Tropeognathus

Genus of anhanguerid pterosaur from the Early Cretaceous

Tropeognathus (meaning "keel jaw") is a genus of large pterosaurs from the late Early Cretaceous of South America. This genus is considered to be a member of the family Anhangueridae, however, several studies have also recovered it within another family called Ornithocheiridae. Both of these families are diverse groups of pterosaurs known for their keel tipped snouts and large size. Tropeognathus is regarded as the largest pterosaur found in the Southern Hemisphere, only rivaled by the huge azhdarchids. The holotype, BSP 1987 I 46, was discovered in a layer of the Romualdo Formation within the Santana Group, dating to the latest Aptian and earliest Albian stages. Along with the holotype, several other pterosaur specimens were found in the fossil site, these specimens however, were referred to genera such as Anhanguera and Cearadactylus. The uncovered holotype consists of a skull with lower jaws. A second specimen was referred by André Jacques Veldmeijer in 2002: SMNS 56994, which consists of a partial mandible. In 2013, Brazilian paleontologist Alexander Kellner referred a third, larger, specimen: MN 6594 1, a skeleton with skull, with extensive elements of all body parts, except the tail and the lower hindlimbs. It was considered an Anhanguera mesembrinus by Alexander Kellner in 1989, a Criorhynchus mesembrinus by Veldmeijer in 1998 and a Coloborhynchus mesembrinus by Michael Fastnacht in 2001. In 2006, Veldmeijer accepted that Tropeognathus and Ornithocheirus were cogeneric, but rejected O. simus as the type species of Ornithocheirus in favor of O. compressirostris, which was named as Lonchodectes by Unwin due to an analysis by English paleontologist Reginald Walter Hooley in 1914. This made Veldmeijer use the names Criorhynchus simus and Criorhynchus mesembrinus instead. Back in 1987, Wellnhofer had named a second species called Tropeognathus robustus, based on specimen BSP 1987 I 47, which is a more robust lower jaw. The maximum wingspan estimate for Tropeognathus reaches ,

The skull of Tropeognathus bore a distinctively convex, "keeled" crests on the lower end of its snout, with an opposing, smaller mass on the underside of the lower jaws. This structure was prominent, well developed, and relatively large in Tropeognathus (especially in males); however, by comparison, these crests were somewhat weakly formed as opposed to the thicker skull crests of other pterosaurs, such as Ornithocheirus. The upper crests arose from the snout tip and extended back to the fenestra nasoantorbitalis, the large opening in the skull side. An additional, smaller crest projected down from the lower jaws at their symphysis ("chin" area). The similar anhanguerid Anhanguera possessed jaws that were tapered in width, but expanded into a broad, spoon shaped rosette at the tip, which differed from Tropeognathus for having a narrower appearance. The jaws can be distinguished from its relatives by a few differences in the crest: unlike its close relatives Coloborhynchus and Ornithocheirus, the crest on the upper jaw of Tropeognathus was more prominent and much larger, and therefore resulting in a broader skull. However, many subsequent analyses made in 2019 and 2020 have recovered Tropeognathus within the family Anhangueridae, with a specific one by Borja Holgado and Rodrigo Pêgas in 2020, placing Tropeognathus more specifically within the subfamily Tropeognathinae, sister taxon to Siroccopteryx. Topology 1: Andres & Myers (2013).]] Tropeognathus mesembrinus was the subject of an entire episode of the award winning BBC television program Walking with Dinosaurs (which used the first name of its cousin Ornithocheirus but was incorrectly named as a species of it, as Ornithocheirus mesembrinus). However, the largest definite Ornithocheirus mesembrinus specimens described at the time measured , in terms of wingspan. Nevertheless, specimen MN 6594 V in 2013 was, at its degree of completeness, the largest known pterosaur individual.