Name: __________________________ Period: ____ Date: __________ Score: ______

The Evolution of the Horse in North America Purose:__________________________________________________________________________________________________________________________________________________ Background: “FOSSILS” supply physical evidence to biologists that indicate continuous changes have occurred in organisms throughout very long periods of time. FOSSILS are our link to the past, often giving a clear picture of organisms’ form, type behavior, kin, habitat, etc. FOSSILS are the remains of organisms which have withstood the passage of time. They can be bones or teeth, skulls, or whole plants and/ or animals, or the imprints of such preserved in rocks. FOSSILS are preserved in rocks by a series of lucky accidents. Unless the right conditions exist, dead organisms will quickly disappear (either by decaying away or perhaps being eaten as food by scavengers or decomposers). The concept of organic evolution has introduced the idea that species may change, and under appropriate conditions, new species may result from older species over long periods of time. This same theory explains that extinct forms of life (known only from fossil evidence) may represent the possible ancestors of our present-day organisms

The real origin of horses is unknown! However, through fossil evidence, the Family Equidae provides about the most complete record of evolution of any animal series which led to the formation of the present-day donkeys, zebras, and horses. The principal changes in the horse forms over the last 54,000,000 years include:

a. AN INCREASE IN OVERALL SIZE from that of a cat to that of today’s horse (and the many different forms arising from human “selective breeding”)

b. A LARGER HEAD AND LONGER HEAD-SNOUT AREA anterior to the eyes c. AN INCREASE IN LENGTH AND MOBILITY OF THE NECK d. AN INCREASE IN SIZE OF PREMOLAR AND MOLAR TEETH to allow

horses to change from eating tropical leaves/fruits to grazing in grasslands. e. AN ELONGATION OF LIMBS resulting in a greater running ability f. A REDUCTION OF THE TOES from five to one which today is covered by a

hoof Due to these changes, the horse became a long-legged, swift-running mammal, suited to live and feed on open grasslands, with tall strong teeth having may enameled edges to grind harsh grassy vegetation through a long life Pre-lab Discussion Questions 1. What is a fossil? _________________________________________________

2. Read and Study Figure 17-2 on pg 418. The outline how a FOSSIL might get

formed:__________________________________________________________ ________________________________________________________________

3. Describe a place that provides the BEST conditions for a FOSSIL to form: _____

________________________________________________________________

4. What type of animal might fossilize well?_______________Why?____________ ________________________________________________________________

5. There is an abundance of fossils of an animal type who dominated the earth during the Mesozoic Era and no longer lives today. Name this animal type? _________________ Are there plant fossils? ____________________

6. Does the “fossil record” indicate that life on the planet is different today than life that occurred in the past? ______________(yes or no)

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Procedures: The table below contains information collected on specific Horse Genera over a 54,000,000 year period

• Genus: Eohippus sp. Or (Hyracotherium sp.) • Overall height at the shoulders….11 inches • Eye-snout tip distance ….5 centimeters • Complexity rating of “cheek teeth”…(see table: Cheek teeth”) • Trunk/ leg length differential…+0.5 • Number of toes on forefoot (pad-footed)...(determine from diagram,

page 4) • PRECIPITATION: (PPT)…134.5cm • POTENTIAL EVAPOTRANSPIRATION (PE) …86.6 cm

• Genus: Mesohippus sp or (Miohippus sp.) • Overall height at the shoulders….24 inches • Eye-snout tip distance ….11 centimeters • Complexity rating of “cheek teeth”…(see table: Cheek teeth”) • Trunk/ leg length differential…+1.0 • Number of toes on forefoot (pad-footed)...(determine from diagram,

page 4) • PRECIPITATION: (PPT)…89.3cm • POTENTIAL EVAPOTRANSPIRATION (PE) …62.3 cm • Genus: Merrychippus sp. Or (Protohippus sp.) • Overall height at the shoulders….40 inches • Eye-snout tip distance ….19 centimeters • Complexity rating of “cheek teeth”…(see table: Cheek teeth”) • Trunk/ leg length differential…+1.5 • Number of toes on forefoot (pad-footed)...(determine from diagram,

