A protracted-tailed marine reptile from China gives new insights into the Center Triassic pachypleurosaur radiation

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Systematic paleontology

Sauropterygia Owen, 186048.

Eosauropterygia Rieppel, 19949.

Pachypleurosauroidea Huene, 195649.

Pachypleurosauridae Nopcsa, 192850.

Honghesaurus longicaudalis gen. et sp. nov.

Etymology The genus identify refers to Honghe Prefecture, the place the holotype was positioned; the species epithet is derived from longi plus caudalis (Latin for lengthy tail), referring to its extremely lengthy tail.

Holotype A whole skeleton within the assortment of the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese language Academy of Sciences (IVPP V30380).

Locality and horizon Luxi, Honghe, Yunnan, China; Second (Higher) Member of Guanling Formation, Pelsonian (~ 244 Ma), Anisian, Center Triassic.

Analysis A pachypleurosaurid distinguishable from different members of this household by the next autapomorphies: snout longer than postorbital portion of cranium, 47.8% of cranium size; exterior naris longitudinally retracted, 47.7% of orbital size; supratemporal fossa oval, 46.2% of orbital size; about ten tooth in anteriorly pointed premaxilla; two fossae in retroarticular course of; 20 cervical, 29 dorsal, three sacral, and 69 caudal vertebrae; single ossified carpal; and phalangeal formulation 2-3-2-4-1 for manus and 2-3-4-5-2 for pes.

Comparative description The holotype and solely at present identified specimen of Honghesaurus is 47.1 cm in whole size. From its physique measurement, Honghesaurus is in accordance with most of different pachypleurosaurs which might be small-sized with a most whole size hardly ever exceeding 50 cm. Nonetheless, three pachypleurosaurs are notably bigger, i.e., Diandongosaurus cf. acutidentatus35 (88 cm), Neusticosaurus edwardsii (120 cm) and Wumengosaurus delicatomandibularis (~ 130 cm). Generally morphology, essentially the most hanging characteristic of Honghesaurus is its extremely lengthy tail, which measures 117% of the precaudal size (Desk 1). The entire vertebral column consists of 121 vertebrae (Fig. 2; see descriptions under), documenting the biggest quantity identified on this group. The snout is extra anteriorly pointed than most of different pachypleurosaurs (besides Wumengosaurus). As well as, the exterior naris within the snout is unusually retracted (Fig. 3), resembling the circumstances in Wumengosaurus and Qianxisaurus; in contrast, the exterior naris is usually oval-shaped (not retracted) in different pachypleurosaurs.

Desk 1 Measurements (in mm) of the holotype (IVPP V30380) of Honghesaurus longicaudalis gen. et sp. nov.Determine 2figure 2

Honghesaurus longicaudalis gen. et sp. nov., Holotype (IVPP V30380). Photograph (a) and line-drawing (b) of complete specimen. c, cervical vertebra; ca, caudal vertebra; d, dorsal vertebra; s, sacral vertebra.

Determine 3figure 3

Cranium and mandible of Honghesaurus longicaudalis gen. et sp. nov., IVPP V30380. Photograph earlier than (a) and after (b) dusted with ammonium chloride. (c) Line- drawing. (d) Reconstruction in dorsal view. an, angular; ar, articular; at, atlas; ax, axis; c, cervical vertebra; den, dentary; en, exterior naris; eo, exoccipital; f, frontal; j, jugal; m, maxilla; n, nasal; op, opisthotic; p, parietal; pat, proatlas; pm, premaxilla; po, postorbital; pof, postfrontal; prf, prefrontal; pt, pterygoid; q, quadrate; sa, surangular; so, supraoccipital; sq, squamosal; stf, supratemporal fossa.

The snout portion anterior to the orbit is longer than the postorbital portion of the cranium, measuring 47.8% of the cranium size (the premaxillary symphysis to the occipital condyle). The paired premaxillae are almost triangular, and every bears an extended posterodorsal course of that sharply inserts between the anterior elements of nasals and tapers off to a degree on the degree of posterior margin of the exterior naris (Fig. 3). This course of is separated from the frontal by the posterior elements of nasals which meet alongside the median line of the cranium. The nasal, barely longer than the premaxilla, posteriorly contacts the frontal in an interdigitating suture. The maxilla contacts the premaxilla on the anterior margin of the exterior naris and bears a brief anteroventral course of extending under the premaxilla. The massive triangular ascending technique of the maxilla medially inserts between the nasal and the prefrontal. Posteriorly, the maxilla bears a reasonably lengthy posterolateral course of underling the anterior two-thirds of the jugal. The size of the retracted exterior naris is 47.7% of the orbital size, being a few quarter of the snout size. The lateral border of the naris is outlined by the maxilla, and its medial border primarily by the nasal with little contribution by the premaxilla. This situation is in any other case current in Qianxisaurus; in different pachypleurosauroids, nonetheless, the premaxilla contributes significantly to the medial border of the exterior naris.

