SVP 2018: Doswellia skull chimaera reconfigured

Wynd, Newbitt and Heckert 2018
“redescribe Doswellia sixmilensis on the basis of extensive repreparation of the skull material to identify cranial elements, morphological details previously not described, and cranial suture patterns. As such, we reinterpret what was previously regarded as the antorbital fenestra to be the orbit and, as a consequence, the identification of bones and the diagnosis of the taxon must be substantially modified.”

Today I learned
the larger rostrum was attributed to a second Doswellia species, D. sixmilenesis. (Heckert et al. 2012). The reconstructions below created a chimaera of the two skulls, and two reconstructions based on the old and new interpretations of the larger rostrum.

Figure 1. Doswellia restored two ways using two species. In this restoration, the pmx ascending process is gracile and missing, along with the anterior naris. The insert shows the vestige of the lateral temporal fenestra. If the large specimen includes an orbit and jugal here is a new reconstruction reflecting that change.

Figure 1. Doswellia restored two ways using two species. In this restoration, the pmx ascending process is gracile and missing, along with the anterior naris. The insert shows the vestige of the lateral temporal fenestra. If the large specimen includes an orbit and jugal here is a new reconstruction reflecting that change.

Either way
the sum of the parts largely match sister taxa (Fig. 2) in the large reptile tree (LRT, 1315 taxa).

Figure 3. Click to enlarge. Updated image of various proterosuchids and their kin. When you see them all together it is easier to appreciated the similarities and slight differences that are gradual accumulations of derived taxa.

Figure 2. Updated image of various proterosuchids and their kin. When you see them all together it is easier to appreciate the similarities and slight differences that are gradual accumulations of derived traits.

The taxon list for the abstract
was not published, but I hope it includes the taxa used in the LRT where Doswellia nests closer to certain proterochampsids than to proterochampsids.

The authors report,
“What is clear, is that D. sixmilensis shares character states with typical proterochampsians (e.g., rimmed orbit) that are not found in D. kaltenbachi.” In the first (earlier) reconstruction (Fig. 1), the orbits were not preserved, except ventrally by the large jugal.

Figure 2. Cladogram of basal archosauriforms. Note the putative basalmost archosauriform, Teyujagua (Pinheiro et al 2016) nests deep within the proterosuchids. The 6047 specimen that Ewer referred to Euparkeria nests as the basalmost euarchosauriform now.

Figure 3. Cladogram of basal archosauriforms. Note the putative basalmost archosauriform, Teyujagua (Pinheiro et al 2016) nests deep within the proterosuchids. The 6047 specimen that Ewer referred to Euparkeria nests as the basalmost euarchosauriform now.

The genus Doswellia
is distinct from all other genera, but trait scores nest it closest to a derived proterosuchid, the SAMPK K10603 specimen (Figs. 1, 2).

References
Dilkes D and Sues H-D 2009. Redescription and phylogenetic relationships of Doswellia kaltenbachi (Diapsida: Archosauriformes) from the Upper Triassic of Virginia. Journal of Vertebrate Paleontology 29(1):58-79
Heckert AB, Lucas SG and Spielmann JA 2012. A new species of the enigmatic archosauromorph Doswellia from the Upper Triassic Bluewater Creek Formation, New Mexico, USA. Palaeontology 55(6):1333–1348.
Weems RE 1980. An unusual newly discovered archosaur from the Upper Triassic of Virginia, U.S.A. Transactions of the American Philosophical Society, New Series 70(7):1-53.
Wynd BM, Nesbitt SJ, Heckert AB 2018. Skull elongation in stem archosaur cranial displarity: Reevaluationg Doswellia sixmilensis (Archosauriformes: Proterochampsia) to examime phylogenetic distribution of morphological disparity. SVP Abstracts.

wiki/Doswellia

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.