The oldest frog crabs (Decapoda: Brachyura: Raninoida) from the Aptian of northern South America

Abstract

Raninoida, also known as "frog crabs," is a clade of extant true crabs (Brachyura) characterized by a fusiform carapace (raninid-type), narrow thoracic sternum, pleon partially exposed dorsally, and paddle-like limbs, all of which are well suited to their cryptic burrowing lifestyle. However, the most basal raninoids from the Cretaceous were morphologically different, with ornamented carapaces that were wider than long (necrocarcinid-type), a broader thoracic sternum, and the pleon fitting between the legs assisted by pleonal locking mechanisms. During Albian times (∼112 to 99.6 Ma.) both body plans flourished worldwide. In contrast, pre-Albian (older than ∼112 Ma.) fusiform families have not yet been reported. The discovery of Notopocorystes kerri n. sp., a fusiform crab from the upper Aptian (∼115 Ma.) of Colombia, South America, and the re-examination of Planocarcinus olssoni (Rathbun, 1937) n. comb., a necrocarcinidlike crab from the same age and locality, extend the record of the two body plans back into the Aptian of the equatorial Neotropics. Notopocorystes kerri is the oldest fusiform raninoid known to date, revealing that the morphological innovation of a fusiform carapace was already evolved in Raninoida before the rapid radiation experienced during Albian times. Our findings are suggestive of a still unresolved Palaeocorystidae, containing the rootstock for the post-Aptian Raninidae/Symethidae clade, with the most basal palaeocorystids lying in proximity to, and possibly derived from, a necrocarcinid-like ancestor.

Evolution of crabs – history and deconstruction of a prime example of convergence

“…Raninoidea are included despite the fact that the Recent species display an elongated and sometimes cylindrical carapace and an almost straight pleon. However, the fossil record demonstrates that Raninoidea plesiomorphically possessed a proper crab-shape (Luque et al, 2012;van Bakel et al, 2012).…”

The oldest higher true crabs (Crustacea: Decapoda: Brachyura): insights from the Early Cretaceous of the Americas

“…); marine vertebrates including fishes and reptiles (Acosta et al . ; Hampe , ; Schultze and Stöhr ; Páramo ); invertebrates such as ammonites and bivalves (Etayo‐Serna , b, ; Villamil ; Patarroyo ; Hoedemaeker ; among many others); and most recently decapod crustaceans such as the homoloid crab Mithracites takedai Van Bakel, Guinot et al ., , the raninoidans Planocarcinus olssoni (Rathbun, ), Joeranina kerri (Luque, Feldmann et al ., ), Colombicarcinus laevis Karasawa, Schweitzer et al ., , a new genus and species of necrocarcinoid crab (Luque In press), and other podotreme crabs (D. Cortés and J. Luque, unpub. data).…”

“…J . kerri (Luque, Feldmann et al ., ), specimen IGM p881013, internal negative mould of anterior right dorsal carapace. All scale bars represent 10 mm.…”

Decapod crustaceans from the Cretaceous (Aptian-Albian) San Gil Group in the Villa de Leyva section, central Colombia

“…The sternum of specimen LP06837b is similar to that of Necrocarcinus labeschei (eudeS-deSLonGCHAmPS, 1835) (see KArASAwA et al 2011: fig. 10B-C;SCHweitzer et al 2012: fig. 2B-C).…”

“…The dorsal carapace of Planocarcinus bears similarities to the subfamily Paranecrocarcininae FrAAiJe, VAn BAKeL, JAGt & ArtAL, 2011, such as the subhexagonal carapace shape, the front projecting beyond the orbits, and the possession of postorbital slits (barely visible in the anterior portion of carapace in fig. 3A of Luque et al 2012). However, better-preserved specimens are needed to confirm placement in that subfamily.…”