Crocodylomorpha
Encyclopedia
The Crocodylomorpha are an important group of archosaur
s that include the crocodilia
ns and their extinct relatives.
During Mesozoic
and early Tertiary times the Crocodylomorpha were far more diverse than they are now. Triassic forms were small, lightly built, active terrestrial animals. These were supplanted during the early Jurassic by various aquatic and marine forms. The Later Jurassic, Cretaceous, and Tertiary saw a wide diversity of terrestrial and semi-aquatic lineages. "Modern" crocodilians do not appear until the Late Cretaceous.
When their extinct species and stem group are examined, the crocodylian lineage (clade Crurotarsi
) proves to have been a very diverse and adaptive group of reptiles. Not only are they an ancient group of animals, at least as old as the dinosaur
s, they also evolved into a great variety of forms. The earliest forms, the sphenosuchia
ns, evolved during the Late Triassic
, and were highly gracile
terrestrial forms built like greyhounds. During the Jurassic
and the Cretaceous marine forms in the family Metriorhynchidae
such as Metriorhynchus
evolved forelimbs that were paddle-like and had a tail similar to modern fish. Dakosaurus andiniensis, a species closely related to Metriorhynchus, had a skull that was adapted to eat large marine reptiles. Several terrestrial species during the Cretaceous
evolved herbivory, such as Simosuchus clarki and Chimaerasuchus paradoxus. A number of lineages during the Tertiary and Pleistocene became wholly terrestrial predators.
containing Crocodylus niloticus (Laurenti 1768) but not Poposaurus gracilis
Mehl 1915, Gracilisuchus stipanicicorum
Romer 1972, Prestosuchus chiniquensis
Huene 1942, Aetosaurus ferratus
Fraas 1877."
This a stem-based definition and therefore includes all taxa closer to extant crocodilians than to other crurotarsan
clades.
Crocodilia. However, beginning in the late 1980s many scientists began restricting the order Crocodilia to the living species and close extinct relatives such as Mekosuchus
. The groups which variously had previously been known as Crocodilia were re-named Crocodylomorpha and the slightly more restricted Crocodyliformes
.
The old Crocodilia was subdivided into the suborders:
Mesosuchia is a paraphyletic group as it does not include eusuchians (which nest within Mesosuchia). Mesoeucrocodylia
was the name given to the clade that contains mesosuchians and eusuchians (Whetstone and Whybrow, 1983).
The previous definitions of Crocodilia and Eusuchia do not accurately resemble the evolution of the group. The only order-level taxon that is currently considered valid is Crocodilia in the present definition. Prehistoric crocodiles are represented by many taxa, but since few major groups of the ancient forms are recognizable, a decision where to delimit new order-level clades is not yet possible. (Benson & Clark, 1988).
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
s that include the crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns and their extinct relatives.
During Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
and early Tertiary times the Crocodylomorpha were far more diverse than they are now. Triassic forms were small, lightly built, active terrestrial animals. These were supplanted during the early Jurassic by various aquatic and marine forms. The Later Jurassic, Cretaceous, and Tertiary saw a wide diversity of terrestrial and semi-aquatic lineages. "Modern" crocodilians do not appear until the Late Cretaceous.
Evolutionary history
Crurotarsi
The Crurotarsi are a group of archosauriformes, represented today by the crocodiles,...
) proves to have been a very diverse and adaptive group of reptiles. Not only are they an ancient group of animals, at least as old as the dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s, they also evolved into a great variety of forms. The earliest forms, the sphenosuchia
Sphenosuchia
Sphenosuchia is a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Late Jurassic. Most were small, gracile animals with an erect limb posture. They are now thought to be ancestral to crocodyliforms, which include all living crocodilians.-Stratigraphic...
ns, evolved during the Late Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
, and were highly gracile
Gracile
The English word "gracile" means slender. It derives from the Latin adjective gracilis , or gracile which in either form means slender, and when transferred for example to discourse, takes the sense of "without ornament", "simple", or various similar connotations.In his famous "Glossary of Botanic...
terrestrial forms built like greyhounds. During the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
and the Cretaceous marine forms in the family Metriorhynchidae
Metriorhynchidae
Metriorhynchidae is an extinct family of metriorhynchoid crocodyliforms from the Middle Jurassic to the Early Cretaceous period of Europe, North America and South America. Metriorhynchids are fully aquatic crocodyliforms. Their forelimbs were small and paddle-like, and unlike living crocodilians,...
such as Metriorhynchus
Metriorhynchus
Metriorhynchus is an extinct genus of marine crocodyliform that lived in the oceans during the Middle to Late Jurassic. Metriorhynchus was named by the German palaeontologist Christian von Meyer in 1830. Metriorhynchus was a carnivore that spent much, if not all, its life out at sea...
evolved forelimbs that were paddle-like and had a tail similar to modern fish. Dakosaurus andiniensis, a species closely related to Metriorhynchus, had a skull that was adapted to eat large marine reptiles. Several terrestrial species during 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...
evolved herbivory, such as Simosuchus clarki and Chimaerasuchus paradoxus. A number of lineages during the Tertiary and Pleistocene became wholly terrestrial predators.
