Stage 3

System (period)	Series	Stage (age)	Lower boundary, Ma
Ordovician	Lower	Tremadocian	485.4±1.9
Cambrian	Furongian	Stage 10	~489.5
		Jiangshanian	~494
		Paibian	~497
	Miaolingian	Guzhangian	~500.5
		Drumian	~504.5
		Wuliuan	~509
	Series 2	Stage 4	~514
		Stage 3	~521
	Terreneuvian	Stage 2	~529
		Fortunian	538.8±0.2
Ediacaran			older
Subdivisions and "golden spikes" according to IUGS as of September 2023

Stage 3 is an unnamed lower stage of the Cambrian Series 2, corresponding to the Stage 3 age of the Series 2 epoch. It lasted from approximately 521 Ma to around 514 Ma (million years ago). It is preceded by the Stage 2 age of the Terreneuvian and is followed by the Stage 4 age of the Series 2. GSSP and naming have not yet been chosen for this stage, and this is one of the most important tasks, since stratigraphers propose to choose the first appearance of trilobites, the iconic animals of the Paleozoic, as a marker of the lower boundary of this subdivision. The earliest megacheirans, radiodonts and vertebrates are also known from this stage.

Definition

The GSSP of Stage 3 has not yet been accepted and there are no sections selected as candidates. Stratigraphers propose the first appearance of trilobites in fossil record as a marker of the lower boundary.

Coincidences with regional stages

Some regional stages overlap partially or completely with Stage 3. From upper to lower:

Siberia:

• Botomian (lower part)
• Atdabanian

North America:

• Dyeran (lower part)
• Montezuman
• Begadean (upper part)

West Avalonia:

• Branchian (lower part)
• Placentian (uppermost)

China:

• Nangaoian

Life during Stage 3 age

About 521 million years ago an important event occurred. Trilobites appeared in the seas of our planet. Similar to modern woodlice, these arthropods inhabited the seas throughout the rest of the Paleozoic, being primarily detritus eaters. They protected themselves from predators with the help of their chitinous armor. The oldest trilobites are known from the regional stages of Siberia (Profallotaspis), Spain (Lunagraulos, Serrania), Morocco (Hupetina, Bigotina, Eofallotaspis) and China (Abadiella).

Fortiforceps fossil specimens

Amplectobelua

Chuandianella

Pectocaris spatiosa

Megadictyon

Haikouichthys

Diverse faunas of this age have been found in Europe and Asia. Palaeoscolecid worms (Cowiella), helcionelloid molluscs (Latouchella, Pelagiella), brachiopods (Eccentrotheca, Lapworthella, Acrothyra, Obolus) and conodonts (Amphigeisina, Hertzina, Prooneotodus) are known from the Atdabanian strata of England. Archaeocyathan sponges (Gordonicyathus, Alataucyathus), helcionellid (Latouchella, Obtusoconus), tommotiids (Camenella, Lapworthella) and Markuelia, a worm-like animal, lived in the sea on the territory of modern Mongolia. Various sponges (Hazelia, Choiaella, Allantospongia, Leptomitus), brachiopods (Heliomedusa, Wufengella, Lingulellotreta, Eoglossa), arthropods and chordates were discovered in Yunnan, China. Some arthropods, such as Fortiforceps, Houcaris, Anomalocaris, Parapeytoia and Amplectobelua, have evolved claws for collecting and holding food. Others, like Chuandianella, Waptia and Pectocaris, have developed broad shells to protect them from large predators. Megadictyon, a lobopodian, searched for food on the seabed. Among chordates, in addition to conodonts, animals appeared that are considered the first fish. These are Haikouichthys and Myllokunmingia that reached about 1 inch in length. Unlike conodonts, they did not have teeth, and they apparently fed on plankton and dead organic matter on the seabed.

External links

• https://paleobiodb.org/classic/displayTimescale?interval=Stage%203