After the Proterozoic and during the Phanerozoic Eon, in The Paleozoic Era: the EARLY CAMBRIAN PERIOD; Cambrian Explosion; Cambrian Fauna

Cambrian Fauna: EDRIOASTEROIDS; HELICOPLACOIDS; EOCRINOIDS

*Eocrinoids* share similarities to modern crinoids Instead of a holdfast (root) for anchoring in the seafloor, this echinoderm had a blunt stem *Helicoplacoids* also lived as sediment stickers with their blunt stem stuck into the seafloor *Helicoplacoids* have no close modern relatives Early *edrioasteroids* have a broad stem at their base that they used as sediment stickers as well These fossils also have no modern relatives *EDRIOASTEROIDS* *SEDIMENT STICKER LIFESTYLE* As microbial mats vanish, edrioasteroids became encrusters and eocrinoids developed holdfasts Helicoplacoids don't adapt and thus go extinct

Cambrian explosion

......... marks the diversification of animals following their appearance as fossils Most major groups of animals show up quickly The emergence of animals during the .............. is due to the emergence of shells A shell is necessary for preservation as a fossil

Evolutionary Faunas: Cambrian Fauna, and examples of Cambrian Fauna: EDRIOASTEROIDS; HELICOPLACOIDS; EOCRINOIDS trilobites

Over the course of the Phanerozoic Eon, there have been recognized three Evolutionary Faunas Each new fauna replaces the old fauna in time Each of these Evolutionary Faunas is defined by the dominance of a specific group of organisms Each was dominant during a different time The first Evolutionary Fauna is the ...... whose fossils dominate in the Cambrian This early fauna is one that is very short‐lived Echinoderms emerge in the Cambrian, and most look very different from those of today These echinoderms were sediment stickers eg. *EDRIOASTEROIDS; HELICOPLACOIDS; EOCRINOIDS*

Proterozoic fossils

Proterozoic events recorded in Death Valley: layer1- SNOWBALL EARTH ICE AGE, layer2- DIVERSE MULTICELLUAR LIFE of EDIACARAN ORGANISMS, layer3- FIRST SHELLED ANIMAL: CLOUDINA The late Proterozoic Stirling Quartzite in DV preserves small impressions of a tube‐shaped animal The impressions are of the layered shell Cloudina that belongs to the first shelled animal ever Cloudina marks the emergence of shells on Earth Cloudina is considered to be a sediment sticker The animal (its shell) would have sat upright, embedded within a seafloor microbial mat During the Proterozoic, aside from small horizontal burrows, bioturbation was nonexistent No vertical mixing was taking place in the ocean

Precambrian‐Cambrian boundary and the importance of Bioturbation by Treptichnus pedum

The Precambrian‐Cambrian boundary is marked by the first occurrence of Treptichnus pedum Treptichnus pedum is a specific trace fossil The Cambrian marks the first occurrence of vertical burrowing and complex behavior Treptichnus pedum is the first trace fossil to incorporate a significant vertical component It records several probes deep into the seafloor Bioturbation refers to the mixing of sediment through the burrowing activity of animals Bioturbation destroys sedimentary structures Bioturbation is measured using a semi‐ quantitative scale called the Ichnofabric Index (ii) Step into the Cambrian, when more animals arrive, and bioturbation increases significantly ii rises from a 1 to a 3 during the Cambrian Past the Cambrian and into the Ordovician, bioturbation would increase further to a 5 These levels persist for much of later history The Cambrian marks a transition from microbial mat‐covered seafloors to bioturbated seafloors Bioturbation and grazing from animals begins to consume and destroy existing microbial mats By the end of the Cambrian, mats are gone These effects can be seen by examining the record of stromatolite diversity through time When animals show up, stromatolites decline

Cambrian sponges:

The earliest recognizable ............. fossils belong to a group called the *archaeocyathans* They share many similarities with sponges Unlike modern .............. that have one wall, *archaeocyathans* are notable for having two *archaeocyathans* have an inner and outer wall *archaeocyathans* are also notable for being the first animals ever to construct reefs They built reefs long before corals ever did These early *archaeocyathans* built isolated reefs that stuck straight up from the seafloor These were the first animal reefs ever built Fossils within reef limestone are still preserved in their life position and have not been moved All of the *archaeocyathans* found within the reef are in their life position, sticking straight up By the Middle Cambrian, the *archaeocyathans* decline severely and eventually go extinct

Proof of Fauna before Shells and Bones

The emergence of animals during the Cambrian explosion is due to the emergence of shells A shell is necessary for preservation as a fossil Animals surely existed before shells first appear It is common to find tracks from trilobites before their shelled fossils show up in rocks Tracks from snail feeding predate snail shells Snails use a jagged tongue called a radula to scrape algae off of rocks and sediment grains Snail‐like animals certainly left radula scratch marks on the seafloor during the Proterozoic These scratch marks predate snail shells Radula scratch marks from the late Proterozoic predate Cambrian‐age snail shell fossils

Cambrian arthropods:

first recognizable fossil ...... of the Cambrian Period are the *trilobite* Trilobites are .................. most closely related to *chelicerates* like the horseshoe crab They share a similar morphology and lifestyle The name *trilobite* comes from the fact that their body contains three lobes They also contain a head, thorax, and tail *chelicerates* are .................. that have fangs, rather than jaws, often used for eating prey Spiders and scorpions are also *chelicerates* Animals surely existed before shells first appear It is common to find tracks from *trilobite* before their shelled fossils show up in rocks