by Luigi Lorenzo CAPASSO, Louis TAVERNE & Roy NOHRA Résumé Abstract Introduction - PDF


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BULLETIN DE L INSTITUT ROYAL DES SCIENCES NATURELLES DE BELGIQUE BULLETIN VAN HET KONINKLIJK BELGISCH INSTITUUT VOOR NATUURWETENSCHAPPEN SCIENCES DE LA TERRE, 80: , 2010 AARDWETENSCHAPPEN, 80: , 2010 A re-description of Hensodon spinosus, a remarkable coccodontid fish (Actinopterygii, Pycnodontiformes) from the Cenomanian (Late Cretaceous) of Haqel, Lebanon by Luigi Lorenzo CAPASSO, Louis TAVERNE & Roy NOHRA Capasso, L.L., Taverne, L. & Nohra, R., 2010 A redescription of Hensodon spinosus, a remarkable coccodontid fish (Actinopterygii, Pycnodontiformes) from the Cenomanian (Late Cretaceous) of Haqel, Lebanon. Bulletin de l Institut royal des Sciences naturelles de Belgique, Sciences de la Terre, 80: , 21 figs, 2 tables, Brussels, October 31, 2010 ISSN Abstract Hensodon spinosus, a rare and very peculiar pycnodontiform fish from the Upper Cenomanian limestone of the Haqel fossils quarry (Lebanon) is re-described on the basis of four new specimens. It is the only species assigned to the genus. It shares with the family Coccodontidae (sensu Po yat o-ariza & Wenz, 2002) almost all its synapomorphies but is also characterized by several unique autapomorphies. The species exhibits a rounded general shape of the body, an enormous head, an extremely reduced snout with a minute mouth gash, a horny frontal showing modifications that we interpret as dimorphic sexual differences, styliform teeth, a giant occipital process with many spines on its margins and formed by the dermosupraoccipital, the parietal and the supratemporal, a prefrontal, an edentulous, unornamented, elongated rhomboid maxilla, a very massive spiny cleithrum, a big spiny post-coelomic bone, and a few elongated bar scales. All those characters award a unique impressive aspect to the fish. Remains of the original colour pattern add information about the external aspect of this remarkable fish. Keywords: Actinopterygii, Pycnodontiformes, Coccodontidae, Hensodon spinosus, osteology, systematics, Cenomanian, Haqel, Lebanon. Résumé Hensodon spinosus, un pycnodonte rare et très particulier provenant des calcaires du Cénomanien supérieur de la carrière à fossiles de Haqel (Liban) est redécrit sur la base de quatre nouveaux spécimens. Il s agit de la seule espèce du genre. Elle partage presque toutes les synapomorphies de la famille des Coccodontidae (sensu Po yat o- Ariza & Wenz, 2002) mais est aussi caractérisée par quelques autapomorphies uniques. L espèce montre un corps de forme arrondie, une tête énorme, un museau extrêmement réduit avec une minuscule fente buccale, un frontal cornu montrant des différentes que nous interprétons comme du dimorphisme sexuel, des dents styliformes, un processus occipital gigantesque, garni d épines sur ses bords et formé par le dermosupraoccipital, le pariétal et le supratemporal, un préfrontal, un maxillaire rhomboïde, édenté, lisse et allongé, un cleithrum très massif et épineux, un grand os postcoelomique épineux, ainsi que quelques écailles réduites et en forme de barre. Tous ces caractères donnaient un aspect tout à fait remarquable au poisson. Des restes de la coloration ajoutent des informations sur l aspect extérieur de ce curieux poisson. Mots-clefs: Actinopterygii, Pycnodontiformes, Coccodontidae, Hensodon spinosus, ostéologie, systématique, Cénomanien, Haqel, Liban. Introduction The fish fauna collected in the past three centuries from the Upper Cenomanian limestones of the quarry of Haqel includes a large series of pycnodontiforms offering an impressive variability of forms. The most abundant pycnodontid species of all in the thanatocoenosis of Haqel is Nursallia goedeli (Heckel, 1856), which is really common there. This abundance of pycnodonts revealed that the environmental conditions typical of the habitat of this area were particularly favourable to these types of fishes during Late Cenomanian times. The pycnodontiform local fauna includes also a number of rare and sometimes very rare forms, prevalently of little size, collected during the last twenty years (see e. g. Forey et al., 2003; Nursall & Capasso, 2004; Capasso et al., 2009). The interest for these rare species consists in the unusual combination of its anatomical characters that demonstrate the impressive variability of the members of the pycnodont group, despite it is considered a monophyletic group, inside the thanatocenosis of one of the most famous fossil fish localities over the world. Hennig (1907) briefly described and figured one of 146 Luigi Lorenzo CAPASSO, Louis TAVERNE & Roy NOHRA those rare pycnodontiform fishes from the Cenomanian of Haqel under the name Mesodon spinosum. Later, Steinmann (1928) also figured the specimen as Mesodon spinosus Hennig. A modern re-description has been done by Kriwet (2004) but remains very superficial because of the bad preservation of the holotype and single known specimen at that time. However, Kriwet (2004) has shown that this fish was not a Mesodon but belonged to a new genus for which he erected the taxon Hensodon located by him within the pycnodontiform family Coccodontidae. One of us (R. N.) has recently found at the Haqel quarry four new and better preserved specimens referable to Hensodon spinosus (Hennig, 1907) but showing some osteological differences between one specimen and the three others, differences due in our opinion to a remarkable sexual dimorphism. The aim of our paper is thus to give a more complete re-description of this very peculiar pycnodontiform fish. Material (Figs 1a, 1b; Table 1) Fig. 1a Hensodon spinosus (Hennig, 1907). A: CLC # S.357; B: CLC # S.718. Fig. 1b Hensodon spinosus (Hennig, 1907). C: CLC # S.572; D: CEH # 115. The material examined here consists of the following four samples, all in only one part, without counterparts, coming from the Haqel fossil quarry (see next paragraph): (1) Specimen CLC # S.357: near complete fish (only the tip of the tail is missing), 64 mm long (but this measure did not represent the Total Length (TL), because the final part of the caudal fin is missing); the fish is seen by its left side (Fig. 1a-A). We interpret this specimen as a male because its frontal horns are bigger and its skeleton more heavily ossified than in the three following specimens, considered as female. In our opinion, the holotype described by Kriwet (2004) is also female. We do not think that there were two different but closely allied species of The coccodontid fish Hensodon spinosus from the Cenomanian of Lebanon 147 Table 1 Main measurements (in mm) and main numeric characters of the examined samples of Hensodon spinosus. Sample TL SL TD nv ndp nap ncr npr nvr CLC # S CLC # S CLC # S CEH # TL = total length, measured as horizontal distance between tip of pre-maxilla and the posterior limit of the caudal fin (in our case the TL is sensibly minor to the total length of the other fish, because the spines of the frontal region are not included in this measure, as these spine exceeding the anterior margin of the premaxilla); SL= standard length; TD = total (maximum) depth (measured as the greatest vertical distance of the body); nv = total number of vertebral segments; ndp = number of dorsal pterygiophores; nap = number of anal pterygiophores; ncr = number of principal caudal fin rays; npr = number of principal pectoral fin rays; nvp = number of principal pelvic fin rays. The sign --- indicates that the character is not visible or not countable. Hensodon living in the same marine Late Cretaceous environment at Haqel. (2) Specimen CLC # S.718: near complete fish, with TL = 50 mm; the fish shows its left side (Fig. 1a-B). (3) Specimen CLC # S.572: near complete fish on a limestone slab with many fractures, with TL = 55 mm; the fish shows its right side (Fig. 1b-C). (4) Specimen CEH # 115: near complete fish, with TL = 57 mm; the fish shows its left side (Fig. 1b-D). CLC: Public collection of fossil fish called Luigi Capasso Collection, Registered by the Italian Ministery of Cultural Heritage, with Protocol STRAP n. 21 of the Situated in via d Aragona, Chieti (Italy); complete list of the Luigi Capasso Collection is available upon request to the quoted postal address, or throught the Italian Government Ministery of Cultural Heritage Soprintendenza Archeologica dell Abruzzo Via dei Tintori, Chieti (Italy). CEH: Collection of Dr. Roy Nohra, stored at the Expo Haqel, Main Road, Haqel, Lebanon. Location and preservation of fossils (Figs 2, 3) The specimens described herein are preserved in lagerstätten, formed by fine-grained (micritic), finely laminated plattenkalk of the Haqel quarry. The little village of Haqel lies in northern Lebanon, in the district of Jbel, province of Jabal Loubnan, on the eastern slope of Mount Lebanon, near the head of the Haqel River valley, 700 m above sea level. Haqel is a small village, with about 775 inhabitants in 70 houses (Fig. 2). The only quarry open in this region is on the left (South) wall of the valley near the source of the Haqel River, about 1 km East of the village, at an altitude of 700 m. The site of the quarry extends for ca square metres (Fig. 3). At the same level on the opposite wall of the valley the prevalent outcrop is of massive sterile limestone in the upper levels; but recently an excavation made by the family Abi Saad identified near the same formation, and apparently the same fossil fishes at the bottom of the sterile limestone also on the right (North) side of the Haqel River quarry. Nazih Nohra began to work at Haqel in The quarry continues until now to be an abundant source of fossils. Today, only two families are active in the fossil quarry: chiefly the Nohra family of Haqel, less frequently the Saad family of Byblos. Extraction is manual, but extension of a power cable from the village to the quarry by the Nohra family enables collectors to use an electric cutter to reduce the weight of the blocks containing fossils. The composition of the Haqel flint