Description of two early Middle Eocene marine fish from eastern Cuba

Geological Setting

In 1961, workers discovered specimens from a 45-meter-high wall outcrop at the “El Ají” quarry, situated near Campechuela, Granma province, eastern Cuba. This location exposes the early Middle Eocene El Caney Formation (Fm), and the specimens seem to originate from it (refer to Figure 1).

The El Caney Formation belongs to the upper part of El Cobre Group and crops out on the northwestern and northeastern slopes of the Sierra Maestra (Granma and Santiago de Cuba provinces). It is characterized by pyroclastic and sedimentary rocks, conglomerates, and lava flows (García-Delgado and Torres-Silva, 1997García-Delgado, D., and Torres-Silva, A. (1997). Sistema Paleógeno. In: Furrazola-Bermúdez, G., and Núñez Cambra, K. (eds.), Estudios sobre Geología de Cuba (pp. 115-140). La Habana, Centro Nacional de Información Geológica.; Iturralde-Vinent, 1996Iturralde-Vinent, M. (1996). Cuba: El archipiélago volcánico Paleoceno-Eoceno medio. In: Iturralde-Vinent, M., (Ed.) Cuban Ophiolites and Volcanic Arcs vol. 364. IGCP, Miami, FL, USA, pp. 231-241., 2021Iturralde-Vinent, M. (2021). Geología de Cuba, Compendio 2021. Apk. Ediciones CITMATEL (https://www.libreriavirtualcuba.com/geologia-de-cuba-compendio-2021).; Sokolova, 1966Sokolova, E. A. (1966). Conferencia sobre las formaciones vulcanógeno-sedimentarias que contienen manganeso en la provincia de Oriente. Oficina nacional de Recursos Minerales, La Habana, 15.). It lies concordantly over the Lower Eocene Pilón Formation and below the Middle Eocene Puerto Boniato Formation. The foraminifera assemblage includes the following index taxa: Morozovella aequa, M. aragonensis, Acarinina brodermanni, Discocyclina barkeri, Pseudophragmina (Pseudophragmina) cedarkeyensis, Amphistegina cubensis, Eoconuloides wellsi, Helicolepidina spiralis (Iturralde-Vinent, 2021Iturralde-Vinent, M. (2021). Geología de Cuba, Compendio 2021. Apk. Ediciones CITMATEL (https://www.libreriavirtualcuba.com/geologia-de-cuba-compendio-2021).). The El Caney Fm was deposited in an open marine basin, in the final stage of the Paleogene volcanic arc, mostly during the early Middle Eocene, with abundant contribution of tuffogenic and terrigenous material.

Systematic paleontology

Material

MHNCT 12-23-A, a complete articulated fish skeleton with traces of soft tissues and scales on matrix (preserved in halves) - Figures 2- 7.

Locality and age

The specimen was collected from “El Ají” quarry, near Campechuela, Granma, in matrix of the early Middle Eocene El Caney Formation.

Description

Elongated specimen with a large head and well-developed pelvic and dorsal fin. The specimen seems to have been preserved in an oblique or slanted position, and the head is thus preserved perpendicularly (on dorsal view). The skull is widest posteriorly, with a narrow supraoccipital, but rounded cranium. A sagittal suture is slightly visible running midway through the cranium. There is no evident raised crest. There are no apparent, additional sutures. The orbit is not visible, but the upper maxillary and dentary do not seem to extend closely to the front of the eyes. The opercular bones are large and ovoid, scattered posteriorly, and openly. The ceratohyal is elongated and arched (Figures 2- 4). Several possible accessory fin rays and spines can be observed towards the dorsum-neck area. The anterior portion of the skull (nasal frontal) tapers gradually into a thin point towards what could be the maxilla, premaxilla, or palatine. Traces of possible stub-like teeth are hardly detectable on this specimen (X-ray imaging has not been possible). Traces of the basipterygia can be inferred in the ventral nape, behind the opercular or supraopercular bones. The cephalic canal is not evident in this specimen. The hypohyal and anterior ceratohyal elements are not well preserved in this specimen, but there are large flat-bone impressions that could represent this element (Figure 4). The dorsal spine does not originate at the occiput.

