1. Fish
Lecture 1

2. 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.

3. 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.

4. 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.

5. 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

6. 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.

7. From jawless to jawed:

8. 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

9. Placoderms
Placoderms were some of the earliest jawed fishes, that did not have teeth
They had bony plates covering ½ 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

10. 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

11. 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)