The stromatoporoidHabrostromain the upper Silurian (uppermost Pridoli)–Lower Devonian (Lochkovian) of North America, and the paleobiogeographic significance ofH.centrotum(Girty, 1895)

Abstract

Three species of Habrostroma dominate stromatoporoid faunas in the Lower Devonian (Lochkovian) of five areas in North America: New York, Virginia, Maine, Bathurst Island, and Ellesmere Island. In addition, they occur in what could be the upper Silurian (uppermost Pridoli) of Virginia, and possibly New York. Measurements of nine morphologies from 127 specimens of Habrostroma were subjected to an average linkage cluster analysis. Using average linkage between groups, three distinct clusters were revealed. Group assignments made from the cluster analysis were saved, and entered into a canonical discriminant analysis with the nine morphological variables. An overall Wilks’ lambda was calculated, and is statistically significant at alpha <0.001. The hit rate for classifying group 1 is 98%, that for group 2 is 100%, and that for group 3 is 97.9%; the total hit rate is 100%. The morphological variables contributing most to group membership are: (1) percent cystlike microlaminae, (2) microlaminae per mm, (3) gallery height, (4) laminae per mm, and (5) laminar thickness. The statistics confirm that there are three species: H. centrotum, H. microporum, and H. consimile.Habrostroma centrotum occurs in all five areas. This is unusual because Virginia, New York, and Maine are part of the Eastern Americas Realm, and the arctic islands are part of the Old World Realm. Separation of the realms is based on a high percentage of unique genera in each. A breach in the inter-realm barrier is proposed to have existed across the Canadian Shield during the Lochkovian. The nature of the breach is determined to be a shallow-water filter, allowing the passage of a limited number of taxa.

Rare stromatoporoids from the Lower Devonian (Emsian) of Nevada, and their biostratigraphic and paleobiogeographic significance

“…Conclusions drawn here are very similar to those of Stock and Burry-Stock (2020, p. 24, fig. 11), who proposed an Early Devonian (Lochkovian) seaway across the Canadian Shield that allowed the stromatoporoid Habrostroma centrotum (Girty, 1895) to simultaneously inhabit the Eastern Americas Realm (Virginia, New York, Maine) and the Old World Realm (Bathurst and Ellesmere islands, Canadian arctic) in what is now North America.…”

“…It has become clear that stromatoporoids were able to overcome the barrier formed by the Canadian Shield and Transcontinental Arch during the Lochkovian (Stock and Burry-Stock, 2020), and now during the Emsian as well. It is doubtful that stromatoporoids were able to circumnavigate what is now the southwestern end of the Transcontinental Arch, even as planktonic larvae.…”

“…Stock and Burry-Stock (2020, p. 20–24) summarized in detail the faunal realms of the Devonian Period, and how the geographic distribution of stromatoporoids was affected by these paleogeographic constraints. Traditionally, the Devonian world has been divided into three realms: (1) Eastern Americas Realm (EAR), southeastern North America; (2) Old World Realm (OWR), western and northern North America, northwestern Africa, Europe, Asia, and Australia; and (3) Malvinokaffric realm, southern high latitudes (Stock et al, 2015).…”

“…We must ask the question, “How did stromatoporoids manage to breach barriers that were closed to other taxa?” Stock and Burry-Stock (2020, p. 20–22) summarized the ecological characteristics of stromatoporoid-hosting depositional environments: (1) warm water; (2) normal salinity; (3) shallow subtidal depth; (4) medium to high turbulence; (5) firm substrate; and (6) low turbidity. These characteristics do not seem like the type of criteria necessary either for biostratigraphic correlation or inter-realm transport, especially the exclusion of deep water, and the nature of the substrate.…”

An efficient method for estimating vein density ofGlossopterisand its application

“…Hong et al . 2014; Sproat & Zhan 2019; Jacobs & Carlucci 2019; Stock & Burry‐Stock 2020; Bardhan et al . 2021; Conceição et al .…”