The paired frontals every has a comparatively slender and elongate most important physique with a big posterolateral wing inserting into the parietal posteriorly. The lateral margin of the frontal contacts the crescent-shaped prefrontal anteriorly and the almost triangular postfrontal posteriorly, and contributes to a small a part of the medial border of the big and oval orbit (measuring 26.6% of the cranium size). The postfrontal tapers anteriorly and ventrally, and bears a notch in its posterior margin receiving the dorsal technique of the triradiate postorbital. The descending technique of the postorbital kinds the ventral a part of the posterior border of the orbit, and its posterior course of sharply inserts the squamosal and contributes to the lateral border of the almost oval supratemporal fenestra (measuring 46.2% of the orbital size). The jugal is open L-shaped, and kinds the lateral border of the orbit. Posteriorly, the bone extends past the ventral margin of the postorbital and would attain the anterior course of the squamosal (Fig. 3). A separate lacrimal is absent, as generally in different sauropterygians.

The paired parietals are pretty huge. The center portion of the parietal is concave laterally, defining the medial border of the supratemporal fenestra. Anteriorly, the parietal contacts the frontal in a zig-gag suture and the postfrontal in a virtually straight suture. Posteriorly, the bone kinds a barely concave occipital edge, and bears an extended posterolateral course of that contacts the posteromedial extension of the squamosal laterally. The median pineal foramen between parietals is comparatively giant and oval, positioned barely anterior to the extent of the parietal heart, just like the circumstances in Qianxisaurus and European pachypleurosaurs (e.g., Neusticosaurus, Serpianosaurus and Odoiporosaurus). The comparatively broad supraoccipital kinds the posterior roof of the braincase. It’s considerably heart-shaped in dorsal view, missing a median ridge. Different seen components of the braincase embody the paroccipital portion of the opisthotic-exoccipital advanced, however the full form of this advanced remains to be unknown.

The squamosal is giant, bearing lengthy medial and anterior processes and a brief descending course of. The medial course of kinds the primary a part of the posterior border of the temporal fossa and inserts into the parietal. The anterior course of sutures the postorbital, and along with it, kinds the bar between the supratemporal fossa and the ventrally open infratemporal fenestra. The descending course of is brief and triangular, effectively separated from the condyle of the quadrate. This resembles the situation in Wumengosaurus. In different pachypleurosaurids, nonetheless, the descending technique of the squamosal extends additional ventrally, and almost reaches the condyle of the quadrate. The left quadrate is effectively uncovered in lateral view with its dorsal course of extending beneath the bottom of the descending technique of the squamosal (Fig. 3). The posterior margin of the quadrate is excavated. Moreover a robust mandibular condyle, the quadrate has a posteriorly projecting head, which kinds the bottom of the posterior quadrate notch. An identical situation can be current in European pachypleurosaurids (e.g., Pachypleurosaurus and Serpianosaurus). No distinct quadratojugal is discernable related to the quadrate.

The dentary is lengthy and wedge-shaped, extending posteriorly to the posterior margin of the orbit. The posteroventral margin of the dentary is distinctly notch which might accommodate the anterior tip of the angular (not absolutely uncovered; Fig. 3). Laterally, the dentary bears a longitudinal groove parallel to the oral margin of the bone. The surangular is barely a couple of third of the entire size of the mandible. The bone tapers anteriorly and overlies the elongate angular and the posterior technique of the dentary. Posteriorly, the surangular kinds the lateral wall of the articular fossa for the quadrate and abuts towards the stout articular. The retroarticular technique of the articular is comparatively brief, ending in a rounded posterior margin. The dorsal floor of the method has two giant fossae, separated by a low and longitudinal ridge; the lateral fossa is deeper than the medial one (Fig. 3). Against this, a longitudinal ridge is current on the dorsal surfaces of the retroarticular processes in Wumengosaurus, Qianxisaurus and Dawazisaurus, and a single fossa or trough in different pachypleurosaurs.

