Hongshanxi xiei, Dong & Wang & Mou & Zhang & Evans, 2019

Dong, Liping, Wang, Yuan, Mou, Lijie, Zhang, Guoze & Evans, Susan E., 2019, A new Jurassic lizard from China, Geodiversitas 41 (16), pp. 623-641: 626-634

publication ID

http://doi.org/ 10.5252/geodiversitas2019v41a16

publication LSID

lsid:zoobank.org:pub:urn:lsid:zoobank.org:pub:D6AEA459-651C-4E73-AA82-89739193D783

DOI

http://doi.org/10.5281/zenodo.3703493

persistent identifier

http://treatment.plazi.org/id/838578B0-E550-4498-B541-6612FBA25A6C

taxon LSID

lsid:zoobank.org:act:838578B0-E550-4498-B541-6612FBA25A6C

treatment provided by

Valdenar

scientific name

Hongshanxi xiei
status

n. sp.

Hongshanxi xiei   n. sp.

( Figs 1-7 View FIG View FIG View FIG View FIG View FIG View FIG View FIG )

urn:lsid:zoobank.org:act:838578B0-E550-4498-B541-6612FBA25A6C

TYPE SPECIMEN. — Jianping County Museum , HS-0001 ( Fig. 2 View FIG ), the part and counterpart of a small block bearing a complete lizard specimen.  

TYPE LOCALITY AND HORIZON. — Guancaishan (41°24.373’N, 119°26.995’E), 1.2 km northeast of Muyingzi Village, Shahai Town, Jianping County, Liaoning Province; Tiaojishan (Lanqi) Formation; Oxfordian, Jurassic.

ETYMOLOGY. — The species name honours Mr. Xie Jingguo who recovered the fossil.

DIAGNOSIS. — Small-bodied lizard characterized by the following unique combination of features that distinguishes it from all known Mesozoic taxa: elongate fused frontal with trifurcate posterior border that clasps anterior and lateral margins of the parietal; short parietal; nasals fused at least posteriorly; robust jugal meets prefrontal and excludes maxilla from orbital margin; jugal contacts squamosal in upper temporal bar to exclude postorbital from lower temporal fenestra; squamosal with strongly hooked posteroventral process; lower temporal fenestra covered by large thin osteoderms of varying size; osteoderms in supraocular scales; no continuous osteoderm covering of skull surface or body; manus longer than humerus+radius; pes longer than femur+tibia.

DESCRIPTION

The holotype specimen of Hongshanxi xiei   n. gen., n. sp. represents a small lizard, preserved in dorsal view, with a snout-pelvis length (SPL) of 55 mm ( Fig.2 View FIG ). Most of the bone is on the main part, but some details of the temporal bones, osteoderms, and pectoral girdle are provided by the counterpart. The individual was skeletally immature at death, as evidenced by the incomplete mineralization of the epiphyses, unfused pelvic elements, the separate olecranon, and the nearly fused astragalocalcaneum, but the well-formed skull sutures and postcranial elements suggest that the animal was probably subadult rather than juvenile.

Skull

The skull is 15 mm in length and is relatively well-preserved, with most detail on the main block ( Fig. 3A View FIG ) and some on the counterpart ( Fig. 3B View FIG ). None of the skull bones bears any trace of ornamentation. The external nares are large and dorsoventrally deep. The orbits are also large and ovoid. They appear to be partially covered by thin osteoderms that probably lay below the supraocular scales. The upper temporal fenestra is narrow and rather small. The lower temporal fenestra is larger and, like the orbit, appears to be covered by a mosaic of large thin osteodermal plates. However, there is no indication that the rest of the skull was covered in this way.

Nasal. Each nasal has a slender posterior tab that fits into an anterolateral frontal recess, but anterior to the frontal the nasals meet and appear to fuse in the midline. The nasals seem to taper anteriorly but whether they remain fused anteriorly is unclear as this region is damaged.

Premaxilla. Compression of the skull has pushed the left mandible under the rostrum and through the premaxilla and the anterior part of the nasals ( Fig. 3A View FIG ). As a result, the premaxilla has been broken into two unequal parts. Had the premaxilla been paired, it is likely that the two parts would have separated cleanly under compression, rather than breaking through one of the rami. However, there seem to be two long, slender nasal processes separated from the alveolar plate of the premaxilla(e), as seen more clearly on the CT scan images of the counterpart ( Fig. 7 View FIG ; Appendix 3). Therefore it is possible that the premaxillae were paired in the juvenile and were in the process of fusing from ventral to dorsal. The nasal process is similar in length to the total width of the alveolar plate of the premaxilla. The scan images of the main part block show more of the premaxillary dentition, with at least eight pleurodont tooth positions of similar size to those on the maxilla (Appendix 3). However, due to the damage to the central region of the bone, it is not possible to determine whether a median tooth was present. Bilaterally, the premaxilla bears recessed facets for the maxillae. Based on the scanned images (Appendix 3), the palatal plate of the premaxilla seems to be at least moderately developed and articulated with the medial branch of the maxillary anterior process.

