Question

Exercise: Many older classifications are not monophyletic, and do not reflect the evolutionary relationships among species. As an introduction to phylogenetic classification, think about the tetrapods (animals with four legs). These animals have traditionally been classified into four groups, all of the same rank: Class Amphibia (frogs, salamanders, newts, etc.) Class Reptilia (snakes, lizards, crocodiles, turtles, etc.) Class Aves (birds) Class Mammalia (mammals) Reptiles possess a common ancestor with certain extinct amphibians, the birds are derived from a group of reptiles, and the mammals probably branched off before the rest of the reptiles (and birds). One hypothesis for the actual evolutionary relationships among the tetrapods is shown in the phylogeny. In this diagram, we show only one characteristic for a clade (the amniotic egg), which may be useful in providing a name for the clade of tetrapods that have this characteristic.

Answer 1

Answer 1) i) The old classifications: Amphibia, Reptilia, Aves, and Mammalia are labeled on the phylogeny given below-

This is because the lineages labeled as snake, lizard, crocodile, and turtle comes under reptilia.

Amphibia Reptilia Aves. Ancestral tetrapod - Mammalia Amniotie

ii) No, the traditional class of reptilia is a non-monophyletic group because the organisms that come under reptilia i.e. snakes, lizards, turtle, and crocodile shares a common ancestor with Aves (birds). Therefore, all the descendants are not from the same recent ancestor. So, the traditional class of reptiles comes under the paraphyletic group.

iii) For reptilia to become the monophyletic group Aves must form another lineage which does not share the common ancestor with reptiles. By doing this all the organisms of reptiles will then share a common ancestor and become a monophyletic group.