New records of the echinoid Clypeaster from the Upper Eocene-Lower Oligocene Damují Formation in Rodas, south-central Cuba

Introduction

Clypeaster is a relatively large, thick-shelled, irregular echinoid known for its highly differentiated external surface and internal morphology (Mortensen, 1948Mortensen, T. (1948). A monograph of the Echinoidea. Clypeasteroida. Clypeasteridæ, Arachnoidæ, Fibulariidæ, Laganidæ and Scutellidæ. Volume 4 (2), C.A.vReitzel, Copenhagen, 471 pp.; Durham, 1966Durham, J.W. (1966). Clypeasteroids. En: Moore, R.C. (Ed.) Treatise on Invertebrate Paleontology, Echinodermata 3. The Geological Society of America and The University of Kansas Press, Boulder. ; Mooi, 1989Mooi, R. (1989). Living and fossil genera of the Clypeasteroida (Echinoidea, Echinodermata): an illustrated key and annotated checklist. Smithsonian Contributions to Zoology, 488, 1-51.; Mihaljević et al., 2011Mihaljević, M., Jerjen, I., Smith, A.B. (2011). The test architecture of Clypeaster (Echinoidea, Clypeasteroida) and its phylogenetic significance. Zootaxa, 2983, 21-38.). The genus is distinguished by its remarkable species richness with approximately 400 nominal species, making it the most diverse genus among echinoids (Mihaljević and Rosenblatt, 2018Mihaljević, M., Rosenblatt, A.J., 2018. A new fossil species of Clypeaster (Echinoidea) from Malaysian Borneo and an overview of the Central Indo-Pacific echinoid fossil record. Swiss Journal of Palaeontology, 137(2), 389-404.). Its members are broadly distributed across tropical and subtropical waters, inhabiting all the shallow water environments of major oceans where they are infaunal, detritus feeders (Clarkson, 1998Clarkson, E. N. K. (1998). Invertebrate palaeontology and evolution. John Wiley & Sons.). The fossil record of Clypeaster, dating back to the Middle Eocene, highlights its extensive history and evolutionary import (Mihaljević et al., 2011Mihaljević, M., Jerjen, I., Smith, A.B. (2011). The test architecture of Clypeaster (Echinoidea, Clypeasteroida) and its phylogenetic significance. Zootaxa, 2983, 21-38. and references therein; Lee et al., 2023Lee, H., Lee, K.S., Hsu, C.H., Lee, C.W., Li, C.E., Wang, J. K., Janies, D. (2023). Phylogeny, ancestral ranges and reclassification of sand dollars. Scientific Reports, 13 (1), 10199.). Its extensive geographical distribution, along with high taxonomic diversity, excellent preservation potential, and rich fossil record makes Clypeaster a valuable subject for biogeographical and palaeobiological studies (Mihaljević et al., 2010Mihaljević, M., Klug, C., Aguilera, O., Lüthi, T., Sánchez-Villagra, M.R. (2010). Palaeodiversity of Caribbean echinoids including new material from the Venezuelan Neogene. Palaeontologia Electronica, 13(3), 20A., 2011Mihaljević, M., Jerjen, I., Smith, A.B. (2011). The test architecture of Clypeaster (Echinoidea, Clypeasteroida) and its phylogenetic significance. Zootaxa, 2983, 21-38.; Mihaljević and Rosenblatt, 2018Mihaljević, M., Rosenblatt, A.J., 2018. A new fossil species of Clypeaster (Echinoidea) from Malaysian Borneo and an overview of the Central Indo-Pacific echinoid fossil record. Swiss Journal of Palaeontology, 137(2), 389-404.; Lee et al., 2023Lee, H., Lee, K.S., Hsu, C.H., Lee, C.W., Li, C.E., Wang, J. K., Janies, D. (2023). Phylogeny, ancestral ranges and reclassification of sand dollars. Scientific Reports, 13 (1), 10199.).

