Osteology and relationships of Rhinopycnodus gabriellae gen. et sp. nov. (Pycnodontiformes) from the marine Late Cretaceous of Lebanon

The osteology of Rhinopycnodus gabriellae gen. and sp. nov., a pycnodontiform fi sh from the marine Cenomanian (Late Cretaceous) of Lebanon, is studied in detail. This new fossil genus belongs to the family Pycnodontidae, as shown by the presence of a posterior brush-like process on its parietal. Its long and broad premaxilla, bearing one short and very broad tooth is the principal autapomorphy of this fi sh. Within the phylogeny of Pycnodontidae, Rhinopycnodus occupies an intermediate position between Ocloedus and Tepexichthys.


Introduction
Pycnodont fossil fi shes are by far the largest group within Halecostomi (about 40 genera and more than 650 nominal species). They lived from the Late Triassic to the Middle Eocene and reached a nearly worldwide distribution during the Late Cretaceous (Nursall 1996a;Kriwet 2001). They were mostly marine fi shes, generally having a deep and laterally compressed body. Their mode of feeding was durophagous, as can be deducted from the molariform teeth on the vomer and the prearticulars (Nursall 1996a: fi g. 3). They are considered as closely related to the teleosts (Nursall 2010). Formerly all pycnodont fi shes were grouped in one order, the Pycnodontiformes (Nursall 1996b;Poyato-Ariza & Wenz 2002;Kriwet 2005). They are now ranged in a new superorder Pycnodontomorpha, comprising two orders, the Gyrodontiformes and the Pycnodontiformes [new usage for the former Pycnodontoidei] (Nursall 2010).The aim of our paper is to describe a new pycnodontiform genus from the marine Upper Cenomanian of Haqel, Lebanon and to determine its systematic position within the order.

Diagnosis
As for the species (monospecifi c genus).

Etymology
From the Greek ris, rinos, the nose. Indeed, the upper jaw of the fi sh looks like a hog snout when seen in profi le. The generic name Pycnodus is added.   temporal fossa. Exoccipital-basioccipital region well visible behind the dermopterotic. Mouth gape obliquely oriented. Preopercle larger than the exposed region of the hyomandibula-dermohyomandibula. Maximum body depth: 67.6 % of the SL. Pectoral fi n with 9 rays. Ventral fi n with 3 rays. Dorsal fi n with 49 pterygiophores. Origin of the dorsal fi n behind the dorsal apex and at 76.2 % of the SL. Anal fi n with 47 rays and 45 pterygiophores. Origin of the anal fi n on the ventral apex and at 63.8 % of the SL. Neural and haemal arches almost completely surrounding the notochord. 32 vertebral elements (neural spines) before the epichordal series. Neural spines 1-8 autogenous. 11 pairs of ribs. Postcoelomic bone reaching the axial skeleton and the ventral margin. 15 haemal spines before the hypochordal series. 7 epichordal and 11 hypochordal elements in the caudal skeleton. Caudal fi n with 30 principal rays. Body scales only in the abdominal region. Complete scales ventrally and scale bars dorsally. 19 dorsal ridge scales. First dorsal ridge scale small, triangular in shape and not sutured to the dermosupraoccipital. Some spiny scales in the dorsal ridge and in the ventral keel. 3 pelvic scales. 2 postcloacal scales.

Etymology
The species name of the new Lebanese fossil fi sh is dedicated to Mrs. Gabriella di Tota, the co-author's wife.

Holotype and unique specimen
Sample CLC S-725, a complete specimen seen by its right side (Figs 1, 2) from Haqel, Lebanon. Total length: 223 mm.

Holotype morphometric data
The morphometric data are given in % of the standard length (183 mm) of the holotype.
Length of the head (opercle included) Depth of the head (in the occipital region) Maximum depth of the body (at the anal fi n origin level) Prepelvic length Predorsal length Basal length of the dorsal fi n Preanal length Basal length of the anal fi n Osteology

