Microleter mckinzieorum

Microleter is an extinct genus of parareptile which existed in Oklahoma during the Early Permian period. It was first named by paleontologists Linda A. Tsuji, Johannes Muller, and Robert R. Reisz in 2010. The type species is Microleter mckinzieorum. A very well preserved skull and lower jaw is the only known specimen. It was found from the Early Permian (early Kungurian stage) fissure-fill deposits near Richards Spur in Comanche County, often referred to as the Fort Sill locality. The Fort Sill locality has yielded many other well preserved tetrapod fossils, including those of other parareptiles such as Bolosaurus, Colobomycter, and Delorhynchus.

The surfaces of the bones of the skull are covered in pits, with large pits surrounded by much smaller ones. There is also a radial pattern of grooves on some bone surfaces. Like many other basal parareptiles,Microleter has a temporal fenestra. The temporal fenestra is not entirely surrounded by bone, and opens ventrally at the bottom of the skull. Microleter also has a wide palatine bone and a lacrimal that reaches the naris, or nasal opening.

Microleter is one of the most basal parareptiles, and the most basal parareptile from Laurasia. It is phylogenetically positioned between the more basal millerettids from the Late Permian of South Africa and a more derived group of parareptiles consisting of Acleistorhinidae and Lanthanosuchidae. Before the description of Microleter, parareptiles were thought to have originated in Gondwana. However, Microleter appears in Laurasia soon after the earliest known parareptiles and is among the most basal members of the group. Its age and phylogenetic position seems to make a parareptilian origin in Gondwana less likely.