BIOLOGY 622 – FALL 2014 BASAL AMNIOTA - STRUCTURE AND PHYLOGENY WEEK – 8 NYCTIPHRURETUS, BOLOSAURIDAE and MORE S. S. SUMIDA

Nyctiphruretus Nyctiphruretus is a Middle Permian from the Mezen River Basin of Russia that has been variously classified as a nycteroleterid (part of Paraiesauria), a procolophonid, and entirely on its own. The latter is the position given by Tsuji and Muller, and that provisionally adopted in the phylogeny used for organizing this class. Most recently, SäiIä (2010) placed it as the sister-taxon to procolophonids, though that is still debated. The skull is generalized, with fairly simple teeth suggestive of insectivory. In other words, it is primitive and might fit anywhere. One thing that is worth noting is the relative huge orbits – possibly suggestive of a nocturnal lifestyle.

Nyctiphruretus

THE BOLOSAURIDAE A small, but important group of [mostly] Early Permian parareptiles is the Bolosauridae. The family has been known for over a century, and although its phylogenetic placement has been all over the map during much of that time, membership in the Bolosauridae has been stable and unquestioned. All bolosaurs are characterized by dramatic jaw and dental features, particularly the extremely cuspate teeth and the lower jaw with extremely high coronoid process.

Bolosaurid’s are unmistakable, and though somewhat low in diversity, they are apparently pan-Laurasian in distribution. After discovery of a nearly complete body fossil of the new genus Eudibamus, Berman et al. (2000) assessed the Bolosauirdae’s phylogenetic position and for the first time assigned the family to the Parareptilia. It has since remained a consistent and well-defined family of the group.

MORE DERIVED ANKYRAMORPH PARAREPTILES: PROCOLOPHIDS AND PAREIASAURS Although we will not be surveying the diversity of these groups until later, it is worth mentioning them at this point, particularly given the [until recently] variable placement of the Russian group known as the Nycteroleteridae and the occasional placement of Nyctiphruretus in or near that group.

PROCOLOPHONOIDEA Procolophonids have been variously placed, difficult to define, and not surprisingly considered as a potential ancestors to turtles. As a group they appear to hang together by virtue of the broadly flared shape of their cheeks. This is the first group we examine this term that survived the end-Permian extinction, persisting until the end of the Triassic. Cisneros (2008) defined the group with the following features: Maxilla premaxillary subnarial process absent. External naris subcircular or dorsoventrally expanded. Maxillary depression present. Three to four premaxillary teeth. Maxillary teeth with labiolingually expanded bases present. Ten to 12 maxillary teeth. Anterior vomerine dentition consisting of true teeth.

Maxilla premaxillary subnarial process absent. External naris subcircular or dorsoventrally expanded. Maxillary depression present. Three to four premaxillary teeth. Maxillary teeth with labiolingually expanded bases present. Ten to 12 maxillary teeth. Anterior vomerine dentition consisting of true teeth.

PAREIASAUROMORPHA Pareiasaurs attained some of the greatest sizes and most unusual of cranial ornamentation of all reptilian groups predating dinosaurs. They ranged through the Permian, but did not make it into the Triassic. Pareiasaurs are most famous for their incredible range of size, from small lizard-shaped animals to huge animals estimated at as much as 1300 pounds. They also have widely variable skulls, often with dramatic lumps and/or spikes.

A ventral flange of the quadratojugal. A posterior extension of the squamosal that covers the area occupied by the quadrate emargination in other anapsids. A large boss on the supratemporal. A large ventral process on the angular (a bone in the lower jaw).

Pareiasaurus are also important to consider given that nycteroleterids are usually included within the Pareiasauromorpha. Note the position of Nyctiphruretus.

And, whereas nycteroleterids may be considered a monophyletic group by some, it may be that they grade into pareiasaurs. One of the reasons nycteroleterids have been of so much interest is because they have been interpreted as having what are known as “impedence-matching” middle ear structures. A big deal has been made of this. Impedance matching is one of the important functions of middle ear, herein the middle ear transfers the incoming vibration from the comparatively large, low impedance tympanic membrane to the much smaller, high impedance oval window. In mammals, this is done by the chain of middle ossicles known as the stapes, incus, and malleus.

Phylogeny of the non-pareiasaurian parareptiles from the Mezen River Basin. Muller and Tsuji noted that the skulls of nycteroleterids have a deep notch posteriorly in which a tympanic membrane may have fit.

Here is a specimen of Macroleter showing the stapes preserved in place.

And here is a reconstruction of the occipital region of the skull with their interpretation of the position of the stapes and its cartilaginous extension.

They are in fact, probably correct. But here’s the deal. ALL terrestrial hearing (with ears at least) is impedence matching. Otic notches are known for numerous Paleozoic amphibians. Diadectids had a well developed tympanum as well. So…nycteroleterids could hear! Uh…yeah. And so could lots of other things.