The Origin and Evolution of Mammals - Moodle

The salient feature of Widanelfasia is the presence of
incipiently zalambdodont molar teeth. The trigonid
cusps, especially the protoconid are very high and
form a narrowly acute triangle, and the talonid is
much lower. The fully zalambdodont molar of
solenodontids is presumed to be convergent, but
that of the tenrecs and the rather specialised version
found in chrysochloridans may well be homologous.
It is therefore possible, though by no means
positively demonstrable yet, that Widanelfasia is a
stem afrosoricid. Seiffert and Simons (2000) also
point to the upper teeth of an Early Eocene primitive
‘insectivore’ from Tunisia, Chambilestes,
described by Gheerbrant and Hartenberger (1999)
and note that they have a structure compatible with
the lower teeth of their Fayum mammal.
Chrysochlorida. The golden moles have a very poor
fossil record. It is entirely restricted to Africa, dates
from no earlier than the Early Miocene, and consists
of specimens that can be placed in the same family
as the nine living genera.
Tenrecida. The tenrecs of Madagascar along with the
otter shrews of sub-Saharan Africa have the poorest
fossil record of all the afrotherian orders, consisting
solely of zalambdodont teeth of an Early Miocene
African form Parageogale (Butler 1984), prior to subfossils
of the Pleistocene.
Laurasiatheria
Carnivora
The very early appearance of members of the order
Carnivora has already been described, and within the
Early Palaeocene differentiation of the two primary
subgroups of the order had apparently also occurred,
for one of them, Feliformes, is represented by the
viverravids of that time (Fig. 7.14(f)). The miacids
(Fig. 7.14(e)), which appear in the Late Palaeocene,
are basal members of the other group, Caniformes
(Flynn 1998; Janis et al. 1998b). Both of these primitive
groups, consisting of relatively small animals, radiated
through the first half of the Eocene, during
which period it was the creodonts that provided the
larger carnivorous mammals.
The family Nimravidae were the earliest group of
modern-style Feliformes, a group specialised for
LIVING AND FOSSIL PLACENTALS 259
pure carnivory and convergent in many features on
the true cats, the Felidae (Martin 1998a). They
appeared in the Late Eocene of North America and
Eurasia, and radiated primarily during the
Oligocene; the last survivor, Barbourofelis (Fig.
7.18(d)), disappeared no later than the Late
Miocene of North America. Nimravids, like felids,
had short, powerful skulls, highly developed carnassial
teeth and reduction of the more posterior
molars. Their postcranial skeleton indicates that
they were long-legged, cursorial predators with
feline-like claws. Even more markedly than in the
felids, nimravids had a tendency to evolve sabretoothed
forms. The early, leopard-sized
Hoplophoneus (Fig. 7.18(c)) already had evolved
enlarged canines. The trend is most dramatically
expressed in the lion-sized Barbourofelis (Turner and
Antón 1997).
The first true cat, the felid Proailurus (Fig.
7.18(b)), is well known from the Oligocene and
Early Miocene of Europe. It was the size of a modern
ocelot and its relatively short, robust limbs and
retractile claws indicate an accomplished arboreal
animal (Agustí and Antón 2002). The major radiation
of felids commenced in the Late Miocene
(Martin 1998b), including their entry into North
America, where they rapidly replaced the nimravids
as the top carnivores. A number of genera
independently evolved into sabre-toothed cats,
most famously Smilodon, huge numbers of which
are preserved in the Rancho La Brea asphalt pits of
Los Angeles and which survived until the end-
Pleistocene about 10,000 years ago.
The other feliform families, Viverridae (civets),
Herpestidae (mongooses), and Hyaenidae also
commenced their radiations during the Miocene,
and apart from a single Pliocene hyaenid, were
restricted to Eurasia and Africa. This is in inexplicable
contrast to the Felidae, which were abundant
in North America.
The second branch of the Carnivora are the
Caniformes, all the families of which do occur in
the fossil record of North America, as well as
Eurasia and Africa. As mentioned, the earliest
caniniforms are believed to be the Late Palaeocene
miacids of North America and Europe. The modern
caniform families appeared at various times after
this, in a complex biogeographic pattern. Canids