Kenolamna, Siversson & Lindgren & Newbrey & Cederström & Cook, 2015

Siversson, Mikael, Lindgren, Johan, Newbrey, Michael G., Cederström, Peter & Cook, Todd D., 2015, Cenomanian-Campanian (Late Cretaceous) mid-palaeolatitude sharks of Cretalamna appendiculata type, Acta Palaeontologica Polonica 60 (2), pp. 339-384 : 374-377

Genus Kenolamna nov.

Type species: Cretalamna gunsoni Siverson, 1996 ; Upper Gearle Siltstone (Cenomanian?, Late Cretaceous), Thirindine Point ridge, Pillawarra Plateau , lower Murchison River area, Western Australia; monotypic .

Etymology: Combination of Ken (after the former Curator of Palaeontology at the Western Australian Museum, Kenneth McNamara, in recognition of his work on various groups of fossils from Western Australia) and Lamna , the genus name for Porbeagle sharks.

Diagnosis.—Upper anterior teeth with cusp labially curved in profile view and straight, distally inclined or recurved in labial/lingual views. Lower anterior teeth with cusp lingually curved in profile view and straight in labial/lingual views. Root gracile in all anterior teeth. Cusplets, present on all teeth, often taller than wide and with elongated, concave outer cutting edge. Posteriorly situated lower lateroposterior teeth taller than wide. Posteriorly situated upper lateroposterior teeth with basal face of root set almost at right angle to labial face of crown in profile view.

Remarks.—The range of tooth-morphologies in Kenolamna gen. nov. most closely resembles that of Cretalamna and Palaeocarcharodon .

The dentition differs from that of Cretalamna in the following aspects: (i) the LP 1 is not significantly smaller than the other anteriorly situated upper lateroposterior teeth in LACM 128126, the only Cretalamna specimen with a preserved palatoquadrate showing in situ teeth across the anterior/lateroposterior hollows boundary ( Fig. 13B ). In contrast, evidence at hand [presence of small, labiolingually compressed teeth with a recurved cusp, large cusplets and a flat labial face in profile view (latter two characters separating the teeth from the otherwise similar A3)] indicate that the LP 1 is reduced in size compared to the adjacent teeth in Kenolamna gen. nov.; (ii) posteriorly situated lateroposterior teeth in Cretalamna are wider than tall and have quadrangular root-lobes. Posteriorly situated teeth of Kenolamna gen. nov. have rounded to acute root-lobes and are taller than wide; (iii) cusplets are taller than wide in Kenolamna gen. nov. but typically wider than tall in Cretalamna .

SIVERSSON ET AL.—LATE CRETACEOUS MID-PALAEOLATITUDE SHARKS 375

B2 A1 A 2 A 3 B1 D1 B3 B4 D2 D3 D4 C3 C1 C2 C4 10 mm E1 E2 E3 F1 F 2 F 3

Differences between Kenolamna gen. nov. and Palaeocarcharodon include: (i) cutting edges are smooth in Kenolamna gen. nov. compared with smooth to strongly serrated in Palaeocarcharodon ( Cappetta 2012: fig: 238A–E); (ii) anterior teeth of Palaeocarcharodon have a broad, labiolingually compressed cusp, whereas the corresponding teeth in Kenolamna gen. nov. are equipped with a slender, slightly to moderately compressed cusp; (iii) the basal edge of the root is more deeply excavated medially in Kenolamna gen. nov. than it is in Palaeocarcharodon .

There are a number of similarities in tooth morphology (and total range of tooth-types) between Kenolamna gunsoni ( Siverson, 1996) and the Paleocene taxon Palaeocarcharodon orientalis . In both species the cusp is strongly labiolingually compressed in lateroposterior files (although primarily in the upper jaw in the former), the inner edge of the cusplets is shorter than the outer edge, and the labial face of the tooth is strongly concave in profile view in posteriorly situated upper lateroposterior teeth ( Dartevelle and Casier 1943: pl. 11: 1b; Fig. 24H 2 ). An origin of Palaeocarcharodon from a species of Kenolamna gen. nov. in the Southern Hemisphere could explain the current lack of a plausible ancestor of the former in the comparatively well researched Late Cretaceous of the Northern Hemisphere.

