Carl W. Stock

Biogeography of the Devonian stromatoporoids

Abstract Stromatoporoids were a common component of shallow carbonate environments of North America, Eurasia, and Australia during the Devonian. They were least abundant during the Early Devonian. After that time abundance increased, and remained high steadily through the Frasnian. At the Frasnian-Famennian boundary the number of stromatoporoids was greatly diminished, but they did not become extinct until the end of the Devonian (at the end of the Strunian). The geographic extent of stromatoporoids expanded and contracted concurrently with increases and decreases in total population size. Provincialism at the genus level prevailed during the Early Devonian, with stromatoporoids inhabiting the Old World and Eastern Americas Realms; none are known from the Eastern Americas during the Siegenian. For the remainder of the Devonian stromatoporoids were cosmopolitan at the genus level. The abundance of stromatoporoids varied directly with eustatic sea level during the Devonian. Variations in depositional conditions apparently controlled the local distribution of genera.

Late Ordovician and Early Silurian stromatoporoid sponges from Anticosti Island, eastern Canada: Crossing the O/S mass extinction

During Late Ordovician and Early Silurian time, from 450 to 428 million years ago, stromatoporoid sponges were some of the most common and abundant fossils in shallow water tropical settings of the Anticosti Basin (Gulf of St Lawrence). They formed dense, massive coralline skeletons of calcium carbonate, some up to a meter or more across, especially in reef environments, but also in deeper waters of the Anticosti shelf, down to the margins of the photic zone, where light faded. The Anticosti Basin reveals one of the most fossiliferous carbonate sequences worldwide for rocks of this age, straddling a global mass extinction boundary, and thus revealing not only those taxa that became extinct, but also how the seas were repopulated in an equatorial setting after the mass extinction.

Lower Devonian (Gedinnian) Stromatoporoidea of New York: redescription of the type specimens of Girty (1895)

Girty (1895) named six species of stromatoporoids from the Lower Devonian of central and east-central New York, which are here redescribed and reillustrated. Additional new specimens provide data on variations within the following species: Anostylostroma jewetti, Parallelostroma foveolatum, ?Parallelostroma centrotum, and ?Parallelostroma microporum.

STROMATOPOROIDEA, 1926–2000

Abstract The history of research on the “true” stromatoporoids, a presumably monophyletic group of sponges that occurred from the Ordovician through the Devonian, is examined in detail. Stromatoporoid published research is summarized in five categories: quantity of publication; biological affinities; systematics; skeletal microstructure; and paleoecology. Quantity of publication is measured from each of the 75 years. Moderate levels of publication in the late 1920s and 1930s declined in the early 1940s, and were reduced to zero for four years due to the impact of World War II. Levels similar to that of the 1930s returned in the 1950s, after which there was an overall increase until the mid-1980s, when levels began a decrease that persists today. The proportion of research on paleoecology has increased as research on systematics decreased through time. Post-Devonian forms assigned to the stromatoporoids are a polyphyletic grouping of several apparently unrelated taxa, possibly representing both Porifera and Cnidaria. Publications on the post-Devonian “stromatoporoids” amount to less than one-third that on the true stromatoporoids during the same 75 years.

Upper Silurian/Lower Devonian Stromatoporoidea from the Keyser Formation at Mustoe, Highland County, west-central Virginia

Stromatoporoids are the major fossil faunal element of the Upper Limestone Member of the Keyser Formation in an outcrop at Mustoe, Virginia. The member is divided into four subunits at Mustoe, in ascending order: a bioherm, two biostromes, and a laminated micritic subunit. Stromatoporoids are found in all subunits, and they decrease in quantity upward. Nine species are described in three genera: Plexodictyon cf. P. waparksi Steam, Parallelostroma typicum (Rosen), P. kaugatomicum (Riabinin), P. barretti (Girty), P. cf. P. barretti, P. keyserense n. sp., P. longicolumnum n. sp., P. multicolumnum n. sp., and Densastroma pexisum (Yavorsky). With the exception of P. barretti, a Lower Devonian stromatoporoid, the species of stromatoporids found at Mustoe have been known only from Silurian rocks in other areas.

Lower Devonian (Lochkovian) Stromatoporoidea from the Coeymans Formation of central New York

, C. J. HUMPHRIES, AND K. J. GASTON. 1994. Centres of seedplant diversity: the family way. Proceedings of the Royal Society of London B, 256:67-78. WILSON, E. O. (ed.). 1988. Biodiversity. National Academy Press, Washington, D.C. . 1992. The Diversity of Life, Belknap Press, Cambridge, Massachusetts. , C. J. HUMPHRIES, AND K. J. GASTON. 1994. Centres of seedlant diversity: the family w y. Proceedings of the Royal Society of ondon B, 256:67-78. ILSON, E. O. (ed.). 1988. Biodiversity. National Academy Press, ashington, D.C. . 19 2. The Divers ty of Life, Belknap Press, Cambridge, MasWINSTON, J. E. 1992. Systematics and marine conservation, p. 144168. In N. Eldredge (ed.), Systematics, Ecology, and the Biodiversity Crisis. Columbia University Press, New York.

