# An enigmatic teleost fish from the Eocene of Bolca
(Italy) with unusual larval-like features

Donald Davesne, Giorgio Carnevale

<figure><img src="image_1.png" /></figure>

► To cite this version:

Donald Davesne, Giorgio Carnevale. An enigmatic teleost fish from the Eocene of Bolca (Italy) with unusual larval-like features. Papers in Palaeontology, 2025, 11 (3), pp.e70017. 10.1002/spp2.70017. hal-05062296

HAL Id: hal-05062296

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Submitted on 10 May 2025

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but without anatomical arguments to support such
attribution.

MATERIAL & METHOD

Only two specimens are known. The holotype, MNHN.F.BOL65/BOL66, in part and counterpart (Fig. 1), is housed at the Muséum national d'Histoire naturelle (MNHN), Paris, France. The other specimen, MCSNV T.293/T.294, also in part and counterpart, belongs to the Baja collection housed at the Museo Civico di Storia Naturale (MCSNV), Verona, Italy. Both specimens show the anterior portion of the body, including the head, but the posterior end is not preserved. They are remarkably similar in morphology and are in the same size range (c. 6.6 mm head length for MNHN.F.BOL65/BOL66 and 5.7 mm head length for MCSNV T.293/T.294).

The fossil taxon was initially described by Volta (1796). In the original cursory mention, Volta named it *Pegasus Volans*. *Pegasus volans* is a preoccupied name erected by Linnaeus (1766), and is itself a junior synonym of *Pegasus volitans* (Linnaeus 1758), an extant seamoth (Pegasidae, Syngnathiformes) from the Indo-Pacific region (Fricke et al. 2024). There is very little in common morphologically between the extant *Pegasus* and the fossils studied herein: the extant *Pegasus* is a benthic, dorsoventrally flattened animal with an elongate rostrum, conspicuous bony plates and well-developed pectoral fins. In contrast, the fossil described by Volta is a laterally flattened animal with no rostrum or bony plates. Despite these obvious differences, the name *Pegasus volans* has been used in the literature ever since for these fossils (Agassiz 1833; Blot 1980), even though recent authors have acknowledged the need for a new genus and referred it to as *Pegasus* volans (Bannikov 2014; Carnevale et al. 2014; Brignon 2019).

For the present study, fossils were re-examined using a
Leica M80 stereomicroscope equipped with a camera
lucida drawing arm. To enhance details, specimens were
moistened with alcohol. Additional photographs (not fig-
ured) were taken under UV light to elucidate potentially
hidden structures.

SYSTEMATIC PALAEOONTOLOGY

TELEOSTEI Müller 1845

ACANTHOMORPHA Rosen 1973

PERCOMORPHA Cope 1871

PERCOMORPHA incertae sedis

Genus †Dibango nov.

LSID. https://zoobank.org/NomenclaturalActs/a578ed0e-6dd1-
4647-829e-3eef8876686e

*Derivation of name.* Named in honour of the Cameroonian musician and singer Manu Dibango (1933–2020), for his work as an artist and cultural ambassador.

Diagnosis. As for type and only species.

Type species. †Dibango volans gen. et sp. nov.

†Dibango volans sp. nov.
Figures 1–5

1796 *Pegasus Volans*; Volta p. 174, pl. 42, fig. 2.

1833 *Pegasus volans*; Agassiz p. 35.

1980 *Pegasus volans*; Blot p. 384.

2014 ‘*Pegasus*’ volans; Bannikov p. 26.

2014 ‘*Pegasus*’ volans; Carnevale *et al.* p. 42

2018 ‘Pegasus’ volans; Carnevale & Bannikov p. 175.

2019 ‘*Pegasus*’ volans; Brignon p. 50, fig. 19I.

2023 ‘*Pegasus*’ sp.; Davesne *et al.* p. 14.

2024 'Pegasus' volans; Davesne & Carnevale p. 1, figs 1-5.

LSID. https://zoobank.org/NomenclaturalActs/e8f1e08d-82d2-
4970-8ae0-b8c663560a3b

*Derivation of name.* From the Latin *volans*, 'flying, moving swiftly'. This name references the original description of the species as *Pegasus volans*.

