The miniature fish Habroichthys (Actinopterygii; Peltopleuriformes): seven new species from the Middle Triassic of Italy and Slovenia reveal insights on its palaeobiology, palaeobiogeography, and palaeoecology

In this paper we describe new specimens belonging to the miniature fish Habroichthys (Actinopterygii; Peltopleuriformes) that come from recently discovered Middle Triassic Southern Alpine localities in the Dolomites and Lombardy (Northern Italy), as well as in Slovenia. Habroichthys is known from the Western to the Eastern Tethys (Europe to southern China), and the new specimens expand our knowledge on its anatomy. Habroichthys had an oval body outline, a box-shaped head, and sexually dimorphic anal hooklets. Otoliths and snout bones are documented for the first time. Seven new species are established: H. zuitaensis and H. dincae from the upper Ladinian Pelsa/Vazzoler Lagerstätte (Dolomites), H. flaviae from the mid-Ladinian of Castelveccana (western Lombardy), and H. nietorum , H. bosi , H. veronikae and H. celarci from various Anisian sites in the Kamnik-Savinja Alps (Slovenia). The study shows that Habroichthys had an ocean-scale distribution in the Tethys, and a chronostratigraphic range of ca. 7 myr. The oldest occurrence dates back to the early–middle Anisian of Western Tethys (Slovenia). The widest palaeogeographic distribution and the last occurrence date to the late Ladinian in the Dolomites, Germany, and in southern China. Habroichthys exhibited a stable anatomical structure with significant species-specific variability. The number of flank scales, combined with the scale-row of insertion of the pelvic, dorsal, and anal fins, are the most distinctive characters for species identification. Juvenile specimens allowed us to study its ontogenetic development characterised by body lengthening and thickening, ossification and broadening of skull bones and of flank scales, and appearance of dorsal and ventral scales. Finally, we propose some hypotheses about the habitat, sexual behaviour, diet, life mode and modern analogues of Habroichthys .