Ctenocheles sp.

Ctenocheles sp.

( Fig. 7 View FIG )

MATERIAL EXAMINED. — United States • 1 specimen; Alabama, Lowndes County, Mussel Creek roadcut ( 31°58’17”N, 86°42’15”W), ALMNH loc. 3; Clayton Formation, Pine Barren Member , lower middle NP2 nannofossil zone; Paleocene (lower Danian); ALMN-H: Paleo:21514 (finger) GoogleMaps .

MEASUREMENT. — Finger length: 12.0 mm.

DESCRIPTION

Incomplete pectinate finger, thin, rounded to slightly oval in cross-section, somewhat curved in lateral and occlusal views. Teeth on occlusal surface of at least three sizes; with smaller ones in between larger ones, number of which varies. Inner, outer, and lower sides with small, variably sized pits.

DISCUSSION

Tshudy & Sorhannus (2000) and Hyžný & Dulai (2014) pointed out that pectinate claws evolved in multiple, often distantly related decapod lineages including Astacidea Latreille, 1802 ( Nephropidae Dana, 1852 : Acanthacaris Bate, 1888 [extant], Oncopareia Bosquet, 1854 [Early Cretaceous-Paleocene], Thaumastocheles Wood-Mason, 1874 [extant], Thaumastochelopsis Bruce, 1989 [extant]); Astacidea ( Stenochiridae Beurlen, 1928 : Stenochirus Oppel, 1861 [Early to Late Jurassic]); Axiidea ( Ctenochelidae : e.g., Ctenocheles [Early Cretaceous-Holocene]); Brachyura Latreille, 1802 ( Iphiculidae Alcock, 1896 [Miocene-Holocene] and Leucosiidae Samouelle, 1819 [Eocene-Holocene]); Glypheidea Van Straelen, 1925 ( Litogastroidae Karasawa, Schweitzer & Feldmann, 2013 : Lissocardia von Meyer, 1851 [Middle Triassic]); and Polychelida ( Palaeopentachelidae Ahyong, 2009 : Palaeopentacheles von Knebel, 1907 [Late Jurassic]). Thus, uncritical assignment of isolated claw elements to any of these is not justified, but a combination of stratigraphic and geographic occurrence can narrow down possibilities substantially. The stratigraphic occurrence of the aforementioned taxa excludes most taxa, leaving Ctenochelidae and Oncopareia as possibilities.Tshudy et al. (2022) revised Oncopareia to include European records only, making assignment of ALMNH:Paleo:21514 to this taxon unlikely. Within Ctenochelidae , some representatives of multiple genera bear pectinate claws including Ctenocheles , Ctenocheloides , and Kiictenocheloides . Of these, only Ctenocheles is recognized in the fossil record thus far. Therefore, we assign the specimen to Ctenocheles with some provision. This early Danian specimen differs from the late Danian Ctenocheles cookei ( Rathbun, 1935a) from Alabama because the teeth of C. cookei are more similar in size and the pits on the sides are more aligned. It also differs from the late Danian Ctenocheles cultellus ( Rathbun, 1935a) from Alabama in that C. cultellus has an oval rather than a rounded cross-section of the finger. In the absence of more complete specimens with both fingers and a propodus preserved, we refer the specimen to Ctenocheles sp.