Judithemys kranzi, Robert & Weems, 2014

Robert & Weems, E., 2014, Paleogene chelonians from Maryland and Virginia, PaleoBios 31 (1), pp. 1-32 : 5-6

Judithemys Parham & Hutchison 2003 Judithemys kranzi n. sp.

( Figs. 4–7)

Synonymy — Osteopygis roundsi (partem) Weems 1988.

Holotype — CMM-V-4755 , slightly more than half of a carapace, nearly complete on its right side except for the first peripheral and in its medial region except for the nuchal and first and second neurals; on the left side only a fragment of the central and posterior portions of the carapace are preserved.

Type locality, horizon, and age — This specimen was recovered at a construction site in Fort Washington, west of Maryland Route 210, Prince Georges County, Maryland (in the vicinity of 38.7435 N, 77.0104 W); in a block of lime-cemented rock broken from an Aquia Formation hard-bed, very probably “Zone 3” or “Zone 5” of the Piscataway Member ( Clark and Martin 1901); late Paleocene (early Thanetian) .

Referred specimen — USNM 357710, left hyoplastron and hypoplastron, discussed and illustrated in Weems (1988).

Locality, horizon, and age — Found in the Blue Banks south of Liverpool Point, eastern bank of the Potomac River, Prince Georges County, Maryland; from “zone 2” of the lower Piscataway Member of the Aquia Formation ( Clark and Martin 1901); late Paleocene (early Thanetian) .

Etymology —The species is named for Dr. Peter Kranz, who recovered and donated the holotype.

Diagnosis —The deeply impressed sulcal grooves, the wide but only ligamentously connected plastral bridge, and the large size of Judithemys kranzi readily places it among the “ Macrobaenidae .” Of the two North American genera in this family, J. kranzi differs from O. emarginatus in having only two suprapygals, a wide nuchal, a pygal that does not appear to be posteriorly elongated, and a hyoplastron with an external margin that shows a narrow outer anterior extension ( Fig. 6). All of these traits are present in Judithemys . Compared to the two known species of Judithemys ( Brinkman et al. 2010) , J. kranzi differs from J. sukhanovi Parham and Hutchison 2003 in having a much more regularly elliptical-shaped carapace not much widened posteriorly, neurals much longer than wide, a seventh neural that is distinctly shortened anteroposteriorly, and much more elongate second and third vertebral scales. It differs from J. backmani ( Russell 1934) in having a relatively wider nuchal, a relatively longer second vertebral scale, a relatively narrower fifth vertebral scale, and a sulcus on the eighth costal located near and along its posterior border and not near its anterior edge.

Description —The carapace is elliptical, longer than wide, with anterior border rounded and posterior border slightly scalloped at the lateral margins of the pygal ( Fig. 5). The bone has an anastomosing surface texture and deeply impressed sulcal grooves. Nuchal much wider than long and apparently somewhat “T”-shaped. Neurals are longer than wide except for the seventh which is shortened and about as wide as long. Two suprapygals are present; the pygal is smaller and anteroposteriorly shorter than the adjacent peripherals. The vertebral scales are hexagonal, with the first being wide and short, the second being longer than wide, the third and fourth being about as long as wide, and the fifth wider than long.

Remarks —The pygal region is variable in “macrobaenids,” so comparison of that region with other species, based only on a single specimen, is not instructive. These similarities and differences are summarized in Table 1. This specimen is the first reported occurrence of Judithemys in the eastern United States, though part of its plastron was previously illustrated by Weems (1988) and incorrectly assigned to Osteopygis roundsi .