is: CaCO 3 75%; SiO 2 20%; remainder mostly clay minerals (Hückel, 1970). The limestone is well stratified (Fig. 3C). The strata are variably inclined downward, from 25 to 50 degrees to the West, but inclination is highly variable both in angle and direction. In addition, stratification is very irregular, as many micro-faults and curved strata are often present (Figs 3A, B). Chert is present in lenses and nodules, varying from few centimetres to 50 cm or more in diameter without concentric structure, often of irregular shape. The thickness of lamination is also very variable from a few millimetres to 50 cm. The thickest strata are usually sterile (Fig. 3B). The colour is also impressively variable from a pale yellow to a brown-beige, to grey and near black. Haqel, in particular among Lebanese fossil localities, has an abundant preserved ichthyofauna. In fact the limestone of this restricted area probably represents one of the richest deposits of fossil fish in the world. Mass 148 Luigi Lorenzo CAPASSO, Louis TAVERNE & Roy NOHRA Fig. 2 Geographic position of the Haqel fossils quarry. mortality layers are relatively frequent; multiple fish slabs are regularly found in this locality. It is impossible to obtain very large slabs because the laminations of the richest strata are distorted, and cherty deposits are frequent. As already said, fishes are the most common fossils, but crustaceans are also frequent, and plants, reptiles, echinoderms, insects and birds are also present as rare finds (listed in decreasing order of frequency) (Gay e t et al., 2003). Bits and pieces of fossils are often seen in different layers at the edges of blocks, which are not cut square. Forey et al. (2003) recorded 55 genera and 69 species of fishes in Haqel deposits, but this number is increased in the last two years, compared to 47 genera and 58 species in nearby Hajula, and 25 genera and 30 species in En Nammoura, although it must be kept in mind that these figures will change with further collection and description. Five (9%) of 56 species of actinopterygians described by Forey et al. (2003) from Haqel are pycnodontiform fishes, all of which are highly derived. Hückel (1970) described the probable conditions of deposition at Haqel, with concentration of sediments in small basins, influenced by tectonic activity causing slippage at shelf margins. Hemleben (1977) invoked the probability of biological toxicity ( red tides ) and oxygen deficiency in the mortalities recorded at Haqel. Fishes are the most common and noticeable fossils at the sites, usually complete with scales (Hückel, 1970). Hemleben (1977) noted that 87% of fishes oval in shape lay in a stable position on their The coccodontid fish Hensodon spinosus from the Cenomanian of Lebanon side, but that 13% were found lying on their back or belly. Often the fish are strongly arched, with head and tail raised, and sometimes a telescoping of the vertebrae (Hückel, 1970). The four specimens described here are generally not badly deformed. However, the specimen CLC # S.357 seems to be a little compressed in supero- 149 inferior direction. The Haqel fish layers have been defined as Cenomanian V, in the analysis of Hückel (1970). The actual quarries that produce the new specimens of Hensodon spinosus are shown in Figure 3. Systematic paleontology Class Osteichthyes Huxley, 1880 Subclass Actinopterygii Cope, 1887 Division Halecostomi Regan, 1923 sensu Patterson, 1973 Order Pycnodontiformes Berg, 1937 Suborder Pycnodontoidei Nursall, 1996 Family Coccodontidae Berg, 1940 sensu Poyato-Ariza & Wenz (2002) Genus Hensodon Kriwet, 2004 Type species: Hensodon spinosus (Hennig, 1907) Hensodon spinosus (Hennig, 1907) Figs 4-21 Description General shape (Figs 4-6) Hensodon spinosus is a pycnodontid of little dimension, between 5 to 10 cm of total length. The fish is discshaped and laterally compressed, with a very short abdominal region. The head and the pectoral girdle are enormous in comparison with the body, representing a little more than the half of the entire fish. The snout is short, with a reduced mouth gash. The frontal region bears big horns. A very large occipital horny process exists in the post-frontal region. Many large bones of the skull are spongy, allowing the big head to be lighter than with internally solid bones. The pectoral girdle is spiny. The maximum body depth corresponds to the posterior margin of the post-frontal osseous process, with a mean of the ratio SL (standard length)/td (maximum body depth) = 87.3 (see Table 2) (as the Total Length is the horizontal distance between the tip of the premaxilla and the posterior limit of the caudal fin, in our case the TL is sensibly minor to the total length of the other fish, because the spines of the frontal region are not included in this measure, as these spine exceeding largely the anterior margin of the premaxilla). Fig. 3 Three aspects of the extant situation and works for fossils extraction at the Haqel quarry. Skull, teeth and hyoid skeleton (Figs 7-10, 