromangasaurus. Turtle remains from turtles that were proposed to be prey for pterosaurs[52] were also found within the Toolebuc Formation, this included the genera Bouliachelys, Cratochelone and Notochelone. The Winton Formation consisted on a more terrestrial environment, containing several sauropod dinosaurs like Austrosaurus, Diamantinasaurus, Savannasaurus and Wintonotitan as well as large carnivorous dinosaurs such as Australovenator[53] and crocodylomorphs like Isisfordia. The formation's only pterosaur is the derived ornithocheirid Ferrodraco[54], which is considered as one of the last ornithocheiromorphs (if not the last) and a close relative of Mythunga[49]. Although these two Australian formations contain some of the most derived members of this group, some specimens from the Chalk Formation in Kent, England probably had a similar or younger age. These were the first ornithocheiromorph fossils discovered, and belonged to the lonchodectid Lonchodraco, as well as Cimoliopterus[1], a former ornithocheirid which is now reclassified as a targaryendraconian[55] and sister taxon of Camposipterus. Lonchodraco, formerly known as Pterodactylus giganteus[56], is considered one of the last ornithocheiromorphs; though along with Lonchodectes, both are classified as basal members due to complex taxonomy issues.

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