Gymnammodytes oranensis, Carnevale, 2004

Carnevale, Giorgio, 2004, New species of sand lance (Teleostei, Ammodytidae) from the Miocene of Algeria, Geodiversitas 26 (2), pp. 297-307 : 299-304

Gymnammodytes oranensis n. sp. ( Figs 1-8 )

MATERIAL EXAMINED. — Holotype: MNHN ORA 1203 d+g; ORA 1203 is a fragmentary specimen with a well preserved skull; most of the axial skeleton is missing.

Paratypes: MNHN ORA 1204, and MNHN ORA 1207 ; ORA 1204 single plate, head to right, is a relatively complete specimen lacking caudal skeleton and fin. MNHN ORA 1207 is a relatively complete specimen. The anterior portion of the snout and the posteriormost section of the axial skeleton are missing ; the bones of the head are much displaced and somewhat dissociated.

Referred specimen: MNHN ORA 1205; ORA 1205 is fragmentary; the bones of the head are poorly preserved and widely flattened.

TYPE LOCALITY AND HORIZON. — The present study is based on the examination of four individuals from the Messinian (uppermost Miocene) Tripoli of Gambetta, near Oran, NW Algeria. This locality is placed at the margin of the Djebel Murdjadjo carbonate platform in the Chelif Basin. This area of the Chelif Basin is characterized by a large development of carbonate platforms with abundant reef complexes ( Rouchy 1982; Cornée et al. 1994), which peripherally grades into marls and diatomite deposits ( Perrodon 1957). A rich fossil biota was discovered in this area, including algae, foraminifers, sponges, corals, anellids, molluscs, brachiopods, bryozoans, crustaceans, echinoderms, and vertebrates (see e.g., Moissette 2000). According to Arambourg (1927), fossil fishes were collected in the quarry of the “Usine de Chaux et Ciments oranais”. Fossiliferous layers consist of white, inframillimetrically-laminated diatomite (Tripoli). These layers lie over a rhythmic sequence of Messinian marls and limestone. The top of the sequence is represented by Pliocene sediments of the Arcole Plateau.

Many fishes were found associated with Gymnammodytes oranensis n. sp., including clupeids, sternoptychids, myctophids, syngnathids, and scombrids. In particular, the ichthyofauna was dominated by epipelagic ( Alosa Linck, 1790 , Sarda Cuvier, 1829 , Euthynnus Lütken in Jordan & Gilbert, 1883) and midwater ( Diaphus Eigenmann & Eigenmann, 1890 , Myctophum Rafinesque, 1810 , Maurolicus Cocco, 1838 ) taxa, but some neritic species were also found ( Diplodus oranensis Woodward, 1901 , Boops roulei Arambourg, 1927 ).

ETYMOLOGY. — Oranensis, after the region of Oran, northwestern Algeria, which contains the type locality. DIAGNOSIS. — A species of Gymnammodytes that differs from other species of the genus by the absence of the premaxillary specializations (sensu Ida et al. 1994) (see Remarks below).

DESCRIPTION

A complete series of counts and measurements was not possible to take because of the incompleteness of the specimens. Few morphometric and meristic values are summarized in Table 1.

Although all the specimens are incomplete, they appear to be adults based on the strong ossification of most skeletal elements. The body is elongate and slender, as evidenced by MNHN ORA 1204 ( Fig. 2). The orbit is large (c. 16.4 mm in head length).

The neurocranium is low ( Fig. 3 ). The anteriormost element of the neurocranium is the vomer. The anterior portion of this bone is not clearly observable on the specimens examined. The ventral margin of the vomer is slightly convex. Vomerine teeth are absent, as in other ammodytids ( Kayser 1962; Pietsch & Zabetian 1990). The mesethmoid is elongate and narrow. Posteriorly, this bone is sutured to the large lateral ethmoids. The lateral ethmoids provide the anterior margin of the orbit. The nasals are tubular pa pto bones that form a continuation of the supraorbital sensory canal of the frontals. The frontals are the largest bones of the skull roof. The dorsal surface of these bones is smooth. The sutural connection between the two contralateral frontals is smooth. The parietals are flat bones, not meeting in the midline, where they are separated from each other by the supraoccipital. The sphenotic and the pterotic are only partially preserved in the holotype. The other bones of the neurocranium (epiotic, prootic, exoccipital, intercalar, and basioccipital), with the exception of the parasphenoid, are too damaged to be described. The parasphenoid is an elongate bone, which is visible in lower third of the orbit.