Chapter 5 Devonian stromatoporoid originations, extinctions, and paleobiogeography: how they relate to the Frasnian-Famennian extinction

Abstract Origination and extinction of stromatoporoid genera show that the rate of origination exceeded that of extinction from the early Early Devonian (Lochkovian) through the early Middle Devonian (Eifelian). For the remainder of the Devonian (Givetian-Famennian), extinction outpaced origination. During the Early and Middle Devonian, tropical to subtropical marine habitats were divided into the Eastern Americas Realm and the Old World Realm—in North America these were separated by the Transcontinental Arch and the Canadian Shield. Eustatic sea level, which had been rising since the Emsian, reached a point late in the Givetian (Taghanic Onlap) where the land barrier was breached, and Old World taxa invaded the Eastern Americas. Sea level continued to rise episodically through most of the Frasnian, followed by an abrupt fall in conjunction with the Frasnian-Famennian extinction. It is concluded that the decrease in stromatoporoid genus diversity, which occurred as Old World and Eastern Americas faunas came into competition, continued with further sea-level rise during the Frasnian. This lowered diversity put the stromatoporoids in a vulnerable position for extinction when climatic disturbances occurred at the end of the Frasnian.

Lower Devonian (Lochkovian) Stromatoporoidea from the Manlius Formation of New York

Stromatoporoids are found in all five members of the Manlius Formation of New York and are abundant at many localities. The fauna is dominated by two closely related species, Habrostroma microporum (Girty) and H. centrotum (Girty). Present in lesser numbers are Intexodictyon manliusense n. sp., Plectostroma micum (Bogoyavlenskaya), Actinostromella vaiverensis Nestor, Densastroma pexisum (Yavorsky), Habrostroma cf. H. centrotum (Girty), and ? Parallelostroma sp. The assemblage displays both Silurian and Devonian affinities.

Two new genera of Upper Silurian actinostromatid stromatoporoids

Two new genera of Upper Silurian stromatoporoids in order Actinostromatida are described. Genus Bicolumnostratum Stock, with type species B. micum (Bogoyavlenskaya), is characterized by two kinds of pillars and nonaligned colliculi, and is assigned to family Actinostromatidae. Genus Acosmostroma Stock, with type species A. ataxium Stock new species, contains irregular micropillars and microcolliculi, and is assigned to family Densastromatidae. Two additional new species are Acosmostroma glascoense Stock and A.? cobleskillense Stock. A fourth species is A. tenuissimum (Parks). Bicolumnostratum is known from Ludlow- and Pridoli-age strata, whereas the occurrences of Acosmostroma are strictly Pridoli in age.

Quasiaulacera, A New Hirnantian (Late Ordovician) Aulaceratid Stromatoporoid Genus from Anticosti Island, Canada

Abstract A large and abundant columnar stromatoporoid, Quasiaulacera n. gen., from the Ellis Bay Formation, up to 3 m long and 40 cm in diameter, marks the Hirnantian (latest Ordovician) of Anticosti Island. Two species are present: Quasiaulacera stellata n. sp. from the basal Ellis Bay Formation (basal Prinsta Member, lower Hirnantian) along the northeastern coast of the island, and the type species Q. occidua n. sp. from the upper Ellis Bay Formation (Lousy Cove Member, upper Hirnantian) in the western carbonate facies of the island. Quasiaulacera is rare or absent in the reefal Laframboise Member (uppermost Hirnantian) of the formation. The new genus differs from Aulacera in the underlying Vaureal Formation (upper Katian) in having a large central axial zone marked by a single stack of large, convex-up cyst-plates, that is surrounded by a middle layer of small, concentric microcyst-plates, in places denticulate, and an outer layer composed of concentric laminae with dense pillars, in which microcyst-plates are either absent or rare. The outer two layers are defined by longitudinal fluting; there are no branching forms. Both species demonstrate a ball-like holdfast system, some with diameters of 30 to 70 cm, microbially cemented into the substrate. Quasiaulacera “gigantism” in the paleotropical Anticosti Basin evolved at a time of global cooling associated with the Hirnantian glaciation in south polar Gondwana, but terminated in mass extinction of the aulaceratids at the O/S boundary in Laurentia. This supports other evidence that the Hirnantian featured not only generic loss, but also innovation and migration in tropical latitudes.