Calverteca osbornei, Godfrey & Feldmann & Schweitzer, 2024

Calverteca osbornei gen. et sp. nov.

Figures 2 View FIGURE 2 and 3 View FIGURE 3

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Holotype. The sole specimen, the holotype, of Calverteca osbornei sp. nov., CMM-V-11695, is deposited in the vertebrate paleontology collection in the Calvert Marine Museum , Department of Paleontology , Solomons, Maryland, USA. It was included in the vertebrate paleontology collection because the coprolite was deemed to be vertebrate in origin.

Etymology. Named in honor of Jason E. Osborne who found and donated the type specimen to the Calvert Marine Museum. “Osbornei” was created by adding an “i” to “Osborne” in accordance with Article 31.1.2. of the ICZN.

Locality and stratigraphic position. The specimen was collected on the bed of the Pamunkey River, Virginia, USA in association with sediments of the Newport News beds in the lower Miocene Calvert Formation.

Diagnosis. As for genus.

Decription. Impressions of the cephalon and antennae do not appear to have been preserved and neither are there any impressions of pereopods. However, the seven pereonites and five pleonites are clearly visible. Within the pereon, the first six pereonites increase evenly in width from 3.3 mm for the first pereonite to 5.9 mm for the width of the sixth pereonite. Pereonite 7 decreases to approximately 5.2 mm wide. The midline length of the pereonites ranges from 0.7 mm for the second to 1.1 mm for the seventh ( Figure 2 View FIGURE 2 ). The entire pleon is approximately 2 mm long by 4 mm wide across the first pleonite. Along the midline, the length of each pleonite is about 0.3 mm. The pleonites decrease in width evenly to approximately 1.9 mm for the fifth. The pleopods are also preserved. They are strong and eliptical in outline.

Remarks. The sole specimen is preserved as a mold of the exterior situated transverse to the long axis of the vertebrate coprolite that embraces it. The mold is embedded deeply enough within the coprolite to suggest that the isopod was not well exposed on the surface. Preservation in this fashion, with no matrix material filling the mold, suggests that the isopod was complete both when ingested and voided to be incorporated as it is into the coprolite.

Cymothoids are parasitic isopods (Smit et al., 2014) that attach to the tongue and other soft-tissue regions in fishes. It has been well-established that isopods of this family and body form are parasitic on fish (Smit et al., 2014). A search of the literature did not reveal any reference to cymothoids as parasites on reptiles. Very large isopods, Bathynomus , have been observed to scavenge upon dead crocodiles. Thus, several scenarios may be visualized to account for the small isopod within a fecal mass. 1) The individual enclosed within the coprolite might have been ingested by the reptilian producing the coprolite when the isopod was detached from its original host. 2) This cymothoid may have parasitized a wider variety of hosts in the Miocene than today. However, the fossil is sufficiently similar to modern cymothoids that one can safely say that it was an external parasite of fish. 3) The coprolite may have been produced by a fish, and the isopod was, indeed, a parasite that was dislodged and ingested.

There are over 10,000 known extant species of isopods that inhabit terrestrial, freshwater, and marine environments (Poore and Bruce, 2012; Schram and Koenemann, 2021). Most members are less than 2 cm (0.8 in) in length. For being such a successful cosmopolitan and speciose group of crustaceans, isopods have a poor and very incomplete fossil record (Schram, 1970; Maguire et al., 2018; Schram and Koenemann, 2021). Although they first appeared in the fossil record during the Carboniferous (Schram, 1970), remarkably few extinct species have been described (Wieder and Feldmann, 1992; Schram and Koenemann, 2021).

GODFREY, FELDMANN, & SCHWEITZER: ISOPOD IMPRESSION IN A COPROLITE

Maguire et al. (2018) attributed this not to their numerical paucity through time, but rather, likely due to the physical and chemical composition of their thin and lightly sclerotized cuticle. Furthermore, their cuticle would have rapidly disintegrated following their destructive biphasic molting behavior (Tait, 1917). These attributes decrease the chances of fossilization.