The Origin and Evolution of Mammals - Moodle

252 THE ORIGIN AND EVOLUTION OF MAMMALS
(a)
Lepticis
Macroscelidea (elephant shrews)
Tenrecida (tenrecs and otter shrews)
Chrysochlorida (golden moles)
Tubulidentata (aardvark)
Plesiorycteropus
Hyopsodus (‘condylarth’)
Meniscotherium (‘condylarth’)
Phenacodus (‘condylarth’)
Hyracoidea
Desmostylia
Sirenia (sea cows)
Embrithopoda (arsinoitherians)
Proboscidea (elephants) Pilgrimella
Figure 7.15 (a) Asher et al.’s 2003 cladogram of Afrotheria based on an Adams consensus of molecular and morphological data. (b) Dentition
of the anthacobunid Pilgrimella: lower teeth in occlusal and buccal views, upper teeth in buccal and occlusal views. Length of lower jaw
fragement approx. 10 cm. (Wells and Gingerich 1983)
are limited to a few low-yielding sites in North Africa
(Gheerbrant 1995; Gheerbrant et al. 1996), and
the Early Eocene is barely any better represented. It is
not until the great Qatrini Formation of the Fayum
Depression in Egypt, which dates from Late Eocene
through Early Oligocene (Rasmussen et al. 1992), that
abundant collections of good quality fossil mammals
have been made. The next oldest mammals come
from the much sparser Late Oligocene fauna at
Chilga in Ethiopia (Kappelman et al. 2003). What
these and other localities indicate is that throughout
the Oligocene afrotherians dominated the African
mammalian fauna, with only a few of the northern
groups, notably primates, present. The orders of large
mammals that are so conspicuous in Africa today,
artiodactyls, perissodactyls, and carnivorans, made
little impact until the Miocene, from which time a
good fossil record comprehensively illustrates the
later Cenozoic history of mammals in Africa.
(b)
During the Late Eocene and Oligocene, the two
main herbivorous mammalian taxa in Africa were
the Hyracoidea and Proboscidea. Until recently
opinion diverged about their mutual relationship
(Prothero 1993). One group argued that the
Hyracoidea were more closely related to
Perissodactyla, citing a range of morphological
details of the braincase, teeth, and foot structure in
support (Fischer 1989; Prothero and Schoch 1989).
Another group argued for a relationship between
Hyracoidea and Proboscidea, along with the
Sirenia, the three forming a taxon Paenungulata
(Shoshani 1986; Novacek et al. 1988). Tassy and
Shoshani (1988) noted the incongruent evidence
and were unable to decide between these possibilities.
However, molecular evidence strongly supports
the paenungulate group. The morphological
characters that define Paenungulata, as listed by
Archibald (1998), are an astragalus with flattened