Tangasauridae is a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

diapsids Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years ag ...

. Specimens have been found that are of

Late Permian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...

in age from the

Sakamena Group Sakamena is a village near Betroka in the region of Anosy in Madagascar. Sakamena is also the name of a Permian sedimentary geological formation that has yielded many vertebrate fossil, including Triadobatrachus (the first lissamphibian), Claudio ...

of western

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...

. They lived alongside other taxa present from the Sakamena Group, including

temnospondyls Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carbo ...

rhynchosaur Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...

s, and gomphodont eucynodonts.

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 ...

s have been found of numerous specimens of common members of this family such as ''

Hovasaurus ''Hovasaurus'' is an extinct genus of diapsid reptile belonging to the order Eosuchia. It lived in what is now Madagascar during the Late Permian and Early Triassic, being a survivor of the Permian–Triassic extinction event and the paleontologi ...

'' and ''

Thadeosaurus ''Thadeosaurus'' is an extinct genus of diapsid reptile belonging to the family Younginidae. Fossils have been found in the Lower Sakamena Formation ( Sakamena Group) of the Morondava Basin, Madagascar in 1981, and date to the late Permian to ...

'' in different stages of ontogenic development.Currie, Philip J and Carroll, Robert L. (1984) Ontogenic changes in the eosuchian reptile ''Thadeosaurus''. ''

Journal of Vertebrate Paleontology The ''Journal of Vertebrate Paleontology'' is a bimonthly peer-reviewed scientific journal that was established in 1980 by Jiri Zidek (University of Oklahoma). It covers all aspects of vertebrate paleontology, including vertebrate origins, evolu ...

'' 4(1):68-84 Recent material from the

Middle Sakamena Formation Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek ...

of the

Morondava Basin Morondava Basin is one of the major sedimentary basins of Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island c ...

of Madagascar that dates back to the early

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

suggests that the Tangasauridae were relatively unaffected by the Permian-Triassic extinction event.

Description and phylogeny

Tangasaurids are known to have been a highly

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

group of

. One

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

, Kenyasaurinae, is composed of taxa that were fully terrestrial. They had long toes and highly developed

sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sh ...

s that made them well suited to life on land. On the other hand, the other subfamily, Tangasaurinae, is composed of taxa that were adapted to an aquatic life. They had webbed feet and a laterally compressed tails that allowed them to be able to swim in the freshwater

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

environment present at the time. Because of their highly derived aquatic characteristics and occurrence in time, it has been suggested that the tangasaurids were a direct ancestor of the superorder

Sauropterygia Sauropterygia ("lizard flippers") is an extinct taxon of diverse, aquatic reptiles that developed from terrestrial ancestors soon after the end-Permian extinction and flourished during the Triassic before all except for the Plesiosauria became ...

, which includes many highly

marine aquatic reptiles such as

placodonts Placodonts ("Tablet teeth") are an extinct order of marine reptiles that lived during the Triassic period, becoming extinct at the end of the period. They were part of Sauropterygia, the group that includes plesiosaurs. Placodonts were generally ...

nothosaurs Nothosaurs (order Nothosauroidea) were Triassic marine sauropterygian reptiles that may have lived like seals of today, catching food in water but coming ashore on rocks and beaches. They averaged about in length, with a long body and tail.F. v. ...

, and

plesiosaurs The Plesiosauria (; Greek: πλησίος, ''plesios'', meaning "near to" and ''sauros'', meaning "lizard") or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared i ...

.Carroll, R.L. 1988. ''

Vertebrate Paleontology and Evolution ''Vertebrate Paleontology and Evolution'' is an advanced textbook on vertebrate paleontology by Robert L. Carroll, published in 1988 by WH Freeman. It provides a very detailed technical account of various groups of living and fossil vertebrate ...

''. WH Freeman and Company, New York

Classification

Despite the controversy over the definition of the order Eosuchia (to which the Tangasauridae are considered to have belonged) and as to which taxa should be considered to fall within it, the position of the tangasaurids as part of this group has rarely been questioned. An alternative order has been proposed to resolve the issues surrounding Eosuchia, the

Younginiformes Younginiformes is a replacement name for the taxon Eosuchia, proposed by Alfred Romer in 1947. The Eosuchia having become a wastebasket taxon for many probably distantly-related primitive diapsid reptiles ranging from the late Carboniferous to ...

. Because their

quadratojugal The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...

and

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 ...

bones meet to form an arch in the skull, as is a characteristic of many primitive diapsids, tangasaurs would be included in Younginiformes. The Tangasauridae is divided into two subfamilies, as shown below: *Family Tangasauridae :*Subfamily Kenyasaurinae ::*''

Kenyasaurus ''Kenyasaurus'' is an extinct genus of basal (phylogenetics), basal tangasaurid known from the Early Triassic geological timescale, period of Coast Province, southeastern Kenya. It contains a single species, ''Kenyasaurus mariakaniensis''. Disco ...

'' :*Subfamily Tangasaurinae ::*''

Acerosodontosaurus ''Acerosodontosaurus'' is an extinct genus of neodiapsid reptiles that lived during the Upper Permian of Madagascar. The only species of ''Acerosodontosaurus'', ''A. piveteaui'', is known from a natural mold of a single partial skeleton including ...

'' ::*''

Tangasaurus ''Tangasaurus'' is an extinct genus of aquatic basal tangasaurid neodiapsid known from the Late Permian period (late Changhsingian stage) of Tanga, northeastern Tanzania. It contains a single species, ''Tangasaurus mennelli''. Discovery ''Ta ...

References

Permian reptiles Triassic diapsids Lopingian first appearances Early Triassic extinctions Prehistoric neodiapsids Prehistoric reptile families {{triassic-reptile-stub