Phylogenetic definition
The Crocodylomorpha are defined phylogenetically by Sereno 2005 as "The most inclusive cladeClade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
containing Crocodylus niloticus (Laurenti 1768) but not Poposaurus gracilis
Poposaurus
Poposaurus is a genus of reptile from the Late Triassic of the southwestern United States. It was a crurotarsan archosaur which lived in what is now Wyoming, Utah, Arizona and Texas. The type species, Poposaurus gracilis, was described by M. G. Mehl in 1915. The second species, P...
Mehl 1915, Gracilisuchus stipanicicorum
Gracilisuchus
Gracilisuchus is an extinct genus of tiny crurotarsan from the Middle Triassic. It was a suchian close to the ancestry of crocodiles, and was at one time thought to be a dinosaur, but this hypothesis has since been rejected...
Romer 1972, Prestosuchus chiniquensis
Prestosuchus
Prestosuchus is an extinct genus of a group of rauisuchians called prestosuchids. Friedrich von Huene named the genus in honor of Vicentino Prestes de Almeida....
Huene 1942, Aetosaurus ferratus
Aetosaurus
Aetosaurus is an extinct genus of archosaur reptile belonging to the order Aetosauria. It is generally considered to be the most primitive aetosaur. Three species are currently recognized: A. ferratus, the type species from Germany and Italy; A. crassicauda from Germany; and A. arcuatus from...
Fraas 1877."
This a stem-based definition and therefore includes all taxa closer to extant crocodilians than to other crurotarsan
Crurotarsi
The Crurotarsi are a group of archosauriformes, represented today by the crocodiles,...
clades.
Taxonomy and phylogeny
Historically, all known living and extinct crocodiles were indiscriminately lumped into the orderOrder (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Crocodilia. However, beginning in the late 1980s many scientists began restricting the order Crocodilia to the living species and close extinct relatives such as Mekosuchus
Mekosuchus
Mekosuchus is a genus of extinct Australasian crocodiles within the subfamily Mekosuchinae. They are believed to have been made extinct by the arrival of man on the South Pacific islands where they lived...
. The groups which variously had previously been known as Crocodilia were re-named Crocodylomorpha and the slightly more restricted Crocodyliformes
Crocodyliformes
Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians."In 1988, Michael J. Benton and James M. Clark argued that all traditional names for well-known groups of animals should be restricted to their crown clades, that is, used only for...
.
The old Crocodilia was subdivided into the suborders:
- EusuchiaEusuchiaEusuchia 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:...
: true crocodilies (which includes crown-group Crocodylia) - MesosuchiaMesosuchia"Mesosuchia" is an obsolete name for a group of terrestrial, semi-aquatic, or fully aquatic crocodylomorph reptiles. The marine crocodile Metriorhynchus had paddle-like forelimbs, Dakosaurus andiniensis had a skull that was adapted to eat large sea reptiles, and Shamosuchus was adapted for eating...
: 'middle' crocodiles - ThalattosuchiaThalattosuchiaThalattosuchia is the name given to a clade of marine crocodylomorphs from the Early Jurassic to the Early Cretaceous that had a cosmopolitan distribution. They are sometimes colloquially referred to as marine crocodiles or sea crocodiles, though they are not actually members of Crocodilia.The term...
: sea crocodiles - ProtosuchiaProtosuchiaProtosuchia is a group of extinct Mesozoic crocodyliforms. They were small in size and terrestrial. In phylogenetic terms, Protosuchia is considered an informal group because it is a grade of basal crocodyliforms, not a true clade....
: first crocodiles
Mesosuchia is a paraphyletic group as it does not include eusuchians (which nest within Mesosuchia). Mesoeucrocodylia
Mesoeucrocodylia
Mesoeucrocodylia is the name of the clade that includes Eusuchia and the paraphyletic group Mesosuchia. The group appeared during the Early Jurassic, and continues to the present day....
was the name given to the clade that contains mesosuchians and eusuchians (Whetstone and Whybrow, 1983).
Phylogeny
Here is the consensus of Larsson & Sues (2007) and Sereno et al. (2003):The previous definitions of Crocodilia and Eusuchia do not accurately resemble the evolution of the group. The only order-level taxon that is currently considered valid is Crocodilia in the present definition. Prehistoric crocodiles are represented by many taxa, but since few major groups of the ancient forms are recognizable, a decision where to delimit new order-level clades is not yet possible. (Benson & Clark, 1988).
External links
- Crocodylomorpha - webpages by Ross Elgin on the University of BristolUniversity of BristolThe University of Bristol is a public research university located in Bristol, United Kingdom. One of the so-called "red brick" universities, it received its Royal Charter in 1909, although its predecessor institution, University College, Bristol, had been in existence since 1876.The University is...
server- Major subgroups classification (used here)
- Crocodylomorpha from PalaeosPalaeosPalaeos.com is a web site on biology, paleontology, cladistics and geology and which covers the history of Earth. The site is well respected and has been used as a reference by professional paleontologists such as Michael J. Benton, the professor of vertebrate palaeontology in the Department of...
- Crocodylomorpha - hyperlinked cladogram at Mikko's Phylogeny ArchiveMikko's Phylogeny ArchiveMikko's Phylogeny Archive is an amateur paleontology website maintained by Mikko Haaramo, a student at the University of Helsinki's Department of Geology, Division of Geology and Palaeontology....
- Sereno, P. CPaul SerenoPaul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
. 2005. Stem Archosauria—TaxonSearch [version 1.0, 7 November 2005]