What is Romeriscus?
Baird and Carroll (1967) announced the discovery of Romeriscus (YPM-PU16 982, Fig. 1), the oldest known reptile. From their abstract: “The description of Romeriscus, a new genus of limnoscelid reptile, is based on a partial skeleton from the Early Pennsylvanian (Westphalian A) of Nova Scotia. Although it is the earliest and most primitive reptile yet known, it is probably already too late and too specialized to be ancestral to the more advanced Carboniferous and Permian captorhinomorphs and pelycosaurs.”
Laurin and Reisz (1992) considered Romeriscus Tetrapoda incerta sedis and the taxon a nomen dubium. They thought it could be a large microsaur or a primitive lepospondyl, due to spool-shaped centra.
Figure 1. Romeriscus (YPM-PU16 982) in situ. Laurin and Reisz 1992 were not able tl determine the affinities of this specimen other than to say it could not be included in the Amniota or the Limnoscelidae.
Not much detail in earlier reports
Neither Baird and Carroll (1967) nor Laurin and Reisz (1992) were able to glean much detail from the specimen, especially the skull (Fig. 2) and left large areas unidentified. They also disagreed on the identification of certain elements.
Figure 2. Prior illustrations of the skull of Romeriscus along with differeing identifications of elements. A. (left) by Baird and Carroll (1967). B. (right) by Laurin and Reisz (1992). Scale = 1 cm. Neither identified any teeth or other details.
Digitial Graphic Segregation (DGS)
I scanned a printed image of the specimen and colorized elements, then reassembled the elements into a reconstruction. (Figs. 3, 4).
Figure 3. Romeriscus colorized.
Reconstruction and Cladistic Analysis
Identification of the skeletal elements permits phylogenetic analysis. Adding Romeriscus to the large reptile tree nests it with Macroleter and Lanthanosuchus, both considered parareptiles by earlier studies. Here they nest deep within the new Lepidosauromorpha, close to the ancestry of turtles and pre-Lepidosaurs and not far from the limnoscelids, diadectids, millerettids and captorhinids.
Figure 4. Click to enlarge. Romeriscus reconstructed. This specimen has longer toes and more gracile limbs than its closest known kin.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.
References
Baird D and Carroll RL 1967. Romeriscus, the oldest known reptile. Science. 1967 Jul 7;157(3784):56-9.
Laurin M and Reisz RR 1992. A reassessment of the Pennsylvanian tetrapod Romeriscus. Journal of Vertebrate Paleontology 12(4): 524-527.
2012-10-28 17:22:35
Source: http://pterosaurheresies.wordpress.com/2012/10/29/what-is-romeriscus/
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