Caprovesposus daniltshenkoi, Bannikov & Tyler & Tyler, 2025

† Caprovesposus daniltshenkoi sp. nov.

Figures 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4

Chaetodon View in CoL ( Heptodon sp. n.) Smirnov, 1939: 139, text-fig. on p. 140.

Chaetodon haplodon Smirnov, 1939 (lapsus calami).— Danil’chenko, 1980: 140.

Caprovesposus sp. Bannikov & Tyler, 1992: 816.

Caprovesposus sp. 2 . Bannikov, 2010: 125.

Holotype. PIN 5917 View Materials /6, a relatively well preserved, nearly complete, articulated skeleton with counterpart; SL 28 mm ( Figs. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 ).

Horizon and locality. Left bank of the Pshekha River, upstream of Shirvanskaya settlement, and just downstream from the local bridge ( Krasnodar Region, Apsheronsk District, southwestern Russia; 44.367936°N, 39.795570°E; Popov et al. 2023: fig. 36); uppermost part of the Maikop Group (correlated with the basal Langhian), basal-most Middle Miocene (not less than 15 mya; Popov et al. 2023).

Referred specimens. PIN 5917 View Materials /7, a relatively well preserved, nearly complete, articulated skeleton in a single plate; SL 18 mm; from the type locality. The following incomplete specimens, mentioned by Bannikov & Tyler (1992: 816) from the upper Maikopian , also likely belong to the new species : PIN 3363 View Materials /102, Belaya River, Adygea, North Caucasus ; PIN 3974 View Materials /9, Kerch Peninsula, Crimea .

Diagnosis. A † Caprovesposus species that differs from † C. parvus Daniltshenko, 1960 by the following combination of characters: (1) no serrations on the frontal, mesethmoid, preopercle, and basipterygium; and (2) needle-like elongate scales present only on the anterior and middle parts of the body (versus on the entire body), whereas closer to the caudal peduncle the scales become rounded.

Description. Measurements of the holotype as percent of SL are as follows: body depth 53.0; caudal peduncle depth 10.0; length of head 33.8; least distance between anterior edge of orbit and profile (approximately medial edge of frontal) 4.7; length of first dorsal-fin spine 6.1; length of second dorsal-fin spine 13.6; length of last dorsal-fin spine 15.0; length of spiny dorsal-fin base 27.7; length of entire dorsal-fin base 60.5; pre-anal distance 56.3; length of first anal-fin spine 5.9; length of second anal-fin spine 12.2; length of third anal-fin spine 13.8; length of entire anal-fin base 43.2; length of pelvic-fin spine 13.1; length of caudal fin 24.9.

The body is deep, ovoid in shape, with the dorsal profile slightly more convex than the ventral profile, apparently laterally compressed; the caudal peduncle is short and shallow. The maximum body depth is at the anal-fin origin. The eyes are relatively large and located above the middle of the head; the horizontal diameter of the orbit is ~3 times less than the head length.

Most of the head bones are poorly preserved. The head is deeper than long. The neurocranium is relatively deep. The parasphenoid projects along the lower border of the orbit; it is strong, almost straight, and has a ventrally directed longitudinal ridge. The supraoccipital is a low triangular dome above the deep braincase. The frontal is large; it forms most of the oblique antero-dorsal border of the head. The lateral ethmoid forms the anterior border of the orbit. The cheek region is covered by dense scales; therefore, the bones of the suspensorium are poorly distinguishable ( Fig. 2A View FIGURE 2 ). The mouth is small, terminal, and apparently not protractile. The mandibular joint is located in front of the orbit. The teeth are large, few in number, and apparently uniserial. The teeth of the right and left sides of the jaws are superimposed upon each other, so their exact number is unknown, but there are approximately six to eight teeth in a single row in both the upper and lower jaws ( Fig. 2 View FIGURE 2 ). The teeth are highly lobate; the few completely preserved teeth have 9–12 lobes ( Fig. 2B View FIGURE 2 ). The symphyseal border of the lower jaw is deep and oblique, and a single pore of the lateral line sensory canal is visible behind it ( Fig. 2A View FIGURE 2 ); the dentary of the referred specimen PIN 5917/7 bears at least two prominent serrations along its lower edge. The shaft of the hyomandibula is strong and inclined anteroventrally. The opercular region is deep and narrow, but the limits of its individual bones are unclear. The preopercle is only slightly curved along its anterior edge, and no serrations are evident along its posterior and ventral edges. The bones of the hyoid and branchial arches are too poorly preserved to be described.

The vertebral column is almost straight and consists of 22 (9+13) vertebrae. Most of the vertebral centra are somewhat elongate, rectangular, and longer than high. A few of the anteriormost centra are shortened. The length of the abdominal portion of the vertebral column of the holotype is 1.9 times shorter than its caudal portion. The neural spines are stout; most of them are broadened antero-posteriorly. The neural spines of the anterior caudal vertebrae are the longest; they become shorter and somewhat narrower posteriorly in the series. Most of the neural spines are only slightly inclined posteriorly; those of the caudal peduncle are the shortest and are strongly inclined. The neural spine of PU3 is broad and pointed (as evident in the holotypic counterpart; Fig. 1B View FIGURE 1 ), whereas that of PU2 is a short crest. The anterior haemal spines are broad antero-posteriorly and almost vertical; they are longer than their corresponding neural spines. The haemal spines of PU2 and PU3 seem to be autogenous. Parapophyses are not evident. There are apparently seven pairs of ribs, which are moderately long and only slightly inclined; epineurals are not evident .

