Agnostida are an order of extinct arthropods which have classically been seen as a group of highly modified trilobites, though some recent research has doubted this placement. Regardless, they appear to be close relatives as part of the Artiopoda. They are present in the Lower Cambrian fossil record along with trilobites from the Redlichiida, Corynexochida, and Ptychopariida orders, and were highly diverse throughout the Cambrian. Agnostidan diversity severely declined during the Cambrian-Ordovician transition, and the last agnostidans went extinct in the Late Ordovician.
Archaeocyatha is a taxon of extinct, sessile, reef-building marine sponges that lived in warm tropical and subtropical waters during the Cambrian Period. It is believed that the centre of the Archaeocyatha origin is now located in East Siberia, where they are first known from the beginning of the Tommotian Age of the Cambrian, 525 million years ago (mya). In other regions of the world, they appeared much later, during the Atdabanian, and quickly diversified into over a hundred families.
The Late Ordovician mass extinction (LOME), sometimes known as the end-Ordovician mass extinction or the Ordovician-Silurian extinction, is the first of the "big five" major mass extinction events in Earth's history, occurring roughly 445 million years ago (Ma). It is often considered to be the second-largest known extinction event just behind the end-Permian mass extinction, in terms of the percentage of genera that became extinct. Extinction was global during this interval, eliminating 49–60% of marine genera and nearly 85% of marine species. Under most tabulations, only the Permian-Triassic mass extinction exceeds the Late Ordovician mass extinction in biodiversity loss. The extinction event abruptly affected all major taxonomic groups and caused the disappearance of one third of all brachiopod and bryozoan families, as well as numerous groups of conodonts, trilobites, echinoderms, corals, bivalves, and graptolites. Despite its taxonomic severity, the Late Ordovician mass extinction did not produce major changes to ecosystem structures compared to other mass extinctions, nor did it lead to any particular morphological innovations. Diversity gradually recovered to pre-extinction levels over the first 5 million years of the Silurian period.
Stromatoporoidea is an extinct clade of sea sponges common in the fossil record from the Middle Ordovician to the Late Devonian. They can be characterized by their densely layered calcite skeletons lacking spicules. Stromatoporoids were among the most abundant and important reef-builders of their time, living close together in flat biostromes or elevated bioherms on soft tropical carbonate platforms.
Hexasterophora are a subclass of glass sponges in the class Hexactinellida. Most living hexasterophorans can be divided into three orders: Lyssacinosida, Lychniscosida, and Sceptrulophora. Like other glass sponges, hexasterophorans have skeletons composed of overlapping six-rayed spicules. In addition, they can be characterized by the presence of hexasters, a type of microsclere with six rays unfurling into multi-branched structures.
Vauxia is an extinct genus of demosponge that had a distinctive branching mode of growth. Each branch consisted of a network of strands. Vauxia also had a skeleton of spongin common to modern day sponges. Much like Choia and other sponges, Vauxia fed by extracting nutrients from the water.
Choia is a genus of extinct demosponge ranging from the Cambrian until the Lower Ordovician periods. Fossils of Choia have been found in the Burgess Shale in British Columbia; the Maotianshan shales of China; the Wheeler Shale in Utah; and the Lower Ordovician Fezouata formation. It was first described in 1920 by Charles Doolittle Walcott.
The extinct Solenoporaceae have traditionally been interpreted as a group of red algae ancestral to the Corallinales.
Anthaspidellidae is an extinct family of sponges whose dendroclone spicules form ladder-like trabs.
Halichondrites, sometimes mis-spelt Halicondrites is an extinct genus of sea sponge known from the Middle Cambrian Burgess Shale. 7 specimens of Halichondrites are known from the Greater Phyllopod bed, where they comprise < 0.1% of the community.
Hamptonia is an extinct genus of sea sponge known from the Middle Cambrian Burgess Shale and the Lower Ordovician Fezouata formation. It was first described in 1920 by Charles Doolittle Walcott. 48 specimens of Hamptonia are known from the Greater Phyllopod bed, where they comprise < 0.1% of the community.
Pirania is an extinct genus of sea sponge known from the Middle Cambrian Burgess Shale and the Ordovician Fezouata formation. It is named after Mount St. Piran, a mountain situated in the Bow River Valley in Banff National Park, Alberta. It was first described in 1920 by Charles Doolittle Walcott. 198 specimens of Pirania are known from the Greater Phyllopod bed, where they comprise 0.38% of the community.
Choiaella is an extinct genus of sea sponge ranging from the Chengjiang lagerstatten until the Lower Silurian.
Hazeliidae is an extinct family of spicular Cambrian sea sponges known from the Burgess Shale, the Marjum Formation of Utah, and possibly Chengjiang. It was described by Charles Walcott in 1920.
Reticulosa is an extinct order of sea sponges in the class Hexactinellida and the subclass Amphidiscophora. Reticulosans were diverse in shape and size, similar to their modern relatives, the amphidiscosidans. Some were smooth and attached to a surface at a flat point, others were polyhedral or ornamented with nodes, many were covered in bristles, and a few were even suspended above the seabed by a rope-like anchor of braided glass spicules.
The geological history of North America comprises the history of geological occurrences and emergence of life in North America during the interval of time spanning from the formation of the Earth through to the emergence of humanity and the start of prehistory. At the start of the Paleozoic Era, what is now "North" America was actually in the Southern Hemisphere. Marine life flourished in the country's many seas, although terrestrial life had not yet evolved. During the latter part of the Paleozoic, seas were largely replaced by swamps home to amphibians and early reptiles. When the continents had assembled into Pangaea, drier conditions prevailed. The evolutionary precursors to mammals dominated the country until a mass extinction event ended their reign.
Variabiloconus is an extinct genus of conodonts.
Histiodella is an extinct genus of conodonts.
Eodictyonella is a genus of rhynchonelliform brachiopods belonging to the extinct class Chileata. It is characterised by a non-strophic shell covered by a net-like ornament. Like in most chileates, the perforation in the umbonal region of the ventral valve is covered by a colleplax. Eodictyonella is known from the Ordovician to the Lower Devonian.
Calathium is an extinct genus of organism found in marine beds of Ordovician age. Its classification is enigmatic: It has long been placed among the receptaculites, but it has also been described as a quasi-sponge, possibly akin to the archeocyathids or other hypercalcified sponge. The chief difference from archaeocyathids is that their walls were connected by rods rather than septae.
