Cretalamna ewelli, Siversson & Lindgren & Newbrey & Cederström & Cook, 2015
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publication ID |
https://doi.org/ 10.4202/app.2012.0137 |
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persistent identifier |
https://treatment.plazi.org/id/B63E4546-4337-FF80-FCCB-FB7E6CF95B99 |
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treatment provided by |
Felipe |
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scientific name |
Cretalamna ewelli |
| status |
sp. nov. |
Cretalamna ewelli sp. nov.
Fig. 12.
Etymology: Named after Keith Ewell, who collected most of the material in 2004.
Type material: Holotype: first upper left anterior tooth, FHSM VP-18510 ( Fig. 12A). Paratypes: FHSM VP-18511–18516 ( Fig. 12C–H).
Type horizon: Between 1–2 m below Hattin’s (1982) Marker Unit 2 (late Coniacian).
Type locality: Unnamed outcrop in Trego County, Kansas, USA (see Appendix 2) .
Additional material.— One A 2 tooth from the “Quinter South” site ( FHSM VP-18517), collected 0.3 m below the base of MU4 (i.e., somewhat younger than the type series) ( Fig. 12B) .
Diagnosis. —Upper anterior teeth with awl-shaped, slightly distally inclined cusp or with broader, recurved cusp. Cuseroposterior tooth; labial (D 1), basal (D 2), and lingual (D 3) views. E. Paratype, FHSM VP-18513, left A3?; labial (E 1), profile (E 2), basal (E 3), and lingual (E 4) views. F. Paratype, FHSM VP-18514, left lp1?; labial (F 1), profile (F 2), lingual (F 3), and basal (F 4) views. G. Paratype, FHSM VP-18515, lower lateroposterior tooth; labial (G 1), profile (G 2), lingual (G 3), and basal (G 4) views. H. Paratype, FHSM VP-18516, lower lateroposterior tooth; labial (H 1), profile (H 2), lingual (H
3
), and basal (H
4
) views.
plets minute to moderately large and erect to divergent on upper anterior teeth. Lateroposterior teeth with slender cusp and deep, moderately tightly curved median indentation of basal edge of root. Inner cutting edge of cusplets in lateroposterior teeth typically more convex than outer edge.
Description.— First upper anterior tooth file: A 17.5 mm high tooth is referred to the A1 position ( Fig. 12A). The tooth is complete apart from a worn apex and slight weathering damage on one side of the cusp. The cusp is very slender and slightly inclined in labial/lingual views, presumably in a distal direction. It is lingually curved in profile view. The cusplets are very small, divergent and relatively blunt. The root is symmetrical in labial/lingual views but asymmetrical in basal view, with one lobe, presumably the distal one, being more compressed than the other lobe ( Fig. 12A 3 View Fig ). Although the strongly lingually curved cusp in profile view is a characteristic feature in lower anterior teeth of the C. borealis group, the well demarcated lingual protuberance in basal view and the relatively straight labial root/crown boundary indicate that the tooth is derived from an upper anterior file.
Second upper anterior tooth file: Two teeth are referred to the A2 position. One is complete and measures 20.5 mm in height ( Fig. 12C). The second tooth is considerably larger than the other specimen, measuring 25 mm in height, and is missing the mesial cusplet ( Fig. 12B). It is also somewhat younger as it was collected from a stratum just below MU4 (the other tooth was collected below MU2). The cusp is awl-shaped, especially in the larger tooth, and moderately distally inclined. The tip of the cusp is very slightly recurved. The cusplets are erect (in the largest tooth) or divergent and minute (the largest tooth) to moderately large. The cusp is somewhat sigmoidally curved in profile view ( Fig. 12B 2 View Fig , C 3 View Fig ). The root is gracile (the smaller tooth) to robust (the larger tooth) and moderately asymmetrical in labial/lingual views with the mesial lobe being more elongated and longer than the distal lobe.
Third upper anterior tooth file: One complete tooth, 18 mm high, is assigned to the A3 file ( Fig. 12E). The cusp is relatively broad, labiolingually compressed (compared with that of the A1 and A2 teeth) and distally inclined but with a markedly recurved apex. It is strongly labially curved in profile view Fig. 12E 2 View Fig ). The relatively small cusplets are sub-triangular and divergent. The root is asymmetrical in labial/lingual views with a longer but narrower mesial lobe. The lingual protuberance is well demarcated in basal view. The distal lobe is more labiolingually compressed than is the mesial lobe.
