Friday 11 October 2019

Ferrodraco lentoni: A new species of Anhanguerian Pterosaur from the Late Cretaceous of Queensland, Australia.

The Pterosaurs were an extinct group of flying Archosaurs that existed from the late Triassic to the end of the Cretaceous Period (210 to 65.5 million years ago). They are thought to have been warm blooded, as  many specimens have been found that appear to have had fury skins. Their wings were flaps of skin membrane, similar to that of Bats, supported by elongated fourth fingers and attached to the flanks of the body and legs. Unlike Birds they appear to have been capable of flying before reaching their full adult size, and appear to have taken several years to reach maturity. The largest Pterosaurs achieved wingspans in excess of 7 m, roughly twice that of the largest extant Birds. Despite their long history and high diversity, the fossil record of Pterosaurs is somewhat limited, probably due to their lightweight, fragile skeletons, with most known Pterosaur fossils coming from a relatively small number of localities. Less than twenty Pterosaur fossils are known from Australia, and all of these fragmentary specimens from the Cretaceous.

In a paper published in the journal Scientific Reports on 3 October 2019, Adele Pentland and Stephen Poropat of the Faculty of Science, Engineering and Technology at Swinburne University of Technology, and the Australian Age of Dinosaurs Natural History Museum, and Travis Tischler, Trish Sloan, Robert Elliott, Harry Elliott, Judy Elliott, and David Elliott, also of the Australian Age of Dinosaurs Natural History Museum,describe a new species of Ornithocheirid Pterosaur from the Late Cretaceous Winton Formation of Queensland, Australia.

The Winton Formation is an iron rich sandstone laid down in a shallow inland sea (the Etomanga Sea) and associated river systems that covered parts of Queensland and central Australia during the early Late Cretaceous (98-95 million years ago). which extends from Hungerford on the New South Wakes border northwest to the area around Kynuna, a distance of over 1000 kilometres. This formation is famous for its Dinosaurs, but also produces Crocodylians, Turtles, Fish and a wide range of Invertebrates. It is also noted for the production of opals, which are typically found in cracks in ironstone concretions (themselves formed by precipitation from water that has accumulated iron as it peculated through the feruginous sandstone), and is commonly called 'boulder opal'.

The species is named Ferrodraco lentoni, where 'Ferrodraco' means 'Iron Dragon', as the specimen from which the species is described is preserved in ironstone, and 'lentoni' honours former Winton Shire mayor Graham Thomas ‘Butch’ Lenton, in recognition of his years of service to the Winton community and support to the Australian Age of Dinosaurs Natural History Museum. The species is described from a single, fragmentary, specimen excavated at Belmont Station in Winton Shire, Queensland.

Location of the Ferrodraco lentoni type locality. (a) Map of Australia showing the location of Queensland. (b) Map of Queensland showing the distribution of Winton Formation outcrop. (c) Map of the Winton area showing Winton Formation outcrop, the location of Belmont Station, and museums in the region. Stephen Poropat in Pentland et al. (2019).

The specimen from which the species is described comprises the anterior portion of skull comprising a partial premaxillae, the maxillae and dentaries (including premaxillary and mandibular crests and the mandibular symphysis), a partial left frontal, the left mandibular articular region comprising the surangular, angular and articular, as well as five partial cervical vertebrae, a partial right scapulocoracoid, a partial left ulna, a partial left radius, the left proximal and distal carpals, the left metacarpal IV, an the proximal end of right metacarpal IV, fragmentary left non-wing manual phalanges, partial left first wing phalanx (IV-1), and associated fragments. Several elements, including the skull and mandible and many of the appendicular elements were clearly articulated post-fossilisation; however, erosion and soil rotation led to fragmentation of the specimen prior to its excavation.

Ferrodraco lentoni, holotype skull and mandible AODF 876. (A) dorsal view; (B) anterior view; (C) left lateral view; (D) ventral view; (E) right lateral view; (F) schematic of left lateral view; and (G) schematic of right lateral view. Abbreviations: d, dentary; dcr, (preserved base of) dentary crest; ll#, lower left (alveolus number); lr#, lower right (alveolus number); man, mandibular ramus; ms, mandibular symphysis; pmcr, premaxillary crest; pmx-mx, premaxilla–maxilla; ul#, upper left (alveolus number); ur#, upper right (alveolus number). Scale bar is 50 mm. Pentland et al. (2019).

Ferrodraco lentoni is diagnosed to be a Anhanguerian Pterodactyloid based upon the following criteria, (1) first tooth pair of the premaxilla and mandible smaller than other anterior teeth; (2) fourth up to seventh teeth smaller than third and eighth. There have been two previously described Pterosaurs from the Cretaceous of Queensland, Mythunga camara and Aussiedraco molnari, both of which are from slightly older strata than Ferrodraco lentoni.

There is little overlap between the material used to describe Ferrodraco lentoni and that used to describe Mythunga camara, but the latter has quite different dentition, making it unlikely the two specimens represent the same speces.

