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Fossil Preservation

Identifying Fossil Shark Teeth

Megatoothed Sharks

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Megatoothed Sharks

Another exercise explores the evolution of the megatoothed shark lineage leading to Carcharocles
megalodon, the largest predatory shark in history
with teeth up to 17 cm long (Figure 7). Megatoothed shark teeth have an excellent fossil record and show continuous transitions in morphology from the Eocene to Pliocene (Figure 8).

Fig 7

Figure 8. Megatoothed Shark Lineage. From left to right: Otodus obliquus (Paleocene to Early Eocene), Carcharocles aksuaticus (Early Eocene to Middle Eocene), C. auriculatus (Middle Eocene to Early Oligocene), C. angustidens (Early Oligocene to Late Oligocene), C. chubutensis (Late Oligocene to Early Miocene), C. megalodon (Early Miocene to Pliocene)

Objectives

Upon completing this activity students should be able to:

Sort fossil shark teeth into biologically reasonable species
Form hypotheses about evolutionary relationships among fossil shark teeth
Describe and interpret evolutionary trends in the fossil megatoothed lineage

Materials

One set of shark tooth cards for each group of students (Figure 9)
Photographs of teeth from the different megatooth sharks
Geologic timescale with ranges of sharks

Fig 9


Procedure
Put the students into groups of two or three and give each group a set of shuffled shark tooth cards. Instruct the students to group the cards into what they believe are separate species of sharks (Figures 10 and 11). Have the groups of students consider the evolutionary relationships among their species and ask them to arrange their species chronologically according to their first appearance in the fossil record. Have each group place the older appearing species below the younger appearing species. Engage the groups in a class discussion of their predictions and explain why some predictions may be more reasonable than others. Hand out the figures showing the ages and different species of megatooth sharks in their cards. Have students describe the evolutionary trends in the fossil megatooth lineage. Then ask the students to formulate several hypotheses that could explain the observed evolutionary trends. Conclude this exercise with a discussion of the environmental and biotic events occurring between the Eocene and Miocene epochs that may have caused the evolutionary charges in the megatooth shark’s teeth.
Fig 10	Fig 11

Resources
http://www.elasmo.com/frameMe.html?file=genera/cenozoic/sharks/carcharocles. html&menu=bin/menu_genera-alt. http://www.elasmo-research.org/education/evolution/origin_megalodon.htm http://www.elasmo.com/genera/slides/o_lineage/o_segue.html