Supplementary Material for: Sleep-Related Electrophysiology and Behavior of Tinamous (Eudromia elegans): Tinamous Do Not Sleep Like Ostriches

The functions of slow wave sleep (SWS) and rapid eye movement (REM)
sleep, distinct sleep substates present in both mammals and birds,
remain unresolved. One approach to gaining insight into their function
is to trace the evolution of these states through examining sleep in as
many taxonomic groups as possible. The mammalian and avian clades are
each composed of two extant groups, i.e., the monotremes (echidna and
platypus) and therian (marsupial and eutherian [or placental]) mammals,
and Palaeognaths (cassowaries, emus, kiwi, ostriches, rheas, and
tinamous) and Neognaths (all other birds) among birds. Previous
electrophysiological studies of monotremes and ostriches have identified
a unique “mixed” sleep state combining features of SWS and REM sleep
unlike the well-delineated sleep states observed in all therian mammals
and Neognath birds. In the platypus this state is characterized by
periods of REM sleep-related myoclonic twitching, relaxed skeletal
musculature, and rapid eye movements, occurring in conjunction with
SWS-related slow waves in the forebrain electroencephalogram (EEG). A
similar mixed state was also observed in ostriches; although in addition
to occurring during periods with EEG slow waves, reduced muscle tone
and rapid eye movements also occurred in conjunction with EEG
activation, a pattern typical of REM sleep in Neognath birds.
Collectively, these studies suggested that REM sleep occurring
exclusively as an integrated state with forebrain activation might have
evolved independently in the therian and Neognath lineages. To test this
hypothesis, we examined sleep in the elegant crested tinamou (Eudromia elegans),
a small Palaeognath bird that more closely resembles Neognath birds in
size and their ability to fly. A 24-h period was scored for sleep state
based on electrophysiology and behavior. Unlike ostriches, but like all
of the Neognath birds examined, all indicators of REM sleep usually
occurred in conjunction with forebrain activation in tinamous. The
absence of a mixed REM sleep state in tinamous calls into question the
idea that this state is primitive among Palaeognath birds and therefore
birds in general.