Clidastes propython Cope, 1869
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https://doi.org/ 10.5281/zenodo.13507164 |
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https://treatment.plazi.org/id/038787FB-FFFB-FF93-FFFF-40F348D54924 |
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treatment provided by |
Felipe |
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Clidastes propython Cope, 1869 |
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Clidastes propython Cope, 1869
For synonyms.—See Russel (1967).
Material examined (see also Table 1).—Marginal teeth: Åsen 100 teeth ( LO 8231t, 8232t and 86 unnumbered, Lund University; RM PZ R 1776, 1777, 1794–1803); Ignaberga, three teeth (all unnumbered, Lund University); Ivö Klack, one tooth (RM PZ R 1966); Ugnsmunnarna, two teeth (both unnumbered, Lund University). Pterygoid teeth: Åsen, 13 teeth (RM PZ R 1804, 1805; 11 unnumbered, Lund University). Jawbones: Ugnsmunnarna, four fragments (of which one is a pterygoid) from a large individual (RM PZ R 1790– 1793). Cervical vertebrae: Åsen, four vertebrae (RM PZ R 1778, 1779, 1782, 1789); Axeltorp, one axis vertebra from a very large individual (RM PZ R 1752a–b); Ivö Klack, one vertebra (unnumbered, Department of Geology and Geochemistry, Stockholm University). Dorsal vertebrae: Åsen, two vertebrae (RM PZ R 1780, 1781). Cervical/dorsal vertebrae: Åsen, six vertebrae (RM PZ R 1783–1788). Terminal caudal vertebrae: Åsen, 11 vertebrae (RM PZ R 1806–1816); Ivö Klack, 10 vertebrae (one unnumbered, Lund University; PMU R 415, 417, 1255; RM PZ R 911, 958, 1015, 1027, 1028, 6081).
Occurrence.— Clidastes propytho n has been recorded in the early Campanian Mooreville Chalk, Alabama ( Russell 1967, 1970; Shannon 1977; Bell 1985; Wright 1986a, b; Kiernan 2002); the early Campanian Roxton Limestone, Texas ( Echols 1972); the early Campanian lower Pierre Shale, Colorado ( Carpenter 1990); the middle Santonian to earliest Campanian part of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas ( Everhart 2001); the late early Campanian Sharon Springs Member of the lower Pierre Shale, Kansas and South Dakota ( Russell 1967); the earliest Campanian part of the Niobrara Formation, South Dakota, ( Russell 1967; Martin et al. 1998), and the late early Campanian part of the Pembina Member of the Pierre Shale, southern Manitoba ( Nicholls 1987, 1988).
Description.— Marginal teeth. Premaxillary and the most anteriorly situated dentary tooth−crowns are posteriorly curved and more or less oval in basal cross−section ( Figs. 2 View Fig , 3B). The teeth are equipped with a strong anterior carina ( Fig. 2B 2 View Fig ) and a weak, often incomplete (may be absent altogether; Fig. 2A 2 View Fig ) bucco−posterior carina (both carinae without serrations). The buccal surface is relatively narrow and gently convex, while the lingual face is strongly U−shaped. The lingual surface lacks distinct facets, whereas two or three buccal facets may be present on teeth from juvenile individuals. There is only one tooth of a large, presumably adult animal from this part of the marginal dentition present in our collection, and it lacks both buccal and lingual facets. The tooth−crowns are up to approximately 17–18 mm high (estimated original height and width of RM PZ R 1776, a basally and apically incomplete 11.5 mm high crown).