The infraorbital series of Gymnammodytes oranensis n. sp. consists of four elements. The lacrimal is appreciatively triangular. The second and the third infraorbitals are elongate and tubular bones. The dermosphenotic appears to be sutured to the frontal and the sphenotic. The integration of the dermosphenotic with the neurocranium is a typical feature of ammodytids, trachinids, and uranoscopids ( Pietsch 1989; Pietsch & Zabetian 1990). The reduction of the number of infraorbital bones into four is distinctive of the genera Ammodytes , Gymnammodytes , and Hyperoplus ( Ida et al. 1994) . This reduction represents a derived condition within the Ammodytidae . The genera Bleekeria and Lepidammodytes show the generalized condition with the complete infraorbital series characterized by eight bones. The intermediate condition can be observed in the species of the genera Protammodytes and Ammodytoides , in which respectively, seven and six infraorbital bones are present ( Ida et al. 1994). Fragments of weakly ossified sclerotic bones are visible in the holotype and MNHN ORA 1204.

The mouth is oblique, forming an angle of about 20-25° to the horizontal axis of the body. Premaxillary and dentary teeth are absent. Among the Ammodytidae teeth are present only in the genus Bleekeria ( Ida 1976; Reay 1986; Pietsch & Zabetian 1990). The premaxilla is highly protrusible (see Van Dobben [1935] and Pietsch [1984] for a discussion on modification of jaws structure of ammodytids) ( Fig. 4 ). The ascending process of the premaxilla seems to be autogenous. Each premaxilla bears a small articular process and a well developed postmaxillary process. A small concavity is present along the symphyseal margin of the premaxillae. The maxilla has a prominent and strongly ossified articular head. The lower jaw extends anteriorly far beyond the upper jaw. The dentary bears an anteriorly directed symphyseal process ( Fig. 5 ). This projection is probably related to the sand diving behaviour of ammodytids ( Randall et al. 1994), and is morphologically similar to that of Gymnammodytes cicerelus figured by Ida et al. (1994). The anterolateral perforation of dentary is thin. The articular is well exposed in the holotype. There are small fragments of what appear to be labial ossicles ( Ida 1973).

The outline of the hyomandibula is partially obscured by other bones but the dorsal portion of it is visible in the holotype. As other ammodytids, Gymnammodytes oranensis n. sp. has an anteriorly directed spur laterally on the hyomandibula ( Fig. 6 ). The presence of this structure is also reported for other trachinoid families, such as Cheimarrichthyidae , Pinguipedidae , Percophidae , Trichonotidae , Creedidae, Chiasmodontidae , and Leptoscopidae ( Kayser 1962; Pietsch 1989; Pietsch & Zabetian 1990). The symplectic is an elongate subcylindrical bone. The quadrate lies almost horizontally within the suspensorium ( Fig. 6 ). The metapterygoid is rather large. Of this bone, only the external outline can be recognized. The mesopterygoid is a well developed bone that forms a suborbital shelf. The ectopterygoid is a small triangular bone visible at the base of the palatine. The palatine is narrow and elongate.

The opercular series is well exposed in the holotype ( Fig. 7 ). The vertical arm of the preopercle is longer than the horizontal one. The opercle is a thin bone with a horizontal strongly ossified ridge. The most striking element of the opercular series is the subopercle. This bone is very large, posteriorly expanded beyond extend of the opercle. Its posterior and ventral margins are ornamented with deep radially disposed grooves. The interopercle is clearly visible in the holotype.

The hyoid bar is well preserved in the holotype. There are seven branchiostegal rays: the anteriormost five articulate with the ceratohyal, while the sixth and the seventh articulate with the epihyal.

Some fragmented bones of the gill skeleton, probably the ceratobranchials, are visible in the holotype.

As discussed above, because of the incompleteness of the examined material, a precise vertebral count is unknown. However, the number of abdominal vertebrae ranges from 41 to 43. Following the values reported by Ida et al. (1994), a similar number of abdominal vertebrae is also observed in Gymnammodytes semisquamatus . The abdominal vertebrae are clearly more numerous than the caudal vertebrae. The anteriormost centrum is reduced relative to the others. Posterior centra are subrectangular, longer than high. Each centrum has developed dorsal prezigapophyses. With the exception for the three anterior, neural spines are weak. The neural and haemal spines of the posteriormost preserved caudal vertebrae are expanded and flattened ( Fig. 8 ). Pleural ribs are well preserved on the specimens examined; some of them are laterally expanded, blade-like. Many epineural bones are visible attached to the axial skeleton.

Supraneural bones are absent. The dorsal fin originates between the ninth and the 10th vertebrae. The dorsal fin is spineless. The anal fin is not well preserved in any of the specimens examined.

