41-12 Morphometric analysis of lateral arm plates in a modern brittle star

Session: Paleontology, Stratigraphy, Sediments, and Soils (Posters)

Poster Booth No.: 33

Presenting Author:

Alaina Johnson

Authors:

Johnson, Alaina¹, Veal, Paige², Sumrall, Colin D.³, Thuy, Ben⁴, Deline, Bradley L.⁵

(1) Earth and Environmental Sciences, University of West Georgia, Carrollton, GA, USA, (2) Earth and Environmental Sciences, University of West Georgia, Carrollton, GA, USA, (3) Department of Earth, Environmental and Planetary Sciences, University of Tennessee, Knoxville, TN, USA, (4) Department of Paleontology, Natural History Museum Luxembourg, Luxembourg City, Luxembourg, (5) Earth and Environmental Sciences, University of West Georgia, Carrollton, GA, USA,

Abstract:

Brittle stars are diverse, abundant, and ecologically important components of modern marine ecosystems.  Although modern ophiuroids are incredibly abundant, their skeletons disarticulate rapidly after death, providing scientists with a taphonomically biased fossil record essentially limited to Lagerstätte.  Recent work has shown that specific skeletal elements, the Lateral Arm Plates (LAPs), contain a wealth of taxonomic, phylogenetic, and ecological information, thus providing a long and detailed microfossil record of the clade. The LAPs bear spines and run along both sides of the arm adjacent to the vertebra.  Recent work has focused on qualitative rather than quantitative methods to describe LAP morphology. To explore how LAPs vary between individuals and with respect to position along the arm, two modern ophiuroid specimens (Ophiolepis elegans) were disarticulated and left and right LAPs were sampled along individual arms. Plates were mounted and imaged using a scanning electron microscope, external features and plate shape of the LAPs were characterized using outline analysis, and the resulting outlines were compared using principal component analysis. Preliminary results show a clear separation between the two individuals and LAP shape varies along the arm. For both individuals, there is a clear and steady progression across morphospace from the proximal to distal elements in the arms. However, the LAPs embedded within the disk are morphologically distinctive and separated in morphospace from the rest of sampled LAP elements. In addition, differences between individuals decreased at the distal tip of the arms, converging on similar outlines in the smallest LAP elements. These results suggest that proximal LAPs are preferable for taxonomic and phylogenetic studies. However, the results are preliminary and will be further explored by characterizing the internal surface of the LAPs, characterizing additional individuals, and incorporating additional taxa (both modern and fossil).  

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

doi: 10.1130/abs/2026SE-13189

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