Navajosphenodon sani Simões &amp; Kinney-Broderick &amp; Pierce 2022, gen. et sp. nov.
Creators: name: Simões, Tiago R.
name: Kinney-Broderick, Grace
name: Pierce, Stephanie E.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Sphenodontia
Sphenodontidae
Navajosphenodon
Navajosphenodon sani

description: <i>Navajosphenodon sani</i> gen. et sp. nov. <b>Etymology</b>. Genus epithet comes from a combination of “Navajo,” in honor of the native people from North America that inhabit the Colorado Plateau where the specimens were found, and “sphenodon,” in reference to the modern tuatara <i>Sphenodon punctatus</i>. Species epithet “sani,” meaning “old age” in the Navajo language. <b>Holotype</b>. MNA. V.12442 (previously cataloged as MCZ VP 9016), a fully articulated skeleton, including the skull, mandibles, axial and appendicular skeleton (Fig. 1). <b>Referred materials</b>. MCZ VP 9098, MCZ VP 101562, MCZ VP 9099, MCZ VP 101564, MCZ VP 101575, MCZ VP 9094, MCZ VP 9102, MCZ VP 9103, MCZ VP 101569, MCZ VP 101563, MNA. V.8726(A-F), MNA. V.8727. (2022) 5:195 | https://doi.org/10.1038/s42003-022-03144-y | www.nature.com/commsbio <b>Locality and horizon</b>. “Silty facies” of the Kayenta Formation, Glen Canyon Group—Gold Springs Quarry and Main Quarry, Adeii Eechii Cliffs, Coconino County, Arizona, USA. Sinemurian-Pliensbachian, Early Jurassic26. <b>Diagnosis</b>. Can be distinguished from all other species of sphenodontians by the following combination of features: premaxillae with no posterior maxillary process*; premaxillae with welldeveloped posterodorsal process; jugal with a wide posterodorsal process and a well-developed posteroventral process (contributing to a complete lower temporal bar); absence of a dorsolateral concavity on the surface of the postorbital; squamosal dorsal process bifurcated distally*; quadrate-quadratojugal completely fused; straight posterior margin of the quadrate-quadratojugal complex; presence of pterygoid teeth; presence of arcuate flanges on the pterygoids; dentary symphysial region small and slightly curved medially, premaxillary teeth present as discrete elements; quadrangular tooth bases for the additional tooth series; presence of caniniform successional teeth on the anterior end of the dentary; presence of posteromedially directed flanges on maxillary alternating teeth; presence of a midventral crest throughout the entire vertebral series; penultimate phalanges longer than preceding phalanges*; ungual phalanges tall at their bases. (*) Indicates features exclusively known in <i>N. sani</i> relative to all other sphenodontians. <b>Morphological description and comparisons—skull</b>. The premaxillae are paired (Fig. 2), with the left premaxilla better preserved than its right counterpart and in articulation with the left maxilla (Fig. 3). The nasal process is slightly curved and directed posterodorsally (Fig. 3a), indicating the anterior end of the snout was smoothly curved and was not dorsoventrally deep as in clevosaurids3,27,28. The posterodorsal process of the premaxilla is extremely elongate, reaching posteriorly as far as the apex of the nasal (=facial) process of the maxilla and forming most of the posterior margin of the external nares. In contrast to most sphenodontians and other diapsid reptiles, the premaxillae do not possess a maxillary process distinct from the posterodorsal process extending posteriorly to contact the maxilla (Fig. 2). Instead, the maxilla reaches anteriorly to contact the main body of the premaxilla at the level of the distalmost premaxillary tooth. The left premaxilla has three acrodont teeth preserved in situ and not forming the ventrally expanded dentigerous beak observed in most sphenodontians—a condition more commonly observed in early sphenodontians, such as <i>Gephyrosaurus</i> and <i>Diphydontosaurus</i> 7,29 (and TRS, pers. obs.). Both maxillae are preserved, with the right element split into two (Figs. 2 and 3b). The premaxillary process of the maxilla extends well anteriorly to contact the body of the premaxilla. The nasal process is relatively well-developed and descends anteriorly at a smooth angle towards the anterior extremity of the maxilla. Small mental foramina are observed along the edge of the dentigerous margin. At the base of the nasal process, a relatively larger foramen might represent the anterior superior alveolar foramen. The dentigerous portion of the maxilla extends well posteriorly on the skull to the level of the posterior margin of the orbit. The suborbital process of the maxilla thus forms most of the ventral margin of the orbit (more clearly visible on the right maxilla of MNA.V.12442). The holotype has nine teeth preserved on the right maxilla, with space allowing for at least five additional teeth, whereas the left maxilla has eight preserved teeth. Details on dental morphology, replacement, and ontogeny are further discussed below in the sections for “Dentition” and “Ontogeny of jaws and teeth.” Fragments of the paired nasals are preserved in MNA.V.12442 with the left element lying medially to