The Origin and Evolution of Mammals - Moodle

condition. This particular combination is the
ancestral artiodactyl arrangement as seen, for
example, in Diacodexis (Fig. 7.20(b)).
The foot structure of these primitive whales therefore
supports a relationship between Cetacea and
Artiodactyla, but is not adequate to determine
whether a monophyletic Artiodactyla as a whole, or
just the Hippopotamidae is the sister-group of the
whales. However, Naylor and Adams’s (2001)
investigation of the different cladistic relationships
generated by different categories of characters
included the limb features. Their conclusion was
that a cladogram based on all the evidence except
the dentition points to a sister-group relationship of
whales and hippos. However, one using only dental
characters indicates a relationship of whales with
mesonychid ‘condylarths’. The authors believe that
non-independence of the different dental characters,
combined with convergence of tooth structure
(a)
Eomanis
(c) (d)
Eotalpa
Domnina
LIVING AND FOSSIL PLACENTALS 267
between these two groups, creates a misleading
indication of the relationships.
Pholidota
The earliest undisputed relative of the living pangolins
are some astonishing specimens from the
Eocene oil shales of Messel in Germany. Eomanis (Fig.
7.22(a)) is represented by complete skeletons of a
50 cm long, essentially modern-type pholidotan. Even
the overlapping horny scales are preserved. It lacks
teeth, the jaw is long and slender, and the limbs powerfully
built for digging. There are also gut contents
preserved, and they consist mainly of plant material,
which is very surprising indeed since the full complement
of supposedly ant-eating adaptations are present.
Storch and Richter (1992b) ingeniously suggested
that the ant-eating habit evolved initially in a lineage
of folivores that started to catch leaf-carrying ants
with the help of an elongated tongue.
(b)
Icaronycteris
Figure 7.22 Early laurasiatherians. (a) Skeleton and restoration of the Eocene pangolin Eomanis from Messel (Storch and Richer 1992). (b) The
early Eocene bat Icaronycteris (redrawn from Jepsen 1996). (c) Isolated molar tooth of the Eocene mole Eotalpa (Savage and Long 1986). (d)
Partial skull and dentition of Domnina, a Middle Eocene shrew.