The skull (Figs 3, 4)
The head is high, with the preorbital region much longer than the orbital-postorbital region. The dermal bones of the skull are slightly ornamented with small granulations. The mouth gape is inclined ventrally.
The mesethmoid is broad, very long and its upper margin is covered by a pair of long and very narrow prefrontals. The vomer is seen in profi le and only six rounded molariform teeth ranged in one rank are visible. The frontal is rather short and not very broad. The posterior margin of the bone is a little enlarged and meets the dermosupraocciptal, the parietal and the small autosphenotic, but not the dermopterotic. Posteriorly, the dermosupraoccipital ends in a short pointed tip. The parietal bears a large posterior brush-like process. There is no temporal fenestra. The dermopterotic is not deepened and is located at the level of the upper border of the orbit. The opisthotic, intercalar, basioccipital and exoccipital are visible behind the dermopterotic and the hyomandibula. A small orbitosphenoid is pressed against the posterior border of the mesethmoid. The parasphenoid is very long and its trabecular region is obliquely oriented. Posteriorly, the parasphenoid reaches the level of the basioccipital. The sensory canals on the braincase are not visible.
The quadratic arch contains a well developed quadrate, a large metapterygoid, a large entopterygoid and a small ectopterygoid. The quadrate and the symplectic are both articulated on the lower jaw. European Journal of Taxonomy 67: 1-14 (2013) The premaxilla is long and very broad. It bears only one short but very broad tooth. The maxilla is small, deeper than long, reniform, toothless and pressed against the premaxilla by its upper margin. When seen in profi le, the upper jaw is hog snout-like because of the broadening of the premaxilla and of its tooth. The lower jaw is small and triangular in shape. The dentary is reduced to its ventral branch and it bears two small incisiform teeth. The angular covers a great part of the external face of the mandible. The small articular and the dentary are articulated together. The coronoid process of the prearticular is well marked. Three deep molariform teeth fallen from the prearticular are visible just behind the jaw. The last infraorbital is long, well ossifi ed and forms the posterior and ventral margins of the orbit. No other infraorbital is preserved. The dermosphenotic is lost.
The preopercle is the largest bone of the skull, all together deep and broad. The hyomandibula and dermohyomandibula are fused and their exposed part is important but, however, much smaller than the preopercle. The opercle is well developed, with a pointed ventral tip and a broader upper part. No branchiostegal ray is preserved.
The anterior ceratohyal is the only preserved part of the hyoid bar. A few hook-like branchial teeth and some branchial fi laments are visible under some broken regions of the opercle and preopercle. (Figs 3-5) Only the ventral part of the posttemporal is preserved. The hypercleithrum (= supracleithrum) is deep, rather broad and not splint-like as usual in Pycnodontiformes. The cleithrum is a large bone with a broad palaform ventral branch and a sinus in its posterior margin to house the pectoral fi n, which is short and contains a least 9 rays.

The girdles
The two pelvic bones are vertically oriented. The ventral fi ns are rather long. Each of them contains 3 rays. The origin of the ventral fi ns is located a little before the midpoint of the ventral contour. (Fig. 2) Starting from the caudal region, the vertebral axis progressively elevates to reach the level of the orbit anteriorly. The vertebrae are constituted by only the dorsal and ventral arcocentra. No chordacentrum or autocentrum is visible. The neural and haemal arches surround the notochord almost completely. There are 32 neural spines before the epichordal series and thus 32 vertebral segments before the elements involved in the caudal fi n support. The fi rst 17 vertebral segments are abdominal and the following 15 caudal. The anteriormost 8 neural spines are autogenous. The fi rst seven lean on the occipital region of the braincase and the eighth spine is located just above the fi rst ossifi ed but small basidorsal. The basiventrals are strongly reduced in the abdominal region but well developed in the caudal region. There are 11 pairs of long alate ribs and 15 haemal spines before the hypochordal series. The two last pairs of ribs are noticeably shorter than the nine preceding ribs. The fi rst three haemal spines are pressed together and against the postcoelomic bone. The fi rst haemal spine is incomplete and does not reach the axial skeleton. The neural and haemal spines bear an anterior sagittal fl ange, except for the fi rst fi ve neural and  (2013) the fi rst three haemal spines. A well developed postzygaphophysis links each neural and haemal arch with the following one. The postcoelomic bone is a long and robust bone dorsally reaching the axial skeleton and ventrally the lower margin of the abdomen. (Fig. 2) The dorsal fi n begins a little behind the dorsal apex. The fi n is supported by 49 long and strong pterygiophores. The fi rst seventeen of them have lost the corresponding rays. The last thirty two pterygiophores bear short segmented and branched rays. The fi rst two pterygiophores are broader than the following ones.