*Diagnosis.* Body narrow and slender. Premaxilla with a long and pointed ascending process and a well-developed and distally spatulate articular process. Maxilla large and hourglass shaped. Dentary with a prominent symphyseal spine. Oral jaw teeth tiny and conical. At least six sabre-like branchiostegal rays. Three abdominal vertebrae. First dorsal-fin ray vexillum-like, extremely elongate, flexible, unsegmented and unbranched. Dorsal and anal-fin rays unbranched and unsegmented. Anal-fin rays longer than their dorsal-fin counterparts and gradually increasing in length posteriorly. Dorsal- and anal-fin pterygiophores horizontally oriented, hourglass shaped. One-to-one relationship between median-fin pterygiophores and vertebrae. Cleithrum massive, straight and almost vertically oriented. Coracoid small, bearing a remarkably elongate ventral process almost parallel to the pelvic bone (basipterygium). Pelvic bone hypertrophied, protruding ventrally from the body wall for a length equal to that of the anterior 20 vertebrae. Pelvic fin with a greatly elongate, robust and distally flexible spinous ray plus two delicate unbranched and unsegmented rays. Entire body covered with tiny dermal spinules characterized by a stellate basal plate supporting an upright spine.

*Holotype.* MNHN.F.BOL65/BOL66, partially complete articulated skeleton lacking the posterior portion of the body (Fig. 1), in part and counterpart.

*Referred specimens.* MCSNV T.293/T.294, partially complete articulated skeleton, lacking the posterior portion of the body (Fig. 2), in part and counterpart.
<figure><img src="image_3.png" /><figcaption>FIG. 1. †Dibango volans gen. et sp. nov., holotype MNHN.F.BOL65. A, photograph of the entire specimen. B, detail of the cephalic and pectoral regions, moistened with alcohol. C, interpretative drawing of the suspensorium and jaws. Counterpart MNHN.F.BOL66 is poorly preserved and not figured here. Photographs by P. Loubry (MNHN). *Abbreviations*: af, anal-fin rays; ang-ar, anguloarticular; cl, cleithrum; d, dentary; df1, dorsal-fin ray 1 (vexillum-like); ecp, ectopterygoid; enp, endopterygoid; mpt, metapterygoid; mx, maxilla; nsp, bifid spine at the posterodorsal corner of the neurocranium; pal, palatine; pcf, pectoral-fin rays; plb, pelvic bone (basipterygium); plf, pelvic-fin rays; pmx, premaxilla; q, quadrate; s, symplectic; vp.co, ventral process of the coracoid. Scale bars represent: 10 mm (A, B); 1 mm (C).</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>**FIG. 2.** †Dibango volans gen. et sp. nov., MCSNV T.293. Photograph of the entire specimen. Photograph by D. Davesne. Abbreviations: af, anal-fin rays; df1, dorsal-fin ray 1 (vexillum-like); pcf, pectoral-fin rays; plb, pelvic bone (basipterygium); plf, pelvic-fin rays; sts, soft-tissue stain (presumably skin); vc, vertebral column; vp.co, ventral process of the coracoid. Scale bar represents 10 mm.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**FIG. 3.** †Dibango volans gen. et sp. nov., MCSNV T.293. Detail of the skull, and interpretative drawing. Abbreviations: ang-ar, angular-articular; br, branchiostegal rays; d, dentary; ecp, ectopterygoid; enp, endopterygoid; fr, frontal; h, hyomandibula; io, infraorbitals; iop, interopercle; le, lateral ethmoid; mx, maxilla; op, opercle; pal, palatine; pas, parasphenoid; pmx, premaxilla; pop, preopercle; q, quadrate; s, symplectic; soc, supraoccipital; sop, subopercle. Scale bar represents 1 mm.</figcaption></figure>

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## Description

Both of the available specimens are incomplete and lack the posterior part of the body; the caudal skeleton is therefore unknown. The body is extremely narrow and slender.