page 4) • PRECIPITATION: (PPT)…101.9cm • POTENTIAL EVAPOTRANSPIRATION (PE) …67.3 cm

• Genus: Pliohippus sp. Or (Hipparion sp.) • Overall height at the shoulders….43 inches • Eye-snout tip distance ….23 centimeters • Complexity rating of “cheek teeth”…(see table: Cheek teeth”) • Trunk/ leg length differential…+3.5 • Number of toes on forefoot (pad-footed)...(determine from diagram,

page 4) • PRECIPITATION: (PPT)…55.1cm • POTENTIAL EVAPOTRANSPIRATION (PE) …63.3 cm • Genus: Epuus sp • Overall height at the shoulders….60 inches • Eye-snout tip distance ….34 centimeters • Complexity rating of “cheek teeth”…(see table: Cheek teeth”) • Trunk/ leg length differential…+5.0 • Number of toes on forefoot (pad-footed)...(determine from diagram,

page 4) • PRECIPITATION: (PPT)…18.3 cm • POTENTIAL EVAPOTRANSPIRATION (PE) …42.4 cm

1. Following the instructions below, extract all necessary data from information above, and then place these data appropriately on the Data Table (page 4)

EOCENE EPOCH 54-38 MYA

OLIGOCENE EPOCH 38-26 MYA

MIOCENE EPOCH 26-12 MYA

PLIOCENE EPOCH 12-2 MYA

PLEISTOCENE EPOCH 3 MYA- 10,000 Y

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A. GENUS NAME Transfer each Genus Name to the Data Table (Note: two names are given for some; those in parentheses are the older names, no longer in popular use. B. SHOULDER HEIGHT Before transferring these data, convert inches to centimeters by multiplying the known heights (given in inches) by 2.54 centimeters. Remember 1 inch= 2.54 centimeters. C. ENVIRONMENTAL CONDITIONS 1) PRECIPITATION (PPT) represents the average annual amount of ground water obtained from rain, snow, hail, sleet, fog, etc; indicated in centimeters. Plot this amount directly in the upper portion of the box. 2) POTENTIAL EVAPOTRANSPIRATION (PE) represents the average amount of water that could be lost to the atmosphere from evaporation from earth (drying out) plus from transpiration from plants (natural water loss from plants; in centimeters). Plot this amount directly in the lower portion of the box. 3) WET or DRY ENVIRONMENT…PPT and PE are rarely equal; one is usually is usually greater than the other. Use the rules below to determine ‘wet” or “dry”:

If PPT is GREATER than PE……..WET conditions exist If PE is GREATER than PPT….. DRY conditions exist

4) BIOMES are determined by comparing the “extent of how wet” or “extent of how dry” in centimeters using the information below: WET DRY D. NUMBER OF TOES on forefoot. Transfer all data to data table.

TROPICAL FOREST when PPT is 40 cm or more than PE TEMPERATE FOREST when PPT is 10-39 cm more than PE SAVANNA when PPT is 00-09 cm more than PE BRUSHLAND when PE is 00-09 cm more than PPT GRASSLAND when PE is 10-39 cm more than PPT DESERT when PE is 40 cm more than PPT

Examine the number of toes and answer this question: Why do you think having smaller number of toes is more advantageous to a modern horse?

4 toes 3 toes 3 toes 1 toe

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E. TOOTH COMPLEXITY When soft, juicy, succulent foods are eaten, few grinding surfaces are evident on teeth. As drier conditions result in dry grass and dry seeds, more chewing is needed and greater, more complex grinding surfaces become evident on parietal or ”cheek teeth”. The RATING SCALE for molars and premolars is

#1….LEAST COMPLEX….fewest grinding surfaces for “soft” foods #2 #3 #4 #5….MOST COMPLEX….most grinding surfaces for “hard” dry foods

Table: “Cheek Teeth” F. GRAPHING extract data from the Data Table onto the appropriate Graphs: 1) Shoulder Heights 2) PPT/PE 3) Number of Toes 4) Tooth Complexity Results: DATA TABLE…Evolution of the Horse in North America ‘

EPOCH SHLDR

HT.

