Laboratory 15
The Evolution of the Vertebrates

Pamela J. W. Gore

Department of Geology, Georgia Perimeter College

Clarkston, GA 30021

Copyright ã 1982-1999, 2001, 2003, 2004, 2005, 2006, 2007, 2009 Pamela J. W. Gore

This lab is to be done using the Internet. It may be done in the lab if computers are available, or as an outside assignment. Click on the hyperlinks to reach outside web pages to look for the answers to the questions.

A. Introduction to the Chordata

Use this reference to answer the questions below.

University of California Berkeley Museum of Paleontology Introduction to the Chordata http://www.ucmp.berkeley.edu/chordata/chordata.html

  1. The vertebrates belong to Phylum Chordata. What are four characteristics of the Chordata?

    1. _________________________________  

    2. _________________________________  

    3. _________________________________  

    4. _________________________________  

Vertebrates are animals that have a dorsal, hollow nerve chord surrounded by supportive material, the vertebral column (commonly called the spine or backbone), and an internal skeleton. The skeleton is usually composed of bone (hard material) and cartilage (soft and flexible material, such as that in your nose or ears), and serves for muscle attachment. In most vertebrates, the skeleton is first formed in cartilage and then replaced by bone before birth.

Use this reference to answer the following questions:

University of California, Berkeley, Museum of Paleontology, 1995, Vertebrates: More on Morphology, available online: http://www.ucmp.berkeley.edu/vertebrates/vertmm.html

  1. The main bony disk-shaped or spool-shaped portion of the vertebra is called the ________________________.

  2. The nerve or spinal cord passes through the ____________________________. The neural arch is elongated into spines in some vertebrates.


  3. Vertebrates possess two types of bone. What are they?

    1. _________________________________  

    2. _________________________________  


B. The Earliest Chordates - Pikaia


Pikaia, Burgess Shale

The history of the vertebrates may begin with Pikaia, a pre-vertebrate with a notochord, which places it in Phylum Chordata. See the notochord near the dorsal surface. The rib-like features are muscles.

Use these references to answer the following questions:

Hooper Virtual Paleontological Museum, 1996, Chordate, Pikaia grailens, available online, http://hannover.park.org/Canada/Museum/burgessshale/chordate.html

Smithsonian Institution Museum of Natural History http://paleobiology.si.edu/burgess/index.html

The Smithsonian has a sketch of Pikaia (http://paleobiology.si.edu/burgess/pikaia.html), emphasizing the "muscle blocks" which give Pikaia a segmented appearance. The color picture of Pikaia's habitat (http://paleobiology.si.edu/burgess/cambrianWorld.html) gives a better illustration of its mode of life.

  1. What was its mode of life? ________________________________

  2. Explore these several links to Pikaia, and give its age (period name and years).

    _______________________________________________________

  3. In which well-known geologic formation is it found? ______________________________

C. Ostracoderms - Class Agnatha


Ostracoderm

The earliest fish fossils are found in marine rocks, suggesting that fishes evolved in the sea.

Use these references to answer the following questions:

University of California, Berkeley, Museum of Paleontology, 1995, Vertebrates: Fossil Record, available online: http://www.ucmp.berkeley.edu/vertebrates/vertfr.html .

Gee, Henry, 1996, Fishy fragments tip the scales. http://www.geology.ucdavis.edu/~cowen/HistoryofLife/Anatolepis.html.
Or see Nature, v. 383, p. 757-758 in your college library.
See also:
A possible Late Cambrian vertebrate from Australia by Gavin C. Young, Valya N. Karatajute-Talimaa & Moya M. Smith.

Janvier, Philippe, 1996, 1998, Arandaspida, Tree of Life Project, University of Arizona, available online: http://tolweb.org/tree?group=Arandaspida&contgroup=Pteraspidomorphi

Janvier, Philippe, 1996, 1998, Astraspida, Tree of Life Project, University of Arizona, available online: http://tolweb.org/tree?group=Astraspida&contgroup=Pteraspidomorphi

  1. How old are the oldest known fish fossils, according to the 1996 Henry Gee article? _______________________________

  2. Where were they collected? ________________________________

  3. What are ostracoderms? ________________________________

  4. What material comprised the internal skeleton of the ostracoderms? ________________________________

  5. Why is the internal skeleton of ostracoderms poorly preserved or not preserved? ________________________________

  6. Why do you think that fishes once had external skeletal armor? ___________________________________

A more recent discovery has led to even older fossil fish. Use the reference(s) below to answer the following questions.