The first fossil species ever documented in Cuba was a Clypeaster. This specimen was published in La Habana by Antonio Parra in the late 18^th century (Parra, 1787: 181Parra (1787). Descripción de diferentes piezas de historia natural, las más del ramo marítimo, representadas en sesenta y cinco láminas. Imprenta de la Capitanía General, La Habana.), and subsequently named Clypeaster parrae in his honor. Nearly a century later, 41 echinoid taxa had been described for Cuba, primarily by M. C. Cotteau from specimens collected by Spanish geologists working for the Commission for the Geological Map of Spain, including Pedro Salteraín, Policarpo Cía, Manuel Fernández de Castro, and Justo Egozcue (Nuñez-Jiménez, 1998). Historical accounts trace the discovery of Clypeaster echinoid fossils in Rodas, Cienfuegos, south-central Cuba, to 1891, based on reports by the Spanish Geological Survey (Cotteau, 1897). These initial findings, documented at the old San Lino sugar mill, included two species: Clypeaster planipetalus Cotteau 1875 and C. concavus Cotteau 1875, of Miocene age. Later, fossil records of this echinoid genus in Cuba have predominantly emerged from strata dating to the Oligocene and Miocene epochs (Jackson, 1922Jackson, R.T. (1922). Fossil echini of the West Indies (No. 306). Carnegie Institution of Washington, 100 pp.; Kojumdgieva and Popov, 1982Kojumdgieva, E., y Popov, N. (1982). Distribución geográfica y estratigráfica de los moluscos y equinodermos del terciario en la antigua provincia de Las Villas, Cuba. Ciencias de la Tierra y el Espacio, 4, 71-79.; Donovan, 1994Donovan, S.K. (1994). Some Fossil Echinoids (Echinodermata) from the Cenozoic of Jamaica, Cuba and Guadaloupe. Caribbean Journal of Science, 30 (3-4), 164170.; Sanchez-Roig, 1924Sánchez-Roig, M. (1924). Revisión de los equínidos fósiles cubanos. Memorias de la Sociedad Cubana de Historia Natural Felipe Poey, 6: 6-42., 1926Sánchez-Roig, M. (1926). Contribución a la paleontología cubana. Los equinodermos fósiles de Cuba. Boletín de Minas, 10: 1-179., 1949Sánchez-Roig, M. (1949). Los equinodermos fósiles de Cuba. Paleontología Cubana, 1: 1-330., 1952Sánchez-Roig, M. (1952). Los Clypeasteridos fósiles de Cuba. Revista de Agricultura. 1951-1952, 118-177.; Franco, 1983Franco, G.L. (1983). El género Clypeaster Lamarck en el Neógeno-Cuaternario de Cuba Oriental. Contribución a la Geología de Cuba Oriental, Editorial Científico-Técnica, La Habana, 239249.). Therefore, the discovery of specimens within the Upper Eocene Damují Formation at the Parque Alto locality in Rodas is particularly noteworthy. These findings, alongside significant paleontological evidence such as large foraminifera, corals, and isolated fish teeth, paint a vivid picture of a rich and dynamic marine ecosystem during the latest Eocene, and particularly during the Eocene-Oligocene Transition (EOT) cooling event.

The primary objective of this communication is to present novel Clypeaster specimens from the Upper Eocene deposits of Rodas. These findings are significant for enhancing our understanding of Clypeaster's evolutionary history and paleobiogeographical distribution, contributing to the reconstruction of the paleoecological landscape during the latest Eocene - earliest Oligocene. This work not only expands our knowledge of Clypeaster's variability and range but also underscores the paleontological richness of Cuba’s Paleogene fossil record (Orihuela et al., 2020Orihuela, J., Ceballos-Izquierdo, y., Portell, R.W. (2020). First report of the Eocene bivalve Schedocardia (Mollusca, Cardiidae) from Cuba. Journal of South American Earth Sciences, 103, 102771., 2023Orihuela, J., Ceballos-Izquierdo, y., Figueredo Garcés, E. (2023). Descripción de dos peces marinos del Eoceno Medio temprano de Cuba oriental. Poeyana, (514), https://cu-id.com/2403/n514e06. ).

