Prodiplocynodon
Encyclopedia
Prodiplocynodon is an extinct genus
of basal
crocodyloid
crocodylian. It is the only crocodyloid known from the Cretaceous
and existed during the Maastrichtian
stage. The only species of Prodiplocynodon is the type species
P. langi from the Lance Formation
of Wyoming
, known only from a single holotype
skull lacking the lower jaw.
The skull was collected by the American Museum Expedition of 1892
from exposures near the Cheyenne River
in Niobrara County. It was described by Charles C. Mook of the American Museum of Natural History in 1941. The generic name means "before Diplocynodon" because Mook saw close similarities between the holotype skull and that of the alligatoroid
Diplocynodon
from the Eocene
of Europe
.
ns. The skull is short and triangular, being around 50 centimetres (19.7 in) in length. The orbits
, or eye sockets, are quite large and subtriangular. The teeth are short and somewhat sharp, and in comparison to modern crocodiles show little variation. The orbits face directly upwards, but this may have been the result of slight compression in the holotype skull. The external nasal aperture
, the opening for the nostrils, is very large. There is a constriction at the point of contact between the premaxilla
and maxilla
which would have been an area of reception for a large mandibular
tooth. In Prodiplocynodon, the constriction is not deep, being intermediate between that of Alligator
and Crocodylus
.
. More recently, Prodiplocynodon was proposed to be an alligatorine
.
Wu et al. 1996
Brochu 2000
Prodiplocynodon was not included in a phylogenetic study until 1996. In that study, Prodiplocynodon was excluded from the Alligatorinae because it lacked all seven of the unequivocal synapomorphies
that were proposed for the clade. According to the 1996 study, characters that exclude Prodiplocynodon from Alligatorinae include the presence of a distinct lateral constriction between the premaxilla and maxilla, a contact between the nasal
and lacrimal
, and the lack of posterior massive crushing teeth. The 1996 analysis considered Prodiplocynodon to be the sister taxon to the Alligatorinae rather than the Crocodylinae because in Prodiplocynodon, the jugal
-lacrimal suture is much shorter than the ventral border of the orbit. However, the authors of the study mentioned that this character is also seen in some derived
crocodylines, and is lost in some ingroups of Alligatorinae.
More recent phylogenetic studies have indicated that Prodiplocynodon is a crocodyloid. Brochu (2000) placed Prodiplocynodon as a basal member of Crocodyloidea along with Asiatosuchus
. This was also the case for Brochu & Gingerich, who conducted their own phylogenetic study which resulted in Prodiplocynodon and Asiatosuchus being basal members of Crocodyloidea. The same result occurred in the phylogenetic analysis of Hua & Jouve (2004). In all three analyses, the topology of the trees is essentially the same for basal crocodyloids, as shown below:
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 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:...
crocodyloid
Crocodyloidea
Crocodyloidea is a superfamily of crocodilians that evolved in the Late Cretaceous period. Cladistically, it is defined as Crocodylus niloticus and all crocodylians more closely related to C. niloticus than to either Alligator mississippiensis or Gavialis gangeticus .- Phylogeny :Cladogram after...
crocodylian. It is the only crocodyloid known from 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...
and existed during 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...
stage. The only species of Prodiplocynodon is 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...
P. langi from the Lance Formation
Lance Formation
The Lance Formation is a division of Late Cretaceous rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the latest Mesozoic vertebrate faunas...
of Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
, known only from a single holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
skull lacking the lower jaw.
The skull was collected by the American Museum Expedition of 1892
American Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
from exposures near the Cheyenne River
Cheyenne River
The Cheyenne River is a tributary of the Missouri River in the U.S. states of Wyoming and South Dakota. It is approximately 295 mi long and drains an area of...
in Niobrara County. It was described by Charles C. Mook of the American Museum of Natural History in 1941. The generic name means "before Diplocynodon" because Mook saw close similarities between the holotype skull and that of the alligatoroid
Alligatoroidea
Alligatoroidea is a superfamily of crocodilians that evolved in the Late Cretaceous period. Cladistically, it is defined as Alligator mississippiensis and all crocodylians more closely related to A. mississippiensis than to either Crocodylus niloticus or Gavialis gangeticus ....
