Fig 1.
Geographic and geologic maps of the southern portion of the Ischigualasto-Villa Unión Basin (modified from [46] Martínez et al., 2012 [57]).
Fig 2.
Pseudotherium argentinus, a comparison of image processing methods based on μCT scans.
(A) Isosurface rendering; (B) volume rendering, scattering algorithm, no digital matrix removal; (C) volume rendering, HQ scattering algorithm, digital matrix removal; (D) volume rendering, Phong algorithm, digital matrix removal; (E) cross section, no digital matrix removal; (F) cross section, digital matrix removal. Dashed line indicates position of cross sections (E) and (F).
Fig 3.
Pseudotherium argentinus, digitally colored 3D volume renderings of the holotype.
Skull in dorsal (top), right lateral (middle), and ventral (bottom) views. Abbreviations: al, alisphenoid; alqr, quadrate ramus of alisphenoid; bo, basioccipital; ce, cavum epiptericum; eo, exoccipital; fr, frontal; if, incisive fossa; ju, jugal; la, lacrimal; mx, maxilla; na, nasal; os, orbitosphenoid; pal, palatine; par, parietal pbc, parabasisphenoid complex; pet, petrosal (= periotic); pf, prefrontal; po, postorbital; pt, pterygoid; ptqr, quadrate ramus of pterygoid; smx, septomaxilla; so, supraoccipital; sq, squamosal; st, stapes; tb, tabular; vo, vomer.
Fig 4.
Line drawings of Pseudotherium argentinus holotype.
(Top) Reconstructive drawing of fossil in dorsal view. Zygomatic arches depicted with dashed lines. Major cracks in the fossil specimen were avoided in the drawing. The more complete right half of the fossil was mirrored to reconstruct the less complete left half. Drawings of fossil in its original, preserved condition, depicted in right lateral (middle) and ventral (bottom) views. Abbreviations: al, alisphenoid; alqr, quadrate ramus of alisphenoid; bo, basioccipital; ce, cavum epiptericum; eo, exoccipital; fr, frontal; if, incisive fossa; ipv: interpterygoid vacuity; ju, jugal; la, lacrimal; mx, maxilla; na, nasal; os, orbitosphenoid; pal, palatine; par, parietal pbc, parabasisphenoid complex; pet, petrosal (= periotic); pf, prefrontal; po, postorbital; pt, pterygoid; ptqr, quadrate ramus of pterygoid; smx, septomaxilla; so, supraoccipital; sq, squamosal; st, stapes; tb, tabular; vo, vomer.
Fig 5.
Pseudotherium argentinus, cross-section through the snout, showing the palatine processes of the premaxilla.
Abbreviations: can, canine; if, incisive fossa for lower canine; mx, maxilla; mxpp, palatine process of maxilla; na, nasal, pmxpp, palatine process premaxilla; vo, vomer.
Fig 6.
Pseudotherium argentinus, the septomaxillary canal.
(A) 3D volumetric rendering of dorsal view of skull showing septomaxillae in aqua tint (A), and dashed lines that indicate positions of cross sectional CT image slices (B) and (C). Abbreviations: ir, broken incisor root; mx, maxilla; na, nasal; smc, septomaxillary canal; smx, septomaxilla, vo, vomer.
Fig 7.
Pseudotherium argentinus, wall and floor of the orbit.
(A) Oblique posteriodorsal view. White arrows indicate plane of coronal slice (B). Abbreviations: fr, frontal; la, lacrimal; lac, lacrimal canal; mx, maxilla; pal, palatine; pf, prefrontal; po, postorbital; pt, pterygoid.
Fig 8.
Pseudotherium argentinus, isosurface rendering of maxillary nerve.
(A) skull in left lateral and (B) dorsal views. Maxillary nerve = green. Maxillary antrum = purple. Skull rendered semitransparent to view canal and antrum in situ. Abbreviations: cal, caudal alveolar ramus; inas, internal nasal rami of infraorbital nerve; ion, infraorbital nerve; mxa, maxillary antrum; slab, supralabial ramus of infraorbital nerve.
Fig 9.
Pseudotherium argentinus, thin bone fragments of the nasal capsule.
One may represent a turbinal (tb?), but others are probably exfoliated fragments of the nasopharyngeal wall.
Fig 10.