12) The two frontals are large and horny bones. They protrude, forming so not only the frontal region but also 150 Luigi Lorenzo CAPASSO, Louis TAVERNE & Roy NOHRA Fig. 4 Fig. 6 Hensodon spinosus (Hennig, 1907). Reconstruction of the entire fish based on the supposed male specimen CLC # S Hensodon spinosus (Hennig, 1907). Reconstruction of the entire living fish. The supposed female pattern. the anterior part of the skull. There are two patterns of frontal region and horns, very probably representing a sexual dimorphism. In specimen CLC # S.357, the frontals are rather narrow above the orbit. They support two huge, elongate, anteriorly directed conic horns, with a pointed pit, one on each frontal. Above that horn, the frontal margin exhibits a series of eight small spines, contributing to determine a serrated aspect on the superior margin of the frontal. Ventrally, at the base of the big horn, there are two other smaller spines. As already said, we interpret that morphology as the male pattern. In the holotype, the frontal exhibits two smaller horns, one dorsally, the other more ventrally (Hennig, 1907: fig. 3; Kriwet, 2004: fig. 1, 3). We think that Fig. 5 Hensodon spinosus (Hennig, 1907). Reconstruction of the entire living fish. The supposed male pattern. is the female pattern. In specimen CLC # S.572, the horny region of the frontal is lost, while samples CLC #S.718 and CEH # 115 have preserved the upper part of the frontal, with the dorsal horn, but have lost the lower part of the bone, with the ventral horn. These last three specimens also show that the frontal is much broader above the orbit in the supposed female fishes than in the male. Kriwet (2004: fig. 3) described on the holotype a horizontally elongate parietal (= postparietal in Kriwet s text) behind the frontal. This bone bears the same sort of horn as on the frontal. Hennig (1907: fig. 3) figured the same structure. Our own observations show that the parietal offers a quite different shape and is not horny. Kriwet s horny parietal simply is a fragment of one of the two frontals posteriorly displaced by the fossilisation. Behind the frontal, the crown of the skull develops a gigantic tower-like occipital process, like the one of Trewavasia carinata (Dav i s, 1887) and Ichthyoceros spinosus Gay e t, 1984, two other Late Cretaceous coccodontid fishes from Lebanon (Gay e t, 1984: fig. 1 and 2; Nursall & Capasso, 2008: fig. 5), but still much higher. The very large dermosupraoccipital forms Table 2 Value of the ratio SL/ TD in described samples of Hensodon spinosus. Sample SL TD Ratio CLC # S CLC # S CLC # S CEH # 115) Mean 87.3 The coccodontid fish Hensodon spinosus from the Cenomanian of Lebanon 151 the anterior part of the process, while its posterior part is constituted ventrally by the thin but very deep parietal, and dorsally by the supratemporal (= extrascapular). The long anterior margin of the dermosupraoccipital is serrated and its superior margin bears two welldeveloped spines. This serration is less pronounced in the supposed female samples than in specimen CLC # S.357. The dorsal margin of the supratemporal also bears a few spines. This character is the same in both presumed sexes but the anterior margin of the process follows the frontal profile in the supposed male fish (CLC # S.357) while it forms a marked angle with the frontal profile in our three female specimens and in the holotype (Kriwet, 2004). The dermopterotic is very long but not high and it bears a long horizontal crest. Its acuminate anterior Fig. 7 Hensodon spinosus (Hennig, 1907). The skull and girdles of the supposed male specimen CLC # S.357. 152 Luigi Lorenzo CAPASSO, Louis TAVERNE & Roy NOHRA extremity overhangs the orbit in the male specimen. In our three female samples, the dermopterotic is a little shorter and less acuminate. The dermopterotic and the frontal serve as the basis of the tower-like occipital process. Between the dermopterotic and the big anterior dorsal spine of the cleithrum, specimen CLC # S.357 shows the print of the autopterotic. On the same specimen, below the anterior part of the dermopterotic and just behind the orbit, a small autosphenotic is visible. Fig. 8 Hensodon spinosus (Hennig, 1907). Part of the skull of the supposed female specimen CLC # S.718. The coccodontid fish Hensodon spinosus from the Cenomanian of Lebanon 153 The ethmoid complex consists of the dermal prefrontal and the endochondral mesethmoid. The prefrontal is well preserved on specimen CLC # S.357. It is a long and thin bone located just under the basis of the frontal and before the mesethmoid, partly covering the premaxilla. There are four small spines on the lower part of the anterior margin of the bone. Such a prefrontal exists in a few pycnodontiform fishes. It is a paired dermal bone of the ethmoid region perhaps homologue with the laterodermethmoid. The mesethmoid is a large and massive bone contacting the frontal and the prefrontal anteriorly an
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