Ornithocheiromorpha

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Ornithocheiromorphs
Temporal range:
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

azhdarchoids. The Ornithocheiromorpha was defined in 2014 by Andres and colleagues, and they made Ornithocheiromorpha the most inclusive clade containing Ornithocheirus, but not Pteranodon.[3]

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

paleontologists also consider ornithocheiromorphs an earlier step of evolution to the pteranodontids
, 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

Lonchodraco giganteus

The first specimens of ornithocheiromorphs were unearthed at a chalk pit near

Reginald Walter Hooley in 1914.[8] Confusingly, this species was also long regarded, incorrectly, as the type species of Ornithocheirus.[9]

In 1861, further pterosaur specimens were found in the

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.[12]

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.[13]

Istiodactylus latidens

In 1887, Seeley had described new fossil remains from the

Ornithodesmus cluniculus.[14] 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".[15] 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.[16] 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.[17]

In 1993, the British paleontologists

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.[18] 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.[19]

Discoveries outside Europe

Ornithocheirus simus

Other important ornithocheiromorph discoveries include the anhanguerids

junior synonym of Ornithocheirus simus by British paleontologist David Unwin in 2001, but he then proposed an Ornithocheirus mesembrinus in 2003.[26][27] In 2013 however, Taissa Rodrigues and Alexander Kellner concluded that Tropeognathus would be valid again, and containing only T. mesembrinus, the type species.[13]

Hamipterus tianshanensis

A discovery in Asia, specifically northwestern

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]

Description

Size

Istiodactylus latidens
compared to a human

Ornithocheiromorphs were large pterosaurs, with wingspans normally ranging between 3 and 6 meters (9.8 and 19.7 ft).[4] Istiodactylus for example, had a wingspan ranging from 4.3 to 5 meters (14 to 16 ft), with the most complete known skull estimated to have been about 45 centimeters (1.48 ft) in length, based on a long-lost fragment of its jaw reported in 2012.[29] Though its jaws measured only 28.5 centimeters (11.2 in), which was less than 80 percent of the skull's length.[17] 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 8.26 meters (27.1 ft), and 8.70 meters (28.5 ft) as the maximum estimate.[30] Another species which was impressively large is Coloborhynchus capito, with a total skull length that could have been up to 75 centimeters (2.46 ft), leading to an estimated wingspan of 7 meters (23 ft).[31] However, this species may belong to a different genus called Nicorhynchus.[32]

Skull and crests

Skull comparison between different species of ornithocheiromorphs; notice their different structures

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.[33] 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.[34]

Other anhanguerids like

teeth suggested that Cearadactylus had a piscivourous diet, allowing the animal to keep hold of slippery fish.[36] Another smaller genus similar to Cearadactylus is Guidraco. Its holotype skull has a length of 38 centimeters (15 in), 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.[37]

Even though most ornithocheiromorphs didn't have a

cranial crest like the closely related pteranodontids, there were some exceptions, this included Caulkicephalus and Ludodactylus.[38] 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.[39][40] Caulkicephalus was also a large pterosaur, with wingspan estimates of around 5 meters (16 ft).[40]

Vertebrae

The vertebral column of ornithocheiromorphs was heavily pneumatized by an extensive system of air sacs, leaving prominent pneumatic foraminae.[41] The neck of ornithocheiromorphs was typically relatively long and robust, being longer than the torso in some derived clades.[42] The neural spines of ornithocheiromorph cervical vertebrae were generally tall and spikelike.[37][34] In some genera such as Tropeognathus and Istiodactylus, up to six dorsal vertebrae are fused into a notarium.[43] In some genera such as Anhanguera, four to seven sacral vertebrae are fused into a synsacrum.[34] The tail is not well known in ornithocheiromorphs, however. Zhenyuanopterus, which is known for having 13 caudal vertebrae, formed one of the longest tails of any pterodactyloid.[44] Anhanguera, another well-known genus, had a shorter tail, with broad caudal vertebrae that bore a "duplex" cross-section similar to Pteranodon.[34]

Pelvic structure

Anhanguera santanae
, showing its right side

The

hip joint of ornithocheiromorphs was not perforated and allowed considerable mobility to the leg, and suggests that it was vertical, as therefore had a function in breathing, compensating the relative rigidity of the chest cavity.[47][45]

Classification

Holotype mandible of the recently named Targaryendraco

Several studies show that ornithocheiromorphs were less derived than the toothless pteranodontids such as Pteranodon, and based on the different evolutionary changes, they therefore need to be grouped in a different clade than Pteranodon, though still within Pteranodontoidea.[48] In 2003, David Unwin considered the family Istiodactylidae to group with the toothless Pteranodontidae, within the group Ornithocheiroidea,[27] but Alexander Kellner however, grouped it with the toothed Anhangueridae instead, resulting in a more understandable change of evolution between the two toothed families.[49]

Brian Andres and colleagues found the families Istiodactylidae, Ornithocheiridae and Anhangueridae to form a group in 2014, which he called Lanceodontia, and consists of the more advanced ornithocheiromorphs. The clade however, excludes the more poorly known family Lonchodectidae, even though members of the family had previously been seen as some of the most derived forms of toothed pterosaurs. In their analysis, they also included the family Boreopteridae within the clade Anhangueria, though placed in a more basal position, while also containing the genus Guidraco.[3] In 2018 however, Nicholas Longrich and colleagues found Boreopteridae outside Anhangueria as the sister taxon of the family Lonchodectidae, both groups placed as basal members of the Ornithocheiromorpha.[50]