There are eight tooth preserved in every premaxilla. Contemplating two apparent gaps for lacking tooth, the whole quantity can be ten. 12 tooth are discernable in left maxilla, and 5 or 6 tooth are lacking (Fig. 3). The tooth quantity within the dentary is tough to estimate as a consequence of occlusion of jaws. The tooth are homodont with a tall peduncle and a brief, conical crown. The lateral floor of the crown is sort of clean.

The vertebral column consists of 121 vertebrae, together with 20 cervical, 29 dorsal, three sacral, and 69 caudal vertebrae (Figs. 2, 4). The proatlas is small and triangular, and the atlas is offered by a pair of bigger, trapezoid neural arches. The axis has a neural backbone 1.3 occasions longer than that within the third cervical (Fig. 3). The cervicals present pachyostotic neural arches with a low neural backbone. Some cervical ribs are discernable within the left facet and their lengths enhance posteriorly. The 21th vertebra is taken into account as the primary dorsal vertebra as a result of its rib is for much longer than that of the final cervical rib (Fig. 4a). The dorsal ribs bow posteromedially and present distinct pachyostosis in posterior ones. The sacral ribs are comparatively brief and stout with the final being the longest. 5 pairs of caudal ribs are current (Fig. 4c), just like these in Wumengosaurus (three to 5 pairs) in quantity; in contrast, different pachypleurosauroids usually have seven or extra pairs of caudal ribs. The primary haemapophysis happens within the fifth caudal, and the chevron bones proceed as much as the 23th caudal.

Determine 4figure 4

Girdles, limbs and vertebrae of Honghesaurus longicaudalis gen. et sp. nov., IVPP V30380. Photograph (a) and line-drawing (b) of pectoral girdle, forelimbs and anterior dorsal vertebrae. Photograph (c) and line-drawing (d) of pelvic girdle, hind limbs and posterior vertebrae. as, astragalus; ca, caudal vertebra; cal, calcaneum; automotive, caudal rib; cl, clavicle; co, coracoid; d, dorsal vertebra; ecr, ectepicondylar ridge; fe, femur; fi, fibula; h, humerus; il, ilium; is, ischium; mc, metacarpal; mt, metatarsal; pu, pubis; ra, radius; s, sacral vertebra; sc, scapula; sr, sacral rib; ti, tibia; ul, ulna; uln, ulnare.

The uncovered portion of the clavicle is broad and blade-like. It tapers posterolaterally and lacks an anterolaterally expanded nook (Fig. 4a). The interclavicle is unexposed. The scapula consists of a flat ventral portion and a comparatively slender dorsal wing. The width of the dorsal wing varies little by means of its size. The humerus is bowed posteromedially. The deltopectoral crest is hardly differentiated. A low ectepicondylar ridge is clearly current, and an entepicondylar foramen is absent within the expanded distal portion of the bone (Fig. 4a). The radius, barely longer than the ulna (Desk 1), is extra expanded proximally than distally. The ulna is straight with a barely constricted shaft. In every forelimb, there’s a single, small and rounded carpal ossification, which doubtless represents the ulnare deduced from its form. The intermedium might be unossified. Amongst 5 metacarpals, Metacarpal I is the shortest with an expanded proximal finish; Metacarpal II is longer than Metacarpal V however barely shorter than Metacarpal IV (Desk 1). The phalangeal formulation is 2-3-2-4-1 for the manus.

Within the pelvic girdle, solely the iliums are effectively uncovered, and they’re roughly trapezoidal with a dorsal course of (Fig. 4c). The plate-like pubes and ischiums are partially coated by the ribs and vertebrae, and no important particulars are seen. The femur is barely longer than the humerus with the proximal finish barely extra expanded than the distal finish (Fig. 4c). The tibia and fibula are almost equal in size. The tibia is straight, thicker than the marginally curved fibula. Two ossified tarsals, calcaneum and astragalus, are rounded; the previous is tiny and the latter considerably bigger. All metatarsals are effectively preserved, and the relative lengths between them present an analogous sample in metacarpals (Desk 1). The phalangeal rely is 2-3-4-5-2 for the pes.

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