56 CUSP NOMENCLATURE CHAP. 
even earlier representatives of these families. Fig. 56 (p. 51) 
illustrating a series of mammalian teeth will illustrate the above 
remarks. That there is such a convergence in tooth structure 
shows that it is, theoretically at least, possible to determine the 
ancestral form of the mammalian tooth. Practically, however, 
the difficulties which beset such theorising are great ; that there 
are such divergent and such strongly-held antithetical views is 
sufficient proof of this. Two 
main views hold the field: 
one, which has found most 
favour in America, and is due 
chiefly to the labours and per- 
suasiveness of Professors Cope, 
Fria. 38.—Molar teeth of A, Phenacodus, and Scott, Osborn, and others, is 
B, the Creodont Palaeonictis. End, endo- c 
conid 5 hid, hypoconulid ; hyd, hypo- known as “ trituberculy.” ' 
conid's ed) matacnid spr, proto. ‘The alternative view, as urged 
by Forsyth Major, Woodward, 
and Goodrich, attempts to show that the dentition of the 
original mammal included grinding teeth which were multi- 
cuspidate or “multitubercular.” There is much to be said for 
both views, and something to be said against both. 
This question is, however, wrapped up in a wider one. Its 
solution depends upon the ancestry of mammals. If the Mam- 
malia are to be derived from reptiles with simple conical teeth, 
then the first stage in the development of trituberculy is proved. 
On the other hand, however, the evidence is gradually growing 
that the Theromorpha represent more nearly than any non- 
mammalian group with which we are acquainted the probable 
ancestral form of the mammals. These animals offer some 
support to both the leading views. Cynognathus had triconodont 
teeth which, as will be pointed out later, are a theoretically 
intermediate stage in the evolution of tritubercular teeth; on 
the other hand, the teeth of Diademodon and some others are 
multituberculate, and have been very properly compared to the 
multitubercular teeth of such primitive mammalia as the Ornitho- 
rhynchus. Professor Osborn is no doubt correct in italicising a 
remark of an anonymous writer in Science to the effect that in 
Diademodon the teeth, though multitubercular, show the pre- 
valence of three cusps arranged in the tritubercular fashion. 
! See for a summary, Osborn, American Nat. Dec. 1897, p. 993. 
