Probelesodon
Encyclopedia
Probelesodon is an extinct genus
of chiniquodontid
cynodont
. Fossil
s have been found from Argentina
and Brazil
of Triassic
age. Specimens were first discovered from the Chañares Formation
in La Rioja Provence
, Argentina that date back to the Anisian
stage of the early Middle Triassic
. A new species, P. sanjuanensis, was named in 1996 on the basis of a skull found from the Ischigualasto Formation. This extends the temporal range of Probelesodon into the Carnian
stage of the Late Triassic
. The occurrence of the genus in these strata suggests that it also existed during the deposition of the Los Rastros Formation, which also outcrops in the same area as the localities where fossils have been found, although specimens have yet to be found from this formation. The presence of the genus in the Ischigualasto Formation is restricted to the earlier strata, becoming completely extinct soon after along with the last of the carnivorous cynodonts in the area. This has been taken as evidence for the gradual replacement of therapsid
fauna with the later mainly archosaur-dominated faunas of the Late Triassic. Evidence from the
Chañares Formation also seems to support this faunal transition.
of Probelesodon is P. lewisi from the Chañares Formation. This species is the best known as many relatively complete specimens have been found. A long secondary palate distinguishes it from other closely related genera such as Belesodon
. The molars are multicuspidate and the main cusps curve back. One species, P. sanjuanensis, differs from other species of Probelesodon by such characteristics as a highly arched zygomatic arch
and the presence six postcanines. Another species, P. kitchingi was named in 1982 from material found from Rio Grande do Sul
, Brazil. P. minor is similar in appearance to the type species and has been found from the same formation. It differs mainly in size, being about half the length of the type species. This size difference is too great to be considered sexual dimorphism
. The close similarities between all four species have led to recent suggestions that they are synonymous with one another. It has even been suggested that the entire genus is synonymous with Chiniquodon theotonicus
.
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 chiniquodontid
Chiniquodontidae
Chiniquodontidae is a family of meat-eating advanced mammal-like reptiles that lived during the Upper Triassic of South America and perhaps Europe. A further possible representative, Aleodon, has been identified from the Middle Triassic of Africa...
cynodont
Cynodont
Cynodontia or cynodonts are a taxon of therapsids which first appeared in the Late Permian and were eventually distributed throughout all seven continents by the Early Triassic . This clade includes modern mammals and their extinct close relatives. They were one of the most diverse groups of...
. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been found from Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
and Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
of 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...
age. Specimens were first discovered from the Chañares Formation
Chañares Formation
The Chañares Formation in La Rioja Provence, Argentina, dates to the Anisian stage of the early Middle Triassic.Some localities are well known for their abundance of tetrapods. Theraspids include the kannemeyeriid Dinodontosaurus, and cynodonts such as Probainognathus and Massetognathus, the latter...
in La Rioja Provence
La Rioja Province (Argentina)
La Rioja is a one of the provinces of Argentina and is located in the west of the country. Neighboring provinces are from the north clockwise Catamarca, Córdoba, San Luis and San Juan.-History:...
, Argentina that date back to the Anisian
Anisian
In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...
stage of the early Middle Triassic
Middle Triassic
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...
. A new species, P. sanjuanensis, was named in 1996 on the basis of a skull found from the Ischigualasto Formation. This extends the temporal range of Probelesodon into the Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
stage of the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
. The occurrence of the genus in these strata suggests that it also existed during the deposition of the Los Rastros Formation, which also outcrops in the same area as the localities where fossils have been found, although specimens have yet to be found from this formation. The presence of the genus in the Ischigualasto Formation is restricted to the earlier strata, becoming completely extinct soon after along with the last of the carnivorous cynodonts in the area. This has been taken as evidence for the gradual replacement of therapsid
Therapsida
Therapsida is a group of the most advanced synapsids, and include the ancestors of mammals. Many of the traits today seen as unique to mammals had their origin within early therapsids, including hair, lactation, and an erect posture. The earliest fossil attributed to Therapsida is believed to be...
fauna with the later mainly archosaur-dominated faunas of the Late Triassic. Evidence from the
Chañares Formation also seems to support this faunal transition.
Species
The type speciesType 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...
of Probelesodon is P. lewisi from the Chañares Formation. This species is the best known as many relatively complete specimens have been found. A long secondary palate distinguishes it from other closely related genera such as Belesodon
Belesodon
Belesodon is a genus that was described by the species Belesodon magnificus.- Species:Belesodon magnificus, was the first cynodont found in the Santa Maria Formation in Paleorrota, Brazil. It was described by Friedrich von Huene in...
. The molars are multicuspidate and the main cusps curve back. One species, P. sanjuanensis, differs from other species of Probelesodon by such characteristics as a highly arched zygomatic arch
Zygomatic arch
The zygomatic arch or cheek bone is formed by the zygomatic process of temporal bone and the temporal process of the zygomatic bone , the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process...
and the presence six postcanines. Another species, P. kitchingi was named in 1982 from material found from Rio Grande do Sul
Rio Grande do Sul
Rio Grande do Sul is the southernmost state in Brazil, and the state with the fifth highest Human Development Index in the country. In this state is located the southernmost city in the country, Chuí, on the border with Uruguay. In the region of Bento Gonçalves and Caxias do Sul, the largest wine...
, Brazil. P. minor is similar in appearance to the type species and has been found from the same formation. It differs mainly in size, being about half the length of the type species. This size difference is too great to be considered sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
. The close similarities between all four species have led to recent suggestions that they are synonymous with one another. It has even been suggested that the entire genus is synonymous with Chiniquodon theotonicus
Chiniquodon
Chiniquodon is a genus of carnivorous "mammal-like reptile", , which lived during the lower Upper Triassic in South America. These animals were up to the size of a dog. This genus seems to be most closely related to a contemporary genus, Probelesodon...
.
External links
- Probelesodon 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...