Palaeoxanthopsidae, Schweitzer, 2003

Palaeoxanthopsidae indet.

( Fig. 19 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); ALMNH: Paleo:21482 (carapace) GoogleMaps • 51 specimens; idem; ALMNH: Paleo:21497 (51 carapaces/venters) GoogleMaps • 1 specimen; idem; ALMNH: Paleo:21505 (fixed finger) GoogleMaps • 2 specimens; idem; ALMNH: Paleo:21506 (fixed fingers) GoogleMaps • 1 specimen; idem; MMNS IP-7256.1 (fixed finger) GoogleMaps • 1 specimen; idem; UF 303867 (fixed finger) GoogleMaps • 1 specimen; idem; UF 303870 (fixed finger) GoogleMaps • 1 specimen; idem; ALMNH: Paleo:21507 (dactylus) GoogleMaps • 4 specimens; idem; ALMNH: Paleo:21508 (dactyli) GoogleMaps • 1 specimen; idem; MMNS IP-7256.2 (dactylus) GoogleMaps • 1 specimen; idem; UF 303868 (dactylus) GoogleMaps • 1 specimen; idem; UF 303869 (dactylus) GoogleMaps • 1specimen; idem; UF 303871 (dactylus) GoogleMaps • 1 specimen; idem; UF 303872 (dactylus) GoogleMaps .

MEASUREMENTS. — Maximum carapace width (mm): ALMN-H:Paleo:21482: 24.6

DESCRIPTION

Preserved carapace c. 24.6 mm wide without anterolateral projections, weakly vaulted transversely, moderately vaulted longitudinally. Fronto-orbital width c. 55% of maximum width. Anterolateral margin with bases of four projections. Carapace with five large protuberances, one marking base of mesogastric region, two adjacent to anterior part of mesogastric region, and two lateral to cervical groove at level of mesogastric region base.Transverse row of small bumps anterolaterally of posteriormost set of protuberances. On cuticle, tubercles on protuberances and in front of anteriormost protuberances. Pit present in front of each side of posterior part of mesogastric region. Flanks steep. Preserved pterygostome appears subtriangular. Sternite 3 wider than long, separated from sternite 4 by a concave groove. Sternite 4 intersected by narrow sternopleonal cavity, both sides appear square-shaped. Coxa and basis of pereiopod 1, and parts of maxilliped 3 preserved. Sternum and appendages covered by tubercles, except for grooves and sternopleonal cavity. Rostrum, posterior carapace, most of ventral side, pleon, and appendages missing.

Fixed finger robust; curved inward; with row of oval tubercles, variably sized, diminishing in size to tip on average; outer and inner lateral sides with row of pits. Dactylus curved; with strong tubercle on outer side of occlusal surface near base, followed by smaller, similar-sized tubercles toward tip.

REMARKS

The single carapace lacks the posterior portion, the frontal region including the orbital structure and the rostrum, and the projections on the anterolateral margins. The preserved characters fit those of Palaeoxanthopsidae (e.g., Schweitzer 2003; Schweitzer et al. 2018a, 2025; Vega et al. 2018), including the location of the spherical swellings on the carapace and the anterolateral margins with bases of projections. Specimens of the Maastrichtian genera Palaeoxanthopsis Beurlen, 1958 , and Parazanthopsis Vega, Feldmann, García-Barrera, Filkorn, Pimentel & Avendano, 2001 , are morphologically close to the single, incomplete carapace specimen herein. The collection of more complete carapaces is necessary for identification beyond the family level.

We also found various fingers attributable to Palaeoxanthopsidae . Both fixed fingers and dactyli conform well to those seen in Palaeoxanthopsidae such as Paraverrucoides alabamensis ( Rathbun, 1935a) from the upper Danian Porters Creek Formation of Alabama (GSA-I21006 and GSA-I21010) and Lobulata lobulata ( Feldmann, Casadio, Chirino-Galvez & Aguirre-Urreta, 1995) , from the Maastrichtian-Danian of Argentina (their fig. 7.6). It is very likely that these isolated fingers belong to the same species as the carapace, but associated chelipeds with a carapace are needed for verification.