Vertebrate Origins Flashcards Preview

BIOL 3326 Exam 2 > Vertebrate Origins > Flashcards

Flashcards in Vertebrate Origins Deck (18):

vertebrate evolution

Descended from marine protochordate ancestor


Suspension feeders with ciliary pumps

Pre-verts (ancestral chordates)

But ciliary pump ineffective for larger animals


First vertebrates

Larger than protochordate ancestor, more Energetic demand with larger size


Proposed major events of vertebrate evolution

1. Pharynx evolution
2. Appearance of gills
3. Appearance of mineralized tissue
4. Evolution of jaws


Pharynx evolution

Shift from ciliary pump (protochordate) to muscular pharyngeal pump (craniates/verts)

-pharynx of vert ancestor developed encircling muscle -->muscle contracts, decrease lumen size
-change in pharyngeal arch support: collagen to cartilage

Water squeezed out of pharynx; elastic recoil
Increased efficiency, more efficient suspension and sediment (deposit) feeding than ciliary pump
Would enable larger size


Appearance of gills

Absent in protochordates, better oxygen delivery

Ex. Lancelets (protochordates) diffuse oxygen across skin which works well for their very small size


Appearance of mineralized tissue

In general: deposition of Ca salts

Cell deposition of Calcium and Phosphorus in matrix of connective tissue

First appeared in pharynx (conodonts) and skin (ostracoderms)


Evolution of jaws

Jaws from anterior pharyngeal arches

Shift from suspension feeder/sediment feeder to "grasping feeder"

Predator and scavenger

Wary prey and difficult to obtain prey now accessible



Fish-like in appearance

Conodont elements: tooth-like; found in muscular pharynx

S &M elements: anterior, prey acquisition, attached to tongue or moving cartilage plates

P elements: posterior, grinding, crushing

Possessed notochord and myotomes

NO BONE -- just mineralized tissue



Somites forming lateral wall skeletal muscle groups, mesoderm origin


Evidence that conodonts must be vertebrates

Conodont elements made of CaPO4, calcified cartilage, enamel, dentin

Dentin from odontoblasts (neural crest origin)

Neural crest cells = apomorphic trait of craniates (extant taxa)

Dentin only in vertebrate clades


Ostracoderm fishes

First undisputed vertebrates: bone

Dermal bone

Armored jawless fishes: all are extinct taxa

Taxon Ostracodermi now considered paraphyletic -- phylogeny of ostracoderms not resolved

Had mineralized dermal exoskeleton

Bony head shield (dermal bone beneath epidermis), smaller bony plates on trunk

Plates composed of bone, dentin, enamel


Origin of bone

Apomorphic; no homologue in other taxa but...

Composed of Ca salts
Produced by specialized cells
Secreted into matrix formed by specialized cells

ex: have skeletal support system that is characterized by these features: mollusks, echinoderms, arthropods

Some protochordate ancestor developed ability to form bone


Proposed selective advantages of bone:

1. Protective armor
2. Insulation/protection of sense organs in skin (electroreceptors/mechanoreceptors)
3. Mineral storage


Insulation/protection of sense organs in skin (electroreceptors/mechanoreceptors)

Insulator = non-conductor, would enhance transduction

Transduction: cells convert one kind of signal/stimulus to another

Context: transport signals to CNS

ostracoderms had bony tubercles with distinct openings; sensory function?

Electrical field channeled to hair cells in tubercles


Mineral storage

Deposition of Ca salts; mobilized when needed


Hyperotreti (hagfish)

Ancestry largely unknown

Little or no cartilage; no bone or mineralized tissue, no vertebral elements --> do not fossilize well

Eel-like scavengers

Slime= anti-predator, gill-clogging


Evolution of Bone essay

the hard fraction of vertebrate bone is calcium phosphate (hydroxyapatite) rather than calcium carbonate (calcite or aragonite) of invertebrate skeletons

possibly more stable under conditions of physiological stress associated with active lifestyles

Bursts of activity lead to lactic acid production and fluctuations of blood pH and prolonged acidosis. Calcium carbonate of invert bone tends to dissolve under these conditions making it unsuitable for an active lifestyle. Calcium phosphate makes bone matrix more stable.