 |
| Chaohusaurus brevifemoralis
Huang, Motani, Jiang, Tintori, Rieppel, Zhou, Ren & Zhang, 2019
DOI: 10.7717/peerj.7561
|
Abstract
A new species of ichthyosauriform is recognized based on 20 specimens, including nearly complete skeletons, and named Chaohusaurus brevifemoralis. A part of the specimens was previously identified as Chaohusaurus chaoxianensis and is herein reassigned to the new species. The new species differs from existing species of Chaohusaurus in a suite of features, such as the bifurcation of the caudal peak neural spine and a short femur relative to trunk length. The specimens include both complete and partially disarticulated skulls, allowing rigorous scrutiny of cranial sutures. For example, the squamosal does not participate in the margin of the upper temporal fenestra despite previous interpretations. Also, the frontal unequivocally forms a part of the anterior margin of the upper temporal fenestra, forming the most medial part of the anterior terrace. The skull of the holotype largely retains three-dimensionality with the scleral rings approximately in situ, revealing that the eyeball was uncovered in two different directions, that is, laterally and slightly dorsally through the main part of the orbit, and dorsally through the medial extension of the orbit into the skull roof. This skull construction is likely a basal feature of Ichthyosauromorpha. Phylogenetic analyses place the new species as a sister taxon of Chaohusaurus chaoxianensis.
 |
| Figure 4: Skull of the holotype of Chaohusaurus brevifemoralis sp. nov. (AGB7401). (A) Dorsal view. (B) Lateral and slightly dorsal view. (C) Approximate bone map for (A). (D) Same for (D). See the section “Osteological abbreviations” for abbreviations. Scale bar is one cm in total. |
 |
| Figure 2: Holotype of Chaohusaurus brevifemoralis sp. nov. (AGB7401). (A) Photograph. (B) Approximate bone map. See the section “Osteological abbreviations” for abbreviations. Scale bar is five cm in total. |
Chaohusaurus brevifemoralis sp. nov.
Chensaurus chaoxianensis Motani and You 1998a, in part, Motani et al. 2015c, in part, Zhou et al. 2017, in part
Chaohusaurus geishanensis Motani and You 1998b, in part
Diagnosis. Humeral anterior flange poorly developed, with weakly concave preaxial margin near midshaft; radial antero-proximal flange poorly developed; ulnar distal fan asymmetrical relative to bone axis, due to anterior expansion of distal preaxial margin; femur short for trunk length in comparison to Chaohusaurus chaoxianensis; tibia proximally narrow for trunk length in comparison to Chaohusaurus chaoxianensis; bifurcated neural spine near caudal peak; three tarsal ossifications in most individuals except newborns (Figs. 3 and 7).
Locality. Majiashan, Chaohu, Anhui Province, China.
Horizons. Ammonoid Subcolumbites zone, Spathian, Lower Triassic. Known specimens are from beds 621 to 638 (about 248.53–248.34 Ma) that were previously dated using astrochronology (Fu et al., 2016).
Etymology. The specific name refers to the shortness of the femur relative to the body in comparison to other species.
Conclusions:
The new ichthyosauriform Chaohusaurus brevifemoralis is distinguished from existing species based on a suite of features, including the bifurcation of the neural spines near the caudal peak and short femora relative to the body. These differences are unlikely to be sexual dimorphisms, which are present in the species as an independent suite of characters (Motani et al., 2018). Chaohusaurus brevifemoralis is larger than its sister taxon, Chaohusaurus chaoxianensis, in body size. The two species were sympatric but likely pursued different resources from each other’s.
Jian-Dong Huang, Ryosuke Motani, Da-Yong Jiang, Andrea Tintori, Olivier Rieppel, Min Zhou, Xin-Xin Ren and Rong Zhang. 2019. The New Ichthyosauriform Chaohusaurus brevifemoralis (Reptilia, Ichthyosauromorpha) from Majiashan, Chaohu, Anhui Province, China. PeerJ. 7:e7561. DOI: 10.7717/peerj.7561