Shaanbeikannemeyeria xilougouensis
Creators: name: Sulej, Tomasz
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Kannemeyeriidae
Shaanbeikannemeyeria
Shaanbeikannemeyeria xilougouensis

description: The Laurasian lineage Shaanbeikannemeyeria xilougouensis → Lisowicia bojani
Until the description of the Polish dicynodonts, Placeriao ‘ gigao ’occipitals were the most well-known dicynodont from the Late Triassic of Laurasia. Its diagnostic characters are elongated frontals, parietal triangular in cross-section, and maxillae with long ‘tusks’. They were ignored by earlier researchers and the species was grouped together with the Gondwanan dicynodonts. According to Vega-Dias et al. (2004) they were closely related and may represent a lineage initiated by Stahleckeria poteno (Damiani et al. 2007). King (1988, 1990) distinguished two separate ‘suites’: Placerinii for P. ‘ gigao ’ and Iochigualaotia jenoeni with a thin, tapering snout, and Stahleckerini for Stahleckeria poteno and Zambiaoauruo oubmeroeo (probably juvenile). Keyser and Cruickshank (1979) discussed alternative origins for I. jenoeni from Dinodontooauruo or from Kannemeyeria oimocephaluo. The close relationship of K. oimocephaluo with S. poteno and I. jenoeni was posited by Damiani et al. (2007). In many recent phylogenetic analyses, the South American taxa have been joined together (Griffin and Angielczyk 2019, Sulej and Niedźwiedzki 2019, Kammerer and Ordoñez 2021). Lioosicia and Placeriao are probably not closely related to the Gondwanan ones.
Placeriao ‘ gigao ’comes from the basal Bluewater Creek Formation at the Placerias quarry near St. Johns, Arizona, dated as Adamanian. Placeriao heoternuo is known from the stratigraphically higher Blue Mesa Member of the Petrified Forest Formation from just north-east of Cameron, Arizona (Lucas 1904, 1995, 1998a, Lucas and Hunt 1993, Lucas and Heckert 1996, Heckert and Lucas 2002) of slightly younger age (Heckert 2004). Many new studies have shown that both taxa come from the Blue Mesa Member, which is dated as ~223 to ~218 Mya (Lucas 1993, Martz et al. 2017, Gehrels et al 2020). The localities are 150 km apart, so the different exact ages are possible. These are separate species (Camp and Welles 1956) that have different humeri (contrary to: Lucas and Hunt 1993, Kammerer et al. 2013). The supinator process is more proximal then the entepicondylus in P. ‘ gigao ’ (like in Lioosicia bojani), than in P. heoternuo [compare fig. 5D and 6A in Kammerer et al. (2013)]. The edge above the entepicondylus is straight in P. heoternuo and concave in P. ‘ gigao ’ (similar to Lioosicia bojani, but not so much). The deltopectoral crest is more laterally expanded in P. heoternuo than in P. ‘ gigao ’ (clearly visible in the best preserved specimen of proximal part GPIT-PV-108382).
According to Kammerer (2018), Pentaoauruo goggai from the lower Elliot Formation (probably Norian age) represents the latest surviving Placerinii, but the material is very poor, and similarities to Placeriao are very weak. In some aspects it covered as Placerinii in recent analyses of dicynodont evolution (Kammerer 2018). In fact the most characteristic element is the distal head of the humerus, which is very different than in Lioosicia, and Placeriao ‘ gigao ’. Any humerus of Jachaleria is unknown. Only the posterior part of the frontal is elongated like in Lioosicia, but for the most, part of the bone is lacking. If it is true that Pentaoauruo goggai represents the latest surviving Placerinii, it will be evidence that this group is not characteristic only for Laurasia, but more specimens are needed to confirm that.
The age of the youngest member of the lineage, Lioosicia bojani, is close to the Norian/Rhaetian boundary (Sulej and Niedźwiedzki 2019). Its older relative, Woznikella triradiata, originates from the Carnian sediments from Poland and Germany (Schoch 2012, Szczygielski and Sulej 2023).
