The Origin and Evolution of Mammals - Moodle

172 THE ORIGIN AND EVOLUTION OF MAMMALS
(a)
P 1
P 2
P 3
PM1 PM2 PM3
M 1
M 1
M 2
Asiatherium
M 2
M 3
M 3
M 4
M 4
lower jaws have been found (Kielan-Jaworowska
1975; Rougier et al. 1998), dating from the Coniacian
to the Campanian of the Late Cretaceous. Fox
(1974) has referred some isolated molar teeth from
North America to the group, indeed to the same
genus, Deltatheroides, as one of the Mongolian forms
and an upper and lower molar from as early as the
Albian of Oklahoma has been tentatively attributed
to the Deltatheroida by Kielan-Jaworowska and
Cifelli (2001). Deltatheroidans are relatively large
(c)
(b)
Kokopellia
Figure 5.18. Early metatherians. (a) Basic marsupial postcanine dental structure illustrated by Asiatherium reshetovi: lowers in lingual and
occlusal views, uppers in occlusal views. Length of tooth rows approx. 1 cm (Szalay and Trofimov 1996). (b) Internal view of lower jaw and lower
molar of Kokopellia juddi. Length as preserved approx. 2 cm (Cifelli 1993a). (c) Lateral view of lower jaw and dentition, and reconstruction of
skeleton of Sinodelphys szalayi. Presacral length approx. 7 cm (Luo et al. 2003).
for Cretaceous tribosphenidans, with a skull length
of about 4 cm. The cusps of the molar teeth
(Fig. 5.19(a) and (b)) are high and sharp, indicating
a carnivorous mode of life.
Views on the phylogenetic relationships of
deltatheroidans have shifted markedly over the
years. When originally described by Gregory and
Simpson (1926), they were interpreted as placentals,
certainly incipiently carnivorous, and possibly
related to the post-Mesozoic creodonts. However,