Theria

The terios (Theria) (from the Greek θηρίον [thɛː'rion]) are a subclass of mammals that are characterized by Unlike the prototheria, the embryo does not develop inside an egg, but inside the maternal uterus. Includes marsupials and placentals. They appeared during the Cretaceous, about 120 million years ago.

Features

Therios give birth to live young without using an egg. This is possible thanks to key proteins called syncytins, which allow exchanges between the mother and her offspring through a placenta, which is rudimentary in marsupials. Genetic studies have shown the viral origin of syncytins through the endogenization process. Syncytins play a very important role in the formation of the syncytiotrophoblastic layer of the placenta generated by the fusion of trophoblast cells.

Another feature of therians is that they have lost their coracoid bone, unlike their monotreme cousins.

The external ears or pinna are also a distinctive and exclusive feature of therios.

Evolution

The oldest known terium fossil is Juramaia, from the Middle Jurassic of China. However, molecular data suggests that therians may have originated even earlier, during the Early Jurassic.

Subclades

• Trituberculata †
• Metatheria (includes marsupials)
• Eutheria (includes placencies)

Phylogenetic tree

A summary cladogram:

- or subclass Theria (Parker ' Haswell, 1897) I don't know. Gender Aethomylos Novacek, 1976 (†)
I don't know. Gender Anisorhizus Ameghino, 1902 (†)
I don't know. Gender Dakotadens Eaton, 1993 (†)
I don't know. Gender Falepetrus Clemens " Lillegraven, 1986 (†)
I don't know. Gender Kasserinotherium Crochet, 1986 (†)
I don't know. Gender Paleomolops Cifelli, 1994 (†)
I don't know. Gender Tetraprothomo Ameghino, 1907 (†)
I don't know. Gender Tribotherium Sigogneau-Russell, 1991 (†)
I don't know. Gender Zygiocuspis Cifelli, 1990 (†)
Russellmyinae subfamily Estravis, 1990 (†)
I don't know. Family Endotheriidae Shikama, 1947 (†)
I don't know. Holoclemensiidae Aplin & Archer, 1987 (†)
I don't know. Kermackiidae Family Butler, 1978 (†)
I don't know. Pappotheriidae Slaughter, 1965 (†)
I don't know. Family Picopsidae Fox, 1980 (†)
I don't know. Plicatodontidae Ameghino, 1904 (†)
I don't know. Family Potamotelsidae Nessov, 1987 (†)
Русский Ord Asiadelphia Trofimov " Szalay, 1993 (†)
Δ-o Orden Deltatheroida Kielan-Jaworowska, 1982 (†)
Cohorte Marsupialia (Illiger, 1811) Cohorte Placentalia (Owen, 1837)