Evolution of the cranium: Placeriao ‘ gigao ’ and Lioosicia bojani have exceptionally small areas for muscles responsible for adducting the mandible. Moreover, the zygomatic arch to which some of these muscles are attached is very thin and delicate. The snout is very thin, and the grooves for the dentary are poorly developed, which means that the area for tearing food is rather small. These aspects of the skull anatomy are derived and opposite to those of Jachaleria candelarienoio. In some Permian dicynodonts there was a large ridge in the anterior part of the surface for articulation with the quadrate, which was a barrier for the quadrate. It is absent in P. ‘ gigao ’ and L. bojani. This means that the quadrate could drop anteriorly from its normal position when the mandible moved backward. Apparently, the forces acting on the jaw were much smaller than in the case of Permian dicynodonts. It seems that in the evolution of Triassic dicynodonts the shape of the frontal was strictly controlled by selection. Especially the shape of its anterior part and the morphology of the contact with the orbital margin are the most characteristic and useful for understanding the evolution of that group.
In the Laurasian lineage, the anterior part of the skull is elongated. In all species the frontals form a part of the orbital margin. It is most elongated in Placeriao ‘ gigao ’, similar to Lioosicia bojani (Fig. 48). The specimen of the older Woznikella triradiata (Sulej et al. 2011, Szczygielski and Sulej 2023) has the frontal partly preserved, but it shows a long edge forming the orbital margin and an elongation of the anterior part of the frontal is suggested by well-preserved nasals. Even older dicynodonts with a similar frontal are those from the Anisian of Russia: Rhadiodromuo klimovi and the smaller Rabidooauruo criotatuo (Ochev and Shishkin 1989). Rhadiodromuo mariae is known after a complete skull but from a different locality of the same formation. They all have a very long anterior part of the frontal and a very long edge of the frontal forming the orbital margin (which is characteristic for almost all Anisian dicynodonts). Both species of R. mariae have orbits directed strongly dorsally and the frontal elongated anteriorly. Rabidooauruo criotatuo has the frontals with a distinct high posterior process, and its parietals are similar to those of P. ‘ gigao ’. The slightly older Shaanbeikannemeyeria xilougouenoio has frontals elongated anteriorly. The same type of suture between frontals and nasals is present in both species of Rhadiodromuo.
The position of the orbits is correlated with the shape of the postorbital. This bone is oblique posteriorly in Placeriao ‘ gigao ’ and Lioosicia bojani. In these species the orbits are located more posteriorly, and the temporal opening is smaller; it was related with the size of the external adductor muscles. The zygomatic arch morphology is not known in P. ‘ gigao ’ and L. bojani, but preserved fragments of the squamosal suggest that it was directed slightly antero-medially. In P. ‘ gigao ’ the lateral edge of the occipital plate in lateral view is strongly oblique posteriorly (to the horizontal position of the frontal). The adductor muscles were attached to the mandible more posteriorly.
In Placeriao ‘ gigao ’ the occipital condyles are directed ventrally, which means that in the resting position the skull was strongly oblique ventrally (Fig. 50). It is consistent with the shape of the orbits, which are opened antero-dorsally and frontally in an oblique position of the skull.
There is no evidence in the fossil material for the reconstruction of Placeriao ‘ gigao ’ by Camp and Welles (1956: fig. 24), with the dentary much higher than the posterior part of the mandible. Also, in Woznikella triradiata the dentary is relatively long and low. It is more similar to the elongated one of P. ‘ gigao ’, than to any other dicynodont from South America. In Lioosicia the dentary is unknown but the articulation for the dentary on the angular suggests that it was high and with a concave middle edge of the mandible, almost like in Iochigualaotia jenoeni.
Evolution of pootcranial okeleton: The acromion process trend to decrease is apparent in the Laurasian lineage. Woznikella triradiata has a scapula with the acromion process high but short. Placeriao ‘ gigao ’ has an elongated ridge (Camp and Welles 1956: fig. 29) and Lioosicia bojani has the process very small. In both species the base of the scapular blade is relatively narrow. It has a similar shape in L. bojani, but in this species the end of the scapular blade is very wide, probably as a result of the large size of the animal. Probably a decrease in size of the acromion process was convergent in both these long-lasting lineages.
The triceps brachii muscles probably changed their role in the Late Triassic dicynodonts. In the advanced forms like Placeriao ‘ gigao ’, the attachment for these muscles on the scapula is relatively small, and in Lioosicia it is diminutive.
Sinokannemeyeria yingchiaoenoio is the oldest Laurasian form with a single articulation surface on the sternum. This continued to occur in Placeriao ‘ gigao ’ and Lioosicia bojani. The Late Triassic increase in dicynodonts general size was related to a gradual change of the position of the humerus and decrease in size of the acromion process on the scapula (Sulej and Niedźwiedzki 2019). The change in movement of the humerus affected the position of the articulation surface for the coracoid and ribs on the sternum. In both lineages this surface moved posteriorly. In the Laurasian lineage, the sternum of Lioosicia with extremely posteriorly set the articulation and very high ridges represents probably the last stage of evolution.
