| Sphenothallus | |
|---|---|
 | |
| Sphenothallus holdfast from the Kope Formation (Upper Ordovician), Gunpowder Creek, Kentucky. | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Cnidaria |
| Class: | Staurozoa |
| Order: | † Conulatae |
| Clade: | † Conulariida |
| Genus: | † Sphenothallus Hall, 1847 |
Sphenothallus is a problematic extinct genus lately attributed to the conulariids. It was widespread in shallow marine environments during the Paleozoic. [2] [4]
Sphenothallus is represented in the Cambrian period in the Kaili biota and the Mount Stephen trilobite beds, where it co-occurs with the similar organisms Cambrorhythium and Byronia . [1] It is known in younger strata in Canada and the US, surviving at least until the Mississippian. [3]
Sphenothallus lived in groups as an opportunist in environments from hardgrounds to soft mud, even if depleted in oxygen. [3] It probably dispersed via larvae. [3]
Conodonts are extinct agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements found in isolation and now called conodont elements. Knowledge about soft tissues remains limited. The animals are also called Conodontophora to avoid ambiguity.
The halkieriids are a group of fossil organisms from the Lower to Middle Cambrian. Their eponymous genus is Halkieria, which has been found on almost every continent in Lower to Mid Cambrian deposits, forming a large component of the small shelly fossil assemblages. The best known species is Halkieria evangelista, from the North Greenland Sirius Passet Lagerstätte, in which complete specimens were collected on an expedition in 1989. The fossils were described by Simon Conway Morris and John Peel in a short paper in 1990 in the journal Nature. Later a more thorough description was undertaken in 1995 in the journal Philosophical Transactions of the Royal Society of London and wider evolutionary implications were posed.
Octocorallia is a subclass of Anthozoa comprising around 3,000 species of water-based organisms formed of colonial polyps with 8-fold symmetry. It includes the blue coral, soft corals, sea pens, and gorgonians within three orders: Alcyonacea, Helioporacea, and Pennatulacea. These organisms have an internal skeleton secreted by mesoglea and polyps with eight tentacles and eight mesentaries. As with all Cnidarians these organisms have a complex life cycle including a motile phase when they are considered plankton and later characteristic sessile phase.
Conulariida is a poorly understood fossil group that has possible affinity with the Cnidaria. Their exact position as a taxon of extinct medusozoan cnidarians is highly speculative. Members of the Conulariida are commonly referred to as conulariids and appear in the fossil record from the mid or late Cambrian Period until the Triassic.
Leiosphaeridia is a form-genus of acritarchs proposed by Eisenack in 1958. The grouping was refined to represent a more natural group by Jankauskas.
Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor. A hardground is essentially, then, a lithified seafloor. Ancient hardgrounds are found in limestone sequences and distinguished from later-lithified sediments by evidence of exposure to normal marine waters. This evidence can consist of encrusting marine organisms, borings of organisms produced through bioerosion, early marine calcite cements, or extensive surfaces mineralized by iron oxides or calcium phosphates. Modern hardgrounds are usually detected by sounding in shallow water or through remote sensing techniques like side-scan radar.
Euthycarcinoidea are an enigmatic group of extinct possibly amphibious arthropods that ranged from Cambrian to Triassic times. Fossils are known from Europe, North America, Argentina, Australia and Antarctica.
The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian Period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the late Ediacaran and early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span.
Matthevia is a genus of Cambrian molluscs, perhaps related to the chitons. It consists of repeated monoplacophoran-like shells; according to one hypothesis, chitons arose when these tall shells began to overlap over the generations. The tall element of the shell was retained and forms the tips of modern chiton plates. There are distinct head, 'centre', and tail valves, which occur approximately in the ratio 1:5:1 — suggesting a seven-plated configuration.
Robustum nodum is the one species of a problematic genus of Ordovician hemithecellid mollusc proposed by Stinchcomb and Darrough in 1995. Its similarities to Matthevia were outlined by Vendrasco & Runnegar.
The extinct Solenoporaceae have traditionally been interpreted as a group of red algae ancestral to the Corallinales.
A trab is structural element within a sponge formed by the fusion of dendroclones.
Anthaspidellidae is an extinct family of sponges whose dendroclone spicules form ladder-like trabs.
Cambrorhytium is an enigmatic fossil genus known from the Latham Shale (California), and the Chengjiang (China) and Burgess Shale lagerstätte. 350 specimens of Cambrorhytium are known from the Greater Phyllopod bed, where they comprise 0.7% of the community.
Eiffelia is an extinct genus of sponges known from the Middle Cambrian Burgess Shale as well as several Early Cambrian small shelly fossil deposits. It is named after Eiffel Peak, which was itself named after the Eiffel Tower. It was first described in 1920 by Charles Doolittle Walcott. It belongs in the Hexactinellid stem group. 60 specimens of Eiffelia are known from the Greater Phyllopod bed, where they comprise 0.11% of the community.
Trilobites are used as index fossils to subdivide the Cambrian period. Assemblages of trilobites define trilobite zones. The Olenellus-zone has traditionally marked the top of the Lower Cambrian, and is followed by the Eokochaspis zone.
Sachites is an extinct genus of halkeriid that is only known from fossilised spiny sclerites; many Sachites specimens are now referred to as other halkieriid taxa. Although believed to be related to the halkieriids, a chancelloriid affinity has more recently been proposed.
Byronia is a genus of theca-bearing cnidarians with a close affinity to the coronatid scyphozoans.
Achiasterella is a genus of scleritophoran known from the Burgess Shale and earlier (Branchian) deposits, and originally described as Chancelloria by Walcott. The species may represent form taxa rather than true species.
Halysis is a genus of red alga thought to fall in the coralline stem group. It has only been recovered in thin sections, and thus is only known in two dimensions; however, an interpretation as a sheet of cells rather than a sheet of tubes or a single row of cells is the most plausible.