Frontal. In the dorsal midline, the most characteristic element is the large frontal. Although there is a linear groove along the main axis, this does not appear to be a suture as it does not bisect the bone into equal parts and seems to be a combination of a midline groove and both anterior and posterior cracks. The bone is relatively narrow between the orbits and expands anteriorly and posteriorly. The anterior margin appears to be trifurcate, with a broad central triangular process and smaller lateral processes separated by recesses for the nasals. The posterior margin of the frontal is also, unusually, trifurcate. It has a broad median tab and two long lateral processes. These overlap the anterior and anterolateral margins of the parietal, lying within recesses along the lateral edges of the parietal. There is no obvious facet for a postfrontal seen on the frontal, but this may lie ventrolaterally. The CT scan images show that the crista cranii (sub-olfactory processes) are shallow and not fused in the ventral midline.

Parietal. The parietal is thin and is partly obscured by broken pieces of the braincase. Although the left side of the parietal is mostly preserved on the part block and the right side is on the counterpart block, the fact that the bone extends across the midline on the counterpart block suggests that it was originally single. The body of the parietal was short by comparison with the frontal (less than half the frontal length), and there is no obvious parietal foramen. As described above, the parietal has an unusual articulation with the frontal such that the body of the bone enters the margin of the upper temporal fenestra for a limited distance. Moreover, there are impressions of paired parietal tabs on either side of the midline, bracing the fronto-parietal articulation. A portion of the posterior, nuchal, margin of the parietal is preserved on the left side (main block, Fig. 3A View FIG ) and appears shallow and vertical in orientation. The postparietal processes (counterpart block, Fig. 3B View FIG ) are shorter than the body of the bone, tapered at the tip, and posterolaterally directed.

Maxilla. The maxilla is well preserved on both sides of the skull ( Fig. 3A, B View FIG ). It has a short premaxillary process, a large facial process with a horizontal rather than tapering dorsal margin, and a posterior process that extends just short of the mid-length of the orbit. The premaxillary process bears a lateral ramus that tapers to a tip in lateral view and fits into the recess on the corresponding premaxilla. Dorsally, the rectangular facial process overlaps the edge of the nasal; posteriorly it broadly overlaps the prefrontal, and just reaches the anterolateral process of the frontal. The palatal shelf of the maxilla seems well developed. Its anterior part, the medial process of the premaxillary process meets the palatal shelf of the premaxilla and, together with the lateral process, forms a dorsal depression. The teeth are homodont, simple cones with sharp tips. The left maxilla has 16 or 17 tooth positions, of which 12 are filled and another four contain immature replacement teeth; the right maxilla has 17 tooth positions of which 13 are filled and at least three contain small replacements.

Jugal. The left jugal is preserved in lateral view on the main block, the right is seen in medial view on the counterpart. It is a large, laterally compressed, element with a relatively deep suborbital process that sat in a shallow groove on the shallow posterior process of the maxilla, excluding the maxilla from the orbital margin and meeting the prefrontal anteriorly. The postorbital process is slightly wider than the suborbital process and meets it at an oblique angle. The posteroventral border of the postorbital process is thin by comparison with the thickened anterodorsal border. The medial view on the counterpart reveals the presence of a low median ridge. Dorsally, the jugal articulates with the postorbital and has a small contact with the tip of the squamosal. The postorbital bar is thus complete.

Prefrontal. The prefrontal is large and convex. Its anterolateral surface is covered by the facial process of the maxilla, but beneath the maxilla, the prefrontal also has a contact with the nasal. Ventromedially, the prefrontal may have met the tip of the jugal, and/or a lacrimal bone. The frontal process does not extend beyond the mid-orbit. Along the anterior margin of the orbit, the bone develops a weak ridge.

Lacrimal. There seems to be a separate bone between the prefrontal and maxilla on the right side, based on the scan images of the part block (Appendix 3), which might correspond to the lacrimal, and between this bone and the prefrontal is a foramen that we tentatively interpret as a lacrimal foramen.

