Rotating a tree

An evolutionary tree reads like a family tree: each node is a common ancestor. But it can be drawn in many ways.

The question

In this drawing, are mammals more closely related to turtles or to birds?

Without JavaScript, here are the animation’s data.

The tree follows the source’s example: turtles and birds share one ancestor with mammals, which makes them equally closely related to mammals.

The takeaway Rotating a branch changes nothing in the relationships. What counts is the last common ancestor, not the position in the drawing.

Photo credits 3

Vulpes vulgaris, the fox: hand-coloured print, between 1818 and 1842 (Iconographia Zoologica, Special Collections, University of Amsterdam). Jacques Christophe Werner and Charles Philibert de Lasteyrie, Public domain, source
Testudo mauretanica, a land tortoise: print, between 1700 and 1880 (Iconographia Zoologica, Special Collections, University of Amsterdam). Unknown author, Public domain, source
Erythacus rubecula, the robin: hand-coloured print, between 1700 and 1880 (Iconographia Zoologica, Special Collections, University of Amsterdam). Unknown author, Public domain, source

Sources 1

Gregory, T. Ryan, “Understanding Evolutionary Trees”, Evolution: Education and Outreach, vol. 1, 2008, p. 121-137, sections “Misconception #3: Reading across the Tips” and “Misconception #9: More Intervening Nodes Equals More Distantly Related”.
A more rapid approach is to mentally rotate a few internal nodes with no effect on the topology of the tree, as shown in Fig. 11b. […] In Fig. 17a, both turtles and birds share one ancestor with mammals (node W), making them equally closely related to mammals.
Open access · checked on 24 October 2026