New Cretaceous crabs (Crustacea, Brachyura) from Moscow Oblast and Dagestan (Russia): patterns in phylogeny and morphospace of the oldest eubrachyurans (Dorippoidea)

Abstract

Four new brachyuran species, assigned to two new genera and one existing genus, are recorded from Lower and Upper Cretaceous strata of Moscow Oblast (Moskovskaya Oblast) and Dagestan, Russia. Three new taxa, Personadorippe levashiensis gen. et sp. nov., Levashidromites cornutus gen. et sp. nov. and Vectis collinsi sp. nov., were recovered from Aptian strata in Dagestan; these constitute the first formal description of Cretaceous crabs from the northern Caucasus. Of these, Personadorippe levashiensis gen. et sp. nov. represents one of the oldest eubrachyuran crabs known to date, being of middle Aptian age and thus predating the late Aptian Telamonocarcinus antiquus Luque, 2014 (see Luque, 2014a) from Colombia. A single carapace of Personadorippe kalashnikovi gen. et sp. nov. constitutes the first ever record of crabs from Upper Cretaceous deposits of the Moscow region. Vectis collinsi sp. nov. represents only the third species of the genus, and the first outside the United Kingdom. The genus Vectis is reassessed and here reassigned to the Viaiidae, which now comprises three genera. Rathbunopon? atherfieldense Wright, 1997 is also transferred to Vectis. The family Longodromitidae is here restricted to six genera, inclusive of Levashidromites gen. nov., and a new diagnosis is supplied. Navarrara, previously assigned to the Longodromitidae, is reassigned to the Telamonocarcinidae. Withersella is also transferred to the Telamonocarcinidae; the genus constitutes the oldest dorippoid (and hence, currently assigned eubrachyuran) crab. Personadorippe gen. nov., here described on the basis of two new species, follows shortly after. Eodorippe connori Nyborg, Garassino, Vega and Kovalchuck, 2019 is here reassigned to Personadorippe gen. nov. Carapace tripartition and branchial condensation, i.e., the ratio between the median carapace portion and the relative distance of the branchial groove to the cervical groove, are here used as important proxy characters for reconsidering the taxonomic placement of primitive crabs. Phylogenetic analyses and assessment of phylomorphospace have revealed that the new genera described herein are part of a Jurassic–Cretaceous radiation of primitive crabs. This radiation proceeded via a high-magnitude morphological shift away from the morphology typical of Tanidromites, with subsequent expansion in all directions of morphospaces occupied.