Insights into Atlantic-Pacific divergence in Arbacia (Echinoidea) using revised systematics of Neogene fossils from the Caribbean and southeastern United States
Data files
Jul 30, 2026 version files 56.83 KB
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Material_studied.csv
53.39 KB
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README.md
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Abstract
The regular echinoid Arbacia Gray, 1835 is a key model in evolutionary, ecological, and biogeographic research, yet its fossil diversity and paleobiogeographic history in the western Atlantic remain understudied. We present a comprehensive revision of Plio–Pleistocene Arbacia from the southeastern United States and Caribbean based on examination of more than 400 specimen lots from institutional collections, including preserved material retaining spines.
Our results resolve longstanding taxonomic confusion by recognizing Arbacia improcera as encompassing A. sloani and A. crenulata, confirming the distinctiveness of A. waccamaw and A. rivuli, and describing Arbacia percaribbeana sp. nov., from Venezuela, the Caribbean, and southern Florida. The revised taxonomy establishes a coherent regional succession: A. improcera in the Late Pliocene, A. waccamaw and A. rivuli at the Pliocene–Pleistocene transition, and A. punctulata persisting from the Late Pleistocene to the present. These species occur in well-dated formations and provide useful biostratigraphic markers. The absence of Arbacia from Miocene deposits of the eastern United States aligns with molecular estimates suggesting a Pliocene origin of modern Atlantic lineages.
Morphological comparisons reveal a previously unrecognized biogeographic structure. Four western Atlantic species share a distinctive trait combination separating them from extant Pacific taxa, whereas A. percaribbeana sp. nov. exhibits stronger Pacific affinities. This pattern suggests a North Atlantic lineage and a lineage with Pacific relationship, possibly reflecting trans-isthmian exchanges during the progressive closure of the Central American Seaway. Together, these results establish Arbacia as a robust model for investigating macroevolutionary dynamics in Neogene western Atlantic echinoids.
Dataset DOI: 10.5061/dryad.d7wm37qh3
Description of the data and file structure
This file brings together all 402 specimen lots examined in this study, the collections in which these specimens are housed, the identification of all specimens, the number of specimens in each lot, the geographic origin, the geological formation, and the age of the formation from which these specimens were collected.
File: Material_studied.csv
The column header “Collection” indicates the five institutional collections where the studied specimens were examined and are available for further study. These are: the Florida Museum of Natural History (Gainesville, Florida, USA); the Smithsonian Institution (Washington, DC, USA); the Natural History Museum (London, UK); the University of California Museum of Paleontology (San Francisco, California, USA); and the North Carolina Museum of Natural Sciences (Raleigh, North Carolina, USA).
The column header “Species name” lists all updated taxonomic names following the detailed work presented in the manuscript. This includes the previously known Arbacia improcera (Conrad, 1843), Arbacia rivuli Cooke, 1941, Arbacia waccamaw Cooke, 1941, and the modern Arbacia punctulata (Lamarck, 1816), as well as the newly described Arbacia percaribbeana sp. nov.
The column header “Institutional number” provides the institutional code that allows direct identification of the specimen in the mentioned collections. It is composed of the abbreviated institutional code (as given in the “Collection” column) and the numerical identification.
The column header “Lot” indicates either the number of sub‑complete or complete echinoid tests in the lot studied (ranging from 1 to 11), or “spine” in cases where the studied lot was based only on disconnected spines, and “fragments” in cases where the lot is composed only of very small, fragmented echinoid plates.
The column headers “Country”, “State”, “County”, and “Area” provide all available information about the geographic origin of the specimens.
The column header “Formation” indicates, when available, the geological Formation from which the specimens were collected. An additional “?” following the Formation name reflects uncertainties in the specimen labels.
The column header “Member/bed/unit” provides, when available, additional stratigraphic data, such as named members within the Formation or less formal subdivisions of the Formation (e.g., “lowermost”).
The column header “Age” provides a defined age for the Formation from which the specimens were collected, ranging from the Pliocene (5.33–2.58 Ma) to the Pleistocene (2.58–0.017 Ma). Additional information is given when known, such as “Late” or “Early” Pleistocene.
Empty cells were filled with “NA” (not available) for specimens for which no geographical data (columns Country, State, County, and Area), no geological data (columns Formation, Member/bed/unit), or no temporal data (column Age) were available for the associated specimen ID. This is the case for specimens that were collected without additional geological information.