The earliest vertebrates- dating back up to 500 mya

Question 1

describe the early two ostracoderms ()

Answer 1

a) Antolepis - late cambrian (500 mya)
○ Oldest mineralized fragments - earliest group of vertebrates
○ Soft bodied loaded with mineralized fragments - evidence
b) Astraspis - mid to late ordovocian (480 mya)
○ oldest complete, articulated fossil
Bony scales with dentine

Question 2

describe Haikouichthys and myllokunmingia (lamprey and hagfish?)

Answer 2

• Early cambrian (500 mya)
• Neither have bone or mineralized tissue
• Myllokumnigia - notochord, gill slits, muscles - W myomeres
Lamprey - breathe via aquatic environment, appandages that extend to a form of fins (to an early level)

Question 3

describe conodonts) what are the evidence of?

Answer 3

• Many “conodont elements” isolated in marine deposits
  
  • Late cambrian - late triassic
  • Misidentified as marine algae and invertebrates, etc
  • Mineralized tissue similar to dentine and enamel - have to be vertebrates
  • No gill aparatus - gas exchange via simple diffusion
  • Large eyes, segmented muscles - W shaped myomeres - couldn’t be algae
  • Conodonts and ostracoderms are evidence of early vertebrate forms
  • Apparatus to help them move, dental evidence ( feeding structure)
  • These could have developed into ostracoderms - from worm to modern fish in look

Question 4

what are the general characteristics of ostracoderms

Answer 4

• Small size - most less than 10 cm
  
  • Dermal plates of bone
  • Jawless
  • Absence of paired lateral appendages (fins- not pectoral or paired)
  • Notochord
  • Pharyngeal gill pouches (slits)

Question 5

what happened to ostracoderms?

Answer 5

• Ultimately, the ostracoderms were outcompeted by fish that possessed the next big evolutionary development - JAWS
  
  • By the end of the devonian, ostracoderms had become extinct
  • Conodonts survived into the Jurassic, and a few other agnathans have survived to today

Question 6

what are the living agnathans? their general characteristics?

Answer 6

• Cartilaginous endoskeletons (Primative - cartilage rather than bones)
  
  • Round, jawless mouth
  • Lack paired appendages
  • Notochord in adult
  • Fossil record very poor
  • Origin possibly approx. 530 mya
  • Specialized lifestyles

Question 7

describe myxinoidea - hagfish

Answer 7

• Marine, worldwide except polar
• No scale, no bone, no paired fins
• Lack vertebrae and dermal bone - notochord persists (not protected as they lack the vertebral column)
Possess cartilage plates in head
Hence, “craniates”
Scavenger
Protrusible keratinized tongue with multicusped plates
Eyes degenerate
Direct developmet - no larval stage
Some species hermaphroditic
Single semicircular canal - hearing is not as good
Lacks lateral line - not active swimmers or active predators - lack most of the sensory structures
Single nasal opening
• Gills: 1-15 pairs of gill openings
• Ventral heart; also acessory hearts (unique) - aneural (no CNS input)
• Body fluid isomotic (unique)

Question 8

what are the hagfish defense mechanism?

Answer 8

• Mucous (slime) glads - defense mechanism - one of their major endowments - has two components- mucous and fiber
○ Mucus in reaction with sea water forms hygroscopic fibrils (once it gets out of the body) - similar to spider silk
• Can tie itself in knots to increase leverage when burrowing into a dead fish or to evade predators

Question 9

describe the generalized characteristics of lamprey (peyromyzontoidea)

Answer 9

• Worldwide distribution, except tropical and high polar
• Marine, anadromous (adults mostly in marine, but will go down to freshwater for reproduction), fresh water
• Thick, scale-less skin, non-living cuticle (thick integument)
• No mucous/slime glands
• No tentacles
• Jawless ectoparasites (most)
○ Keratinized spines in mouth
○ Protrusible tongue with spines - spine will rough chop the integument of their prey
○ Anticoagulants produced by oral glands
○ Reduced digestive tract
• No lateral appendages
• Notochord and cartilaginous vertebral elements
• Simple cartilaginous cranium
• Eyes and pineal gland well developed
• Single nasal opening
• 7 pairs of gills
• 2 semicircular canal
• Heart not aneural
• Moat anadromous- live in marine, move to freshwater for spawning
• Metamorphosis - ammocoete larvae

Question 10

when were lamprey an issue?

Answer 10

• Landlocked sea lampreys made their way into the great lakes around 1918
  
  • Caused major decline of whitefish populations complete collapse of lake trout fishery by 1950’s
  • Lamprey numbers fell as their prey base collapsed and control measures introduced
  • Trout numbers since recovered somewhat, but wounding rates still high

Question 11

phylogeny of agnathans

Answer 11

• Hagfish are the most primitive
  
  • Ostracoderms form sister group to gnathostomes
  • Position of lamprey varies

Question 12

what significant advances on early vertebrates do they have?

Answer 12

• Development of bone 
		○ First forms external plates 
		○ Poor swimmers 
		○ Bone moved inward 
	• Development of muscular pharynx 
		○ Ciliary mechanism limited growth and size 
		○ Muscular form (suction) evolved