Eosuchia
Encyclopedia
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
.
Eosuchia was initially defined to include all "thecodontian" reptiles which did not have an antorbital fenestra but did retain tabulars, postparietals and a large pineal foramen (Broom, 1914). Broom coined the term as a new suborder for Youngina
.
A definition for inclusion in the order is difficult: it is almost easier to list the primitively-diapsid reptiles that have not been included at one time or another. The order has almost been treated as a dustbin for diapsids that are not obviously lepidosaurian or archosaurian. One consequence has been Romer's suggestion of the alternative order Younginiformes
to be applied strictly to those forms with the primitive diapsid form, in particular, a complete lowermost arch as the quadratojugal and jugal bones of the skull meet.
The one constant eosuchian has been Youngina
, a small lizard-shaped reptile from the Upper Permian of South Africa
. This and a couple of other genera, which may or may not be synonymous with Youngina, make up the family Younginidae.
The tangasaurids, a family that includes forms apparently adapted for swimming in fresh water, is also usually included.
In some phylogenies Eosuchia has been treated (probably erroneously) as a sister lepidosaur taxon to Squamata
and Rhynchocephalia.
)
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of diapsid
Diapsid
Diapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...
reptiles. Depending on which taxa are included the order may have ranged from the late Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
to 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...
but the consensus is that eosuchians are confined to the 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...
and 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...
.
Eosuchia was initially defined to include all "thecodontian" reptiles which did not have an antorbital fenestra but did retain tabulars, postparietals and a large pineal foramen (Broom, 1914). Broom coined the term as a new suborder for Youngina
Youngina
Youngina is an extinct genus of diapsid reptile from the Late Permian Beaufort Group of the Karoo Red Beds of South Africa. This, and a few related forms, make up the family Younginidae, within the Order Eosuchia...
.
A definition for inclusion in the order is difficult: it is almost easier to list the primitively-diapsid reptiles that have not been included at one time or another. The order has almost been treated as a dustbin for diapsids that are not obviously lepidosaurian or archosaurian. One consequence has been Romer's suggestion of the alternative order 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...
to be applied strictly to those forms with the primitive diapsid form, in particular, a complete lowermost arch as the quadratojugal and jugal bones of the skull meet.
The one constant eosuchian has been Youngina
Youngina
Youngina is an extinct genus of diapsid reptile from the Late Permian Beaufort Group of the Karoo Red Beds of South Africa. This, and a few related forms, make up the family Younginidae, within the Order Eosuchia...
, a small lizard-shaped reptile from the Upper Permian of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. This and a couple of other genera, which may or may not be synonymous with Youngina, make up the family Younginidae.
The tangasaurids, a family that includes forms apparently adapted for swimming in fresh water, is also usually included.
In some phylogenies Eosuchia has been treated (probably erroneously) as a sister lepidosaur taxon to Squamata
Squamata
Squamata, or the scaled reptiles, is the largest recent order of reptiles, including lizards and snakes. Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the...
and Rhynchocephalia.
Classification
Eosuchia s.s. (Syn:YounginiformesYounginiformes
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...
)
-
- ?Noteosuchus
- ?AcerosodontosaurusAcerosodontosaurusAcerosodontosaurus is an extinct genus of diapsid reptile....
- Family: Galesphyridae
- Galesphyrus
- Family: Younginidae
- HeleosuchusHeleosuchusHeleosuchus is an extinct genus of diapsid reptile from the Late Permian of South Africa. It was originally described as a species of Saurosternon, but was later recognized as a separate taxon by Robert Broom....
- YounginaYounginaYoungina is an extinct genus of diapsid reptile from the Late Permian Beaufort Group of the Karoo Red Beds of South Africa. This, and a few related forms, make up the family Younginidae, within the Order Eosuchia...
- Heleosuchus
- Family: TangasauridaeTangasauridaeTangasauridae is a family of eosuchian diapsids. Specimens have been found that are of Late Permian to Early Triassic in age from the Sakamena Group of western Madagascar. They lived alongside other taxa present from the Sakamena Group, including temnospondyls, rhynchosaurs, and gomphodont...
- HovasaurusHovasaurusHovasaurus is an extinct genus of diapsid reptile belonging to the Order Eosuchia. It lived in what is now Madagascar during the Late Permian....
- Tangasaurus
- ThadeosaurusThadeosaurusThadeosaurus 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....
- Kenyasaurus
- Hovasaurus