Yuxisaurus kopchicki Yao &amp; Barrett &amp; Yang &amp; Xu &amp; Bi 2022, gen. et sp. nov.
Creators: name: Yao, Xi
name: Barrett, Paul M
name: Yang, Lei
name: Xu, Xing
name: Bi, Shundong
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Ornithischia
Yuxisaurus
Yuxisaurus kopchicki

description: <i>Yuxisaurus kopchicki</i> gen. et sp. nov. urn:lsid:zoobank.org:pub:6C8204FE-1A51-4E7D-B9B5-BE9939460D6E Holotype CVEB (Centre for Vertebrate Evolutionary Biology, Yunnan University) 21,701 a partial skeleton with cranial and associated postcranial elements (<i>Figure 2</i>), including: the right-hand side of the skull (fused maxilla, lacrimal, nasal, prefrontal, jugal, and supraorbitals); braincase; partial skull roof; posterior parts of the hemimandibles; four articulated cervical vertebrae; five dorsal vertebrae; left proximal and right distal scapulae; right humerus; left distal femur; more than 120 osteoderms; and several unidentifiable elements. Etymology The generic name refers to the type locality in Yuxi Prefecture, with the suffix -saurus from the Greek, meaning reptile. The specific name is after Dr. John J. Kopchick in recognition of his contributions to biology and the IUP Science Building. Horizon and locality Upper part of the Fengjiahe Formation, near Jiaojiadian village, Yimen County, Yuxi Prefecture, Yunnan Province, China; late Sinemurian – Toarcian (<i>Huang et al., 2005</i>; <i>Figure 1C</i>). Diagnosis A medium-sized armored dinosaur that can be distinguished from all other thyreophorans by the following autapomorphies: deep, subtriangular, dorsoventrally elongated depression on either side of the nuchal crest; a ‘V’-shaped notch on the dorsal margin of the paroccipital process; basal tubera that are considerably ventrally offset with respect to the occipital condyle, so that they are clearly visible in posterior view; basipterygoid processes that are ventrally offset with respect to the basal tubera, creating a dorsoventrally deep, ‘stepped’ basicranial profile in lateral view; cultriform process ventrally offset with respect to the occipital condyle in lateral view; angular with elongate, dorsally deflected posterior process that almost reaches the posterior margin of the retroarticular process; atlas intercentrum with symmetrical anterolaterally directed low ridges and associated arrow-like depressions on its ventral surface; relatively short anterior cervical centra (length/height ratio&lt;1.5); cervical centra lack ventral keels; border of the medial condyle of the distal femur invaginated to form a broad, ‘U’-shaped trough. In addition, <i>Yuxisaurus</i> can be distinguished from other early thyreophorans using the following combination of character states: antorbital fossa subtriangular in outline, unlike that of <i>Scelidosaurus</i>, and with rounded corners, unlike that in <i>Scutellosaurus</i>; anterior ramus of the jugal projects posteroventrally, rather than horizontally as in <i>Emausaurus</i>, <i>Scelidosaurus,</i> and <i>Scutellosaurus</i>; maxillary tooth row bowed medially to a greater degree than in <i>Emausaurus</i>, <i>Scelidosaurus,</i> or <i>Scutellosaurus</i>; maxillary tooth crowns bearing well-defined ridges, which are absent in <i>Emausaurus</i>, <i>Scelidosaurus,</i> and <i>Scutellosaurus</i>; a relatively short axial neural spine with a sinuous dorsal margin in lateral view, contrasting with the straight margin and significant posterior expansion of the neural spine present in <i>Scelidosaurus</i>; elongate axial rib, which extends to the midpoint of cervical vertebra 3, unlike the shorter rib present in <i>Scelidosaurus</i>; absence of lateral ridge on the axial rib, which is present in <i>Scelidosaurus</i>; proximal and distal expansions of the humerus relatively larger than in <i>Scelidosaurus</i> and <i>Scutellosaurus</i>; deep notch separating the humeral head and dorsal margin of the internal tuberosity, which is absent in <i>Scelidosaurus</i> and <i>Scutellosaurus</i>; and broad, ‘U’-shaped fossa on anterior surface of distal