The pectoral girdle consists of posttemporal, supracleithrum, cleithrum, scapula, and coracoid. Two postcleithra are also present (see Gosline iop

1963). The posttemporal is connected with three fragmented extrascapular bones. There are four large and elongate pectoral radials. Similar pectoral-fin radials also occur in chiasmodontids, among the trachinoids (see Johnson & Cohen 1974). The pectoral fin radials support 13 to 14 fin rays.

The pelvic fin and girdle are absent, as in other species of the genus Gymnammodytes . The absence of the pelvic fin is also shared by the genera Ammodytes , Bleekeria , Hyperoplus , and by some species of the genus Ammodytoides .

A series of small tubular lateral line scales are visible on the body high in position. These scales are absent in the posteriormost part of the body. The lateral line canal appears to be branched with pores at the end of the branches. As Gymnammodytes capensis and Gymnammodytes cicerelus , Gymnammodytes oranensis n. sp. lacks patches of scales in the posterior part of the body.

REMARKS

Specimens here examined show many characters that allow the placement within the Ammodytidae , including: physiognomy of the body; abdominal vertebrae more numerous than caudal vertebrae; orbit large; presence of an elongate mesethmoid; premaxillae highly protrusible; lower jaw extending anteriorly beyond upper jaw; dentary with an anteriorly directed symphyseal process; presence of a large anterolateral foramen of the dentary; presence of an anteriorly directed spur on the hyomandibula; palatine elongate ( Gosline 1963); mesopterygoid large and forming a subocular shelf; infraorbitals tubular; dermosphenotic as integral part of the neurocranium; subopercle large and expanded ventrally; presence of seven branchiostegal rays; presence of expanded pleural ribs; elevate position of the lateral line; absence of spines in median fins.

Gymnammodytes oranensis n. sp. fits the definition of the genus as given by Ida et al. (1994) for the following characters: presence of labial ossicles; presence of four infraorbital bones; absence of predorsal bones; absence of premaxillary and dentary teeth; neural and haemal spines of the caudal vertebrae expanded; absence of pelvic fins; morphology of lateral line scales. The species of the genus Gymnammodytes are characterized by an extreme degeneration of scales. According to Ida et al. (1994), only tubular lateral line scales are retained in this genus, with the exception of small patches of small scales present on the posterior part of the body in Gymnammodytes semisquamatus . The other members of the subfamily Ammodytinae , Ammodytes and Hyperoplus , have small scales arranged in oblique rows, partially embedded by skin folds. Gymnammodytes oranensis n. sp. clearly differs from extant congenerics by the absence of the premaxillary specializations. As reported by Ida et al. (1994), the premaxillae of living species of the genus Gymnammodytes are characterized by a firm fusion of the two contralateral ascending processes and by a widening of their articulating surfaces. By contrast, the premaxillae of Gymnammodytes oranensis n. sp. greatly resemble those of other ammodytid genera, which are characterized by the presence of not fused pedicel-like ascending processes (see Fig. 4 ), suggesting a more basal position of this species within the genus Gymnammodytes .

Figures

FIG. 1. — Gymnammodytes oranensis n. sp., holotype (MNHN ORA1203). Scale bar: 2 mm.

FIG. 3. — Gymnammodytes oranensis n. sp., reconstruction of the neurocranium, left side, lateral view. Abbreviations: bsp, basisphenoid; dsp, dermosphenotic; fr, frontal; le, lateral ethmoid; mes, mesethmoid; pa, parietal; pas, parasphenoid; pto, pterotic; pts, pterosphenoid; soc, supraoccipital; spo, sphenotic; vo, vomer.

FIG. 4. — Gymnammodytes oranensis n. sp., reconstruction of the left premaxillary, dorsal view.

FIG. 5. — Gymnammodytes oranensis n. sp., left dentary, lateral view (MNHN ORA1203). Scale bar: 1 mm.

FIG. 6. — Gymnammodytes oranensis n. sp., reconstruction of the left suspensorium, lateral view. Abbreviations: ect, ectopterygoid; h, hyomandibula; hs, hyomandibular spur; msp, mesopterygoid; mtp, metapterygoid; pal, palatine; q, quadrate; sym, symplectic.

FIG. 7. — Gymnammodytes oranensis n. sp., left opercular series, lateral view (MNHN ORA1203). Abbreviations: iop, interopercle; op, opercle; pop, preopercle; sop, subopercle. Scale bar: 1 mm.

FIG. 8. — Gymnammodytes oranensis n. sp., caudal vertebrae, right side, lateral view (MNHN ORA1204). Scale bar: 1 mm.