the nasal process of the left premaxilla, whereas the right nasal bone is preserved medially to the broken apex of the right maxilla (Figs. 2 and 3d). Both are too poorly preserved to recognize how much they contribute to the medial margin of the external nares, but the available data suggests that the nasal process of the premaxilla was the main structure separating the external narial openings. Aventrolateral process of the nasal is present and preserved on the right element. The prefrontals are dorsoventrally deep and form most of the anterior margin of the orbits (Figs. 2 and 3e), as in most sphenodontians, some stem lepidosauromorphs such as <i>Vellbergia</i> 30, and early-diverging squamate lineages (e.g., geckos). Dorsally, the prefrontal has an extensive articulation with the lateral margin of the frontal, reaching as far back as the midpoint of the orbit. Ventrally, the prefrontal contacts the ascending process of the palatine. There is no evidence of a lacrimal bone nor an articulatory facet on the lateral margin of the prefrontal for a lacrimal articulation and thus we consider the lacrimal to be absent, as in most other sphenodontians. The anteroventral margin of the prefrontal is slightly concave and forms a lateral opening for the exit of the lacrimal duct along with the dorsal margin of the maxilla, as observed in <i>Sphenodon</i>. The external surface has no visible sculpturing or a prefrontal crest, although the level of sculpturing may have changed in later ontogenetic stages. One element preserved in between the nasals (dorsally) and the palatal region (ventrally) is interpreted here as the right septomaxilla (Figs. 2 and 3f). It is longer than wider and preserves a large facet that would have accommodated the vomeronasal organ. The left postfrontal is located mostly ventral to the left frontal and separated from the postorbital, indicating it was displaced anteromedially (Fig. 2). The right postfrontal is located between the right postorbital and the right frontal. The postfrontal is tri-radiated with a relatively broad distal process that articulated with the anterior margin of the postorbital, thus providing a small contribution to the posterodorsal margin of the orbit (Figs. 2 and 3g). The jugal is a robust element lying medially adjacent to the suborbital process of the maxilla and contributing to the ventral border of the orbit with the latter (Figs. 2 and 3h, j). The posterodorsal process of the jugal is considerably wide compared to most other diapsids, including other sphenodontians, and it bears along the orbital margin an articulatory facet for articulation with the ventral process of the postorbital (Figs. 2 and 3k). The posteroventral process is extremely well-developed and the right jugal on MNA.V.12442 suggests this process extends posteriorly to the level of the quadrate-quadratojugal, thus forming a complete (or nearly complete) lower temporal bar (Figs. 2 and 3h). As the degree of development of the posteroventral process of the jugal is known to be quite variable throughout postembryonic ontogeny both in early sphenodontians7,27 and squamates with a lower temporal bar31— besides considering the subadult stage of the holotype (see “Ontogeny of jaw and teeth”)—it is expected that most subadult and adults would have had a complete lower temporal bar, although the condition remains unknown in young juveniles and hatchlings. The quadrates and quadratojugals form a single fused quadrate-quadratojugal complex with no suture being visible between both elements (Figs. 2 and 3i), as similarly observed in later ontogenetic stages of the modern <i>Sphenodon</i>. Aquadratojugal fenestra is seemingly present between the quadrate and quadratojugal and the posterior margin of the quadrate is pillarlike and relatively straight, as observed in <i>Sphenodon</i>, instead of forming a posterior emargination as in early evolving sphenodontians—e.g., <i>Gephyrosaurus</i> and <i>Diphydontosaurus</i> (TRS, pers. obs. and refs. 7,29). Medially, the quadrate-quadratojugals have a well-developed anteromedially directed and dorsoventrally deep process to contact the pterygoids. Two condyles are distinct on the ventral margin of the quadrate-quadratojugal and are in close proximity to the glenoid facet of the articular bone in the lower jaw. (2022) 5:195 | https://doi.org/10.1038/s42003-022-03144-y | www.nature.com/commsbio The postorbitals are preserved on both sides of the skull in MNA.V.12442, with the left postorbital nearly completely preserved (apart from a crack dividing its posterior process) and in close contact with the jugal, maxilla, squamosal, and postfrontal (Fig. 2). The postorbitals are triradiate, with slender dorsal and ventral processes, and a much more dorsoventrally deep and elongate posterior process for the contact with the squamosal (Figs. 2 and 3k). The anteromedial margin of the dorsal and ventral processes of the postorbital preserved the articulatory facets for postfrontal and jugal, respectively. The squamosals are preserved on either side of the skull