2: Innovations in Ostracoderms

BIOL 465 Lecture Video/Class Notes

Two lineages that came from Haikouichthys

• Jamoytius, lamprey/hagfish

• Bony-plated Ostracoderms

Innovations/Traits of Ostracoderms (“Shell-Skinned”)

• Bone

• Paired Fins

• Well developed Vertebrae (Jaws in Decedents)

Dermal Bone

Bone cells along membranes (such as dermis) that produce FLAT PLATES. ex: Skull, Shoulder Blades

Endochondral Bone

Mineralization of cartilage produces 3-D structures.

Bone and the Ostracoderms Rise as a Consequence

• Dermal bone evolved first providing armor

• Protection from predators (i.e. large arthropods and cephalopods)

• May have been used for mineral storage

Calcium Ion Storage

• Needed for muscle and nerve function

• Ostracoderms began swimming a lot more; heavier muscles and bone means needing more support

  • Well-developed cartilaginous vertebrae evolve quickly because of this.

Early Paired Fins: How Ostracoderms became more Pelagic Swimmers

• Later forms of Ostracoderms had pairs of membranous flaps eventually supported by rays of dermal bone.

• Then had bony vertebral column (First endochondral bone) with better attachment for swimming muscles.

Pelagic Swimming

Open water swimming, leaving the bottom of the ocean floor.

Gill Structure of Agnathans (Jawless Fish)

Water flows into mouth (Or pulled by branchial skeleton expansion) over pockets of gill tissue → then out of pores.

Evolution of Gnathostomes - How Jaws Evolved

Jaws are derived from modified gill arches (Mandibular and Hyoid arches) can now facilitate more water intake.

Initial Function of Jaws

Gill Ventilation through rapid opening and closing of the mouth.

Gill Tissue Rearrangement

• Gill tissue now external to skeletal supports to prevent it from collapsing under high water flow.

• Filamentous feather-like structures allowed flow rather than pushed.

• New Arrangement = More SA.

Later Function of Jaws

• Aiding in feeding with stronger muscle attachments and teeth (dermal bone form)

• Pivots in Jaw allowed for stronger bite force (Predatory evolution)