Creatures of the early Paleozoic

This list briefly describes the creatures appeared (and not necessarily when they disappeared, if they did). Keep in mind that all of the creatures listed are marine, and most are soft-bodied invertebrates. Of course, this list doesn't even come close to covering all the Paleozoic creatures, just the ones I found worth mentioning -- if you think I missed one, let me know in the comments! Click on the images to enlarge; hover to see photo credit in alt-text (many are from Nobu Tamura).


The Cambrian, which lasted 542 - 485 million years ago, saw O2 levels of 12.5% (versus 21% today), temperatures averaging 7°C warmer, and sea levels 30 - 90 m higher. The so-called "Cambrian Explosion" characterized this period, with an astounding variety of creatures appearing; however, the stage for life's rapid advancement (inasmuch some 70 million years can be called "rapid") had already been set in the Proterozoic, as suggested by the imprints left by soft-bodied Ediacaran fauna (see this photo). Watch the first eight minutes of this video to experience life in Cambrian oceans.

Spongesone of the earliest "animals" to appear, sponges seem boring, but I explain that they are actually pretty awesome
Anomalocarissegmented, armored, dorsoventrally-flattened predator up to 2 m long with two large eyes and two feeding appendages protruding from the mouth; related to the ancestor of arthopods
Opabinia7 cm long dorsoventrally-flattened stem-arthropod with five stalked eyes and a proboscis
Hallucigenia3.5 cm long spiky ancestor of velvet worms
Wiwaxia5 cm long slug-like creature with armored plates and spikes on the top of its body
Pikaia5 cm eel-like laterally-flattened creature with muscle segments; related to the ancestor of vertebrates
Haikouichthys2.5 cm fish-like chordate
Halkieriids5-cm long, armored, slug-like creature with a "shell" on each end; possesses features of arthopods, brachiopods, and molluscs


The Ordovician, which lasted 485 - 443 million years ago, saw O2 levels of 13.5% (versus 21% today), temperatures averaging 2°C warmer, and sea levels 140 - 220 m higher. During this period, cephalopods became awesome, the first jawed fish appeared, and plants crept onto land. An extinction related to glaciation marked the end of this period. Watch this video to experience life in Ordovician oceans.

Horseshoe crabsthis familiar beach-going arthropod and distant cousin of spiders appeared 540 million years ago and has been going strong ever since (they come on land to lay eggs); in recent times, their unique blood has helped study medicine
extinct at the end of the Paleozoic
Agnostida: small (5 mm), no eyes, head (cephalon) and tail (pygidium) equal in size, few thoracic segmentsPolymerida: the quintessential trilobite; larger (up to 0.7 m), large eyes, distinct cephalon, several thoracic segments
CoralRugose: bilateral, solitaryTabulate: radial, colonial
Brachiopodsan abundant reef-building phylum in the Paleozoic with a few extant species today; superficially resemble bivalves but internally, have a different setup and feeding mechanisms, and externally, different symmetry
Cephalopodsearly cephalopods had straight shells, with evolution would ultimately shaped into the curled, chambered shells of nautiloids and ammonites
Crinoidsthe first echinoderms, a filter-feeding animal resembling a pant; "forests" of crinoids existed in the Paleozoic, evidenced by their abundance in ancient limestones (encrinites), which contain crinoid segments (columnals)


The Silurian, which lasted 443 - 419 million years ago, saw O2 levels of 14% (versus 21% today), temperatures averaging 3°C warmer, and sea levels 180 m higher. The first bony fish appeared, but the day of the fish is yet to come. Moss forests spring up on land followed by the first vascular plants--and perhaps encouraged by this new food source, millipedes, shortly followed by arachnids, became the first creatures ever to invade land! Watch from minutes 7:40-18:40 in this video to experience life in Silurian seas.

Eurypteridscorpion-like predators with pincers and the largest arthropods ever discovered at a whopping 2.5 m long
Stromatoporidsimportant but poorly-undestood Silurian reef-builder with similarities to both sponges and corals
Bryozoanssuperficially and behaviorally similar to coral, but more complex (with organs) and in their own phylum, these are colonial calcifiers (and made part of Florida!)


The Devonian, which lasted 443 - 419 million years ago, saw O2 levels of 14% (versus 21% today), temperatures averaging 3°C warmer, and sea levels 180 m higher. Lots happened during the Devonian! Known as the Age of the Fish, amazing and varied fish, including bus-sized armored ones, roamed the seas. The early tetrapods took the first steps onto land (although the arthropods had beat them to it). Plants extensively colonized land during this time, and actually caused an extinction! I'll cover this period and all of its excitement in a later post.

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