User:Ichthyovenator/Prognathodon

Prognathodon is an extinct genus of marine lizard belonging to the mosasaur family.

Research history [WIP]
Prognathodon was first described by Louis Dollo in 1889 based on specimens gathered in Belgium. There is some confusion over the correct generic name for the taxon. Dollo first mentioned the taxon as "Prognathodon" in some preliminary notes and provided a provisional diagnosis, but replaced the name Prognathodon with "Prognathosaurus" and used Prognathosaurus in all of his subsequent papers mentioning the genus. The first later use of "Prognathodon" was by Dale A. Russell in a comprehensive monograph on North American mosasaurs in 1967, where the priority of Prognathodon was made apparent. Russell also revised the species assigned to Prognathodon from North America, but only briefly commented on the Belgian specimens.

Though the original remains of the genus were rather comprehensive and the original description was brief, no additional studies of the type material was done for a century. The lack of a comprehensive original description of the genus and the species referred to it from Belgium is not unusual for mosasaur specimens discovered in the Craie de Ciply Formation of Belgium. Large amounts of work was commonly invested in extracting and mounting the specimens, but scientific study of them remained limited with diagnoses and descriptions mainly focusing on peculiar points of their anatomy, such as the quadrate and tympanic membrane of Plioplatecarpus houzeaui. Prognathodon giganteus, named by Dollo in 1904, is one of species with the most brief descriptions, apparently only intended to provide a name for the skeleton of the mosasaur for exhibition in the museum hall.

The first comprehensive study of the Prognathodon specimens from Belgium (including the type specimen) was done by Theagarten Lingham-Soliar and Dirk Nolf in 1989 and the diagnosis in this study remains the latest published emended diagnosis for the genus.

In 1998, an intact fossil skull was found in the Maastricht limestone quarries. Shortly after, it was nicknamed "Bèr", and put on display in the Maastricht Natural History Museum. This specimen was then identified as a Prognathodon, and received the species name Prognathodon saturator. This specimen was the first reasonably complete mosasaur specimen recovered from the Maastricht area since 1957; the skeleton is on display at the Natural History Museum at Maastricht, and is from an animal that was probably 12 metres long.

A very large specimen found in Israel was for some time informally named "Oronosaurus", but eventually described as a new species of Prognathodon, P. currii. Two specimens of Prognathodon overtoni described in 2011 from the early late Campanian (c. 74.5 Ma) Bearpaw Formation in Alberta, Canada provided the first fully articulated skeletons of the genus. Detailed studies of these and previously discovered specimens allowed several characters to be established that distinguishes Prognathodon from closely related genera like Liodon and long-snouted mosasaurines. The preserved teeth and gut contents also allowed studies into the inferred paleoecology of the genus.

A new fossil found in 2008 and described in 2013 belonging to a 1.8 m juvenile Prognathodon was found in Jordan's Harrana Site. The fossil was remarkable in that it preserved the outline of the mosasaur's tail fins, revealing that Prognathodon, like Platecarpus, had a bilobed tail fluke resembling a downturned shark's tail, the shape of which may have aided the creature in surfacing, as well as attacking prey. The discovery also lends evidence to the theory that later mosasaurs were even more well-adapted to the lifestyle first occupied by the ichthyosaurs.

Classification
Historically, Prognathodon was believed to be a close relative of the genus Platecarpus, within the subfamily Plioplatecarpinae. Louis Dollo was one of the earliest researchers to work on mosasaur systematics, initially placing them as a distinct lizard suborder and dividing the group into two families, the Mosasauridae and the "Plioplatecarpidae". In this early taxonomy, the Mosasauridae contained the genera Clidastes, Mosasaurus, Platecarpus, Halisaurus and Tylosaurus and the Plioplatecarpidae was monotypic, only containing Plioplatecarpus. In 1890, following further mosasaur discoveries (including that of Prognathodon), Dollo revised his taxonomy, dividing the Mosasauridae into three groups. Prognathodon was placed alongside Platecarpus in a "microrhynchous" group. The two other groups were the "megarhynchous" (including Tylosaurus and Hainosaurus) and the "mesorhynchous" (including Mosasaurus and Clidastes) groups. Dollo realized that Plioplatecarpus shared characters with the "microrhynchous" group in 1894 and abandoned his previous two family-system, starting to use only one family of mosasaurs, the Mosasauridae, and placing Prognathodon as closely related to Platecarpus and Plioplatecarpus. In 1967, Dale Russell retained Prognathodon within the Plioplatecarpinae, but erected a tribe for the genus and the related Plesiotylosaurus, the Prognathodontini. He considered the mosasaurs within the Prognathodontini to "clearly be of plioplatecarpine derivation", but justified the tribe by that they can be differentiated from other plioplatecarpines by their massive jaws and robust teeth.

