The Origin and Evolution of Mammals - Moodle

150 THE ORIGIN AND EVOLUTION OF MAMMALS
Eutriconodonta
The taxon Triconodonta was erected in the nineteenth
century for those Mesozoic mammals whose
molar teeth possessed three main cusps arranged in
a longitudinal row along the length of the crown.
For a brief period after its discovery in the 1950s,
Morganucodon was included in the group but it
soon became clear that morganucodontans have
many characters, including several primitive ones,
not found in other tricodonodont-toothed mammals.
(a)
(c)
M 2
M 1
(e)
M 1
Jeholodens
M 2
M 2
Austrotriconodon
M 3
M 3
M 4
Triconodon
There is still considerable doubt about whether
the remaining forms included in the group, now
renamed Eutriconodonta, are monophyletic (Kielan-
Jaworowska et al. 2004).
The family Triconodontidae lies at the core. It
occurs from the Middle Jurassic through to the Late
Cretaceous, and is characterised by the approximately
equal size of the three main cusps, the welldeveloped
cingulum, and particularly by a unique
tongue and groove mechanism for interlocking
(b)
(d)
M 1
M 3
M 4
M 2
Gobiconodon
M 2
M 5
Amphilestes
Figure 5.7 Eutriconodontan dentitions. (a) Triconodon (Simpson 1928). (b) Amphilestes lower jaw and molar tooth (Jenkins and Crompton 1979,
after Owen 1971). (c) Upper molars and lower last premolar and molars of Jeholodens jenkinsi. Length of upper row approx. 4.2 cm (Ji et al.
1999). (d) Gobiconodon an upper and two lower molars in lateral view, and last three upper molars in crown view (Kielan-Jaworowska and
Dashzeveg 1998). (e) Isolated molar of Austrotriconodon (Bonaparte 1992).