Hendrixella grandei, Bannikov & Carnevale, 2009

Alexandre F. Bannikov & Giorgio Carnevale, 2009, A new percoid fish from the Eocene of Monte Bolca, Italy: Hendrixella grandei gen. & sp. nov., Swiss Journal of Geosciencei 102, pp. 481-488 : 482-486

Hendrixella grandei sp. nov. (Figs. 1-5)

Diagnosis: As for the genus.

Etymology: Species named in honour of the distinguished paleoichthyologist Dr. Lance Grande.

Holotype: FMNH PF 3456, single plate, complete skeleton,

101.5 mm SL; Upper Ypresian (uppermost Lower or lowermost Middle Eocene), Alveolina dainelli Zone (Papazzoni & Trevisani 2006); Monte Bolca locality, Pesciara cave site. Paratypes: MCSNV T 424, single plate, complete skeleton, 83.5 mm SL; MCSNV I.G. 186677, single plate, complete skeleton , 72 mm SL.

Referred specimen: MCSNV T 426, single plate, incomplete skeleton, estimated SL 73 mm.

Measurements (of the holotype): SL of the holotype: 101.5 mm. Other measurements as percentage of SL: Head length: 26; maximum body depth: 15; caudal peduncle depth: 8; predorsal (1 st fin) distance: 40; predorsal (2 nd fin) distance: 67.5; preanal distance: 70.5; distance between pelvic and anal fins: 37.5; 1 st dorsal-fin base length: 20; 2 nd dorsal-fin base length: 12; distance between 1 st and 2 nd dorsal fins: 8; anal-fin base length: 13; longest dorsal-fin spine: 11; longest dorsal-fin ray: 14; longest caudal fin ray: 19.

Description: The body is elongate and slender, with a relatively long caudal peduncle (Figs. 1-2). The caudal peduncle depth is about 53% of maximum body depth. The head is long and pointed, and its length is contained approximately four times in SL. The orbit seems to be located approximately in the middle of the head length. The mouth is terminal and horizontal. The gape of the mouth is wide, apparently reaching almost to the half of the orbit (Figs. 1-3). The body probably was subcylindrical.

The neurocranium is oblong and moderately wide (Fig. 2); it is preserved dorso-ventrally in all four specimens available. The frontals are rather large (Fig. 3); these bones appear only moderately narrowed between the orbits. The ethmoid and otic sectors of the neurocranium are damaged and poorly preserved .

The bones of the infraorbital series are difficult to recognize .

The alveolar process of the premaxilla is narrow. The ascending process of the premaxilla is relatively short and oblique, whereas the articular process is broad. Premaxillary teeth are of moderate size, sharp, conical, slender, and the anteriormost posteriorly recurved (Fig. 3). The lower jaw is very narrow. The dentary is extremely shallow in the symphyseal region. The retroarticular process of the mandible is slightly expanded posteriorly . The mandibular teeth are sharp, conical and moderate in size (Fig. 3).

The bones of the suspensorium cannot be distinguished from each other (Fig. 3). Although the hyomandibula is not completely preserved, it is evident that its shaft is anteroventrally inclined, and its articular head appears to be relatively broad. the articular process of the quadrate is small.

the preopercle is robust, crescent-shaped, with a smooth posterior margin (Fig. 3). the posterior portion of the opercle is not evident.

the hyoid bar is slender and elongate. the anterior ceratohyal possesses a distinct anteroventral process that supports the ventral hypohyal. there are seven sabre-like branchiostegal rays (Fig. 3).

the vertebral column consists of 24 vertebrae, 11 abdominal and 13 caudal, including the urostyle (Fig. 2). the length of the caudal portion of the vertebral column is about 1.05 times greater than the length of the abdominal portion. The vertebral centra are rectangular, longer than high. The first vertebra appears to be fore shortened. The neural spines are short and slender; these arise obliquely from the posterior half of the centrum . The haemal spines are short and relatively slender. The vertebrae 3 through 11 bear robust parapophyses. Thin, slender pleural ribs insert along the posterior margin of the parapophyses . There are two series of intermuscular bones (Figs. 2, 4), which are well exposed in the holotype. Based on their relative position, the bones of the two series are interpreted herein as being epineurals and epicentrals respectively (Tab. 1). The epineurals insert just below or slightly posterior to the bases of the neural arches of vertebrae 1 and 8 through 15 (Figs. 2, 4). The epicentrals of the first two vertebrae originate close to the ventral margin of the centra, those of vertebrae 3 through 7 insert along the posterior margin of the parapophyses, and those of vertebrae 12 through 16 insert just behind the bases of the haemal arches.

