Bronson and Maisey—Re-identification of Platylithophycus Materials and methods


Materials.—Well-preserved gill arches and cartilage fragments (UNSM IP16868). Three small chips of the holotype (pre- viously numbers 26071, 26072, and 26073 in Princeton Uni- versity’s geology collection) had been given to the American Museum of Natural History in 1982 with a note to rejoin the holotype (then residing at the Carnegie Museum). These frag- ments are now reunited with UNSM IP 16868.


Locality information.—No coordinates were provided at the time of this specimen’s collection, so its exact position is unknown beyond the following: “Upper Cretaceous Niobrara Formation, three miles northeast of Monument Rocks, Cove County, Kansas” (Johnson and Howell, 1948, p. 632).


Methods.—Specimen was examined using a dissecting micro- scope, and photographed using a DinoLite handheld microscope (AnMo Electronics Corporation), and photographed under UV light (byMike Eklund, ThinkLabz),which produced fluorescence consistentwith use of some kind of sealant or epoxy treatment (not necessarily consistent with biological or geological fluorescence). Morphology of UNSM IP16868 was compared with figures and descriptions from the work of Johnson and Howell (1948) and Miller and Walker (1968). The fragments previously known as Princetonspecimens 26072and 26073(nowpartofUNSMIP 16868) were imaged using scanning electron microscopy, with a Zeiss EVO 60 Variable Pressure SEM.


Repository and institutional abbreviation.—Specimen housed at the University of Nebraska State Museum (UNSM).


Systematic note.—The original species name has been emended here to agree with the gender of the genus name (Latin phycus, masculine noun III declension; cretaceus, adjective I class).


Systematic paleontology Class Chondrichthyes Huxley 1880


Subclass Elasmobranchii Bonaparte 1838 Elasmobranchii incertae sedis


Genus Platylithophycus Johnson and Howell, 1948


Platylithophycus cretaceus (Johnson and Howell, 1948) Figures 1–3, 4.1, 5, 6, 7.1, 7.3


1948 Platylithophycus cretaceum Johnson and Howell, p. 632, pl. 93, figs. 1, 2.


1968 Platylithophycus cretaceum; Miller and Walker, p. 181, pls. 2, 3.


Holotype.—Gill arches and associated cartilage fragments (UNSM IP 16868) from the Niobrara Chalk, Kansas (Johnson and Howell, 1948, pl. 93, figs. 1, 2).


Diagnosis.—Cartilaginous gill arches of a large chondrichthyan fish, embedded in chalk matrix. Calcified cartilage of the gill arches possesses a filamentous appearance (Fig. 2), while


Figure 3. Holotype of Platylithophycus cretaceus (UNSM IP 16868), detail of features interpreted here as gill rakers, scale=1cm. Photo courtesy ofM. Eklund.


the cartilage present on gill rakers (Fig. 3) is tessellated (“canaliculate” according to Miller and Walker, 1968).


Occurrence.—Upper Cretaceous Niobrara Chalk, 3 miles northeast of Monument Rocks, Cove County, Kansas (Johnson and Howell, 1948).


Description.—The specimen is 48 cm in length and 24 cm across at its widest point. Gill arch elements are all fairly stout


745


Figure 2. Holotype of Platylithophycus cretaceus (UNSM IP 16868), detail of mineralized cartilage on surface of features interpreted as gill arches, scale=1 cm. Photo courtesy of M. Eklund.


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