[Campbell Biology P.726] Which of the following statements accurately describes the animal l... | Practice Question

Which of the following statements accurately describes the animal life associated with the Cambrian explosion?

  • A: The Cambrian explosion primarily led to the diversification of soft-bodied organisms, similar to those of the Ediacaran period.
  • B: Bilaterians, characterized by bilateral symmetry and a complete digestive tract, represent a significant portion of the animal phyla that emerged during the Cambrian explosion.
  • C: The oldest fossils of all extant animal phyla were discovered in pre-Cambrian strata.
  • D: Arthropods, chordates, and echinoderms only appeared after the Ordovician period.

Explanation

The text explicitly states that 'paleontologists have found the oldest fossils of about half of all extant animal phyla, including the first arthropods, chordates, and echinoderms.' It further describes that 'most of the fossils from the Cambrian explosion are of bilaterians, an enormous clade whose members... typically have a two-sided or bilaterally symmetric form and a complete digestive tract.'