Q42 - Reading a Cetacean Phylogeny for Lifestyle and Trait Evolution

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Figure 1 shows the evolution of cetaceans. Studies using stable isotopes indicate that Pakicetus and Amburocetus ate freshwater fish, while Remingtonocetus, Miacetus and Basirosaurus ate seawater fish. Indhyus was, like most extant artiodactyls, a terrestrial herbivorous animal. Judging ONLY from this phylogenetic tree, indicate whether each of the following statements is true or false.

A phylogenetic tree of cetaceans and artiodactyls. Extinct fossil species are shown with†. All extant cetaceans are classified into two subfamilies: Mysticeti (baleen whales, which do not possess enamel-based teeth but possess baleen plates) and Odontoceti (toothed whales, which possess teeth). A phylogenetic tree of cetaceans and artiodactyls. Extinct fossil species are shown with†. All extant cetaceans are classified into two subfamilies: Mysticeti (baleen whales, which do not possess enamel-based teeth but possess baleen plates) and Odontoceti (toothed whales, which possess teeth).

Using the information and data, determine which of the statements are true or which are false.

A. Under the maximum-parsimony criterion, the most recent common ancestor of the hippopotamus and modern cetaceans is amphibious.

B. There were no fully-aquatic cetaceans 50 MYA.

C. Based on these studies, the evolutionary scenario of cetaceans is speculated as follows: 1. becoming carnivorous, 2. becoming fully aquatic, 3. invasion to oceanic environments, 4. divergence into baleen whales and toothed whales.

D. The enamelin gene, which encodes an essential protein for the formation of teeth enamel, was lost during the evolution of cetaceans before 35 MYA.

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Question reproduced from IBO 2020, Theoretical Exam 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)