The Deseado Formation of Patagonia

by Frederic Brewster Loomis

Fig. 70. Lower
dentition
of male—
½ natural size.

Fig. 71. Lower
dentition
of female—
½ natural size.

This species is represented in the Amherst Collection by five more or less complete skulls, and over twenty jaws, being by far the commonest fossil of the Deseado beds on the Chico del Chubut River, west of Puerto Visser. As mentioned above, there are two types, the first, with larger canines and heavier mandibles, designated by Ameghino as L. gaudryi, which I consider males; second, those with smaller canines, and lighter mandibles, slightly smaller in size, which Ameghino designated L. oxyrhynca and I consider females. Practically all of the other species are based on mandibular symphyses varying in details from the above, but in no case sufficiently for me to see a specific variation.

The general features have been discussed under the generic description. Incisor 1 has a long crown and a long root, and is greatly crowded by the tushes. Incisor 3 and pm. 1 have the same crowded appearance. In giving the measurements I have used a skull which is typically L. gaudryi, a male, and parallel to it have put another skull, which is typically L. oxyrhynca, the female. By comparing the two sets of figures, the shortening, of which Ameghino speaks, will be seen to be all in the region of the tushes.

		Specimen 3290 Male	Specimen 3291x Female
Upper dentition,	length from inc. 1 to m. 3	227 mm.
Upper dentition,	length from pm. 1 to m. 3	180 mm.
Incisor 1,	length	12 mm.
Incisor 2,	length	25 mm.
Incisor 3,	length	11 mm.
Canine,	length	12 mm.
Premolar 1,	length	12 mm.
Premolar 1,	width	18 mm.
Premolar 2,	length	18 mm.
Premolar 2,	width	28 mm.
Premolar 3,	length	20 mm.
Premolar 3,	width	34 mm.
Premolar 4,	length	22 mm.	20 mm.
Premolar 4,	width	38 mm.	34 mm.
Molar 1,	length	28 mm.	24 mm.
Molar 1,	width	40 mm.	38 mm.
Molar 2,	length	36 mm.	33 mm.
Molar 2,	width	48 mm.	45 mm.
Molar 3,	length	46 mm.	46 mm.
Molar 3,	width	48 mm.	47 mm.
Lower dentition,	height of mandible under m. 1	66 mm.	56 mm.
Incisor 1,	length	8 mm.	8 mm.
Incisor 2,	length	10 mm.	10 mm.
Incisor 3,	length	23 mm.	13 mm.
Canine,	length	8 mm.	9 mm.
Premolar 1,	length	13 mm.	8 mm.
Premolar 1,	width	12 mm.	12 mm.
Premolar 2,	length	18 mm.	16 mm.
Premolar 2,	width	17 mm.	15 mm.
Premolar 3,	length	21 mm.	18 mm.
Premolar 3,	width	19 mm.	16 mm.
Premolar 4,	length	24 mm.	21 mm.
Premolar 4,	width	19 mm.	18 mm.
Molar 1,	length	33 mm.	27 mm.
Molar 1,	width	20 mm.	20 mm.
Molar 2,	length	40 mm.	37 mm.
Molar 2,	width	20 mm.	20 mm.
Molar 3,	length	57 mm.	57 mm.
Molar 3,	width	20 mm.	20 mm.

Fig. 72. Top view of skull of L. gaudryi
(female)—¼ natural size.

In the skulls there is considerable variation in size in the different individuals, but the proportions remain very much the same throughout. In the female the snout is relatively a little shorter, and in general the female skulls are from 5 to 10 per cent. smaller throughout. The following two sets of figures illustrate the comparative sizes of the two sexes.