The Origin and Evolution of Mammals - Moodle

268 THE ORIGIN AND EVOLUTION OF MAMMALS
Fossil pholidotans occur sporadically through
the rest of the Cenozoic in Eurasia and Africa, corresponding
to their modern distribution, and there
is a single North American genus, Patriomanis, dating
from the Oligocene. The possibility that the
Pholidota are related to the Palaeocene and Eocene
palaeanodonts of North America (Rose and Emry
1993) was mentioned earlier in the chapter.
Chiroptera
Early Eocene bats are almost identical in structure
to modern forms. The skeletons of Icaronycteris (Fig.
7.22(c)) from North America and Archaeonycteris
from Europe show that full evolution of the flight
mechanism had occurred by that time, and the only
primitive features they possessed that are absent
from modern bats are such details as retention of a
claw on the second finger. Isolated teeth attributed
to chiropterans have actually been described from a
slightly earlier time, the Late Palaeocene of Europe,
but unaccompanied by any cranial or postcranial
material (Russell et al. 1973). Unlike the case of the
whales, the chiropteran fossil record consequently
reveals absolutely nothing at all concerning intermediate
stages in the evolution of their highly specialised
locomotion.
Bats also achieved a Gondwanan distribution very
early in their history, for they were present in
Australia in the Late Palaeocene or Early Eocene
Tingamarra Fauna, as the sole certain representatives
of placental mammals on that continent prior to the
immigration of Pliocene rodents (Hand et al. 1994).
The date of the first appearance of Megachiroptera
(fruit bats) in the fossil record is unclear. There are
isolated teeth of a possible pteropodid from the Late
Eocene of Thailand, and a disputed Oligocene form
Archaeopteropus from Italy (Schutt and Simmons
1998), but otherwise they are unknown prior to the
Miocene, when they occurred throughout the Old
World.
Simmons and Geisler (1998; Simmons 2000)
undertook a morphological cladistic analysis, and
concluded that the Eocene bats are basal members
of a monophyletic Microchiroptera, containing all
the echolocating families of modern bats. The
Megachiroptera are their sister-group. This is at
odds with molecular evidence suggesting that the
Megachiroptera nest within a non-monophyletic
Microchiroptera. Teeling et al.’s (2000, 2002; Murphy
et al. 2001b) phylogenetic analysis of four nuclear
and three mitochondrial genes concluded that the
megabats are the sister-group of the rhinolophoid
microbats alone amongst the microbats. Apart from
reducing Microchiroptera to a paraphyletic group,
their conclusion carries the implication that echolocation
either evolved more than once in microbats,
or, as seems more plausible, was lost in the ancestor
of the mainly fruit-eating megabats.
Eulipotyphla
The successive stages in dismemberment of the
classic ‘Insectivora’ were outlined earlier. As a
result, finally, of molecular evidence, the remaining
living members, referred to as Eulipotyphla, are
reduced to the Soricidae (shrews), Erinaceidae
(hedgehogs), Talpidae (moles), and Solenodontidae
(the extinct solenodons of the West Indies). It is a
difficult group to define by unambiguous derived
dental, cranial, and skeletal characters (Butler 1988;
MacPhee and Novacek 1993). The earliest fossils
that can confidently be placed into the modern families
occur relatively late. Litolestes is an erinaceid
from the Late, and possibly earlier Palaeocene of
North America; Domnina (Fig. 7.22(d)) is a Middle
Eocene soricid also from North America; Eotalpa
(Fig. 7.22(b)) is a Late Eocene European talpid. The
solenodontids are unknown prior to Solendon itself
in the Pleistocene of Cuba.
However, various Late Cretaceous and early
Cenozoic fossil genera have been regarded by different
authors as erinaceomorphs, soricomorphs, or
stem eulipotyphlans. Discussion of relationship to, if
not actual membership of the order mainly centres on
two primitive, insectivorous groups that appeared in
the Late Cretaceous and radiated in the Palaeocene.
McKenna et al. (1984) proposed that the palaeoryctidans,
notably the Late Cretaceous Batodon, are primitive
soricomorphs, although others rejected this
view. Alternatively, Novacek (1986a; MacPhee and
Novacek 1993) have argued for a relationship
between the leptictidans and the Eulipotyphla.
Euarchontoglires
The fossil record has long supported, or at least
been seen to be consistent with a relationship