Problem 6 - Biology: The Unity and Diversity of Life

Question

Turtles, lizards, and birds belong to one major lineage of amniotes, and ____ belong to another. a. sharks b. frogs and toads c. mammals d. salamanders

Step-by-Step Solution

Answer

Mammals belong to the other major lineage of amniotes.

Step 1: Understanding Amniotes

Amniotes are a clade of tetrapod vertebrates comprising the reptiles, birds, and mammals. They are distinguished by having an amniotic egg, which contains a membrane that allows them to lay eggs on land rather than in water.

Step 2: Identifying Major Lineages

The major lineages of amniotes are divided primarily into two groups: the sauropsids, which include turtles, lizards, and birds; and the synapsids, which are primarily mammals. Each lineage has its own unique characteristics.

Step 3: Choosing the Correct Group

Given that turtles, lizards, and birds are part of the sauropsid lineage, we need to identify which options belong to the other major lineage, synapsids. Among the options provided, mammals are the only members of the synapsid lineage.

Step 4: Eliminating Incorrect Options

Let's briefly review the other incorrect options: - Sharks: They are fish, not amniotes. - Frogs and toads: They are amphibians, not amniotes. - Salamanders: Like frogs and toads, they are amphibians and do not belong to the amniote clade.

Key Concepts

Sauropsids

Sauropsids are one of the two major groups within the clade of amniotes. This diverse lineage includes modern reptiles such as turtles and lizards, as well as birds. Unlike their fellow amniotes, the synapsids, sauropsids showcase a unique evolutionary path especially suited for diverse environments.

Some of the key traits that define sauropsids include:

• Scales covering their bodies, which help in water conservation.
• Efficient energy usage for regulating body temperature, particularly in reptiles.
• Birds have adapted to flight with features such as feathers and a high metabolic rate.

These adaptations have enabled sauropsids to thrive across numerous ecological niches around the world.

Synapsids

Synapsids are the second major group of amniotes, primarily consisting of mammals. This lineage diverged from sauropsids around 312 million years ago. Synapsids include modern mammals and their extinct ancestors, known as the "mammal-like reptiles."

Some defining characteristics of synapsids include:

• A single opening in the skull, known as the temporal fenestra, behind the eyes, which aids in muscle attachment.
• Warm-bloodedness (endothermy), allowing them to maintain a constant internal body temperature.
• The presence of hair or fur for insulation and sensory purposes.

Mammals, as the most recognized members, exhibit a wide range of complex behaviors and a high degree of parental care, setting them apart from many other vertebrates.

Amniotic Egg

The amniotic egg represents a significant evolutionary adaptation that distinguishes amniotes from other tetrapod vertebrates. This unique type of egg includes a protective shell and several membranes, which work together to support and conserve the developing embryo.

Key features of the amniotic egg include:

• The amnion, a membrane that creates a protective fluid-filled cavity around the embryo.
• The chorion, which facilitates gas exchange with the environment.
• The allantois, responsible for waste management and gas exchange.
• The yolk sac, providing essential nutrients for the growing embryo.

This innovation permitted amniotes to lay eggs on land, facilitating their widespread colonization of terrestrial habitats.

Tetrapod Vertebrates

Tetrapod vertebrates are a broad group that includes all vertebrates with four limbs. This group encompasses amphibians, reptiles, birds, and mammals. While some tetrapods have lost limbs during evolution (like snakes), they still belong to this group based on their ancestry.

Significant evolutionary developments in tetrapods include:

• Limbs with digits, which provided mobility and support on land.
• Evolution of lungs for breathing air outside aquatic environments.
• Development of a robust skeletal structure to accommodate life on land.

Tetrapods play crucial roles in ecosystems throughout the world, showcasing a remarkable diversity adapted to a multitude of lifestyles.