The Origin and Evolution of Mammals - Moodle

160 THE ORIGIN AND EVOLUTION OF MAMMALS
(a)
ol.b
ol.b
Pit
Pit
cer.hem
cer.hem
The brain of multituberculates (Fig. 5.12(a)) has
been reconstructed from the endocranial casts of a
number of genera, particularly Chulsanbaatar and
Nemegtbaatar (Kielan-Jaworowska et al. 1986) and
Ptilodus (Simpson 1937; modified by Krause
and Kielan-Jaworowska 1993). All give the same
general picture of relatively very large olfactory
bulbs and no exposure of midbrain structures dorsally,
which suggests that olfaction was a more
important sense than vision, and therefore that they
had a nocturnal habit. The relative size of the brain
of Ptilodus, in terms of the Encephalisation Quotient
(actual brain weight divided by expected brain
weight for a mammal of that body weight) has been
estimated by Krause and Kielan-Jaworowska (1993).
It lies between a minimum of 0.37 and a maximum
of 0.62, depending on which procedure is used, and
whether the olfactory bulbs are, or are not included
in the estimates of brain mass. Despite the lack of
precision, it is clear that the multituberculate brain
fl
fl
cerb
Chulsanbatar
(b)
os tympanicum
process anterior
caput mallel
manubrium
crus breve incudis
crus longum incudis
stapes
Didelphis
Figure 5.12 Brain and ear ossicles of multituberculates. (a) Reconstructed brain of Nemegtbaatar in dorsal, ventral, and lateral views
(Kielan-Jaworowska et al. 1986). (b) Ear ossicles of Chulsanbaatar (left) compared to Didelphis (right) in situ, and enlarged. (Hurum et al. 1996).
cerb, cerebellum; cer.hem, cerebral hemisphere; fl, flocculus; ol.b, olfactory bulb; pit, pituitary.
was significantly smaller than those of modern
mammals.
Multituberculates are one of the extremely few
fossil mammal groups from any period where
the presence of hair has been positively demonstrated.
Skeletal remains of Lambdopsalis along with
the exceptionally detailed impressions of hair have
been found in fossilised coprolites from Late
Palaeocene beds of Inner Mongolia (Meng and
Wyss 1997). Unfortunately, there are no organic
remains of the material, so the attractive prospect of
finding out what colour the animal was cannot be
satisfied.
Kielan-Jaworowska (1979) speculated that multituberculates
were viviparous. She based her argument
on the very acute angle at which the two sides
of the pelvic girdle meet ventrally, about 40 o instead
of the 180 o or so typical of most mammals. This
would allow an egg or neonate with a diameter
no greater than about 3.4 mm in Kryptobaatar to