The Origin and Evolution of Mammals - Moodle

232 THE ORIGIN AND EVOLUTION OF MAMMALS
(a)
(c)
Heomys
Anagale
Apatemyida
The apatemyidans such as Sinclairella (Fig. 7.4(d))
are another Early Palaeocene North American and
European group of obscure relationships, again
possibly highly derived relatives of palaeoryctidans.
They have a very unusual dentition, in which
the single lower incisor is a huge, procumbent
tooth, with what is described as a spoon-shaped
blade meeting an enlarged first upper incisor.
Immediately behind the lower incisor there is a
large, blade-like premolar. The molar teeth tended
to evolve into a flattened form with bunodont
cusps. The group survived into the Late Oligocene.
(d)
(b)
Sinclairella
Mimotona
Figure 7.4 New groups of small Palaeocene placentals. (a) Anagale skull and lower jaw. Length of skull approx. 5.5 cm (Lucas 2001.
(b) Mimotona. Skull and jaw fragments in lateral view, with occlusal view of lower dentition. Length approx. 2.0 cm (Li and Ting 1993).
(c) Palatal view of front part of the skull of the eurymylid Heomys. Length approx. 1.7 cm (Carroll 1988, after Li and Ting). (d) Skull of the
apatemyid Sinclairella in three views. Length of skull approx. 60 cm (Savage and Long 1986, after Scott and Jenson).
Plesiadapiformes
At one time, the genus Purgatorius (Fig. 7.5(a)) was
regarded as a highly significant fossil, because it
was believed to be a Late Cretaceous primate.
However, this early date was based on a single
tooth from the Hell Creek Formation of Montana,
which spans the Cretaceous–Palaeocene boundary,
and the specimen has since been reinterpreted as
Early Palaeocene, and therefore contemporaneous
with more complete specimens from Wyoming.
Furthermore, Purgatorius is the earliest member of a
diverse group, Plesiadapiformes, which many
authors no longer believe to be primates. That they