Apomesodon surgens, Poyato-Ariza F. J. & Wenz S., 2002

Poyato-Ariza F. J. & Wenz S., 2002, A new insight into pycnodontiform fishes, Geodiversitas 24 (1), pp. 139-248 : 219-220

Apomesodon surgens n. sp.

( Figs 3A, B ; 14A ; 21B, C ; 28B ; 39A, B ; 40B ) Mesodon gibbosus – Thiollière 1858: 783 (name only); 1871: 33; 1873: 13, pl. 2, fig. 2.

Mesodon macropterus – Woodward 1895: 200 (infrapaginal note).

Eomesodon gibbosus – Saint-Seine 1949: 105, 129-132, 313; figs 56-58, pl. 14, fig. A.

HOLOTYPE. — ML 15443 (specimen figured by Thiollière 1873: pl. 2, fig. 2; Figs 14A ; 21B, C ).

PARATYPE. — ML 15660 / MNHN CRN-69 (part and counterpart of the same individual; Figs 3A, B ; 28B ; 39A, B ; 40B ). No other specimens are known .

ETYMOLOGY. — From the Latin verb “surgere”: ascending, rising, in reference to the shape of the dorsal prominence.

TYPE HORIZON. — Kimmeridgian.

TYPE LOCALITY. — Cerin, Ain, France.

DIAGNOSIS. — Apomesodon n. gen. with the following unique combination of primitive and derived characters: body depth more than 100% of standard length; dorsal prominence pointed, with both anterior and posterior borders inclined; extrascapular fused to parietal; posterior teeth on main vomerine tooth row oval; 11 hypochordal elements on caudal endoskeleton; more than 20 anal axonosts; caudal fin with distal bor- der convex; three or four spines on dorsal ridge scales; 18 to 21 ventral keel scales; seven or more spines on ventral keel scales.

Superfamily PYCNODONTOIDEA Agassiz, 1833 new rank TYPE FAMILY. — Pycnodontidae Agassiz, 1833 sensu Nursall 1996b .

DIAGNOSIS. — Pycnodontoid fishes with the following autapomorphies: dermohyomandibular present, with a small to enlarged ornamented superficial portion that articulates ventrally with the preoperculum; opercular process of dermohyomandibular absent; sagittal flanges on neural and haemal spines present only anteriorly. Unique combination of primitive and derived characters: dorsal prominence absent; premaxillary and dentary teeth fully incisiform; three or less dentary teeth; neural and haemal adjacent arcocentra in contact; two or less urodermals; nuchal plates absent; less than 18 dorsal ridge scales; spines on each dorsal ridge scale of increasing size in cephalocaudal sense; less than 18 ventral keel scales; less than seven postcloacal ventral keel scales; anterior and posterior cloacal scales modified, not forming a mosaic.

Figures

FIG. 3. — Forms previously referred to the genus Eomesodon Woodward, 1918; A, B, Apomesodon surgens n. gen., n. sp. Part and counterpart of the same specimen, currently housed in different collections; A, MNHN CRN 69; B, ML 15660. Photos Serrette, both under ultraviolet light; C, Apomesodon gibbosus n. comb., JM 4120. Photo courtesy G. Viohl; D, Stenamara mia Poyato-Ariza & Wenz, 2000, silicone cast of the holotype, LH – 14365. Photo Serrette, from Poyato-Ariza & Wenz (2000). Scale bars: A, B, D, 1 cm; C, 5 cm.

FIG. 14. — A, skull of Apomesodon surgens n. gen., n. sp., from specimen ML 15433, holotype. Right side, lateral view. Arrows on the left upper corner points at the portion of the supratemporal commissure piercing the parietal (1) and the dermopterotic (2); arrows on the ethmoidal region point at the tubular infraorbitals (3), the ossicle(s) of the ascending branch of the infraorbital sensory canal (4), and the ossicles of the ethmoid commissure (5). Photo Serrette, under ultraviolet light; B, Apomesodon gibbosus n. comb., ethmoidal and oral region of specimen FSL 93095. Arrows on the left point at the tubular infraorbitals. Photo Serrette. Abbreviations: D, dentary; lPmx, left premaxilla (tooth); rPmx, right premaxilla. Scale bars: A, 1 cm; B, 5 mm.

FIG. 21. — A, camera lucida drawing of the prearticular teeth as shown by the holotype of? Eomesodon barnesi (Woodward, 1906), NHML 12511, right side, occlusal view; B, camera lucida drawing of the oral region of Apomesodon surgens n. gen., n. sp., specimen ML 15433, holotype, showing mostly the teeth on the dentary and on the vomer, right side, lateral view; C, anteroventral region of the skull of A. surgens n. gen., n sp., specimen ML 15660, showing crenulated oval teeth in occlusal view on the right prearticular (pointed by arrows on the left) and some small branchial teeth (pointed by arrows on the right), left side, lateral view. Abbreviations: D, dentary; Part, prearticular; Pmx, premaxillary teeth; Vo, vomerian teeth. Scale bars: 2 mm.

FIG. 28. — A, camera lucida drawing of the caudal vertebrae and of the last dorsal and anal axonosts as shown by the holotype of Eomesodon liassicus (Egerton, 1855), NHML 19864. Notice some bifid neural and haemal spines; B, caudal region of specimen ML 15660 of Apomesodon surgens n. gen., n. sp. Notice some bifid dorsal axonosts. Photo Serrette, under ultraviolet light. Both left side. Abbreviations: aax, anal axonost; dax, dorsal axonost; epel, epichordal elements; ha, haemal arcocentrum; hyel, hypochordal elements; na, neural arcocentrum; ud, urodermals. In both A and B, arrows point some of the autogenous neural spines. Scale bars: 5 mm.

FIG. 39. — Apomesodon surgens n. gen., n. sp. Camera lucida drawings from specimen ML 15660; A, two consecutive dorsal ridge scales, placed just posterior to the apex; B, two consecutive postcloacal ventral keel scales. Notice the progressively increasing size of the spines in this case. Both left side, lateral view. Scale bars: A, 1 mm; B, 2 mm.

FIG. 40. — Ventral keel scales and mosaic cloacae; A, specimen JM 3710 of Gyrodus hexagonus (Blainville, 1818). Photo courtesy G. Viohl; B, specimen ML 15660 of Apomesodon surgens n. gen., n. sp. Photo Serrette, under ultraviolet light. Both left side, lateral view. Abbreviations: aax, anal axonosts; af, anal fin; an, anal notch; csc, complete scales; cv, cloacal vestibule; mcls, mosaic cloacal scale; opv, opening for pelvic fin; pvf, pelvic fin; vks, ventral keel scales. Scale bars: A, 5 mm; B, 2 mm.