Mystriosaurus laurillardi Kaup, 1834
|
publication ID |
https://doi.org/ 10.4202/app.00557.2018 |
|
persistent identifier |
https://treatment.plazi.org/id/F030E160-FFDF-FF8D-9D66-4604FE55E1E4 |
|
treatment provided by |
Felipe |
|
scientific name |
Mystriosaurus laurillardi Kaup, 1834 |
| status |
|
Mystriosaurus laurillardi Kaup, 1834
Figs. 1–4 View Fig View Fig View Fig View Fig .
1834 Mystriosaurus laurillardi gen. et sp. nov.; Kaup 1834: p. 28 [not figured].
1876 Steneosaurus brevior sp. nov.; Blake 1876: pl. 1:1, 2.
Holotype: HLMD V946-948 About HLMD , an incomplete cranium and mandible.
Type locality: Altdorf bei Nürnberg, Nürnberger Land district, Bavaria, southern Germany.
Type horizon: Posidonienschiefer Formation, Schwarzjura Group, probably Harpoceras serpentinum Sub-Mediterranean Ammonite Zone , lower Toarcian, Lower Jurassic ( Page 2003; German Stratigraphic Commission 2016).
Emended diagnosis.—Teleosauroid crocodylomorph with the following unique combination of characters (proposed autapomorphic characters indicated by an asterisk): robust skull with well-developed and extensive ornamentation on the premaxillae, maxillae, nasals*, frontal, prefrontal, lacrimal, jugal*,postorbital and squamosal*; frontal ornamentation composed of small sub-circular to elongate pits that are closely spaced or that fuse and become a ridge-groove pattern; mesorostrine snout (preorbital length is approximately 66% of skull length), which is broad near the orbits but narrows and becomes slightly more slender anteriorly; slight constriction of the snout in front of the orbits; large and numerous neurovascular foramina on the premaxillae, maxillae and dentaries (shared with Machimosaurini); external nares oriented anteriorly*; the anterior and anterolateral margins of the premaxilla are orientated anteroventrally and extend ventrally in lateral view (shared with Mycterosuchus nasutus Andrews, 1913 , Platysuchus multiscrobiculatus Berckhemer, 1929 , the Chinese teleosauroid previously referred to as Peipehuschus (see Li 1993), Bathysuchus megarhinus Hulke, 1871 ; Foffa et al. 2019); antorbital fenestrae almost equidistant to the orbits and alveolar margins (shared with P. multiscrobiculatus ); the antorbital fenestrae are large relative to the orbits (anteroposterior length equals 25% of orbital length), being slightly anteroposteriorly elongated and subcircular in shape; supratemporal fossae form an approximate isosceles trapezoid-shape*; anterolateral margin of supratemporal fossae (i.e., lateral processes of the frontal and the dorsal processes of the postorbitals) noticeably inclined anterolaterally (shared with Mycterosuchus nasutus , Platysuchus multiscrobiculatus, Chinese teleosauroid, Bathysuchus megarhinus ); the anterolateral corners of the supratemporal fossae extend significantly lateral to the lateral margin of the orbits (= the anterior region of the supratemporal fenestrae are very wide); medial margin of supratemporal arch is straight, with no significant concavity*; the orbits are subcircular in shape, and are dorsolaterally orientated; postorbital reaches the orbit posteroventral margin (shared with P. multiscrobiculatus, Chinese teleosauroid, B. megarhinus ); short frontal anteromedial process, being noticeably shorter than the prefrontals when seen in dorsal view; ventral border of angular horizontal and poorly curved shared with Steneosaurus gracilirostris Westphal, 1961 ); mandibular fenestra poorly elliptic*; four teeth per premaxilla; large, slightly robust teeth that have numerous conspicuous apicobasally aligned ridges, and a pointed apex, with some anteriorly-placed tooth crowns being procumbent*.
