|Skull of Kryptobaatar
visualised by CT scan. Notice the big lower incisors and the large
blade-like premolars. Source: DigiMorph
Click on image to enlarge.
SkullThe skull of multituberculates is wide and massive, compressed from front-to-back rather than from side-to side as in placental mammals. The snout is also wide and bluntly pointed, and bends downwards.
The zygomatic arches, the bones supporting the muscles of the face and extending to the side of the skull - equivalent to our cheekbones, are stout and have prominent ridges where the muscles for chewing would have attached. The solidity of this area of the skull suggests that multituberculates had strong chewing muscles.
The orbits of the eyes are very large, and they have a roof but no floor, unlike in placentals where the orbits have a floor but are not roofed. The eyes were very big and situated quite far back to either side of the head.
The incisors changed during the evolutionary history of Multituberculata, because they were used differently. In Ptilodontidea, the incisors were used to grasp, hold and pierce. In Taeniolabididae, the lower incisors were more robust and used for gnawing.
In advanced multituberculates, the canine is absent. Canines are present in most Jurassic forms, where they resemble the premolars.
The front part of the dentition, the incisors and canines, are separated from the premolars and molars by a gap, the diastema, also seen in rodents. The number of molars and premolars is different for each group; the particularity of multituberculates is that, when the number of teeth is reduced in a lineage, the tooth that disappears tends to be in the middle of the tooth series. Most other mammals lose teeth from the beginning or the end of the tooth series.
The lower premolars distinguish multituberculates because they are blade-like.
Ornamentation of the enamel, such as grooves, pits and ridges, varies within the multituberculates. The Allodontidae, for example, have smooth enamel, whilst Plagiaulacidae teeth can be strongly ornamented.
Lower jaw of Kryptobaatar dashzevegi (suborder Cimolodonta), seen from the side and showing large incisors and the blade-like premolars. The canines are absent and the diastema is large.
(from Wible and Rougier, 2000).
Click on image to enlarge
Author: Aude Caromel
Last updated: 20/11/06
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