GREAT TRANSITIONS INTERACTIVE Using the HHMI Click and Learn “Great Transitions Interactive,” you will explore the evolution of four- limbed animals from fish, focusing on transitional forms with features of both fish and tetrapods, and see the progression of anatomical changes from reconstructed fossil skeletons. INTRODUCTION 1. Tetrapods are 2. Tetrapods first appear in the fossil record 3. Charles Darwin predicted that tetrapods evolved from that hypothesis? Examples of tetrapods include _and ANATOMICAL FEATURES OF TRANSITIONAL FORMS Gills or Lungs? 5. Fish use d you 4. What evidence would you expect to find to support that hypothesis? What age rocks would y look in and why? million years ago. 8. Lungs allow an animal to breathe 9. Tetrapods use evolved during the Devonian period also had 6. In fossils, what anatomical evidence indicates that gills were present? 7. Many transitional species had gills which means that they lived in What observation leads to to breathe underwater. (However, many species of l
The Correct Answer and Explanation is:
Here is a completed version of the worksheet introduction section based on the HHMI Click and Learn: Great Transitions Interactive:
INTRODUCTION
- Tetrapods are: vertebrate animals that have four limbs or limb-like appendages.
- Tetrapods first appear in the fossil record: about 365 million years ago, during the Devonian period.
- Charles Darwin predicted that tetrapods evolved from: fish, particularly lobe-finned fish.
- What evidence would you expect to find to support that hypothesis?
- Transitional fossils that show a mixture of fish and tetrapod characteristics, such as fins with bones resembling limbs.
- Fossils with both gills and lungs.
- Rock layers from the Devonian period that contain these transitional fossils.
- Examples of tetrapods include: amphibians, reptiles, birds, and mammals.
ANATOMICAL FEATURES OF TRANSITIONAL FORMS
- Fish use: gills to breathe underwater.
- In fossils, what anatomical evidence indicates that gills were present?
- Presence of gill arches or grooves on the side of the skull, similar to those in modern fish.
- Many transitional species had gills, which means that they lived in: aquatic or semi-aquatic environments.
- Lungs allow an animal to breathe: air from the atmosphere instead of water.
- Tetrapods use: lungs to breathe on land, and their lungs likely evolved during the Devonian period.
- What observation leads to that hypothesis?
- Fossils such as Tiktaalik and Acanthostega show a mix of features including both gills and lungs.
- Some fish today (e.g., lungfish) also have both gills and lungs, supporting the idea that lungs evolved before full land transition.
Explanation (300+ words):
The transition from aquatic lobe-finned fish to four-limbed land-dwelling tetrapods is a landmark in vertebrate evolution. Tetrapods are vertebrates with limbs (arms, legs, wings, or flippers), and they include amphibians, reptiles, birds, and mammals. According to the fossil record, tetrapods first appeared about 365 million years ago during the Devonian period, a time of significant evolutionary change in aquatic ecosystems.
Charles Darwin hypothesized that tetrapods evolved from fish, specifically lobe-finned fish that possessed fleshy, lobed fins supported by bones. To support this, scientists have sought fossils from Devonian-age rocks, since that’s when tetrapods emerged. Evidence would include transitional species—organisms that show characteristics of both aquatic fish and early land-dwelling animals. For example, Tiktaalik roseae, discovered in 2004, is a pivotal transitional fossil. It lived about 375 million years ago and had both fish-like features (such as gills, scales, and fins) and tetrapod-like features (such as a neck, a flat head, and bones in its fins that resemble wrists).
Anatomical features in these fossils help scientists determine whether the animal used gills or lungs. For instance, the presence of gill arches in the skull indicates aquatic respiration, while a ribcage capable of supporting lungs and evidence of nostrils suggest the ability to breathe air. Many transitional species, like Acanthostega, had both gills and primitive lungs, suggesting they lived in shallow water or swampy environments and could survive temporary exposure to air.
This evolutionary journey highlights how gradual anatomical changes, driven by environmental pressures, allowed vertebrates to move from water to land. Transitional fossils bridge the gap between fish and tetrapods, confirming Darwin’s prediction and illuminating one of life’s great transitions.