Caboellimma, a new genus for “Ellimma” cruzae Santos, 1990, an ellimmichthyiform fish (Teleostei: Clupeomorpha) from the Cabo Formation (Lower Cretaceous) of the Pernambuco-Paraíba Basin, north-east Brazil

Abstract

Caboellimma gen. nov. is erected to accommodate “Ellimma” cruzae, an archaic herring-like fish known only from the Lower Cretaceous mudrocks assigned to the Cabo Formation in north-east Brazil. Although Caboellimma cruzae comb. nov. shows a mix of characters between Ellimma branneri and species of Ellimmichthys, it does possess remarkable features indicating more complex affinities than previously thought, such as: (1) a transversely narrow and very elongate parietal; (2) of the dermal bones of the skull roof, only the frontal is ornamented; (3) a supraoccipital commissural canal runs the parietal through a straight tube; (4) there is a long parietal branch of supraorbital sensory canal reaching the boundary with the parietal and a long curved branch towards the otic region; (5) in contrast with nominal species of Ellimma, tubercles and “cannabis leaf”-shaped ornament on predorsal scutes are lacking; (6) a very reduced post-parietal region of the skull roof. Since its original description, anatomical data on “Ellimma” cruzae have been considered insufficient for comparative purposes causing problems in cladistic analyses. Here we present a comprehensive redescription; the generic validity is tested with a parsimony analysis performed with the TNT 1.5 program, including 19 selected ellimmichthyiform taxa and 63 unweighted and unordered characters. Only a single tree (L = 181 steps; CI = 0.403; RI = 0.520) has been obtained, the topology of which indicates placement of Caboellimma cruzae comb. nov. far from Ellimma and appearing as sister group of Thorectichthys marocensis.