FIGURE 1. Map showing the geographic location of Cañadón Vaca fossil locality (white star) in Chubut province, Argentina, and other geographic references mentioned in the text.

FIGURE 2. Tetragonostylops aff. T. apthomasi (Price and Paula-Couto, 1950). 1, MPEF PV 5479, partial skull in lateral view; 2, idem, in dorsal view; 3, idem, detail of the glenoid surface, in ventrolateral view; 4, idem, right cheek teeth series in occlusal view; 5, MACN Pv CH1248, left M1 or M2 in occlusal view; 6, MPEF PV 5481, partial left M3, in occlusal view. Abbreviations: F=frontal, glf=glenoid fossa, H=hypocone, Ju=jugal, mcl=metaconule; Me=metacone, Mst=mesostyle, Mx=maxillary, N=nasal, NFs=naso-frontal suture (remarked), P=protocone, Pa=paracone, pgp=postglenoid process, Pst=parastyle, sc=sagittal crest, Sq=squamosal, tc=temporal crest. Arrows indicate mesial and lingual sides.

FIGURE 3. cf. Scaglia cf. kraglievichorum, MPEF PV 5478, partial skull. 1, lateral view; 2, dorsal view; 3, ventral view. Abbreviations: apf=accessory palatine foramina, As= alisphenoid, Bo=basioccipital, Bs=basisphenoid, Eo=exoccipital, F=frontal, ftr=foramina for temporal rami, iof=infraorbital foramen, Ju=jugal, lf=lacrimal foramen, Mx=maxillary, mpf=major palatine foramen, N=nasal, nms= naso-maxillary suture, Pa=parietal, Pe=petrosal, ptp= posttympanic process of squamosal, Sq=squamosal.

FIGURE 4. cf. Scaglia cf. kraglievichorum, MPEF PV 5478. Schematic partial reconstruction of the skull, in lateral view.

FIGURE 5. cf. Scaglia cf. kraglievichorum, MPEF PV 5478. 1, skull base in ventral view (anterior to top); 2, detail of the auditory region in ventrolateral view (anterior to left); 3, detail of the auditory region in posteroventral view. 4, occipital view. Abbreviations: aas=accessory articular surface of the basioccipital, As=alisphenoid, Bo=basioccipital, cpc= foramen for the craniopharyngeal canal, eam=external acoustic meatus, Eo=exoccipital, fm=foramen magnum, fo=foramen ovale, gf=glenoid fossa, hf=hypoglossal foramina, jf=jugular foramen, mp=mastoid process, Pa=parietal, pcp=paracondilar process, Pe=petrosal, pf=piriform fenestra, pgf=postglenoid foramen, pgp=postglenoid process, ptp= posttympanic process of squamosal, rtp=rostral tympanic process, rt?= possible exit for an anterior derivation of a temporal ramus, sEt= sulcus for the Eustachian tube, sc=sagittal crest, Sq=squamosal, vt=ventral stem (vestige of the ectotympanic?).

FIGURE 6. cf. Scaglia cf. kraglievichorum, MPEF PV 5478. Detail of the left P2-M3 series in occlusal view.

FIGURE 7. Astrapotheriidae genus and species A, MPEF PV 5477, anterior portion of right dentary with i3, p2-p4 and partial alveoli for i1, i2, c1, p1, and m1. 1, lateral view; 2, dorsal view; 3, medial view; 4, i3 in occlusal view; 5, detail of p2-p4 in occlusal view. Abbreviations: ai1= alveolus for right i1, ai2=alveolus for right i2, arc1=alveolus for right c1, alc1=alveolus for left c1, ed=entoconid, hd=hypoconid, md=metaconid, pd=protoconid, pld=paralophid, rp1=root of p1.

FIGURE 8. Trigonostylops wortmani Ameghino, 1897 from Cañadón Vaca. 1. MPEF PV 5482, left P4, in occlusal view; 2. MACN Pv CH1211, right m2, in occlusal view. Arrows indicate mesial and lingual sides.