Tropeognathus

*Tropeognathus mesembrinus*

***Tropeognathus*** (meaning "keel-tipped jaw") is a genus of large pterosaurs from the late Cretaceous Period of South America. It was member of the Ornithocheiridae (alternately Anhangueridae), a group of pterosaurs known for their keel-tipped snouts, and was closely related to species of the genus *Anhanguera*. It is known primarily for the species *Tropeognathus mesembrinus*, though a second species, *Tropeognathus robustus*, has been named in the genus. The keel-tipped mouth had a similar appearance to that of the Coloborhynchus.

## Discovery and naming

In the 1980s the German Bayerische Staatssammlung für Paläontologie und historische Geologie at Munich acquired a pterosaur skull from Brazilian fossil dealers, that had probably been found in Ceará, in the Chapade do Araripe. In 1987 it was named and described as the type species *Tropeognathus mesembrinus* by Peter Wellnhofer. The generic name is derived from Greek τρόπις, tropis, "keel", and γνάθος, gnathos, "jaw". The specific name is derived from Koine mesembrinos, "of the noontide", "southern", in reference to the provenance from the Southern hemisphere.[1]

The holotype, BSP 1987 I 46, was discovered in a layer of the Romualdo Member of the Santana Formation, dating from the Aptian-Albian. It consists of a skull with lower jaws. A second specimen was referred by André Jacques Veldmeijer in 2002: SMNS 56994, consisting of partial lower jaws.[2] In 2013, Alexander Wilhelm Armin 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.[3]

After *Tropeognathus mesembrinus* was named by Peter Wellnhofer in 1987[4] other researchers tended to consider it part of several other genera, leading to an enormous taxonomic confusion.[3] It was considered an *Anhanguera mesembrinus* by Alexander Kellner in 1989, a *Coloborhynchus mesembrinus* by Veldmeijer in 1998 and a *Criorhynchus mesembrinus* by Michael Fastnacht in 2001. In 2001, David Unwin referred the *Tropeognathus* material to *Ornithocheirus simus*, making *Tropeognathus mesembrinus* a junior synonym,[5] though he again reinstated a *Ornithocheirus mesembrinus* in 2003.[6] Veldmeijer in 2003 accepted that *Tropeognathus* and *Ornithocheirus* were cogeneric but rejecting *O. simus* as the type species of *Ornithocheirus* in favor of *O. compressirostris* (named *Lonchodectes* by Unwin), used the names *Criorhynchus simus* and *Criorhynchus mesembrinus*.[7] In 2000, Kellner again began to use the original name *Tropeognathus mesembrinus*. In 2013, Taissa Rodrigues and Kellner concluded *Tropeognathus* to be valid, and containing only *T. mesembrinus*.[3]

In 1987 Wellnhofer named a second species, *Tropeognathus robustus*, based on specimen BSP 1987 I 47, a more robust lower jaw.[1] Today, this is no longer considered cogeneric with *Tropeognathus mesembrinus*.

## Description

*Tropeognathus mesembrinus* is known to have reached wingspans of up to 8.2 m (27 ft), as can be inferred from the size of specimen MN 6594-1.[8] *T. mesembrinus* bore distinctive convex "keeled" crests on its snout and underside of the lower jaws.[9] 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).[10] While many ornithocheirids had a small, rounded bony crest projecting from the back of the skull, this was particularly large and well-developed in *Tropeognathus*.[7] The first five dorsal vertebrae are fused in to a notarium. Five sacral vertebrae are fused into a synsacrum. The third and fourth sacral vertebrae are keeled. The front blade of the ilium is strongly directed upwards.

## Links

https://web.archive.org/web/20050307005256fw\_/http://www.jpinstitute.com/dinolab/dino\_academy/art\_gallery\_class\_gallery.jsp?CLASSID=5