Pseudotherium argentinus, pterygoid (blue) in right lateral (top) and ventral (bottom) views. Abbreviations: iptv, interpterygoid vacuity; ptlr, pterygoid lateral ridge; ptmk, pterygoid median keel; ptqr, quadrate ramus of pterygoid; pttp, pterygoid transverse process.
Fig 11.
Pseudotherium argentinus, ventral view of skull showing quadrate processes of right alisphenoid (pink) and right pterygoid (blue). The quadrate process of the pterygoid is broken at its base but its terminal end is preserved at the distal end of the quadrate process of the alisphenoid.
Fig 12.
Pseudotherium argentinus, right lateral view of skull showing the postorbital in Pseudotherium.
(Left) Right postorbital highlighted in magenta. (Right) Cross section through orbital region illustrating how a sliver of frontal is wedged between dorsal parietal sand ventral postorbitals. Dotted line indicates position of cross sectional slice. Abbreviations: fr, frontal; par, parietal; po, postorbital.
Fig 13.
Comparison of orbital vacuities in Pseudotherium and Brasilitherium riograndensis.
The ventral limit of the endocranium in Pseudotherium (A) is dorsal to the orbital vacuity and lined by ossified orbitosphenoids. The orbitosphenoids are missing in Brasilitherium (B) but were likely present, suggesting a shallower endocast than previously hypothesized. Brasilitherium riograndensis CT images from Rodrigues et al., ([60]: Fig 3). Abbreviations: al, alisphenoid; fr, frontal; os, orbitosphenoid; par, parietal; po, postorbital; pt, pterygoid.
Fig 14.
Pseudotherium argentinus, CT cross section through the back of the skull of the skull.
Note the extensive hollow spaces in the parietal, petrosal, and squamosal. Abbreviations: bo, basioccipital; fm, foramen magnum; lhv, lateral head vein; par, parietal; pet, petrosal; sq, squamosal.
Fig 15.
Pseudotherium argentinus, ventral view showing notches in temporal process of squamosal.
The quadrate notch (medial) and the quadratojugal notch (lateral) are divided by a hook-shaped squamosal septum. A squamosal notch is present within the quadratojugal notch and abuts the anterior process of the bifurcated paroccipital process. The squamosal notch does not completely cover the lateral face of the anterior paroccipital process. Abbreviations: app, anterior paroccipital process; qn, quadratojugal notch; qjn, quadratojugal notch; sn, squamosal notch; ss, squamosal septum.
Fig 16.
Pseudotherium argentinus, the quadratojugal.
(Left) Fragment of right quadratojugal (qj), green, in quadratojugal notch. (Right) Cross section through back of skull illustrating the quadratojugal inserted into quadratojugal notch in the squamosal flange. Abbreviations: qj, quadratojugal; qjn, quadratojugal notch; sq, squamosal; sqs, squamosal septum.
Fig 17.
Pseudotherium argentinus, incomplete right stapes of Pseudotherium.
(A) Anteromedial view of stapes, (B) medial view of footplate of stapes, and (C) semitransparent isosurface render of stapes in situ and skull in oblique-ventral view.
Fig 18.
Pseudotherium argentinus, lateral flange of the petrosal right anterolateral (left) and dorsal (right) views. The lateral flange (indicated with arrows) is broad and has a slightly vertical slant. The lateral margin of the lateral flange bears a notch which may be apomorphic of Pseudotherium argentinus.
Fig 19.
Pseudotherium argentinus skull in posterodorsal view illustrating open pterygoparoccipital foramina (indicated by arrows).
Each pterygoparoccipital foramen is almost entirely enclosed by the lateral flange of the petrosal (periotic) anteriorly and the squamosal posteriorly. The lateral flange and the squamosal do not contact, so that pterygoparoccipital foramen is laterally open. Because each foramen is open to a similar extent, this is not likely to be an artifact of post-mortem deformation.
Fig 20.
Pseudotherium argentinus, inner ear volume.
(Top) Ventral view of inner ear endocranial space in situ with a semitransparent isosurface model of skull. White tracings outline the parasphenoid alae and posterior border of basisphenoid. (Middle) Left inner ear volume in dorsal view. (Bottom) Left inner ear volume in ventral view. Abbreviations: ascc, anterior semicircular canal; c, cochlea; cc, common crus; cn, cochlear nerve (VIII); fn, facial nerve (VII); lscc, lateral semicircular canal; plf, perilymphatic foramen; pscc, posterior semicircular canal; va, vestibular aqueduct; vn, vestibular nerve (VIII). Arrow legend key: A = anterior, L = lateral, M = medial.