The specimen contains ~30 vertebrae, of which seven are precaudal, located in the anterior portion of the dorsal nape. The thoracic contains hemal and hemapophyses on the ventral side of the vertebral body, originating dorsally, and zygapophyses also on the dorsal, with traces of intermuscular bones, and what could be remains of rays. The ribs and spines are generally attached to the centrum of the vertebrae, except towards the caudal fin. Some of the vertebral processes seem fused. The neural spines are usually attached to the vertebral centrum and arched posteriorly. The vertebral intercentrumise is well-defined, with accentuated pleurocentrae. Prezygapophises are more accentuated than postzygapophyses in the cephalad vertebrae, whereas the opposite is true in the caudal, tapering towards the hypurals (Figures 3, 5, and 6).

The specimen has well-preserved and developed dorsal and anal fins, of which the first is the largest. The anal fin is sub-squared, and its posterior margin is near straight. The dorsal fin is curved and tapers at the tip. The dorsal fin lies midway between the pelvic (anterior-most) and anal fins (posterior-most). The pelvic fin is poorly preserved, but it is represented by five thick spines. Small traces of accessory thin rays or fragments of a pectoral fin lie immediately posterior to it.

Articulated to the pelvic fin is a series of ribs, intermuscular bones, and hemal spines. These fins have both spinous and soft rays. The anal fin has ~ eight hard spines and ~ eight soft bifurcating rays towards the tips. The dorsal fin has nine hard, spines in the same mode as the dorsal fin (Figure 7). These spines tend to bifurcate towards the distal ends, whereas they are thicker toward their origins. There seem to be a few floating ribs at the distal spinous ray fins in the anal and pelvic fins. There are no vestiges of an adipose fin on this specimen. However, evidence of a possible tissue bulge (‘?’ in Figure 3) between the dorsal fin and caudal peduncle. This area does not contain superficial evidence of spines or rays, and thus cannot be identified as a small fin.

The tail is incomplete, containing hard, grooved spines and bifurcation fin rays towards the tips of the fin. The caudal fin is truncated and does not seem forked or notched. There are at least six, well-defined caudal vertebrae with preural centrum (Figure 7). The most posterior attachment of neural-hemal spines occurs at the third caudal vertebrae from the hypural. The parahypural are slanted, covered in soft fine rays. The hypural seems more solid and fussed. From both structures, at least 15-16 hard spines arise. Six accessory or rudimentary fin rays lie over them on the vertices of the tail.

Thanks to the exceptional preservation of this specimen, a soft tissue silhouette is evident. It shows a round, bulging head with an elongated nape and caudal peduncle. Remnants of scales and fragments of skin are also observable towards the head and trunk. The scales have a crosshatching cycloid pattern of laterally compressed ganoid (rhomboid) scales (Figure 5). The openings or lateral line canals are thin. Since the specimen is slightly rotated, what seem to be parts of the second pelvic fin can be observed behind the head, and in front of the dorsal fin. The full ossification suggests the specimen was likely an adult (although perichondral elements have not been preserved in this specimen).

Comparisons

Percopsidae is a family of five genera of small, elongated fish that are endemic to North America, where they are known from both marine and freshwater environments. Only one genus remains extant, Percopsis, whereas four are extinct: Amphiplaga, Erismatopterus, Lateopisciculus, and Libotonius, known from Paleocene-Eocene (~66-41 Ma) freshwater-lake deposits (Wilson, 1979Wilson, M.V. (1996). The Eocene fishes of Republic, Washington. Washington Geology, 24 (2), 30-31.; Grande, 1984Grande, L. (1984). Paleontology of the Green River Formation, with a review of the fish fauna. Geological Survey of Wyoming Bulletin, 63, 1-133. ; Murray and Wilson, 1996Murray, A. M., and Wilson, M. V. (1996). A new Palaeocene genus and species of percopsiform (Teleostei: Paracanthopterygii) from the Paskapoo Formation, Smoky Tower, Alberta. Canadian Journal of Earth Sciences, 33 (3), 429-438. ). Their earliest fossils are known from the Paleocene, but their origins could extend to the Cretaceous (Cavender, 1986Cavender, T. M. (1986). Review of the fossil history of North American freshwater fishes. In: Hocutt, C. H., and Wiley, E. O. (eds), The Zoogeography of North American Fresh Water Fishes (pp. 699-724). John Wiley and Sons, New York. ). Percopsids have a diet of insects and small crustaceans.

