Eogaleus bolcensis Cappetta, 1975

Conte, Gabriele Larocca, Trevisani, Enrico, Guaschi, Paolo & Fanti, Federico, 2020, New specimen of the rare requiem shark Eogaleus bolcensis from the Bolca Lagerstätte, Italy, Acta Palaeontologica Polonica 65 (3), pp. 547-560 : 550-554

Eogaleus bolcensis Cappetta, 1975

Material.— MSNPV 24625-24626, a partially articulated specimen, 120 cm TL ( Figs. 2–6 ) most likely from Monte Postale ( GPS 45°36’13.85” N, 11°13’21.41” E), Bolca locality, Vestenanova, Verona, Italy; Eocene, Ypresian, middle– late Cuisian, SBZ 11 Alveolina dainelli Biozone ( Serra-Kiel et al. 1998; Trevisani 2015). The specimen is in a massive limestone matrix. The teeth are only preserved on slab MSNPV 24625, while the dermal denticles patches are preserved on both slabs. The individual is disarticulated, with an S-shaped vertebral curvature due to postmortem muscular contraction. A cluster of bivalves is preserved posterior to the head.

Description. —A partially preserved carcharhinid with the following overall features: teeth of different shape and size, of height up to 6 mm; disarticulated cartilages in the head region; 132 preserved vertebral centra, wider than high, showing an S-shaped curvature posterior to the head; clusters of fin radials run ventrally along the vertebral column; two types of dermal denticles (arrow- and teardrop-shaped) arranged in patches.

The whole individual ( MSNPV 24625-24626) measures 120 cm (preserved body length; Fig. 2 ). The head region and the proximal section of the trunk are twisted clockwise. A bivalve cluster is preserved posteriorly to the head region ( Figs. 2 , 3 ).

In the head region ( Fig. 3 ), the palatoquadrate and the Meckel’s cartilage are fragmented and associated with patches of dermal denticles, that overall mark an arched trend. The right nasal capsule extends from the palatoquadrate to the anterior proximity of the preserved head. The first vertebral centrum is placed distal to the Meckel’s cartilage. In slab MSNPV 24625, a branchial arch is preserved posterior to the 7 th and 8 th centra, and is covered by dermal denticles patches ( Fig. 3 ).

No teeth are preserved in slab MSNPV 24626 . Twentyfive teeth are observed on slab MSNPV 24625 ( Fig. 4 ). All teeth are exposed in labial view. The variation in shape and size of preserved teeth indicate high heterodonty ( Fig. 4 ). All the measurements of teeth are provided in SOM 2. Lateral teeth are the most abundant type of the preserved tooth set ( Fig. 4A 2, B 2 ). Teeth are triangular in overall shape and asymmetrical along the basal-apical axis. The total tooth height is 44% of the root length. The crown is smooth. The mesial edge is straight and has up to eight serrations. The mesial inflection point is sharp. The main cusp is approximately 20% of the root length and it is inclined distally. The distal angle (i.e., the angle set up by the intersection between the distal edge and the main cusp) is acute, approximately 45°, with a deep notch at the main cusp-distal edge intersection. The distal edge bears three secondary cusps that decrease in size distally. The distal edge is about half of the mesial one. The root is wider than high and flat on its labial surface. Several foramina run along the root surface. The anterior teeth are different in shape and size ( Fig. 4B 2 : teeth 17, 19, and 21). The shape is overall triangular, with a mesial edge that bears up to two distally secondary cusps. The crown is smooth. The main cusp is robust or slender. The distal angle is approximately right or slightly higher than 90°. The distal edge is smooth or bears one secondary cusp. One symphyseal tooth ( Fig. 4A 2 : tooth 12) is preserved. It is a triangular, symmetrical tooth as high as wide (th/rl 1). Mesial and distal edges are about 25% of total height. The main cusp is approximately 3/4 of the total height and lacks serrations. The crown is smooth and convex. The distal angle is slightly higher than 90°, with a deep notch. The distal edge bears one secondary cusp .

