Aphanosauria ("hidden lizards") is an extinct group of reptiles distantly related to dinosaurs (including birds).

Aphanosaurs possessed features from both groups, indicating that they are the oldest and most primitive known clade of avemetatarsalians, at least in terms of their position on the archosaur family tree.

Other avemetatarsalians include the flying pterosaurs, small bipedal lagerpetids, herbivorous silesaurids, and the incredibly diverse dinosaurs, which survive to the present day in the form of birds.

Aphanosauria is formally defined as the most inclusive clade containing Teleocrater rhadinus and Yarasuchus deccanensis but not Passer domesticus (house sparrow) or Crocodylus niloticus (Nile crocodile).

[2] They were fairly slow quadrupedal long-necked carnivores, a biology more similar to basal archosaurs than to advanced avemetatarsalians such as pterosaurs, lagerpetids, and early dinosaurs.

Nevertheless, they possessed elevated growth rates compared to their contemporaries, indicating that they grew quickly, more like birds than other modern reptiles.

Coupled with an antorbital depression (a collapsed area of bone which surrounded the fenestra), these indicate that aphanosaurs belonged to the group Archosauria.

In the past it was believed that only dinosaurs possessed supratemporal fossae, but its presence in aphanosaurs (and Asilisaurus, a silesaurid) shows that it was variable among many avemetatarsalians.

As with most other reptiles, the vertebrae are composed of a roughly cylindrical main body (centrum) and a plate-like neural spine jutting out of the top.

As a result, there are two areas on the side of each vertebra for connecting to a rib: the diapophysis in the upper part of the centrum and the parapophysis in a lower position.

These additional prongs are termed epipophyses, and are common in dinosaurs but likely independently evolved due to being absent in other groups of avemetatarsalians.

A small structure (hyposphene) below the postzygapophyses fits into a lip (hypantrum) between the prezygapophyses of the following vertebra, forming additional articulations to assist the zygapophyses.

These hyposphene-hypantrum articulations are present in saurischian dinosaurs as well as raisuchids, and are often considered to help make the spine more rigid.

In anterior (front) view, its midshaft was pinched while the proximal (near) and distal (far) ends were wide, making the bone hourglass-shaped.

[2] The hand is mostly unknown in members of this group, but it was presumably small and five-fingered as in most archosaurs (apart from specialized forms like pterosaurs or theropod dinosaurs).

This ridge, called a fourth trochanter, is an attachment point for the M. caudofemoralis, a tail muscle which helps to retract the hindlimbs.

A scar on the anterolateral (front and outer) edge of the femur may have attached to the M. iliotrochantericus caudalis, a muscle which connects to the hip and helps to stabilize the thigh.

This particular scar may be the same thing as the anterior (or lesser) trochanter, a specific structure present in dinosaurs and their close relative.

[2] The thin tibia and fibula (lower leg bones) of aphanosaurs do not possess unique traits to the same extent as the femur.

A short lower leg is inversely correlated with running abilities, indicating that aphanosaurs were not as fast or agile as more advanced members of Avemetatarsalia.

Pseudosuchians (including modern crocodiles), as well as the crocodile-like phytosaurs have a different configuration, where the calcaneum is much larger and more complex, connecting to the astragalum with a joint that allows for movement between the two.

For example, Yarasuchus was first considered a prestosuchid[6] and later a poposauroid by different analyses,[3] with Martin Ezcurra (2016) placing both it and Dongusuchus as Euparkeria-grade archosaur relatives in his analysis.