Material and Methods

The two echinoid specimens investigated in this study are housed at the Museo Municipal de Rodas, Cienfuegos, Cuba (MMR), with the registration numbers MMR-PA-001 and MMR-PA-002. They were collected about 2015 at Parque Alto, a locality along the route to the Damují River, to the northeast of Rodas, Cienfuegos Province, south-central Cuba (Fig. 1). The locality name is due to the presence of a homonymous sugar mill since 1852. The collection site where the Clypeaster specimens were found is 3 km west of the old sugar mill settlement, on the banks of the Damují River. Several outcrops of the Upper Eocene Damují Formation are exposed, due to river erosion. Loose echinoid specimens are frequently encountered on the surface in this area, primarily due to the agricultural activities that disturb the land. Farmers often collect these fossils, attracted by their ambulacra, which they interpret as “flower drawings,” turning them into collectibles. Additionally, other Clypeaster specimens remain embedded in the local rocks, indicating that the loose specimens are a result of the erosive processes affecting these strata.

The morphological characteristics of the collected specimens were compared with existing descriptions of Clypeaster taxa from the literature. Key references included works by Sánchez-Roig (1924Sánchez-Roig, M. (1924). Revisión de los equínidos fósiles cubanos. Memorias de la Sociedad Cubana de Historia Natural Felipe Poey, 6: 6-42., 1926Sánchez-Roig, M. (1926). Contribución a la paleontología cubana. Los equinodermos fósiles de Cuba. Boletín de Minas, 10: 1-179., 1949Sánchez-Roig, M. (1949). Los equinodermos fósiles de Cuba. Paleontología Cubana, 1: 1-330., 1952)Sánchez-Roig, M. (1952). Los Clypeasteridos fósiles de Cuba. Revista de Agricultura. 1951-1952, 118-177., Mortensen (1948)Mortensen, T. (1948). A monograph of the Echinoidea. Clypeasteroida. Clypeasteridæ, Arachnoidæ, Fibulariidæ, Laganidæ and Scutellidæ. Volume 4 (2), C.A.vReitzel, Copenhagen, 471 pp., Durham (1966)Durham, J.W. (1966). Clypeasteroids. En: Moore, R.C. (Ed.) Treatise on Invertebrate Paleontology, Echinodermata 3. The Geological Society of America and The University of Kansas Press, Boulder. , Mooi (1989)Mooi, R. (1989). Living and fossil genera of the Clypeasteroida (Echinoidea, Echinodermata): an illustrated key and annotated checklist. Smithsonian Contributions to Zoology, 488, 1-51., Mihaljević et al. (2011)Mihaljević, M., Jerjen, I., Smith, A.B. (2011). The test architecture of Clypeaster (Echinoidea, Clypeasteroida) and its phylogenetic significance. Zootaxa, 2983, 21-38., and Mihaljević and Rosenblatt (2018)Mihaljević, M., Rosenblatt, A.J., 2018. A new fossil species of Clypeaster (Echinoidea) from Malaysian Borneo and an overview of the Central Indo-Pacific echinoid fossil record. Swiss Journal of Palaeontology, 137(2), 389-404.. Specimens observed in the field embedded in the rocks were compared with cross-sections of a Clypeaster specimen from Matanzas, which was also used as a reference for terminology and comparisons (Fig. 2).

Results

Discussion

The morphological features of MMR-PA-001 (Fig. 3 A-B) and the field specimens (Fig. 4) align closely with those described for the genus Clypeaster. Specifically, specimen MMR-PA-001 exhibits strong morphological similarities to Clypeaster, particularly in its oval shape and dense tuberculation. Due to the incomplete preservation of specimen MMR-PA-002 (Fig. 3C), it has been broadly assigned to the family Clypeasteridae. The missing fragment in this specimen may be a sign of predation, as suggested by comparison with the scientific literature (Nebelsick and Mancosu, 2022Nebelsick, J. H., y Mancosu, A. (2022). Fish Predation on Clypeaster humilis from the Red Sea: Potential for recognition in the fossil record. Contributions from the Museum of Paleontology, University of Michigan, 33 (2) 29-64), but this feature requires further investigation with additional specimens exhibiting similar characteristics from other localities.

