DIVERSITY, CLASSIFICATION &

EVOLUTIONPART III

VERTEBRATE ZOOLOGY (VZ Lecture03 – Spring 2012 Althoff - reference PJH Chapters 1,2 & 7)

Two Embryonic Features that may account for difference betweenvertebrates and other chordates

In vertebrates: development of tissue called ______________. Forms many new structures found only in vertebrates

Duplication of the ______________________

chicken embryoI – migrates to form mandibleII—migrates to form hyoid apparatusIII & IV—migrate to form outflow tract of heart

_______________ “migrating” to branchial arches1

Neural Crest Cells

• Originally thought that neural crest was derived from ectoderm germ layer

• Recently (Hall 2000) proposed that neural crest actually is a truly “independent germ layer”—not part of ecto-, endo-, or mesoderm. If true….

• Vertebrates are the only animals that have __ germ layers making them ____________

• Helps explain significant advancement in variety of structures in “true” vertebrates

1

Hox gene complex

• = Homeobox genes that characterize animals

• Don’t code for specific features, but regulate expression of the hierarchy of other genes that control the shape of the body

• Jellyfishes – 1 or 2 Hox genes Echinoderms & Nonvertebrate Chordates

—7 up to 13 vs. Vertebrates which have undergone

___________ of entire Hox complex

2

Hox gene complex…con’t

• So, what is the minimum number of Hox genes in vertebrates? Likely ____

• Mammals appear to have ____ such genes• Bottomline: “More complex animals usually

have a greater amount of genetic material…and it is thought that the ________ of this gene sequence at the _______ of vertebrate evolution made possible the evolution of a more complex type of animal”

Pough, Janis, & Heiser 2005

Early History & Vertebrate Evolution

• Vertebrates first appeared in the early Paleozic, about 540 MYA….earth at the time was mostly water covered, extensive continental movements, and an O2 rich atmosphere formed as a result of ________________________ of autotrophs

• Movement of land masses and climatic differences/changes resulted in major evolutionary effects on vertebrates.

WHY?

Early History: PALEOZOIC

• Vertebrates first appeared in the early Paleozoic, about ~________….earth at the time was mostly water covered, extensive continental movements, and an O2 rich (in relative terms) atmosphere.

• 490 MYA 443 MYA many shallow seas appeared, allowed for major radiation among marine animals, followed by first appearance of primitive vertebrates—primarily _____________, followed by _______________

Early History: PALEOZOIC…con’t• 443 417 MYA vascular plants and arthropods

just starting to appear, Jawless fishes continued to radiate and jawed fishes (including sharklike forms) appeared

• 417 354 MYA major freshwater basins appeared with first tetrapods. End of this period marked by disappearance of ________________ ____________ (ostracoderms)

• 354 290 MYA major glaciation. First appearance of ___________ and modern types of jawless fishes. Extensive radiation of non-amniote tetrapods. First __________ appeared.

Early History: PALEOZOIC…con’t• 290 251 MYA Single continent (Pangea) formed

near end of this period.-largest non-amniote tetrapods declined

-amniotes radiatedmodern reptiles

mammal-like reptiles first known ___________ tetrapods

• Largest known ______________ event occurred at end of period—impacting both land and sea fauna: THE END OF THE PALEOZOIC

MESOZOIC• 251 206 MYA Single continent high, few shallow

seas, no evidence of glaciationmammal-like reptiles declinedarchosaurian reptiles (including dinosaur

ancestors) diversifiedall large nonamniote tetrapods now aquatic

formstrue mammals appeardinosaurs, pterousaurs, marine reptiles,

crocodiles, lepidosaurs, frog-likeamphibians, and teleost fishes appear

• 206 144 MYA Continent breakup. Modern sharks and rays appear._________________________________

PALEOZOIC (late Carboniferous Period)

Aquaticnonamniotetetrapods

Terrestrialnonamniotetetrapods

12

3 4

5

Fig. 7-5 p165 PJH