Lonchidiidae Herman, 1977

Brand, Nickolas A., Heckert, Andrew B., Sanchez, Israel, Foster, John R., Hunt-Foster, Rebecca K. & Eberle, Jaelyn J., 2022, New Late Cretaceous microvertebrate assemblage from the Campanian-Maastrichtian Williams Fork Formation, northwestern Colorado, USA, and its paleoenvironmental implications, Acta Palaeontologica Polonica 67 (3), pp. 579-600 : 583-585

Lonchidiidae Herman, 1977

Genus Lonchidion Estes, 1964

Type species: Lonchidion selachos Estes, 1964 ; Lance Formation , Upper Cretaceous .

Lonchidion griffisi Case, 1987 Fig. 3A–D .

Material.— MWC 8851, numerous tooth and teeth fragments; MWC 9580, tooth fragment; MWC 9581, tooth fragment; MWC 9582, tooth fragments; MWC 9583, tooth fragments; MWC 9584, tooth; MWC 9585, tooth fragment; MWC 9967, 13 tooth fragments; all from the Campanian–Maastrichtian, Williams Fork Formation, J&M site, northwest Colorado, USA.

Emended diagnosis.— Lonchidion species with multiple (three or more) well defined “lateral cusplets” located mesio-distally, to each side, of the principal cusp. Also possesses between two and five serrations on the labial peg of the crown. Teeth may be almost perfectly straight, or may exhibit strong curvature (modified from Case 1987).

Description.—We assign chondrichthyan teeth that are gracile, narrow labiolingually and elongated laterally to Lonchidion griffisi . The crown is prominent and low, and the occlusal surface forms a crest that has well defined individual cusplets. The lateral margins of the crown are pointed and may resemble the lateral cusps.

Remarks.—We have recovered mostly crown fragments, with little to no root material remaining, totalling 19 different tooth crowns and fragments. Two of the fragments fit together to form a single tooth. Lonchidion species are a ubiquitous component of Campanian fresh and estuarine fossil assemblages in North America ( Kirkland et al. 2013). Lonchidion griffisi was originally described as Lissodus griffisi by Case (1987), however, revisions by Rees and Underwood (2002) reassigned many species of “ Lissodus ’’ to Lonchidion , including Lissodus griffisi , an assignment followed by Fischer (2008). Material of L. griffisi is known only from the Mesaverde Formation ( Case 1987; Fischer 2008). The original material was recovered from the Teapot Sandstone Member of the Mesaverde Formation, and the deposits were determined to be of estuarine nature due to the presence of both marine and nonmarine fish fossils ( Case 1987).

Stratigraphic and geographic range.— Lonchidion griffisi was previously known only from the Late Campanian Teapot Sandstone Member of the Mesaverde Formation in Wyoming.

Lonchidiidae gen. et sp. indet.

Fig. 3I .

Material.— MWC 9800 , dorsal fin spine; from the Campanian–Maastrichtian , Williams Fork Formation, J &M site, northwest Colorado, USA .

Description.— We interpret a short segment of bone with small, offset denticles ( MWC 9800, Fig. 3I ) as a fine spine fragment. The hybodont fin spine we illustrate here was found while preparing larger fossils. Best exposed in lateral view, it preserves nine posteriorly recurved denticles that are offset from each other in an alternating pattern, but do not comprise two rows. The lateral side of the spine bears many relatively fine ridges.

Remarks.—Lonchidiid fin spines are striated and possess small, hooked denticles (e.g., Duffin 1985: fig. 25). The single row of alternating denticles and relatively smooth lateral surface are features that distinguish MWC 9800 from fin spines of most other hybodonts, including Hybodus , which typically have at least two distinct rows of parallel denticles and strongly developed lateral ridges (e.g., Kirkland et al. 2013; fig. 9.4a–e) and Lissodus , which bear alternate denticles but retain the strongly developed lateral ridges ( Kirkland et al. 2013). The specimen we illustrate here wellmatches fin spine fragments assigned to Lonchidion by Kirkland et al. (2013: fig. 9.5j–m).

Elasmobranchii Bonaparte, 1838

Neoselachii Compagno, 1977

Galeomorphii Compagno, 1973

Orectolobiformes Applegate, 1972 Ginglymostomatidae Gill, 1862

Genus Cantioscyllium Woodward, 1889

Type species: Cantioscyllium decipens Woodward, 1889 ; Lower Chalk , Upper Cretaceous .

Cantioscyllium markaguntensis Kirkland, Eaton, and Brinkman, 2013

Fig. 3E, F .

Material.— MWC 8866, tooth, MWC 9586, tooth; from the Campanian–Maastrichtian, Williams Fork Formation, J&M site, northwest Colorado, USA.