Material.— NHMUK PV OR 14781, an almost complete skull associated with a fragmentary limb bone (holotype of “ Steneosaurus ” brevior ) from Whitby, Yorkshire, UK; Mulgrave Shale Member, Whitby Mudstone Formation, Lias Group, Harpoceras serpentinum Sub-Boreal Ammonite Zone , lower Toarcian, Lower Jurassic ( Blake 1876).
Description.—The holotype of Mystriosaurus laurillardi HLMD V 946-948) is a three-dimensionally preserved skull ( Fig. 1 View Fig ) that measures approximately 650 mm along the dorsal midline. HLMD V946-948 consists of an isolated rostrum and the posterior part of the skull, preserved as a slab and counter-slab. The majority of the skull roof, the occipital part and the rear portion of the mandible are either missing or obscured by matrix. Infillings of the internarial cavities are preserved in the counter-slab. The block with the post-symphyseal mandibular portion has two carved holes, which Kaup in Bronn and Kaup (1841) discussed as Gaumenlöcher (“palatal fenestrae”). The anterior rostrum (premaxillae, maxillae, and dentary) are cemented together.
NHMUK PV OR 14781 comprises a nearly complete cranium and mandible ( Fig. 2 View Fig ) which are adhered together tightly so that the cranium in palatal view and mandible dorsal view are inaccessible. Both the left posterior region and occipital of the cranium are not preserved; in addition, the right posterior portion of the cranium is partially covered with matrix (mainly seen in dorsal view; Fig. 2A 2 View Fig ). In ventral view ( Fig. 2A View Fig 3 View Fig ), the posterior part of the cranium is likewise covered in matrix, and therefore cannot be described at present. In dorsal view, there is a limb bone ( Fig. 2A 2 View Fig ) preserved in the matrix; however, only the shaft is well-preserved, making identification difficult (the anterior part appears to resemble the humeral head found in other teleosauroids, making this bone a possible humerus). All information pertaining to the jugal, prefrontal, lacrimal, frontal, postorbital, squamosal, quadratojugal, and surangular was inferred from NHMUK PV OR 14781.
Cranium: The cranium of NHMUK PV OR 14781 is approximately 595 mm from the anterior tip of the rostrum to the anterior margin of the orbit. The overall appearance of the preorbital skull is mesorostrine and is slightly more robust, shorter, and rugose than those seen in the other Toarcian teleosauroids (e.g., Steneosaurus bollensis, SMNS 51753; S. gracilirostris, NHMUK PV OR 14792; Platysuchus multiscrobiculatus, SMNS 9930). The anterior premaxillae and dentaries are laterally expanded similarly to the condition in other teleosauroids (e.g., Andrews 1909, 1913; Hua 1999; Young et al. 2014; Johnson et al. 2017). The orbits are large, circular and anteroposteriorly oriented ( Fig. 2A View Fig 1 View Fig , A 2 View Fig ), and in dorsal view the partially preserved right supratemporal fenestra is sub-rectangular in shape, with the anteroposterior axis being more than 10% longer than the lateromedial axis. The anterolateral margin of the supratemporal fossae are inclined anterolaterally; the anterolateral corners of the supratemporal fossae extend noticeably more anterior than the anteromedial corners of the supratemporal fossae ( Fig. 2A 2 View Fig ). The medial margin of the supratemporal arch is relatively straight in dorsal view.
