Tsoabichi
Encyclopedia
Tsoabichi is an extinct genus
of alligatoroid
. Fossils are known from the Eocene
Green River Formation
in Wyoming
, and date back to the Wasatchian
. The genus was named and described in 2010, with the type species being T. greenriverensis. It is thought to be closely related to living caimans, and is probably within the subfamily Caimaninae.
have a "spectacle", or a bony ridge between the eyes. Tsoabichi lacks a spectacle, but it does have three smaller ridges between the orbits
, or eye sockets. In Tsoabichi, distinct rims are seen around the supratemporal fenestrae, two holes on the skull table
. Much of the supraoccipital bone is also found on the skull table, and forms a V-shape. To either side of the V-shaped supraoccipitals are the parietal bone
s, which form the posterior margin of the skull table. Along the snout, the nasal bone
forms a thin ridge, and narrows as it approaches the external naris where the nostrils are located.
The dorsal osteoderm
s, or bony scutes along the back, are wider than those of other caimans. Some have two keels on their outer surface. Tsoabichi also has bipartite ventral osteoderms on its underside.
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 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 ....
. Fossils are known 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...
Green River Formation
Green River Formation
The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes. The sediments are deposited in very fine layers, a dark layer during the growing season and a light-hue inorganic layer in winter. Each pair of layers is called a varve and...
in 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...
, and date back to the Wasatchian
Wasatchian
The Wasatchian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology , typically set from 55,400,000 to 50,300,000 years BP lasting . It is usually considered to be within the Eocene, more specifically the...
. The genus was named and described in 2010, with the type species being T. greenriverensis. It is thought to be closely related to living caimans, and is probably within the subfamily Caimaninae.
Description
Some living caimans such as the Spectacled CaimanSpectacled Caiman
The spectacled caiman , also known as the white caiman or common caiman, is a crocodilian reptile found in much of Central and South America. It lives in a range of lowland wetland and riverine habitat types and can tolerate salt water as well as fresh; due in part to this adaptability it is the...
have a "spectacle", or a bony ridge between the eyes. Tsoabichi lacks a spectacle, but it does have three smaller ridges between 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. In Tsoabichi, distinct rims are seen around the supratemporal fenestrae, two holes on the skull table
Skull roof
The skull roof , or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes and all land living vertebrates. The bones are derived from dermal bone, hence the alternative name dermatocranium...
. Much of the supraoccipital bone is also found on the skull table, and forms a V-shape. To either side of the V-shaped supraoccipitals are the parietal bone
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....
s, which form the posterior margin of the skull table. Along the snout, the nasal bone
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....
forms a thin ridge, and narrows as it approaches the external naris where the nostrils are located.
The dorsal osteoderm
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...
s, or bony scutes along the back, are wider than those of other caimans. Some have two keels on their outer surface. Tsoabichi also has bipartite ventral osteoderms on its underside.