Aphanius crassicaudus AGASSIZ, 1839

Martinetto, Edoardo, Irace, Andrea & Marramà, Giuseppe, 2024, Messinian Age Of An “ Oligocene ” Fossil Flora From Italy, Fossil Imprint 80 (1), pp. 161-180 : 173-174

Aphanius crassicaudus AGASSIZ, 1839

Text-fig. 6

M a t e r i a l. Specimen (MGPT-PU135802) is a small, articulated and partially incomplete skeleton, lacking the head and the distalmost margin of the caudal fin ( Text-fig. 6). The preserved skeleton is 39.8 mm in length, with a maximum body depth at dorsal-fin origin of 10.3 mm.

D e s c r i p t i o n. The body of the fossil specimen is laterally compressed, moderately elongate and shallow, with nearly straight dorsal and abdominal profiles ( Text-fig. 6a). The caudal peduncle is short and stocky, with its height about two-thirds of its length. There are 24 vertebrae preserved, but it is likely that their original number was higher, being the anteriormost portion of the vertebral column not preserved. Of these, 16 vertebrae are caudal. The centra are subrectangular, longer than high and characterised by a high degree of hyperostosis of their neural and haemal arches and spines, these latter being posteriorly oriented with an angle measuring about 45°. At least seven epipleurals can be recognized on the posteriormost abdominal vertebrae ( Text-fig. 6b): they are short, remarkably thick, nearly fusiform and not bifid, with their distal margin posterodorsally directed. Dorsal and anal fins are short based. The dorsal fin is located at about mid-length, with its origin being clearly anterior to the anal fin, this latter originating below the perpendicular to posterior end of the dorsal fin. There are 10 or 11 dorsal-fin rays and 9 or 10 anal-fin rays, both supported by an equal number of pterygiophores. The pelvic fins are small and placed anteriorly to the dorsal-fin origin, with about six rays. The caudal-fin skeleton has all hypural plates fused into a single hypural fan ( Text-fig. 6c). The caudal fin is incomplete in its distalmost margin, but at least 28 caudal-fin rays (15 principals + 13 procurrent) can be counted in its proximal part. Body scales are mostly not preserved, but large and thick scattered cycloid scales cover part of the dorsal and ventral margins of the body.

Despite its incompleteness, the fossil preserves many features that support its inclusion in the cyprinodontid genus Aphanius , including the general body physiognomy and its small size, hypural plates fused into a hypural fan, presence of an undivided dorsal fin positioned slightly in front of the anal fin, epipleurals not bifid, and meristic count ranges consistent with that of the genus ( Parenti 1981, Vasilyan et al. 2009). Moreover, the specimen exhibits a combination of features that support its alignment with the species A. crassicaudus AGASSIZ, 1848 , an euryhaline estuarine species widespread in the Mediterranean basin throughout the Messinian (e.g., Carnevale et al. 2006, 2019, Caputo et al. 2009, Reichenbacher and Kowalke 2009, Carnevale and Schwarzhans 2022). These traits include the number of caudal vertebrae (16), dorsal- and anal-fin rays (10–11 and 9–10, respectively), caudal-fin rays (28+), and hyperostosis that often characterises the bones A. crassicaudus as evident enlargement of the bone structures ( Gaudant 1979, Parenti 1981, Vasilyan et al. 2009, Bedosti et al. 2015).