Oldest known phosphatic stromatoporoid sponge discovered in south China

International scientists have uncovered the oldest known phosphatic stromatoporoid sponge, dating back approximately 480 million years to the Early Ordovician, in South China.

Stromatoporoid sponges were key reef builders during the Palaeozoic era, playing a crucial role in constructing biological frameworks—similar to the role of modern corals. They were especially important during the middle Paleozoic era (from the late Middle Ordovician to Devonian), a time marked by a major transition from microbial-dominated to skeletal-dominated reef ecosystems. Previously, stromatoporoid reefs were thought to have emerged suddenly in the late Darriwilian period (around 460 million years ago), leading to questions about their origins and early evolutionary history.

Recently, an international research team led by scientists from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences discovered an exceptionally preserved phosphatic stromatoporoid sponge from the Early Ordovician, dating back about 480 million years, in Yuan'an, Yichang, South China. This newly identified stromatoporoid, Lophiostroma leizunia, not only extends the fossil record of stromatoporoid reefs by about 20 million years but also provides valuable insights into the early biomineralization strategies of ancient animals.

South China is renowned for its exceptional fossil preservation and its diverse Early Paleozoic marine ecosystems. Researchers have extensively studied the Ordovician strata in this region, documenting the early diversification of marine life during the Great Ordovician Biodiversification Event (GOBE)—a critical period marked by dramatic increases in marine biodiversity.

Lophiostroma leizunia is unique among all known sponges for constructing its skeleton using fluorapatite, a phosphate mineral. This finding establishes the phylum Porifera (sponges) as the first animal group known to utilize all three principal biominerals: silica, calcium carbonate, and calcium phosphate. This distinctive skeletal composition suggests that early sponges had the genetic capacity to employ diverse biomineralization strategies.

Fossil evidence indicates that Lophiostroma leizunia formed complex reef structures and played a crucial role in framework construction, binding together other reef components, including calcimicrobes, lithistid sponges, Calathium, and echinoderms. These reef ecosystems exhibit remarkable ecological complexity—comparable to those found in later reef systems.

This study enhances our understanding of early reef ecosystems and the evolution of biomineralization across the animal kingdom, providing new insights into how environmental factors influenced biological evolution during this critical period in Earth's history.

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