Premaxilla: The premaxillae ( Figs. 1–3 View Fig View Fig View Fig ) in both HLMD V946-948 and NHMUK PV OR 14781 are large and dorsoventrally deep. They surround the external narial opening and are oriented anteriorly. The external nares are laterally expanded and their posterior margins do not reach beyond the third premaxillary alveolar pair. In NHMUK PV OR 14781, there is a small premaxillary septum protruding into the nares, giving them a slight B-shape in anterior view ( Fig. 3B View Fig 2 View Fig ). This septum is broken off in HLMD V946-948. The anterior two-thirds of the premaxilla is laterally expanded, anteroposteriorly shortened and the anterior margin is ventrally deflected, giving the snout a scoop-like appearance. In dorsal view, the premaxilla-maxilla suture is slightly interdigitating and rounded. In lateral view, the anterior and anterolateral premaxillary margins are orientated anteroventrally and extend ventrally (which is similar to Platysuchus multiscrobiculatus, SMNS 9930 and differs from Steneosaurus bollensis, RE 551.762.130 A 0248 (see SOM: fig. S1, Supplementary Online Material available at http://app.pan.pl/SOM/app64_3-Sachs_ etal_SOM.pdf). The dentigerous anterior portion of the conjoint premaxillae forms a rosette with undulated margins. A prominent diastema is present that starts after the last premaxillary tooth position and here the premaxillae are transversely constricted ( Figs. 1 View Fig , 2 View Fig ). The posterodorsal portions of the premaxillae together form a prominent tip that terminates at the level of the third maxillary tooth position and separates the maxillae anterodorsally. In both HLMD V946-948 and NHMUK PV OR 14781, the mandible obscures the majority of the ventral view of the premaxillae; however, in both ventral views ( Fig. 3C, D View Fig ), the lateral margins of four alveoli are visible. The first and second alveoli are placed anteriorly, and are nearly confluent. A small, slightly indented gap is present between the first premaxillary tooth and the midline suture, and between the second and third premaxillary teeth, there is an additional, larger gap that is indented in ventral view. The third premaxillary tooth is prominent, more so when compared to the other premaxillary teeth. Between the third and fourth premaxillary teeth there is a prominent concave gap, such as in other teleosauroids (e.g., Steneosaurus leedsi Andrews, 1909 , NHMUK PV R 3806). The last premaxillary tooth is the smallest of the four teeth. Both premaxillae are well ornamented with conspicuous pits and grooves ( Figs. 1 View Fig , 2 View Fig ). Best seen in NHMUK PV OR 14781, there is a cluster of large circular foramina along the anterior and lateral margins of the external nares visible in dorsal, lateral and anterior views ( Figs. 2 View Fig , 3 View Fig ).
Maxilla: The maxillae ( Figs. 1 View Fig , 2 View Fig ) form a substantial part of the rostrum. In HLMD V946-948, the anterior portions of the maxillae are well preserved, but the dorsal midline suture is barely visible. The maxillae are elongate, transversely narrow elements, and anterodorsally separated by the premaxillae ( Figs. 1 View Fig , 2 View Fig , 4 View Fig ). Their lateral margins are sub-parallel in dorsal view. The maxillae seperate the nasals from the premaxillae. The lateral maxillary margins are undulated and slightly bulged at the tooth positions, especially in the anterior part (indicating deep reception pits). In HLMD V946-948, the posterior maxillary portion is only partly preserved on the left side, adjacent to the nasal. The latter contacts the maxilla via a smooth, straight suture that extends anteromedially. All pointed tooth crowns ( Figs. 1–3 View Fig View Fig View Fig ) are intersected and expose the pulp cavity in lateral view. In HLMD V946-948, the exact number of maxillary teeth cannot be provided, as both maxillae are incomplete. In NHMUK PV OR 14781, the precise maxillary tooth count is also difficult to determine, but there are at least 29 alveolar pairs. The maxilla is heavily and extensively ornamented with conspicuous pits and grooves. In addition, there are deep, well-spaced foramina (arranged in a single line parallel to the maxillary ventral margin) that are visible in dorsal, lateral and anterior views (best seen in NHMUK PV OR 14781). In both specimens, the mandible obscures the ventral sides of the maxillae.
Jugal: The right jugal in NHMUK PV OR 14781 is complete ( Fig. 2 View Fig ) whereas the left jugal is partially preserved (the posterior area is missing). It is triradiate, forms the lateral border of the orbit as seen in other teleosauroids ( Andrews 1909, 1913), and participates in the ventral margin of the orbit. The anterior jugal is short and does not extend anteriorly past the orbits ( Figs. 2 View Fig , 4 View Fig ). The postorbital-jugal contact best seen in right lateral view) appears to be anteroposteriorly straight (with the postorbital overlapping the jugal). The quadratojugal-jugal contact cannot be clearly seen. The jugal is also ornamented with elongate, deep grooves and small sub-oval pits.
