Tangasauridae is a family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of eosuchian

Eosuchia

Eosuchians are an extinct order of diapsid reptiles. Depending on which taxa are included the order may have ranged from the late Carboniferous to the Eocene but the consensus is that eosuchians are confined to the Permian and Triassic....

 diapsids. Specimens have been found that are of Late Permian

Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 to Early Triassic

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 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...

 in age from the Sakamena Group of western Madagascar

Madagascar

The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...

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

Temnospondyli

Temnospondyli is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian, and Triassic periods. A few species continued into the Cretaceous. Fossils have been found on every continent...

, rhynchosaurs

Rhynchosaur

Rhynchosaurs were a group of Triassic diapsid reptiles related to the archosaurs.-Description:Rhynchosaurs were herbivores, and at times abundant , with stocky bodies and a powerful beak...

, and gomphodont eucynodonts

Eucynodontia

Eucynodontia is a grouping of animals that includes both mammals, such as dogs, and mammal-like non-mammalian therapsids such as cynodonts . Its membership was and is made up of both carnivores and herbivores. The chronological range extends from at least the Lower Triassic, possibly the Upper...

. Fossils

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

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

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 Thadeosaurus

Thadeosaurus

Thadeosaurus is an extinct genus of diapsid reptile belonging to the Order Eosuchia. Fossils have been found in Madagascar, and date to the late Permian period....

at in different stages of ontogenic

Ontogeny

Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...

 development. Recent material from the Middle Sakamena Formation of the Morondava Basin

Morondava Basin

Morondava Basin is one of the major sedimentary basins of Madagascar. It encompasses the large Tsimiroro heavy oil field and giant Bemolanga ultra heavy oil field....

 of Madagascar that dates back to the early 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...

 period

Geologic time scale

The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...

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

Permian-Triassic extinction event

The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...

.

Description and phylogeny

Tangasaurids are known to have been a highly derived

Derived

In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...

 group of diapsids. One subfamily, the Kenyasaurinae, is composed of taxa that were fully terrestrial. They had long toes and highly developed sternums

Sternum

The sternum or breastbone is a long flat bony plate shaped like a capital "T" located anteriorly to the heart in the center of the thorax...

 that made them well suited to life on land. On the other hand, the other subfamily, the Tangasaurinae, 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

Lake

A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

 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

Sauropterygia were a group of very successful aquatic reptiles that flourished during the Mesozoic before they became extinct at the end of the era. They were united by a radical adaptation of their shoulder, designed to support powerful flipper strokes...

, which includes many highly derived

Derived

In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...

 marine aquatic reptiles such as placodonts, nothosaurs, and plesiosaurs

Plesiosauria

Plesiosauria is an order of Mesozoic marine reptiles. Plesiosaurs first appeared in the Early Jurassic Period and became especially common during the Jurassic Period, thriving until the K-T extinction at the end of the Cretaceous Period.The name "plesiosaur" is used to refer to the order...

.

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

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

. Because their quadratojugal

Quadratojugal

The quadratojugal is a small jaw bone that is present in most amphibians, reptiles, and birds, but has been lost in mammals. It is connected to the jugal as well as other bones, though these may vary with species....

 and jugal

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....

 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
• Thadeosaurus
  Thadeosaurus
  Thadeosaurus is an extinct genus of diapsid reptile belonging to the Order Eosuchia. Fossils have been found in Madagascar, and date to the late Permian period....
  
  
  • Subfamily Tangasaurinae
• Hovasaurus
  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....
  
  
• Tangasaurus