The oldest dairoidid crab (Decapoda, Brachyura, Parthenopoidea) from the Eocene of Spain

Eubrachyurans, or ‘higher’ true crabs, are the most speciose group of decapod crustaceans and have a rich fossil record extending into Early Cretaceous. However, extant families first found in Palaeogene, particularly Eocene. Unfortunately, fossils many early eubrachyuran groups often fragmentary, only few studies combined extinct taxa phylogenetic context using different optimality criteria. Here, we report dairoidid crab Phrynolambrus sagittalis sp. nov., an enigmatic from upper Eocene Huesca (northern Spain), whose completeness exquisite preservation permit examination its anatomy context. Dairoidids previously been considered among oldest stone crabs (Eriphioidea) elbow (Parthenopoidea), two disparate distantly related living today. Mechanical preparation computed tomography material revealed several diagnostic features that allow detailed comparison with across tree life, test hypotheses about affinities. is genus Iberian Peninsula, represents one crown parthenopoidean worldwide, expanding our knowledge biogeographical distribution during as well their origins, anatomical diversity systematic Understanding disparity eubrachyurans pivotal to disentangling relationships families, interpreting spatio-temporal patterns leading evolution modern faunas.