Question

Answer and explain both please.

Use this evolutionary tree representing the relationships among a group of vertebrates to answer questions 17 and 18. According to evolutionary theory, the letters at each branch point indicate the common ancestor for groups beyond that point. - Lung fishes Amphibians Mammals Lizards and snakes . Crocodiles - Birds 17. Which was the last (most recent) common ancestor of crocodiles and lizards/snakes? 18. Which of the following can be concluded from this evolutionary tree? A. Lungfish are not related to any of the other groups B. Birds and mammals are more closely related than are birds to lizards and snakes C. Birds are more closely related to lizards and snakes than to mammals D. Mammals are more closely related to amphibians than to birds E. Mammals are more closely related to lizards and snakes than to birds

Answer 1

17. The last (most recent) common ancestor of crocodiles and lizards/snakes was D.

From species D, two groups are evolved, one is lizards and snakes, and another one is species E. E is the ancestor of crocodiles and birds.

Species A, B, C and D were the common ancestors of crocodiles and lizards/snakes. But species D was their most recent common ancestor, as it has evolved most recently compared to the other common ancestors (species A, B and C). In other words, we can also say that no common ancestor of crocodiles and lizards/snakes is present after species D in the given evolutionary tree.

18.

A. "Lungfish are not related to any other groups". - this statement is wrong.

In the given evolutionary tree, lungfish are the outgroup, i.e., most distantly related group with the other groups of vertebrates under study. This does not mean that lungfish are not related to other groups of vertebrates at all. This means that, the number of common characteristics between lungfish and other groups of vertebrates is very low compared to the number of shared characteristics of any two groups of vertebrates.

B."Birds and mammals are more closely related than are bird to lizards and snakes." - this statement is wrong.

The most recent common ancestor of birds and lizards/snakes was species D. The most recent common ancestor of birds and mammals was species C. Species D evolved later than species C. That is why the number of shared common characters between birds and mammals should be lesser than the number of shared common characteristics between birds and lizards/snakes.

In an evolutionary tree internodes correspond to at least one either character state change or accumulation of new character. There are two internodes between species C and birds, where as there is only one internode between species D and birds. That means species D is more closely related to birds than species C.

In an evolutionary tree a node denotes the point from which two species were evolved and internode is the lineage between two nodes. Each node corresponds to a common ancestor.

C. "Birds are more closely related to lizards and snakes than to mammals". - this statement is true.

The explanation of this statement is same as the explanation of option 'B'.

D. "Mammals are more closely related to amphibians than to birds". - this statement is true.

Distance between most recent ancestor of mammals (species C) and most recent ancestor of amphibians (species B) is one internode. Distance between the most recent ancestor of mammals (species C) and the most recent ancestor of birds (species E) is two internodes. This means mammals are more closely related to amphibians than to birds.

E. "Mammals are more closely related to lizards and snakes than to birds". - this statement can't be concluded from the given evolutionary tree.

The most recent ancestor of both the groups - birds and lizards/snakes is tha same, i.e., species E. Hence, the distance between mammals and birds is same to the distance between mammals and lizards/snakes. For this reason from the given evolutionary tree we can not determine which group is more closely related to mammals, birds or lizards/snakes.