The genus Clypeaster is well-documented in the geological and paleontological literature of Cuba (Donovan, 1994Donovan, S.K. (1994). Some Fossil Echinoids (Echinodermata) from the Cenozoic of Jamaica, Cuba and Guadaloupe. Caribbean Journal of Science, 30 (3-4), 164170.; Sanchez-Roig, 1924Sánchez-Roig, M. (1924). Revisión de los equínidos fósiles cubanos. Memorias de la Sociedad Cubana de Historia Natural Felipe Poey, 6: 6-42., 1926Sánchez-Roig, M. (1926). Contribución a la paleontología cubana. Los equinodermos fósiles de Cuba. Boletín de Minas, 10: 1-179., 1949Sánchez-Roig, M. (1949). Los equinodermos fósiles de Cuba. Paleontología Cubana, 1: 1-330., 1952Sánchez-Roig, M. (1952). Los Clypeasteridos fósiles de Cuba. Revista de Agricultura. 1951-1952, 118-177.; Franco, 1983Franco, G.L. (1983). El género Clypeaster Lamarck en el Neógeno-Cuaternario de Cuba Oriental. Contribución a la Geología de Cuba Oriental, Editorial Científico-Técnica, La Habana, 239249.). However, assigning specimens to specific species within this genus is often challenging due to the proliferation of nominal species. This difficulty is exacerbated by paleontologists who have described new species based on minor morphological differences observed in poorly preserved fossil specimens (Mihaljević et al., 2011Mihaljević, M., Jerjen, I., Smith, A.B. (2011). The test architecture of Clypeaster (Echinoidea, Clypeasteroida) and its phylogenetic significance. Zootaxa, 2983, 21-38.; Mihaljević and Rosenblatt, 2018Mihaljević, M., Rosenblatt, A.J., 2018. A new fossil species of Clypeaster (Echinoidea) from Malaysian Borneo and an overview of the Central Indo-Pacific echinoid fossil record. Swiss Journal of Palaeontology, 137(2), 389-404.). Consequently, many records lack detailed descriptions or illustrations. Furthermore, the genus is challenging to subdivide taxonomically due to the extensive gradation and variation in test characteristics across species (Rose and Poddubiuk, 1987Rose, E.P.F., Poddubiuk, R.H. (1987). Morphological variation in the Cenozoic echinoid Clypeaster and its ecological and stratigraphical significance. Ann. Inst. Geol. Public. Hung., 70, 463-469.). These variations include differences in test size and profile, medial outline, tuberculation, ambulacral shape, and the positions of the peristome and periproct (Mihaljević et al., 2011Mihaljević, M., Jerjen, I., Smith, A.B. (2011). The test architecture of Clypeaster (Echinoidea, Clypeasteroida) and its phylogenetic significance. Zootaxa, 2983, 21-38.). For these reasons, MMR-PA-001 and the four specimens in the field have been classified only at the genus level.

Of particular interest is the abundance of specimens at the locality that are partially embedded in the rock, often exposed in cross-section and frequently showing signs of erosion (Fig. 4). The orientation and partial exposure of these specimens offer valuable insights into the taphonomic processes that occurred during and after fossilization. The way these specimens are embedded can indicate sedimentary processes, such as the direction of current flow or the degree of burial over time (Nebelsick, 1999Nebelsick, J. H. (1999) Taphonomy of Clypeaster fragments: preservation and taphofacies. Lethaia, 32, 241-252.). For instance, the orientation might suggest post-mortem transport or in situ burial under relatively low-energy conditions, which could explain the lateral exposure observed in the field. The exposed specimens have also suffered erosion, as indicated by the wear patterns on their surfaces. This suggests prolonged exposure to environmental elements, which further complicates their extraction and study. The partial exposure poses challenges for extraction and study, emphasizing the potential value of non-invasive techniques in future research. Such approaches would not only preserve the integrity of the specimens but also provide a more accurate context for their analysis.

