Eureptilia

Romeria is a genus of small single-tooth-rowed captorhinids. Two species are currently recognized: R. texana, known from two partial skulls and one poorly preserved postcranial skeleton, and R. prima known from one skull with associated forelimbs, all of which come from the Lower Permian red beds of North Texas.

Scientific History: The type species R. texana was discovered during field collections of the Museum of Comparative Zoology in the in the second half of the 1930s. Its description was published in 1937 and is based on one single cranium whithout braincase. In 1973 a juvenile individual, collected together with material of the microsaur Pantylus, was attributed to that species.

The circumstances of discovery of the second species, R. prima, are not documented. R. prima was first described in 1973 on the basis of one single, almost complete skull and a few postcranial bones. Since 1973 no new material of Romeria has been found by scientific collectors.

Characteristics of the genus: Romeria is caracterized by a unique composition of features that are present in other basal eureptiles rather than by distinct apomorhies. Its pineal foramen, the opening in the center of the skull table, is very large, relative to skull size, as seen in Protocaptorhinus and Concordia. In other respects the skull of Romeria is quite similar to that of more basal eureptile taxa such as Protorothyris or Concordia: it is rather lightly built, has large orbitae compared to skull size, numerous denticles on the palatal bones, a bilaterally embayed posterior margin of the skull roof, and supratemporals that, in dorsal view, project anteromedially into the posterolateral corners of the parietals. However Romeria shows the typical captorhinid traits such as the lost of the tabular bone, the down-curved premaxilla, or the absence of large teeth on the transverse flange of the pterygoid.

Type species: The structure of Romeria texana's skull corresponds primarily to the characteristics of the genus. Therfore only description of the dentition is given here. All teeth have the shape of simple cones. The anteriormost premaxillary teeth are the largest in these bones. Posteriorly they decrease in size rapidly. The anteriormost maxillary teeth are similar in size to the posterior premaxillary teeth but become larger posteriorly to reach maximum size at the 6th position. Posterior to that postiton they become successively smaller again. Unfortunately the juvenile postcranial skeleton mentioned above is enclosed in a nodule of ironstone, being very resistant to efforts of preparation. Therefore nothing is known about the postcranium of R. texana.

Second species: R. prima differs from R. texana in having a much shorter anterior process of the prefrontal bone. The dentition resembles that of R. texana with the exception of that R. prima has two less premaxillary teeth and that the teeth are generally more gracile. Besides those differences the skull structure of both species of Romeria is nearly identical. Unfortunately little is known about the palate of R. prima. However, is seems quite plausible that it closely resembles that of R. texana including the shagreen dentition.

In contrast to R. texana also the forelimbs of R. prima are known. Admittedly, these bones are rather poorly preserved. As far as one can judge they show no major differences to that of other basal generalized amniotes.

Validity of the genus: Recently reasonable doubts are casted on the validity of the genus since no unequivocal apomorhies are included in its definition. There is possibility that such apomorphies could be discovered by further examination of the postcranial type material of R. prima. Because such new findings might not be made in the type species R. texana probably both names will have to be declared nomina dubia and a new genus will have to be erected on the basis of the type material of R. prima subsequently.

Below follow succinct accounts on the recognized species of Romeria.

Protocaptorhinus pricei is a small single tooth-rowed captorhinid from the Lower Permian red beds of North Texas and Central Oklahoma.
It is the only recognized member of the genus Protocaptorhinus.

Within captorhinids it is an "intermediate" form showing basal traits in skull structure such as a large pineal foramen in relation to skull size, single tooth-rows, small denticles on the bones of the palate, or a small, slender supratemporal that is excluded from contribution to the skull table. However P. pricei is derived in having a single median embayment of the posterior margin of the skull table, a trait shared by all "higher" captorhinids, up to and including the moradisaurines. In Romeria and Protorothyris, however, this margin is embayed bilaterally, i.e. on both sides of the median suture of the skull roof. The supratemporal in P. pricei lies transversely at the posteromedial margin of the squamosal as seen in Captorhinus, whereas in Romeria and Protorothyris it projects, in dorsal view, into the posterolateral corner of the parietal.

Two partial skulls of Protocaptorhinus have been reported from Upper Permian deposits of Zimbabwe implying that this genus spread from northwestern Pangaea into the southeastern regions of the supercontinent and survived from the Early to the Late Permian. Given both the large temporal and the large spatial distance it seems, however, quite unlikely that no divergence on a generic level should have taken place between the North American and the southern African "protocaptorhinus-like" forms and thus occurrence of Protocaptorhinus in Upper Permian strata of Zimbabwe is rather questionable. The state of knowledge on the Zimbabwean captorhinid does not allow an unequivocal assignment to Protocaptorhinus or another known or new genus so far. Thus these fossils are currently considered as Captorhinidae incertae sedis. Nevertheless it is remarkable that basal "protocaptorhinus-like" forms apparently survived through to Late Permian times.

Rhiodenticulatus heatoni, the only recognized species of the genus, is a small, single-tooth-rowed captorhinid.