Maxillary and the corresponding dentary tooth−crowns are up to 19 mm high (estimated original height of RM PZ R 1777, a 15 mm high crown with a worn apex and an incomplete base). In lateral view, the tooth−crowns have a triangular outline with an upright ( Fig. 4D View Fig ) to slightly medio−posteriorly curved apex ( Fig. 4B View Fig ). In occlusal view, the prominent anterior and posterior carinae divide the crown into an angular buccal face (does not apply to the most posteriorly situated teeth, in which both sides are gently rounded) and an equally large (the most posteriorly situated teeth; Fig. 4E View Fig 2 View Fig ) to much larger (anteriorly situated teeth; Fig. 4C View Fig 2 View Fig ) lingual face. The lingual surface has a rounded ( Fig. 4B View Fig 2 View Fig ) to sub−rectangular ( Fig. 4D View Fig 2 View Fig ) basal cross−section. Most teeth have facets; three to four on the buccal face and five to ten, usually less distinct, on the lingual face. The buccal facets are indistinct on most of the larger teeth (e.g., Fig. 4C View Fig 3). The most anteriorly situated maxillary and corresponding dentary teeth are relatively more slender in lateral view (but thicker bucco−lingually) than are teeth from a more posterior position.
Crowns from the posterior part of the maxillae and dentaries are comparatively short and wide, with buccal and lingual surfaces of equal convexity ( Fig. 4G View Fig ). In lateral view, the anterior margin is strongly curved medio−posteriorly, while the posterior margin is straighter. The enamel−covered surfaces are either smooth or obscurely faceted, and are separated from one another by marked anterior and posterior carinae. In basal cross−section, the crowns have a thick oval outline.
Pterygoid teeth.—Pterygoid tooth−crowns ( Fig. 5 View Fig ) are up to 8 mm high and 5.5 mm wide at the base. The crowns are strongly distally curved in lateral view. The surface of the enamel is entirely smooth. An indistinct antero−buccal carina and a much stronger posterior cutting edge separate the crown into a flat to gently convex external surface and a strongly convex lingual side. The outline of the basal cross−section has the shape of a swollen ellipse.
Cervical vertebrae.—An associated group of eleven fragmentary cervicals and dorsals from Åsen (RM PZ R 1778– 1788), representing a juvenile individual, are indistinguishable from the corresponding vertebrae in similarly−sized Clidastes propython from the upper Smoky Hill Chalk Member, Niobrara Formation, in western Kansas, and the Mooreville Chalk of west−central Alabama. In addition to the former vertebrae, we also refer three isolated cervicals from Ivö Klack (unnumbered, Department of Geology and Geochemistry, Stockholm University), Axeltorp (RM PZ R 1752a–b) and Åsen (RM PZ R 1789) respectively, to C. propython . The three best preserved cervical vertebrae (two from the natural association of juvenile vertebrae from Åsen and a very large axis vertebra from Axeltorp) are described separately below.
RM PZ R1778 ( Fig. 6A View Fig ) is the third, or possibly fourth, cervical from a small juvenile (estimated total length of 2–2.5 m). The condyle articulation is sub−triangular in outline with rounded apices, and is wider than it is tall (12.8 mm wide and 10.4 mm high). Basal remains of the right half of the neural arch indicate that the neural canal was wide (approximately 8 mm at its base). Only the most proximal part of the right synapophysis is preserved, and it is situated on the anterior portion of the lateral surface of the centrum. The hypapophyseal peduncle is large and occupies more than half of the length of the, incomplete, ventral surface of the centrum. The cotyle is very incomplete, and only the most central parts of the surface are preserved. The length of the vertebral centrum is 21.1 mm, as measured between the centres of the interarticular surfaces .
RM PZ R 1779 ( Fig. 7A View Fig ) is the sixth or possibly seventh cervical. The condylar articulation surface is kidney−shaped and wider than it is high (14.2 mm and 10.8 mm, respectively). In lateral view, the posterior margin of the right (and only preserved) half of the neural arch is evenly curved and terminates in a slightly abraded but clearly visible posterior zygapophysis. A rudimentary hypapophyseal peduncle occupies the posterior half of the ventral surface of the centrum. As in RM PZ R 1778, only the central parts of the cotyle surface are preserved. The length of the centrum (measured between the centres of the interarticular surfaces) is 21.5 mm.