**Skull.** The skull roof is notably inflated, apparently due to the presence of a frontal crest, probably bilateral (Fig. 3). The frontal crest has a gently rounded outer profile. It is difficult to determine whether an occipital crest and spine were present or not. The holotype has a bifid spine at the posterodorsal corner of the
<figure><img src="image_7.png" /><figcaption>**FIG. 4.** †Dibango volans gen. et sp. nov., MCSNV T.294. Photograph of the entire specimen, and interpretative drawing of the pectoral girdle region. Photograph by D. Davesne. *Abbreviations:* c, centra of vertebrae 1–4; cl, cleithrum; co, coracoid; pcf, pectoral-fin rays; plb, pelvic bone (basipterygium); pt, posttemporal; scl, supracleithrum; vp.co, ventral process of the coracoid. Both scale bars represent 1 mm.</figcaption></figure>

neurocranium (Fig. 1). This spine is in close proximity to the base of the greatly elongate vexillum-like dorsal-fin ray.

The configuration of the ethmoid region is only partially recognizable (Fig. 3), showing what appears to be the lateral ethmoid, which is in close association with the anterior articular end of the palatine.

The parasphenoid is a stout median bone that forms most of the basicranium, running in the lower half of the orbit. The basioccipital is visible only in MCSNV T.294 (Fig. 4); it is very thick and bears a dorsal ascending process that articulates with the exoccipital. The bones of the otic region of the neurocranium cannot be properly recognized due to inadequate preservation.

The eyeball is marked in both specimens by a circular, thin and dark pigmented film (Figs 1, 3, 4).

What appear to be the second, third and fourth infraorbital bones can be recognized in MCSNV T.293 (Fig. 3). These bones are ventral to the pigmented orbit, weakly defined due to their limited ossification. While the second and fourth elements are almost tubular, the third infraorbital is ventrally expanded.

**Jaws.** The gape of the mouth is moderately developed (Figs 1, 3). The premaxilla has a long and pointed ascending process, approximately equal in length to the alveolar process (Figs 1, 3). There is a well-developed and distally spatulate articular process forming a deep notch with the posterior margin of the ascending process, which possibly accommodated a large rostral cartilage in origin. The premaxilla bears very small conical teeth arranged in multiple rows, which are recognizable only in MCSNV T.293 (Fig. 3).

The maxilla is toothless, large, apparently excluded from the border of the mouth, almost hourglass shaped, and bearing a thick anterodorsal process and concave dorsal, ventral and posterior margins (Figs 1, 3). There is no evidence of a supramaxilla.

The mandible is almost triangular in outline (Figs 1, 3). The dentary bears a prominent pointed and posteroventrally directed symphyseal spine. Numerous tiny conical teeth, similar to those of the premaxilla, can be observed along the alveolar process of MCSNV T.293. The anguloarticular is irregular in outline. There is a thick spine emerging from the posteroventral corner of the mandible (Fig. 1).
*Suspensorium.* Overall, the suspensorium is inclined forward (Fig. 1). The quadrate is almost triangular in shape and bears a thick articular condyle. There is a small posterodorsal notch to accommodate the rod-like symplectic. The ectopterygoid and endopterygoid are partially preserved in both specimens, while what appears to be a quadrangular metapterygoid can be recognized in the holotype (Fig. 1). There is a prominent palatine, bearing a thick and ventrally directed anterior process. The hyomandibula has a long and slender ventral shaft and a triangular dorsal portion, with two articular heads (Fig. 3).

*Opercular region.* The opercular bones are thin and only partially recognizable in the holotype (Fig. 1). The two large arms of the preopercle form an obtuse angle; the anterior margin of the bone is thickened, while the posterior margin is distinctly rounded. The opercle appears to be subrectangular in outline, with an oblique ventral margin. Interopercle and subopercle are laminar, recognizable in MCSNV T.293 (Fig. 3).

*Hyoid apparatus.* The hyoid bar is compact and shows a ventral concavity at its midlength (Fig. 1). Six sabre-like branchiostegal rays appear to be present in the holotype, although their exact number is unclear due to inadequate preservation (Figs 1, 3).

*Vertebral column.* There are three abdominal vertebrae (Fig. 4). Twenty-four caudal vertebrae are preserved in the holotype and 18 in MCSNV T.293 (Figs 1, 2). In both specimens the posteriormost portion of the body is not preserved, preventing a count of the original vertebral number.

