The Origin and Evolution of Mammals - Moodle

248 THE ORIGIN AND EVOLUTION OF MAMMALS
(a)
(b)
(c)
No equivalent new evidence about the relationships
of the creodonts has yet emerged, and it is
not even possible to be sure whether they are a
monophyletic group, because the two constituent
families, Oxyaenidae and Hyaenodontidae, have
no known unique similarities (Janis, et al.1998b;
Gunnell 1998). The oxyaenids(Fig. 7.14(a) and (b))
are the earlier of the two to appear in the fossil
record, in the form of the small, cat-sized Tytthaena
Escavadon
Metacheiromys
Ernanodon
Figure 7.13 Early Tertiary diggers. (a) Escavadon, a primitive palaeanodont. Presacral length approx. 30 cm (Rose and Lucas 2000). (b) The
Middle Eocene palaeonodont Metacheiromys. Rose and Emry 1993 after Simpson. Presacral length approx. 25 cm. (c) The Late
Palaeocene Chinese Ernanodon. Presacral length approx. 50 m (Rose and Emry 1993 after Ding).
from the Middle Palaeocene of North America. It
was not until into the Eocene that any large bodied
oxyaenids, such as the wolverine-sized Oxyaena
(Fig. 7.14(a)), evolved, and by the middle of that
period they were extinct in North America,
although lingering until the Late Eocene in Europe
and Asia. In contrast, hyaenodontids made their
appearance not in North America, but in Europe at
the end of the Palaeocene (Agustí and Antón 2002).