16 Paleontology of North America

Added from Discipline submissions.

Monday, 9 March 2026
1:30 PM - 4:30 PM
RCC, 106

Morphometric Differentiation of Atlantic Encope (Echinoidea: Scutelloida) using Fossil and Extant Specimens

Paper number: 16-0
Program: Technical Sessions
Time: 1:30 PM – 1:45 PM

Authors

Abstract

The sand dollar genus Encope is endemic to the New World. Of the eight living species, three occur in the Atlantic Ocean (Encope aberrans, E. michelini, and E. emarginata), whereas the remaining five are found in the Pacific. Two Atlantic-endemic extinct species, E. macrophora and E. tamiamiensis, are morphologically very similar. Encope is thought to evolve more slowly at the molecular level than closely related genera, which can result in incomplete lineage sorting and poorly resolved species boundaries. Consequently, morphological differences within species may reflect slow genetic divergence rather than true species-level separation. In this context, morphometric analyses provide an important complement to molecular data by helping to clarify species limits and improve phylogenetic interpretations that include both fossil and living taxa. This study uses geometric morphometrics to distinguish Atlantic Encope species, excluding E. emarginata. Live-collected specimens were obtained from the Conservation Paleobiology collections at the Florida Museum of Natural History, and fossil specimens were obtained from the Invertebrate Paleontology collections. Thirty-two homologous two-dimensional landmarks were digitized for each specimen using TPSDig software. The first two principal components explained 55.33% of the total shape variation, and all four species formed distinct clusters. Since the main taxonomic feature used to separate E. macrophora and E. tamiamiensis is the angle between the two anterior paired ambulacra, this angle was measured for all four species. Watson–Williams tests showed significant differences in mean angles between E. aberrans and E. michelini, between E. macrophora and E. tamiamiensis, and among all four species. However, overlap between E. macrophora and E. tamiamiensis suggests that this character alone may not be a reliable diagnostic feature. Allometric analyses showed that all species follow the same growth trajectory. Overall, these results demonstrate that geometric morphometrics can effectively distinguish Atlantic Encope species and provide a useful tool for resolving taxonomic questions in both fossil and living taxa.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411886

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