Bio of Fishes Lecture 13: Fossil Fishes

Major challange to ichthyology pertaining to fossil fishes

unraveling the evolutionary pathways of both modern and past fish taxa in the process of determining relationships among groups

for common traits of all chordates

post-anal tail, pharyngeal slits, dorsal (hollow) nerve cord, and notochord

two main innovations to become actual fishes

true bone and muscular feeding pump

true bone

probably evolved independently in several ancestral vertebrate groups: first existed only as an external covering, but provided better protection from predators, as well as serving as a metabolic reserve for calcium and phosphate

muscular feeding pump

more efficient for moving food-bearing water through a filtration mechanism than the ciliary feeding mechanism of protochordates

all of the early fossilized fishes were _____, meaning:

craniates, with a head region containing a brain with specialized sensory capsules and cranial nerves, all contained in a protective skeletal braincase

two things all vertebrate craniates possess

dermal skeleton and neural crest

Conodonta

“cone shaped teeth”- Between Late Proterozoic and Late Triassic times (600 to 200 mybp), Known since the mid 1800s, their abundance allowed them to serve as stratigraphic landmarks in determining the age of fossil beds. It was not until the 1980s that fossilized soft body parts were discovered, allowing speculation on true relationships Before these discoveries, the elements were identified variously as copulatory structures of nematodes, as radulae of snails, or as jaws of annelid worms, among other things

Ostracoderms

the first fishes, bony shield that covered head and thorax, now considered an artificial, potentially paraphyletic designation that includes perhaps four distinct superclasses of jawless craniate fishes: Pteraspidomorphi, Anaspida, Thelodonti, and Osteostracomorphi.