Urochordate larva free swimming with a notochord, but as an adult it morphs into a sessile sponge like form.
Cephalochordate Amphioxus has a notochord with V-shaped body muscles, a primitive brain at the anterior end and is free swimming
Jawless fish (agnathids) develop from the Ordovician through the Devonian in three groups: Heterostracans- headshields with eyes on sides Osteostracans- headshields with eyes atop and lateral fins Furcacaudiformes- (forktails) GOKWTA
The Ostracoderm Astrapis from the Ordovician of Colorado. Jawless, lacked an internal bony skeleton and sported bony armor and a heavy headshield, eyes on side.
The jawless Heterostracan Anglaspis heavily armored, lacked jaws with a crude ventral mouth, eyes on side of skull Silurian and Devonian
The Devonian Heterostracan Pteraspis with typical heavily plated headshield but flexible trunk and tail, lateral eyes.
The configuration of gills in early jawless fish was simplicity itself with water taken in at the mouth and passing out through several gill slits shown in black. Between each gill slit was a thin strip of bone, the gill arch (in white) that supported the gill. …….To adapt a simple jaw required only the development of a crude hinge on the first gill arch.
Reconstruction of the gill structure of the Heterostracan Amphiaspid closely resembles an automobile manifold structure
Gill structure and function on most living fish are remarkably similar regardless of the taxonomy with plates mounted on a rigid axis and two pumps; one for blood and one for water (In a similar fashion a water cooled engine requires a water pump and a fan)
The Osteostracan cephalaspid Hemicyclaspis had the typical armored headshield of a jawless fish but featured paired fins, a flexible tail for propulsion and eyes atop skull (Late Silurian to Devonian)
Unlike the Heterostracans the Osteostracans as Hemicyclaspis shown here had small eyes set very close together atop their heads.
Only discovered in 1998 the early Devonian Furcacudiformes or “forktails” don’t conform to the other jawless fish (heterostracans & osteostracans) and seem to be an entriely new group of agnathids
Fish with jaws (the Gnathostomes)
DEVONIAN FISH Fish first appear in the Ordovician period but the number and variety of fish explodes in the Devonian so the name “age of fish” is highly apropos for this period
The Upper Devonian primitive gnathostome placoderm arthrodire Dunkleosteus featured a massive 6 foot long headshield with scissor-like jaws mounted on a 20 foot long body
The second group of placoderms, the Antiarchs are characterized by the genus Pterichthys shown here with a well armored body and small mouth sited below the eyes. Restricted to the Devonian period they were probably sediment feeders like an earthworm or snails.
The anterior-ventral pectoral appendages of the antiarch Pterichthys tell us they groveled about the bottom only rarely rising off the sediment water interface
Sharks (Chondrichthyes) Legendary resistance of phosphate parts to dissolution CaPO 4 Apatite composition Tooth classification (natural) Denticle classification (classically artificial) Mainly used in marine geology for deposits well below CCD Sharks remarkable for slow evolution and subsequent looooong stratigraphic ranges
The Actinopterygiians or ray-finned bony fish (Osteichthyes) include the zillions of species of extant bony fish the Teleosts that underwent a phenomenal evolutionary explosion beginning in the Jurassic
The Devonian lungfish Dipterus is remarkably similar to modern coelacanths found in very deep water off South Africa and Indonesia today.
A living fossil! The coelacanth Latameria is a lobe finned fish with close relatives dating back to the Devonian period over 400 million years ago
As soon as the first specimen of the coelacanth Latimeria was brought to the surface the demand from museums and ichthyologists world wide quickly threatened their dwindling stocks. The animal was very nearly studied to death!
Anterior ventral, posterior ventral and posterior ventral fins lobe fins of the extant Sarcopterygian coelacanth Latimeria all display a well developed (robust) internal bony skeleton in stark contrast to the ray finned fish (Actinoperygians)
Bony Fish (Teleostei) Extremely “successful” group, regardless if you measure success by diversity, biomass or adaptive radiation Bone, otoliths, scales, teeth Bone of little use unless skeleton is articulated Otoliths – used to assess age of populations by annular growth rings Scales – extremely useful in subdividing deeper portions of Los Angeles Basin (Lore Rose David)
Teleost – (bony) fish
Angel Fish Pliocene, Po Valley, Italy ~3 m.y.a.
Thermal Maturation - Conodonts (also utilized with palynomorphs) Pigment change due to enclosed organics Experimental work by Harris et. al. Munsell soil color chart- –Pale yellow 50 ° - 80° C –Very pale brown 50 ° - 90 ° C –Brown to dark brown 60 ° ° C –Very dark greyish brown-dark reddish brown-black 110 ° °C –Black 190 ° ° C –Black +300 ° C –Clear to crystal clear >300 ° C