The shapes of Paleozoic and modern reef-builders: a critical review

Abstract

Paleoecologists studying Paleozoic reef-builders have interpreted their growth forms as responses to conditions of depth and turbulence in reef complexes. Comparison of the shapes of Paleozoic stromatoporoids and corals with the growth forms of modern scleractinians has been used to reconstruct Paleozoic conditions. A review of shape zonation on modern reefs indicates that no general pattern is applicable to all reefs and variations in shape are the result of the interaction of many environmental factors with the genetically dictated growth pattern of the coral. In most zones of a reef a wide range of shapes co-exist. The growth forms of corals on modern reefs are not a simple vegetative response to the many environmental parameters that have been shown to influence form, but are constrained by phylogenetic and developmental influences as well as functional ones.Interpretations of the environments of western Canadian and other mid-Paleozoic reefs have been based on the growth forms of stromatoporoids. The environmental significance of the shapes has been deduced from comparison with the shapes of modern scleractinians, functional morphology, nature of the enclosing sediment, position of growth, position within the reef, and diversity gradients. The validity of these criteria is open to question and considerable doubt remains concerning the significance of the growth forms. The shapes of reef animals are not specific guides to environments of modern reefs and should not be expected to be guides for ancient ones.

Treatise Online, no. 25: Part E, Revised, Volume 4, Chapter 9B: External morphology of the Paleozoic Stromatoporoidea: Shapes and growth habits

“…Hence, some caution needs to be exercised in interpreting results of studies of external shapes of stromatoporoids, for example, based only on cores drilled in oil exploration work of subsurface reservoirs in Devonian carbonate reefs (murray, 1966;FiSchBuch, 1968;NoBle, 1970;emBry & KlovaN, 1971). StearN (1975StearN ( , 1982 has previously reviewed aspects of studies of stromatoporoid Fig. 1.…”

“…These laminar shapes are more likely to remain in situ in more turbulent conditions, but then they can also be reworked into forereef slopes. StearN (1982) fur ther questioned the validity of using shapes to interpret the paleoenvironments of Paleozoic reef complexes, given that, in terms of the shapes of modern reef organisms (e.g., scleractinian corals), such complex patterns of distribution existed and they were not specific guides to the environments. The patterns of distribution of stromatoporoid shapes across ancient reefs may similarly have rather doubtful paleoenvironmental significance, unless the analyses are properly focused on the documentation of individual species: the taxonomic identification based on internal structures, and the shape related to paleoenvironmental factors, as well as the genetic make up of the species.…”

“…These stromatoporoid-bearing Paleozoic carbonate sequences have proved particularly useful for establishing the range of skeletal morphotypes, and for defining models that employ stromatoporoid shapes in paleoenvironmental analyses (KerShaW, 1984(KerShaW, , 1990KerShaW & KeeliNg, 1994), though the results cannot be completely validated until the genetically related influences on these stromatoporoid species are more fully understood (StearN, 1982).…”

Treatise Online, no. 31: Part E, Revised, Volume 4, Chapter 13: Paleoecology of the Paleozoic Stromatoporoidea

“…Stearn's (1982) comparison of stromatoporoids with modern coral growth forms, which may provide analogues, revealed no parallel patterns; and the forms of modern reef animals are not even useful guides to modern reef environments, thereby emphasizing the care needed for interpretation of stromatoporoids. neStor (1984) discussed the range of controls on stromatoporoids.…”

Treatise Online, no. 8, Part E, Revised, Volume 4, Chapter 9F: Functional morphology of the Paleozoic stromatoporoid skeleton

“…The competitive advantages of many of the clonal organisms that shared growth patterns and environments with stromatoporoids have been considered by CoateS and JaCkSon (1985), but the applicability of their conclusions, based on corals and bryozoans, to stromatoporoid sponges is in doubt (Stearn, 1982). These organisms are or were typically shallow water, sessile benthos living in reef and level-bottom environments.…”