Cryptovaranoides microlanius Whiteside &amp; Chambi-Trowell &amp; Benton 2022, sp. nov.
Creators: name: Whiteside, David I.
name: Chambi-Trowell, Sofía A. V.
name: Benton, Michael J.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Squamata
Cryptovaranoides
Cryptovaranoides microlanius

description: <b> Type species— <i>C. microlanius</i> sp. nov. (by monotypy)</b> Etymology—The genus name <i>Cryptovaranoides</i> is derived from the Greek word crypto, “hidden,” new Latin varan (from Arabic Waran meaning “dragon-lizard”), and the Greek suffix oides meaning “like.” The generic name is thus “hidden, lizard-like” (animal), referring to the fact that this fossil has remained unrecognized in a collection for nearly 70 years and that it was a small lizard-like animal (skull length maximum about 30 mm), living on karst limestone, perhaps hiding in the grykes (crevices). The species name <i>microlanius</i> derives from the Greek “micro” = small and Latin “lanius” meaning butcher. The recurved blade-like teeth demonstrate that the animal was a small efficient predator that could capture and immobilize prey quickly. Holotype — NHMUK PV R36822, a partly articulated anterior skeleton and associated partial skull and lower jaws preserved on and in the red matrix of a small block of conglomeratic limestone. The left mandible and a partial skull (Fig. 1, A and B), including both maxillae and associated bones, are close to the articulated partial skeleton. The left side of the skull comprising the maxilla, prefrontal, jugal, and lacrimal in near-life positions (Fig. 1, B and E) has twisted away from the right side. The partial skeleton (Fig. 1C) includes the right mandible with associated quadrate, jugal, postorbital, otoccipital, basicranial bones, articulated cervical and anterior dorsal vertebrae, as well as pectoral girdle and forelimb elements. Nearby are further articulated dorsal vertebrae, followed by a basioccipital (Figs. 1, A and D, and 7B) from a larger individual of <i>Cryptovaranoides</i>. Bone preservation (Fig. 1, A and E) is superb and detail in the CT scans (Fig. 1, B to D and F) is often excellent, allowing us to identify numerous characters of modern squamates. Referred fossils—Referred isolated bones (all NHMUK PV) are as follows: left maxilla R 36999; right maxilla R 37279; fragment of right maxilla R 37280; left dentary R 37001; fragment of left dentary R 37282; right dentary R 37281; left coronoid R 37273; left frontal R 37274; left quadrate R 37604; braincase R 37377; premaxilla R 37378; sacral vertebrae R 37275; cervical vertebra R 37276; dorsal vertebra R 37277. 1 School of Earth Sciences,University of Bristol,Bristol, BS8 1RJ, UK. 2 Palaeontology Section, Earth Science Department, The Natural History Museum, Cromwell Road, London SW7 5BD,UK. *Corresponding author.Email: mike.benton@bristol.ac.uk Locality and age—Triassic fissure deposit in Carboniferous Limestone, Cromhall Quarry, Tortworth, Gloucestershire, United Kingdom. Age is Rhaetian, probably late Rhaetian (equivalent of Cotham Member, Lilstock Formation), 201.6 to 201.8 Ma (<i>15</i>). Diagnosis—Characterized by the following apomorphies: (i) maxillary and dentary with frequently replaced conical, pleurodont recurved teeth (Figs. 1, A to C, E, and F, 2, C and D, 3, A to G, and 4A) displaying labio-lingually compressed apices (upper part of the crown) and a prominent sharp carina on mesial and distal edges (Fig. 3, F and G). The mesial compressed region is somewhat more pronounced than the distal, and overall cross section of compressed region is oculiform-lanceolate. The mesial region of mid and posterior maxillary teeth develops a pronounced blade-like flange. The lingual surface of the dentary and maxillary teeth has 2 to 10 vertical striae (higher number on younger, smaller unworn teeth), including a few branching striae (observed on dentary teeth), on compressed upper part of crown; (ii) tripartite maxilla (Figs. 1B, 2A, and 3, A to C, and fig. S1, A and F) with high facial process that curves medially encompassing a prominent nasal fossa bordered dorsally with a distinct ridge; also, there are long anterior and posterior processes; (iii) lateral faces of dentary and maxilla are perforated by many foramina (Fig. 3, A and D; <i>c</i> 20+ for the large maxillae) for branches of the mandibular and maxillary nerve (CN 5), respectively, with a range of sizes; about 20% of maxillary foramina have maximum length greater than observable lateral tooth width; mandibular foramina usually form double row anteriorly; (iv) premaxillae fused in larger individuals (Fig. 4, B and C) with four teeth on one premaxilla and three on the other; (v) the fused premaxillae dentition includes a median tooth derived from the premaxilla with the greater number of teeth; (vi) the sphenoid contains a vidian canal (Fig. 5, E and F) that is enclosed as it passes over the basipterygoid processes and an internal carotid foramen that opens into a deep hypophysial fossa (Fig. 5B) bounded posteriorly by the dorsum