''Prodiplocynodon'' is an extinct
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
basal crocodyloid
Crocodyloidea is one of three superfamilies of crocodilians, the other two being Alligatoroidea and Gavialoidea, and it includes the crocodiles. Crocodyloidea may also include the extinct Mekosuchinae, native to Australasia from the Eocene t ...
crocodylia
Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period (Cenomanian stage) and are the closest living ...
n. It is one of the only crocodyloids known from the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
and existed during the
Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval ...
stage.
The only species of ''Prodiplocynodon'' is the
type species
In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...
''P. langi'' from the
Lance Formation
The Lance (Creek) Formation is a division of Late Cretaceous (dating to about 69 - 66 Ma) rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the late ...
of
Wyoming
Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to the s ...
, known only from a single
holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...
skull lacking the lower jaw.
The skull was collected by the
American Museum Expedition of 1892 from exposures near the
Cheyenne River
The Cheyenne River ( lkt, Wakpá Wašté; "Good River"), also written ''Chyone'', referring to the Cheyenne people who once lived there, is a tributary of the Missouri River in the U.S. states of Wyoming and South Dakota. It is approximately 2 ...
in
Niobrara County. It was described by
Charles C. Mook
Charles is a masculine given name predominantly found in English language, English and French language, French speaking countries. It is from the French form ''Charles'' of the Proto-Germanic, Proto-Germanic name (in runic alphabet) or ''*k ...
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 is one of three superfamilies of crocodylians, the other two being Crocodyloidea and Gavialoidea. Alligatoroidea evolved in the Late Cretaceous period, and consists of the alligators and caimans, as well as extinct members mor ...
''Diplocynodon
''Diplocynodon'' is an extinct genus of alligatoroid that lived during the Paleocene to Middle Miocene 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
The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...
of Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...
.
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 ]eusuchia
Eusuchia is a clade of crocodylomorphs that first appeared in the Early Cretaceous with '' Hylaeochampsa''. Along with Dyrosauridae and Sebecosuchia, they were the only crocodyliformes who survived the K-T extinction. Since the other two clades ...
ns. The skull is short and triangular, being around in length. The orbits
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
, 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
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...
and maxilla
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...
which would have been an area of reception for a large mandibular
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
tooth. In ''Prodiplocynodon'', the constriction is not deep, being intermediate between that of ''Alligator
An alligator is a large reptile in the Crocodilia order in the genus ''Alligator'' of the family Alligatoridae. The two extant species are the American alligator (''A. mississippiensis'') and the Chinese alligator (''A. sinensis''). Additiona ...
'' and '' Crocodylus''.[
]
Classification
Mook suggested that ''Prodiplocynodon'' may be ancestral to alligatorid
The family Alligatoridae of crocodylians includes alligators, caimans and their extinct relatives.
Phylogeny
The superfamily Alligatoroidea includes all crocodilians (fossil and extant) that are more closely related to the American alligator t ...
s and crocodylid
Crocodiles (family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant memb ...
s 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 convergence
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
,[ and thus ''Prodiplocynodon'' was also proposed to be an ]alligatorine
Alligatorinae is a subfamily within the family Alligatoridae that contains the alligators and their closest extinct relatives, and is the sister taxon to Caimaninae (the caimans). Many genera in Alligatorinae are described, but only the genus ''A ...
.
Phylogeny
''Prodiplocynodon'' was not included in a phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
study until 1996. In that study, ''Prodiplocynodon'' was excluded from the Alligatorinae
Alligatorinae is a subfamily within the family Alligatoridae that contains the alligators and their closest extinct relatives, and is the sister taxon to Caimaninae (the caimans). Many genera in Alligatorinae are described, but only the genus ...
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
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and ...
to the Alligatorinae rather than the Crocodylinae because in ''Prodiplocynodon'', the 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.
Anatomy ...
-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.
Successive phylogenetic studies have placed ''Prodiplocynodon'' as a basal member of Crocodyloidea
Crocodyloidea is one of three superfamilies of crocodilians, the other two being Alligatoroidea and Gavialoidea, and it includes the crocodiles. Crocodyloidea may also include the extinct Mekosuchinae, native to Australasia from the Eocene to th ...
along with ''Asiatosuchus
''Asiatosuchus'' is an extinct genus of crocodyloid crocodilians that lived in Eurasia during the Paleogene. Many Paleogene crocodilians from Europe and Asia have been attributed to ''Asiatosuchus'' since the genus was named in 1940. These specie ...
'', as shown in the cladogram below:
A 2018 tip dating Tip dating is a technique used in molecular dating that allows the inference of time-calibrated phylogenetic trees. Its defining feature is that it uses the ages of the samples to provide time information for the analysis, in contrast with traditio ...
study by Lee & Yates simultaneously using morphological, molecular ( DNA sequencing), and stratigraphic
Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks.
Stratigraphy has three related subfields: lithostra ...
(fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
age) data established the inter-relationships within Crocodilia
Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...
, which was expanded upon in 2021 by Hekkala ''et al.'' using paleogenomics Paleogenomics is a field of science based on the reconstruction and analysis of genomic information in extinct species. Improved methods for the extraction of ancient DNA (aDNA) from museum artifacts, ice cores, archeological or paleontological site ...
by extracting DNA from the extinct ''Voay
''Voay'' is an extinct genus of crocodile from Madagascar that lived during the Late Pleistocene to Holocene, containing only one species, ''V. robustus''. Numerous subfossils have been found, including complete skulls, noted for their distinctiv ...
''.
The below cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
shows the results of the latest studies, which placed ''Prodiplocynodon'' outside of Crocodyloidea, as more basal than Longirostres
Longirostres is a clade of crocodilians that includes the crocodiles and the gavialids, to the exclusion of the alligatoroids. Named in 2003 by Harshman ''et al.'', Longirostres is a crown group defined phylogenetically as including the last c ...
(the combined group of crocodiles and gavialids).
References
External links
''Prodiplocynodon''
in the Paleobiology Database
The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.
History
The Paleobiology Database (PBDB) originated in the NCEAS-funded Phanerozoic Marine Pale ...
{{Taxonbar, from=Q7247624
Late Cretaceous crocodylomorphs of North America
Late Cretaceous reptiles of North America
Crocodilians
Prehistoric pseudosuchian genera