Morphological study identifies probable first Miocene Selaginella macrofossil in Dominican amber

A morphological study documented a new species of spike moss, Selaginella jorelisiae, preserved in Dominican amber. The authors identify the specimen as the first amber-preserved Selaginella fossil from the Western Hemisphere and the probable first Miocene macrofossil record for the genus. The holotype came from amber-bearing sediments in the Cordillera of the Dominican Republic.

Dominican amber is estimated to be 15–20 million years old, spanning the Early to early Middle Miocene. The researchers excluded preservation in younger copal because the included plant tissue is partly replaced by minerals, probably pyrite. This was a comparative study based on macromorphology.

Investigators manually ground and polished the amber, then examined it with dissecting and compound microscopes. Photographs were assembled from 8 to 34 focal planes. The fossil was described using established terminology and compared with published descriptions and herbarium specimens representing living Selaginella species from the West Indies.

The preserved shoot was once branched, with branches measuring 12 and 8.8 mm. Its vegetative leaves, or trophophylls, were dimorphic. Dorsal trophophylls measured 0.80–0.98 by 0.2–0.32 mm and were ovate and symmetric, with rounded bases, slightly keeled surfaces, aristate tips and minutely serrated margins.

The dorsal leaves had aristae measuring 0.27–0.35 mm, approximately one-third of leaf length, and margins bearing scattered teeth or cilia. Ventral trophophylls measured 1.20–1.45 by 0.45–0.62 mm. They were elliptic, with rounded, slightly asymmetric bases and apiculate tips.

Rhizophores, axillary trophophylls, strobili, spores and the leaf epidermis were not preserved. Despite these limitations, the combination of leaf shape, symmetry, apex form, auricles and the placement of marginal features distinguished the fossil from 10 living Greater Antillean species included in the comparison. Specific differences separated the fossil from S. heterodonta, which has broadly ovate dorsal trophophylls with cilia around the margin, and S. armata, which has broadly ovate, asymmetric ventral trophophylls.

Further distinctions in leaf-base symmetry, apex form and marginal cilia and teeth separated it from S. confusa, S. phiara, S. tenella, S. cordifolia, S. consimilis, S. urquiolae and S. flabellum. Although the fossil lacks reproductive structures, its anisophyllous vegetative shoot placed it within the rhizophoric clade of Selaginella. Its preservation was insufficient for confident assignment to the subgenera Ericetorum, Exaltatae, Gymnogynum, Lepidophyllae or Stachygynandrum.

The shoot also excluded the selaginella clade, whose members have isophyllous shoots, and subgenus Rupestrae, whose members have helically arranged vegetative leaves. Plant, fungal and lichen inclusions in Dominican amber have previously been associated with diverse Miocene Caribbean forest communities, including epiphytic habitats. Terrestrial and epilithic life forms are the most common among Selaginella species, although some species grow on tree trunks or other plants.

On this basis, the authors considered S. jorelisiae most likely a member of the herbaceous layer, potentially growing on cliffs, boulders, soil banks, mossy rocks or leaf litter. They could not exclude an epiphytic occurrence. The single incomplete specimen therefore documents Selaginellaceae in Greater Antillean humid forests during the Miocene, while leaving its subgeneric placement and precise ecological setting unresolved.

Subject of Research: Description and morphological comparison of a Miocene Selaginella fossil from Dominican amber

Article Title: First record of Selaginella from Miocene amber

Article References: López-García, A. G., Schmidt, A. R., Serguera, M., & Regalado, L. (2025). First record of Selaginella from Miocene amber. Fossil Record, 28(1), 57-66. https://doi.org/10.3897/fr.28.138310

Image Credits: AI Generated

DOI: 10.3897/fr.28.138310

Keywords: Selaginella, spike moss, Miocene, Dominican amber, fossil plant, macrofossil, paleobotany, Greater Antilles, morphology, First, record, amber