The abdominal and first two caudal vertebrae are compact, shorter than the other vertebrae, and gradually increase in size posteriorly (Figs 4, 5). The subsequent vertebrae are almost equal in size. The vertebral centra are hourglass shaped and significantly longer than high (Figs 4, 5). The neural and haemal arches are weakly ossified, anteroposteriorly expanded, extensively ornamented with circular pits and irregular in outline. Short dorsal and ventral pre- and post-zygapophyses can be recognized. The very short neural and haemal spines are thin, pointed and vertically oriented.

What appears to be a short pair of ribs can be recognized ventrally to the second abdominal vertebra in MCSNV T.293. There is no evidence of intermuscular bones.

*Median fins & supports.* There is no evidence of supraneurals. The first element of the dorsal fin is closely associated with the occipital region of the neurocranium (Figs 1–2, 5). It is an extremely elongate, flexible, unpaired, unsegmented and unbranched stout ray, which is supported by a short but relatively thick, almost horizontal pterygiophore. In the holotype, this elongate and flexible ray appears fairly complete and tapers at its distal extremity (Fig. 1). In MCSNV T.293 it is associated with the remains of a band of soft tissue that probably formed a flap along its posterior margin (Fig. 2). Numerous melanophores can be recognized along this band, which was probably pigmented in life.

The rest of the dorsal fin is separated from the elongate ray by a wide gap, such that the second dorsal-fin ray inserts just above the neural spine of the fourth caudal vertebra (Fig. 5). The dorsal-fin rays are short, thin, and unsegmented, supported by horizontally oriented pterygiophores, which are hourglass

shaped, bifurcated anteriorly and posteriorly, possibly representing fused proximal and middle radials (Fig. 5).

The first anal-fin ray inserts on the first caudal vertebra (Fig. 5). Anal-fin rays are unsegmented, notably longer than their dorsal-fin counterparts and gradually increase in length posteriorly in the series. The anal-fin pterygiophores have a similar morphology to their dorsal-fin counterparts, but they are more robustly ossified (Fig. 5).

Dorsal- and anal-fin pterygiophores bear a one-to-one relationship with the vertebrae (Fig. 5).

*Pectoral girdle & fin.* The posttemporal is anteriorly bifurcated and articulates ventrally with a thick and almost straight supraGLEYPH<3>cleithrum (Fig. 4).

The cleithrum is massive, straight and almost vertical, with a pointed ventral end and a moderately developed posterodorsal flange (Figs 1, 4). The postcleithra and the scapula are not clearly recognizable. The small coracoid articulates with the posterior margin of the cleithrum just below the vertebral column. It bears a massive and remarkably long ventral process, which runs roughly parallel to the pelvic bone extending ventrally for about two-thirds of the length of the pelvic bone (Figs 1, 2, 4).

There are five elongate pectoral-fin rays, which extend posteriorly almost to the sixth caudal vertebra (Figs 1, 4, 5). The pectoral-fin radials are not clearly visible, but the pectoral fin inserts high on the flanks, just above the level of the vertebral column.

*Pelvic girdle & fin.* The pelvic bone (basipterygium) is remarkably developed and strongly ossified, projecting ventrally from the body wall, reaching a length comparable to that of the anterior 20 vertebrae (Figs 1, 2, 4, 5). It gently curves ventrally and posteriorly, and seems to bear ventral and dorsal carinae at its distal extremity, giving it an oar-like appearance. Its proximal end is expanded and articulates with the cleithrum at approximately three-quarters of its vertical length (Figs 1, 4, 5).

The pelvic fin contains a greatly elongate, robust and distally flexible stout ray plus two unbranched and unsegmented delicate rays (Figs 1, 2, 5). The pelvic-fin rays are associated with a pigmented band of soft tissue similar to that described above for the stout first dorsal-fin ray (Figs 2, 5).

*Squamation & soft tissues.* The whole body, including the head, median and pelvic fins, and the abdominal region (Fig. 5), is covered with tiny dermal spinules. Each spinule is characterized by a stellate basal plate supporting an upright spine. These spinules are often associated in densely packed clusters, especially around the abdominal area (Fig. 5). Examination of the holotype under UV light shows the presence of pigmented blotches below the abdominal vertebrae and behind the (ventral process of the) coracoid-basipterygium complex.