Nasals: In both specimens, the dorsal surfaces of the nasals are exposed ( Figs. 1 View Fig , 2 View Fig ). The nasals are large triangular bones exposed on the dorsal surface of the posterior rostrum and orbital area. The straight midline suture is clearly visible and so is the anteromedially extending lateral suture to the maxilla. The overall anteroposterior elongation of the nasals is slightly shorter and mediolaterally broader than in other Toarcian teleosauroids (e.g., S. gracilirostris NHMUK PV OR 14792). The nasal anterior processes are approximately one-third of the posterior rostrum and have a well-developed near-parallel suture contact with the maxillae. There is no dorsoventral abrupt “doming” of the nasals see Lemmysuchus obtusidens ( Andrews, 1913) , Johnson et al. 2017, NHMUK PV R 3168, LPP.M.21, PETMG R39). A midline concavity (“midline trench”) is present in NHMUK PV OR 14781. There is a faint internarial suture in HLMD V946-948 and NHMUK PV OR 14781, suggesting that the nasals are unfused. The nasals, similarly to the premaxillae and maxillae, are noticeably ornamented in (best seen in NHMUK PV OR 14781, Fig. 2A 2 View Fig ), with multiple, deep grooves, which differs from other Toarcian teleosauroids e.g., S. gracilirostris, NHMUK PV OR 14792; S. bollensis, SMNS 51563, MMG BwJ 565).
Prefrontal: The prefrontals in NHMUK PV OR 14781 are slightly sub-circular in shape, longer than wide in dorsal view ( Figs. 2 View Fig , 4 View Fig ), and ornamented with deep grooves. The prefrontal forms the anteromedial border of the orbit, and contacts the nasal and frontal medially and the lacrimal laterally ( Figs. 2 View Fig , 4 View Fig ). The prefrontal-frontal suture is irregular and the prefrontal-lacrimal contact is regular.
Lacrimal: The lacrimal in NHMUK PV OR 14781 is a large, triangular bone that constitutes the majority of the anterolateral margin of the orbits ( Figs. 2 View Fig , 4 View Fig ). The lacrimal is ornamented as in the other aforementioned bones. The paired antorbital fenestrae are large relative to the orbits, subcircular in shape and slightly anteroposteriorly elongated. The right antorbital fenestra is better preserved than the left, and it is almost equidistant between the orbit and alveolar margin, although it is still slightly closer to the orbit, which is similar in P. multiscrobiculatus ( SMNS 9930), whereas in other teleosauroids (e.g., Steneosaurus leedsi, NHMUK PV R 3806) the antorbital fenestrae are much closer to the orbits (e.g., Andrews 1913). The anteroposterior length of the antorbital fenestrae is approximately 25% of the orbital anteroposterior length.
Frontal: The frontal in NHMUK PV OR 14781 is a large, dorsoventrally deep bone with no evidence of a midline suture ( Figs. 2 View Fig , 4 View Fig ). The frontal contributes to the posteromedial border of the orbit and forms the anterior medial borders of the supratemporal fenestra, as well as an almost straight vertical contact with the postorbital in dorsal and lateral views ( Fig. 2A View Fig 1 View Fig , A 2 View Fig ). The anterior process is short as in other teleosauroids (e.g., S. bollensis, SMNS 51753). The frontal is heavily ornamented with large pits and grooves that irradiate from the centre of the bone and extend to the anteriormost and lateral-most regions, similar to other Toarcian teleosauroids (e.g., P. multiscrobiculatus, SMNS 9930; S. bollensis, RE 551.762.130 A 0248; see SOM: fig. S2). The posterior-most portion of the frontal is not preserved.