Relationships

There are competing theories of ornithocheiromorph

phylogeny (evolutionary relationships). Below is cladogram following a topology recovered by Brian Andres, using the most recent iteration of his data set (Andres, 2021).[51]

 Pteranodontoidea 

Pteranodontia

Ornithocheiromorpha

Serradraco

Aussiedraco

Hongshanopterus

Targaryendraco

Lonchodectes

Ikrandraco

Lonchodraco

Lanceodontia

Istiodactylidae

Ornithocheiriformes

Boreopteridae

Hamipterus

Brasileodactylus

Barbosania

Cearadactylus

Ornithocheirae

Ornithocheiridae

Anhangueridae

Ludodactylus

Guidraco

Cimoliopterus

Camposipterus

Aetodactylus

Below is a

phylogenetic analysis presented by Longrich et al. (2018). In the analysis, they placed the genus Hongshanopterus as a basal member.[50]

Ornithocheiromorpha

Hongshanopterus

Lonchodectidae

Lonchodraco

Lonchodectes

Boreopteridae

 Lanceodontia 

Istiodactylidae

Ornithocheiriformes

Aetodactylus

Cimoliopterus

 Anhangueria 

Guidraco

Ludodactylus

Cearadactylus

Brasileodactylus

Ornithocheirae

Ornithocheiridae

Anhangueridae

In 2019, several new species of ornithocheiromorphs were found, and the former species Ornithocheirus wiedenrothi was renamed as

eupterodactyloid Haopterus was reclassified due to the description of Mimodactylus, and is placed in a new family called Mimodactylidae.[54] However, a more recent analysis using the data in the description of Mimodactylus has found Haopterus as a basal member of the more inclusive group Istiodactyliformes.[55] Many recent analyses have also recovered several ornithocheirids, including Tropeognathus, Coloborhynchus, and Caulkicephalus within the family Anhangueridae, meaning that they were more closely related to Anhanguera than to Ornithocheirus.[52][39][55][54][32]

Paleobiology

Diet and feeding

stegosaur
derived members of this group and possible fish hunters

Ornithocheiromorphs were originally regarded as

skimmers, and suggested that Istiodactylus probably fed on fish, this was mainly based on his 1913 jaw reconstruction of the animal.[16] In 1991, Peter Wellnhofer 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.[56] An analysis by Witton in 2012 found that the teeth of Istiodactylus were unlike the recurved and enlarged teeth seen in the more derived ornithocheirids such as Ornithocheirus, he instead pointed out that it was more "razor-edged" and better suited for carrion rather than fish.[29]

Another ornithocheiromorph that possessed similar features to Istiodactylus is Liaoxipterus, which is known from a skull with several unique traits, including numerous peg-like teeth. The shape of its teeth indicated that Liaoxipterus was a possible insectivore,[57] though this conclusion isn't considered entirely accurate.[58]

Anhanguerids 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.[36] Another difference that can be seen in more primitive ornithocheiromorphs their eyes being proportionally smaller compared to the assumed predatory and more advanced anhanguerids, this again adds to the fact that the more primitive groups were most likely scavengers, and later got more successful within the food chain, leading the later, more advanced groups to be the dominant fish hunters during the early Late Cretaceous.[59]

Locomotion and flight

Restoration of a flying 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.[60] 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, traveling very long distances without flapping while at the same time flying close the surface of the water with exploited wind speed, and without the necessity of thermals.[61] 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 and Nurhachius, with powerful musculature attachments and well-developed pectoral and upper arm bones.[29][62] It is also possible that ornithocheiromorphs ran (but not walked) bipedally, or that they used a hopping gait.[60] Many pterosaur researchers like Mike Habib have noted that the limb proportions of some ornithocheiromorphs such as Anhanguera are consistent with hopping, though the scavenging istiodactylids are probably still the best examples of pterosaurs with a more terrestrial setting.[63][16]

Paleoecology

Geological map of the Araripe Basin, with the extent of the Santana Group shown in dark blue
Mounted skeleton of Irritator with a possible anhanguerid in its jaws

Even though the ornithocheiromorphs were discovered worldwide, most of them were concentrated in specific places. One of which is the fossil site called Romualdo Formation, which contains an impressive amount of pterosaur fossils. It is a diverse

enantiornithine Cratoavis, the neosuchian Susisuchus, and several species of fish, including Belonostomus, Calamopleurus,[68] Cladocyclus,[69] Dastilbe[70] and Lepidotes.[71] These fish genera were suggested to be prey for the pterosaurs that lived in the formation, but fossil remains are limited, so the subject is still controversial.[36]

Another important fossil site is the

ray-finned fishes such as Belonostomus, Caturus, Lepidotes and Scheenstia, as well as the mammals Eobaatar, Loxaulax and Yaverlestes.[71][77][78]

Reconstruction of the skeleton of Ferrodraco on a diagram showing the known material, and based on the related Tropeognathus mesembrinus

A few fossils reported from the

sauropod dinosaurs like Austrosaurus, Diamantinasaurus, Savannasaurus and Wintonotitan as well as large carnivorous dinosaurs such as Australovenator[84] and crocodylomorphs like Isisfordia. The formation's only pterosaur is the derived genus Ferrodraco,[85] which is also considered as one of the last ornithocheiromorphs, and a close relative of Mythunga.[80]

See also

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Further reading

External links