Squalus sp.

Boles, Zachary M., Ullmann, Paul V., Putnam, Ian, Ford, Mariele & Deckhut, Joseph T., 2024, New vertebrate microfossils expand the diversity of the chondrichthyan and actinopterygian fauna of the Maastrichtian-Danian Hornerstown Formation in New Jersey, Acta Palaeontologica Polonica 69 (2), pp. 173-198 : 181-182

publication ID	https://doi.org/ 10.4202/app.01117.2023
persistent identifier	https://treatment.plazi.org/id/03E18741-130C-EF09-DF1E-FE75FAD9FC8C
treatment provided by	Felipe
scientific name	Squalus sp.
status

Treatment

Squalus sp.

Fig. 2I, J View Fig .

Material.—One lateral tooth (RU-EFP-00157-7) from the MFL; eight partial squalid fin spines including one (RU- EFP-00267-1) from the lower Hornerstown Formation below the MFL, two (RU-EFP-02582 and 3942) from the MFL, one (RU-EFP-03567) from the lower Hornerstown Formation above the MFL, and four (RU-EFP-00157-8, 0157-9, 0267, and 4146) collected as float. All from the MaastrichtianDanian Hornerstown Formation, Edelman Fossil Park, Mantua Township, New Jersey, USA. Because the tooth can be assigned to Squalus , we tentatively assign the fin spines to this genus as well.

Description.—The single cusp is broad, low, labiolingually narrow, and strongly turned distally. Weak serrations are present along its mesial cutting edge. The distal heel is proportionately short, with a tall, rounded profile, and is separated from the cusp by an acute notch. A distinct, tongue-shaped apron of the crown extends below the basal border of the root from the center of the labial face. The sides of the apron are parallel, and its distal tip is circular. The mediolingual uvula of the crown is large and forms a rounded, linguodistally directed apex. The root is short and approximately the same breadth as the crown, with a well-developed basal lobe descending from its midpoint nearly to the apex of the apron. A pronounced horizontal shelf traverses the lingual face of the root. It is perforated beneath the uvula by a subcircular, moderately-broad infundibulum. The basal face of the root is shallowly concave and only slightly turned lingually.

Remarks.—Among Squalinae, the tooth can best be assigned to Squalus based on the basal face being only slightly lingually turned, presence of a modestly broad infundibulum, and a long mediolabial apron on the crown with parallel sides ( Cappetta 1987; Adolfssen and Ward 2014). Although teeth of Centrophoroides Davis, 1887 , and Centrosqualus Signeux, 1950 , are very similar in form ( Adolfssen and Ward 2014), the basal face is more strongly turned lingually in Centrophoroides and the apron in Centrosqualus is more bulbous in form owing to narrowing of its base ( Müller and Schöllmann 1989). The apron is comparatively broader and more triangular in Protosqualus Cappetta, 1977 , and Megasqualus Herman, 1982 ( Cappetta 1987). Teeth of Deania Jordan & Snyder, 1902, and Centrophorus Müller & Henle, 1837 , lack the projection of the apron beneath the basal plane of the root ( Cappetta 1987). While absence of well-developed serrations suggests the specimen is not S. serriculus Jordan & Hannibal, 1923, or S. crenatidens Arambourg, 1952 ( Cappetta 1987), other features used to diagnose species within the genus are known to vary in form ontogenetically ( Adolfssen and Ward 2014), individually Cappetta et al. 2016), and by gender ( Siverson 1993). Thus, we refrain from assigning the specimen to any particular species at this time.

To our knowledge, among Squalus species only S. minor Daimeries, 1888 , has been reported in Paleocene deposits in northeastern North America. This species is reported from the Danian Brightseat Formation in Maryland ( Ward and Wiest 1990) and from the lower (Danian) portion of the Hornerstown Formation in Monmouth County, New Jersey Case 1996). The teeth described by Case (1996) thus derive from the same stratigraphic range as our tooth. However, Case (1996) did not provide a differential diagnosis among Squalus species; therefore, we view his species assignment as inconclusive and do not follow it; instead assigning RU- EFP-00157-7 to Squalus sp. This specimen derives from the MFL, placing it in the very earliest Danian, and the fin spines tentatively inferred to also pertain to Squalus include a specimen from beneath the MFL in the Hornerstown Formation, indicating squalid sharks crossed the K/Pg at this site.

Synechodontiformes Duffin & Ward, 1993

Orthacodontidae Glikman, 1957

Genus Sphenodus Agassiz, 1843

Type species: Lamna longidens Agassiz, 1843 , Late Jurassic , Switzerland .

Sphenodus lundgreni (Davis, 1890)

Fig. 2K View Fig .

Material.—Two teeth: one (RU-EFP-02913) from the MFL and another (RU-EFP-04159) collected as float. All from Fossil Park, Mantua Township, New Jersey, USA.

Description.—RU-EFP-02913 is essentially complete, measuring 30.2 mm in maximum height, with a root that is 25.5 mm in width and 12.3 mm in length. The crown is nearly vertically oriented and weakly sigmoidal in mesial and distal views. The crown is smooth, with the lingual surface being more convex than the labial surface. Two sharp carinae extend from the crown to form lateral heels on the root. The carinae thin towards the tooth tip and at the base of the crown. Numerous folds are present along the crown-root junction, with enamel ridges extending onto the root. Folds are more tightly spaced and shorter on the lingual side of the tooth. The root is short with a nearly flat basal surface. Abundant nutrient foramina are present, especially on the lingual surface, as well as distinct labiolingually-oriented grooves on its basal surface.

Remarks.—The teeth can be confidently assigned to Sphenodus due to their possession of a straight, sharp central cusp, lateral heels of each carina extending onto the lingual surface of the root, a more lingually convex crown (in cross section), and shallow, basally-flat root with labiolingually-oriented vascularization ( Cusumano et al. 2021). Among the currently-recognized species of Sphenodus , S. lundgreni is the only species known from the Maastrichtian ( Adolfssen and Ward 2014) and Danian ( Cappetta 2012). The presence of numerous folds across the crown-root junction further supports assignment to this species ( Kanno et al. 2017).

Callahan et al. (2012) reported the first known occurrence of the synechodontiform shark S. lundgreni , a single lateral tooth ( NJSM 23223), from the EFPQ, which was also the first report of this taxon from North America. However, NJSM 23223 was not found in situ, thus its exact stratigraphic provenance within the Hornerstown Formation remains uncertain. Recovery of RU-EFP-02913 constrains the occurrence of this taxon at least to the MFL. We also report the second and third known occurrences of this taxon from the EFPQ, and thus from North America.

Stratigraphic and geographic range.—Upper Cretaceous (Maastrichtian) to Paleocene (Thanetian) of New Jersey in USA, Denmark, Sweden, UK, and Kazakhstan.