Postfrontal and Postorbital. The posterodorsal corner of the orbit is difficult to resolve because of the supraocular osteoderms and both palatal and jaw elements that have pushed through from the underside. The postorbital (or possibly postorbitofrontal) is clearest on the counterpart block. It is roughly triangular, with a curved anterior orbital margin (forming roughly 35-40% of the posterior orbital border) and a tapering body that fills the anterior part of the upper temporal fenestra, reaching roughly one third of the length of the squamosal. However, whether the postorbital met the frontal directly or there was an intervening postfrontal is not known. There is a bone fragment between the postorbital and skull roof on the left side of the skull ( Figs 3 View FIG ; 4A View FIG ), but it is not clear whether this is a slender postfrontal, or part of a jaw or palatal element that has been pushed dorsally. The reconstruction ( Fig. 4B View FIG ) therefore shows this region with a dashed line.

Squamosal. The squamosal is preserved on both sides, with the left bone on the main block and the right bone on the counterpart. It has a relatively long tapering anterior body that articulates dorsally with the postorbital and meets the jugal at its tip. The posterior tip has a strong ventral hook that presumably met a pit in the quadrate, and a slight dorsal expansion where the bone probably met the postparietal process of the parietal. A slender bone fragment distal to the (anatomical) left postparietal process ( Figs 3 View FIG ; 4 View FIG ; 7 View FIG ; Appendix 3) may be a supratemporal.

Quadrate. Neither block shows the quadrate clearly, but part of the right bone may be present. The right postorbital and squamosal are mostly preserved on the counterpart, and there is a quadrate-shaped impression with a little of the tympanic crest preserved lateral to the squamosal. In the same position on the part block, the impressions of the postorbital and squamosal are clearly visible and they are associated with a mass of bone that represents fragments of the right quadrate. This mass is located ventral to the postorbital and squamosal, and lateral to the pterygoid quadrate process. Its posterior end (probably the dorsal condyle) is close to the posterior curved end of the squamosal, and the anterior end (probably the ventral condyle) is close to the mandibular condyle. The scan images show that this bone mass bears a narrow anterior end that shows a condylar structure (Appendix 3) and is slightly divided. No further details can be recognized. However, the ‘hockey-stick’ shape of the squamosal provides strong evidence that the quadrate was streptostylic.

Epipterygoid. A slender columnar epipterygoid ( Figs 3 View FIG ; 4A View FIG ), shown more clearly in the CT scan images (Appendix 3), lies parallel to the quadrate process of the right pterygoid and medial to the squamosal.

Palate. The palate is largely obscured in surface view, but some details are revealed by the CT scans. Within the right naris, there is a sub-triangular, laminar bone fragment that, by position, could be the septomaxilla or vomer, but by shape is more likely to be the latter ( Fig. 3 View FIG ). On the part specimen, a short single row of 4-5 small teeth is revealed lying roughly beneath the left naso-maxillary suture ( Fig. 7 View FIG ; Appendix 3), and anterior to the right prefrontal, with a similar but shorter row running roughly parallel to it on the left side. Given their position, these must be palatine teeth and their separation suggests the interpterygoid vacuity probably extended forward between the palatines. The right pterygoid is visible on the surface ( Fig. 3 View FIG ), but is seen more clearly in the scan of the part block ( Fig. 7 View FIG ; Appendix 3). It is Y-shaped, with a lamina between the palatine ramus and the pterygoid flange. The palatal plate is partially obscured within the orbit, but a row of three teeth can be seen on the CT scans, marking the medial edge of the palatine ramus ( Fig. 7 View FIG ). The quadrate process is moderately long, and terminates medial to the quadrate. The left pterygoid is only partially visible (the base of the quadrate process is just visible on the surface), but a J-shaped patch of teeth, in which the medial arm of the ‘J’ is longer than the lateral one, can be seen on the CT scans. In both cases, the pterygoid teeth appear larger than the palatine ones.

The right ectopterygoid articulates with the dorsal surface of the pterygoid flange from anterior to posterior, and then extends almost directly anteriorly to meet the maxilla in the anterior margin of the orbit. The bone also meets the jugal.