Although generally primitive it shows some remarkable features in its skull structure: the lacrimal, a bone of the anterior side wall of the skull, is very high dorsoventrally, hence the snout has, in contrast to other captorhinids, a somewhat domed appearance. One of the middle upper jaw teeth has a base diameter about as twice the base diameter of the adjacent teeth but exceeds them only little in height. The premaxillary teeth are homodont whereas in most other captorhinids the first tooth is the largest and the following teeth are succesively smaller. Besides the skull also some postcranial bones are known, showing, however, no significant differences to that of other captorhinids. R. heatoni is the only representative of the, compared to other Permian taxa, poor captorhinid fossil record of the terrestrial Permian deposits of New Mexico.

Saurorictus australis is a small single-tooth-rowed captorhinid from Upper Permian terrestrial deposits of the Karoo Basin, South Africa. Its fossil record comprises one single however almost complete, moderately deformed skull and a few scrappy postcranial elements. It is the only recognized species of the genus.

Although coming from Upper Permian strata S. australis strikingly resembles the basal single-tooth-rowed captorhinids from the Lower Permian of North America. What distinguishes S. australis from those Lower Permian representatives is the presence of a foramen on the anteriormost portion of the maxillary bone. This foramen opens anterodorsally and thus seems not to be one of the supralabial foramina that commonly line the alveolar margins of maxillary or dentary. Another difference in the skull structure of S. australis to that of other basal captorhinids is the full reduction of the supratemporal bone whose position is occupied by the anterolateral portion of the parietal. Moreover its posterior margin of the skull roof is rather straight or even pointed posteriorly instead of being embayed as seen in other captorhinids.

S. australis seems to be the most derived basal captorhinid and its presence in Upper Permian deposits implies, accompanied with its placement within captorhinid phylogeny, a ghost lineage leading back to the Early Permian for this taxon. A close relationship of S. australis to another southern African captorhinid formerly referred to Protocaptorhinus seems obvious but is as yet not confirmed.

Acrodenta irerhi is a poorly known multiple tooth-rowed captorhinid from terrestrial Upper Permian deposits of central Morocco. Its remains solely include one fragment of upper jaw bone bearing three rows of conical teeth. Because the rocks in which A. irerhi was found have been considerd to be Triassic in age the fossil was originally described as a rhynchocephalian. A. irerhi is the only recognized species of the genus.

Baeotherates fortsillensis is a small multiple-tooth-rowed captorhinid. It is known from one tiny lower jaw fragment coming from the Lower Permian Fort Sill fissure fills of Oklahoma. It is the only recognized species of the genus.

The lower jaw fragment measures only 1.3 cm in length, bears 15 teeth and shows some unique features. The articulation surface of the symphysis (symphysial pad) is enlarged antero-posteriorly and not bipartite. In most captorhinids the symphysial pad is much narrower antero-posteriorly, somewhat sinuous and consists of an upper buttress (usually formed by the dentary) and a lower buttress (usually formed by the splenial). Moreover the Meckelian canal usually contributes to the symphysis in the shape of a horizontal notch that points anteriorly from half the height of the lingual margin of the symphysial pad. In B. fortsillensis both splenial and Meckelian canal are completely excluded from contribution to the symphysial pad. Above all the lateral surface of the dentary is only weakly sculptured.

The single tooth row comprises no caniniform teeth, i.e. there are no teeth in the anterior portion of the jaw that are significantly higher than the more posterior or most anterior teeth. Such caniniforms are widely observed in captorhinids and also in "protorothyridids". The anterior teeth are conical and have recurved tips. The posteriormost teeth are similar to those in Captorhinus aguti and the intermediate teeth are transitional in shape. On the posteriormost portion of the jaw fragment a second tooth row, consisting only of two teeth is present.

Although quite similar to them it is not fully clear whether B. fortsillensis is truly a representative of the captorhinids since it also shows close affinities to the microsaur Cardiocephalus, which occurs in the Fort Sill fissure fills as well but has no multiple tooth rows. For example, in both B. fortsillensis and Cardiocephalus the splenial appears to reach the dorsal dentary-coronoid suture, whereas in Captorhinus it only reaches the ventral edge of the coronoid. Moreover B. fortsillensis shares the expanded symphysial pad of the dentary with Cardiocephalus. However, these structures are subject to intergeneric variation in both microsaurs and captorhinids. Finally, assignment of B. fortsillensis to the family Captorhinide is solely based on the presence of multiple tooth rows, a feature not known from microsaurs.

The small size, accompanied with the less developed sculpturing on the lateral surface of the mandible, suggests immaturity of the specimen. Because the ontogeny of Captorhinus aguti is well documented by hundreds of fossils of juvenile specimens this species can be ruled out. Furthermore the presence of a second tooth row makes it unlikely that B. fortsillensis represents an early developmental stage of C. laticeps or C. magnus. Nevertheless the dentition seen in B. fortsillensis is more similar to that in the members of the genus Captorhinus than to that in more basal captorhinids. If it truly is a captorhinid, B. fortsillensis may represent a taxon close to that genus.