Postorbital: The large, robust postorbital in NHMUK PV OR 14781 ( Fig. 2A View Fig 1 View Fig , A 2 View Fig ) reaches the posteroventral margin of the orbit (with the postorbital overlapping the jugal), and extensively forms part of the orbital ventral margin (similar to P. multiscrobiculatus SMNS 9930). The postorbital also forms the lateral and posteroventral margins of the supratemporal fenestra ( Figs. 2 View Fig , 4 View Fig ). The anterodorsal suture interdigitates tightly with the frontal and forms the posterior margin of the orbit. The postorbital is noticeably larger and more elongate than the squamosal, and the postorbital-squamosal contact is straight (best seen in lateral view). The anterodorsal area of the postorbital is slightly anteroposteriorly constricted ( Fig. 2A View Fig 1 View Fig ), whereas the rest of it is anteroposteriorly broad. The postorbital-jugal contact is difficult to discern due to the rugosities of the skull. The postorbital bar (formed by the frontal-postorbital contact) is similar to other teleosauroids (e.g., S. bollensis, SMNS 51753; Andrews 1913). It is slightly anteroposteriorly thickened, is ornamented by pits and grooves and forms the posterolateral margin of the orbit.
Squamosal: The right squamosal is preserved in NHMUK PV OR 14781 ( Fig. 2A View Fig 1 View Fig ), and is a large, elongate L-shaped bone ( Fig. 4 View Fig ). The anterior process is anteroposteriorly elongated (in dorsal view) and forms the posterolateral border of the supratemporal fenestra. The posterolateral surface of the squamosal is concave in lateral view and convex in dorsal view ( Fig. 2A 2 View Fig ). The squamosal bar is robust and anteriorly contacts the postorbital bar (together forming the supratemporal arch). The anterior squamosal bar is ornamented with pits and grooves, as in the postorbital.
Quadratojugal: The anterior part of the right quadratojugal is preserved in lateral view in NHMUK PV OR 14781; it is a thin, elongate bone ( Fig. 4 View Fig ).
Other cranial elements: In HLMD V946-948, remnants of the right palatine and possibly also the pterygoid are exposed in ventral view ( Fig. 1A View Fig 3 View Fig ), but the poor preservation precludes a detailed description. The palatal elements are unavailable in NHMUK PV R 14781. The parietals, prootics, laterosphenoids and quadrates are not preserved in either specimen and therefore cannot be described. In addition, the majority of bones representing the occipital are not preserved, and the basicranium is unavailable (as mentioned above).
Mandible: In HLMD V946-948, the mandible is partially preserved ( Fig. 1A View Fig 2 View Fig , A 4 View Fig ), with sections of the posterior dentaries and articulars missing. The anterior portion of the dentary is cemented to the cranium. In NHMUK PV OR 14781, the mandible is nearly complete on the right side and partially preserved on the left ( Fig. 2A View Fig 1 View Fig , A 3 View Fig ). It is likewise cemented to the cranium, so the dorsal surface is not visible, as mentioned above. In NHMUK PV OR 14781, the mandible measures approximately 870 mm in length (with the articular missing). The contact including the dentary, angular and splenial (best seen in right ventral view) is formed posterior to the mandibular symphysis on the ventral side. The posterior-most area of the mandible is partially covered with ironstone matrix.
