Review of Paleozoic Invertebrate lecture • Major theme of ESCI 102: plate tectonics drives biology • Oceans open and close,changing climate, creating & destroying ecological niches • Paleozoic starts with Cambrian period – Cambrian explosion – appearance of multicelled organisms/Homeobox/hox genes
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Review of Paleozoic Invertebrate lecture Major theme of ESCI 102: plate tectonics drives biology Oceans open and close,changing climate, creating & destroying.
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Review of Paleozoic Invertebrate lecture
• Major theme of ESCI 102: plate tectonics drives biology
• Oceans open and close,changing climate, creating & destroying ecological niches
• Paleozoic starts with Cambrian period– Cambrian explosion– appearance of multicelled
organisms/Homeobox/hox genes
Mass extinctions are followed by adaptive
radiations• Big three Cambrian organisms:
– Trilobites, brachiopods, archaeocyathids• After Cambrian comes Ordovician
– transgression -> adaptive radiation• Ordovician ends with a mass
extinction• Silurian, Devonian
– Ordovician, Devonian extinctions followed by adaptive radiation
The situation was bad as the Permian ended, and then it got
worse.
Tetrapod trackway at Valentia Island Ireland
These fossilized fooprints– 365 million years old – evidence of one of the
earliest four-legged animals on land
Paleozoic Life History — Vertebrates and Plants
Photo courtesy of Ken Higgs, U. College Cork, Ireland
– gill slits (pharyngeal slits)• Openings connecting inside throat to
outside neck
– tail
• The most primitive vertebrates are fish – oldest fish remains are in Upper Cambrian
rocks
• All known Cambrian and Ordovician fossil fish – found in shallow nearshore marine deposits – earliest nonmarine fish remains in Silurian
strata
• suggests saltwater origins
Fish started in saltwater
– fragment of a plate from Anatolepis cf. A. Heintzi , Upper Cambrian marine Deadwood Formation of
Wyoming: a primitive member of the class Agnatha
(jawless fish)
• Fish range from the Late Cambrian to the present
• The oldest and most primitive of the class Agnatha: the ostracoderms, “bony skin”
• These are armored jawless fish that first evolved during the Late Cambrian– reached their zenith during the Silurian and Devonian– and then became extinct
Ostracoderms — “Bony Skinned” Fish
Devonian Seafloor
ostracoderm (Hemicyclaspis)
placoderm (Bothriolepis)
acanthodian (Parexus)
ray-finned fish (Cheirolepis)
• Major evolutionary advantage – jawless ancestors could only feed on detritus– jawed fish could chew food and become active
predators, thus opening many new ecological niches
• The vertebrate jaw is an excellent example of evolutionary opportunism– the jaw probably evolved from the first three
gill arches of jawless fish
Evolution of Jaws
• The fossil remains of the first jawed fish are found in Lower Silurian rocks and belong to the acanthodians:
• large spines• scales covering much of the body• jaws• teeth
• and reduced body armor
Acanthodians
Geologic Ranges of Major Fish Groups
• The other jawed fish that evolved during the Late Silurian were the placoderms, “plate-skinned”
• Placoderms were heavily armored jawed fish – lived in both freshwater and the ocean– like the acanthodians, reached their peak of abundance and
diversity during the Devonian
Other Jawed Fish
Geologic Ranges of Major Fish Groups
• A Late Devonian marine scene from the midcontinent of North America
Late Devonian Marine Scene
• Many fish evolved during the Devonian Period including – the abundant acanthodians– placoderms– ostracoderms– other fish groups
Age of Fish
• Class Chrondrichthyes, – represented today by sharks, rays, and skates, – first evolved during the Middle Devonian
• Cartilaginous fish have never been as numerous nor as
diverse as their cousins, the bony fish, – but they are important members of the marine vertebrate
fauna
Cartilaginous Fish
http://www.iopus.com/iim/demo/slideshow.htm
• Because bony fish are the most varied and numerous of all the fishes – and because the amphibians evolved from
them, – their evolutionary history is particularly
important
• There are two groups of bony fish– the common ray-finned fish – and the less familiar lobe-fined fish
Bony Fish
• Arrangement of fin bones for
(a) a ray-finned fish
(b) a lobe-finned fish– muscles extend
into the fin allowing greater flexibility
Ray-Finned and Lobe-Finned Fish
• Began in freshwater in the Devonian
• predicessors of familiary fish like trout, bass, perch, salmon, and tuna
– rapidly diversified to dominate the Mesozoic and Cenozoic Seas