The caudal skeleton and fin are relatively well preserved in the material examined (Fig. 5). The terminal centrum is characterized by the fusion of the first preural centrum with one or two ural centra. The five hypurals, parhypural and haemal spine of the second preural centrum are autogenous. The parhypural bears a long and thick parhypurapophysis. There is a reduced diastema between the epaxial and hypaxial hypurals. The neural and haemal spines of the third preural centrum are evidently longer than those of the preceding vertebrae, and the haemal spine appears to be fused to the centrum. The neural spine of the second preural centrum is extremely reduced. There are three epurals; the ventral portion of the second epural is widely enlarged with a rounded profile. There are two uroneurals, the first forming the stegural. The caudal fin is relatively small and forked. The caudal fin consists of 17 principal rays, 15 of which are branched, and 11 upper and eight lower procurrent rays.

There are two small supraneurals; the first supraneural precedes the neural spine of the first vertebra, while the second one lies anterior to the neural spine of the second vertebra. The predorsal formula is 0/0/1 + 1/1/ (Fig. 2). There are two dorsal fins separated by a broad gap, roughly corresponding to the length of 2.5 vertebrae. The first dorsal fin originates above the fourth vertebra and terminates at the level of the 11 th vertebra. The first dorsal fin contains nine slender and flexible spines. The first spine, which is in supernumerary association with the first dorsal-fin pterygiophore is 1.15 times shorter than the second . The second and third spines are approximately equal in length, whereas the succeeding spines progressively decrease in size. The first two pterygiophores interdigitate with the second and third neural spines, and the space between the fourth and fifth neural spines accommodates the fifth and sixth pterygiophores . The pterygiophores of the first dorsal fin are strongly inclined posteriorly and are characterized by longitudinal thickened ridges. The ninth pterygiophore is rayless, located in the interneural space between the eighth and ninth vertebrae. The second dorsal fin originates above the border between the 13 th and 14 th vertebrae and terminates over the 18 th vertebra. It consists of one spine and eight soft rays supported by nine pterygiophores. The first soft ray seems to be unbranched. The rays progressively decrease in length posteriorly in the series. The length of the longest soft rays exceeds the length of the longest spines of the first dorsal fin. The proximal and middle radials of the pterygiophores appear to be fused. The four anterior pterygiophores of the second dorsal fin penetrate into the interneural spaces, whereas the proximal shaft of the posterior five do not reach the tips of the neural spines.

The anal fin is opposite and approximately symmetric to the second dorsal fin. The anal fin comprises two short, slender spines and eight soft rays, supported by nine pterygiophores. The first anal-fin spine is supernumerary. The anal-fin pterygiophores are slender, markedly inclined posteriorly, and they decrease in length posteriorly in the series.

The posttemporal is difficult to recognize, whereas the flat, elongate supracleithrum is clearly exposed. The cleithrum and coracoid are primarily preserved as impression. The cleithrum is elongate, relatively large, sigmoid in shape (Fig. 3). The coracoid is narrow and wedge-shaped. A small scapular foramen is also present. There is a single slender and relatively short postcleithrum. There is no evidence of preserved pectoral radials . The pectoral fin inserts on the lower half of the body. The original complement of pectoral-fin rays cannot be estimated due to inadequate preservation; however, there are not fewer than nine rays.

The pelvic fin (Fig. 2) inserts behind the pectoral-fin base and contains a short and slender spine and five soft rays. The basipterygium is rather small and poorly ossified.

The entire body and head are covered by thin and moderately large scales. A number of scales exhibit up to 10 delicate basal radii. These scales also show multiple circuli on the surface and minute tubercles on the apical field. Delicate transforming ctenii are also visible. The posterior portion of the lateral line series is preserved in the holotype; due to taphonomic processes, this appears to be displaced below the caudal part of the vertebral column.