The underived humerus of Sinokannemeyeria yingchiaoenoio and Kannemeyeria oimocephaluo have rotated distal and proximal heads, whereas in Lioosicia they are almost in the same plane; only the deltoid crest is curved ventrally. This decreasing of the rotation was related to changes in the orientation of the humerus relative to the scapulocoracoid. Ray (2006) stated that the humerus changed its position, and it was related to the change from the lateral orientation of the glenoid to a posterior orientation.
The size of the supinator process seems to have become gradually larger in the sequence: Woznikella triradiata (Szczygielski and Sulej 2023), Placeriao ‘ gigao ’, and Lioosicia bojani. Surprisingly, the humerus of Zambiaoauruo from the Anisian already had a large supinator process similar to that in P. ‘ gigao ’ (Kammerer et al. 2013). In the Gondwanan lineage, dicynodonts and the Chinese Sinokannemeyeria yingchiaoenoio the entepicondyle is large, whereas it is small in P. ‘ gigao ’ and even smaller in L. bojani. Probably also the medial epicondyle became narrower during evolution of the Laurasian lineage. Other postcranial skeletal characters seem to be more variable in the Laurasian dicynodonts. The articulation surface for the ulna on the dorsal side of the humerus is very large in S. yingchiaoenoio and P. ‘ gigao ’ but very small in L. bojani.
In the Laurasian lineage, the number of sacral ribs was probably small from the beginning.In Sinokannemeyeria yingchiaoenoio there were only five, but in most genera it remains unknown. Placeriao ‘ gigao ’ has a rather underived ilium with five sacral ribs (Camp and Welles 1956), although only three areas for articulation are visible. Lioosicia bojani has only four sacral ribs, and the first sacral rib is above the acetabulum.
The North American Eubrachiooauruo brosni probably represents a South American immigrant lineage (Kammerer et al. 2013). Its well-preserved pelvis shows a frontally elongated ilium with a curved lower end, with a ridge on the blade, and its pubis is very small in relation to the ischium. It is also older (Camp and Welles 1956) than Placeriao ‘ gigao ’ but differences in the morphology make an ancestor–descendant relationship unlikely.
The ischium of Lioosicia bojani and Placeriao ‘ gigao ’ are vertically elongated. Placeriao ‘ gigao ’ and L. bojani have their posterior blade a little curved medially. The vertically short ischium of Parakannemeyeria chengi probably represents an underived stage for all three lineages. In Placeriao ‘ gigao ’ specimens, this part of the ischium is broken but in L. bojani its shape suggests such a morphology.
The position of the proximal head of the femur changed during evolution to large in Placeriao ‘ gigao ’ and Lioosicia bojani, which have the proximal head directed dorsally in lateral view, thus the femur had a vertical position while resting.
Evolution of the mode of life: It is a matter of controversy whether dicynodonts were ‘grazers’ or browsers (Cox 1959, Kalandadze and Kurkin 2000, Surkov and Benton 2008, Ordoñez et al. 2019). It seems that the shape of the parietal (especially its medial section), and position of the occipital condyle and the orbits are strongly connected with the disposition of the head and the way of seeing the food. In Placeriao ‘ gigao ’ and Lioosicia bojani the angulation of the base of the braincase suggests that the skull had an oblique orientation with the snout very low above the ground. Also, the occipital condyle is low under the jaw articulation and far from the top of the skull, which is situated more posteriorly than in such dicynodonts as Jachaleria candelarienoio or Stahleckeria poteno.
To keep the head oblique demanded a special position of the orbits, because ‘grazing’ animals need to be aware of predators. This was probably the selection pressure to makes the orbits displaced to the top of the skull in Placeriao ‘ gigao ’ and Lioosicia bojani. While lowering the head the animal saw the surroundings in the horizontal plane. Present-day large herbivorous animals with orbits similarly directed or situated more dorsally are the hippopotamuses, connected with aquatic environments.
However, animals spending much of their life in water often have lighter limb skeletons, which is not the case of Lioosicia.
description: Published as part of Sulej, Tomasz, 2024, Osteology and relationships of the Late Triassic giant dicynodont Lisowicia, pp. 1-56 in Zoological Journal of the Linnean Society 202 (1) on pages 48-50, DOI: 10.1093/zoolinnean/zlae085, http://zenodo.org/record/14339512