Agnostida is an order of arthropod which first developed near the end of the Early Cambrian period and thrived during the Middle Cambrian.

Mineralized skeletons of bryozoans first appear in rocks from latest Cambrian period, about, making it the last major phylum to appear in the fossil record.

There are many other comparable Cambrian lagerstätten ; indeed such assemblages are far more common in the Cambrian than in any other period.

All bilaterians are thought to have descended from a common ancestor that appeared early in the Cambrian period, 550 – 600 million years ago, and it has been hypothesized that this common ancestor had the shape of a simple tubeworm with a segmented body.

The first vertebrates appeared over 500 million years ago ( Mya ), during the Cambrian period, and may have resembled the modern hagfish in form.

The Cambrian is the first geological period of the Paleozoic Era, lasting from million years ago ( mya ) ; it is succeeded by the Ordovician.

The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's Cambrian rocks are best exposed.

Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralised – hence readily fossilised – organisms became common.

The Ediacaran Period, named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon.

Lagerstätten span geological time from the Cambrian period to the present.

This set the beginning of the Cambrian period.

In bilaterian animals, which make up the great majority of existing species, the nervous system has a common structure that originated early in the Cambrian period, over 500 million years ago.

Lapworth, recognizing that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian periods, realized that they should be placed in a period of their own.

Life continued to flourish during the Ordovician as it did in the Cambrian, although the end of the period was marked by a significant mass extinction.

The Precambrian is so named because it precedes the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the classical name for Wales, where rocks from this age were first studied.

( 542 Ma is the beginning of the Cambrian Period, the earliest period of the Paleozoic Era.

Its name derives from the Ancient Greek words and, meaning visible life, since it was once believed that life began in the Cambrian, the first period of this eon.

He named the sequences for a Celtic tribe of Wales, the Silures, inspired by his friend Adam Sedgwick, who had named the period of his study the Cambrian, the Latin name for Wales.

Fossilised animal embryos are known from the Precambrian, and are found in great numbers during the Cambrian period.

Aside from the hard-to-classify Arkarua ( a Precambrian animal with Echinoderm-like pentamerous radial symmetry ), the first definitive members of the phylum appeared near the start of the Cambrian period.

It follows the Cambrian Period and is followed by the Silurian Period.

More sharp twists and turns in the forestry and through the village of Ganllwyd brings the road up onto the high plateau of the Cambrian dome where the road follows the ancient track of Sarn Helen Roman road passing the redundant nuclear power station at Trawsfynydd.

The GSSP of the upper boundary of the Ediacaran is the lower boundary of the Cambrian on the SE coast of Newfoundland approved by the International Commission on Stratigraphy as a preferred alternative to the base of the Tommotian Stage in Siberia which was selected on the basis of the ichnofossils Treptichnus pedum.

The Cloudinids, an early metazoan family containing the genus Cloudina, lived in the late Ediacaran period and became extinct at the base of the Cambrian.

The extreme cooling of the global climate around 700 million years ago ( the so called Snowball Earth of the Cryogenian period ) and the rapid evolution of primitive life during the subsequent Ediacaran and Cambrian periods are often thought to have been triggered by the breaking up of Rodinia.

The first group of cratons would eventually, around 550 million years ago ( on the boundary between the Ediacaran and Cambrian ), fuse again with Amazonia, West Africa and the Rio de la Plata craton.

Shu ( 2006 ) recently described Stromatoveris psygmoglena as a possible bilateran missing link between Ediacaran fronds and Cambrian ctenophores.

Some Precambrian ( Ediacaran ) organisms produced tough but non-mineralized outer shells, while others, such as Cloudina, had a calcified exoskeleton, but mineralized skeletons did not become common until the beginning of the Cambrian period, with the rise of the " small shelly fauna ".

The first bona fide radula dates to the Early Cambrian, although trace fossils from the earlier Ediacaran have been suggested to have been made by the radula of the organism Kimberella.

The formation is of particular interest because it appears to cover the boundary between the problematic organisms of the Ediacaran geological period and the more familiar fauna of the Cambrian explosion of lifeforms whose descendents are recognizable.

Taken as a whole, the Doushantuo Formation ranges from about 635 Ma ( million years ) ago at its base to about 551 Ma at its top, predating by perhaps five Ma the earliest of the ' classical ' Ediacaran faunas from Mistaken Point on the Avalon peninsula of Newfoundland, and recording conditions a good forty to fifty million years before the Cambrian explosion.

They cite the Cambrian explosion — the appearance of abundant fossils in the upper Ediacaran ( Vendian ) Period and lower Cambrian Period — as the pre-Flood / Flood boundary, the presence in such sediments of fossils that do not occur later in the geological record as part of a pre – flood biota that perished and the absence of fossilized organisms that appear later, such as angiosperms and mammals, as due to erosion of sediments deposited by the flood as waters receded off the land.

Skania is a Cambrian fossil arthropod that may be related to the Ediacaran organism Parvancorina, and bears a strong, albeit superficial resemblance to the Vendiamorphans Vendia, Praecambridium and Onega.

It is in diameter and the age is estimated to be 550 ± 100 million years ( Ediacaran or Cambrian ).

The age of the impact structure is estimated to be about 543 ± 12 Ma ( million years ago ), at the boundary between the Ediacaran and Cambrian periods.

Rangeomorphs are a key part of the Ediacaran biota which survived about 30 million years, until the base of the Cambrian.

Owing to the complete absence of mountain building and glaciation since the Permian ( in many areas since the Cambrian ) ages, the outback is extremely rich in iron, aluminium, manganese and uranium ores, and also contains major deposits of gold, nickel, iron, lead and zinc ores.

At ( Middle Cambrian ) old it is one of the earliest fossil beds containing the imprints of soft-parts.

This is mainly due to the limited extent of burrowing activity ; as such bioturbation became more prevalent throughout the Cambrian, environments capable of preserving organisms ' soft parts became much rarer.

The Cambrian is unique in its unusually high proportion of lagerstätten.

The base of the Cambrian is defined on a complex assemblage of trace fossils known as the Treptichnus pedum assemblage.

Nevertheless, the usage of Treptichnus pedum, a reference ichnofossil for the lower boundary of the Cambrian, for the stratigraphic detection of this boundary is always risky because of occurrence of very similar trace fossils belonging to the Treptichnids group well below the T. pedum in Namibia, Spain and Newfoundland, and possibly, in the western USA.

The Cambrian is divided into four epochs or series and ten ages or stages.

In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian ( Caerfai or Waucoban, mya ), Middle Cambrian ( St Davids or Albertian, mya ) and Furongian ( mya ; also known as Late Cambrian, Merioneth or Croixan ).

The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance:

As to the Treptichnus pedum, a reference ichnofossil for the lower boundary of the Cambrian, its usage for the stratigraphic detection of this boundary is always risky because of the occurrence of very similar trace fossils belonging to the Treptichnids group well below the T. pedum in Namibia, Spain and Newfoundland, and possibly, in the western United States.

The age of the top is the same as the widely recognised age for the base of the Cambrian Period 542 ± 0. 3 Mya ( million years ago ).< ref name = Amthor2003 >

They bear little resemblance to modern lifeforms, and their relationship even with the later lifeforms of the Cambrian explosion is difficult to interpret.

An example of modern paleontological progress is the application of synchrotron X-ray tomographic techniques to early Cambrian bilaterian embryonic microfossils that has recently yielded new insights of metazoan evolution at its earliest stages.

A continuous section is available from beds that are clearly Precambrian into beds that are clearly Cambrian.