Comparison and discussion

A general overview of the morphology of Hendrixella grandei gen. & sp. nov. clearly support its alignment with perciform fishes. In particular, the characteristics of the unpaired fins, which contain true dorsal- and anal-fin spines, in combination with completely ossified supraneurals, absence of a free second ural centrum, presence of five autogenous hypurals, presence of a free uroneural, haemal arch and spine of the second preural centrum autogenous, possession of transforming ctenoid scales, caudal fin with 17 principal rays, pelvic fin with one spine and five rays, supracleithrum developed, and anterior neural spines thin and slender unquestionably indicate that it is a member of the highly diverse order Perciformes (see Fujita 1990; Johnson & Patterson 1993; Parenti 1993; Stiassny 1993; Tyler et al. 2003).

Within the Perciformes, Hendrixella lacks the features that define all perciform suborders except the Percoidei, the largest group of the order (see Bannikov & Carnevale 2007). Like the order Perciformes, the suborder Percoidei has not been adequately defined and there is no evidence that it represents a monophyletic assemblage (Johnson 1993). In general, the Percoidei has been commonly considered as a convenient repository for those perciforms that cannot be placed elsewhere (see Johnson 1984). For this reason, Percoidei is uniquely diagnosed by several plesiomorphic perciform characters.

Hendrixella possesses a combination of derived features that is unique within percoid fishes, although some of these features can be found in various combination in a few of the percoid groups. The combination of the vertebral number, structure of median fins (including the caudal one), dorsal and anal fins with a single supernumerary spine, predorsal formula, caudal skeleton with fused haemal spine of the third preural centrum, and intermuscular bones complement, as well as general physiognomy clearly distinguish Hendrixella from the known representatives of Recent and fossil percoid families and incertae sedis genera. Therefore, Hendrixella cannot be accommodated in any existing group of percoid fishes. However, the position of Hendrixella within the Percoidei is rather problematic to define, even with a detailed comparative analysis of the distribution of its derived features.

As described above, the vertebral column of Hendrixella consists of 24 vertebrae; although the possession of 24 vertebrae is considered the primitive condition for percoids (see Gosline 1968, 1971), their relative complement of abdominal (11) and caudal (13) vertebrae is quite unusual, observed only in selected members of the families carangidae, chaetodontidae , Lobotidae , and Serranidae (see Johnson 1984).

Hendrixella possesses two externally separated dorsal fins with a spineless pterygiophore that continue beneath such an external gap. A similar arrangement of the dorsal fin also has been observed in the Acropomatidae , Ambassidae , Apogonidae , Emmelichthyidae , Enoplosidae , Epigonidae and Quasimullidae (Johnson 1984; Bannikov 1999).

The dorsal fin of Hendrixella contains 10 spines plus eight soft rays; even though the presence of 10 spines is considered as the primitive condition for percoids (see springer et al. 1977), shared by many families ( Acropomatidae , callanthiidae, centrarchidae , Coracinidae , Gerreidae , Haemulidae , Kuhliidae , Kyphosidae , Lethrinidae , Lutjanidae , Malacanthidae , Microcanthidae , Moronidae , Nemipteridae , Percichthyidae , Priscacaridae , sciaenidae, scorpididae, sillaginidae, sparidae, etc.) and incertae sedis genera (e.g., Jimtylerius, Hemilutjanus), the concurrent occurrence of as few as eight soft rays is rather uncommon and only certain members of the families Callanthiidae , Pentacerotidae , Percichthyidae and Plesiopidae exhibit the same dorsal-fin formula.

The first dorsal-fin pterygiophore of Hendrixella supports two spines and only one of these is supernumerary. As pointed out by Patterson (1992), the possession of two supernumerary spines is the primitive condition in percoids (and more generally in perciforms) and the presence of a single spine is relatively uncommon within percoid groups.