The caudal skeleton is characterized by the fusion of PU1, U1, and U2 into the terminal centrum; the parhypural and the five hypurals are separate. The large uroneural forms the stegural (as evident in the holotypic counterpart and referred specimen PIN 5917/7); the number of epurals is unclear. The caudal fin is moderately large and truncated; there are 16 principal rays (I,7-7,I) plus about six upper and about five lower procurrent rays.

There are no supraneurals. The single dorsal fin is long at the base; its spinous portion is shorter than its soft portion. There are nine spines and 20 or 21 soft rays in the dorsal fin; each spine has a prominent groove along its length. The two anteriormost dorsal-fin spines are supernumerary on the first pterygiophore; the first spine is the shortest, being less than half the length of the second spine; the second to ninth dorsal-fin spines of the holotype are almost equal in length, whereas in the much smaller referred specimen PIN 5917/7, the second spine is significantly longer than the subsequent spines. Several anterior soft dorsal-fin rays are equal in length to the posterior dorsal-fin spines, but subsequent rays become gradually shorter. The first dorsal-fin pterygiophore is long and wide antero-posteriorly; it contacts the occipital region of the skull and the neural spine of the first vertebra (located in a preneural space). Anterior to the second dorsal-fin spine, the upper portion of the pterygiophore forms a rounded flange and has a deep indentation in front of it, thereby creating a complex locking mechanism of the first two dorsal-fin spines. The succeeding dorsal-fin-spine pterygiophores become gradually shorter and narrower; each of them occupies a single interneural space, except for the third interneural space (between the third and fourth neural spines), which is vacant. The pterygiophores of the soft dorsal-fin rays are moderately narrow; usually two of them are located in each interneural space.

The anal fin is long along the base; it has 3 spines and 20 soft rays; each spine has a prominent groove along its length. The first two anal-fin spines are supernumerary on the first pterygiophore. The first spine is the shortest, being less than half the length of the second spine. The second anal-fin spine of the holotype is somewhat shorter than the third spine, whereas in the much smaller referred specimen PIN 5917 View Materials /7, the second spine is somewhat longer than the third. In the holotype, several anterior soft anal-fin rays are longer than the third anal-fin spine; subsequently, the rays become gradually shorter. The first anal-fin pterygiophore is very long and stout; anteriorly, it is in close contact with the first haemal spine. The lower end of this pterygiophore is widened antero-posteriorly and forms a complex locking mechanism similar to that of the first two dorsal-fin spines. The second and succeeding anal-fin pterygiophores are similar to those of the soft dorsal fin, although the more anterior ones are somewhat longer. The interhaemal spaces above the anal fin usually accommodate two anal-fin pterygiophores .

The posttemporal and supracleithrum are poorly preserved. The cleithrum is large and stout; its anterior margin is gently sigmoid. The strongly expanded coracoid and the posteroventral portion of the cleithrum form a very broad basin for muscle attachment. The scapula and pectoral radials are poorly preserved. The ventral postcleithrum is very long, almost straight, stout, and terminates distally close to the expanded anteroventral end of the first anal-fin pterygiophore. The pectoral fins are moderately large; they are positioned under the fourth vertebra and approximately midway between the vertebral column and the ventral edge of the body. The number of pectoral-fin rays is unclear in the holotype; at least 15 rays are recognizable in referred specimen PIN 5917 View Materials /7.

The basipterygium is very long, has a low ventral ridge, and is attached to the cleithrum well above its ventral edge. The pelvic bone has a narrow posterior process behind the level of the base of the rays; this process terminates close to the distal end of the postcleithrum. The pelvic fin has a single spine and about five short soft rays. The pelvic-fin spine is similar to the second and third anal-fin spines in shape and length.

The entire body and the cheek region of the head are covered with scales. Anteriorly and mid-body the scales are narrow and strongly vertically elongate, have smooth edges, lack surface ornamentation, and have rounded distal edges ( Fig. 3A,B View FIGURE 3 ). Toward the posterior of the body, the individual scales become shorter ( Fig. 4 View FIGURE 4 ), and those of the caudal peduncle are ovoid or even rounded rather than elongate ( Fig. 3C View FIGURE 3 ). No evidence of caudal peduncle armature is recognizable. The lateral line is also not evident, except for a single pore posterior to the symphyseal border of the lower jaw.

Etymology. Named in honor of Dr. Pavel Georgiyevich Danil’chenko (1903–1993), a prominent Russian ichthyologist and paleontologist at the Borissiak Paleontological Institute of the Academy of Sciences, Moscow, who worked to advance the knowledge of the fossil fish fauna of Russia and surrounding areas.