Automobility in Tabulata, Rugosa, and extant scleractinian analogues: Stratigraphic and paleogeographic distribution of Paleozoic mobile corals

Abstract

Freeliving corals capable of automobility (e.g., lateral migration) were rare during Paleozoic time, but some species within the tabulate genera Procterodictyum, Procteria (Granulidictyum), P. (Pachyprocteria), Palaeacis and Smythina, and the rugose genera Combophyllum, and Baryphyllum, have morphologic characters that suggest they were capable of such self-directed movement. The rugose corals Gymnophyllum and Hadrophyllum, sensu stricto may have exhumed and righted themselves. No single morphological character is diagnostic for an automobile habit, but the following characters appear to be important indicators: 1) lack of an external attachment surface; 2) concentric skeletal accretion; 3) discoid corallum shape; 4) concavo-convex, plano-convex, and, less commonly, biconvex corallum profile; and 5) small, lightweight corallum. Additionally, the occurrence of corallites on the base of the corallum (hypocorallites) is a good indicator of automobility in freeliving corals, but the character is so far known only in Procterodictyum. All known fossil automobile taxa appear to have inhabited relatively quiet environments on muddy or silty, soft substrates.The earliest known automobile corals were early Emsian (Devonian) Procterodictyum. Paleozoic automobile corals were most abundant during Devonian time, with Procterodictyum, Procteria (Granulidictyum), and Combophyllum distributed in a narrow longitudinal band in the southern hemisphere on both sides of the Rheic Ocean. Carboniferous and Permian automobile taxa (Palaeacis partim, Smythina and Baryphyllum) were less diverse, but more cosmopolitan. Throughout Paleozoic time, the vast majority of automobile corals was confined to within 40 degrees of the paleoequator. However, additional research will be required before coral automobility can be used to constrain paleolatitude independently.