Gorden L. Bell Jr. conducted the first major phylogenetic analysis of mosasaurs in 1997, utilizing new methodologies and incorporating further taxa described since Russell's 1967 monograph (particularly basal mosasauroids, such as Aigialosaurus). Bell recovered Prognathodon within the Mosasaurinae, for the first time ever, as a close relative of the genera Globidens and Plesiotylosaurus. The tribe Prognathodontini was synonymized with the Globidensini, another tribe coined by Russell in 1967 for Globidens. Bell was also the first to note that his analysis recovered Prognathodon, previously believed to be monophyletic, as paraphyletic. The view of the relationships of the genus to other mosasaur genera has changed little since 1997. Modern researchers often refer to Prognathodon as a globidensine mosasaur, placing it within the Globidensini in the Mosasaurinae. Cau and Madzia (2017) noted that the inclusion of Prognathodon and Plesiotylosaurus within the Globidensini might suggest a closer relationship between the genera than the reality of the situation.

Since the description of the genus in 1889, a large number of mosasaur species have been assigned to Prognathodon. The incompleteness of many Prognathodon fossils, combined with the extreme rarity of specimens from the early to middle Campanian, has made studies of the genus difficult. The systematics of Prognathodon, including its generic characteristics and its diveristy, as well as the early evolutionary history of the genus, are poorly understood. Among modern mosasaur researchers, Prognathodon is widely considered to be paraphyletic. A particular issue is that mosasaur specimens with robust and conical teeth with smooth enamel and blunt, serrated carinae (the ridges along the sharp edges of the teeth) are routinely assigned to Prognathodon, but the generic type species, P. solvayi, differs from these specimens in that it has compressed and gently facetted teeth.

The cladograms below demonstrate the wildly different results of recent phylogenetic analyses pertaining to Prognathodon. The center cladogram (Topology B) is modified from a maximum clade credibility tree inferred by a Bayesian analysis in the most recent major phylogenetic analysis of the Mosasaurinae subfamily by Madzia & Cau (2017), which has been self-described as a refinement of a larger phylogenetic study on mosasaurs by Simões et al. (2017), presented here as Topology A. The leftmost cladogram (Topology C) follows the phylogeny produced through Bayesian analysis by Lively (2020) in the description of Gnathomortis.

Topology A: Maximum clade credibility tree by Simões et al. (2017)

Topology B: Maximum clade credibility tree by Madzia & Cau (2017)

Topology C: Phylogenetic hypothesis under a Bayesian framework by Lively (2020)

Species
P. crassartus (Plioplatecarpus?)

Cope, 1872, Campanian USA

Recognized as a globidensine and a valid species, without comment, by Schulp et al. (2006).

P. currii

Christiansen & Bonde, 2002, Late Campanian Israel and Maastrichtian Morocco

Largest species, approximately 11 metres in length.

Some paleontologists, such as Christiansen and Bonde (2002) have taken to calling P. currii the "T. rex of the seas" on account of its massive size and several of its cranial and dental characteristics.

P. giganteus

Dollo, 1904, Campanian/Maastrichtian of Belgium, late Early Campanian of France, Late Cretaceous of Syria, Maastrichtian of Jordan

P. hashimi (nomen nudum)

P. hudae (nomen nudum)

P. lutugini

P. overtoni

Williston, 1897, Maastrichtian of SD, USA or Campanian of SD, USA

P. kianda

Maastrichtian of Angola

Substantial fossil material of P. kianda was first recovered in 2005, with two skulls found during two separate expeditions, one on May 20 and another on May 22, to a fossil site near the village of Bentiaba. The first skull (ML/MGUAN05, later re-designated MGUAN PA 128) was relatively incomplete, and examinations of the surrounding area suggested that the rest of the skeleton had eroded away. The second skull (ML/MGUAN07, later re-designated MGUAN PA 129) was more complete, but it could only be partially excavated on account of a lack of time. Through phylogenetic analysis it was determined that the fossil material was of a species of Prognathodon. Though the fossils were described in 2006 and then determined to represent a new species on account of their distinguishing features (more gracile teeth and the dorsal keel of the internarial bar being more defined), the researchers did not name the new species immediately, awaiting further planned excavations. These further excavations took place in 2006 and 2007 and additional fossils recovered were entirely composed of more skull material, including, among other elements, dentaries and a braincase. In 2008, the new species was named by Schulp et al, with MGUAN PA 129 designated as the holotype specimen. The species name, kianda, was derived from Kianda, an Angolan goddess of the sea. In addition to the distinguishing features already noted in 2006, a third feature which distinguishes P. kianda from other species was noted in 2008; that the tooth count of P. kianda was higher than that of other Prognathodon.