sellae; (vii) pronounced dorsum sella roofed by a prominent well-developed anteriorly directed crista sellaris that partially covers the fossa (Fig. 5, A and B); (viii) abducens canal present (Fig. 5, E and I); (ix) metotic fissure subdivided with recessus scala tympani developed anteriorly (floored by a prominent occipital recess) bounded posteriorly by the crista tuberalis (Fig. 4, D to H); (x) long thin squamosal with dorsal and posterior processes (Figs. 1B, 2A, and 6, B and C, and fig. S1, A, D, and F), the latter articulated as a “peg-in-socket” with the notch on quadrate; (xi) quadrate with notch for squamosal on lateral side of cephalic condyle (Figs. 1, C and F, and 6, D to F); (xii) jugal: posterior aspect very short and truncated with straight edge; short dorsal process and longer anterior process (Fig. 1F); (xiii) postorbital forms a slender postorbital bar with the dorsal process of the jugal (Figs. 1F, 2A, and 7C, and fig. S1, A and F); (xiv) coronoid is relatively large (Figs. 1E, 2C, and 7, I and J, and fig. S1, B and C); about 20% of lower jaw length and more than 80% of jaw height (measured dorsoventrally from top of coronoid process to ventral base of mandible) in medial view and with a prominent posterior recess, presumably for the bodenaponeurosis; (xv) vomer (Fig. 7A) is in anterior sutural contact with maxilla (Fig. 3C shows vomer facet on the maxilla), separating the vomeronasal opening from the choana; (xvi) ventrally the vomer has two prominent postero-anterior longitudinal toothed ridges that somewhat converge anteriorly (Fig. 7A). Skull The reconstructed skull (Fig. 2, A to E, and fig. S1) is based largely on the holotype, augmented by isolated bones of larger individuals. The holotype is a juvenile, based on its small size (skull length, 14 mm) and unfused cervical neural arches and centra. Isolated bones suggest that an adult skull could be 30 mm long and up to 16 mm wide. The reconstruction started with the palate (Fig. 2D) because we have all elements, with small, conical teeth, on the palatine, on longitudinal ridges of the vomer, and on the pterygoid anterior ramus; teeth are absent from the sphenoid, ectopterygoid, and most of the pterygoid. The proportions of the skull viewed laterally (Fig. 2A) and dorsally (Fig. 2E) follow the ventral view (Fig. 2D), and elements in color, except the frontals and braincase, are based on the three-dimensional (3D) CT scans. These indicate broad skull roof bones and evident streptostyly (Fig. 2A), with a narrow, conch-shaped quadrate, a thin rod-shaped squamosal,andthelowertemporalopeningiswidewithasmall,truncated jugal. The palatal reconstruction (Fig. 2D and fig. S1E) is the most reliable as we have all the bones (but sometimes only the left or right element) from the palate represented in the CT scan images. The palatine, vomer, and anterior ramus of the pterygoid all bear small conical teeth in the anterior and mid-palate. Teeth are absent from the sphenoid and ectopterygoid, and there are no signs of them on the mid- or posterior parts of the pterygoid and its flange. There is a fossa for the base of the epipterygoid on the dorsal surface of the mid-region of the pterygoid (the fossa columellae; fig. S1H), but the CT scan is not distinct enough to ascertain its shape. Therefore, neither do we know the shape of the base of the epipterygoid. There is a possible epipterygoid (labeled “?” in Fig. 1C). However, this is a speculative identification as that element is in two parts, with one part about the right size for an epipterygoid in this skull. If the element was originally a complete unit (rather than from two different bones), then this “epipterygoid” must be some other unidentified bone. The sphenoid forms the larger element of the basicranial region that constitutes a relatively large feature of the skull in ventral view. The other bone is the basioccipital with a maximum width, across the basioccipital tubera, of more than 42% the width between the lateral margins of the quadrate condyles. These proportions are similar to many lizards [calculated from skulls in (<i>16</i>, <i>17</i>)] such as <i>Varanus salvator</i> (overall between 33 and 80% for lizards and usually about 37 to 50% but can reach 80% in, e.g., the skink <i>Typhlosaurus</i>) compared to the smaller proportions found in rhynchocephalians such as <i>Sphenodon</i> (c. 30%), <i>Planocephalosaurus</i> [calculated at c. 27% from (<i>18</i>)], <i>Clevosaurus</i> [calculated at c. 25% from (<i>19</i>)], <i>Diphydontosaurus</i> [calculated at c. 20% from (<i>20</i>)], and <i>Gephyrosaurus</i> [calculated at c. 22% from (<i>21</i>)]. The subtemporal fenestra is relatively large and indicates that the adductor musculature was substantial. The sphenoid is a thin bone, formed from the fused endochondral basisphenoid and the dermal parasphenoid (<i>17</i>); this was difficult to process from the CT scan because it is highly fractured, crushed in many places, with some missing bone, and sediment has filled the interstices. This is almost certainly a