Vertebrate Origins Flashcards Preview

BIOL 3326 Exam 2 > Vertebrate Origins > Flashcards

Flashcards in Vertebrate Origins Deck (18):
1

vertebrate evolution

Descended from marine protochordate ancestor

2

Suspension feeders with ciliary pumps

Pre-verts (ancestral chordates)

But ciliary pump ineffective for larger animals

3

First vertebrates

Larger than protochordate ancestor, more Energetic demand with larger size

4

Proposed major events of vertebrate evolution

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

5

Pharynx evolution

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

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

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

6

Appearance of gills

Absent in protochordates, better oxygen delivery

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

7

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)

8

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

9

Conodonts

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

10

Myotomes

Somites forming lateral wall skeletal muscle groups, mesoderm origin

11

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

12

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

13

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

14

Proposed selective advantages of bone:

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

15

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

16

Mineral storage

Deposition of Ca salts; mobilized when needed

17

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

18

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.