Characters and Anatomy
The neck is quite short relative to the fairly large head. The skull is
somewhat longer in proportion to the body length than in modern rodents
and marsupials of a similar size.
The vertebral count is as follows: 7 vertebrae in the neck, 13 in the
upper back, 7(?) in the lower back, and many in the tail. The tails of
some specimens are not preserved so it is difficult to estimate the
number of vertebrae in the tail, but they tended to be long. In Ptilodus (Suborder
there are about 23 tail vertebrae.
The vertebrae are distinctive in that the various knobs which help
articulate and limit mobility in the spine are poorly developed.
The sacrum, the bone linking the vertebral column of the back to the
tail, and on which the pelvis articulates with the spine, is quite long.
The pelvis possesses extra bones projecting towards the front of the
pelvis, into the body cavity; these bones are quite common in Mesozoic
mammals, but have been lost in placental mammals. The bones
in the pelvis are fused such that the right and left halves of the
pelvis could not separate when giving birth.
The feet are very mobile on the ankle.
The ankle of several species possesses two extra bones, which have been
compared to the extra bones supporting a spur in monotremes.
male platypus, these spurs are used to deliver poison. Whilst the spur
itself is not preserved in multituberculate fossils, the presence of
the two extra bones suggest that it may also have been present. Defence
through poison may have been a strategy used by smaller mammals in a
land dominated by dinosaurs at the time (Hurum et al., 2006).
Reconstruction of Catopsbaatar
for attack, exhibiting the sprawling posture, the ankle spurs and the
Click on image to
The posture of multituberculates has been a point of controversy. Two
types of postures are seen in terrestrial animals: a sprawling posture,
where the limbs stick out on the sides of the body,
and an upright posture, where the limbs are tucked under the body. In
animals with a sprawling posture, the gait
is symmetrical - one of the forelimbs moves at the same time as one of
the hindlimbs, after which the next hindlimb and forelimb move. In an
asymmetrical gait, the forelimbs move in sequence, then the hindlimbs.
This gait is seen in animals with an upright posture. Most mammals have
an upright posture, except for the monotremes, which have a sprawling
posture, like most reptiles.
The posture of multituberculates has been alternatively reconstructed
as upright and sprawling. The sprawling posture hypothesis has received
more support in recent years (Kielan-Jaworowska
this case, the body would have been held closer to the ground
than in mammals today.
The strong vertebrae in some species indicate that some may have moved
around in jumps, in which case they would have had an asymmetrical gait
as well as a sprawling posture. As this is not seen in any modern
mammal, it makes comparison and reconstruction difficult.
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Author: Aude Caromel
Last updated: 20/11/06
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produced by students
on the MSc
Palaeobiology programme in the Department
of Earth Sciences at the University of Bristol for academic