Automobility in tabulata, rugosa, and extant scleractinian analogues: Stratigraphic and paleogeographic distribution of Paleozoic mobile corals

Freeliving corals capable of automobility (e.g., lateral migration) were ra re during Paleozoic time, but some species within the tabulate genera Proct erodictyum, Procteria (Granulidictyum), P. (Pachyprocteria), Palaeacis and Smythina, and the rugose genera Combophyllum, and Baryphyllum, have morphol ogic characters that suggest they were capable of such self-directed moveme nt. The rugose corals Gymnophyllum and Hadrophyllum sensu stricto may have exhumed and righted themselves. No single morphological character is diagno stic for an automobile habit, but the following characters appear to be imp ortant indicators: 1) lack of an external attachment surface; 2) concentric skeletal accretion; 3) discoid corallum shape; 4) concavo-convex, piano-co nvex, and, less commonly, biconvex corallum profile; and 5) small, lightwei ght corallum. Additionally, the occurrence of corallites on the base of the corallum (hypocorallites) is a good indicator of automobility in freelivin g corals, but the character is so far known only in Procterodictyum. All kn own fossil automobile taxa appear to have inhabited relatively quiet enviro nments on muddy or silty, soft substrates. The earliest known automobile corals were early Emsian (Devonian) Procterod ictyum. Paleozoic automobile corals were most abundant during Devonian time , with Procterodictyum, Procteria (Granulidictyum), and Combophyllum distri buted in a narrow longitudinal band in the southern hemisphere on both side s 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 conf ined to within 40 degrees of the paleoequator. However, additional research will be required before coral automobility can be used to constrain paleol atitude independently.