Elasmobranchii Bonaparte, 1838

Potvin-Leduc, Daniel, Cloutier, Richard, Landing, Ed, Hernick, Linda Vanaller & Mannolini, Frank, 2015, Givetian (Middle Devonian) sharks from Cairo, New York (USA): Evidence of early cosmopolitanism, Acta Palaeontologica Polonica 60 (1), pp. 183-200 : 192-193

Sublass Elasmobranchii Bonaparte, 1838 Compound chondrichthyan scales Type 1 sensu Liao et al. 2007

Figs. 8 , 9 ; SOM 4.

Material.—NYSM 17782–17789, scales; NYSM 17960, an incomplete fin spine with associated scales and smaller, rounder elements from Plattekill Formation, Cairo quarry, Cairo, Greene County, New York, USA.

Description.—The scales are of ctenacanth type (sensu Reif 1978). They have either two or three rows of ridge-ornament- ed odontodes ( Fig. 8A, B ). The main row is widest and composed of eight to ten odontodes (except for the smaller NYSM 17787; Fig. 8C ). An underlying row can, in some cases, be distinguished by the apexes of odontodes on the posterior margin of the crown. The overlying, higher row is composed of either one, two, or three odontodes that are not in contact with each other. This higher row contains a main odontode relatively central to the main row. This main odontode originates at the anteriormost point of the base. The odontodes of the higher row are characterized by a small triangular area with a pattern of ridges that occurs at their contact with the base ( Fig. 8D, E 1 ). These ridges taper where the odontodes curve towards the posterior extremity. The base is more often concave ( Fig. 8E 3 ), but a convex base is present in one specimen (NYSM 17788). The overall shape of the base varies between rhomboid and oval, with the anterior side sometimes irregular in outline. A row of vascular openings is present under the crown on the posterior side of the neck ( Fig. 8E 2 ).

The associated scales appear identical to MGUV 5945 of Ginter et al. (2008: fig. 3) and to a specimen assigned to the chondrichthyan dermal denticle type 1 of Liao et al. (2007: fig. 4). In both cases, the specimens came from the Aragonian Pyrenees of Spain. Of interest is the triangular pattern found at the base of the odontodes of the higher row in the Cairo scales. This characteristic form is also present in MGUV 5945 of Ginter et al. (2008) but appears to be absent from the other scales figured by Liao et al. (2007) and Ginter et al. (2008). More specimens from either locality would help to establish if this represents a taxonomically diagnostic character. Liao et al. (2007) suggested an assignment to Phoebodus , but as this taxon has not been found in the Cairo assemblage, and given the similarity with the Cairo scales, it is possible that the ctenacanth-type scales from Cairo belong to Wellerodus . It is interesting to note that a tooth identified as Antarctilamna was also found in the Aragonian Pyrenees ( Ginter et al. 2008).

The Cairo scales are also comparable to NMV P228929 of Elasmobranchii indet. fam. gen. et sp. A of Burrow et al. (2009: fig. 9) from the Aztec Siltstone in Antarctica, who noted a similar morphology in Antarctilamna prisca material. The scales described here, however, have a different morphology from the scales described in the holotype of A. prisca ( Young 1982) . The scales of A. prisca are rounder, flatter and show a circular pattern of ridges ( Young 1982: pl. 87: 6, 7), more similar to the scales of Doliodus problematicus ( Miller et al. 2003: fig.1B) than to the scales found in Cairo. Since then, new articulated material currently under study, including associated scales and dentition, confirms the affiliation of the compound scales with W. priscus (DP-L. and RC, personal observations).

The tip of a small fin spine was recovered in association with the scales just described (NYSM 17790; Fig. 9A, B ). The spine is covered with longitudinal, relatively smooth ridges. The smoothness is likely owing to abrasion as a small section of a ridge at the spine’s tip shows a short series of tubercles. A line of median denticles is present on the ventral face ( Fig. 9D 2 ). The specimen is partly covered with compound chondrichthyan scales and small rounded elements ( Fig. 9A, E 2 ). The interior of the spine, as revealed by micro-CT scan, is mostly occupied by numerous canals running parallel to the long axis of the spine, with the occasional perpendicular connection between canals ( Fig. 9C, D 1, E 1 ; see also SOM 4). A specific pattern does not seem to be present in the organization of the canals.

Figures

Fig. 8. Compound chondrichthyan scales Type 1 sensu Liao et al. (2007), attributed to Wellerodus priscus, from the Givetian of the Cairo quarry, New York. A. NYSM 17785 in dorsal view. B. NYSM 17782 in dorsal (under BES mode) (B1) and dorso-lateral (B2) views. C. NYSM 17787 in dorsal view. D. NYSM 17783 in dorsal view (under BES mode). E. NYSM 17786 in rostral (E1), caudal (E2), and basal (E3) views (under BES mode).

Fig. 9. Incomplete fin spine with compound chondrichthyan scales that are comparable to Type 1 sensu Liao et al. (2007) from the Givetian of the Aragonian Pyrenees, Spain, NYSM 17790. A. Specimen whitened with ammonium chloride. B. Close-up view of associated spine, associated to compound chondrichthyan scales Type 1 sensu Liao et al. (2007). C. Transversal section extracted from a reconstruction of the specimen from micro CT scan data (exposure time: 1650 ms; accelerating voltage: 65kV; current: 120 μA), showing the internal canals. D. Sections extracted from the reconstruction of the fin spine tip from micro-tomodensitometry data; lateral (D1) and dorsal (D2) views, showing the system of internal canals. E. 3D reconstructions of the fin spine tip from micro CT scan data (exposure time: 1650 ms; accelerating voltage: 65kV; current: 120 μA), in lateral (E1) and dorso-lateral (E2) views.

Fig. 1. Location of the Cairo quarry (star) (3.22 km northwest of Cairo, Greene County, 42.32° N and 74.04° W, NAD 83) in eastern New York State, USA (inset map); figure modified from Hernick et al. (2008: fig. 1).

Fig. 3. Juvenile morphotype of the teeth of omalodontid shark Portalodus mannoliniae sp. nov. from the Givetian of the Cairo quarry, New York, USA. A. NYSM 17736, paratype, in labial (A1), lingual (A2), occlusal (A3), and lateral (A4) views. B. NYSM 17756, in occlusal (B1) and lingual (B2) views. C. NYSM 17752, in occlusal (C1) and lingual (C2) views.

Fig. 2. Generalized stratigraphic section of the Plattekill Formation at Cairo quarry. Chondrichthyan specimens described herein originate from the 5-m level. The fish horizon at 7.35 m corresponds to the level of the fossilized forest mentioned by Cloutier et al. (2010).