738 MAMMALIA, 
living types of Reptiles as near the direct line of Mammalian 
pedigree. 
In ‘‘ Anomodontia” there are so many mammalian features in the 
skeleton that in spite of the complex lower jaw articulating with a 
fixed quadrate, the presence of an os transversum, pre- and post- 
frontals, etc., some have doubted whether they should be ranked as 
Reptiles at all. We may note that they were purely terrestrial 
animals (of large size) with limbs lifting the body high off the ground, 
that the squamosal sometimes descends far down outside the quadrate 
and may share in the articulation for the lower jaw, that the quadrate is 
often small, that there is a single temporal arcade comparable to the 
mammalian zygomatic arch, that the teeth are heterodont, that the 
pelvic bones unite in an os innominatum with a continuous ischiac 
symphysis, that the scapula often has a spine, that the occipital condyle 
may be double, that there is a beginning of reduction and consolidation 
of skull bones, and so on. 
But it may quite well be that the Anomodontia are not in the direct 
line of Mammalian ancestry, but represent a side-branch from transi- 
tional forms connecting Reptiles and Mammals. 
The student should look back to the characters common to the 
Amniota (Reptiles, Birds, and Mammals), e.g. the presence of amnion 
and allantois, the absence of gills, etc., for these indicate a close 
alliance far apart from Ichthyopsida, and it seems therefore unprofitable 
to look for the roots of the Mammalian stock so low down as among 
Amphibians. 
Nevertheless, amid so much uncertainty, we may recall the facts that 
in Amphibians we find two occipital condyles, a reduced quadrate, a 
somewhat mammalian carpus, holoblastic ova, and so on. 
The oldest Mammalian fossils are from Triassic strata, but they throw 
little or no light on pedigree, partly perhaps because they are few and 
fragmentary, partly also because they seem already specialised forms. 
They are often grouped together as Allotheria or Multituberculata and 
placed near the Monotremes. 
In the Jurassic period there are more of the dubious Allotheria, 
e.g. Plagiaulax, some ‘‘triconodont” Marsupials, e.g. Zrzconodon and 
Amphilestes, and the Trituberculata, e.g. Amphitherium, some of which 
suggest primitive Insectivora. There are few Cretaceous fossil remains 
of Mammals, but some of them suggest that the orders of Eutheria 
were incipient. 
In the earliest Eocene strata, Mammals related to modern types begin 
to be abundant, but we cannot do more than notice two points—(a) 
there were some generalised types, e.g. Creodonts and Condylarthra, 
with relationships to several extant orders ; (4) that the early forms were 
mostly small animals with small brains, pentadactyle, with 44 teeth 
including small canines and bunodont molars. 
Professor Osborn has suggested that there were two main lines of 
mammalian evolution—(a) the ‘‘ Mesoplacentalia,” e.g. Amblypoda, 
Coryphodontia, Dinocerata, Tillodontia, and many Condylarthra and 
Creodonts, in which the brain remained small and unspecialised, which 
died out in the Miocene (unless the Marsupials, Insectivores, and 
Lemurs represent their descendants), and (0) the successful lines of 