Sci/Tech, Oldest fossil fish caught, BBC News, available online: http://news.bbc.co.uk/1/hi/sci/tech/504776.stm

  1. How old are these more-recently-discovered fossils? ________________________________

  2. Where were they discovered? ____________________________________

  3. What is the name of the two species of fishes? ____________________________________ and ________________________________________

  4. What features do these fossils have that leads paleontologists to conclude that they are fish?

    _______________________________________________________________________

  5. What do these creatures LACK, that most vertebrates have? _________________________________________

  6. What were the skulls and other skeletal features made of? _________________________________________

  7. These fish are from what is known as the ________________________ fossil fauna, where thousands of exquisitely preserved fossils of soft-bodied creatures have been found.

Ordovician fossil fishes are the Arandaspids ( http://tolweb.org/tree?group=Arandaspida&contgroup=Pteraspidomorphi) and the Astraspids http://tolweb.org/tree?group=Astraspida&contgroup=Pteraspidomorphi.

  1. Did they have jaws? ______________________

  2. Did they have armour? _________________________

  3. What surrounds the eyes? _____________________________ (more on this below).

  4. Did they have gills? _____________________

  5. Did they have scales? __________________

  6. Give the age (Period name and dates) of the earliest fishes from these two references.

    _________________________________________________________________

  7. Where did Astraspis live? ___________________________________

D. The Evolution of Jaws

Jawed fishes are gnathostomes, as opposed to the agnathans or jawless fishes.

Janvier, Philippe, 1997, Gnathostomata, Jawed Vertebrates, Tree of Life Project, University of Arizona, available online: http://tolweb.org/tree?group=Gnathostomata&contgroup=Vertebrata

Zimmer, Carl, March 1996, Death From the Pleistocene Sky, Discover Magazine, available online: http://discovermagazine.com/1996/mar/deathfromtheplei720
If you are unable to view this article online, please go to your college library and request DISCOVER, Vol. 17, No. 03, March 1996.

See the diagram relating jaws (in red) to gill arches (in green) in the first reference. (You may need to scroll down).

  1. What animal is shown? (Hint: See caption.) _________________________________

  2. What does the Zimmer article propose as a reason for the development of jaws?

E. Placoderms - Class Placodermi


Dunkleosteus, a Devonian Placoderm

Placoderm fish were primarily confined to the Devonian and became extinct in the Paleozoic era. They had no true teeth (although the jaws had sharp tusk-like projections) and no preservable internal skeleton. The only structure made of bone was the external armor.

Use the following references to answer the questions:

American Museum of Natural History http://www.amnh.org/exhibitions/expeditions/treasure_fossil/Fossils/Specimens/dunkleosteus.html

University of California, Berkeley, Museum of Paleontology http://www.ucmp.berkeley.edu/vertebrates/basalfish/placodermi.html

  1. Which genus was the "undisputed ruler" of the sea, found in the Cleveland shale?

    ______________________________________________________

  2. How long was it? ___________________ feet

  3. How much did it weigh? _________________

  4. Was it a predator or a scavenger? _____________________________

  5. How can we tell? ___________________________________________

    What did Dunkleosteus eat? ________________________________

  6. What was the advantage of having jaws?

  7. How did fish eat that did not have jaws?

    Look at the skull of the Late Devonian placoderm fish, Dunkleosteus, above.

    Notice the sclerotic ring, the bony structure in the eye socket for the protection of the eye. All birds have this sclerotic ring. It protects their eyes against rapid air pressure changes during flights. It is also used to help the eye focus on distant objects.

  8. What might its uses be for this placoderm fish? ______________________

    Examine the dinosaur skulls on the Georgia Perimeter College web site (http://facstaff.gpc.edu/~pgore/geology/geo102/dinos.htm).

  9. Do any of them have a sclerotic ring? _____________

    Name them ______________________________

     

F. Bony Fishes - Class Osteichthyes


Eocene bony, ray-finned fishes from the Green River Formation of Wyoming

The bony fishes are the most numerous, varied, and successful of the aquatic vertebrates. They also are ancestral to the four-legged vertebrates (tetrapods).

Bony fishes are divided into two subclasses:

  1. Ray-finned fish (Subclass Actinopterygii)
  2. Lobe-finned fish (Subclass Sarcopterygii)
    1. Order Crossopterygii - lobe-finned fishes ancestral to amphibians, also includes coelacanths
    2. Order Dipnoi - lungfishes

The lobe-finned fishes appeared in the Late Devonian. They had leg-like muscular fins which they used to "walk" about on pond or stream bottoms. They also had lungs and could gulp air when the water became foul or stagnant.


