Anapsida: Procolophonia

Taxa on This Page

1. Nyctiphruretus X
2. Procolophonia

Nyctiphruretus acudens, a parareptile from the Middle Permian of Russia (Subtropical Pangea) illustration by ArthurWeasley - Wikipedia

Introduction

The Procolophonia are a group of primitively insectivorous, and then early herbivorous reptiles that flourished during the Permian to Triassic periods, and, while rarely exciting or glamorous (although the big lumbering pareaisaurs do have an ideosyncratic appeal, even appearing in a sci fi television series) were among the most successful animals of their time.

Phylogeny

The Procolophonia were originally included as a suborder of the Order Cotylosauria or "stem reptiles". Other groups often included among the cotylosaurs were Diadectids, Captorhinids, and millerosaurs, although these were placed in different suborders. Pareiasaurs were placed with, and then separate from, the procolophonids. (Romer, 1966 Colbert, 1969, Kuhn, 1969, Carroll, 1988).

It is clear that all these and other small unspecialised Permian reptiles were similar in many ways, and that they constitute an evolutionary grade, based on shared features found in early reptile-like amphibians and primitive reptiles. In the 1980s and 90s, the introduction of cladistic methodology and emphasis on shared specialised features (Gauthier et al. 1988, Laurin and Reisz 1995, Lee 1995) demolished the Cotylosauria (and its short-lived synonym Captorhinida (Carroll 1988)) and replaced it with a number of distinct clades (evolutionary lineages), some of which are not even very closely related to each other (the diadectids for example are now considered reptiliomorph amphibians [1]).

Evolutionary history

The Procolophonia appeared suddenly in the middle Permian, as the nyctiphruretid and nycteroleterids, evolving from basic millerettid or bolosaur like ancestors. From this primitive stock, both small Procolophonoids and giant pareiasaurs flourished during the Mid to Late Permian. Only the highly specialised procolophonids and the persistanly primitive owenettids survived to the Triassic, the former group being astonshingly successful for much of the period. They also are good candidates for turtle ancestors. One hypothesis is that turtles evolved from miniature pareiasaurs (Lee 1995), another that are related to owenettids (Reisz & Laurin 1991). However, the pareiasaur origin is now looking much less likely following the discovery of the aquatic turtle-ancestor Odontochelys). MAK, updated 120322.

Nyctiphruretus

A remarkably well preserved skull of Nyctiphruretus acudens, specimen number PIN 4659/1. A, dorsal; B, palatal; C, right lateral; D, anterior, and E, occipital views. Until 2010, no actual specimens of this species were illustrated or described in detail; hence they have the potential to offer much phylogenetic information. Photo from Säilä 2010b fig.1

Nyctiphruretus ("guardian of the night") is a small lizard-like animal from the middle Permian of Russia, at the time a warm equatorial region. Originally considered a primitive procolophonoid, it was interpreted cladistically as not a member of the Procolophonia, but of the Procolophonomorpha, the clade that includes all Procolophonia plus their immediate sister and stem taxa (Lee, 1995, Tsuji et al 2012). A recent monograph by Säilä (2010b) was the first to illustrate and briefly describe some of the best-preserved cranial specimens (the postcrania were not considered in that paper), the new information incorporated into two published data matrixes, The results confirmed that Nyctiphruretus is closely related to procolophonoids, pareiasaurs and Nycteroleterids, but interrelationships within this group remain unresolved. In that study Nyctiphruretus was recovered either as the sister taxon of all other procolophonia, or as the sister taxon of procolophonoids only, the first time the Nyctiphruretus-Procolophonoidea clade received support in a phylogenetic analysis. ( Säilä 2010b). Although the former would seem to be the more popular cladistic option (Müller & Tsuji 2007, Tsuji et al 2012), making Nyctiphruretus a persistantly primitive "living fossil" continuing alongside its descendents, a Nyctiphruretus-Procolophonoidea clade makes more sense evolutionarily, as it would bridge the stratigraphic and morphological gap between Procolophonoidea and basal parareptiles, and allows two lines of very similar ancestral procolophonia, one evolving towards stocky spiny lizard like herbivores, the other to bulky megaherbivores. The close similarities between Nyctiphruretus and the nycteroleterids - (which together constitute the Nyctiphruretia - are simply due to the fact that neither taxon has diverged much from its common ancestor (this applies to either hypothesis in any case). The Nyctiphruretia would then, like other groups such as the rhyniacea, halkeriids, Dendreperton, podokesaurs, iguanodonts, and hyracotheres, represent an assemblage of morphologically very similar species. In each case, they constitute an ancestral (in cladistic jargon, a paraphyletic) evolutionary grade. As their descendents evolve, they branch out in different directions, each of the very similar species in each grade standing at the base of a different evolutionary lineage (monophyletic clade). More insights may be waiting to be revealed through the use of these additional methodologies; as yet no one for example has performed a stratocladistic analysis on these parareptiles for example. Given in any case the ambiguity regarding the exact placement of Nyctiphruretus, and the fact that interrelationships between other Parareptilian groups also remain poorly resolved (Säilä (2010b)), we have retained Nyctiphruretus as an unresolved basal procolophonian, representing along with the Nycteroleterids, a basal assemblage within the Procolophonia, transitional between Millerettids and Bolosaurs on the one hand, and more advanced procolophonioidea and pareiasaurs on the other, representing the evolutionary grade that gave rise equally to pareiasaurs and procolophonids. MAK120326

