EDEP Program Fall 2014| Week 1: Introduction to Megalodon
Lesson Topic
What was Megalodon?
What do we know about Megalodon?
How do we get information about Megalodon?
Lesson Objective
After this week, students will be able to:
· Describe what Megalodon was and discuss some general information about Megalodon
· Understand how we obtain information about Megalodon
· Use shark teeth to estimate body length and use shark centra to determine age
· Discuss the difference between archeology and paleontology
Words to know: Megalodon, cartilaginous skeleton, allometric relationship, archaeology, paleontology, centra, ectothermic
Background Information
Megalodon is the largest shark that ever lived! Estimated to be approximately 60 feet in length, Megalodon was the top predator in the world’s ancient oceans (17 million-2 million years ago). Megalodon contributed to the stability of ecosystems with the vast amount of marine animals consumed. It is important to learn about Megalodon because it improves our understanding of evolution and living shark conservation of today.
Most of what we know about Megalodon comes from this great shark’s teeth that have been found. Shark teeth can tell you a lot about a shark, like shark size and what they eat. Based on the size of Megalodon’s teeth, we know that the shark was larger than all modern and extinct sharks. It is difficult, however, to know the exact size of Megalodon. This is because entire shark skeletons are not preserved. Sharks have cartilaginous skeletons, meaning that their skeletons are composed of cartilage, which does not fossilize. So, only shark teeth and shark centra (vertebrae) can be found, and then estimates are made from these findings. It is fitting that teeth are so important to the study of Megalodon as its name comes from the Greek roots “megal” (big) and “odon” (tooth); thus, Megalodon means “big tooth”.
Modern sharks are also used to estimate the size of Megalodon. Scientists determined that an allometric relationship exists between the width of a tooth of sharks and their body length. An allometric relationship exists when there are anatomical variables that fit an equation. For modern sharks, it has been found that the width of a shark tooth is approximately 1/127th of the length of the shark’s body. Using this knowledge combined with teeth being found, it tells us that a Megalodon tooth that is 5.5 inches wide should yield a body length of about 700 inches. That is approximately 60 feet long!
While Megalodon did not live at the same time as humans, Megalodon still had an effect on ancient people. Ancient people found Megalodon teeth all over the world and collected them. This brings up the discussion of archaeology vs. paleontology. Archaeology is the study of past human cultures. Paleontology, on the other hand, is the study of ancient life (animals and plants). While there always seems to be confusion and overlap between these two terms, they are different. Studying how ancient people collected Megalodon teeth is an example of archaeology, while studying a Megalodon tooth itself is an example of paleontology.
The other part of a shark’s skeleton that is preserved is their centra. Shark centra are their backbones, like our vertebrae. Shark centra also give us information about that shark. Sharks are ectothermic, meaning that they are cold-blooded and control their body temperature through external means. Because of this, they record annual growth rings with the seasons, similar to those of trees. Dark bands indicate slower rates of growth during the winter, while lighter bands indicate faster rates of growth during the summer. This is true in both shark centra and tree rings. Counting these bands can determine the age of a shark at the time of its death. This can be tested by looking at the growth rings of captive sharks of known ages. The width of these lines also provides information about the shark. Wider, more spread out bands indicate faster growth, while narrower, more tightly-spaced bands indicate slower growth rates.
Activity
Warm Up to Program
About 10 minutes
Objective
Students will all design a fin as if they are a shark.
Materials
· Fin template
· Markers/colored pencils
· Tape
Procedure
1. Give each student a fin and allow them time to color/design how their fin would look if they were a shark.
2. Tape the fins onto the students’ backs when finished.
3. Let each student introduce themselves and tell us about their “shark-selves”.
Field Journals
About 10 minutes
Objective
Students will create their field journals that they will use throughout the program to record their observations in.
Materials
· Field journal sheets (Total 3 sheets of paper printed front and back per journal)
· Markers
· Stapler
Procedure
1. Have the students write their name and their school on the first page (the title page). Page numbers are on the bottom right hand corner of each page on a sheet.
2. Students may decorate the front side of the first sheet as they please. This is the front page and the back page.
3. Make sure the students do not write on any of the other pages yet; they will be filled in one week at a time with each activity.
4. Fold the sheets of paper into a booklet with 12 pages. Activity Leaders may need to assist students to help them get this part right.
5. When the field journal is properly assembled, staple it together.
How Big How Old?
About 45 minutes
Objective
Students will look at the only parts of ancient shark skeletons that are preserved – and learn why only these parts are preserved – and use them to determine Megalodon size and lifespan.