DISCUSSION

*Larval-like features*

As described above, the ribbon-like body of †Dibango volans is accentuated by a stout, flexible, unsegmented
<figure><img src="image_8.png" /><figcaption>FIG. 5. †Dibango volans gen. et sp. nov., MCSNV T.293. Details of the postcranium. A, skull, pectoral region and vertebral column. B, interpretative drawing of vertebrae 17–18 and the adjacent dorsal and anal fins and supports. C, detail of the squamation at the level of the abdomen. D, distal end of the pelvic bone, and proximal end of the pelvic-fin rays. *Abbreviations*: af, anal-fin ray; apr, anal-fin pterygiophore; c, vertebral centrum; df, dorsal-fin ray; dpr, dorsal-fin pterygiophore; ha, haemal arch; hs, haemal spine; na, neural arch; ns, neural spine; pcf, pectoral-fin rays; plb, pelvic bone (basipterygium); plf, pelvic-fin rays; vp.co, ventral process of the coracoids. Scale bars represent: 2 mm (A); 1 mm (B); 0.5 mm (C); 5 mm (D).</figcaption></figure>

and unbranched dorsal-fin ray, and by remarkably devel-
oped pelvic fins and girdle, the latter running parallel to,
and associated with, an exceptionally elongate ossified
ventral process of the coracoid.

The elongate and flexible first dorsal-fin ray, inserting
on a thick pterygiophore and probably associated with a
flap of skin in life, is in some ways reminiscent of the
developed first dorsal-fin rays found in various teleost
<figure><img src="image_9.png" /><figcaption>**FIG. 6.** Artistic reconstruction of a living †*Dibango volans* feeding on bioluminescent plankton at night. Notice the developed vexillum-like first dorsal-fin ray, the elongate pelvic fins, and the putative external gut (exterilium) supported by the elongate ventral processes of the coracoid. Digital painting by Margaux Boetsch.</figcaption></figure>

larvae such as some ribbonfishes and crestfishes (Lampri-
formes, Trachipteridae, Lophotidae), pearlfishes (Ophidi-
formes, Carapidae), cusk-eels (Ophidiiformes,
Ophidiidae), flatfishes (Pleuronectoidei) or basslets (Lio-
propomatidae) (Amaoka 1972; Gordon et al. 1984; Govoni
et al. 1984; Olney 1984; Nonaka et al. 2021; Girard
et al. 2023). Most spectacularly, in larval pearlfishes this
so-called ‘vexillum’ is extremely long and ornamented with
fleshy extensions (Olney & Markle 1979; Markle &
Olney 1980, 1990; Gordon et al. 1984; Govoni et al. 1984).

In both specimens of †*Dibango* there are only three
abdominal vertebrae and the body is very narrow and slen-
der, suggesting that the abdominal cavity was extremely
reduced in volume (Fig. 5). In addition, the elongate
coracoid-basipterygium complex provided a ventral pro-
trusion of the body wall. To reconcile these observations,
we propose that viscera may have protruded from the
body and along this ventral structure (Fig. 6), as in
the case of exterilium (external) guts found in a diverse set
of larval teleosts, including: conger eels (Anguilliformes,
Congridae; Miller 2009, 2023), lanternfishes (Myctophi-
formes, Myctophidae; Moser et al. 1984), dragonfishes
(Stomiiformes, Stomiidae; Kawaguchi & Moser 1984),

flatfishes (Pleuronectoidei, Bothidae, Cynoglossidae,
Samaridae; Amaoka 1972; Fraser & Smith 1974), pearl-
fishes (Ophidiiformes, Carapidae; Markle & Olney 1990)
and cusk-eels (Ophidiiformes, Ophidiidae; Gordon et al.
1984; Fahay & Hare 2003; Fahay & Nielsen 2003; Okiyama
& Yamaguchi 2004; Fukui & Kuroda 2007; Suntsov 2007;
Nonaka et al. 2021; Girard et al. 2023). Remarkably, at
least in cusk-eels (Ophidiidae) the exterilium gut is sup-
ported by a very long descending process of the coracoid
(Okiyama & Yamaguchi 2004; Suntsov 2007; Girard
et al. 2023), similar to that observed in †Dibango.