The Late Devonian crossopterygian lungfish, Eusthenopteron (365 million years old, Escuminac Formation, Quebec, Canada) had sturdy fins. It is structurally similar to amphibians and is considered to be transitional to the amphibians.

Another group of lobe-finned crossopterygian fish invaded the sea and gave rise to the coelacanths. The coelacanths are considered to be living fossils because they were long-believed to be extinct, but one was caught in 1938 near Madagascar. More have been caught since.

Use this reference to answer the following questions:

Hamlin, Jerome F., 1999, The Fish Out of Time, Information on the Coelacanth, Third Wave Media Inc., available online: http://www.dinofish.com/

Coelacanth, American Museum of Natural History, available online: http://www.amnh.org/exhibitions/expeditions/treasure_fossil/Treasures/Coelacanth/coelacan.html?aa

  1. Sketch the shape of the tail of the coelacanth.
  2. Compare the tail of the living coelacanth to that of the bony ray-finned fishes from the Green River Formation, above. Sketch both side by side and describe the differences.

  3. Compare the tail of the living coelacanth to that of Eusthenopteron, above. Sketch both side by side and describe the similarities and differences.

    Some living fish that can walk on land and/or breathe air!

    Investigate with this reference:

    University of California Berkeley Museum of Paleontology, 1995, 1997, Actinopterygii: Life History and Ecology available online: http://www.ucmp.berkeley.edu/vertebrates/actinopterygii/actinolh.html.

  4. List and describe the living fish that can walk on land and breathe air:
  5. Where do they live? ____________________________________________________

  6. What do they eat? ____________________________________________________

  7. What do they do during times of periodic drying? ____________________________________________________

    ____________________________________________________

    Read this reference to learn about the function of the swim bladder:

    University of California Berkeley Museum of Paleontology, Actinopterygii: More on Morphology, available online: http://www.ucmp.berkeley.edu/vertebrates/actinopterygii/actinomm.html.

  8. Describe the function of the swim bladder.

  9. Which type of fish was the most likely ancestor to the amphibians? ________________

G. The Transition to Land

During the Paleozoic Era, both plants and animals made the transition from the water to the land. Plants made the transition first, and provided the nutritional support for the animals to make the transition later. For organisms to make the transition from the water to the land, they must meet several requirements.

Use this reference to answer the following questions: http://animals.about.com/b/2008/01/27/land-to-water.htm.

 

  1. List the challenges or problems that must be solved for vertebrates to make the transition to land. Also note how vertebrates solved each problem. You should find at least five challenges.
    1. ___________________________________________________________________________________  

    2. ___________________________________________________________________________________  

    3. ___________________________________________________________________________________  

    4. ___________________________________________________________________________________  

    5. ___________________________________________________________________________________  

    Check your lecture notes or textbook to answer these questions.

  2. When did the first plants appear on the land? __________________ (period name)

  3. When did the first animals appear on the land? ____________________ (period name)

  4. Which group of vertebrate animals was the first to appear on the land? _____________________

  5. Why did plants make the transition to land before the animals? ___________________

H. Amphibians - Class Amphibia

Saurerpeton obtusum
Middle Pennsylvanian, North America 		An ancestral salamander,
Amphibamus lyelli
Middle Pennsylvanian, North America

Amphibians were the first land-dwelling vertebrates. Today, adult amphibians live on land and breathe air, but they lay their eggs in the water. Young amphibians live in the water and are fish-like (tadpoles, for example).

Use this reference to answer the following questions:

University of California Berkeley Museum of Paleontology, 1995, Amphibia: Life History and Ecology, available online: http://www.ucmp.berkeley.edu/vertebrates/tetrapods/amphiblh.html

  1. List the major characteristics of amphibians.

  2. When did the amphibians first appear? _______________ (period name)

  3. What were the ancestors of the amphibians? _______________________


    Ichthyostega stensioei

    Use all of these references to answer the following questions on Ichthyostega:

    Flank, Lenny, 1995, Ichthyostega (sic) as a transition fossil, Creation "Science" Debunked, available online: http://www.geocities.com/CapeCanaveral/Hangar/2437/icthyo.htm. Note: There are some typos or misspellings in this reference.