Specimen MHNCT 12-23-A display the following diagnostic discrete characters of the percopsid family: The premaxilla contains a single row of teeth; the opercular bones are serrated on the posterior margin; the postemporal has a narrow and elongate process, with a lunate-shaped supraoccipital (Agassiz, 1849Agassiz, L. (1849). Two new fishes from Lake Superior. In Proceedings of the Boston Society of Natural History, 3, 1848-1851., 1850Agassiz, L. 1850 (16 July). New species from Lake Superior described by M. Agassiz. American Journal of Science and Arts, 2 (10), 125-127. ; Murray, 1996Murray, A. M. (1996). A new Paleocene genus and species of percopsid, † Massamorichthys wilsoni (Paracanthopterygii) from Joffre Bridge, Alberta, Canada. Journal of Vertebrate Paleontology, 16 (4), 642-652. ; Polly, 2004Polly, W. (2004). Family Percopsidae Agassiz 1850 - trout perches and sand rollers. California Academy of Science Annotated Checklists of Fishes, 23, 1-5. ).

Our specimen differs from Amphiplaga brachyptera and Erismatopterus levatus in several important diagnostic features. The head of A. brachyptera and E. levatus is not as elongated, and the nape is pronounced. The frontal-nasal and occipital areas of the cranium are also shorter and thicker in Amphiplaga and E. levatus. The main difference lies in the morphology of the dorsal and pelvic fins. In Amphiplaga and Erismatopterus, these are near the same size (the dorsal slightly larger). The pelvis is much larger and flipper-like than in both genera. Our specimen lacks a pectoral fin (which could be due to preservation and not morphology), present in Amphiplaga and Erismatopterus. The vertebrae seem much smaller in Amphiplaga and Erismatopterus than in MHNCT 12-23-A, and the thoracic ribs and spines are of unequal size (same size in Amphiplaga and Erismatopterus).

They are similar, however, in having at least eight hard spines, with fine bifurcating rays towards the tips. They both have similar accessory fin rays on the vertices of the tail. The scale pattern crosshatching is also congruent.

Remarks

This specimen may represent a percopsid new genus and species, that existed in the paleo-Caribbean during the Eocene. However, more detailed comparisons and analyses are required to properly diagnose and name this specimen.

Material

MHNCT 12-23-B, near complete articulated fish skeleton with soft tissue silhouette in matrix. Figures 8- 9.

Locality and age

The specimen was collected from the "El Ají" quarry, near Campechuela (Granma Province), in sediments of the early Middle Eocene El Caney Formation.

Description

Well-preserved, near complete, and fully articulated fossil fish skeleton with soft tissue silhouette. The specimen is generally small and short, about ~ 12 cm in length. The head is large with a large, ovoid open orbit, preserved in lateral view (Figures 8- 9). The cranium is short but thick in the frontals and nasals. Two probable sphenotic bones are visible posterior to the orbit. The orbit is smaller than the snout length. The dorsal spine does not originate above the occiput. The premaxilla is regular. The remains of the maxilla are evident below. This element is nearly straight pallet-like, tapering caudally. Small, stubby teeth are preserved in the dentary and distal premaxilla. The dentary is wedge-shaped, and thicker caudally. The dentary articulation lies under or at the anterior margin of the orbit. The premaxilla seems to contain a sinus or fenestra (opening). The supraoccipital is wide and rounded, immediately posterior to and not fully fused to the frontal bone. The opercular bones are large, ovoid, flattened, and moderately wide and striated, covering most of the lateral aspect of the head. A large, flat bone lies (interneural?) just behind the supraoccipital. The remains of a pectoral arch seem to be preserved ventrally at the gills.

Comparisons

Upon first inspection, the specimen resembles a member of the Lutjanidae, Sparidae, or Cichlidae families. These three are teleost percomorph fishes with varied and diverse adaptations and speciosity (Kullander, 1998Kullander, S. O. (2003). Family cichlidae. Check list of the freshwater fishes of South and Central America, 605-654.). Cichlids are particularly diverse, inhabiting mostly freshwater environments, and with a meager fossil record (Bannikov and Zorzin, 2020).