The situation with Aussiedraco molnari is slightly more complex; the most obvious difference between Ferrodraco lentoni  and Aussiedraco molnari is the presence of a mandibular crest in Ferrodraco lentoni  but not Aussiedraco molnari. However this is known to be a sexually dimorphic trait in some Pterosaurs (i.e. one sex had mandibular crests and the other didn't in the same species), making this of little use as a diagnostic trait. However there are other differences between the specimens; the mandible of Ferrodraco lentoni expands towards the tip more than that of Aussiedraco molnari, and is laterally convex, whereas that of Aussiedraco molnari is straight. In Aussiedraco molnari, the anterior portion of the mandibular groove is more prominent than that of Ferrodraco lentoni, and appears most pronounced from the posterior margin of the third alveolus until the posterior margin of the fourth alveolus in the former taxon. Aussiedraco molnari also differs from Ferrodraco lentoni in that its alveolar borders are not raised. Perhaps most tellingly, two sulci (grooves) were observed on the rostral tip of the mandible of Aussiedraco molnari that were notpresent in Ferrodraco lentoni, or any other Pterosaurs.

Ferrodraco lentoni holotype rostral sections AODF 876. Cross-section (A) internal structure of premaxillary crest; (B) weak mandibular groove (grey arrow) and internal structure indicates the mandible is incomplete ventrally; (C)–(I) demonstrate variation in the depth of the palatal ridge and corresponding mandibular groove, with ironstone matrix represented by shaded region; (H) demonstrates replacement tooth is located lingual to the functional tooth; (J) section through (H) demonstrating the replacement tooth is distal to the functional tooth. The location of the functional and replacement teeth was based on their pulp cavities (black). Co-ossified dentaries in (K) anterior and (L) dorsal (occlusal) views. (M) Co-ossified premaxillae and maxillae in ventral (occlusal) view. (N) Schematic of premaxillae and maxillae in ventral (occlusal) view showing the subtle longitudinal palatal ridge. Abbreviations: ft, functional tooth; ll#, lower left; prid, palatal ridge; rt, replacement tooth; ul#, upper left; ur#, upper right. Scale bars are 20 mm for all figures. Pentland et al. (2019).

A phylogenetic analysis was carried out including Ferrodraco lentoni and Mythunga camara, but not Aussiedraco molnari. This recovered Ferrodraco lentoni and Mythunga camara as sister taxa, with their closest (included) relatives being Ornithocheirus simus and Coloborhynchus clavirostris, both of which are from England. This is at first surprising, as England and Queensland were not much closer in the Cretaceous than they are today, but Anhanguerian Pterodactyloid are thought to have been large animals capable of making long-distance, ocean-crossing flights (the wingspan of Ferrodraco lentoni is estimated to have been about 4 m, compared to about 3.1 in the modern Wandering Albatros, Diomedea exulans).

Ferrodraco lentoni holotype specimen AODF 876. All preserved elements were photographed and scaled to the same size, then articulated where possible. These were then used as the basis for the scaling of the skeletal reconstruction, the missing parts of which were based on the skeletal reconstruction of Tropeognathus mesembrinus. Scale bar is 50 mm. Pentland et al. (2019).

It has been suggested that Anhanguerians went extinct at the end of the Cenomanian (93.8 million years ago), based on their apparent absence from post-Cenomanian strata. Their apparent absence follows a period of major environmental disturbance characterised by an increase in atmospheric and oceanic surface temperature, an increase in atmospheric carbon dioxide, a global oceanic anoxic event, and marine transgression.At present, the majority of Anhanguerians are known from restricted lagoon environments, with stable isotopic analysis of isolated teeth derived from the Araripe Basin  of northeastern Brazil indicating a piscivorous diet comprising both freshwater and marine Fish. Given that marine vertebrates and invertebrates were most severely impacted during the Cenomanian–Turonian event, Pentland et al. suggest that Anhanguerians were also impacted by a disruption in trophic interactions. However, if the teeth sampled from the Araripe Basin are not diagenetically altered and are indicative of the feeding behaviours of this clade more broadly, it is possible that anhanguerians in terrestrial settings might have persisted beyond the Cenomanian.

The presence of an anhanguerian in the Winton Formation is not surprising, given that several related Pterosaurs have been reported from the underlying upper Albian Toolebuc and Mackunda formations. However, recent analyses of detrital zircons obtained from localities in the Winton area suggest that deposition of the northern part of the Winton Formation where Ferrodraco lentoni was found might have taken place as late as the early Turonian (i.e. after 93.8 million years ago). Given that Ferrodraco derives from a locality northeast of Winton, it potentially represents a late-surviving member of the Ornithocheiridae specifically, and of Anhangueria more broadly.

Life restoration of Ferrodraco lentoni as an Ornithocheirid Pterosaur. Travis Tischler in Pentland et al. (2019).

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