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The assignment of Kenolamna gen. nov., and by inference,

Palaeocarcharodon , to the Otodontidae is based on the curvature of the cusps on the upper anterior teeth [slightly curved or inclined (A1), moderately distally inclined (A2) and recurved

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(A3)] and their similar size. The morphology and relative size of the upper anterior teeth strongly resemble those of Cretalamna of the C. borealis group ( Fig. 12A, C, E), but this morphology is in stark contrast to those of other Cretaceous lamniforms known from associated/articulated dentitions ( Cretoxyrhina , Archaeolamna Siverson, 1992a , Cardabiodon Siverson, 1999 , Dwardius Siverson, 1999 , and Paraisurus Glikman, 1957 ). The commissural teeth of Kenolamna gen. nov. are, however, quite different from the laterally expand- ed ones in Cretalamna ; Kenolamna gen. nov. may have had a more typical “lamnoid tooth-pattern” (see Siverson et al. 2013 for a discussion of the term) than did Cretalamna , with a disjunct transition in tooth size between the upper anterior and lateroposterior teeth ( Fig. 19D). Because of the latter two differences between Cretalamna and Kenolamna gen. nov. (the latter admittedly largely inferred as it depends on the accuracy of the tooth file assignment of a single tooth-type), we regard our referral of Kenolamna gen. nov. (and Palaeocarcharodon ) to the Otodontidae as tentative.

Figures

Fig. 13. Otodontid shark Cretalamna hattini sp. nov., holotype, LACM 128126, latest Santonian or earliest Campanian (Late Cretaceous); upper Smoky Hill Chalk, Niobrara Formation, close to MU 16, Logan County, Kansas, USA. A. Right palatoquadrate in lingual view. B. Anterior section of right palatoquadrate showing embedded replacement teeth, re-interpreted as (from left to right) A2, LP1 and LP2 (two cusps) C. Disarticulated tooth assigned to the upper “intermediate” file by Shimada (2007) and to the LP5 file herein. D. In situ tooth assigned to the the upper “intermediate” file by Shimada (2007) and to the LP1 file in this work. E. Disarticulated tooth assigned to the LP1 file in this work.

Fig. 24. Otodontid shark Kenolamna gunsoni (Siverson, 1996) gen. nov., upper lateroposterior teeth, uppermost Gearle Siltstone, middle Cenomanian Late Cretaceous), Zone CC10a; CY Creek, Giralia Range, Western Australia. A. WAM 10.9.40, left LP1?; labial (A) and profile (A) views. B. WAM 1 2 09.6.28, left LP2?; labial (B 1), basal (B 2), and lingual (B 3) views. C. WAM 09.6.33, right LP3?; profile (C 1) and labial (C 2) views. D. WAM 09.6.30, right LP3?; labial (D 1), basal (D 2), profile (D 3), and lingual (D 4) views. E. WAM 09.6.34, left LP4?; labial (E 1, stereopair), profile (E 2), and lingual (E 3, stereopair) views. F. WAM 09.6.36, right LP5?; labial (F 1), profile (F 2), and lingual (F 3) views. G. WAM 09.6.39, right LP6?; labial (G 1), profile (G 2), and lingual (G ) views. H. WAM 09.6.37, right LP5?; basal (H ), profile (H ), labial (H , stereopair), and lingual (H , stereopair) views.

Fig. 2. Otodontid shark Cretalamna appendiculata (Agassiz, 1843), upper jaw teeth, Tourtia de Bettrechies, early Turonian (Late Cretaceous); SECAB quarry, Bettrechies, northern France. A. WAM 13.5.2, right A1?; labial (A), basal (A), profile (A), and lingual (A) views. B. UM-BET 1, right A2?; 1 2 3 4 labial (B 1), basal (B 2), profile (B 3), and lingual (B 4) views. C. UM-BET 2, right LP1?; basal (C 1), lingual (C 2), labial (C 3), and profile (C 4) views. D. UM- BET 3, left LP2?; labial (D 1), basal (D 2), lingual (D 3), and profile (D 4) views. E. WAM 13.5.7, left LP3?; labial (E 1), profile (E 2), basal (E 3), and lingual (E ) views. F. WAM 13.5.3, right LP8?; labial (F ), profile (F ), basal (F ), and lingual (F ) views.