The discovery of Clypeaster specimens within the Upper Eocene Damují Formation at the Parque Alto locality in Rodas holds paleontological importance, as these may represent the oldest known specimens of the genus reported from Cuba. While some foraminifera within the formation suggests a stratigraphic age ranging from the late Eocene to the earliest Oligocene (lower Rupelian), the reported specimens likely belong to an Eocene section, offering new insights into the evolutionary history of the genus in the Caribbean. This interpretation is supported by previous studies that have consistently classified the formation as Upper Eocene, based on the identification of index foraminifera of this epoch. Furthermore, the overlying Jia Formation, considered Oligocene in age, crops out several kilometers from the Parque Alto locality. The presence of large foraminifera, bryozoans, and coral remains within the Damují Formation, along with Clypeaster, suggests a warm, tropical, shallow-water, soft-sediment, reef-forereef carbonate shelf environment during the late Eocene. This assemblage reflects a rich and diverse marine ecosystem, consistent with findings by BouDagher-Fadel (2018)Boudaugher-Fadel, M. K. (2018). Evolution and geological significance of larger benthic foraminifera. UCL press. and other studies.

Additionally, the new records provide significant insights into the biogeographical and evolutionary history of this group, not only in the Caribbean region. The presence of Clypeaster fossils from these epochs suggests that the genus was already widely distributed across the tropical belt. This finding supports the hypothesis that Clypeaster and related taxa likely originated in the tropical regions of the eastern Tethys Sea and subsequently expanded their range during the Eocene (Lee et al., 2023Lee, H., Lee, K.S., Hsu, C.H., Lee, C.W., Li, C.E., Wang, J. K., Janies, D. (2023). Phylogeny, ancestral ranges and reclassification of sand dollars. Scientific Reports, 13 (1), 10199.). The Cuban fossils, therefore, represent an important biogeographical link, indicating that the Caribbean may have served as a migration route, refugium, or diversification center during periods of global climatic change, contributing to the evolutionary persistence and radiation of Clypeaster and other Luminacea echinoids in the Cenozoic era (Op. cit.).

Lee and colleagues proposed that the major range expansion of Clypeaster and other Luminacea echinoids occurred primarily during the Miocene (Lee et al., 2023Lee, H., Lee, K.S., Hsu, C.H., Lee, C.W., Li, C.E., Wang, J. K., Janies, D. (2023). Phylogeny, ancestral ranges and reclassification of sand dollars. Scientific Reports, 13 (1), 10199.). Thus, the presence Clypeaster fossils since the late Eocene of Cuba could indicate an earlier diversification event and/or range expansion. Is possible that Clypeaster may have begun its dispersal earlier than previously thought. This earlier expansion could have been restricted by the cooler climatic conditions of the late Eocene and early Oligocene, which may have limited or halted the spread of these taxa into new regions, farther from the Caribbean. This finding provides a crucial piece of evidence that may challenge or refine existing hypotheses about the timing and pathways of echinoid biogeography and evolution.

Conclusions

The new records of Clypeaster specimens from the locality Parque Alto within the Damují Formation provide valuable insights into the diversity and distribution of this genus during the late Eocene. Their well-preserved morphological features contribute to a better understanding of the evolutionary history and paleobiogeography of Clypeaster in the Caribbean, further emphasizing the untapped paleontological richness of Cuba’s Paleogene fossil record. Moreover, the discovery of Late Eocene Clypeaster fossils in Cuba offers valuable insights into the biogeographical and evolutionary history of this group. The presence of these fossils in the Caribbean from the Late Eocene suggests the possibility of an earlier wave of range expansion. The favorable climatic conditions of the Eocene could have driven this earlier dispersal, coinciding with significant speciation, evolution, and migration events. The Cuban fossils, therefore, not only serve as an important biogeographical link but also challenge the current understanding by indicating that Clypeaster may have begun expanding its range earlier than previously thought, or it may have done so in several waves. In this sense, this evidence could suggest that the Caribbean might have played a crucial role as a migration route or speciation hot spot, contributing to the evolution and radiation of Clypeaster and related taxa well before the Miocene.