Gliding Mammals: Taxonomy of Living and Extinct Species

The relationship between living dermopterans and
fossils attributed to extant dermopterans has been highly
uncertain. As suggested by Linnaeus’ original name, the
idea that dermopterans are most closely related to primates
has been supported by various studies. Beard (1991,
1993a) considered primates and dermopterans to form
the mirorder Primatomorpha. The phylogenetic arrangement
that placed Primates near to the Dermoptera was
followed, with modification, in the most recent comprehensive
classification of living and extinct mammals by
McKenna and Bell (1997) and was further supported by
Janečka et al. (2007). The studies by Beard and Janečka et
al. differed from each other in that Beard (1991, 1993a)
included plesiadapiforms in Dermoptera, whereas Janečka
et al. (2007) found plesiadapiforms closer to primates (like
Bloch et al., 2007). Another study investigating mitochondrial
sequences supports an alternative tree topology in
which the Dermoptera are placed with the Anthropoidea,
Prosimii, and Tarsioidea in the clade Dermosimii (Arnason
et al., 2002).
More recent molecular studies proposed a refined
clade known as the Euarchonta that suggested the
morphology- based Archonta be trimmed down to exclude
Chiroptera (Waddell et al., 1999). This group was envisaged
by Adkins and Honeycutt (1991) using mtDNA,
with subsequent support given by various studies including
DNA sequence analyses (Murphy et al., 2001a), retroposon
presence and absence data (Kriegs et al., 2007), and
morphological data (Bloch et al., 2007).
In contrast to the alignment of Dermoptera with Primates,
other studies have concluded that the Dermoptera
and Chiroptera are sister taxa in a group called the Volitantia
(e.g., Szalay and Drawhorn, 1980; Novacek and
Wyss, 1986; Thewissen and Babcock, 1991, 1993; Simmons,
1993, 1995; Szalay and Lucas, 1993, 1996; Wible
and Martin, 1993; Stafford and Thorington, 1998; Stafford
and Szalay, 2000; Bloch and Silcox, 2001; Sargis,
2002a; Silcox et al., 2005). The plausibility of Volitantia
was initially augmented by the traditional consideration
of tree shrews as the sister taxon to primates starting with
Le Gros Clark (1927). However, the Scandentia- Primate
relationship began to fall out of vogue as scientists realized
that many of the originally marshalled synapomorphies
were likely convergent (e.g., Cartmill and MacPhee,
1980; Martin, 1990). Still, some more recent studies have
found the colugos to be the out- group of a pairing of tree
shrews and primates (Bininda- Emonds et al., 2007). Yet
other studies using mitochondrial DNA linked the modern
colugos to primates as a sister group of Anthropoidea,
and they were therefore placed more closely to the higher
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primates than the prosimians (Murphy et al., 2001a; Arnason
et al., 2002; Schmitz et al., 2002). Some evolutionary
morphologists also still consider the Scandentia- Primate
clade a more likely scenario (Godinot, 2007).
Another hypothesis suggested that Dermoptera and
Scandentia form a natural group that is a sister to Primates
that has been coined Sundatheria (Olson et al., 2005). This
hypothesis is supported by both molecular (Liu and Miyamoto,
1999; Liu et al., 2001; Madsen et al., 2001; Murphy
et al., 2001a, 2001b; Springer et al., 2003; Van Den
Bussche and Hoofer, 2004; Olson et al., 2005) and morphological
(Sargis, 2002b; Bloch et al., 2007) evidence.
The relationship of the modern dermopterans to the
fossil forms has also created a great deal of debate with
two studies proposing that species of two different plesiadapiform
families, Paromomyidae and Micromomyidae,
share a number of morphological characters with living
dermopterans (Beard, 1989, 1990, 1993a, 1993b; Kay et
al., 1990). It was proposed that some of the shared morphological
features are evidence that the micromomyids
and paromomyids were “mitten gliders” similar to the
modern day colugos in having webbing between the fingers
(i.e., interdigital patagia). More specifically, it was
argued by Beard and Kay and their colleagues that fossils
representing the paromomyid genera Phenacolemur
and Ignacius show that these animals are not primates
and share functionally important postcranial derived features
that originated in their last common ancestor with
extant colugos, suggesting that paromomyids possessed a
gliding membrane. As a result of these conclusions it was
proposed that the taxon Euprimates is unnecessary and
should be disregarded (Kay et al., 1990). The great uncertainty
of the relationship of the living Dermopterans to the
fossil record has resulted in very different classifications
being proposed by authors such as Simpson (1945), Beard
(1993a), and McKenna and Bell (1997).
New paromomyid fossils and more detailed studies
of postcranial material provide strong evidence against
the hypotheses that paromomyids are related to and
glided like dermopterans (Krause, 1991; Runestad and
Ruff, 1995; Bloch et al., 2007; Boyer and Bloch, 2008).
In contrast, these subsequent studies have suggested that
paromomyids did not glide like the living colugos but were
committed arborealists adapted for locomotion on large
vertical supports, similar to the one of two modern primate
groups with clawed hands and feet, the marmosets
and tamarins of South America (Boyer et al., 2001; Boyer
and Bloch, 2008). It thus appears that all plesiadapiform
fossils so far attributed to Dermoptera are not related to
the Dermoptera. It also appears that the paromomyids are