Laboratory 15 - The Evolution of the Vertebrates
Pamela J. W. Gore, Department of Geology, Georgia Perimeter College, Clarkston, GA 30021
1982-1999, 2001, 2003, 2004 Pamela J. W. Gore
This lab is to be done using the Internet. Click on the hyperlinks to reach outside web pages to
look for the answers to the questions.
Using this reference to answer the following question:
University of California, Berkeley, Museum of Paleontology, 1995, Introduction to the
Chordata, available online: http://www.ucmp.berkeley.edu/chordata/chordata.html.
The vertebrates belong to Phylum Chordata.
What are four characteristics of the Chordata?
(a) _______________________________________
(b) _______________________________________
(c) _______________________________________
(d) _______________________________________
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
The main bony disk-shaped or spool-shaped portion of the vertebra is called the
________________________.
The nerve or spinal cord passes through the ____________________________.
The neural arch is elongated into spines in some vertebrates.
Vertebrates possess two types of bone. What are they?
(a) _______________________________________
(b) _______________________________________
The Earliest Chordates - Pikaia
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
The Smithsonian has a sketch of Pikaia
(http://nmnhgoph.si.edu/paleo/shale/ppikaia.htm), emphasizing the "muscle blocks"
which give Pikaia a segmented appearance. The color picture of Pikaia's habitat
(http://nmnhgoph.si.edu/paleo/shale/pamsci.htm) gives a better illustration of its mode of
life.
What was its mode of life? ________________________________
Explore these several links to Pikaia, and give its age (period name and years).
_______________________________________________________
In which well-known geologic formation is it found? ______________________________
Sharks - Class Chondrichthyes
Sharks are unique in that their entire skeleton is permanently made of cartilage. Only their teeth
are made of hard material. Read about the Late Devonian shark, Cladoselache in the following
reference:
Williams, Michael E., 1992, Jaws: The early years, Feeding behavior in Cleveland Shale
sharks, Cleveland Museum of Natural History, available online:
http://www.cmnh.org/collections/vertpaleo/jaws/jaws.html.
In what type of rock is the shark preserved? ______________________________
Describe the depositional environment of the rock (marine or non-marine? shallow water or
deep water?) ______________________________________________________________
The cartiledge that makes up the shark skeleton is not normally preserved. What remains of
sharks are most common in the geologic record? ____________________________________
Rare complete articulated shark skeletons with soft tissue preservation are present in the
Cleveland shale. What are two factors that probably caused the preservation of the shark soft
parts?
(1)_______________________________________________________
(2)_______________________________________________________
What was the mode of preservation of the sharks in the Cleveland shale?
_______________________________________________________
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 tusklike projections) and no
preservable internal skeleton. The only structure made of bone was the external armor.
What was their internal skeleton made of? ___________________________
Use the following references to answer the questions:
American Museum of Natural History
http://www.amnh.org/exhibitions/expeditions/treasure_fossil/Fossils/Specimens/dunkleos
teus.html
University of California, Berkeley, Museum of Paleontology
http://www.ucmp.berkeley.edu/vertebrates/basalfish/placodermi.html
Williams, Michael E., 1992, Jaws: The early years, Feeding behavior in Cleveland Shale
sharks, Cleveland Museum of Natural History, available online:
http://www.cmnh.org/collections/vertpaleo/jaws/jaws.html.
Which genus was the "undisputed ruler" of the sea, found in the Cleveland shale?
______________________________________________________
How long was it? ___________________ feet
How much did it weigh? _________________
Was it a predator or a scavenger? _____________________________
How can we tell? ___________________________________________
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.
What might its uses be for this placoderm fish? _______________________________
Bony Fishes - Class Osteichthyes
Picture: 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)
a. Order Crossopterygii - lobe-finned fishes ancestral to amphibians, also includes
coelacanths
b. Order Dipnoi - lungfishes
Use this reference to answer the following questions:
Herbert, Thomas J., 1999, Vertebrate Evolution I, Chordates and the Evolution of the
Craniata, Biology 160, University of Miami, available online:
http://www.bio.miami.edu/tom/bil160/bil160goods/19_verts1.html.
The ray-finned fishes are the dominant fishes in the world today.
When did they first appear? __________________________________
Did they arise in freshwater or in marine water? _______________________________
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 m.y., 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 Ceolacanth, 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/coela
can.html?aa
Sketch the shape of the tail of the coelacanth.
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.
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 question:
Herbert, Thomas J., 1999, Vertebrate Evolution I, Chordates and the Evolution of the
Craniata, Biology 160, University of Miami, available online:
http://www.bio.miami.edu/tom/bil160/bil160goods/20_verts2.html.
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)
When did the first plants appear on the land? __________________ (period name)
When did the first animals appear on the land? ____________________ (period name)
Which group of vertebrate animals was the first to appear on the land?
_____________________
Why did plants make the transition to land before the animals? ___________________
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 fishlike (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
List the major characteristics of amphibians.
When did the amphibians first appear? _______________ (period name)
What were the ancestors of the amphibians? _______________________
Ichthyostega, an amphibian that appeared in the Late Devonian, retained many of the features
of its fish ancestors. For 50 million years, from the Late Devonian to the Middle Carboniferous,
amphibians were the only vertebrates to 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 mya
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 mya,
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
An additional reference on amphibian fossils in Iowa .
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. 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 proceses of an animal by looking at the modifications of is skeleton.
Reptiles - Class Reptilia
Complete colonization of land was achieved by the reptiles which could lay eggs on land. Egglaying, 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.
This is an example of a Late Permian plant-eating reptile,
Dicynodon (250-230 mya),
from Cape Province, South Africa.
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/Unit390/300.html#Edaphosaurus
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 peglike teeth and probably dined on plants.
For more information on Dimetrodon and Edaphosaurus, including comments on
thermoregulation, see these references:
California State University, Fullerton:
http://biology.fullerton.edu/courses/biol_404/web/hol/hol_ch10.html .
Paul Olsen's dinosaur course at Columbia University
http://www.ldeo.columbia.edu/dees/courses/v1001/permtrias8.html
This page created by Pamela J. W. Gore