MHNCT 12-23-B resembles the extinct cichlids Gymnogeophagus eocenicus, Proterocara argentina, and other spp. from the Eocene of Argentina (Malabarba et al., 2006Malabarba, M. C., Zuleta, O., and Papa, C. D. (2006). Proterocara argentina, a new fossil cichlid from the Lumbrera Formation, Eocene of Argentina. Journal of Vertebrate Paleontology, 26 (2), 267-275.) and Nandopsis spp (= Cichlostoma). known from the Caribbean Miocene (Chakrabarty, 2006Chakrabarty, P. (2006). Taxonomic status of the Hispaniolan Cichlidae. Occasional Papers of the Museum of Zoology, University of Michigan, 737: 1-17. ).

Proterocara and MHNCT 12-23-B share the following morphologies: the overall body-tail shape is similar; the lachrymal bone lies right underneath the orbit and slightly posterior to the maxilla-premaxilla; the anal fin base is posterodistally inclined; the origin of the anal fin at the posterior half of the dorsal fin. They are most dissimilar in that MHNCT 12-23-B has a more elongated head, with a more dorsally positioned eye (bulkier, more erect, with lower orbit in Proterocara); ~ 20 vertebra in total, much less than the diagnostic nine abdominal and 19 caudal reported for Proterocara spp., a wide below, serrated, and elongated dorsally pre-opercle (erect, slender, and straight dorsally, wider and ached ventrally in Proterocara spp.). The caudal skeleton includes palette-like, wide hypurals, with thin and small uroneurals (elements not visible in specimen 00); thicker caudal peduncle in Proterocara spp. (elongated and thinner in MHNCT 12-23-B). Compared to Gymnogeophagus eocenicus, specimen MHNCT 12-23-B is slender, with a more elongated head; the orbit lies higher in the skull and is more ovoid (rounder and lower, with thicker frontals in Gymnogeophagus eocenicus). MHNCT 12-23-B lacks the diagnostic forward-directed spine on the first dorsal pterygophore and loss of supraneurals (Kullander, 1998Kullander, S. O. (2003). Family cichlidae. Check list of the freshwater fishes of South and Central America, 605-654.; Reis and Malabarba, 1988Reis, R.E., and Malabarba, L. R. (1988). Revision of the Neotropical Cichlid genus Gymnogeophagus Ribeiro, 1918, with descriptions of two new species (Pisces, Perciformes). Revista Brasileira de Zoologia, 4, 259-305. ).

MHNCT 12-23-B shares several morphologies with the Lutjanidae and Sparidae families. These include a forked tail, a single dorsal fin, and a small mouth, an ovate to elongate body shape, the presence of small conical teeth, a serrated operculum, a continuous dorsal fin that does not extend to the caudal peduncle space, a snout that extends to below the eye, with a complete lateral line (Gill, 1861Gill, T. N. (1861). On several new generic types of fishes contained in the museum of the Smithsonian Institution. Proceedings of the Academy of Natural Sciences of Philadelphia, 13, 77-78. , 1864Gill, T. N. (1864). Several points in ichthyology and conchology. Proceedings of the Academy of Natural Sciences of Philadelphia, 16(3), 151-152. and 1893Gill, T. N. (1893). Families and sufamilies of fishes. Memories of the National Academy of Sciences, 6, 127-138. ; Van Der Laan et al., 2014Van Der Laan, R., Eschmeyer, W. N., and Fricke, R. (2014). Family-group names of recent fishes. Zootaxa, 3882 (1), 1-230.). The presence of a subterminal mouth, pelvic fin originating posterior or at the level of the pectoral fin, and slightly forked tail suggest it belongs to the Lutjanidae family (Gill, 1861Gill, T. N. (1861). On several new generic types of fishes contained in the museum of the Smithsonian Institution. Proceedings of the Academy of Natural Sciences of Philadelphia, 13, 77-78. ), resembling genera such as Apsilus, Rhomboplites and Lutjanus spp.