in MNA.V.12442 with the left element in a much better state of preservation (Fig. 2). The squamosals are tetraradiate as in other sphenodontians and many other early evolving diapsid reptiles— e.g., <i>Youngina</i> and <i>Prolacerta</i> (TRS pers. obs.), and differing from the triradiate condition observed in early evolving squamates, such as <i>Megachirella</i> and <i>Huehuecuetzpalli</i> 32,33. The squamosal has a strongly developed dorsal process, which would have contacted the supratemporal process of the parietal, and which is bifurcated distally (Figs. 2 and 3l). The anterior process is dorsoventrally deep, elongate, and bears a deep lateral parabolicshaped articulatory facet for the reception of the posterior process of the postorbital. The anteroventral process is very elongate, being much longer than the posteroventral process, with both processes forming a dorsal cap that is likely to have embraced the quadrate-quadratojugal element as in the modern <i>Sphenodon</i>. The frontals are paired and are well-preserved along the orbital margins, but their anterior and posterior margins are shattered (Figs. 2 and 3m, n). The frontals have greatly elevated anterolateral articulatory facets to receive the prefrontal dorsal process and elongate posteroventrolateral articulatory facets to receive the postfrontal (Figs. 2 and 3o). Both suggest that the frontals contributed little to the dorsal margin of the orbits. On their ventral side, the frontals have weakly developed subolfactory processes. Asmall level of sculpturing is observed on the external surface of the frontals. The parietals are both poorly preserved and in tight articulation with each other (Figs. 2 and 3m). Although the anterior margin of the left parietal is preserved, it was bent dorsally and thus the nature of its contact with the left frontal cannot be determined. The left element suggests the parietals are broad, resembling the condition on <i>Homeosaurus</i> (TRS, pers. obs. and34), but this condition may be the result of compression of the specimen. There is no evidence for a developed sagittal crest, suggesting this feature was either absent or weakly developed in MNA.V.12442. Considering the parietals experience a great degree of ontogenetic change in extant and fossil lepidosaurs31,35,36, we consider that additional specimens with undistorted parietals and from a later ontogenetic stage would be necessary to fully understand the morphology of this element. The posterior margin of the parietals is poorly preserved and the contact with the supraoccipital cannot be determined. (2022) 5:195 | https://doi.org/10.1038/s42003-022-03144-y | www.nature.com/commsbio (2022) 5:195 | https://doi.org/10.1038/s42003-022-03144-y | www.nature.com/commsbio Both palatines are preserved on the ventral side of the skull (Fig. 4), mostly represented by the well-developed single palatine tooth row with teeth of similar size to the anterior teeth in the maxillae and dentaries (Figs. 2 and 4a, b). The palatine has a welldeveloped dorsal process that contacts the prefrontal dorsally, and the maxilla and jugal laterally. Owing to poor preservation, it is not possible to determine if the palatines met at the midline anteriorly, as in most sphenodontians. The pterygoids are mostly preserved on their posterior portion, including the transverse and the quadrate processes (Figs. 2 and 4a, b). The transverse process is broad and contacts the ectopterygoid distally, but it is not possible to tell the degree of development of the transverse pterygoid flanges. Both pterygoids have well-developed arcuate flanges on the midline for the articulation with the basipterygoid processes of the basisphenoid. The quadrate processes are elongate and curved posterolaterally, being located medially to the pterygoid process of the quadratequadratojugal. The body of the pterygoid features small denticles organized in at least one dental row. The ectopterygoid is better preserved on the left side of the skull (Figs. 2a and 4a, b). The element is mostly distorted but seems to have had a broad articulation with the transverse process of the pterygoid and a well-developed posterolateral process. The left epipterygoid is preserved ventral to the left parietal and exiting the skull on the space between the left parietal and left postorbital (Figs. 2 and 4a). It is delicate and rodlike with an expanded base as in most sphenodontians and early diapsids. The first ceratobranchial is preserved on the right side of the skull extending from the main body of the pterygoids to the posterior end of the right surangular (Fig. 2). Very few of the braincase elements are preserved or diagnosable. The most informative component is the basisphenoid, located immediately posterior to the pterygoids and ventrally to the parietals’ posterior margin (Fig. 2). It has welldeveloped basipterygoid processes with distally expanded elliptical articulatory surfaces for the pterygoids (Fig. 4c–f). In ventral view, a short cultriform process extends anteriorly and includes a pair of short trabeculae