Notes:

[1] cladists of course do not recognise the term Amphibia

Descriptions

Procolophonia. Seeley 1888: defined as LCA Pareiasaurs + Procolophonoids or Pareiasaurs + turtles. A stem group definition (say, closer to Procolophon than Bolosaurus) would also include Nyctiphruretus

Phylogeny: Procolophonomorpha : + Lanthanosuchoidea + (Bolosauridae + * : Nyctiphruretus + (Nycteroleteridae + Pareiasauridae) + Procolophonoidea.

Comment: In the most recent cladistic analysis (at the time of writing) of Tsuji et al 2012, if the node-based (or crown-group so to speak) using the LCA-based definition is used, then Nyctiphruretus is not a procolophonian. If a stem based definition is used, say, Procolophon > Bolosaurus, then it almost certainly is. We have followed the latter interpretation MAK120325

illustration from Dinosauria A to Z

Nyctiphruretus acudens Efremov, 1938 (monotypal Nyctiphruretidae)

Horizon: Belebei-Mezen Cotylosaur Complex, Lower Tatarian (Roadian/Wordian)

Locality: Mezen River, Arkhangelsk Region, northern European Russia

Length skull 4.4 cm; total length 36 cm

Characters: thickened, finely-sculptured prefrontal; pineal foramen at the posterior edge of the skull table (also found either convergently or as a synapomorphy that is later lost (a reversal) in bolosaurs). (Lee, 1997 p.203)

Comments: [1] Nyctiphruretus is a small insectivorous Procolophonomorph that has been found preserved in lake sediments. The name means "Guardian of the Night" (indicating perhaps that it is thought that these animals were nocturnal). These animals probably lived among the undergrowth in pond and lake margins, and filled the terrestrial small lizard niche. The diet consisted of invertebrates, and possibly also water plants. This is the most common animal known from the Mezen locality, amounting to over two-thirds of total number of specimens MAK

[2] Differs from the more related but more primitive Lanthanosuchus in having larger naris, orbit and pineal openings, less ornamentation and probably no lateral temporal fenestra on a greatly reduced postorbital area (David Peters)

[3] Originally considered an ancestral procolophonoidean and/or included with Barasaurus and Owenetta (Colbert, 1946; Romer, 1966, Ivachnenko et al 1979; Carroll, 1988), Nyctiphruretus shares no synapomorphies with the procolophonoids, and those similarities it does have are are primitive for Procolophonomorpha as a whole (Lee, 1995). Cladistic analysis by Lee 1995 and 1997 places Nyctiphruretus with the Nycteroleterids in the somewhat tentative new clade Nyctiphruretia, defined by three unambiguous traits (long external naris; maxilla broadly entering orbital margin; pineal foramen near or on parietal-postparietal suture) and four doubtful ones. More recent studies however show the Nyctiphruretia to be a paraphyletic or polyphyletic assemblage of basal procolophonia (Müller & Tsuji 2007, Säilä 2010b, Tsuji et al 2012). Or to be more precise, the Nyctiphruretia (Nyctiphruretus + nycteroleterids) appear, the ceratosauria to be a monophyletic clade when only few obvious synapomorphies are used, but more recent computaionally intensive statistical analysis shows both to be pseudomonophyletic ancestral taxon. For now, Nyctiphruretus resides as the only species in a monotypal family, although of course that could always change with new discoveries and analyses. MAK120326

Graphics image above left from Nyctiphruretus (in German); Drawing of skull © David Peters, used with permission, compare with photo