Cretalamna hattini, Siversson & Lindgren & Newbrey & Cederström & Cook, 2015
|
publication ID |
https://doi.org/ 10.4202/app.2012.0137 |
|
persistent identifier |
https://treatment.plazi.org/id/B63E4546-4332-FF8B-FCBD-F8A36DED5F7C |
|
treatment provided by |
Felipe |
|
scientific name |
Cretalamna hattini |
| status |
sp. nov. |
Cretalamna hattini sp. nov.
Figs. 13–17 View Fig View Fig View Fig , 19A.
2007 Cretolamna appendiculata (Agassiz, 1843) ; Shimada 2007. 2010 Cretalamna appendiculata (Agassiz, 1843) [partim]; Shimada et al. 2010: figs. 2.43 and 2.69.
Etymology: Named in honour of Donald E. Hattin, for his work on the stratigraphy of the Niobrara Formation, western Kansas.
Holotype: LACM 128126, partial skeleton comprising the palatoquadrates, Meckel’s cartilages, 35 vertebrae and about 120, mostly disarticulated, teeth.
Type horizon: Close to Hattin’s (1982) Marker Unit 16, latest Santonian or earliest Campanian, Late Cretaceous.
Type locality: Logan County, Kansas (precise locality data on file at LACM; see Shimada 2007: 584)
Material.— Type material only.
Diagnosis.—Quadrate process more than twice as high as dorsoventrally narrowest part of palatoquadrate, anterior to quadrate process but posterior to section harbouring ante-
Fig. 15. Otodontid shark Cretalamna hattini sp. nov., upper jaw teeth of LACM 128126 (A1?– LP4 ?), holotype, latest Santonian or earliest Campanian (Late → Cretaceous); upper Smoky Hill Chalk , Niobrara Formation, Logan County, Kansas, USA. A. Right A1?; basal (A 1), lingual (A 2), profile (A 3), and labial (A 4) views. B. Parasymphyseal tooth; profile (B 1), lingual (B 2), basal (B 3), and labial (B 4) views. C. Right A2?; basal (C 1), lingual (C 2), labial (C 3), and profile
C 4) views. D. Right LP1?; basal (D 1), lingual (D 2), and labial (D 3) views. E. Left LP2?; basal (E 1) and lingual (E 2) views. F. Right LP3?; labial (F 1) and lingual (F 2) views. G. Right LP2?; labial (G 1), basal (G 2), and lingual (G 3) views. H. Right LP4?; basal (H 1), lingual (H 2), profile (H 3), and labial (H 4) views.
rior tooth files. No tooth-size reduction across the anterior/ lateroposterior boundary in upper jaw. Gradational change in root morphology in basal view from second upper anterior to lateroposterior teeth. All aspects of tooth morphology in second upper jaw tooth closer to those of adjacent upper lateroposterior teeth than to first upper anterior tooth. No teeth in dentition with recurved cusp. Apical two thirds of mesial cutting edge of cusp markedly convex in all teeth. Vertebral centra with moderately robust, densely packed radial lamellae, sometimes bifurcating distally, next to corpus calcarea. Circular lamellae absent. Neural arch foramina moderately narrow, subovate, extending full length of centrum. Thickness of corpus calcareum 1/7th of length of centrum.
Description.—See Shimada (2007) for a description of palatoquadrates, Meckel’s cartilage and teeth. His description of the disarticulated teeth pertaining to LACM 128126 was based largely on suboptimally prepared material. Subsequent preparation revealed important additional information regarding the morphology of the root in basal view. However, rather than repeating much of Shimada’s (2007) description we have restricted our revision of LACM 128126 to the inclusion of a diagnosis for C. hattini sp. nov., a revised reconstruction of the dentition, a somewhat more in-depth description of the vertebral morphology, and photographs (including basal views of the root) of fully prepared teeth.
Vertebral column: The preserved part of the vertebral column comprises 35 midtrunk centra (denominated “v1” through “v35” by Shimada 2007) ranging in size from 38– 48 mm diameter. The centra are approximately 2.5 times wider than they are long (v30 sensu Shimada 2007: fig. 1D, is 45 mm wide and 19 mm long). As indicated by Shimada (2007), many of the centra are severely deformed, preventing many meaningful measurements. The dorsal foramina are subovate with very rounded corners and abut the anterior and posterior corpus calcareum ( Fig. 14B View Fig ). The neural arch interforaminal width is 10–13 mm, whereas the intraforaminal width is 7–8 mm. Ventral foramina extend the full length of the centrum, abutting each corpus calcareum ( Fig. 14C View Fig ), and are narrow (4.25 mm; v11 and v 32 in Shimada 2007) relative to their length (14 mm; v10); although, most are greatly distorted. The region around the ventral foramina is greatly reinforced with calcified cartilage giving it a smooth and even raised appearance ( Fig. 14C View Fig ).