consequence, at least in large part, of the juvenility of the animal in life and therefore incomplete ossification. However, with additional close-up photography, the major features are shown in Fig. 5 (A to I). The base of the parasphenoid process lies between the trabeculae cranii (Fig. 5D), which diverge posteriorly forming the floor of the deep hypophysial fossa (Fig. 5, A and B), either side of which is a large foramen for the internal carotid artery (Fig. 5B). The hypophysial fossa is bounded posteriorly by a pronounced dorsum sella, and this is roofed by a prominent well-developed anteriorly directed crista sellaris that partially covers the fossa (Fig. 5, A and B). The sphenoid contains the closed vidian canal with the anterior opening at the base of the basipterygoid process (Fig. 5, E and F). The vidian canal, incorporating the internal carotid artery and the base of the palatine artery, enclosed by the sphenoid as it passes over the basipterygoid process is a squamate apomorphy (<i>22</i>). The position of the posterior opening is more difficult to discern. There is a foramen positioned on the lateral “wings” of the sphenoid (Fig. 5G) somewhat behind the posterior base of the basipterygoid process that may be toward the posterior entry. However, because of repeated fractures and some crushing and missing bone, it is not possible to follow this foramen continuously toward the front of the sphenoid, although there are enclosed foramina in the anterior region of the bone (Fig. 5, H and I). It is possible that the enclosed vidian canal is quite short and the posterior entry may be as suggested in Fig. 5C. The anterior exit of the abducens canal (Fig. 5E) is confirmed from the CT slice across the anterior of the sphenoid (Fig. 5I). The posterior opening of the abducens canal is more problematic to identify but is suggested to be as shown in Fig. 5B. The vomers form a large portion of the palate and are bounded laterally by extensive choanae. We have searched carefully for facets on the posterior side of the premaxillae or the anterior margin of the vomer (Fig. 7A), but they appear to be lacking in the juvenile and an isolated vomer is absent in the larger bones of the collection. The anterior region of the vomer imaged from the CT scan has a small, truncated process positioned medially, which probably formed the connection to the premaxilla. The large, fused premaxillae (Fig. 4, B and C) is important as it is composed of a right bone with four teeth and a left bone with three teeth. The fusion of the two bones results in the most mesial tooth of the right premaxilla forming a median tooth; this is a synapomorphy of modern Squamata. The asymmetry in number of tooth positions of the two premaxillae is also found in the juvenile holotype. Although not discernible on the juvenile holotype, <i>Cryptovaranoides</i> has incisive processes on a larger specimen of the premaxillae (Fig. 4B), and the connection with the vomer was probably ligamentous. An important aspect of the palate is the connection between the maxilla and the vomer in the most anterior region; the vomerine facet, which is ridged, is distinct above the subdental shelf of the maxilla (Fig. 3C), and the CT scan image of the vomer (Fig. 7A) has a clear laterally positioned and matching maxillary facet. The vomer facet on the maxilla demonstrate that the maxilla-vomer connection was strong and not simply a vomeromaxillary overlap. These positions result in a small gap on both lateral sides of vomer where it would have contacted the premaxillae. As there appears to be no palatal posterior process of the premaxillae, which would (in squamates) often border the vomeronasal fenestra on the medial side, we suggest that these small gaps are the external openings of the vomeronasal openings. There is a small emargination and a groove on the lateral side of the vomer at the anterior end, which we suggest is the vomeronasal notch (Figs. 2D and 7A). A vomeronasal opening bordered by the vomer posteromedially and the maxilla laterally is common in extant squamates, but an anterior premaxilla margin is rare. However, just such an arrangement of bones occurs in the amphisbaenians <i>Amphisbaena alba</i>, which has a similarly small external vomeronasal opening, and <i>Diplometopon</i> (<i>23</i>). We can also compare <i>Cryptovaranoides</i> with, for example, <i>Varanus</i> (<i>24</i>, <i>25</i>) where the vomeronasal opening lies anterior to the vomer/maxillary suture and is therefore separate from the choana. No other constriction (which might suggest an alternative position for the vomeronasal fenestra) in the choana is observed in <i>Cryptovaranoides</i>. We have therefore concluded that, like <i>Varanus</i>, <i>Cryptovaranoides</i> was neochoanate. The hypothesized position of the vomeronasal opening is strengthened by the recognition of a right septomaxilla (Fig. 1B) that lies near the separated premaxillae and anterior of the disarticulated vomer and maxilla of the holotype. In life, the septomaxillae lay above