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The cranial anatomy of Neoaetosauroides engaeus Bonaparte, 1969 from the upper part of the Los Colorados Formation, western Argentina, is addressed herein. This description is based on material collected recently, which permits a complete restoration of the skull; previously, a partial lower jaw and premaxillary and maxillary fragments were the only cranial remains known. Unlike other aetosaurs for which the premaxillary dentition is known, in N. engaeus the upper tooth row extends anteriorly to reach near the expanded tip of the snout; this condition is not compatible with the presence of a keratinous beak previously suggested for other aetosaurs. The conical shape of the teeth of N. engaeus differs from the slightly compressed teeth of Desmatosuchus, Stagonolepis and Typothorax, and the distinctly recurved teeth of Aetosaurus and Aetosauroides. This diversity of dental morphology suggests a variety of food‐item preferences among aetosaurs.

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BackgroundTeleosts constitute more than 99 % of living actinopterygian fishes and fossil teleosts have been studied for about two centuries. However, a general consensus on the definition of Teleostei and the relationships among the major teleostean clades has not been achieved. Our current ideas on the origin and early diversification of teleosts are mainly based on well-known Mesozoic marine taxa, whereas the taxonomy and phylogenetic relationships of many Jurassic continental teleosts are still poorly understood despite their importance to shed light on the early evolutionary history of this group. Here, we explore the phylogenetic relationships of the Late Jurassic (Oxfordian – Tithonian) freshwater †Luisiella feruglioi from Patagonia, in a comprehensive parsimony analysis after a thorough revision of characters from previous phylogenetic studies on Mesozoic teleosts.ResultsWe retrieved †Luisiella feruglioi as the sister taxon of the Late Jurassic †Cavenderichthys talbragarensis, both taxa in turn forming a monophyletic group with the Early Cretaceous †Leptolepis koonwarri. This new so far exclusively Gondwanan freshwater teleost clade, named †Luisiellidae fam. nov. herein, is placed outside crown Teleostei, as a member of the stem-group immediately above the level of †Leptolepis coryphaenoides. In addition, we did not retrieve the Late Jurassic †Varasichthyidae as a member of †Crossognathiformes. The position of †Crossognathiformes within Teleocephala is confirmed whereas †Varasichthyidae is placed on the stem.ConclusionsThe general morphology of luisiellids is that of basal, stem Teleocephala; however, most of their synapomorphies have evolved independently in teleocephalans. Similarly, the resemblance between varasichthyids and crossognathiforms might be due to parallel evolution. In accordance to most teleostean phylogenies, our analysis shows that a major morphological change occurred along the stem line and are currently recorded at the level of †Leptolepis coryphaenoides. A stem-based total clade Teleostei has been accepted for this work.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0551-6) contains supplementary material, which is available to authorized users.

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