humerus, contrasting with the narrow, ‘V’-shaped fossae in <i>Scelidosaurus</i> and <i>Scutellosaurus</i>. Remarks The other thyreophoran taxa named from the Early Jurassic of China (‘ <i>Bienosaurus</i> ’ and ‘ <i>Tatisaurus</i> ’) are based on undiagnostic material (<i>Norman et al., 2007</i>; <i>Raven et al., 2019</i>) and have limited anatomical overlap with <i>Yuxisaurus</i>. Consequently, it is not possible to make meaningful comparisons between them and no shared features can be identified. As a result, additional specimens will be required to establish whether these three named taxa are synonymous or if multiple thyreophoran taxa were present in the Early Jurassic of China. Description and comparisons General comments The cranial bones are highly fused and the neurocentral sutures of all preserved cervical and dorsal vertebrae are invisible, in particular the completely obliterated axial neurocentral suture, suggesting that this specimen might represent an adult individual (<i>Brochu, 1996</i>). Compared to other closelyrelated taxa, the skull of <i>Yuxisaurus kopchicki</i> is larger than those of <i>S. lawleri</i> (<i>Breeden and Rowe, 2020</i>; <i>Breeden et al., 2021</i>), <i>E. ernsti</i> (<i>Haubold, 1990</i>), and <i>S. harrisonii</i> (Natural History Museum, London [NHMUK] PV R1111; <i>Norman, 2020c</i>), and <i>Y. kopchicki</i> has much more robust fore- and hindlimbs than the latter. Skull and mandible The skull includes a braincase, part of the skull roof, the co-ossified right side of the facial region (including the maxilla, anterior and mesosupraorbitals, lacrimal, prefrontal, jugal, and probable nasal), and the posterior parts of both hemimandibles (<i>Figure 2</i>, <i>Figure 3</i>, <i>Figure 4</i>, <i>Figure 5</i>, <i>Figure 6</i>, <i>Figure 7</i>). Maxilla In lateral view, the right maxilla appears to be fused completely with the jugal posteriorly, the lacrimal posterodorsally, and the nasal medially, with few identifiable sutures. Its anterior part is broken. An anteroposteriorly elongated antorbital fossa excavates its lateral surface deeply. The antorbital fossa is rounded and subtriangular in outline with long anterodorsal and ventral margins and a short posterodorsal margin (<i>Figure 3A</i>). The fossa reaches a maximum length of 48 mm and is 20 mm in height at its apex. Most of the antorbital fossa is closed medially by an extensive, sheet-like medial lamina, but a small, oval antorbital fenestra pierces its posteroventral corner (<i>Figure 3A</i>). This region differs from that of <i>Scelidosaurus</i>, which has a relatively smaller antorbital fossa with a dorsoventrally narrow, elliptical outline (NHMUK PV R1111; <i>Norman, 2020c</i>), but is very similar to that of <i>Emausaurus</i> (<i>Haubold, 1990</i>). It differs from those of <i>Lesothosaurus</i> (e.g., NHMUK PV RU B17; <i>Porro et al., 2015</i>), <i>Scutellosaurus</i> (<i>Breeden and Rowe, 2020</i>), and <i>Huayangosaurus</i> (<i>Sereno and Dong, 1992</i>) in having a fossa with smooth, rounded corners, in contrast to the sharp, angular corners seen in the latter taxa. <i>Yuxisaurus</i> also appears to lack the anterior antorbital foramen present in <i>Scelidosaurus</i> (<i>Norman, 2020c</i>), but this area is still encased in matrix. Ventral to the antorbital fossa is the medially inset buccal emargination, which is approximately 30-mm tall along most of its length except where the alveolar margin curves dorsally at its posterior end (<i>Figure 3A</i>). The buccal emargination is generally smooth and mildly depressed and contains several, small irregularly placed shallow depressions that might have been caused by weathering. The dorsal boundary of the buccal emargination is formed by a distinct, rounded ridge. Dorsal to this ridge, most of the lateral surface of the right maxilla is slightly convex, although the part anterior to the antorbital fossa is flat. The alveolar margin is scalloped in lateral view. In medial view, a series of small rounded replacement foramina, which correspond one-to-one