Ediacarin (Vendian) (635-541 mya) - Last part of Proterozoic.

Large multicellular organisms appear.
These have quilt-like structure and are hard to relate to modern animals.

Examples: (Here are some Pictures)

• Tribrachidium
• Dikensonia
• Spriggina

Trace Fossils - Evidence of animal activity, such as trackways or burrows.

Trace fossils of burrowing worm-like organisms appear in the Ediacaran.
     Become more numerous and structured over time.

These are a more likely candidate for the ancestors of modern phyla, many of which started out with a worm like body plan.

Near the end of the Ediacarin, bits of mineralized skeletons first appear.
Ediacarin organisms disappear.
"Small shelly" fossils appear

The small shelly fossils include some coiled shells and a number of forms that look like plates or spicules.
     Some, such as Cloudina, show evidence of predation.

The appearance of large predators (roughly as large as their prey) is significant because two important ways that prey evolve to escape predators are:
1)Get big
2)Get a hard covering or armor.

The significance of this for our interpreting the fossil record is that large organisms with hard shells, spines or skeletons fossilize much better than do small, soft organisms.

This may partially explain the sudden appearance of many fossil groups during the Cambrian.

Kimberella
This was a widespread organism in the late Ediacarin (~555 mya).
It's body plan resembles that of early Molluscs, and it is sometimes found associated with trackways and scratches in the underlying microbial mat - indicating movement and feeding.

The Phanerozoic

Timeline

Know the periods of the Phanerozoic and their dates

Paleozoic Era : 541-252 mya

Periods of the Paleozoic

Cambrian: 541-485 mya

"Cambrian explosion"
Rapid appearance, in the fossil record, of clearly modern metazoan (multicellular animal) phyla.
All of the highly fossilizable phyla are represented.
   Many independent appearances of hard parts such as shells and exoskeletons.

Molluscs, Arthropods, Chordates, Echinoderms, Brachiopods, Annelids, etc.

Metazoan Phylogeny

Using a phylogeny (derived from genomic analysis of modern taxa), we can even infer the existence in the Cambrian of some groups that do not fossilize well (and thus have a poor fossil record from any time).
Reasoning: When we observe two different groups from a particular time, we know that the common ancestor of those groups must predate that time, as must groups that split off prior to this common ancestor.

Example: Rotifers are a group of very small organisms with a very poor fossil record.
Rotifers are related to Molluscs and Annelids, but we have very good phylogenetic evidence that rotifers branched off before the common ancestor of molluscs and annelids.
Since we see clear fossils of both molluscs and annelids in the Cambrian, we can infer that the line that leads to modern rotifers must also have already branched off by that time.

First Jawless Fish appear late in the Cambrian.

Ordovician: 485-444

Further diversification of marine metazoans.

Bryophytes (mosses) are first terrestrial non-vascular plants.
Evidence is the presence of bryophyte spores.

Mass extinction at end of Ordovician

Silurian: 444-419

Vascular plants appear on land

terrestrial arthropods (Myrapods, similar to millipedes)

Jawed fish

Devonian: 419-359

Great diversification of jawed fish

Earliest known fossils of Insects (wingless)

Terrestrial Arachnids.

First Amphibians.

Also on land: First seed plants and large trees

Carboniferous: 359-299

First terrestrial Annelids and Molluscs.

Coal swamps

First winged Insect fossils
     This was the first colonization of the air.

Amniotes appear in late Carboniferous
     More independent of water than amphibians

Permian: 299-252

Diversification of Amniotes

First Gymnosperms

Largest mass extinction at end of Permian

This is also the end of the Paleozoic Era.

Mesozoic Era : 252-66 mya

Periods of the Mesozoic

Triassic: 252-201

Mammals appear
Dinosaurs appear

Note that these span the modern Amniotes

Amniote Phylogeny

(Note that though the exact position of Turtles is still contentious, they are definitely outside of the Crocodile-Dinosaur clade.)

Mass extinction at the end of the Triassic

Jurassic: 201-145

Dinosaurs diversify, Mammals survive.

Earliest Bird fossils (Archaeopteryx)

Angiosperms (flowering plants) appear in the fossil record.

Cretaceous: 145-66

Insects start to diversify greatly in the late Cretaceous.
     Perhaps influenced by coevolution with Angiosperms

Mammals begin to diversify.

Ends with the second largest mass extinction.

This is also the end of the Mesozoic Era

Cenozoic Era: 66-now

Periods of the Cenozoic

Paleogene: 66-23

Major diversification of Mammals.
     Note that it has been quite a while since they first appeared.

First grasslands appear around 30 mya.

Neogene: 23-2.6

Diversification of Apes

Common ancestor of Humans and Chimps (our closest living relatives) at ~6mya

North and South America link up around 3 mya.

Quaternary: 2.6-now

Genus Homo

Recent ice ages Jul 8, 2021