Question

Common dolphin Ichtyor Ichthyosaurs were aquatic dinosaurs. They had dorsal fins and flippers that, at least superficially, resemble dolphins, even though their closest common ancestors were terrestrial reptiles that had neither dorsal fins nor aquatic tails. (See figure at right) Titelů The members of lineages between the dolphins and ichthyosaurs do not have adaptations such as -streamlined bodies -long ased with teeth -Ins and hopers 4. Using terms and concepts from class explain why these organisms look so similar to each other. 5 You have been asked to develop a list of shared ancestral traits that were found in the common ancestor of the Rodents and Primates (see phylogeny above). Of course you know you need to find an outgroup to do this accurately. Looking at the phylogeny above which group would be the best outgroup? a.) Marsupials b.) Whales and dolphins c.) Lizards d.) birds e.) either cord would work as an outgroupe explain your answer: (hint: be sure to tell me what makes a good outgroup!)

Answer 1

4. Ichthyosaurs and dolphins have dorsal fins and flippers but they are not closely related. They don't share any recent common ancestor. So by maximum parsimony principle, Dorsal fins and flippers are the analogous organs. That means Ichthyosaurs developed these dorsal fins and flippers independently as adaptations to a common function. This type of evolution when species have different ancestral origins but have similar traits is called convergent evolution.

5. Option a. Marsupials can be taken as outgroup.

Because, as we know outgroup is the lineage which is outside the clade being studied but it must be closely related to the clade.

Our clade of interest is rodent, primates whales and dolphins and elephants. So Marsupials is an outgroup to our clade because it is outside the clade and closely related to the clade.

○Whales and dolphins can't be outgroup. Because it is in our clade or ingroup.

○Lizards and birds also can't be outgroup because they are not closely related to the clade

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