Based on these traits, which are found today exclusively
in teleost larvae, †*Dibango volans* appears to have had a
larval-like appearance (Fig. 6). In addition, these larval
traits (namely the vexillum and probable exterilium) are
characteristic of open-ocean pelagic larvae, and in certain
cases of deep-sea fishes (e.g. cusk-eels, dragonfishes).
Given that the Bolca localities record shallow marine bio-
topes, the occurrence of a taxon reminiscent of pelagic
modern relatives is particularly striking (Fig. 6).

Although its morphology is larval-like, both the speci-
mens of †*Dibango volans* have a similar, relatively large
body size (56 mm and 33 mm in length, respectively,
with a missing posterior extremity of unknown length). Moreover, the skeleton appears to be entirely ossified while teleost larvae usually lack ossification in at least part of the skeleton. Therefore, we consider it dubious that the known †Dibango specimens were larvae; they may instead have been adults of a paedomorphic taxon retaining traits exclusive to larvae of modern teleosts.

## Functional implications

The very unusual morphology of †Dibango volans means that any interpretation of its ecology is highly hypothetical. Nevertheless, comparisons can be made with extant teleosts, larvae or adults, with similar morphological adaptations.

Filamentous appendages made of elongate fin rays (such as the vexillum), or even skin flaps associated with the extremi gut, are often present on the pelagic larvae of teleost fishes, especially acanthomorphs (Moser 1981; Kendall et al. 1984; Nonaka et al. 2021). Much conjecture has surrounded the possible function of these appendages and several hypotheses have been formulated, including camouflage or predator deception (e.g. Batesian mimicry of gelatinous macroplankton, or possibly bird feathers), sensory perception, and prey attraction (Moser 1981; Govoni et al. 1984; Kendall et al. 1984; Suntsov 2007; Greer et al. 2016; Miller 2023). Given the evidence that a skin flap was present alongside the elongate vexillum-like ray in †Dibango (Figs 2, 6), it is possible that its developed fin rays also had similar functions.

Outside of this larval-like morphology, extreme elongation of the pelvic bone is a rare feature in modern teleosts. A striking example can be found in the three-toothed pufferfish *Triodon macropterus* (Tetraodoniformes, Triodontidae), in which the pelvic bone is mobile and supports a 'pelvic fan' that can be flared and inflated to deter predators (Bemis et al. 2023). However, a similar function can be ruled out for †Dibango volans: there is no trace of a 'fan' and soft-tissue preservation suggests, in contrast, that skin was only covering the coracoid-basipterygium complex and its immediate vicinity (Fig. 5). Moreover, the ventral projection of the robust cleithrum and of the elongate ventral process of the coracoid that runs parallel to the pelvic bone suggests that the pelvic bone was not very mobile, unlike in *Triodon* in which it can perform 80° rotations (Bemis et al. 2023). In the absence of a clear modern analogue, the function of this elongate pelvic complex therefore remains unknown.

## Phylogenetic affinities

Descriptive analysis of the skeletal anatomy of †Dibango volans shows a highly unusual combination of

morphological features, making it challenging to determine its phylogenetic affinities within teleosts. However, it is evident that this peculiar Eocene genus is not closely related to the modern seamoth *Pegasus* or to the synagnathiform family Pegasidae (Santaquiteria et al. 2021). Pegasidae contains two extant genera (*Eurypegus* and *Pegasus*) of benthic fishes characterized by a unique body plan, consisting of a depressed body completely encased in bony plates, a small head bearing a well-developed nasal rostrum protruding anteriorly far beyond the mouth, and large, wing-like and horizontally oriented pectoral fins (Pietsch 1978; Palsson & Pietsch 1989). None of these features can be recognized in †Dibango volans, unquestionably showing the lack of a close affinity with Pegasidae.