The centra are round and have straight, moderately robust radial lamellae, which may bifurcate next to the corpus calcareum. The radial lamellae are 0.9–1.2 mm thick and are generally equidistantly spaced being 1.2–1.7 mm apart. There are no concentric lamellae. The rim of the corpus
SIVERSSON ET AL.—LATE CRETACEOUS MID-PALAEOLATITUDE SHARKS 365
C1 10 mm A1 B1 B3 A 2 B2 E1 E4 D1 D2 C2 F C3 G3 G4 E2 G1 G2 H I1 E3 J1 K1 L1 L 2 I 2 K2 L 3 J2 M
1
2
3
4
calcareum is narrow ( Fig. 14C View Fig ). In hemisected view, it is straight to slightly rounded on the lateral side. The corpus calcareum is consistently thin (v 8 in Shimada 2007: fig. 1) and does not greatly thicken toward the margin. At the lateral margin, the corpus calcareum thickness is approximately 1/14 th of centrum diameter. The thickness of the corpus calcareum is approximately 1/7 th of the length of the centrum. No pores or radial canals are present next to the corpus calcareum.
Remarks. —The teeth of C. hattini sp. nov. most closely resemble those of C. deschutteri sp. nov., and both taxa are here referred to as C. hattini -group species. This species group is characterised (dentally) by the great width of the root in basal view relative to its height in lower anterior teeth (compare Figs. 17A 2 View Fig , 18D View Fig 2 View Fig with Figs. 7A View Fig 3 View Fig , 10A View Fig 2 View Fig , 11F View Fig 4 View Fig ; all probable a1), relatively well demarcated lingual protuberance of the root in basal view of both upper and lower anterior teeth, wide but often poorly demarcated protuberance in basal view in upper lateroposterior teeth, and broad and dome-shaped protuberance of the root in anterior teeth in profile view. In other species of the genus, the protuberance is narrower (apicobasally) and more protruding (see e.g., Figs. 4C View Fig 3 View Fig , 7A View Fig 2 View Fig , 9C View Fig 2 View Fig , 11A View Fig 2 View Fig , 12A 2 View Fig , 20A 2). Note that the protuberance is corroded in Fig. 4A View Fig 2 View Fig , hence the low profile.
The anterior teeth of C. deschutteri sp. nov. are markedly enlarged whereas the anteriorly situated upper lateroposteri- or teeth of C. hattini sp. nov. are almost as large as are the upper anterior teeth ( Fig. 19A). This is well exemplified by a simple tooth-size comparison between the two species. The largest anterior teeth of C. deschutteri sp. nov. from the Tourtia de Bettrechies are slightly larger than are the equivalent anteriors of LACM 128126. In contrast, the lateroposterior teeth at hand of C. deschutteri sp. nov. are significantly smaller than are the corresponding teeth of LACM 128126. Although the lingual and basal views of the root are similar in lateroposterior teeth of the two species, the cusp is narrower in C. deschutteri sp. nov. and much thinner labiolingually than it is in C. hattini sp. nov.
Shimada (2007: fig. 6C) illustrated the right palatoquadrate of LACM 128126 accompanied by what he regarded to represent the first seven teeth in the upper jaw (using disarticulated teeth of LACM 128126 and excluding parasymphyseals) and assigned by him to the first and second anterior files (A1–A2), an intermediate file (I1 = most distal upper anterior file sensu Siverson 1999) and the first four teeth in the upper lateroposterior hollows (denominated L1–4 by Shimada 2007). All disarticulated teeth in Shimada’s (2007: fig. 6C), except for the tooth assigned to the A1 position, were each linked to partially exposed in situ cusps of replacement teeth on the palatoquadrate. The disarticulated tooth regarded by Shimada (2007) as the upper intermediate tooth (I1) is reduced in size compared to the adjacent teeth in Shimada’s (2007: fig. 7B) reconstruction and has a strongly distally curved cusp. We initially attempted to examine in situ teeth using a Siemens Somatom Sensation 64 slice computed tomography (CT) scanner. The CT scan revealed no additional teeth in the right palatoquadrate apart from those figured in Shimada (2007) and no hidden teeth in the left Meckel’s cartilage. In addition, the CT scan indicated that no roots were attached to the cusps protruding through the medial wall of the flattened lateroposterior hollow of the right palatoquadrate. Therefore, our verification of the presence of a reduced third upper tooth with a strongly, distally curved cusp is based on characteristics of the in situ cusp.