GENUS NAME

PPT/ PE

WET/ DRY

BIOME

No. of TOES

TOOTH COMPLEXITY

EOCENE EPOCH

OLIGOCENE EPOCH

MIOCENE EPOCH

PLIOCENE EPOCH

PLEISTOCENE EPOCH

Environmental Conditions

Eohippus Mesohippus Mercyhippus Pliohippus Equus

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Discussion Questions: (answer on separate sheet of paper) 1. List the BIOME types the various horse forms encountered going from the earliest (Eocene) to the most recent (Pleistocene) 2. What single factor in the horses’ environment contributed to this BIOME shift or change? 3. Describe and Contrast the kind of foods available to horses in: A) a tropical Forest biome; and B) a Grassland Biome 4. Which of the “foods” (WET or DRY) would the horse… A. have to eat more of to fulfill its energy requirement? B. find greater difficulty in eating and digesting? 5. How did the tooth size and tooth complexity change to meet dietary requirements over 54 million years? 6. Why is a larger, more involved digestive system found in a “Grassland” horse than in a “Tropical Forest” horse? 7. How might 4-workable toes and short legs be an advantage in a “Tropical Forest” Biome? and a disadvantage in a “Grassland Biome”? 8. Give a definition for the word “ADAPTATION” IN YOUR OWN WORDS. 9. Why would the following “adaptations” help the horse survive in a “Grassland” environment? A) fore feet with a single toe and hoof? B) larger teeth with more grinding surfaces? C) longer snout and a longer, flexible neck? 10. Are “Grassland” HERBIVORES generally larger or smaller than “Grassland” CARNIVORES. Explain/defend your answer. Results: Complete Graphs I-IV using the results from the Data Table.

cm Graph I: Shoulder Height (Centimeters)

Graph I: Label the following: X-Axis with the 5 Epochs Y-Axis with shoulder height 0-160 cm

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cm Graph II: Precipitation (PPT) &

Evapotranspiration (PE)

Graph III: Total Number Toes on Forefoot

Graph IV: Complexity in Grinding Surfaces

Graph II: Label the following: X-Axis with the 5 Epochs Y-Axis with shoulder height 0-160 cm On this graph, you must plot TWO sets of data: • PPT for each Epoch • PE for each Epoch Color BLUE the area where PPT > PE Color BROWN the area where PE > PPT

Graph III: Label the following: X-Axis with the 5 Epochs Y-Axis Toes per forefoot (0-7)

Graph IV: Label the following: X-Axis with the 5 Epochs Y-Axis Grinding Surface (0-7) #5= Most Complex, most grinding surfaces, mostly hard, dry foods. #1= Least complex; fewer grinding surfaces, mostly soft foods

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Other evidences that show that horses have evolved over a long period of time: Background: You have reviewed the fossil evidence from the bone and teeth structures of horses through the different epochs. The fossil evidence clearly shows that the horse has changed in form and function based on environmental pressures. Is there additional evidence available to support the theory of evolution?

A) Homologous Structures: Pg 384 in textbook 1) Define the word ‘homologous’ (margin on Pg 384):

2) What are homologous body structures? Explain with an example.

3) Examine the picture of the homologous structures below: How are the limb structures of all the animals (vertebrates) similar or dissimilar?

4) How does this picture support the theory of evolution of organisms?

B) Vestigial Structures: (Last paragraph Pg 384) 5) What are Vestigial structures?

HUMAN BIRD BAT CAT HORSE WHALE

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6) Give examples of vestigial structures.

7) How are vestigial structures used as evidence for evolutionary theory?

8) Can you think of structures in the ancestral tropical horse that might have become vestigial in the modern horse?

9) Define this word - Speciation: (Pg 404)

10) What can two organisms that belong to different species not able to do?

11) Do you think that if the ancestral horse was still alive, would it be able to mate and interbreed with the modern horse?