Diplocynodon
Diplocynodon
Diplocynodon is an extinct genus of alligatoroid that lived during the Paleocene to middle Miocene 49 million years ago in Europe. It looked very similar to the modern caiman in that it was small and had bony armour scutes covering its neck, back, belly, and tail...
from the 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...
of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
.
Description
Most of the cranial sutures that outline individual bones of the skull are not visible in the holotype, and are often obscured by cracks. However, the overall shape of Prodiplocynodon is similar to that of basal alligatoroids. Many of the features seen in Prodiplocynodon are common among eusuchiaEusuchia
Eusuchia is a clade of crocodylomorphs that first appears in the Early Cretaceous with Hylaeochampsa. All living crocodilian species are eusuchians, as are many extinct forms.-Description:...
ns. The skull is short and triangular, being around 50 centimetres (19.7 in) in length. The orbits
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...
, or eye sockets, are quite large and subtriangular. The teeth are short and somewhat sharp, and in comparison to modern crocodiles show little variation. The orbits face directly upwards, but this may have been the result of slight compression in the holotype skull. The external nasal aperture
Nasal cavity
The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...
, the opening for the nostrils, is very large. There is a constriction at the point of contact between the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
and 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...
which would have been an area of reception for a large mandibular
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
tooth. In Prodiplocynodon, the constriction is not deep, being intermediate between that of Alligator
Alligator
An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. There are two extant alligator species: the American alligator and the Chinese alligator ....
and Crocodylus
Crocodylus
Crocodylus is one of three genera from the Crocodylinae subfamily extending from the Crocodylidae family.Established species include three extinct species:* † Crocodylus acer - probably represents a distinct genus....
.
Classification
Mook suggested that Prodiplocynodon may be ancestral to alligatorids and crocodylids because it possessed features of both families. However, Mook also noted that some of the features observed in Prodiplocynodon that are also found in modern crocodylians may be the result of evolutionary convergenceConvergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
. More recently, Prodiplocynodon was proposed to be an alligatorine
Alligatorinae
Alligatorinae are one of two subfamilies of the family Alligatoridae.-Taxonomy:* Subfamily Alligatorinae** Genus Chrysochampsa ** Genus Hassiacosuchus ** Genus Navajosuchus ** Genus Ceratosuchus...
.
Phylogeny
Prodiplocynodon was not included in a phylogenetic study until 1996. In that study, Prodiplocynodon was excluded from the Alligatorinae because it lacked all seven of the unequivocal synapomorphies
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
that were proposed for the clade. According to the 1996 study, characters that exclude Prodiplocynodon from Alligatorinae include the presence of a distinct lateral constriction between the premaxilla and maxilla, a contact between the nasal
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
and lacrimal
Lacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
, and the lack of posterior massive crushing teeth. The 1996 analysis considered Prodiplocynodon to be the sister taxon to the Alligatorinae rather than the Crocodylinae because in Prodiplocynodon, the jugal
Jugal
The jugal is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the malar or Zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species....
-lacrimal suture is much shorter than the ventral border of the orbit. However, the authors of the study mentioned that this character is also seen in some derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
crocodylines, and is lost in some ingroups of Alligatorinae.
More recent phylogenetic studies have indicated that Prodiplocynodon is a crocodyloid. Brochu (2000) placed Prodiplocynodon as a basal member of Crocodyloidea along with Asiatosuchus
Asiatosuchus
Asiatosuchus is an extinct genus of large crocodilian. It is believed to have been a basal crocodile. Specimens have been found from Russia, Belgium, France, Germany, Mongolia, and possibly Pakistan. It existed from the Danian stage of the early Paleocene epoch to the Lutetian stage of the Eocene...
. This was also the case for Brochu & Gingerich, who conducted their own phylogenetic study which resulted in Prodiplocynodon and Asiatosuchus being basal members of Crocodyloidea. The same result occurred in the phylogenetic analysis of Hua & Jouve (2004). In all three analyses, the topology of the trees is essentially the same for basal crocodyloids, as shown below:
External links
- Prodiplocynodon 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...