Maastrichtian crustacea (Brachyura: Decapoda) from the Ocozocuautla Formation in Chiapas, southeast Mexico

Abstract

More than thirty complete specimens ofCarcineretes planetariusVega, Feldmann, Ocampo, and Pope, 1997, a member of the extinct decapod family Carcineretidae, have been collected from the upper part of the Ocozocuautla Formation in Chiapas, southeast Mexico. Stratigraphic occurrences ofCarcineretesin the Caribbean Province suggest that this crab should be regarded as an index fossil for the early Maastrichtian. Six samples of this species may represent individuals that died during molting. The sudden disappearance of this family at the end of the Maastrichtian and its restricted paleobiogeographic distribution in the vicinity of the impact site suggest that the Carcineretidae may have been affected by the Chicxulub impact. Other decapod specimens collected from the same localities were assigned to the Xanthidae;Parazanthopsis meyapaquensisnew genus and species, andMegaxantho zoque, new genus and species, are described. They constitute the second and third reports of Cretaceous xanthid crabs from Mexico. A lagoonal paleoenvironment is suggested, based on associated fauna and flora. Occurrences of index species of benthic and planktic foraminifera along with that of diagnostic rudist species confirm an early Maastrichtian age.

Specialized shell-breaking crab claws in Cretaceous seas

“…127 mm; figure 1; Vega et al 2001). The right claw is large in this species, measuring approximately 108 mm in length and approximately 57 mm in height on the holotype specimen (IHNCH-3421; figure 1c).…”

“…Calcareous algae, large rudists, other bivalves and gastropods, such as aporrhaids and turritellids, are abundant in the outcrops, which indicate a productive setting. Benthic foraminifera and stratigraphic position indicate an Early Maastrichtian age for the Ocozocoautla Formation ( Vega et al 2001).…”

“…Crustacean decapods have been reported from diverse outcrops of the Ocozocoautla Formation ( Vega et al 2001). Two specimens of a new species of xanthid crab, Megaxantho zoque ( Vega et al 2001), were found near the town of Ocozocoautla (locality 1003 of the Instituto de Historia Natural del Estado de Chiapas, IHNCH).…”

“…Two specimens of a new species of xanthid crab, Megaxantho zoque ( Vega et al 2001), were found near the town of Ocozocoautla (locality 1003 of the Instituto de Historia Natural del Estado de Chiapas, IHNCH). The Ocozocoautla Formation is a Late Cretaceous stratigraphic unit in the central portion of Chiapas, southeastern Mexico, and includes 630 m of prodeltaic sediments, including lagoonal deposits that were deposited in warm well-oxygenated water (Michaud 1988;Vega et al 2001). Calcareous algae, large rudists, other bivalves and gastropods, such as aporrhaids and turritellids, are abundant in the outcrops, which indicate a productive setting.…”

Considerações filogenéticas e biogeografia histórica dos malacostráceos (decápodes e isópodes) cenozóicos do Brasil

“…As famílias Xanthidae e Grapsidae surgiram na região caribeana durante o Maastrichtiano, registradas no México e Pacífico Norte, além do Eoceno e Oligoceno, também do México, e Mioceno do Brasil (Vega et al 2001a). Na Formação Pirabas, a família Xanthidae está representada pelos gêneros Tetraxanthus e Panopeus, que surgiram respectivamente na região caribeana e Pacífico Norte, ocupando em seguida também as regiões temperadas.…”