101-11 Persistent Ancestral Morphologies: Leveraging the Fossil Record of Solitary Corals to Guide Modern Reef Conservation Practices

Abstract:

What is the basal state of the scleractinian skeleton, and how long did it persist in the fossil record? Retention of traits linked to basal morphologies may indicate long-term evolutionary resilience to major global environmental shifts. The main architects of modern reefs, corals from order Scleractinia, evolved during the Middle Ordovician according to molecular data, persisted in mostly soft-bodied forms through shifting climates of the Paleozoic, and retained skeletonized forms from the Middle Triassic to the present day. Modern scleractinian corals face numerous pressures from a warming climate, including rising sea surface temperatures and acidifying oceans. This work utilizes Mesozoic and Cenozoic fossil records of order Scleractinia along with a comprehensive record of Paleozoic scleractiniamorphs and members of subclass Rugosa to reveal skeletal traits basal to all anthozoans. Additionally, the fossil record of scleractinians is examined with extant corals to determine traits basal to order Scleractinia, and their persistence from deep evolutionary time to modern oceans. 

Skeletal macromorphologies were compiled for 31 fossil and 19 extant solitary scleractinian families, 3 fossil scleractiniamorph families, and 74 fossil rugosan families. Occurrences of 69 skeletal traits were quantified for each epoch independent of taxonomy. Results indicate that epitheca, tabulae, dissepiments, synapticulae, axial structure, and septal lobes are basal to all anthozoans. To identify the basal scleractinian state and link it to modern corals, parsimony-based trait node analysis was performed using trait data for extant scleractinian families combined with a published molecular phylogeny. Results indicate the basal scleractinian state possesses a trochoid or discoid shape, laminar septa, septal teeth, ornamented lateral flanks, axial structure and costae. These findings identify specific traits basal to all anthozoans which were lost early or repeatedly within the scleractinian lineage. Pertinent to modern conservation practices are the basal scleractinian traits retained today by extant, solitary, ahermatypic scleractinian corals that inhabit deep water environments, such as Rhombopsammia (Micrabaciidae) and Deltocyathus (Deltocyathidae). The persistence of these basal morphologies through the stratigraphic record guides conservation, biodiversity, and climate research agendas toward the cryptic solitary and deep-water corals, which are often overlooked. Solitary corals inhabiting deep waters, while still at substantial risk, may hold secrets to modern reef resilience.

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