Ordovician '', a large column-shaped aulaceratid from Late Ordovician Canada. The earliest reported labechiid species are from the Early Ordovician of
South China:
Lophiostroma leizunia (late
Tremadocian) During the Darriwilian, 4 genera occur in the
Chazy Group of eastern North America, 9 in the
Machiakou Formation of
North China, and several others are dispersed among Russia,
Kazakhstan,
Korea, and
Malaysia. Most specialists agree that the ancestral labechiid was a member of the family
Rosenellidae, but disagreement persists over which genus serves as the ancestral form. Studies focusing on North America and China generally consider the widespread
Pseudostylodictyon Labechiids as a whole may be descended from non-stromatoporoid sponges in the order
Pulchrilaminida. In the
Sandbian stage of the Late Ordovician, labechiids spread to regions equivalent to
Scotland and Australia, and some former Chinese
endemics (such as the tree-shaped
aulaceratids) populated
Laurentia (North America) for the first time. In any case, Devonian labechiids never managed to repopulate southeast
Laurussia (eastern North America) or high-latitude environments at any time during the period. Unlike other stromatoporoids, labechiids were not adversely affected by the
Kellwasser event (Late Devonian mass extinction) at the end of the Frasnian (~372 Ma). Instead, they experienced a diversification in the
Famennian stage, reacquiring a level of diversity and dominance in their niche not experienced since the Ordovician. Most new genera arose from the families
Stylostromatidae and
Platiferostromatidae, which helped to form dense reef habitats alongside the older relict forms. The labechiid resurgence was strongest in shallow water and the
Eastern Hemisphere. Despite being reinvigorated after the Kellwasser event, labechiids and their reef ecosystems presumably did not survive the
Hangenberg event (~359 Ma), a second mass extinction which marked the end of the Famennian stage and Devonian period. This extinction is generally considered absolute, but several possible exceptions have been reported to imply post-Devonian survival:
Labechia carbonaria (from the
Viséan stage of
Carboniferous England) and
Lophiostroma boletiformis (from
Triassic rocks of the
Pamir Mountains). These discontinuous reports pose the same set of questions applied to Early and Middle Devonian occurrences. Labechiid-like fossils are abundant in early
Pennsylvanian (
Bashkirian) reef deposits of the
Akiyoshi Limestone Group in Japan, representing a
Panthalassan seamount. == References ==