Tasbacka ruhoffi ( Weems 1988 ) Robert & Weems, 2014

Robert & Weems, E., 2014, Paleogene chelonians from Maryland and Virginia, PaleoBios 31 (1), pp. 1-32 : 23

Tasbacka ruhoffi ( Weems 1988) n. comb. ( Fig. 16)

Synonymy – Catapleura ruhoffi Weems 1988 .

Specimen –USNM 358865, disarticulated partial skeleton consisting of the fused dentaries, nuchal, right and left first peripherals, right and left second peripherals, right third peripheral, fifth, sixth and ninth left peripherals, eleventh right peripheral, parts of second costal, sixth right costal, first neural, part of fourth neural, eighth neural, and first suprapygal, described in Weems (1988).

Locality, horizon, and age – West bank of roadcut, Indian Head Road near Piscataway Creek, Prince Georges County, Maryland; Piscataway Member of the Aquia Formation; late Paleocene (early Thanetian).

Remarks –The turtle described by Weems (1988) as Catapleura ruhoffi later was discussed by Tong and Hirayama (2002), who strongly implied but did not explicitly state that the species should be referred to the genus Tasbacka . The first costal of T. ruhoffi is quite similar to that of Catapleura in that its external border is much longer than its internal border. This is due to the fact that the sutures along the anterior border of the first costals are strongly angled outward from the rim of the shell carapace (away from the midline) and not oriented normal to the carapace rim as is typical in pancheloniid turtles. This unusual conformation was why Weems (1988) referred the species to that genus. However, it is now apparent that in this regard the first costal of T. ruhoffi also is very similar to that of Tasbacka , and in all other diagnosable characters the similarity with Tasbacka is greater. Therefore, assignment to Tasbacka is accepted here. Tong and Hirayama (2002) correctly reported the age and stratigraphic horizon of T. ruhoffi , but they erroneously placed the type locality in the “Pamunkie [Pamunkey] River Bluffs, Virginia;” the type specimen actually is from Prince Georges County, Maryland. Tong and Hirayama (2002) thought that, in characters that can be compared between the two taxa, T. ruhoffi is very similar to T. aldabergeni except that T. aldabergeni has a more strongly developed symphyseal ridge on its dentary ( Nessov 1987). It is also true, however, that the nuchal of T. aldabergeni has a much shallower anterior concavity (width:depth ratio = 14) than the nuchal of T. ruhoffi (width:depth ratio = 7), and the seventh to ninth neurals of T. ruhoffi are keeled while the seventh to ninth neurals of T. aldabergeni are unkeeled (compare fig. 2 of Nessov 1987 with fig. 18 of Weems, 1988). Therefore, even though both species are referable to Tasbacka , they appear to be distinctly different. T. aldabergeni was described from the late Paleocene of Kazakhstan and a third species, T. ouledabdounensis Tong and Hirayama 2002 has been described from the late Paleocene of Morocco ( Tong and Hirayama 2002), so Tasbacka seems to have dispersed widely in the early or middle Paleocene and then developed into distinctly different populations in central Asia, north Africa, and the eastern United States. It seems likely that some population of late Paleocene Tasbacka was the ancestor of the early Eocene species Puppigerus camperi (Gray) Moody.