Particularly, MHNCT 12-23-B resembles the genera Lutjanus, Ottaviana, Goujetia, and Veranichthys spp. for having an elongated, but thick body, small, thick heads that gradually slant dorsally, and large orbits, plus a single, wide-based dorsal fin, and smaller anal and pectoral fins. Their caudal fins are hypocentral-like and slightly forked. Ottaviana leptacanthus (Bannikov, 2006Bannikov, A. F. (2006). Fishes from the Eocene of Bolca, northern Italy, previously classified in the Sparidae, Serranidae, and Haemulidae (Perciformes). Geodiversitas, 28 (2), 249-275. ), from the Middle Eocene of northern Italy, holds great similarity but has a wider base, bimodal dorsal fin (same throughout in specimen MHNCT 12-23-B), more elongated skull, with a lower orbit and thicker dentary. It also resembles Goujetia crassispina (op. cit.) in having a similarly stocky body and large head. However, in Goujetia crassispina the head is less slanted dorsally, with more abrupt frontals and post occipitals, and the vertebral bodies seem thicker. The orbit in MHNCT 12-23-B sits closer to the frontal. The dorsal and anal fins are similar. Veranichthys ventralis is similar, but it has more pronounced maxillary and dentary teeth, but a thicker and slanted frontal. The scale pattern seems similar to MHNCT 12-23-B (compared to Fig, 10 in Bannikov, 2006Bannikov, A. F. (2006). Fishes from the Eocene of Bolca, northern Italy, previously classified in the Sparidae, Serranidae, and Haemulidae (Perciformes). Geodiversitas, 28 (2), 249-275. ).

Remarks

Lutjanid or cichlid, likely a new genus + species combination.

Depositional environment and preservation

Based on the preservation and articulation of the specimens, several hypotheses can be made for a paleoenvironmental reconstruction.

Fish decay experiments have demonstrated that temperature, high hydrostatic pressure, and salinity are crucial taphonomic factors in underwater preservation (Gäb et al., 2020Gäb, F., Ballhaus, C., Stinnesbeck, E., Kral, A. G., Janssen, K., and Bierbaum, G. (2020). Experimental taphonomy of fish-role of elevated pressure, salinity, and pH. Scientific Reports, 10 (1), 7839. ; Whitmore, 2003Whitmore, J.H. (2003). Experimental fish taphonomy with a comparison to fossil fishes. Loma Linda University (unpublished doctoral dissertation). ). Hydrostatic pressure in the water column prevents fish carcasses from floating, allowing for rapidly sinking to bottom sediments, whereas high salinity and pH suppress bacterial putrefaction (Elder and Smith, 1988Elder, R. L., and Smith, G.R. (1988). Fish taphonomy and environmental inference in paleolimnology. Paleogeography, Palaeoclimatology, Palaeoecology, 62 (1-4), 577-592.; Gäb et al., 2020Gäb, F., Ballhaus, C., Stinnesbeck, E., Kral, A. G., Janssen, K., and Bierbaum, G. (2020). Experimental taphonomy of fish-role of elevated pressure, salinity, and pH. Scientific Reports, 10 (1), 7839. ; Whitmore, 2003Whitmore, J.H. (2003). Experimental fish taphonomy with a comparison to fossil fishes. Loma Linda University (unpublished doctoral dissertation). ).

Temperature or oxygen-deficient or anaerobic conditions of the deposition environment cannot be ruled out in our samples, given that detailed geochemical analyses are yet to be done, but they are not considered major significant factors to preservation (Gäb et al., 2020Gäb, F., Ballhaus, C., Stinnesbeck, E., Kral, A. G., Janssen, K., and Bierbaum, G. (2020). Experimental taphonomy of fish-role of elevated pressure, salinity, and pH. Scientific Reports, 10 (1), 7839. ). Instead, the presence (preservation) of soft tissue silhouette, scales, and pigmentation suggests that these fish carcasses came to rest in enclosing sediments in a deep marine setting with high salinity, pH, and hydrostatic pressure (op. cit.). These conditions must have persisted long enough to arrest advanced decomposition, scavenging, and bioturbation (or bioerosion). The near complete articulation, and lack of direct evidence for predation, in their skeletons, are congruent with low-energy, deep-water environments.

At the same time, the specimens (MHNCT 12-23-A, MHNCT 12-23-B) are significant for their preservation. Such completely well-preserved fossil fish specimens are rare in Cuban collections. Only a few other specimens with comparable completeness have been discovered from older Cuban geological formations. These include a few Oxfordian (Upper Jurassic) specimens, a Tithonian (Upper Jurassic) specimen, and a Neocomian (Early Cretaceous, encompassing the Berriasian, Valanginian, and Hauterivian periods) specimen. The existence of these other, though older, fossil material presents a potential to gain valuable insights into the ancient aquatic ecosystems during those ages.