with the alveolar sockets, lies immediately above the alveolar margin (<i>Figure 3B</i>). The rest of the surface dorsal to the alveolar margin is smoothly convex, producing a vertical flange that extends dorsally for a short distance. The dorsal margin of this flange bears a shallow horizontal trough, which curves laterally anteriorly as well as posteriorly to communicate with the antorbital fenestra. It then continues posteroventrally for 21 mm (<i>Figure 3B</i>). The dorsal boundary of the flange is straight and oblique anteriorly, but curves downward posteriorly. Another groove starting halfway along the above-mentioned trough extends posteriorly and expands into an elongated deep sulcus (<i>Figure 3B and C</i>). This groove probably represents the articular contact between the maxilla and the lacrimal/jugal. The bone sandwiched between these two grooves has a dorsal concavity terminating posteriorly in a blunt process, which grades into the deep fossa mentioned above. The antorbital fenestra is a rounded opening in medial view. The medial (lacrimal) lamina of the right maxilla is concealed medially by the anterior (medial) process of the lacrimal. The articulation between the lacrimal and maxilla is clear anteriorly but indistinguishable posteriorly. The posterior part of the medial surface dorsal to the tooth row is sculptured, probably indicating the contact surface with the palatine. In ventral view, the alveolar border is bowed medially and the deflection angle between the anterior and posterior axes of the tooth row is approximately 148° (<i>Figure 3D</i>). The curvature in <i>Yuxisaurus</i> is not as extreme as that present in many ankylosaurians where the tooth row is strongly bowed (<i>Vickaryous and Russell, 2003</i>), but is greater than that in <i>Scelidosaurus</i>, <i>Emausaurus</i>, <i>Scutellosaurus,</i> and stegosaurians in which the maxillary tooth row is almost straight and only slightly curved (<i>Colbert, 1981</i>; <i>Haubold, 1990</i>; <i>Sereno and Dong, 1992</i>; <i>Galton, 2004</i>; <i>Breeden and Rowe, 2020</i>; <i>Norman, 2020c</i>; <i>Breeden et al., 2021</i>). Based on the number of alveoli present (<i>Figure 3D</i>), <i>Yuxisaurus</i> possessed at least 14 maxillary teeth. Lacrimal The lacrimal lacks any discernible sutures with the surrounding bones except medially (part of its junction with the maxilla; see above) and with the anterior supraorbital (= palpebral) (where a curved groove might mark the boundary) (<i>Figure 3A–C</i>). Based on comparisons with other thyreophorans, the lacrimal is inferred to comprise the anterior margin of the orbit and to contact the maxilla anteriorly and ventrally, the jugal posteroventrally, and the anterior supraorbital and prefrontal dorsally and posteriorly. The lateral surface of the lacrimal is sculptured and rugose, particularly in the region of the orbital margin. Its posterior surface (i.e., the anterior margin of the orbit) is concave and rounded in lateral view. In the border of the orbit, a rounded opening is present, indicating the exit of the nasolacrimal duct. The posterior margin of the lacrimal expands medially, to form a partition that separates the orbit from the nasal cavity anteriorly (<i>Figure 3B</i>). In medial view, this wall becomes thinner as it curves dorsally and slightly posteriorly to approach the prefrontal. The maxillary ramus of the lacrimal is an anteriorly trending triangular lamina that is concave in medial view, tapering at its anterior end. Due to the absence of recognizable sutures, it is not possible to determine the extent of the lacrimal’s contribution to the antorbital fossa and fenestra. Nasal A small fragment of bone anterior to the right prefrontal might represent part of the right nasal (<i>Figure 3A–C</i>). However, it cannot be identified with confidence and offers no useful information. Prefrontal The right prefrontal roofs the nasal cavity dorsally (<i>Figure 3A</i>) and is flat ventrally but slightly domed in dorsal view (<i>Figure 3C</i>). It contacts the