Despite the absence of true spines in the dorsal, anal and pelvic fins (Rosen 1973; Johnson & Patterson 1993), †Dibango volans should be regarded as a spiny-rayed teleost (Acanthomorpha) based on the very anterior position of its dorsal fin and on the contact between its pelvic and pectoral girdles (Stiassny & Moore 1992; Johnson & Patterson 1993; Parenti & Song 1996; Davesne et al. 2016). In addition, the overall configuration of the jaw bones, with a large premaxilla bearing well-developed ascending and articular processes, and a large toothless maxilla excluded from the relatively short gape of the mouth, also supports the attribution of †Dibango to the acanthomorph clade (Schaeffer & Rosen 1961; Patterson 1964; Rosen & Patterson 1969; Johnson & Patterson 1993; Davesne et al. 2016). Acanthomorphs underwent a massive evolutionary radiation in the aftermath of the Cretaceous–Palaeogene extinction event, and although their Paleocene fossil record is still poorly known and understood (Friedman 2010; Alvarado-Ortega et al. 2015; Argyriou & Davesne 2021; El-Sayed et al. 2021; Friedman et al. 2023; Schwarzhans et al. 2024) it is clear that most of the extant acanthomorph lineages were present by the early Eocene (Friedman & Carnevale 2018; Friedman et al. 2023; Schwarzhans et al. 2024).

Due to its general resemblance to certain larval and juvenile taeniosome lampriforms such as ribbonfishes, crestfishes and oarfishes (Olney 1984; Oka et al. 2020), Bannikov (2014) and Carnevale et al. (2014) tentatively referred †Dibango volans to the Taeniosomi. Lampriformes are known in Bolca with two genera of Veliferidae (Bannikov 1990; Carnevale & Bannikov 2018), and the earliest known fossil taeniosomes hail from slightly younger localities of Iran and the Caucasus (Daniltshenko 1980; Davesne 2017). While †Dibango possesses certain features that also occur in lampriforms (well-developed ascending process of the premaxilla, supramaxillae absent, less than seven branchiostegal rays), it lacks the majority of the lampriform synapomorphies (Olney et al. 1993; Davesne et al. 2014, 2016, 2023;
Delbarre *et al.* 2016), including: the absence of the an-
terior palatine process, the presence of frontal vault to
accommodate the premaxilla and rostral cartilage, and the
mesethmoid posterior to the lateral ethmoids. In addi-
tion, modern taeniosome lampriforms have a reduced or
absent anal fin (Olney 1984; Olney *et al.* 1993), in con-
trast to the well-developed anal fin of †Dibango. There-
fore, based on the available evidence, the attribution of
†Dibango volans to Lampriformes can be ruled out.

Another taxon from Bolca with superficial similarities
to †Dibango volans is †Bajaichthys elegans, formerly inter-
preted as a lampriform and now referred to the Zeiformes
(Sorbini & Bottura 1988; Davesne *et al.* 2017). Similarities
include an elongate body with a long anal-fin base, an an-
teriorly inserting dorsal fin, developed pelvic-fin rays and
unbranched dorsal-fin and anal-fin rays. However,
†Bajaichthys and zeiforms in general possess dorsal-, anal-
and pelvic-fin spines, which are entirely absent in
†Dibango, and no known zeiform shows the extreme ver-
tical expansion of the coracoid and of the pelvic bone
(basipterygium) observed in †Dibango. Other differences
between †Bajaichthys and †Dibango include the dorsal fin
running along the whole body, the absence of supraneur-
als, and much less developed jaws and suspensorium.