and posterior to the external vomeronasal openings. The anterior chamber formed by the septum dividing the ventral space would have housed the Jacobson’s organ for chemoreception. This can be observed in the dorsal reconstruction (Fig. 2E and fig. S1D). We have reconstructed the extent of the nasals (Fig. 2F) based on the facets of the maxillae, indistinct features on the postero-dorsal processes of the premaxillae, and (isolated) frontals. However, the dorsal reconstruction is less certain than the ventral view as CT scan images of the holotype do not show the nasal, frontal, postfrontal, or parietal. The parietal and nasal are shown as single elements analogously to <i>Varanus</i> but may well have been paired to match the frontals. On the basis of the lack of observable anterior nasal facets on the maxilla, we speculate that the anterior part of the olfactory chambers may have been unprotected by the nasal(s) and, if so, presumably would have been covered by thick toughened soft tissue instead. There are isolated frontals (e.g., NHMUK PV R 37274; Fig. 7, F to H), and we are reasonably sure that these are referrable to <i>Cryptovaranoides</i> because the lateral and ventral facets in the anterior and mid-region are complementary to prefrontal facets including those of the long curved posterior process. Also, like the CT scans of the prefrontal, the frontal bone is highly ornamented. The frontal bone (Fig. 7, F to H) has facets for the nasal anteriorly and prefrontal anterolaterally; these extend posteriorly along the lateral side. There are also posterior facets that lie laterally and ventrally for the (presumed) postfrontal [similar to those in <i>Elgaria</i>; figure 1.79 B of (<i>17</i>)] and a small underlap for the parietal posteriorly (Fig. 7H). The olfactory canal running along the ventral anterior half of the frontal is pronounced, but the crista cranii is relatively low as it is in teiids and iguanids (<i>17</i>) but less well developed in comparison to many squamates. The cartilaginous planum supraseptale would have attached to the crista cranii (<i>17</i>). In similar manner to iguanids, there is a median raised area at the end of the olfactory canal but, unlike that group, it is distinctively ridged in <i>Cryptovaranoides</i>. Palpebrals may have been absent or present, but we have no clear evidence either way. The discovery of a good braincase NHMUK PV R 37377 (Fig.4, D to I), albeit missing the mid-region of the fused exoccipitals and some lateral bone, has allowed a reasonable understanding of this region of the skull with the paroccipital processes and the recognition of an otoccipital (fusion of exoccipital and opisthotic). On the right-hand side, the vagus foramen is inferred to lie above two foramina (Fig. 4, F and G) that we identify as hypoglossal foramina, which are positioned on the lower medial region of the broken exoccipital near its contact with the basioccipital. The hypoglossal foramina lie posteriorly to the medial opening of the recessus scala tympani (mrst). The crista tuberalis, which separates the anterior cavity of the metotic fissure (<i>10</i>, <i>17</i>), is present and protects the lateral opening of the recessus scala tympani (lrst; Fig. 4H). There was presumably a lateral vagus opening posterior to the crista tuberalis and anterior to the missing mid-region of the exoccipital, but the fossil provides no evidence. The occipital recess that floors the rst is observed clearly and on the separate basioccipital (Fig. 7B) with the same morphology, confirming that the braincase is from <i>Cryptovaranoides</i>. We confirm that the metotic fissure is divided as in squamates, based on the distinct and separate rst separated by the crista tuberalis (<i>10</i>), the (probable) vagus foramen likely positioned between the mrst and the hypoglossal foramina. Furthermore, where the metotic fissure is undivided as in <i>Sphenodon</i> (<i>17</i>), there is no occipital recess in the basioccipital, nor in basal sphenodontians and rhynchocephalians such as <i>Diphydontosaurus</i> and <i>Gephyrosaurus</i>, but it is pronounced in <i>Cryptovaranoides</i> (Fig. 4, F and I) as in many squamates. This braincase specimen has a partial suture line between the exoccipital part of the otoccipital and the basioccipital (Fig. 4, D and E), but the isolated basioccipital (Fig. 7B) and others in the collection indicate that fusion of the elements was uncommon. Fractures in the fossil (fig. S1D) probably indicate the suture with the supraoccipital. The supraoccipital has an ascending process (Fig. 4D), not extensive but clearly present. There are difficulties in reconstructing the mid- to posterior region of the skull as it is uncertain whether the p
description: Published as part of <i>Whiteside, David I., Chambi-Trowell, Sofía A. V. &amp; Benton, Michael J., 2022, A Triassic crown squamate, pp. 1-18 in Science Advances 8 (48)</i> on pages 1-13, DOI: 10.1126/sciadv.abq8274, http://zenodo.org/record/7401271
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