mesosupraorbital laterally and the middle supraorbital posteriorly. The prefrontal probably contacts the lacrimal anteriorly but this cannot be substantiated due to lack of a clear suture. A fractured bone anterior to the prefrontal, medial to the maxilla, probably belongs to the right nasal (see above). Supraorbitals The anterior supraorbital (= palpebral of other ornithischians) is represented by its anterior part only, which occupies the upper boundary of the orbit (<i>Figure 3A</i>). The anterior supraorbital is a narrow, elongated bone, which is co-ossified with the lacrimal anteroventrally, the prefrontal anteromedially, and the mesosupraorbital medially. Viewed laterally, the anterior supraorbital curves posterodorsally from the anterodorsal margin of the orbit (<i>Figure 3A</i>). In dorsal view, it has a rounded anterior end to contact the lacrimal, while its contact with the mesosupraorbital is unclear. On the dorsal surface of the anterior supraorbital a distinct ridge extends posterodorsally (<i>Figure 3C</i>). The mesosupraorbital is partly preserved. It bulges dorsally but is concave ventrally and contacts the anterior supraorbital anteriorly through an anterolateral-posteromedial directed suture that turns into a groove dorsally. Jugal The partly preserved right jugal articulates with the maxilla and lacrimal anteriorly. In lateral or medial view, the anterior ramus of the jugal projects posteriorly and slightly ventrally, whereas in dorsal or ventral view it extends posterolaterally (<i>Figure 3A–D</i>). <i>Yuxisaurus</i> differs from <i>Emausaurus</i>, <i>Scutellosaurus,</i> and <i>Scelidosaurus</i>, in which the anterior ramus is oriented horizontally (<i>Haubold, 1990</i>; <i>Breeden and Rowe, 2020</i>; <i>Norman, 2020c</i>; <i>Breeden et al., 2021</i>), but is more similar to several ankylosaurians, such as <i>Pinacosaurus</i>, <i>Gobisaurus</i>, <i>Saichania,</i> and <i>Edmontonia</i>, where the anterior ramus projects posteroventrally (<i>Godefroit et al., 1999</i>; <i>Vickaryous et al., 2001</i>; <i>Vickaryous, 2006</i>; <i>Carpenter et al., 2011</i>). The transverse cross-section of the jugal anterior ramus is rhomboidal but its posterior end is transversely compressed and dorsoventrally expanded. The posteromedial margin is inverted, leaving a dorsoventrally oriented embayment exposed in medial view. Postorbital The postorbital is represented only by the left squamosal process, which formed part of the supratemporal bar. This process is bullet-shaped in dorsal view with a wide anterior end and pointed posterior end (<i>Figure 4A and B</i>). It is rhomboidal in cross-section with a flat dorsal surface that lies lateral and dorsal to the squamosal. The postorbital formed part of the dorsal margin of the infratemporal fenestra, but no other details are visible. Squamosal The right squamosal is broken anteriorly and is slightly displaced medially, while the left squamosal articulates with the squamosal process of the left postorbital (<i>Figures 4A, B, 5A and B</i>). The squamosal is broad posteriorly, tapers anteriorly, and the dorsal surface of its central body is flat (<i>Figures 4B and 5A</i>). Its anterodorsal process is about 35-mm long and extends anteriorly and a little ventromedially, so that in dorsal view this process lies both medial and ventral to the squamosal process of the postorbital. In ventral view, this process is transversely narrow. The left anteroventral process is missing but this feature is preserved on the right side. It is rod-like but truncated anteriorly, and its dorsal part encloses a deep oval sulcus on the lateral surface (<i>Figure 4A and B</i>). The posteromedial process is dorsoventrally tall, merging with the squamosal process of the parietal posteriorly without a discernible suture on the posterior wall of the supratemporal fenestra. In medial view, at the base of the squamosal central body, is a fossa that is much broader on the right side than on the left. In lateral view, a similar but deeper recess is situated at the base