Dentary: In HLMD V946-948, the anterior parts of both dentaries and the midsection of the right mandibular ramus are preserved ( Fig. 1 View Fig ), but the midline suture is barely visible. Due to the occlusion with the skull, only the lateral and ventral sides are exposed. The dentary ( Fig. 1A View Fig 2 View Fig ) is a slen- der, elongate bone making up the majority of the lateral and ventral surfaces of the mandible, as seen in many crocodylomorphs ( Andrews 1909, 1913; Romer 1956; Nesbitt 2011; Johnson et al. 2017). The dentaries are overhung and demarcated anteriorly by the premaxillae ( Figs. 2A View Fig 3, 3A View Fig ), unlike the condition seen in Steneosaurus bollensis ( Fig. 3C, D View Fig ). A prominent notch is present that intersects the anterior margin of the conjoint dentaries. It is unclear whether this notch is a preservational artefact or a genuine morphology, but it is found in numerous teleosauroid species (e.g., Platysuchus multiscrobiculatus, UH 1; Steneosaurus bollensis, RE 551.762.130 A 0248, SMNS 18672, SMNS 53422; Steneosaurus leedsi, NHMUK PV R 3320; Steneosaurus edwardsi Eudes-Deslongchamps, 1868 , NHMUK PV R 2076, NHMUK PV R 3701). The dentaries are transversely widened at the level of the premaxillary diastema. In HLMD V946-948, at the posterior part of the symphysis, the dentaries are dorsomedially demarcated by the splenials. Posterior to the symphysis, the coronoid extends medially to the dentary along its entire length. Ventrally, a short contact with the splenial is indicated on the left side. A long suture is present towards the angular, which separates the dentary from the splenial for most of its preserved length. In HLMD V946-948, the teeth are broken off or intersected, exposing the pulp cavity. In both specimens, the alveoli are relatively small and subcircular, with intermediate spacing throughout (the interalveolar distance being slightly larger than the alveolar labiolingual width, similar to S. gracilirostris MNHNL TU 515). In HLMD V946-948, the right ramus bears remnants of 32 teeth. In NHMUK PV OR 14781, the exact number of alveoli is difficult to discern, but there are at least 30 alveolar pairs. The lateral margins of the dentaries are undulated.
Splenial: The splenials ( Fig. 1A View Fig 4 View Fig ) are exposed on the dorsal and ventral side of the mandible in HLMD V946-948. Dorsally the posterior splenial sections are visible; they are slightly indented and form the middle portion of the symphyseal rostrum. A long contact with the dentary is present laterally, with the suture being barely visible. A short, pointed process extends posterior to the symphysis and contacts the anteromedial side of the coronoid. Ventrally, the splenial forms the medial side of the preserved post-symphyseal mandibular ramus and has an elongated contact to the angular. In NHMUK PV OR 14781, only the right splenial is best seen in ventral view ( Fig. 2A View Fig 3 View Fig ).
Surangular and angular: In NHMUK PV OR 14781, the surangular ( Fig. 2A View Fig 1 View Fig ) is a thin and anteroposteriorly elongate bone in lateral view. It appears to form a distinctive V-shape (in conjunction with the angular and presumably the articular) and terminates near the final alveolus of the dentary. The posterior margin of the surangular is slightly rounded and encloses an irregularly shaped mandibular fenestra. In HLMD V946-948, part of the angular is preserved ventrally in the left mandibular ramus as an elongate, transversely thin process that interferes between the splenial and dentary ( Fig. 1 View Fig ). It terminates slightly posterior to the symphysis. In NHMUK PV OR 14781, the angular ( Fig. 2 View Fig ) occupies a larger area than the dorsally placed surangular. The angular is dorsoventrally deeper and more robust than the surangular and has a poor dorsal curvature in lateral view. Both elements extend slightly more posteriorly than the cranium.
Dentition: Both specimens ( HLMD V946-948 and NHMUK PV OR 14781) have teeth preserved in situ. In HLMD V946-948, the pulp cavity is exposed in lateral view, as mentioned above. The maxillary and dentary teeth are large and elongate ( Figs. 3A View Fig , 4 View Fig ). In NHMUK PV OR 14781, the anterior teeth have a more pointed apex than the posterior ones, which are gently rounded. The teeth are slightly more robust than those seen in other Toarcian teleosauroids (e.g., S. gracilirostris, MNHNL TU 515, S. bollensis, SMNS 15172a, SMNS 54046; P. multiscrobiculatus, SMNS 9930). They are more distally curved in the anterior section of the maxillae and dentaries. The enamel ridges are small yet well developed, parallel to one another and reach the top of the apex. There are no serrations present.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
|
Kingdom |
|
|
Phylum |
|
|
Family |
|
|
Genus |
Mystriosaurus laurillardi Kaup, 1834
| Sachs, Sven, Johnson, Michela M., Young, Mark T. & Abel, Pascal 2019 |
Mystriosaurus laurillardi
| Kaup, J. J. 1834: 28 |