158 
PYROTHERIUM 
PALAEOMASTODON 
THE DESEADO FORMATION OF PATAGONIA 
TOXODONT, DIPROTODON 
NESODON 
17|Cervicals 3-7 
Very short 
Very short 
Moderately long {Short 
18| Humerus 
Flattened deltoid 
ridge with post. 
spur 
|Flattened deltoid 
ridge with post. 
spur 
Rounded no spur|Flattened distally, 
on deltoid ridge | tiny spur on del- 
toid ridge 
9|/Radius and Ulna 
= 
Very short and 
massive 
Moderate length |Fairly long 
20|Femur 
Flattened, Gr. tro- 
chanter low, no 
3rd trochanter 
Flattened, Gr. tro- 
chanter low, trace 
of 3rd trochanter 
Rounded, Gr. tro-| Rounded, Gr. tro- 
chanter high, 3rd| chanter very low, 
trochanter no 3rd trochanter . 
nN 
1| Tibia 
Short and massive, 
free from fibula 
Short and massive, 
free from fibula 
Moderate length,]Moderate length, 
fused to fibula at] free from fibula 
upper end 
Still other forms like Amblypoda and Arsinotherium have 
been suggested as having characters in common with 
Pyrotherium, and it is clear that, with such a variety of 
forms, some of the characters must be parallelisms due 
to a common adaptation, and only one of these varied 
groups can be the one to which Pyrotherium is related. 
For myself, | have made comparisons with the Amblypoda 
and Arsinotherium, and feel that such features as the mas- 
sive limbs, shape of individual bones, etc., are due simply 
to the fact that all these are massive animals. In the 
case of Arsinotherium, there are some characters which 
are also common to hyracoids and elephants, like the 
position of various basicranial foramena, the prolongation 
backward of the jugal and the shape of the palatines. 
My conclusion is that Pyrotherium is related to the pro- 
boscideans, and came from the same stock which gave 
rise to hyracoids, elephants and Arsinotherium. 1 think 
further that Pyrotherium belongs definitely to the pro- 
boscidean line. 
Referring back to the foregoing table. The develop- 
ment of tushes may be an adaptive character; but in the 
elepnants it is inc. 2 of the upper and inc. 2 of the lower 