Materials
· Field Journals (one per student)
· Megalodon teeth (one is okay, more is better)
· Shark centra (one is okay, more is better)
· Calculators (one per student)
· 60 foot rope or measuring tape
· Whiteboard
Procedure
1. Begin by getting the students excited by telling them they are about to figure out the size of the largest shark to ever live! Have a short discussion about what Megalodon was. Ask the students how they think scientists have figured out his size (i.e. Are there clues? Are there any Megalodon alive today? Etc.). Lead the students to talk about using fossils to determine the size, tell them there is just one problem – pull out Megalodon tooth and shark centra and show students – these are the only fossils left from Megalodon and other sharks! Ask students what they think “Megalodon” means using the tooth fossil as a clue, and ask if they agree whether or not its name is fitting. Have them fill in the section of their Field Journals.
2. Ask students why they think the rest of a shark skeleton cannot be found. As a hint, tell them to feel/wiggle their nose and ears and compare that texture to that of their arm. Once the students get it, explain how sharks have cartilaginous skeletons, which do not preserve. So, all we have left from Megalodon are teeth and centra (explain what centra are).
3. Continue discussion by asking students how we can figure out how big Megalodon was just using teeth and/or centra. Once you get some good thinking and ideas from the students, try to lead them to come up with looking at modern sharks. Continue leading the discussion for the students, now about how looking at modern sharks can help us discover Megalodon’s size. Lead them to realize that we can find shark teeth from modern sharks and we know that same modern shark sizes. How can this help us?
4. Explain what an allometric relationship is and talk about how it has been studied and discovered that the width of a shark’s tooth is approximately 1/127th of the shark’s length. Give the students the simple equation: Shark Length=127 x (Tooth Width). Have the students write this down in their Field Journals.
5. Using this new knowledge, how can we find Megalodon’s length using the tooth? The students should be able to answer this question quickly. So let’s do it! We are going to measure the length of the Megalodon tooth and get an estimate of his body length.
6. In front of the class, measure the width of the tooth in inches (You can have the students do this themselves in groups, based on how many Megalodon teeth you have).
7. Once you get the width of the tooth, ask the students what you should do with it. Have the students write “Megalodon:” in their journals and then have them rewrite the shark length equation from before, but this time entering the tooth width measurement for the variable. Solve the equation with the class. This is the length of that particular Megalodon, in inches! Have the students write this number down.
8. Ask the students how they can convert it to feet so they can get a better idea of how big Megalodon was. Divide the inch total by 12 with the class, having them write this calculation in their journal as well. When you get a value for Megalodon in feet, have the students record this number with units and put a box around it.
9. Now you have the length of Megalodon. Explain to the students how scientists estimate that Megalodon ranged from approximately 45-60 feet in length. Go to a large open area and have a starting point and then have students predict how far they think 60 feet is by standing different distances away. Once a few students have predicted, use a 60 foot rope to show it. Ask students to compare other large things to the size of Megalodon, like a school bus, an elephant, etc. A modern school bus is typically about 30 feet long. Football field goal posts are also about 30 feet long. Megalodon is thought to be able to have grown to twice that length. Ask the students if they can imagine a shark being this big! Tell them how Megalodon was a top predator.
Additional Activity for Extension and/or if time allows
1. Return to the classroom and show the class the other part of the shark that can fossilize: the shark centra. Tell the students we use shark centra to figure out how old a shark lives to be. How can we do this? Pass centra around and have students offer suggestions. Does it look like anything else that tells how old something is? (Tree rings)
2. Discuss how these rings on the centra act the same way as tree rings. Explain how sharks are ectothermic and what that means, and why they develop these rings. Have the students figure out how old the shark (once again, if you have multiple centra, split them into groups). Have students draw a picture of the centra in their Field Journals, including the rings and labeling the age of that particular shark.
3. Discuss how these lines can also show growth rate. Draw two centra (circles) on the board of the same size. Make one of them have a lot of tightly spaced lines and the other one with less, more widely spaced lines. Ask the students which shark they think grew faster? Have them explain why.
4. Discuss how more widely spaced lines indicate a faster growth rate and vice versa. Show how this makes sense using the centra drawn on the board, explaining how one shark reached this size in a certain amount of years, while the other shark reached that same size in less time.
Wrap Up Activity
About 10 minutes
Objective
Students will calculate how long they would be if they were a shark based on their own teeth.
Materials
• Ruler
• Calculators (one per student)
Procedure
Have students measure the width of one of their front teeth then insert it into the shark length formula to find out how long they would be.
Glossary:
allometric relationship: exists when there are anatomical variables that fit an equation
archaeology: the study of past human cultures
cartilage: flexible connective tissue that is less rigid than bone but stiffer than muscle.
cartilaginous skeleton: skeletons composed of cartilage
centra: backbones, like human vertebrae
ectothermic: cold-blooded and control their body temperature through external means
Megalodon: the largest shark that ever lived, estimated to be approximately 60 feet in length, and was the top predator in the world’s ancient oceans (17 million-2 million years ago)
Paleontology: the study of ancient life (animals and plants)