HL 2 Biology

D.5a: Phylogeny & systematics

Taxonomy: branch of biology with classification of organisms

  • allow for effective communication between scientists

Analogous structures: similar because of convergent evolution; evolved independently

  • e.g. human and octopus eye

clade: a group that includes an ancestral species and all the descendants from that species



1) The cladogram shows the relationship between the clade “aves” and the traditional taxonomic group “the reptiles”. The clade “aves”, or the birds in the cladogram, can be seen to be more closely related to the non-avian dinosaurs than the turtles, lizards and snakes because of the common ancestral species A they both have. As the clade of birds are included into the cladogram, it can be considered a clade as a whole.

2) “Reptilia” represents a clade only if the birds are included into the cladogram. Without the birds, the reptilia will only be the reptiles and does not show full relationships between all the descendants from the ancestral species. The reptilia is the clade of all the species in the cladogram in figure 16. This is because they all have derrived from common ancestry.

3) According to the phylogenetic tree, the non-avian dinosaurs went extinct 60*10^6 years ago.

4) The ancestral crocodiles appeared first.

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