Kenolamna gunsoni ( Siverson, 1996)
Figs. 19D, 23–25.
1996 Cretolamna gunsoni Siverson, 1996 ; Siverson 1996: 829, pl. 3: 9–13.
1999 Cretalamna gunsoni Siverson, 1996 ; Siverson 1999: 52, fig. 4.
Holotype: WAM 95.7.49, an A1 (originally described as an A2), illustrated by Siverson (1996: text-fig. 3, pl. 3: 9–11).
Type horizon: “ Upper Gearle Siltstone” (previously referred to as the uppermost Alinga Formation at Thirindine Point), 0.5 m below the base of the Hayco*ck Marl (= Beedagong Claystone of Siverson 1996). The precise age of the type stratum is yet to be determined but is likely Cenomanian. The overlying basal part of the Hayco*ck Marl yields Cretoxyrhina teeth comparable in morphology to those from the Greenhorn Limestone in theWestern Interior Seaway of North America .
Type locality: Thirindine Point East, Pillawarra Plateau,Southern Carnarvon Basin, Western Australia .
Material.—73 teeth, including WAM 09.6.22, “ Cardabiodon Site ”, tooth found in situ, 5 cm below the top of the Gearle Siltstone; WAM 98.11.1, 5, 09.6.23–39, 10.9.53–91, 11.12.4, “Main Site”; WAM 10.9.40–41, “New Site”; WAM 10.9.42–52, “Camp Site”.
Emended diagnosis.—As for the monotypic genus.
Description.— First upper anterior tooth file: The best preserved tooth assigned to the A1 file is described and illustrated Fig. 23A). As preserved, the specimen is 24 mm high but would originally have been slightly taller. The cusp is somewhat distally directed. In profile view, the labial face of the tooth is slightly concave ( Fig. 23A 2 View Fig ). The basal view of the root is of limited use for comparison as portions of the tall lingual protuberance and the lingual side of the distal lobe are missing.As a result of the corrosion of the root’s basal side, the U-shape of the basal edge of the root in labial/lingual views appears slightly more pronounced than it would have originally.
Second upper anterior tooth file: Several teeth are referred to this file. Collectively, they differ from the teeth assigned to the first upper anterior file by having a slightly less tightly curved basal edge of the (near perfectly symmetrical) root and a distinctly distally inclined and more labiolingually compressed cusp. The best preserved example measures 24 mm in height ( Fig. 23B). The apex of the cusp is worn as a result of prey manipulation, which has reduced the original height by 1–2 mm. The root is almost perfectly symmetrical in this specimen, displaying relatively acute lobes.
Third upper anterior tooth file: Teeth referred to this file have a cusp that is recurved in labial/lingual views ( Fig. 23C 1 View Fig , C 3 View Fig ) and labially curved in profile view ( Fig. 23C 4 View Fig ). They are similar in height to the inferred A1 and A2 but have a somewhat broader cusp. The root is markedly asymmetrical in most A3’s, with an elongated mesial lobe. The illustrated example ( Fig. 23C) is considerably smaller than some of the other teeth referrable to the A3 position but happened to be the best preserved A3.
Upper lateroposterior tooth files: The teeth (measuring up to an estimated 26 mm in height) from the upper lateroposterior hollow have a tall, slightly recurved ( LP 1; Fig. 24A View Fig 1 View Fig ) to strongly distally curved cusp.The LP 1 is significantly small- er than the adjacent A3 and LP 2 and has a tightly curved basal edge of the root.The recurved cusp of the LP 1 is similar to that of the A3 (in labial/lingual views) but it is more labio-lingually compressed, relatively shorter and has a straight labial face in profile view (labially curved in the A3). In profile view, the labial face of the teeth is progressively more concave, moving posteriorly through the upper lateroposterior files. A concave profile view characterises upper lateroposterior teeth of most modern macrophagous lamniform sharks but it is particularly pronounced in this Cretaceous species ( Fig. 24H View Fig 2 View Fig ). A pair of relatively large and sharp cusplets accompanies the labiolingually compressed cusp. The inner cutting edge of the cusplets is shorter than the outer edge. The root exhibits a deeply notched basal edge and sub-rectangular lobes.
First lower anterior tooth file: Two relatively well-preserved teeth can be referred to the a1 position with some confidence, one 26mm high ( Fig. 23D) and the other 28 mm high. The basal edge of the root is tightly curved in both specimens. The cusp is tall and perfectly symmetrical in one of the two teeth ( Fig. 23D) but slightly recurved in the other tooth. In profile view, the labial side of the cusp is moderately or strongly lingually curved. The cusplets are erect or slightly divergent.
Second lower anterior tooth file: Teeth assigned to the a2 position differ from first lower anterior teeth by having a very slightly distally bent cusp (as opposed to a perfectly straight or slightly recurved cusp) and a wider, asymmetrical root with a mesial lobe longer than the distal lobe. Like all teeth assigned to the lower anterior files, the cusp is lingually curved, giving the labial face of the tooth a convex profile ( Fig. 23F 2 View Fig ).
Third lower anterior tooth file: A 27 mm high tooth from a large individual is referred to the a3 position (additional to a few poorly preserved but probable third lower anteriors). The outline of the root is reasonably complete, but large sections of the root are missing on both the labial and lingual side ( Fig. 23E 1 View Fig , E 3 View Fig ). The cusp is barely inclined in labial/ lingual views and increases rapidly in width in its basal part. In profile view, the labial side of the tooth is moderately lingually curved. The mesial lobe is slender and elongated whereas the distal lobe is broader and shorter.
Lower lateroposterior tooth files: The teeth from the inferred lower lateroposterior hollows are up to 24 mm high. The cusp is straight (in anteriorly situated teeth) to moderately distally curved or inclined (in posteriorly situated teeth). The cusp is labiolingually compressed but not to the same degree as in upper lateroposterior teeth. In profile view, the labial side of the cusp is typically straight in anteriorly situated teeth (e.g., Fig. 25C View Fig 4 View Fig ) and lingually curved in more posteriorly situated teeth ( Fig. 25E View Fig 3 View Fig , F 1 View Fig ). The root and cusplets are similar to those in upper lateroposterior teeth.
Geographic and stratigraphic range.—Upper Gearle Siltstone, Murchison River area (most likely Cenomanian) and uppermost part of the Gearle Siltstone (middle Cenomanian), Giralia Range, Western Australia, Australia.
