Page 20 - maxson1928

17.

The region of the skull forward of the premolar-molar series tends

to be uniformly narrow t:tansversely and relatively high above the orbit. The
height of the facial region is a primitive character. I~ is definitely

shown to b'e present by e. root of considerable size. Although the portion
2
of the premaxilla in front of I- is lacking it seems quite possiole that
l 3
a small 1- was present. The root shows I- to be a large tooth. A short
3
diastema separates I- from the slightly smaller canine behind it. A long

diastema separates c! from P~. The latter is definitely and strongly
two-rooted, a character which Wortman used to differentiate Cope's genus
0 . .:
11 Gomphotherium 11 from Protla.bis. Matthew subsequently regarded the former
genus as insufficiently differentiated from Leidy's genus Protomer~x.
1 2
A short diastema. separates P- from P-. The premolars have undergone great
reduction from the stage represented by Poebrotherium from the Vlhite River

Oligocene and a noticeable reduction from Paratylopus from the John Day.
This reduction is nearly the same e.s in Protolabis but less than in
l· 2 3
Procamelu.s. M- is subquadrate in form while M- and M- tend to be elongate.
The dentition as a whole is sub-hypsodont.

The small size, facial proportions, retention of incisors, more
qu.adrate outline of molars, and less hypsodont dentition separate the

specimen from Procamelus and later forms. Assigning it to Protolabis,
Miolabis, or Paratylopus is more difficult. Miolabis transmonte.nus from

the Mascall of centnal Oregon is very closely related to the species.
Protolabis is on the whole more advanced in the line of cameloid

evolution. Incisors are mu.ch reduced and.are even absent in a specimen
from the upper horizon of the Loup Fork beds doubtfully referred to

l .
P. a.ngu.stidens. Premolars are much reduced and P- is absent in one species,
P. montanu.s.

Protolabis heterodontus although similar in shape is much larger.
p! is subquadrate while the molars a.re shorter transversely and longer.

Likewise as Wortman pointed out Pl is definitely a single-rooted tooth