Fossil corals with skeletal lesions comparable to modern ones

Abstract

Whereas post-mortem bioerosional features such as bivalve, sponge or worm borings are frequently preserved in ancient corals, reports of ante-mortem skeletal anomalies on Cretaceous specimens are rare. Here, we document the occurrence of fossil skeletal lesions produced during the life span of the colonies in exceptionally well preserved Aptian (Early Cretaceous) scleractinians from the Maestrat Basin (East Iberia). These ante-mortem damage features are characterized by millimetric to centimetric areas of skeletal depression, as well as upward growth around damaged areas indicating regeneration. Depressed skeletal lesions are commonly overprinted by post-mortem lithophagid borings. Distribution of skeletal anomalies on the colonies can be focal or multifocal, and their location basal, medial and/or apical. The extent of the skeletal anomalies can be mild (occupying <10% of the colony) to extreme (occupying ≥50% of the colony). The edges of the skeletal anomalies are distinct (disk-shaped) or annular (ring-haped), the margins are mainly smooth to uneven, and the shapes are circular, oblong, pyriform, linear, or irregular. The skeletal anomalies exhibited by the corals are comparable to tissue lesions produced in modern corals either by predation, bioerosion or disease, which may be followed by skeletal overgrowth or denudation. Although demonstrating disease in fossil colonies is challenging, there is no reason to believe that corals did not experience diseases back in the Cretaceous. This paper gives an example of the potential of coral anomalies originating from tissue lesions and skeletal damage to be preserved in the geological record, a factor that may have been often overlooked in the study of fossil coral communities.