Difficulty: Easy

Average Score: 83%

What is true of organisms shown on this cladogram?

Diagram for question

Rationale

Sharks and rays have vertebrae but lack a bony skeleton.

Sharks and rays, classified as cartilaginous fish, possess a skeleton made primarily of cartilage rather than bone, which is a defining characteristic of their group. While they do have a vertebral column, their lack of a bony skeleton differentiates them from bony fish and other vertebrates.

A (Birds are the only species that produce eggs with shells.) YOUR ANSWER

This statement is incorrect because while birds do produce eggs with hard shells, reptiles (including turtles and some other species) also lay eggs with shells. Therefore, birds are not the only group capable of this reproductive strategy.

B (Amphibians are four-limbed species but lack a bony skeleton.) YOUR ANSWER

Amphibians do possess a bony skeleton; they are vertebrates with a skeletal structure made of bone that supports their four-limbed body plan. This choice misrepresents the anatomical features of amphibians, which include frogs, toads, and salamanders.

D (Only species with hair produce amniotic eggs.) YOUR ANSWER

This statement is misleading as it suggests that only mammals (the group characterized by hair) produce amniotic eggs. In fact, amniotic eggs are also produced by reptiles and birds, making this claim inaccurate.

Conclusion

The cladogram illustrates the evolutionary relationships among different species, highlighting that sharks and rays are vertebrates with a cartilaginous skeleton. While other groups like birds and amphibians possess distinct characteristics, the unique feature of lacking a bony skeleton stands true for sharks and rays, reinforcing their classification as cartilaginous fish. Understanding these differences is crucial for studying the evolutionary adaptations of various organisms.

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