BI360: Vertebrate Zoology

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BI-360 Vertebrate Zoology

• Vertebrate Origins
• and Evolution

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Geologic Time
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Protochordate - Vertebrate relationships

• Relationship between chordates and invertebrates
• Both resemble echinoderms and hemichordates in
  that they are deuterostomes
• Radial, indeterminate cleavage
• Blastopore forms the anus
• Most primitive living vertebrates are jawless
  fishes (cyclostomes)
• Free-swimming, filter-feeding larval stage of
  lampreys closely resembles protochordate larvae
• ammocoete

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Protostome
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Deuterostome
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Chordate phylogeny
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Cephalochordate v. Vertebrate
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Cephalochordates v. vertebrates

• Almost no cephalization
• No paired sense organs
• No vertebral column
• High number of gill slits
• Segmented musculature extends to anterior tip of
  head
• No paired appendages
• Outer layer of skin (epidermis) one-cell thick
• No muscular heart
• Excretory protonephridia resemble those on
  non-chordates

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Differentiating Vertebrates from other Chordates
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Muscular segmentation
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Origins of the vertebrates

• Marine origins for vertebrates
• All non-vertebrate, deuterostomes are exclusively
  marine
• Earliest vertebrate fossils are found in marine
  sedimentary deposits
• Most primitive, extant vertebrates (hagfishes)
  are marine
• The vertebrate kidney in early forms was most
  likely used for Ca2 and Mg2 regulation these
  being necessary for muscle contraction
• Later, became useful for osmotic regulation, when
  invading fresh-water habitats pre-adapted

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Early vertebrate evolution

• Characterized by increasingly active lifestyle
• Three major steps
• Prevertebrate with muscular pumping of pharyngeal
  apparatus for active filter feeding
• Agnathans with cartilage support of bucchal
  apparatus for more active pumping of muscular
  pharanx
• Gnathostome development of jaws with ability to
  grip and grasp prey

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Vertebrate Zoology . . . What do we mean?

• What organisms are classified as vertebrates?
• Superclass Agnatha - jawless fishes
• Class Myxini - hagfishes
• Class Cephalaspidomorphi - lampreys
• Superclass Gnathostmata - jawed vertebrates
• Class Chondrichthyes - cartilaginous fishes
• Class Sarcopterygii - lobe-finned fishes
• Class Actinopterygii - ray-finned fishes

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Fishes
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Vertebrates

• Class Amphibia - amphibians
• Order Gymnophiona - caecilians
• Order Caudata (Urodela) - salamanders
• Order Anura - frogs and toads
• Class Reptilia - reptiles
• Order Testudines (Chelonia) - turtles and
  tortoises
• Order Sphenodonta - tuatara
• Order Squamata - lizards and snakes
• Order Crocodylia - alligators and crocodiles

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Amphibia
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Reptilia
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Vertebrates

• Birds - those extant vertebrates with feathers
• Class Mammalia - mammals
• Monotremata - egg-laying mammals
• echidna and platypus
• Marsupialia - marsupials
• Eutheria - placental mammals

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Birds
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Monotremes
Monotremes - egg-laying mammals with many
ancestral charactersistics. Duck-billed
platypus Echidna
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Marsupials - pouched mammals
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Eutheria - Placental mammals
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Superclass Agnatha (jawless fishes)

• 70 living species
• Jawless
• Gills supported by pharyngeal bars of cartilage
• No paired appendages
• Single, median nostril
• with blind, sac-like olfactory pouch
• Notochord persists in the adult
• Predators or scavengers
• Fresh- and salt-water species

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Agnatha

• Hagfishes and lampreys sometimes referred to as
  "cyclostomes"
• Class Myxini (hagfishes)
• Order Myxiniformes
• Strictly marine
• Class Cephalaspidomorphi (Monorhina)
• Order Petromyzontiformes (lampreys)
• Marine and fresh-water species
• Parasitic forms and non-feeding adults

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Agnatha
Myxiniformes a hagfish
Petromyzontiformes a lamprey
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Agnathan phylogeny
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Hagfishes
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Ammocoete larvae
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Ammocoete larvae have

• 7 gill slits (respiratory in function)
• Notochord extending from head region into tail
  (no vertebral column)
• Dorsal, hollow nerve tube typical embryonic
  vertebrate brain with three primary vesicles
• A stratified epidermis
• Typical embryonic vertebrate kidney
• Typical closed, embryonic vertebrate circulatory
  system with two-chambered heart and red blood
  cells
• Tadpole-like morphology typical of vertebrate
  larvae (such as frogs)
• Sense organs more numerous than lancelets -
  median naris that leads to an olfactory sac, two
  mid-dorsal eyes on head, otic vesicles that
  develop into inner ears

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Lamprey
Ichthyomyzon castenatus - chestnut lamprey
Petromyzon marinus - sea lamprey attached to lake
trout
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Lamprey life cycle
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Conodonts

• Phylogenetic placement is uncertain
• Soft-bodied
• Series of tooth-like plates that form pharyngeal
  apparatus
• Notochord
• Cranium
• Myomeres
• Small tail fin with fin rays
• Large eyes
• Small size only about 40 mm long
• Occur in fossil record from late Cambrian to late
  Triassic period

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Conodonts
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Oldest fishes

• Fossil finds in China have added to record of
  early fish-like vertebrates
• Myllokunmingia
• Date to over 500 MYA

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Ostracoderms

• Extinct jawless fishes
• Most are known from fossils of the Ordivician,
  Silurian, and Devonian periods
• Paraphyletic assemblage of groups
• Osteostraci, Anapsida, Heterostraci and
  Coelolepida
• Shelled skin
• Had armour-plated body
• Flourished during the Paleozoic Era
• Died out by end of Devonian
• Small
• Most lt 10 cm
• Bottom-dwelling, filter feeders

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Ostracoderms

• Heterocercal tail
• No fins
• Single, median nostril (may have lived buried in
  substrate)
• Pineal eye
• Photoreceptive structure on the dorsal part of
  the head
• Notochord present throughout life
• Bony skeleton
• Most likely preyed upon by eurypterids (large,
  scorpion-like, aquatic arthropods)
• Included Hemicyclapsis, Cephalaspis, and
  Pharyngolepis

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Ostracoderms
Pteraspis sp.
Hemicyclaspis sp.
Zenaspis sp.