Phosphatosaurus is closely related to theCretaceous genusSokotosuchus, which is known from Niger and Mali. BecausePhosphatosaurus is only known fromPaleogene localities, the close relationship withSokotosuchus implies that there is a longghost lineage extending back into theMaastrichtian that is not known in the fossil record.[1]
Phosphatosaurus is a large dyrosaurid estimated at 9 m (30 ft) in length,[4][5] with blunt teeth.[1][2][6] The tip of the snout is spoon-shaped from a lateral expansion of the rostral portion of themandible. The dentition isnonhomodont. Alveolar "couplets" are present in the lower jaw ofPhosphatosaurus in which paired tooth sockets, or alveoli, are closer to one another than to the alveoli next to them. This is not seen in any other dyrosaurid but is seen in some other longirostrine (long snouted) crocodylomorphs such as thegavialoidEosuchus.[7] It is possible that thediastemata between the couplets served to receive largermaxillary teeth.[1]
Phosphatosaurus was assigned in 1979 to the newly namedsubfamilyPhosphatosaurinae byEric Buffetaut, who considered the subfamily to be the clade formed byPhosphatosaurus and the closely relatedSokotosaurus.[8] However, other authors of more recent studies have been tentative in considering the taxon valid because there is currently little knowledge of the anatomy of either genus.[6]
Phosphatosaurus is considered to be abasal dyrosaurid, and is often positioned near the base ofphylogenetic trees of dyrosaurids. An early phylogenetic analysis by Buffetaut (1978), not based on a cladistic data matrix, putsPhosphatosaurus at the base of the tree due to the presence of many primitive characters in the genus.[4] Later phylogenetic analyses, such as the one by Jouve (2005), have also shownPhosphatosaurus to be a basal member of the family.[9] In most analyses,Phosphatosaurus andSokotosuchus form a clade. These two genera are more closely related to one another than to any other genus of dyrosaurid. More recent phylogenetic studies have consideredChenanisuchus, a short-snouted dyrosairid named in 2005, to be even more basal than the clade containingPhosphatosaurus andSokotosuchus.[10]
^abBergounioux, F. M. (1956). "Les reptiles fossiles des dépôts phosphatés sud tunisiens".Annales des Mines et de la Géologie.15: 105.
^Buffetaut, E. (1979). "Présence du CrocodilienPhosphatosaurus (Mesosuchia, Dyrosauridae) dans le Paléocène du Niger et du Mali".Paläontologische Zeitschrift.53 (3–4):323–333.doi:10.1007/bf02986594.S2CID129809504.
^abcBuffetaut, E. (1978). "Les Dyrosauridae (Crocodylia, Mesosuchia) des phosphates de l'Eocène inférieur de Tunisie:Dyrosaurus,Rhabdognathus,Phosphatosaurus".Géologie Méditerranéenne.5 (2):237–256.doi:10.3406/geolm.1978.1046.
^Brochu, C. A. (2006). "Osteology and phylogenetic significance ofEosuchus minor (Marsh, 1870) new combination, a longirostrine crocodylian from the late Paleocene of North America".Journal of Paleontology.80:162–186.doi:10.1666/0022-3360(2006)080[0162:oapsoe]2.0.co;2.
^Buffetaut, E. (1979). "Sokotosuchus ianwilsoni and the evolution of the dyrosaurid crocodilians".The Nigerian Field Monograph.1:31–41.
^abJouve, S. (2005). "A new description of the skull ofDyrosaurus phosphaticus (Thomas, 1893) (Mesoeucrocodylia: Dyrosauridae) from the Lower Eocene of North Africa".Canadian Journal of Earth Sciences.42 (3):323–337.Bibcode:2005CaJES..42..323J.doi:10.1139/e05-008.