    Clack, Jennifer A., 1998, Acanthostega gunneri http://tolweb.org/tree?group=Acanthostega&contgroup=Terrestrial_Vertebrates

    Murphy, Dennis, 1998, The Old Order: Fish Out Of Water, Devonian Times, available online: http://www.devoniantimes.org/Order/old-order.html.

    Murphy, Dennis, 1998, Ichthyostega spp., Devonian Times, available online: http://www.devoniantimes.org/Order/re-ichthyostega.html.

    Murphy, Dennis, 1998, Recent Findings: Fishes With Legs, Devonian Times, available online: http://www.devoniantimes.org/Order/new-order.html.

    Zimmer, Carl, Coming Onto the Land, Discover Magazine, June 1995, available online: http://discovermagazine.com/1995/jun/comingontothelan523.

    Ichthyostega, an amphibian that appeared in the Late Devonian, retained many of the features of its fish ancestors.

  4. What was Alfred Romer's scenario for the evolution of tetrapods in the 1940's and 1950's? (In the Zimmer article.)
  5. What are the fish-like characteristics of Ichthyostega?

    _____________________________________________________________

  6. What are the amphibian-like characteristics of Ichthyostega?

    _____________________________________________________________

  7. Describe the limbs of Ichthyostega.

    _____________________________________________________________

  8. How does the bone structure of the limbs compare with that of the lobe-finned fishes (rhipidistians)?

    _____________________________________________________________

  9. Describe the teeth of Ichthyostega.

    _____________________________________________________________

  10. Which two groups of animals share this type of teeth?

    _____________________________________________________________

  11. What are the new findings that alter our ideas of tetrapod evolution?

    _____________________________________________________________

    _____________________________________________________________

  12. What is the significance of Acanthostega?_____________________________________________________________

  13. Did Ichthyostega and other mid-Paleozoic amphibians inhabit freshwater or marine (salt) water?

    _____________________________________________________________

For 50 million years, from the Late Devonian to the Middle Carboniferous, amphibians were the only vertebrates to the inhabit the land. Some adult amphibians reverted to an aquatic mode of life, while others retained a terrestrial lifestyle.

Seymouria was a land-dwelling amphibian from the Lower Permian of Texas. A primitive amphibian similar to Seymouria was probably ancestral to the reptiles.


Seymouria, fossil amphibian from the Lower Permian of Texas.
260 million years ago
Land-dweller, less than 3 feet long.
Note stout limbs, short body and tail.

Neopteroplax was an aquatic amphibian. Eryops was probably semi-aquatic. Features suggesting an aquatic lifestyle include a flattened body and skull, reduced limbs, and a slender snake-like body.


Skull of Neopteroplax, 290 million years ago
Aquatic amphibian from the Late Carboniferous of Ohio,
Smithsonian Institution, Museum of Natural History, Washington, DC


The large Permian amphibian, Eryops,
Pratt Museum, Amherst College, Amherst, Massachusetts

A huge number of well preserved amphibian trackways have been collected from an abandoned coal strip mine in Walker County, Alabama  between 1999 and 2004.  Use the references below to answer the questions. 

  1. What is the age of the amphibian trackways? _________________________
  2. What sorts of trace fossils are present? ______________________________
  3. What types of organisms made them? ________________________________
  4. How big were the amphibians? ______________________________________

Photographic Trackway Database: http://bama.ua.edu/~rbuta/monograph/database/database.html

Mine Reclamation Threatens Tracksite:  Geotimes, October 2003. http://www.geotimes.org/oct03/NN_mine.html#

Birmingham Paleontological Society http://bps-al.org/trips/20000123.html

Martin, A. J. and Pyenson, N. D. 2005, Behavioral Significance of Vertebrate Trace Fossils from the Union Chapel Site.  in Buta, R. J., Rindsberg, A. K., and Kopaska-Merkel, D. C., eds., 2005, Pennsylvanian Footprints in the Black Warrior Basin of Alabama.  Alabama Paleontological Society Monograph no. 1. http://www.envs.emory.edu/faculty/MARTIN/ResearchDocs/Martin&Pyenson2005.pdf

Reference on amphibian fossils in Iowa .

I. Vertebrate Skeletal Structure

All land vertebrates (amphibians, reptiles, birds, and mammals) have the same bones in their skeletons. They all have a radius, ulna, humerus, femur, ribs, vertebrae (bones of the spine), sternum, and phalanges.

Use the images at eSkeletons and Virtual Bones to familiarize yourself with the names of the bones that make up a vertebrate skeleton.

