Phosphatosaurus
Encyclopedia
Phosphatosaurus is an extinct genus
of dyrosaurid
crocodylomorph. It existed during the early Eocene
, with fossils having been found from North Africa
in Tunisia
and Mali
. Named in 1955, Phosphatosaurus is a monotypic genus; the type species
is P. gavialoides. A specimen has been discovered from Niger
, but it cannot be classified at the species level.
Phosphatosaurus is closely related to the Cretaceous
genus Sokotosuchus
, which is known from Niger and Mali. Because Phosphatosaurus is only known from Paleogene
localities, the close relationship with Sokotosuchus implies that there is a long ghost lineage
extending back into the Maastrichtian
that is not known in the fossil record.
. The dentition is nonhomodont
. Alveolar "couplets" are present in the lower jaw of Phosphatosaurus 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 the gavialoid
Eosuchus
. It is possible that the diastemata
between the couplets served to receive larger maxilla
ry teeth.
Buffetaut 1978
Jouve 2005
Jouve et al. 2005
Phosphatosaurus is considered to be a basal
dyrosaurid, and is often positioned near the base of phylogenetic trees
of dyrosaurids. An early phylogenetic analysis by Buffetaut (1978), not based on a cladistic data matrix, puts Phosphatosaurus at the base of the tree due to the presence of many primitive characters in the genus. Later phylogenetic analyses, such as the one by Jouve (2005), have also shown Phosphatosaurus to be a basal member of the family. In most analyses, Phosphatosaurus and Sokotosuchus 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 considered Chenanisuchus
, a short-snouted dyrosairid named in 2005, to be even more basal than the clade containing Phosphatosaurus and Sokotosuchus.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of dyrosaurid
Dyrosauridae
Dyrosauridae is a family of extinct neosuchian crocodyliforms that lived from the Late Cretaceous to the Eocene. Fossils of this group have been found in almost every continent, specifically Africa, Asia, Europe, North America and South America....
crocodylomorph. It existed during the early Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
, with fossils having been found from North Africa
North Africa
North Africa or Northern Africa is the northernmost region of the African continent, linked by the Sahara to Sub-Saharan Africa. Geopolitically, the United Nations definition of Northern Africa includes eight countries or territories; Algeria, Egypt, Libya, Morocco, South Sudan, Sudan, Tunisia, and...
in Tunisia
Tunisia
Tunisia , officially the Tunisian RepublicThe long name of Tunisia in other languages used in the country is: , is the northernmost country in Africa. It is a Maghreb country and is bordered by Algeria to the west, Libya to the southeast, and the Mediterranean Sea to the north and east. Its area...
and Mali
Mali
Mali , officially the Republic of Mali , is a landlocked country in Western Africa. Mali borders Algeria on the north, Niger on the east, Burkina Faso and the Côte d'Ivoire on the south, Guinea on the south-west, and Senegal and Mauritania on the west. Its size is just over 1,240,000 km² with...
. Named in 1955, Phosphatosaurus is a monotypic genus; the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
is P. gavialoides. A specimen has been discovered from Niger
Niger
Niger , officially named the Republic of Niger, is a landlocked country in Western Africa, named after the Niger River. It borders Nigeria and Benin to the south, Burkina Faso and Mali to the west, Algeria and Libya to the north and Chad to the east...
, but it cannot be classified at the species level.
Phosphatosaurus is closely related to the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
genus Sokotosuchus
Sokotosuchus
Sokotosuchus is an extinct genus of dyrosaurid crocodyliform which existed in Africa.-External links:* at the Paleobiology Database...
, which is known from Niger and Mali. Because Phosphatosaurus is only known from Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...
localities, the close relationship with Sokotosuchus implies that there is a long ghost lineage
Ghost lineage
A ghost lineage is a phylogenetic lineage that is inferred to exist but has no fossil record....
extending back into the Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
that is not known in the fossil record.
Description
Phosphatosaurus is a large-bodied dyrosaurid with blunt teeth. The tip of the snout is spoon-shaped from a lateral expansion of the rostral portion of the mandibleMandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
. The dentition is nonhomodont
Heterodont
The anatomical term heterodont refers to animals which possess more than a single tooth morphology. For example, members of the Synapsida generally possess incisors, canines , premolars, and molars. The presence of heterodont dentition is evidence of some degree of feeding/hunting specialization...
. Alveolar "couplets" are present in the lower jaw of Phosphatosaurus 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 the gavialoid
Gavialoidea
Gavialoidea is one of three superfamilies of crocodylians, the other two being Alligatoroidea and Crocodyloidea. Although many extinct species are known, only the gharial Gavialis gangeticus and possibly the False gharial Tomistoma schlegelii are alive today.-Classification:Gavialoidea contains the...
Eosuchus
Eosuchus
Eosuchus is an extinct genus of gavialoid crocodilian. It is among the most basal of all gavialoids, lying crownward of all other known members of the superfamily, including earlier members such as Thoracosaurus and Eothoracosaurus. Fossils have been found from France as well as eastern North...
. It is possible that the diastemata
Diastema (dentistry)
Diastema is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars.-In humans:...
between the couplets served to receive larger maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
ry teeth.
Classification
Phosphatosaurus was assigned in 1979 to the newly named subfamily Phosphatosaurinae by Eric Buffetaut, who considered the subfamily to be the clade formed by Phosphatosaurus and the closely related Sokotosaurus. 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.Phylogenetics
Phosphatosaurus is considered to be a basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
dyrosaurid, and is often positioned near the base of phylogenetic trees
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
of dyrosaurids. An early phylogenetic analysis by Buffetaut (1978), not based on a cladistic data matrix, puts Phosphatosaurus at the base of the tree due to the presence of many primitive characters in the genus. Later phylogenetic analyses, such as the one by Jouve (2005), have also shown Phosphatosaurus to be a basal member of the family. In most analyses, Phosphatosaurus and Sokotosuchus 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 considered Chenanisuchus
Chenanisuchus
Chenanisuchus is a genus of dyrosaurid crocodyliform from the Late Cretaceous of Mali and the Late Palaeocene of Sidi Chenane in Morocco. It was described in 2005, after expeditions uncovered it in 2000.The type species is C...
, a short-snouted dyrosairid named in 2005, to be even more basal than the clade containing Phosphatosaurus and Sokotosuchus.
External links
- Phosphatosaurus in the Paleobiology DatabasePaleobiology Database' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...