cranii dorsally. A pair of ventral openings represent the entrance of the internal carotids. In dorsal view, the dorsum sellae is exposed forming the posterior margin of a deep pituitary fossa lying on the well-developed sella turcica. Anteriorly, the abducens canals for the cranial nerve VI are located dorsolaterally to the cultriform process and ventrally to the clinoid processes. Overall, these features are similar to the braincase anatomy of many other lepidosaurs, including terrestrial fully-limbed squamates, with the exception of the ventral location of the openings for the carotids37,38. Asmall portion of the basioccipital is preserved in tight articulation with the posterior margin of the basisphenoid. <b>Mandibles</b>. Smaller specimens (inferred as juveniles, see below) have a relatively lower degree of ossification and are slender relative to the dentaries of MNA.V.12442 (Fig. 5), which in turn, is comparatively slender in relation to the largest specimens (inferred as adults) (see “Ontogeny of jaws and teeth”, below). As in other sphenodontians, the dentaries have a strongly developed and ascending coronoid process, as well as a very elongate posteroventral process extending far posteriorly, to the level of the glenoid in MNA.V.12442 (Fig. 5a). The Meckelian canal is open medially and is relatively shallow. The ventral margin of the dentaries curve inwards and upwards creating a ventral crest that forms the ventral border of the Meckelian canal (Fig. 5b, c). The dentary symphyses are not clearly visible in most specimens, but in the holotype, they are small, nearly straight, and slightly expanded dorsoventrally (Fig. 5c), thus differing from the strongly curved condition in <i>Gephyrosaurus</i> and <i>Diphydontosaurus</i> (TRS, pers. obs. and refs. 7,29). It is possible that the more robustly built mandibles in the larger specimens would bear a differently shaped symphysis, especially a greater degree of dorsoventral elongation as implied by their comparatively deeper dentary. For details on dental morphology see section “Dentition” below. The surangular on the right mandible was displaced ventrally relative to the posteroventral process of the dentary, revealing a deep articulatory face for the latter on its lateral surface and indicating that the surangular extended at least to the level of the coronoid process anteriorly (Fig. 2). The left surangular is preserved in articulation with the other postdentary bones, with only a small portion of it being exposed in medial view. It forms the dorsal margin of the mandibular adductor fossa, and its anterior end ascends dorsally to contribute to the coronoid process (Figs. 2 and 5d). The coronoid is reduced as in most sphenodontians, contributing only to the anteromedial portion of the coronoid process (the rest composed by the dentary and surangular) (Figs. 2 and 5d). The coronoid dorsal process is short and, when in articulation, would not have ascended above the level of the coronoid process of the dentary, thus being mostly hidden in lateral view. An anteromedial and a smaller posterodorsal process are present on the left coronoid, thus contrasting with the condition in <i>Sphenodon</i> in which those are highly reduced or absent. The prearticular is elongate, contributing to the retroarticular process ventrally and extending anteriorly at least to the level of the coronoid bone—a small anterior fragment likely belonging to the prearticular indicates it could have reached the level of the posteriormost dentary tooth (Figs. 2 and 5d). The prearticular forms the ventral margin of the mandibular adductor fossa and contacts the other postdentary elements ventrally, except for the coronoid. The angular is not preserved in the holotype, but it is slightly exposed in lateral view on MCZ VP 101569 (Fig. 6). The articular is not fused to any of the other postdentary bones, forming most of the glenoid surface and retroarticular process. It does not have any discernible processes projecting medially or laterally. The dorsal surface of the glenoid has an elongate central ridge for articulation with the quadrate, which would have enabled propalinal movement of the lower jaw (Fig. 5d). <b>Dentition</b>. Different dental types and their changes throughout ontogeny are discussed below in the section “Ontogeny of jaw and teeth” (Fig. 6). Here we provide additional information pertaining to the individual morphology of distinctive dental types. The premaxillary teeth are only observed in the holotype (Figs. 2 and 3a), and at this stage, the teeth are fully &amp;ldquo
description: Published as part of <i>Simões, Tiago R., Kinney-Broderick, Grace &amp; Pierce, Stephanie E., 2022, An exceptionally preserved Sphenodon-like sphenodontian reveals deep time conservation of the tuatara skeleton and ontogeny, pp. 1-19 in Communications Biology 5 (1)</i> on pages 2-13, DOI: 10.1038/s42003-022-03144-y, http://zenodo.org/record/6346784
description: {"references": ["43. Rieppel, O. The skull in a hatchling of Sphenodon punctatus. J. Herpetol. 26, 80 - 84 (1992)."]}