of the squamosal central body to receive the quadrate head (<i>Figure 4A and B</i>). Posteriorly a short vertical process of the squamosal abuts the anterior surface of the paroccipital process (<i>Figure 4</i>). Viewed posteriorly, the squamosal is exposed dorsally, but it is positioned only slightly higher than the paroccipital process, as also occurs in <i>Lesothosaurus</i> (<i>Sereno, 1991</i>). By contrast, the squamosal has a much greater exposure in posterior view in <i>Scelidosaurus</i> and ankylosaurians (<i>Vickaryous and Russell, 2003</i>; <i>Norman, 2020c</i>), although the degree of exposure varies among stegosaurs (<i>Gilmore, 1914</i>; <i>Sereno and Dong, 1992</i>). In dorsal view, the squamosal forms most of the medial margin of the large supratemporal fenestra, as well as its posterior corner. Although the boundaries of neither supratemporal fenestra are complete, the preserved portion on the left-hand side of the skull suggests that it had an ovate to subtriangular outline similar to that of <i>Emausaurus</i> (<i>Haubold, 1990</i>) and <i>Scelidosaurus</i> (NHMUK PV R1111; <i>Norman, 2020c</i>). The squamosal also formed the posterodorsal corner of an open infratemporal fenestra (<i>Figure 5A</i>). Quadrate The right quadrate is partially preserved with its ventral-most part missing and the quadrate head displaced from the squamosal recess. In lateral view, the posterior margin of the quadrate is sinuous, being convex in its dorsal part but inflected at a point around one-third of its length so that ventral to this the rest of this margin is shallowly concave (<i>Figure 4B</i>). In posterior view, the proximal quadrate bears a strong, curved crest. Although the ventral part is missing, it seems to curve ventromedially based on the remaining shaft. The pterygoid wing is laminar and extends anteromedially from the middle of the shaft to meet the quadrate ramus of the pterygoid (<i>Figures 4B and 5B</i>). A large oval depression occupies the medial surface of the pterygoid wing, as in <i>Scelidosaurus</i> (<i>Norman, 2020c</i>). Parietal The parietal fuses with its counterpart to form an hourglass-shaped compound bone in dorsal view that bears a prominent sagittal crest (<i>Figure 5A</i>). The parietal fuses fully with the laterosphenoid anteroventrally and the prootic posteroventrally with no traceable boundaries between them. The posterior portion of the right parietal is damaged. The smooth lateral surfaces are concave anteroposteriorly but convex transversely and curve outward to form a short anterolateral process. In lateral view, the parietal extends to a level much higher than the squamosal (<i>Figure 4B</i>), in contrast to <i>Scelidosaurus</i> and stegosaurs in which the parietal is either only slightly elevated or at the same level (<i>Gilmore, 1914</i>; <i>Sereno and Dong, 1992</i>; <i>Norman, 2020c</i>). A deep sulcus is present on the main body of the left parietal close to the junction between the left medial and posterior supratemporal walls (<i>Figure 5A</i>), but this is not visible on the right-hand side, where it is concealed by the displaced squamosal. The parietal forms the medial boundary of the open supratemporal fenestra. Pterygoid The pterygoid is partially preserved on the right side and is situated between the quadrate and the basipterygoid process of the basisphenoid. In posterior view, its quadrate ramus is a fan-shaped lamina that extends laterodorsally to meet the pterygoid wing of the quadrate (<i>Figure 5D</i>). Its ventral margin curls dorsally to form a narrow trough that is visible in posterior view as in <i>Lesothosaurus</i> and <i>Scelidosaurus</i> (<i>Sereno, 1991</i>; <i>Norman, 202</i>
description: Published as part of <i>Yao, Xi, Barrett, Paul M, Yang, Lei, Xu, Xing &amp; Bi, Shundong, 2022, A new early branching armored dinosaur from the Lower Jurassic of southwestern China, pp. 1-37 in eLife 11</i> on pages 4-31, DOI: 10.7554/elife.75248, http://zenodo.org/record/6376855
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