Both the 2006 description of the first fossil material and the 2008 description of the species supported P. kianda as the basalmost species of Prognathodon, with its inclusion in the genus supported by several synamorphies but the distinguishing features noted clearly separating it from other species and linking it closer to less derived mosasaurines.

P. kianda shared its living environment with other species of mosasaur; Globidens, Plioplatecarpus, a larger Prognathodon and indeterminate large mosasaurine.

Estimated at just over 7 metres in length, medium-sized prognathodon.

Prognathodon teeth, belonging to a different, larger, species, had been recovered at the same sites as early as 1964.

P. mosasauroides, P. compressidens, P. sectorius (originally Liodon)

Because the slender teeth of P. kianda differentiated it from other species of Prognathodon, and most other mosasaur genera, Schulp et al. (2008) compared them to similar material reported as cf. Liodon anceps from Syria and Morocco, finding them similar. On account of Liodon being found to be a dubious genus, with the fossils containing its supposedly distinguishing features being missing, Schulp et al. referred the three species, other than the type L. anceps, to Prognathodon, erecting P. compressidens, P. mosasauroides and P. sectorius.

The holotype specimen of P. compressidens, MNHN-Z-C1878-5, shares several dental characteristics with P. kianda, including, among others, the anterior teeth being recurved and slender, its possession of a markedly heterodont dentition and the posterior teeth being quite small. Distinguishing it from P. kianda is the teeth being less compressed and not as long, as well as the maxilla being relatively low and slender. Heterodont dentition is also reflected in P. mosasauroides and P. sectorius. P. mosasauroides can be distinguished from P. kianda by the labiolingual fattening being much less pronounced in P. kianda, and P. sectorius can be distinguished by the teeth in P. kianda being significantly more slender.

P. mosasauroides - Gaudry, 1892, Maastrichtian of France

P. sectorius - Cope, 1871, Maastrichtian of New Jersey and the Netherlands On the basis of similarities in the dental characteristics between late Campanian fossil material recovered in the Vitoria Formation in Navarre, Spain, and features confidently putting the fossils within Prognathodon but distinguishing them from those of other species, this fossil material was tentatively referred to P. cf. sectorius, extending both the geographical and temporal range of this species. The fossils suggest that P. sectorius might have inhabited the entire northern margin of the Tethys Ocean.

P. compressidens - Gaudry 1892, Campanian of France

The reassignment of all three species to Prognathodon has continued to be supported by subsequent researchers.

Prognathodon with slender teeth: P. kianda, P. mosasauroides and P. sectorius.

P. nov. sp. (Morocco)

There is a new, undescribed, species from the Maastrichtian of Morocco (first mentioned by Bardet et al. (2012)) with more detailed info in Bardet et al. (2015):

The species is mainly based on a partial skull (OCP DEK/GE 497), recovered in Upper Maastrichtian deposits in the Oulad Abdoun Basin, but fragmentary fossils are relatively common. In particular, isolated fossil teeth corresponding to those seen in the skull occur throughout the Maastrichtian in the nearby Gantour Basin. Teeth referrable to the species have been known since at least the 1950s, though they were first attributed to Liodon anceps by Arambourg (1952). Teeth corresponding to those seen in the species have also been recovered throughout the world, from alongside the southern margin of the Tethys Ocean (Angola, Brazil, Egypt and Israel), and possibly the Maastrichtian of Poland.

Based on unpublished specimens, the skull of P. nov. sp. reached 150 centimetres in length, exceeding the size of the skull of P. currii (140 centimetres), meaning that it would have been a very large species of Prognathodon.

Like the teeth of P. currii and P. giganteus, the teeth of the new species of Prognathodon are large, robust cones (up to 6 centimetres high). They can be differentiated by the basal length being about half of the height (as opposed to two thirds, as in the other species) and a sharper and higher apex.

P. rapax

Hay, 1902, Maastrichtian of NJ, USA

P. saturator

Dortangs et al. 2002, Maastrichtian Netherlands

P. solvayi

Dollo 1889, Early Maastricthian Belgium

Smallest species, less than 5 metres in length.

P. stadtmani (Gnathomortis)

Kass, 1999, Early Campanian USA, membership in Prognathodon questioned already in 2006

P. waiparaensis (Marichimaera in 2016 thesis)

Welles & Gregg 1971, Late Cretaceous New Zealand - id:d to Maastrichtian New Zealand

Indeterminate remains

In addition to P. kianda, the Maastrichtian Angolan fossil sites near Bentiaba preserve fossils of another, larger species of Prognathodon. Known only from teeth, the teeth of the second species of Prognathodon are facetted and do not swell or constrict near the base, differentiating them from the teeth of P. kianda.

Prognathodon sp. have also been recovered from Late Campanian Poland, Maastrichtian D. R. of Congo

P. hashimi and P. hudae