The vertebral column includes 132 preserved centra and displays a strongly S-shaped bent ( Fig. 2 , 5 ; measurements provided in SOM 3). Vertebral centra are wider than high with prominent, wedge-shaped intermedial calcifications. The antero-posterior alignment of vertebral centra shows

A 2 10

no evidence of antero-posterior compression during burial and we intepret the arangement to reflect the true anatomical positioning. The size of centra increases posteriorly, hitting a peak at the 39 th centrum, the widest of the series (antero-posterior length 16 mm). The antero-posterior length declines caudally. A further peak in vertebral size is reached at the 49 th centrum (antero-posterior length 16 mm; Fig. 5 ). The caudal decreases in the overall size of vertebral centra are herein grouped in three vertebral segments ( Fig. 5 ): 40 th –67 th centrum (average ~ 10–11 mm), 68 th –98 th centrum (average ~ 7–8 mm), and 99 th –132 nd centrum (average 6 mm).

Basal cartilage is observed between the 16 th and the 22 nd vertebral centra ( Fig. 6A 1, B 1 ). Finally, two clusters of poorly preserved ventral fin radials are preserved between the 88 th and the 98 th and the 115 th and the 125 th vertebral centra (for a total of 15 fin radials counted) ( Fig. 6A 2, B 2 ).

The external morphology of MSNPV 24625-24626 is interpreted using the following criteria: vertebral elements included in the head region extends to the 15 th centrum for a total length of 12.4 cm. The preserved head length (i.e., from the 15 th centrum to the anterior edge of the nasal capsule) is approximately 18 cm; the basal cartilage preserved between the 16 th and the 22 nd is referred to as the pectoral fin. The 16 th centrum marks the beginning of the trunk region. Fin radials clustered among the 88 th –98 th centra are considered as components of the anal fin. The 114 th centrum marks the end of the trunk area (total centra of the trunk 99). According to vertebral centra length, the trunk is 89.3 cm long. The ventral fin radials between the 115 th –125 th centra are interpreted as components of the caudal fin. The 115 th centrum is the first of the caudal series, which measures 10.1 cm.

Patches of dermal denticles occur discontinuously along the entire body of the shark ( Fig. 7 ). SEM imaging of skin samples collected from the head region and the distal part of the trunk revealed two different morphotypes. The first morphotype(herereferredtoasMorphotypeA; Fig.7A )includes arrow-shaped scales. This type of denticles is taller than wide, running along the distal area of the trunk. The number of ridges per scale varies from 5 to 8; the edges of peaks (i.e., apical termination of ridges) are rounded. The crown measures approximately 420 μm in average. The overall thickness is about 100 μm. Hexagonal, micro-cells cover the bottom outline of the scale. In several individual scales, the surface is medio-distally thickened by ridges, developing an upward-pointing spine. Ridges diverge apically and are well separated, arranging subparallel to each other. The interspace of ridges ranges between 100 and 120 μm. The second morphotype (here referred as to Morphotype B; Fig. 7B ) includes teardrop-shaped scales, taller than wide (about 75 μm thick), and they are arranged on the head region. The crown size is about 450 μm. Six subparallel ridges develop on the crown surface, in which the medial ones converge apically. Ridges decrease progressively in thickness apically until they merge with the surface. The ridge interspace average is approximately 74 μm. The apical edge is smooth. The surface is distally covered by hexagonal micro-structures. Medial spines are absent.

Figures

Fig. 2. Eogaleus bolcensis Cappetta, 1975, MSNPV 24625, Monte Postale, Bolca, Italy; middle–late Cuisian. The head region is exposed in dorsal view, while the trunk area is exposed in lateral view. Photograph (A1), explanatory drawing (A2). Dermal denticles are widespread arranged in patches along the body (orange). The yellow patches mark the different typologies of mortar glues employed for the assemblage of the slab. The green dashed lines separate the matrix of the specimens from the rocky blocks used for the preparation of the slabs. The star indicates the anatomical area (i.e., a fragment from identified nasal capsule) where dermal denticle samples were collected. Numerals refer to the arrangement of vertebral elements in life position. Black patches mark casts of vertebral centra.

Fig. 3. Dorsal view of the head region of Eogaleus bolcensis Cappetta, 1975, MSNPV 24625, Monte Postale, Bolca, Italy; middle–late Cuisian. Photograph under UV light (A1), the hard tissues well differentiate from matrix bulk and pigmented mortar glues: photograph under natural light with explanatory drawing (A2). Numerals refer to the arrangement of vertebral elements in life position. Abbreviations: b, benthic organisms; ba, branchial arch; mc, Meckel’s cartilage; mg, mortar glue; nc, nasal capsule; pq, palatequadrate; t, teeth; vc, vertebral centra.

