Evolution__3rd_Edition

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Figure 15.2
Character conflict in the
phylogeny of birds and reptiles.
The gait and the anatomy of the
skull link crocodiles and birds;
leg number, physiology, and
external surface group link the
reptilian groups. The anapsid
skull has no openings, apart
from the eye socket; the key
feature of the diapsid skull is a
single upper temporal opening,
though most diapsids have an
additional lower opening too.
Archosaurs and lepidosaurs
differ in their skulls (to be
exact, lepidosaurs lack a
lower temporal arch).
Similarity according
to external surface,
physiology, and
number of limbs
External surface
Number of legs
Physiology
Skull
Gait
Similarity
according to
skull and gait
Skull
Gait
CHAPTER 15 / The Reconstruction of Phylogeny 427
Bird Crocodile Lizard Turtle
Feathers Scales/skin Scales/skin Shell/skin
Two Four Four Four
Warm-blooded Cold Cold Cold
Diapsid Diapsid Diapsid Anapsid
Archosaur Archosaur Lepidosaur
Upright Semierect Sprawling Sprawling
Bird Crocodile Lizard Turtle
Anapsid Diapsid
Sprawling
Semierect
Upright
15.3 Homologies provide reliable evidence for phylogenetic
inference, and homoplasies provide unreliable evidence
The first stage of cladistic analysis is to distinguish homologies from homoplasies. The
difference between homologies (or a homologous character) and homoplasies (or a
homoplasious character) is as follows. A homology is a character shared between two
or more species that was present in their common ancestor. A homoplasy is a character