As shown in Fig. 13C–E View Fig , there is little resemblance in cusp shape between the in situ tooth indicated as the upper “intermediate” by Shimada (2007: fig. 6C) and a disarticulated tooth assigned by him to the same tooth file ( Fig. 13C View Fig ). The in situ cusp ( Fig. 13D View Fig ) is larger and has a distally inclined as opposed to distally curved cusp. The cusp of Shimada’s (2007: figs. 7B, 8) L1, on the other hand, makes a good match after adjusting for the obvious displacement of the cusplet ( Fig. 13E View Fig ). There is thus no evidence of a reduced “intermediate” tooth in LACM 128126. The disarticulated teeth assigned to the upper “intermediate” tooth file by Shimada (2007) do not show any of the specialised features of the root that characterises upper “intermediates” of modern lamnids. Instead, the basal face of the root features an unremarkable outline ( Fig. 16A View Fig 1, B 1 View Fig ), very similar to that of other upper jaw teeth from the mid-portion of the inferred lateroposterior hollow (Figs. 15H 1, 16C 1). In lamnids ( Lamnidae ) the distal lobe of the root, facing the intermediate bar, is typically labiolingually compressed and may be lingually curved in basal view.
Shimada (2007: 586) indicated the presence of up to 15 indentations on the medial surface of the right palatoquadrate, each potentially corresponding to a separate tooth file (although he assigned 13 upper jaw tooth files, excluding parasymphyseals, to LACM 128126 in Shimada 2007: fig. 5C). We have not been able to verify the presence of 15 distinct indentations and question that number. In our reconstruction of the dentition of LACM 128126, we assigned 12 tooth files to the upper jaw (in addition to at least one file of parasymphyseals) and 10 tooth files to the lower jaw (LP10 and lp8 not shown in Fig. 19A but in Fig. 16H View Fig and 17M). Several of the teeth assigned to the upper jaw by Shimada (2007) are probably lower jaw teeth as indicated by their narrower, more upright cusps and straight to convex profile view of the labial side of the crown (i.e., Shimada 2007: fig. 8, L4 [lp4], L5 [lp5], L7 [lp6], L10 [lp8]). We agree with the relative position of all but two of the lower jaw teeth in Shimada’s (2007: fig. 9). In our reconstruction, the two teeth illustrated as l1 and l2 by Shimada (2007) have swapped places and we have added two additional commissural teeth. Contrary to Shimada (2007), we believe that the second and third tooth files (A2 and LP1) in the upper left jaw are missing. The tooth assigned to the left A2 position by Shimada (2007) is reassigned to the LP2 position as the basal view of its root (Fig. 15E 1) is very similar to that of the right LP2 (Fig. 15G 2). Overall the collection of disarticulated teeth pertaining to LACM 128126 indicates a fairly strong collecting bias towards fully mineralised teeth. The percentage of incompletely mineralised teeth in, e.g., the holotype dentition of the Cenomanian Cardabiodon ricki Siverson, 1999 (WAM 96.4.45; collected by MS and field assistants) is considerably higher than it is in LACM 128126. As in WAM 96.4.45, right and left teeth from the same relative position are not always mirror images of each other [see e.g., the right and left LP5s ( Fig. 16A View Fig 4 View Fig , B 3 View Fig )]. Because of this we chose to illustrate teeth from the same side of the jaw in Fig. 19A even though this meant that a few positions are not represented in the reconstructed dentition.
Shimada (2007) described the centra of LACM 128126 as anteriormost. We suggest that at least the first 10–20 vertebral centra are missing from LACM 128126 because the preserved centra are relatively consistently sized with no marked increase in diameter from v1 as seen in Cretoxyrhina , Archaeolamna , or Squalicorax (see Cook et al. 2011: fig. 6A).
Geographic and stratigraphic range.—Early Santonian Tamayama Formation, Japan, and latest Santonian or earliest Campanian part of the Smoky Hill Chalk, Kansas, USA.
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.