Microleter
Encyclopedia
Microleter is an extinct genus of parareptile which existed in Oklahoma
during the upper 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 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 millerettid
s 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.
Oklahoma
Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3,751,351 residents as of the 2010 census and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...
during the upper 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...
period. It was first named by paleontologists Linda A. Tsuji, Johannes Muller
Johannes Müller
Johannes Müller, Johann Müller or Hans Müller may refer to:* Johannes Müller von Königsberg , known as Regiomontanus, German mathematician and astronomer* Johannes von Müller , Swiss historian...
, and Robert R. Reisz
Robert R. Reisz
Robert Rafael Reisz is a Canadian paleontologist and specialist in the study of early amniote and tetrapod evolution.Robert Reisz was born August 27, 1947, in Oradea, Romania. He received his B.Sc. , M.Sc. and Ph.D. from McGill University as Robert L. Carroll’s first doctoral graduate...
in 2010. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
is Microleter mckinzieorum. A very well preserved skull and lower jaw is the only known specimen. It was found from the Early Permian fissure-fill deposits near Richards Spur in Comanche County
Comanche County, Oklahoma
Comanche County is a county located in the U.S. state of Oklahoma. Built on former reservation lands of the Comanche, Kiowa, and Apache in Indian Territory, Comanche County was open for settlement on August 16, 1901 by lottery. The region has three cities and seven towns as well as the Fort Sill...
, often referred to as the Fort Sill locality. The Fort Sill locality has yielded many other well preserved tetrapod
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
fossils, including those of other parareptiles such as Bolosaurus
Bolosaurus
Bolosaurus is an extinct genus of bolosaurid.-References:*Berman, DS, RR Reisz, D Scott, AC Henrici, SS Sumida & T Martens , Early Permian bipedal reptile. Science 290: 969-972. H. Bolosauridae....
, Colobomycter
Colobomycter
Colobomycter is a small parareptile known from the Early Permian of Oklahoma. The genus was first described from fossil remains in 1958, at which time it was believed to represent a synapsid , specifically, a pelycosaur. However, the discovery of new material and reexamination of the holotype led...
, and Delorhynchus
Delorhynchus
Delorhynchus is an extinct genus of non-mammalian synapsid.-References:*...
.
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
Palatine bone
The palatine bone is a bone in many species of the animal kingdom, commonly termed the palatum .-Human anatomy:...
and a lacrimal
Lacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
that reaches the naris, or nasal opening.
Microleter is one of the most basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
parareptiles, and the most basal parareptile from Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
. It is phylogenetically positioned between the more basal millerettid
Millerettid
The millerettids are an extinct group of anapsids that lived in South Africa during the Upper Permian. They were small insectivores and probably resembled modern lizards in appearance and lifestyle.-External links:*...
s from the Late 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...
and a more derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
group of parareptiles consisting of Acleistorhinidae
Acleistorhinidae
Acleistorhinidae is a family of Early Permian-aged parareptiles. Presently, the clade consists of only two taxa, Colobomycter and Acleistorhinus, both collected from the Permian of Oklahoma. Sister taxa include Nyctiphruretidae and Sclerosauridae....
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.