Braincase. The braincase was relatively large and was probably originally exposed behind the short parietal table. It is badly crushed and difficult to interpret in surface view, but the CT scan images of the main block ( Fig. 7 View FIG ; Appendix 3) reveal the outlines of the basal elements. The sphenoid bears basipterygoid processes that diverge from one another at an angle of around 60˚. They are of medium length and widen slightly towards their tips. The parasphenoid ( Fig. 3A View FIG ) is slender and tapers to a tip that is preserved posterior to the right posterior process of the frontal, exposed due to the loss of the right half of the parietal. The lateral margins of the basisphenoid are fairly straight and the bone expands smoothly towards the suture with the basioccipital. This is the widest part of the basal plate and bears the basal tubera. Behind this point, the basioccipital narrows posteriorly into the condylar region. As a result the whole plate, in outline, forms a rhomboid with the small basal tubera at the lateral apices of the plate and the tripartite occipital condyle posteriorly. The posterior braincase floor is exposed in dorsal view at the surface ( Figs 3A View FIG ; 4A View FIG ), showing the paired exoccipitals, perforated by hypoglossal foramina, meeting a posteriorly tapering central basioccipital. Little can be discerned of the dorsal braincase components, other than a bone mass to each side of the occipital region that must represent the otic capsules. On the right side, this bone mass extends posterolaterally into what is probably a paroccipital process Lower jaw The left lower jaw lies under the skull and is visible only where it has been pushed through the dorsal surface ( Fig. 3A View FIG ). The right mandible lies adjacent to the right maxilla, but is split between the two blocks ( Fig. 3 View FIG ). As a result, very little detail is visible at the surface, although the CT scans provide further information. The left dentary is shallow and tapers anteriorly, with a straight ventral margin. Labially, the bone is perforated by 7-8 neurovascular foramina of roughly equal size (Appendix 3). Lingually, the subdental ridge is shallow with little evident subdental gutter. The Meckelian fossa is also shallow and the presence or absence of a splenial cannot be determined. The teeth are similar to those on the maxilla, with a pleurodont implantation. The left dentary bears 17 tooth positions of which 12 are filled with mature teeth, and the right dentary (counterpart block) has 16-17 tooth positions, of which 11 are filled. The postdentary bones are preserved on both sides but are damaged. The left coronoid is exposed on the main block and the CT scan images show it as a prominent process with a narrow, slightly posteriorly recurved apex and a plate-like medial surface ( Fig. 7 View FIG ). On the right side of the scan, the surangular and prearticular are visible as outlines culminating at the posterior articular region. The surangular has horizontal dorsal margin and there seems to be a short retroarticular process. Hyoid Long slender ceratobranchial elements are visible on both sides on the surface ( Fig. 3 View FIG ) and in the CT scan images ( Fig. 7 View FIG ; Appendix 3) of the main block. Axial skeleton ( Figs 2 View FIG ; 5 View FIG ; 6 View FIG ) The vertebral column is rather crushed, especially in the cervical region, making an accurate description and count difficult. Most of the vertebrae are preserved in an oblique dorsolateral view ( Fig. 6A View FIG ) in which the neural arch and pedicle lie on the same plane and the centrum is obscured. As far as can be determined, these centra are procoelous but the posterior condyles are small and may be incompletely ossified. The neural spines appear to be little developed. On the main block a small rounded structure immediately posterior to the occiput is likely to be the dens of the axis ( Fig. 3A View FIG ), with the remainder of the atlas and axis within the bone mass posterior to the parietal. A short gap separates these two vertebrae from the main group of cervical vertebrae comprising three vertebrae bearing short ribs and a further two with longer ribs that did not meet the sternum (as indicated by preserved ventral cartilages). This gives a minimum count of seven cervicals. However, the counterpart block bears a partial centrum that fits the gap between the axis and the first rib bearing cervical, making a total of eight cervicals, with the first rib borne on the fourth cervical. The last cervical is followed by a series of anterior dorsal vertebrae, of which at least five preserve cartilaginous extensions that curve inward to meet the cartilaginous sternum, of which most is obscured ( Fig. 5A View FIG ). A further 13 dorsal vertebrae follow the sternal series, giving a dorsal count of 18 and a total presacral count of 26. Following the two sacral vertebrae, 19 caudals are preserved, of which the anterior elements bear long, laterally directed transverse processes ( Fig. 6A View FIG ) that gradually decrease in size and are then lost. The loss of the transverse process coincides roughly with the appearance of the autotomy septum ( Fig. 6B View FIG ), making it difficult to determine the relationship between the transverse process and septum, but the septum appears to be positioned roughly mid-centrum on each vertebra. Following the nineteenth caudal, the tail continues as a cartilage replacement ( Fig. 6B View FIG ) for a length roughly similar to that of the remaining tail. However, the tail is then obscured by matrix so it may originally have been longer. The ribs are single headed and are present as free (i.e. unfused) elements on all dorsal vertebrae. Forelimb and pectoral girdle The scapulocoracoids are split between the two blocks. The scapula is longer than wide and is expanded along its dorsal margin. The coracoid is large, but it is not clear whether either scapula or coracoid is fenestrated. Dorsal to the right scapula, there is a calcified lamina that might be the suprascapula. The interclavicle is obscured, but the clavicles are visible ( Fig. 5A, B View FIG ) as curved blades that gradually widen medially but are not abruptly expanded or fenestrate. A cartilage sternum is present but only the margins are visible to either side of the vertebral column, with two of the anterior sternal ribs in contact. Both forelimbs are present, the left being the better pre- served ( Fig. 5C View FIG ). They are conspicuous in the size of the manus which is longer than the humerus and forelimb combined (humerus 8 mm; radius/ulna 5.8 mm; manus 14.4 mm). The humerus has a thick, untwisted shaft. The proximal head is slightly expanded, but lacks a strong deltopectoral crest (although allowance should be made for the immaturity of the specimen). The proximal epiphysis is ossified (on both sides), but is not fused with the humeral body. The distal head is also unexpanded, and the radial and ulna condyles are not ossified. The radius and ulna are of similar width with no conspicuous features. The proximal and distal epiphyses of the radius were still unmineralized. The ulna olecranon is ossified, but is not attached to the shaft. The carpus is ossified with finished surfaces on the individual elements. However, the bones are crushed together making it difficult to get an accurate description. The radiale and ulnare can be identified, as well as a pisiform. In the distal row, there is a large distal carpal 4 and, apparently, no distal carpal five, but the centralia and medial distal elements are too crushed. The hand has a phalangeal formula of 2:3:4:5:3. The phalanges are all of similar length and the unguals are sharp and slightly curved. The ungual on the first digit is somewhat larger than the others.