The dorsal and anal fi ns
The anal fi n is strip-like in shape (type A2 of Poyato-Ariza & Wenz 2002: fi g. 34). The origin of the fi n is located at the ventral apex. There are 45 strong pterygiophores bearing 47 rays. The fi rst fi ve pterygiophores abut against the postcoelomic bone and are progressively lengthened from the fi rst to the fi fth. The fi rst three rays are reduced to short spines. The other rays are segmented and branched. The very short fi rst pterygiophore supports two little spiny rays and the last pterygiophore two soft rays. (Figs 6, 7) There is no caudal peduncle because the dorsal and anal fi ns reach the caudal fi n. The caudal endoskeleton contains 1 urodermal, 7 epichordal and 11 hypochordal elements. The fi rst epichordal neural arch bears a long and narrow neural spine but the length of the neural spines progressively decreases from the fi rst to the seventh epichordal element, which has only a very short neural spine. Some elements in the hypochordal series are broadened but there is no real hypertrophy. This broadening is more important on the eighth and the tenth hypochordal elements than on the other parts of the series. The contour of the caudal fi n is double emarginated (Poyato-Ariza & Wenz 2002: fi g. 36 E) but the median convex part of the fi n is greatly enlarged. There are 30 principal rays, 3 dorsal and 4 ventral procurrent rays. (Figs 2,4,5,8) The dorsal ridge and ventral keel scales are notably differentiated from the fl ank scales.

Squamation
There are 19 dorsal ridge scales between the dermosupraoccipital and the origin of the dorsal fi n but only the fi rst and the seventh to the tenth are well preserved. The fi rst dorsal scale is small, triangular in shape and located just behind the dermosupraoccipital. The fi ve following scales are badly crushed. Only fragments of the last nine are visible in a fi ssure of the substratum at the dorsal apex level. Each upper margin of the seventh to tenth dorsal scales bears up to six small spines.
The total number of ventral ke el scales is unknown. The ventral keel begins with 3 scales located under the cleithrum (Fig. 4). The fi rst one bears a few very small spines. The second one has a large spine and the third one two large spines. A few ventral keel scales bearing very small spines are visible on the European Journal of Taxonomy 67: 1-14 (2013) ventral contour between the cleithrum and the pelvic girdle, but some elements of this series are lost because of the taphonomic events.
There are 3 pelvic scales associated with the pelvic bones and 2 postcloacal scales are located just before the postcoelomic bone.
There are fl ank scales only in the abdominal region of the body, anterior to the origin of the dorsal and anal fi ns. In the ventralmost area of the situs viscerum, between the cleithrum and the postcoelomic bone, the scales are complete, thick, deep, broad, slightly ornamented with small tubercules and articulated together. There are 11 rows of these large ventral fl ank scales. The other body scales are reduced to scale bars. In the dorsal area of the abdominal region the scale bars are badly preserved and only fragments are visible between the neural spines. Scale bars also are associated with the fi rst eight dorsal ridge scales. The scales linked to the eleven other dorsal ridge scales are progressively broader and longer.
The fi rst scale of the lateral line is visible beneath the brush-like process of the parietal.

The most primitive Pycnodontidae is
On the other hand, the subfamilies Pycnodontinae and Nursalliinae are the most specialized Pycnodontidae (Poyato-Ariza & Wenz, 2002: fi g. 43). In Pycnodontinae, the dermopterotic and the dermosphenotic deepen into an elongated bony pillar reaching the lower margin of the orbit, the dilatator fossa being well visible and located between the two bones (Taverne 1997 . In Rhinopycnodus and the more evolved genera of the subgroup, the distance between the cloaca and the anal fi n is shortened, with a strongly reduced number of ventral keel scales between them and no more than two postcloacal scales (Fig. 4). Some of their hypochordal pieces are markedly enlarged and plate-like (Fig. 7).

Thus, Rhinopycnodus occupies an intermediate position between
Ocloedus and Tepexichthys in the phylogeny of Pycnodontidae.

The generic validity of Rhinopycnodus
Rhinopycnodus exhibits a broadened premaxilla bearing a single very broad tooth. No other Pycnodontidae has a premaxilla such as the one of this new Lebanese fi sh. Akromystax also possesses an enlarged premaxilla. However, the ventral part of the bone is plate-like and bears four rows of small molariform teeth (Poyato-Ariza & Wenz 2005: fi g. 7A), a condition quite different from that of Rhinopycnodus. Moreover, many characters of Akromystax are less advanced than in Rhinopycnodus. Polazzodus Poyato-Ariza, 2010, from the Turonian-Santonian of northern Italy, has one broad tooth on the premaxilla but the bone is narrow except in its most ventral part (Poyato-Ariza 2010: fi g. 5B) and this genus belongs to the Pycnodontinae, a subfamily that is more specialized than Rhinopycnodus.
Thus, the premaxillary morphology of Rhinopycnodus is unique among the Pycnodontidae. This character is enough to confi rm the peculiar generic status of the Lebanese fi sh.