Upper lateroposterior tooth files: An incomplete tooth mesial lobe of the root broken off), 12.5 mm high, is referred to the middle part of the inferred upper lateroposterior hollow Fig. 12D). The cusp is strongly distally curved and slender. The median indentation of the basal edge of the root is relatively deep and U-shaped. A more-or-less rectangular outline characterises the root in basal view ( Fig. 12D 2 View Fig ). The lingual protuberance is small but relatively well-defined in basal view. The lobes of the root are strongly labiolingually compressed.
Lower lateroposterior tooth files: Three teeth are referred to the lower lateroposterior hollow. One of them, 19 mm high, has a labiolingually compressed but strongly asymmetrical root, indicating the lp1 position ( Fig. 12F). The cusp is slender, distally inclined and the cusplets divergent. In profile view, the cusp is somewhat lingually curved. The inner cutting edges of the cusplets are convex whereas the outer edges are concave. The lingual protuberance is very well demarcated in basal view ( Fig. 12F 4 View Fig ) and the median indentation of the basal edge is deep and U-shaped ( Fig. 12F 3 View Fig ). Another tooth is most likely from a significantly larger individual. It measures 18 mm in height and 17.5 mm in width ( Fig. 12G). One of its lobes of the root is broken off. The tooth is symmetrical with an erect cusp, slightly lingually curved in profile view. The moderately divergent cusplets are very sharp. A low and relatively poorly demarcated lingual protuberance is seen in basal view ( Fig. 12G 4 View Fig ). A well-preserved tooth, measuring 10 mm in height, is referred to the posterior half of the inferred lower lateroposterior hollow ( Fig. 12H). Apart from its much smaller size, it differs from the previously described, incomplete lateroposterior tooth by its distally inclined cusp, and shallower and less tightly curved median indentation of the basal edge of the root.
Remarks.—See the descriptions above for a comparison of the teeth of C. ewelli sp. nov. with those of the dentally similar C. borealis and C. gertericorum sp. nov. The upper anterior teeth of the narrow-cusped C. catoxodon sp. nov. differ from those of C. ewelli sp. nov. by, e.g., their poorly demarcated lingual protuberance in basal view (compare Fig. 12A 3 View Fig with Fig. 20A 4). In profile view, the protuberance is more prominent in upper anteriors of C. catoxodon sp. nov. (Fig. 20A 2) than it is in those of C. ewelli sp. nov. ( Fig. 12B 2 View Fig ). The likely A3 tooth ( Fig. 12E) in C. borealis -group group species, like C. ewelli , does not have an equivalent amongst the teeth from CY Creek. One of the upper jaw teeth ( Fig. 21A View Fig ) is similar in crown morphology to that of the assigned A 3 in C. ewelli sp. nov. but does not show any features on the root in basal view indicating that it is an A3 tooth rather than an LP1 masquerading as an upper anterior tooth (i.e., median indentation of the basal edge is shallow and the basal view shows a more-or-less rectangular outline without any labiolingual compression of the distal lobe). The upper lateroposterior teeth of C. ewelli sp. nov. differ from those of C. catoxodon sp. nov. by their generally sharp cusplets.
The moderate size of the teeth at hand (largest tooth, a probable A2, is 25 mm high; Fig. 12B), compared to the teeth of early Campanian C. borealis from the Kristianstad Basin, may reflect a smaller adult size in the Smoky Hill Chalk species. It is noteworthy, however, that the maximum size (height) of the teeth of C. borealis from the early Campanian of the nearshore, archipelago deposits in southern Sweden (~ 40 mm) is much greater than it is in early Campanian ( Offaster pilula Zone ) examples of the same species from more offshore, phosphatic chalks in northern France (~ 30 mm in the Beauval quarry; Pieter De Schutter personal communication 2013 and examination of photographs of teeth of his collection of C. borealis from the Beauval quarry). It is therefore possible that the Smoky Hill Chalk material represents sizes of larger juveniles and/or smaller adults. The fact that the geologically older C. gertericorum sp. nov. is dentally closer to C. borealis than is C. ewelli sp. nov. (probable A2s are virtually identical in C. gertericorum sp. nov. and C. borealis ), indicates that the latter did not give rise to C. borealis and might represent a short-lived lineage of the C. borealis group, adapted to the atypical environmental conditions of the restricted Western Interior Seaway.
The documentation of C. ewelli sp. nov. and C. hattini sp. nov. from the Smoky Hill Chalk should by no means be viewed as a complete account of Cretalamna from this lithostratigraphical unit. Future work, especially from the middle part of the unit, might well reveal additional species of the genus, previously described or new to science.
Geographic and stratigraphic range.—Late Coniacian part of the Smoky Hill Chalk, Niobrara Formation, western Kansas, USA.
| FHSM |
Fort Hays Sternberg Museum |
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