.

Hind limb and pelvis

The bones of the pelvis are well-formed but not co-ossified ( Fig. 6A View FIG ). The ilium has a slender blade that appears to have been horizontal or slightly inclined in orientation. There is no anterior tubercle. The pubis is also quite narrow. The blade is directed anteromedially, but more medial than anterior. It tapers towards its distal end, although the tip is hidden below the vertebral column. There is very little development of a pectineal tubercle, just a slight swelling of the anterior margin a little less than half the distance from the acetabulum to the symphysis. The ischium is quadrangular with a small posterior tubercle.

Like the humerus, the femur (13.3 mm) is only slightly expanded proximally and there is no development of the greater trochanter ( Fig. 6A View FIG ). The shaft is of similar width throughout, with a slight curvature towards the distal end. The proximal epiphysis is ossified, and not fused with the shaft, but the distal one is undeveloped. The tibia (9.2 mm) is also robust, with a slight inward curvature. The epiphyses are not ossified making it impossible to determine whether there was a distal notch. The fibula is of similar length and without distinguishing features. The articular surface for the astragalocalcaneum completely covers its distal end. The astragalocalcanum itself is proximodistally short and wide. The astragalus and calcaneum are sutured immov- ably, but the suture line is just visible. The calcaneum has a lateral flange rather than a tuberosity. Tibial and fibular facets are well separated. Distally, there is a large distal tarsal (DT) four and a smaller DT three. The foot is long (24 mm), with phalanges of similar length to one another, although the proximal phalanx of digit 4 is almost as long as the metatarsal of that digit. There is no elongation of the penultimate phalanges and the unguals are sharp and slightly recurved. The angle of the fifth digit indicates that the fifth metatarsal is hooked, but the bones are damaged and do not reveal details of the plantar tubercles. The phalangeal formula is 2:3:4:5:4.

Soft tissue

The body outline is visible as a light stain on the dark surface of the matrix. The outline of the body and limbs is not exceptional, but the tail decreases sharply in diameter at the commencement of the replacement region. Individual scales are visible only in patches, notably on the torso of the counterpart block (square to rhomboid ventral scales) and in the cheek region overlying one of the patches of large osteoderms. Here the scales are seen to be very small and overlapping (dorsal scales).

The body does not have a covering of osteoderms, but there are scattered small patches of white material within the body outline (e.g. Fig. 5A View FIG , small asterisks) suggesting there may have been a diffuse arrangement of mineralizations, perhaps associated with skin tubercles.