fish lecture 1
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Early Fish The earliest known bony fish were a group referred to as the ostracoderms which were fish encased in bony armor. These fish are from the early Cambrian period, 500 mya.TRANSCRIPT
Fish Lecture 1 Early Fish The earliest known bony fish were a
group referred to as the ostracoderms which were fish encased in
bony armor. These fish are from the early Cambrian period, 500 mya.
Early Fish There are two fossils from China, the Myllokumingia and
the Haikouichthys, these two fossils show a small (3 cm)
fish-shaped vertebrate with fish like body structure, they do lack
evidence of bone or mineralized scale like ostracoderms. Both
species had a dorsal fin and ribbon like ventral fins. There are
complete articulated skeletons from jawless fishes from the late
Ordovician time period. These fish were torpedo shaped, ranging
from cm in length. These early fish were heavily armored with many
small, close-fitting, polygonal bony plates 3-5 mm long. These
plates abutted to each other in the head and gill region, forming a
head shield. These bony plates overlap like modern day scales.There
are up to eight gill openings and extra protection around the eyes
as well as the presence of sensory canals. Agnathans Hagfish and
Lampreys
Hagfish lack vertebral elements completely Lampreys have only
cartilage flanking the nerve chord To be classified as Agnathans
the extant species must have no jaws, notochord during embryo and
adult phase, lack paired fins and have 7 or more paired gill slits.
All Agnathans extant and ancestral have no identifiable stomach or
appendages. Agnathans are the jawless fishes and date back to the
Cambrian time period, and are monophyletic Jawless Fishes Today
Modern day (or extant) jawless fishes are lampreys and hagfishes.
We have a lamprey that is native to Idaho, this is the pacific
lamprey or Entospenus tridentatus. From jawless to jawed:
Gnathostomes Considered to have originated within the Aganthan
lineage. Known for certain from the early Silurian time period
(although there is some evidence that they date back to the
mid-Ordovician) Derived characteristics are jaws that bear teeth
(teeth came later), two sets of paired fins or limbs Placoderms
Placoderms were some of the earliest jawed fishes, that did not
have teeth They had bony plates covering to 1/3 of their body,
however this bony plate was divided into separate head and trunk
portions linked by a mobile joint that allowed the head to be
lifted up during feeding. Lived from the Silurian to the Devonian
time period Chondrichthyes Evolved around 530 MYA (mid
Devonian)
Have cartilaginous skeletons This group includes the sharks, rays,
and ratfishes Sharks have 403 species, ranging from 15cm to 10
meters Rays have 534 species, dorsoventrally flattened &
typically bottom dwellers that swim with undulations of their
pectoral fins Ratfishes or Chimaeras have 33 species, have a single
gill cover that extends over all 4 gill openings Osteichthyes The
bony fishes (late Devonian)
Two broad categories are recognized Actinopterygians Ray finned
fishes Includes the sturgeon More than 27,000 species in fresh
& salt water More await discovery, Census of Marine Life
project is describing previously unknown species annually Broken
into 2 main groups Chondrostei (43 species) Neopterygii splint into
three lineages (over 27,000) Sarcopterygians lobe finned or fleshy
finned fishes Includes the coelacanth (2 species) 8 species still
survive (6 species of lung fish)