Prognathodon
Prognathodon is an extinct genus of marine lizard belonging to the mosasaur family. It is classified as part of the Mosasaurinae subfamily, alongside genera like Mosasaurus and Clidastes. Prognathodon has been recovered from deposits ranging in age from the Campanian to the Maastrichtian in the Middle East, Europe, New Zealand, Africa and North America.
Prognathodon means "forejaw tooth", which originates from the Latin pro-, Greek gnathos and odṓn. Twelve nominal species of Prognathodon are recognised, from North America, northern and western Africa, the Middle East, western Europe and New Zealand. Due to the sometimes clear differences between them and the incomplete nature of many of the specimens, the systematics of the genus and which species should properly be considered Prognathodon is controversial. Some species have been assigned to other genera, such as Dollosaurus and Brachysaurana, but this has also been questioned.
Prognathodon is known for its massively built jaws and teeth. Its distinct feeding adaptations have generated much interest in its ecology ever since its discovery, though direct evidence of its diet, such as gastric residues, is rare.
Research history
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 strangely 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 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 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.
In 2009, Hani F. Kaddumi described the new species P. hudae based on a complete right dentary and partial left dentary from the Maastrichtian-age Muwaqqar Chalk Marl Formation of Harrana, Jordan. The specific name hudae honors Kaddumi's daughter Huda. Also described in 2009 by Kaddumi from the same locality was P. primus, based on an articulated upper skull, with the name referencing it being the first near-complete mosasaur skull from the Middle East.
The new species and genus Tenerasaurus hashimi, also described by Kaddumi in 2009 from Harrana from fossils likely belonging to a juvenile specimen was reclassified as Prognathodon hashimi by Kaddumi, Johan Lindgren, and Michael J. Polcyn in 2013. The species name references the Hashemites, in honor of Abdullah II of Jordan. This fossil is about 1.8 m in length, and is remarkable in that it preserves the outline of the mosasaur's tail fins, revealing that Prognathodon had a bilobed tail fluke resembling a downturned shark's tail. While this type of fluke had been suggested for mosasaurs based on skeletal anatomy, this is the first indisputable evidence that derived mosasaurs had bilobed tail flukes.
On September 19, 2012, it was announced that nine days earlier, again a skeleton of what appears to be a Mosasaur was found in the limestone quarry just outside Maastricht, the same quarry that yielded the type specimen of Mosasaurus hoffmanni. Carlo Brauer, an excavator operator at the ENCI quarry, discovered the teeth of the fossil in the shovel of his digger on Monday morning, September 10. In the days following the discovery, museum staff retrieved several large sections of the skull and part of the body and tail of the approximately 13-metre long skeleton. Based on stratigraphy, the age of the specimen was estimated at 67.83 million years, making it about one-and-a-half million years older than "Bèr". From what has been uncovered, this appears to be the oldest known Mosasaurid specimen from the Maastricht area, and it belongs to the genus Prognathodon. The specimen is nicknamed Carlo, after the ENCI worker who discovered it.
An anatomical review of South African mosasaurs by Woolley et al. reclassified T. capensis, originally assigned to Tylosaurus and later to Taniwhasaurus, as a chimera of two different mosasaur genera, but not identifiable at the species level.
Description
Prognathodon constitutes one of the largest-bodied mosasaur genera, with the largest known skull exceeding in length. Despite its massive size, remains of the genus are often fragmentary and incomplete. To date, very few specimens are known with articulated skulls and none with an entire skeleton. In 1967, P. giganteus was estimated to have reached in length. In 2002, Christiansen and Bonde estimated the maximum length of P. currii at. Considering this 2002 study, Schupl and colleagues estimated that P. saturator would have reached in length.Though many species were large with sizes approaching or potentially exceeding, many species were considerably smaller in size. The type species, P. solvayi, was the smallest, reaching around in length. P. hudae is estimated to have reached in length. The largest P. overtoni specimen is TMP 2018.042.0005, a nearly completely preserved individual measuring over in length. P. sectorius would have approached the same size, about in length.
Other than its size and robust nature, another feature that defines Prognathodon is the form of the sclerotic rings, present in all species of the genus. The function of the scleral ossicles is to maintain the shape of the cornea and support the sclera in the region of Brucke's muscle responsible for affecting accommodation in the lacertilian eye. In the type species, P. solvayi, the sclerotic ring is only partially preserved, consisting of five scleral ossicles in each ring. Similar sclerotic rings are seen in several other mosasaur genera, such as Mosasaurus.
The latest published diagnosis for the genus Prognathodon was provided by Lingham-Soliar and Nolf, and states that the premaxilla lacks a rostrum anterior to the premaxillary teeth. The prefrontal forms a large portion of the posterolateral border of the external nares and the supraorbital wing with heavy triangular ala contacts the postorbitofrontal posteriorly over the orbit medial to the external edge of the frontal. The frontal does not emarginate above the orbits and a median dorsal ridge is either present or absent. The foramina on the parietal are small to moderately large, located anteromedially on a small prominence and are closely embraced on either side by short tongues from the frontal or located on the frontoparietal suture.
The margins of the dorsal parietal surface are parallel to one another and the cranial midline to the posterior base of the diverging suspensorial rami, which forms a rectangular field medially on the parietal. The ventral process of the postorbitofrontal to jugal is indistinctly separated from the moderately well exposed dorsal surface of the postorbitofrontal and the ventroposterior process on the jugal is slightly developed to absent. The squamosal wing to the parietal is large. There is a deep groove present in the floor of the basioccipital for the basilar artery.
The suprastapedial process is fused to the infrastapedial process on the quadrate and the tympanic ala are thick. The stapedial pit is nearly circular to elliptical in form. The posterior process on the dorsal surface of the dentary is present, incipient or absent and the dentary terminates abruptly in front of the first dentary tooth. The dentary itself contains thirteen to fourteen teeth and the pterygoid has seven to eight teeth. The medial wing from the coronoid contacts the angular, the anterior process on the coronoid abrupts over the surangular and makes contact with the posterior process of the dentary or ends with the surangular without contacting the dentary. The retroarticular process is rectangular in outline, medially inflected or laterally lacing. The marginal teeth are stout, bicarinate and smooth or striated. Zygosphenes and zygantra are absent, incipient or large and functional.