The anal fin of Hendrixella consists of two spines and eight soft rays. A similar anal-fin formula also has been observed in certain members of the families Acropomatidae , Apogonidae , centrarchidae, Epigonidae , Mullidae , Pentacerotidae , Percidae , sciaenidae, and serranidae. However, only one of the two anal spines is supernumerary. According to Johnson (1984), the same condition is typical of apogonids, resulting from the evolutionary loss of a primitive anteriormost spine. As documented above, the anal fin of Hendrixella is opposite to the second dorsal fin; this could be probably interpreted as the primitive percoid condition, given that the symmetrical position of these anatomical units seems to be coordinated in shared myomeres through a common developmental mechanism (Mabee et al. 2002).

Hendrixella possesses two thin and short supraneurals; the presence of two supraneurals represents a derived condition for percoids (Johnson 1984), which is shared by several groups (e.g., Acanthoclinidae , Ambassidae , Banjosidae , callanthiidae , centrogenysidae, chaetodontidae, cheilodactylidae , chironemidae, congrogadidae, Ephippidae , Eocottidae , Giganthiidae , Girellidae , Inermiidae , Latrididae , Malacanthidae , Mullidae , Nemipteridae , Opistognathidae , Oplegnathidae , Pentacerotidae , Plesiopidae , Pomacanthidae , Pseudochromidae , scatophagidae, serranidae, sillaginidae, Toxotidae ). The predorsal formula (Ahlstrom et al. 1976) of Hendrixella is 0/0/1 + 1/1. Based on the hypothesis proposed by Johnson (1984), this is a derived condition, which also has been observed in certain taxa of the family Ambassidae ; however, such a convergence in the predorsal arrangement is clearly homoplastic, since the convergence in identical patterns of the predorsal configuration has arisen independently many times during the evolutionary history of percoid fishes (see Johnson 1984).

The basic structure of the caudal skeleton of Hendrixella is similar to that of many percoids, except for the presence of a fused haemal spine of the third preural centrum. It consists of five autogenous hypurals, a parhypural with a strong hypurapophysis , two uroneurals, three epurals and second preural centrum with reduced neural spine and free haemal arch and spine. Although a fused haemal spine of the third preural centrum is typical of some families within the Percoidei (e.g., Ambassidae , Apogonidae , callanthiidae, Echeneididae , Nandidae , Opistognathidae , Pentacerotidae , Plesiopidae , Pseudochromidae ), a similar structure of the whole caudal complex is extremely rare and also has been observed in certain members of the families Eocottidae and Malacanthidae (Johnson 1984; Bannikov 2004).

The caudal fin of Hendrixella contains 17 principal rays, plus 11 dorsal and eight ventral procurrent rays. Although the possession of 17 principal caudal fin rays is extremely common within the Percoidei, representing the plesiomorphic condition (see Patterson 1968), the total (principal + procurrent) complement of caudal-fin rays of Hendrixella only occurs in certain percoids (see Johnson 1984), including the Ambassidae , carangidae , centropomidae, Echeneididae , Girellidae , Haemulidae , Lutjanidae , Malacanthidae , Nemipteridae , sparidae and Terapontidae . the possession of two distinct series of intermuscular bones appears to be unique within the Percoidei, representing an unambiguous autapomorphy of Hendrixella . According to Patterson & Johnson (1995), a single series of intermuscular bones characterizes percomorph fishes, and more generally all acanthomorphs except for certain polymixiiforms, beryciforms, and lampridiforms.

In summary, the analysis of the distribution of selected derived features of Hendrixella clearly indicates that its relationships are rather difficult to define. such a comparative discussion has not provided any convincing evidence that would unite Hendrixella to any previously known percoid family or incertae sedis genera. Although Hendrixella shares certain morphological features (fused haemal spine of the third preural centrum; median fin distribution) and meristic (dorsal-, anal- and caudal-fin formulae, etc.) features with some members of the families Ambassidae , Apogonidae , and Eocottidae , it differs from the members of these families in having a different jaw dentition, 11 + 13 vertebrae, and two series of intermuscular bones. Hendrixella possesses a unique combination of features among percoids and it cannot easily be accommodated within any of the known familial categories. However, even considering that the possession of two distinct series of intermuscular bones is unique among percoids, the difficulties in unambiguously identifying the sister-group relationships of Hendrixella strongly support its placement as incertae sedis among the Percoidei.