Ordovician was a stable period but ended by an extiction, caused by drastic temperature changes.

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Sources and more informations :

Constellaria - http://www.ordovicianatlas.org/atlas/...
Dinorthis - http://fossilworks.org/bridge.pl?a=ta...
Rafinesqina - https://www.ordovicianatlas.org/atlas...
Platystrophia - https://www.britannica.com/animal/Pla...
Endoceras - https://www.ordovicianatlas.org/atlas...
Maclurites - https://www.mindat.org/taxon-8139952....
Cyclopyge - https://fossil.fandom.com/wiki/Cyclop...)
Triarthrus - http://fossilworks.org/bridge.pl?a=ta...
Trinucleus - http://fossilworks.org/?a=taxonInfo&t...
Selenopeltis - http://www.trilobites.fr/determinatio...
Arandaspis - http://www.prehistoric-wildlife.com/s...
Astraspis - http://www.prehistoric-wildlife.com/s...
Sacabambaspis - http://www.prehistoric-wildlife.com/s...

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Thumbnail : Beth Zaiken

0:00 Ordovician conditions
1:45 Invertebrates
8:48 Arthropods
13:13 Vertebrates