Hoplosuchus
Encyclopedia
Hoplosuchus is a genus
of crocodylomorph
. It is so far only known definitely from one specimen, a skeleton collected from sandstone
of the Upper Jurassic-age Morrison Formation
rocks at Dinosaur National Monument
, Utah
, during road construction. The individual was small, approximately 20 centimetres (7.9 in) long, although it may have been very young. It is perhaps the basalmost
known crocodylomorph of the Morrison Formation, as suggested by such attributes as still having antorbital fenestra
e in the skull. The limbs were relatively long, suggesting that the animal was terrestrial. Two rows of bony scutes
ran down the back. The crowns of the teeth are not well preserved, so the diet cannot be determined with certainty. Given its small size, it probably ate insects and small vertebrate
s; it may have been carnivorous
or omnivorous
.
Charles W. Gilmore
named Hoplosuchus in 1926; the type species
is H. kayi. He described it as an aetosaur
, a type of armored herbivorous archosaur
related to the crocodylomorphs, but it was later reevaluated as a crocodylomorph itself. Sometimes classified as an atoposaurid
, a 1988 review of atoposaurids found it more likely to be a protosuchia
n-grade
crocodylomorph. A potential second specimen has been recovered from the Morrison Formation of northeastern Arizona
; this individual would have been about 50 centimetres (19.7 in), but the skull is poorly preserved, leaving the identity of the animal unknown.
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 crocodylomorph
Crocodylomorpha
The Crocodylomorpha are an important group of archosaurs that include the crocodilians 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...
. It is so far only known definitely from one specimen, a skeleton collected from sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
of the Upper Jurassic-age Morrison Formation
Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...
rocks at Dinosaur National Monument
Dinosaur National Monument
Dinosaur National Monument is a National Monument located on the southeast flank of the Uinta Mountains on the border between Colorado and Utah at the confluence of the Green and Yampa Rivers. Although most of the monument area is in Moffat County, Colorado, the Dinosaur Quarry is located in Utah...
, Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
, during road construction. The individual was small, approximately 20 centimetres (7.9 in) long, although it may have been very young. It is perhaps the basalmost
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:...
known crocodylomorph of the Morrison Formation, as suggested by such attributes as still having antorbital fenestra
Antorbital fenestra
An antorbital fenestra is an opening in the skull, in front of the eye sockets. This skull formation first appeared in archosaurs during the Triassic Period. Living birds today possess antorbital fenestrae, but the feature has been lost in modern crocodilians...
e in the skull. The limbs were relatively long, suggesting that the animal was terrestrial. Two rows of bony scutes
Osteoderm
Osteoderms are bony deposits forming scales, plates or other structures in the dermal layers of the skin. Osteoderms are found in many groups of extant and extinct reptiles, including lizards, various groups of dinosaurs , crocodilians, phytosaurs, aetosaurs, placodonts, and hupehsuchians...
ran down the back. The crowns of the teeth are not well preserved, so the diet cannot be determined with certainty. Given its small size, it probably ate insects and small vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s; it may have been carnivorous
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
or omnivorous
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
.
Charles W. Gilmore
Charles W. Gilmore
Charles Whitney Gilmore was an American paleontologist, who named dinosaurs in North America and Mongolia, including the Cretaceous sauropod Alamosaurus, Alectrosaurus, Archaeornithomimus, Bactrosaurus, Brachyceratops, Chirostenotes, Mongolosaurus, Parrosaurus, Pinacosaurus, Styracosaurus and...
named Hoplosuchus in 1926; 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 H. kayi. He described it as an aetosaur
Aetosaur
Aetosaurs are an extinct order of heavily armoured, medium- to large-sized Late Triassic herbivorous archosaurs. They have small heads, upturned snouts, erect limbs, and a body covered by plate-like scutes. All aetosaurs belong to the family Stagonolepididae...
, a type of armored herbivorous archosaur
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...
related to the crocodylomorphs, but it was later reevaluated as a crocodylomorph itself. Sometimes classified as an atoposaurid
Atoposauridae
Atoposauridae is a family of crocodile-like archosaurs. Members of the family have been found from France, Spain, Portugal, Romania, Germany, Kazakhstan, the United Kingdom, the United States, Cameroon, and Thailand.-Phylogeny:...
, a 1988 review of atoposaurids found it more likely to be a protosuchia
Protosuchia
Protosuchia 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....
n-grade
Evolutionary grade
In alpha taxonomy, a grade refers to a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit.-Definition:...
crocodylomorph. A potential second specimen has been recovered from the Morrison Formation of northeastern Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
; this individual would have been about 50 centimetres (19.7 in), but the skull is poorly preserved, leaving the identity of the animal unknown.