The Deseado Formation of Patagonia

by Frederic Brewster Loomis

Parastrapotherium insuperabile Ameghino

P. insuperabile Amegh., 1901, Bol. Acad. Nac. Cordoba, t. 16, p. 403.

This is the largest of all the species, and is distinguished by the enormous development of the cingulum on the anterior, inner, and posterior sides of the upper molars, the same being uninterrupted and so elevated, that the internal crests seem to rise out of a basin. The following measurements are taken from Ameghino:

Upper dentition,	premolar 4,	length	37 mm.,	width	48 mm.
Upper dentition,	molar 3,	length	100 mm.,	width	80 mm.
Lower dentition,	premolar 4,	length	43 mm.,	width	23 mm.

CHAPTER XII
Proboscidea

Suborder Pyrotheria

This suborder was established by Ameghino to receive the peculiar genus Pyrotherium and related forms. These animals are of large size, massive build, with narrow elongated skulls, in which the nasal opening is situated far back, as in animals with a proboscis; with a tiny brain case surrounded by cellular spaces; with the maxillae, palatines, pterygoids and alisphenoids developed downward, so that the palatal plane makes a strong angle with the basicranial plane; and with the occipital condyles high up on the back of the skull. Then the first and second upper incisors and the second lower incisors are developed into enormous tushes with enamel on the anterior sides only. The remaining incisors, the canines, upper premolar 1, and lower premolars 1 and 2 are wanting; the remaining premolars and the molars being developed into great quadrilateral grinders, each with two transverse crests. The neck is short, the limbs massive and short, especially the lower members of each limb, and the feet were probably five-toed.

The relationship of these forms has been the subject of extended discussion: Ameghino seeing in this genus the ancestors of the Proboscidea, and comparing them with Palaeomastodon, Dinotherium and Barytherium, even finding resemblances to Diprotodon; Gaudry concludes that they are not proboscidians; and others have suggested that they were specialized toxodonts. I have prepared the following table of comparisons with Palaeomastodon, a toxodont, and Diprotodon.

		Pyrotherium	Palaeomastodon	Toxodont, Nesodon	Diprotodon
1	Upper tush	Inc. 1 enlarged	Inc. 1 enlarged	Inc. 1 reduced	Inc. 1 tush
			in Moeritherium.	Inc. 2 caniniform
		Inc. 2 tush	Inc. 2 tush	tush	Inc. 2 reduced
2	Upper molars	Bilophodont	Bilophodont in	Rhinoceros-like	Bilophodont
			Mastodon and
			Dinotherium
3	Lower tush	Inc. 2 (?)	Inc. 2	Inc. 3	Inc. 1
4	Lower molars	Bilophodont	Bilophodont in	Bicrescentric	Bilophodont
			Mastodon and
			Dinotherium
5	Nasal opening	Over molar 1	Over molar 1	Over incisors	Over diastema
6	Basicranial axis	Plane of base of	Plane of base of	Plane of base of	Plane of base of
		cranium bent up,	cranium bent up,	cranium parallel	cranium parallel
		makes 140° with	makes 155° with	with plane of	with plane of
		plane of palate	plane of palate	palate	palate
7	Pterygoids	Pterygoids plus	Pterygoids plus	Pterygoids normal	Pterygoids normal
		alisphenoids	alisphenoids
		make great	make great
		vertical plates	vertical plates
8	Jugal	Takes small part	Takes small part	Takes no part on	Extends to
		on glenoid fossa	on glenoid fossa	glenoid fossa	glenoid fossa
9	Post-tympanic process	Surrounds meatus,	Surrounds meatus,	Surrounds meatus,	Not surround meatus
	of squamosum	and crowds out	and crowds out	and crowds out	nor crowd out
		tympanic	tympanic	tympanic	tympanic
10	Tympanic bulla	Small, inflated,	Small, inflated,	Large, inflated,
		hollow	hollow	hollow
11	Palatine bones	Narrow in front,	Narrow in front,	Wide in front,
		expanding behind	expanding behind	narrowing somewhat
12	Premaxilla	Crowded out from	Crowded out from	Makes front of	Fused to maxilla
		forming any	forming any	palate
		portion of palate	portion of palate
13	Antorbital foramen	2 foramena	2 foramena	1 foramen	1 foramen
14	Intercellular laminae	Present	Present	None	None
15	Atlas	Long, has	Long, has	Long, no	Long, no
		hypophysis	hypophysis	hypophysis	hypophysis
16	Axis	Hemispherical	Rounded odontoid	Peg like odontoid	Odontoid slightly
		odontoid			flattened on top
17	Cervicals 3-7	Very short	Very short	Moderately long	Short
18	Humerus	Flattened deltoid	Flattened deltoid	Rounded no spur	Flattened distally,
		ridge with post.	ridge with post.	on deltoid ridge	tiny spur on
		spur	spur		deltoid ridge
19	Radius and Ulna	Very short and		Moderate length	Fairly long
		massive
20	Femur	Flattened,	Flattened,	Rounded,	Rounded,
		Gr. trochanter	Gr. trochanter	Gr. trochanter	Gr. trochanter
		low, no 3rd	low, trace of	high,	very low, no
		trochanter	3rd trochanter	3rd trochanter	3rd trochanter
21	Tibia	Short and massive,	Short and massive,	Moderate length,	Moderate length,
		free from fibula	free from fibula	fused to fibula	free from fibula
				at upper end