RM PZ R 1752 ( Fig. 6C View Fig ) comprises two fragments (1752a and 1752b) of an axis vertebra from a very large individual (estimated total length of 6.0 m). The larger of the two parts (1752a, Fig. 6C View Fig 1 View Fig , C 3, C 4) includes a well preserved posterior (condyle) articulating surface, a portion of the hypapophyseal peduncle and the posterior edge of both the left and the right synapophysis. The condyle measures 34.9 mm in width and 32.3 mm in height. The hypapophyseal peduncle has an almost straight posterior border and is very wide, measuring 25.5 mm in basal width. Nothing of the anterior surface is preserved on this fragment. The total length of RM PZ R 1752a is 56 mm.
The smaller fragment (1752b, Fig. 6C View Fig 2 View Fig ) comprises the upper left portion of the anterior end of the centrum. It includes the anterior edge of the base of the left leg of the neural arch and the upper left corner of the rough anterior surface connecting the vertebra to the atlas.
Dorsal vertebrae.— Two partial vertebral centra (RM PZ R1780–1781 ) are identified as dorsal vertebrae (these specimens are part of the Åsen association). The specimens possess sub−triangular to kidney−shaped condylar articulations, and are distinguished from cervicals by their lack of a hypapophyseal peduncle. As preserved, the more complete of the two specimens (RM PZ R1780 ) is 21 mm long and 13.4 mm wide (measured between the centres of the interarticular surfaces and on the condyle, respectively). Basal remains of the neural arch, the posterior edge of the right synapophysis, and the central parts of the cotyle are preserved on the specimen .
Caudal vertebrae.—All caudal vertebral centra of C. propython from the B. mammillatus zone are terminal caudals. The most proximally situated vertebrae have circular articulations and are considerably shorter (measured between the centres of the central articulations) than the width and height of the condyle and cotyle. Further back, the centra retain a more or less circular articular outline, whereas the relative length of the centra increases, approaching the width and the height of the central articulations. One of the illustrated specimens (RM PZ R 1027; Fig. 8A) with this morphology is from a large, presumably adult, individual. The vertebra is 29.0 mm high, 27.5 mm wide and 25.0 mm long (measured on the condyle and between the centres of the central articulations). On some specimens (including RM PZ R 1027) a delicate but distinct crest runs along the medial margin of each chevron ( Fig. 8A 3).
The most distally situated terminal caudal vertebrae have vertically oval to barrel−shaped central articulations. The centra are longer than wide, whereas the height is similar to the length. The illustrated specimen ( PMU R 417; Fig. 8C) in this category is 13.4 mm high, 12.1 mm wide and 13.7 mm long (measured on the condyle and between the centres of the interarticular surfaces). This particular specimen is not as markedly barrel−shaped as some of the other caudals of this group from the Åsen and Ivö Klack localities.
Comparisons.—In addition to a number of skeletal features (see e.g., Russell 1967); C. propython can be separated from C. liodontus by the morphology of its marginal teeth (personal observations of e.g., BMNH R 4547, YPM 1100, 1318, 1319; C. propython, YPM 1335 , 3996 and YPM−PU 17249; C. liodontus ). In C. propython , tooth−crowns from the mid−portion of the dental ramus have a lingual side usually markedly larger than the buccal one ( Figs. 3C 2 and 4D 2), approaching the asymmetry seen in marginal teeth of Mosasaurus . The corresponding crowns of C. liodontus are symmetrically bicarinate ( Fig. 3D 2). Moreover, lateral and posterior tooth−crowns of C. propython are generally thicker bucco−lingually than are the rather flattened crowns of C. liodontus . We have found no dental differences (neither in juveniles nor in adults) between the Kristianstad Basin population of C. propython and those of the Mooreville Chalk of Alabama and uppermost Smoky Hill Chalk of Kansas.