Among the peculiar diagnostic features of †Dibango volans, the stout and flexible vexillum-like first dorsal-fin ray and the possible occurrence of an exterilium gut are shared by certain ophidiiform larvae (Fraser & Smith 1974; Olney & Markle 1979; Gordon et al. 1984; Govoni et al. 1984; Markle & Olney 1990; Girard et al. 2023). In particular, the ventral projection of the coracoid supporting the exterilium gut is seemingly unique to ophidiiform larvae in modern teleosts (Okiyama & Yamaguchi 2004; Suntsov 2007; Girard et al. 2023), in which it is strongly reminiscent of the structure observed in †Dibango. Ophidiiformes (cusk-eels and pearlfishes) are known in the fossil record from the Late Cretaceous onward (Carnevale & Johnson 2015), and are represented in Bolca by *Ophidium* voltianum, a potential ophidiid that is in urgent need of redescription (Bannikov 2014; Carnevale et al. 2014). The few osteolo-gical synapomorphies that have been identified for Ophi-diiformes include the lack of ossified supraneurals (Patterson & Rosen 1989), a supraoccipital that is excluded from the posterior margin of the skull by dorsally enlarged exoccipitals (Carnevale & Johnson 2015), and a reduced second infraorbital overlapping the dorsal margin of the first infraorbital (Ohashi 2018). While supraneurals are also absent in †Dibango, the other two characters cannot be clearly observed due to inadequate preservation of the cranial region in both specimens. In addition, modern ophidiiforms tend to have reduced or entirely absent pelvic fins containing a maximum of one or two rays in both larvae and adults (Gordon

et al. 1984), while †Dibango shows strongly developed
pelvic-fin rays. An attribution to Ophidiiformes, while
tempting due to close similarities with larval representa-
tives of the clade, is therefore difficult to ascertain based
on available data.

The dorsal- and anal-fin pterygiophores of †Dibango volans probably consist of fused proximal and middle radials and appear to bear a one-to-one relationship to the adjacent vertebrae, showing a condition exclusive to certain percomorph acanthomorphs, including blennies (Blennioidei), roundheads and eel-blennies (Plesiopidae), bandfishes (Cepolidae), and eelpouts (Zoarcidae) among others (Gosline 1968; Smith-Vaniz & Johnson 1990; Springer 1993; Mooi & Gill 2004). Conversely, this one-to-one relationship does not appear to be found in modern ophidiiforms (Gordon et al. 1984). These groups of mostly benthic percomorphs commonly possess unsegmented median-fin rays, similar to those observed in †Dibango (Gosline 1968). Finally, the extensive cover of tiny upright dermal spinules emerging from stellate basal plates characteristic of †Dibango may provide a further indication of its percomorph affinities, given that modified plates and spinules are most commonly found in certain representatives of the clade (Roberts 1993).

CONCLUSION

On the basis of the available evidence, the precise phylo-
genetic position of *Dibango volans* remains uncertain.
However, its combination of character states supports an
attribution to Percomorpha, the major Cenozoic radiation
of acanthomorphs that taxonomically dominated the
Bolca fauna (Friedman & Carnevale 2018). Although its
ecology cannot be inferred due to its unique morphology,
similarities to modern pelagic larvae suggest that this ani-
mal may have been associated with a more open-ocean
environment, which could explain its rarity among fossil
teleosts from Bolca.

Acknowledgements. We thank the curators for access to the study specimens: Gaël Clément, Alan Pradel (MNHN) and Roberto Zorzin (MCSNV). Alexandre Bannikov (Borissiak Paleontological Institute), Matt Friedman (University of Michigan), Chase Brownstein (Yale University) and James Andrews (University of Michigan) are thanked for their insights on the fossil taxon studied here. Finally, we thank Philippe Loubry (MNHN) for providing photographs of the MNHN specimens, and Margaux Boetsch for the wonderful artistic reconstruction. Rodrigo Figueroa (Harvard University Museum of Comparative Zoology), Sally Thomas (Palaeontological Association) and one anonymous reviewer are thanked for their constructive feedback on an earlier version of this text. The research of GC was supported by a SYNTHESYS grant and by grants (ex-60% 2023 and 2024) from the Università degli Studi di Torino. DD was
supported by an AvH-Stiftung awarded by the Alexander von Humboldt Foundation.

*Author contributions.* **Conceptualization** D Davesne (DD), G Carnevale (GC); **Funding Acquisition** DD, GC; **Investigation** DD, GC; **Methodology** DD, GC; **Visualization** DD, GC, Mar-gaux Boetsch; **Writing – Original Draft Preparation** DD, GC; **Writing – Review & Editing** DD, GC.

## DATA ARCHIVING STATEMENT

This published work and the nomenclatural act it con-tains, have been registered in ZooBank: https://zoobank. org/References/64c00e83-16fc-4674-9781-f55625252178

Editor. Gustavo Ballen

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