Description.—Small Cantioscyllium species differentiated by the presence of two or more lateral cusplets on either side of the crown, and by very well-defined enamel folding along the labial surface (after Kirkland et al. 2013).

Remarks.—We assign small chondrichthyan teeth with a lingually inclined broad central cusp, that bear clearly distinct lateral cusps at the margins of the crown, and possess a roughly heart shaped root when viewed basally to Cantioscyllium . Because there are two or more cusplets on either side of the crown and the labial surface of the crown is heavily textured we assign these teeth to C. markaguntensis . We have collected two teeth representative of Cantioscyllium . Cantioscyllium markaguntensis is differentiated from all other known freshwater orectolobiformes collected from Utah by the strong labial surface ornamentation ( Kirkland et al. 2013), and has previously been collected only from the Straight Cliffs Formation of the Markagunt Plateau in Cedar Canyon, Utah, so this is the first report of it from the Williams Fork Formation. It is possibly the oldest known freshwater orectolobiform shark from southern Utah ( Kirkland et al. 2013).

Hemiscyllidae Gill, 1862

Genus Chiloscyllium Müller and Henle, 1838

Type species: Chiloscyllium greeni Cappetta, 1973 ; Carlile Shale , Upper Cretaceous .

cf. Chiloscyllium sp.

Fig. 3G, H .

Material.— MWC 8850, tooth with root. MWC 9576, tooth with root. MWC 9968, 17 teeth, many with roots; from the Campanian–Maastrichtian, Williams Fork Formation, J&M site, northwest Colorado, USA.

Description.—Small (less than 2 mm) chondrichthyan teeth that are shortened apico-basally. These teeth lack lateral cusplets on the crown and may be smooth or bear weak enamel folding along the labial surface (after Kirkland et al. 2013).

Remarks.—We assign chondrichthyan teeth that are small and possess strongly triangular crowns, lacking lateral cusplets, and a weakly textured or untextured labial surface to cf. Chiloscyllium sp. A centrally oriented, well-defined ridge may be present on the labial surface of the tooth from the base of the crown to the tip. We have collected 17 specimens that we attribute to this genus. The teeth we describe are most similar to Chiloscyllium missouriense Case, 1979 , because they lack lateral cusplets and most have a smooth labial surface of the crown, though Kirkland et al. (2013) note that the specimens with the central ridge may belong to a new species or even genus. We report two morphs of Chiloscyllium teeth. Morph one tapers aggressively from the tip of the crown to the base, and tends to contain a raised ridge running along the center of the labial surface of the crown ( Fig. 3G ). Morph 2 tapers much more conservatively, to the point of being almost conical in crown shape. The lowermost portion of the labial surface of the crown extends basally and labially to further cover the root, resulting in a noticeable “drop” in the crown ( Fig. 3H ). While these morphs may represent different species, or simply be teeth in different positions in the jaw, such a question is beyond the scope of this paper and will necessitate further, focused study. Because the roots of many specimens were either worn or encrusted with sediment, species level identifications cannot be sufficiently demonstrated. The genus Chiloscyllium contains extant species ( Cook et al. 2014), although fossil species may be in need of revision ( Kirkland et al. 2013). Chiloscyllium missouriense has been recovered from the Teapot Sandstone of the “Mesaverde Formation’’ in Wyoming ( Case 1987), and similar teeth have been reported from the broadly coeval St. Mary’s River Formation of Alberta, Canada ( Kirkland et al. 2013). This is the first report of Chiloscyllium from the Williams Fork Formation.

Figures

Fig. 3. Representative non-batoid chondrichthyans from the J&M site, Colorado, USA, Williams Fork Formation, Campanian–Maastrichtian, Upper Cretaceous. A–D. Lonchidion griffisi Case, 1987. A. MWC 8851, tooth crown in labial (A1) and occlusal (A2) views. B. MWC 9580, fragmentary tooth crown in labial (B1) and occlusal (B2) views. C. MWC 9581, fragmentary tooth crown in lingual (C1), labial (C2), and occlusal (C3) views.D. MWC 9582, fragmentary tooth crown in labial (D1) and occlusal (D2) views. E, F. Cantioscyllium markaguntensis Kirkland, Eaton, and Brinkman, 2013. E. MWC 8866, tooth crown in labial (E1) and occlusal (E2) views. F. MWC 9586, tooth crown in labial (F1) and lingual (F2) views. G, H. cf. Chilloscyllium sp. G. MWC 8850, morph 1 tooth crown in mesial (G1) and labial (G2) views. H. MWC 9576, morph 2 tooth crown in mesial (H1) and labial (H2) views. I . Hybodontoidea gen. et sp. indet., MWC 9800, dorsal fin spine in lateral view.