Nyasasaurus

Nyasasaurus ("[Lake] Nyasa lizard") is a dinosauriform reptile from the Middle Triassic of Tanzania. It is possibly the oldest known dinosaur to be discovered.

Description
Nyasasaurus is known only from a humerus and vertebrae from the neck and spine, but compared to animals believed to be similar it is estimated that it grew to a length of two to three meters. Analysis of the humerus indicates that the bone structure of Nyasasaurus was much more similar to dinosaurs instead of early reptiles.

Classification
Although Nyasasaurus is so incomplete, it can be confidently identified as an archosaur and likely as a basal dinosaur (or at least very closely related to dinosaurs). It was suggested in 1986 that the animal was a type of prosauropod, but this has been disputed. Some phylogenetic analyses place Nyasasaurus within the family Silesauridae, a group of herbivorous reptiles that are close relatives of dinosaurs. Before the discovery of Nyasasaurus, 16 million years separated the earliest dinosaurs from the earliest silesaurids.

History
The genus Nyasasaurus has a long and complicated history. The holotype was first collected in the Middle Triassic Manda Beds near Lake Nyasa, Tanzania by Francis Rex Parrington during the 1930s. The remains were first described in 1956 by Alan Charig, but simply referred to as "Specimen 50b". Charig later published the name "Nyasasaurus parringtoni" in 1976, but it was considered a nomen nudem name because it lacked a description to go along with it.

A second specimen, known only from vertebrae, was discovered in the same locality by G. M. Stockley in the 1930s. They were described in 1932 as a species of Thecodontosaurus, but no formal diagnosis was provided and the classification has since been ignored.

In 2013, both specimens were recovered from storage and described as Nyasasaurus parringtoni by a team led by Sterling Nesbitt and Paul Barrett, formalizing Charig's original name. It was subsequently widely reported in the media as "the oldest known dinosaur".