Mushrooms and molds were once grouped with the plants. Which finding led biologists to place fungi in a kingdom of their own?

Biologists argued for over a century about whether the giant panda belonged with the raccoons or with the bears. What settled the question in the 1980s?

The red panda has been placed at different times in the raccoon family and the bear family, and it is now in a family of its own, Ailuridae. Which evidence drove that final move?

Sequence data place whales inside the even-toed hoofed mammals, with the hippopotamus as their closest living relative. Which further evidence supported that grouping?

Birds are now classified within the dinosaurs because they share derived features, including feathers, a wishbone and hollow bones, with theropod dinosaurs.

Organisms once called blue-green algae were classified with the plants until their cells were examined at high magnification. What was found that moved them to the bacteria?

The elephant shrew is a small insect-eating mammal with a pointed snout, and it looks much like a true shrew. Sequence data place it with elephants, aardvarks and manatees. How should it be classified?

Falcons hunt like hawks and have the same hooked beak and gripping talons, but whole-genome data group them near parrots and songbirds. Which classification does the evidence support?

Swifts and swallows both have narrow curved wings and catch insects on the wing, yet swifts are grouped with hummingbirds. Which evidence should carry more weight in that decision?

Species X shares 96 percent of a gene sequence with species Y and 71 percent with species Z. X and Z look almost identical in the field. What grouping does the sequence evidence support?

A lungfish looks like an ordinary fish, but anatomical and sequence evidence show it is more closely related to amphibians and mammals than to a salmon. What does this mean for classification?

Two populations of insects that look almost identical must always be placed in the same species.

American cacti and African euphorbias both store water in thick, spiny, green stems, yet they are placed in different plant families. What best explains the resemblance?

The sugar glider is a marsupial and the flying squirrel is a placental mammal, yet both glide on a skin flap stretched between the limbs. Why are they not classified together?

The extinct ichthyosaur was a marine reptile shaped almost exactly like a dolphin, which is a mammal. What does a biologist call a similarity of this kind?

An octopus eye and a human eye both focus light through a lens onto a retina, yet the two animals belong to different phyla. Which statement about that similarity is correct?

Carl Woese compared ribosomal RNA sequences and found that methane-producing microbes differ from familiar bacteria as much as either differs from organisms with nuclei. What change followed?

The electron microscope let biologists see cell structures far too small for a light microscope. How did that tool change the classification system?

Gene sequencing showed that the organisms gathered into kingdom Protista are many distantly related lineages rather than one group with a recent shared ancestor. What does that result mean for the kingdom?

Cladistics groups organisms by shared derived characters and requires a group to contain every descendant of its common ancestor. Why does the traditional class Reptilia fail that requirement?