Fig. 4. The head region of Eogaleus bolcensis Cappetta, 1975, MSNPV 24625, Monte Postale, Bolca, Italy; middle–late Cuisian, in dorsal view with preserved teeth in labial view. Close-up photos of left (A) and right (B) lateral areas of the preserved head region. Photographs under natural light (A1, B1), explanatory drawings (A2, B2), preserved teeth (orange), and tooth molds (violet). Numbers refer to teeth count on MSNPV 24625, for measurements see SOM 2. Abbreviations: mc, Meckel’s cartilage; mg, mortar glue.

Fig. 5. Antero-posterior length of vertebral centra of Eogaleus bolcensis, MSNPV 24625. The size of centra increases rapidly the 33th–39th (16 mm). Caudal to the 39th vertebral centrum, the centrum size decreases slowly in 3 steps: (i) the 40th–67th (average: 10.6 mm reaching a peak of 14 mm at the 49th centrum); (ii) the 68th–98th (average: 7.6 mm); (iii) the 99th–132nd (average: 6.0 mm). Vertebrae are numbered from anterior (1) to posterior (132). Measurements and counts are provided in SOM 3.

Fig. 6. The apical area (A) and distal region (B) of the trunk of Eogaleus bolcensis Cappetta, 1975, MSNPV 24625, Monte Postale, Bolca, Italy, middle– late Cuisian, in lateral view. Photographs under UV light (A1, B1) and interpretative drawings (A2, B2). The basal cartilage extends ventrally and parallel to vertebral column among the 16th–22nd centra. In B1 the clusters of fin radials ventrally extend among the 88th–98th and the 115th–125th centra. The arrows in A1 and B1 point out the preserved fin radials. Green patches mark areas covered by mortar glue. Numerals refer to the vertebral counts.

Fig. 1. A. Terminology of longitudinal measurements following Cappetta (1975). Measurements 17–23 have been added in this paper, expanding the original model. 1, total length (TL); 2, head length; 3, trunk length; 4, caudal fin length; 5, head-first dorsal fin length; 6, head-second dorsal fin length; 7, head-pelvic fin length; 8, head-anal fin length; 9, head-caudal fin length; 10, basal lobe length; 11, apical lobe length; 12a-b-c, first dorsal base-anterior edge-height; 13a-b-c, second dorsal base-anterior edgeheight; 14a-b-c, pectoral fin base-anterior edge-height; 15a-b-c, pelvic fin base-anterior edge-height; 16a-b-c, anal fin base-anterior edge-height; 17, first-second dorsal fins length; 18, second dorsal-caudal fin length; 19, pectoral-pelvic fins length; 20, pelvic-anal fins length; 21, anal-caudal fins length; 22, apical lobe-caudal tip length; 23, basal-apical lobes length. B. Terminology of dental characters according to Adnet and Cappetta (2008) and Ebert and Stehemann (2013). MGGC 1976 in labial (B1) and lingual (B2) views. Measurements taken for each tooth: ch, crown height; de, distal edge; mcl, main cusp length; mcw, main cusp width; me, mesial edge; me+mcl, mesial edge + main cusp length; rh, root height; rl, root length; th, total height.

Fig. 7. Dermal denticles at different scales of head and trunk regions (in dorsal view) of Eogaleus bolcensis Cappetta, 1975, Monte Postale, Bolca, Italy; middle–late Cuisian. A. MSNPV 24625, details of a skin patch preserved in the head region (A1), SEM imaging of a Morphotype A denticle (A2); the scale is thick and well ridged, an upward-pointing spine occurs in dorsal view, thickened by the distal convergence of ridges. B. MSNPV 24626, patches of dermal denticles of arranged ventrally to vertebral column, along the distal area of the trunk (B1), SEM imaging of a denticle in dorsal view from the trunk region, where dermal denticles are teardrop-shaped (Morphotype B) (B2); the ridges end apically, without forming peaks, medial-distal upward spines are absent. Abbreviations: p, peak; r, ridge; ri, ridge interspace; s, spine.