Tangasauridae is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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 earliest traditionally identified diapsids, the araeosc ...

known from

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 preserve ...

specimens from

Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...

Kenya Kenya, officially the Republic of Kenya, is a country located in East Africa. With an estimated population of more than 52.4 million as of mid-2024, Kenya is the 27th-most-populous country in the world and the 7th most populous in Africa. ...

and

Tanzania Tanzania, officially the United Republic of Tanzania, is a country in East Africa within the African Great Lakes region. It is bordered by Uganda to the northwest; Kenya to the northeast; the Indian Ocean to the east; Mozambique and Malawi to t ...

that are

Late Permian Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudonym used by Dave Groh ...

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between 251.9 Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which ...

in age. Fossils have been found of numerous specimens of common members of this family such as ''

Hovasaurus ''Hovasaurus'' is an extinct genus of basal diapsid reptile. 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 paleontologically youngest member of t ...

'' in different stages of

ontogenic Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the stu ...

development. Recent material from the Middle Sakamena Formation of the Morondava Basin of Madagascar that dates back to the early

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

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 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 botanical subfamily names with "-oideae", and zo ...

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

sternum The sternum (: sternums or sterna) 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 bl ...

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 often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...

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

superorder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...

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

, which includes many highly derived marine aquatic reptiles such as

placodonts Placodonts ("Tablet (pharmacy), tablet tooth, teeth") are an Extinction, extinct order (biology), order of marine reptiles that lived during the Triassic period, becoming extinct at the end of the period. They were part of Sauropterygia, the gro ...

nothosaurs Nothosaurs (superfamily Nothosauroidea) were Triassic marine sauropterygian reptiles. They averaged about in length, with a long body and tail. The feet were paddle-like, and are known to have been webbed in life, to help power the animal when sw ...

, and

plesiosaurs The Plesiosauria or plesiosaurs are an Order (biology), order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared in the latest Triassic Period (geology), Period, possibly in the Rhaetian st ...

.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 group of diapsid reptiles known from the Permian-Triassic of Africa and Madagascar. It has been used as a replacement for " Eosuchia". Younginiformes (including '' Acerosodontosaurus'', '' Hovasaurus'', '' Kenyasaurus'', '' Ta ...

. 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, tangasaurids would be included in Younginiformes. However, this classification scheme is dependent on the

Younginidae Younginidae is an extinct family of diapsid reptiles from the Late Permian. In a phylogenetic context, younginids are near the base of the clade Neodiapsida. The only species definitively a member of the Younginidae is '' Youngina capensis'' fro ...

forming a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

clade with the Tangasauridae, which is often not recovered in

phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...

. Tangasaurid genera are listed below: *Family Tangasauridae :*''

Acerosodontosaurus ''Acerosodontosaurus'' is an Extinction, extinct genus of Neodiapsida, neodiapsid Reptile, reptiles that lived during the Late Permian of Madagascar. The only species of ''Acerosodontosaurus'', ''A. piveteaui'', is known from a natural wiktionary ...

'' :*''

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 ...

'' :*'' Thadeosaurus'' :*Subfamily Tangasaurinae ::*''

'' ::*''

Tangasaurus ''Tangasaurus'' is an extinct genus of aquatic animal, aquatic basal (phylogenetics), basal tangasaurid neodiapsid known from the Late Permian geological timescale, period (late Changhsingian stage) of Tanga Region, Tanga, northeastern Tanzania. ...

References

Diapsids Lopingian first appearances Early Triassic extinctions Prehistoric reptile families {{triassic-reptile-stub