Examination of reasonably complete Clidastes skeletons (e.g., RMM 070, 2986) housed at McWane Center (former Red Mountain Museum collection) in Birmingham, Alabama, USA, supports Bell’s (1997) conclusion that the Mooreville Chalk contains a third, hitherto undescribed, species of Clidastes (informally denominated C. moorevillensis by Bell). Besides a marked difference in size (tooth−crowns of C. “ moorevillensis ” are considerably larger than are those of similarly sized C. propython ), marginal teeth from the mid−portion of the jaw in C. propython can be separated from those of C. “ moorevillensis ” by their moderately recurved crowns. In C. “ moorevillensis ”, tooth−crowns from a mid−lateral position are strongly distally curved, whereas the corresponding crowns of C. propython are more upright. A second distinguishing character might be the development of granulae on the antero−basal part of the buccal face of the crowns. Marginal tooth−crowns of C. propython occasionally display a small number of indistinct swellings on the buccal face, whereas the lower half of the external surface is covered with more conspicuous small bumps in those specimens of C. moorevillensis that we have examined.
Cervical and anteriorly situated thoracic vertebrae of small individuals of C. propython can be distinguished from those of C. liodontus by the shape of the central articulations. Small−sized individuals of C. propython (e.g., YPM 1123— early juvenile, according to Sheldon 1996, 40354, and see list of material above) have cervical and anteriorly situated thoracic vertebrae with sub−triangular to kidney−shaped central articulations, which are wider than high ( Figs. 6B View Fig 2 View Fig , 7B View Fig 2 View Fig ). In larger (adult) individuals of this species (e.g., YPM 1100, 1316 and RM PZ R 1752a−b) the interarticular surfaces have a sub−circular outline ( Fig. 6C View Fig 3). In C. liodontus (e.g., YPM 3996, 24914, YPM−PU 17249) the cotyle and condyle articulations are more or less circular in both small and large individuals.
In having kidney−shaped central articulations, cervical vertebrae of juvenile C. propython somewhat resemble those of Platecarpus Cope, 1869 (a genus represented by P. cf. somenensis and possibly also Platecarpus ? sp. in the B. mammillatus zone of the Kristianstad Basin, see Lindgren and Siverson 2003). However, cervicals of Platecarpus are very stout compared to the slender and elongated centra of C. propython . They are also significantly shorter relative to their condyle and cotyle widths than are the cervical centra of Clidastes (see Caldwell and Bell 1995).
In 1914, Pravoslavlev described a new nominal species of Mosasaurus , i.e. M. donicus , from the Don Province in Russia. The type specimen comprises an incomplete intermediate caudal vertebra and a marginal tooth−crown ( Pravoslavlev 1914: pl. 1), found in strata of late early Campanian age in the Liski River Basin. Subsequently, in a work devoted to the history of mosasaur research in Russia, Yarkov (1993) referred M. donicus to Clidastes . Judging from the description and illustrations in Pravoslavlev (1914: pl. 1: 1–4), the caudal vertebra has typical mosasaurine proportions and displays fused chevrons of the haemal arch. The tooth−crown is large and robust (45 mm high in lingual view) with smooth enamelled surfaces ( Pravoslavlev 1914: pl. 1: 5). In cross−section, the crown has a gently convex buccal face and a deeply U−shaped lingual surface ( Pravoslavlev 1914: pl. 1: 6). The large size and overall morphology of the tooth−crown are inconsistent with an assignment to Clidastes .
Discussion.—Marginal tooth−crowns of Clidastes have been described as displaying smooth enamel by several workers (e.g., Russell 1967; Thurmond and Jones 1981), even though some (e.g., Williston 1898; Bell and Sheldon 1986) have observed facets on teeth of this mosasaur. Recently, Bell (1997) pointed out that marginal teeth in many juvenile and a few larger specimens of Clidastes possess three distinct facets on the medial [sic] face (this is almost certainly a typographical error, as this number of facets is typical for the buccal side of the crown). Our own examination of marginal teeth of Smoky Hill Chalk C. propython ( BMNH R 4547, YPM 1100, 1318, 1319) and C. liodontus ( YPM 1335, 3996, YPM−PU 17249) largely confirmed Bell’s observation, although it is not uncommon with four buccal facets. Facets are usually more distinct on tooth−crowns from small− to moderate−sized (juvenile) individuals (e.g., Fig. 4A, F View Fig ) than on crowns from large (adult) animals (e.g., Fig. 4C View Fig ).
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