Skeletal differences between the groups of land vertebrates come from the modification of existing bones to perform a special function. Types of modifications include fusion of several bones into one, and elongation of a bone. You can tell a great deal about the life processes of an animal by looking at the modifications of is skeleton.

J. Reptiles - Class Reptilia

Complete colonization of land was achieved by the reptiles which could lay eggs on land. Egg-laying, however, is not easy to identify in the fossil record. Two characteristics of the skull which can be used to distinguish reptiles form amphibians are:

  1. The reptile skull is high and narrow, whereas the amphibian skull is low and broad
  2. The roof of the mouth of the reptile is arched, with small openings. The roof of the mouth of the amphibian is flat with large openings.

Dicynodon, Late Permian plant-eating reptile,
250-230 million years ago,
from Cape Province, South Africa.

Using this reference http://tolweb.org/tree?group=Amniota&contgroup=Terrestrial_Vertebrates , answer the following questions.

  1. What are amniotes? ____________________________________________

  2. What are the oldest amniotes currently know (give genus) and where were they found?
     
    genus ____________________________________

    locality ________________________________________________

    See also this reference, The Tree Stump Animals, available online at: http://museum.gov.ns.ca/fossils/sites/joggins/joggins2.htm.

  3. What is the age of the oldest known amniotes (period name)? _____________________

  4. The amniotes diverged into two lines. List them below. Also list what they include or gave rise to.

    1. _________________, which includes or gave rise to __________________________________

    2. _________________, which includes or gave rise to __________________________________

  5. Describe the amniotic egg.

    Relationships between the various groupings of amniotes can be studied using molecular biology. Genetic similarities between the various groups can be quantified.

  6. Sketch the phylogeny diagram which shows the relationships between the various groups of amniotes as determined by current molecular methods:
  7. Does molecular evidence agree or disagree with paleontologic evidence? _____________

    Read this reference to learn about temporal fenestration (holes in the side of the skull) http://tolweb.org/tree/eukaryotes/animals/chordata/amniote_lichen/Temporal_fenestration.html.

    You may also see diagrams in your textbook, if available.

    More information on temporal fenestration is found here http://www.ucmp.berkeley.edu/anapsids/anapsidamm.html
    and here
    http://www.ldeo.columbia.edu/dees/courses/v1001/permtrias8.html .

  8. List the animals that belong to each group:

    1. Anapsida (no holes) ____________________________

    2. Diapsida (two holes) ____________________________

    3. Euryapsida (upper hole only) ____________________________

    4. Synapsida (lower hole only) ____________________________

K. Mammal-like Reptiles


Permian pelycosaur, Edaphosaurus

In the Permian, the synapsids were the dominant terrestrial vertebrate. The synapsids gave rise to the mammal-like reptiles and then to the mammals. The best known group of Permian synapsids were the pelycosaurs, several of which had sails on their backs, supported by spines from their vertebrae. Two well known pelycosaurs which evolved their sails independently were Dimetrodon and Edaphosaurus.

See these references for information and pictures of Dimetrodon.

American Museum of Natural History http://www.amnh.org/exhibitions/expeditions/treasure_fossil/Fossils/Specimens/dimetrodon.html

Palaeos web page on Synapsids - Sphenacodontia http://www.palaeos.com/Vertebrates/Units/Unit390/400.html#Dimetrodon

See this web page for an illustration of Edaphosaurus:

Palaeos web page on Synapsids - Ophiacodontidae & Edaphosauridae http://www.palaeos.com/Vertebrates/Units/Unit390/390.300.html

Compare the pictures of Dimetrodon and Edaphosaurus (particularly at the Palaeos web site).

  1. Which genus has the larger head? _____________________________

  2. Note the teeth of Dimetrodon. What did it probably eat? _____________

Edaphosaurus, had blunt, almost peg-like teeth and probably dined on plants.

For more information on Dimetrodon and Edaphosaurus, including comments on thermoregulation, see these references:

Paul Olsen's dinosaur course at Columbia University http://www.ldeo.columbia.edu/dees/courses/v1001/permtrias8.html

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This page created by Pamela J. W. Gore Pamela.Gore@gpc.edu
Georgia Perimeter College

Modified June 11, 1999
Links updated April 17, 2001
Links updated June 7, 2001
Link updated April 19, 2002
Modified April 9, 2003
Modified July 9, 2003
Links updated December 11, 2003
Links updated December 10, 2004
Online journal link updated December 13, 2004
Updated April 18, 2006
Modified December 12, 2006
Links updated July 18, 2008