Fig 21.
Pseudotherium argentinus, petrosal (periotic) in medial and cross sectional views.
(A) Dynamic cutaway illustrating medial aspect of petrosal and its associated foramina and fossa. (B) Cross section through facial nerve foramen. (C) Cross section through vestibular nerve foramen. (D) Cross section through cochlear nerve entrance. (E) Cross section through vestibular aqueduct and subarcuate fossa. Abbreviations: c, cochlea; ci, crista interfenestralis; cnf, foramen for cochlear nerve; fnf, foramen for facial nerve; fv, foramen vestibuli; plf, parilymphatic foramen; psa, parasphenoid ala; saf, subarcuate fossa; st, stapes; va, vestibular aqueduct; vnf, foramen for vestibular nerve.
Fig 22.
Pseudotherium argentinus in anterolateral view illustrating dorsal recession of squamosal to expose the lateral surface of the anterior paroccipital process (indicated by arrow).
The quadrate notch is lateral to the anterior paroccipital process and would have housed the quadrate. Petrosal is colored red. Squamosal is colored yellow.
Fig 23.
Pseudotherium argentinus, orbitosphenoid (os) in situ (A), left lateral view (B), anterior view (C), and cross section (D). Left and right orbitosphenoids contact ventrally at midline. Left orbitosphenoid is less fractured than right orbitosphoid and shows distinct optic foramen. Cranium rendered semitransparent to illustrate relationship of orbitosphenoid to sphenorbital fissure and surrounding bony elements. Cross section illustrates the relatively dorsal position of the brain within the cranium.
Fig 24.
Pseudotherium argentinus, ventromedial crest of basisphenoid.
(Left) Ventromedial crest of basisphenoid in left ventrolateral view. (Top right) Parabasisphenoid complex in left lateral view, colored red-orange, and (bottom right) ventral crest of basisphenoid (vbs) in cross section. Dashed line indicates position of cross section. Abbreviations: al, alisphenoid; bpp, basipterygoid process; fr, frontal; icf, internal carotid foramen; os, orbitosphenoid; pa, pila antotica; par, parietal; psa, parasphenoid ala; psr, parasphenoid rostrum; vbs, ventral process of basisphenoid.
Fig 25.
Pseudotherium argentinus, suture between basioccipital and basisphenoid.
Suture between basioccipital and basisphenoid is indicated by the circle. The suture is distinct, marked by a wide gap and flaring articulating surfaces on both elements. An anterior process of the basioccipital overlaps the basisphenoid posteroventrally and medially. Note how different the suture looks in an isosurface model with matrix included in the rendering (left) and a digitally prepared volume render (right).
Fig 26.
Pseudotherium argentinus, cross sections through canines.
(A) right side of snout showing location of cross sections (B), (C), and (D). R = right, L = left. Arrows indicate labial and lingual ridges, an autapomorphy of Pseudotherium.
Fig 27.
Pseudotherium argentinus, left postcanine tooth row.
(A) Occlusal view of left row in volume render. There are nine postcanines which increase in complexity from anterior to posterior, with the first postcanine being a single cusp and the penultimate postcanine having the most distinct cusps. Despite this trend, the postcanine cusps are small and blunt relative to postcanine cusps seen in other cynodonts. More posterior crowns (PC6-9) are mesiolingually in-turned. (B) Left maxillary tooth row in disto-occlusal view. Small accessory cusps are visible distobuccally on PC7 and PC8. (C) Horizontal section through the snout of PVSJ 882 illustrating constricted roots with a figure-eight cross section. The pulp cavity is compressed but never completely divided between root lobes. Nutrient canals run through each lobe of the root.
Fig 28.
Pseudotherium argentinus, isolated right postcanine, PC8.
(A) Occlusal, (B) buccal, (C) lingual, and (D) cross sectional views. The eighth postcanine on the right side of the skull best illustrates the cusp pattern of the distal postcanines. Three main cusps are in alignment with the longitudinal axis of the crown (A, B, C). Three accessory cusps surround the most-distal main cusp buccally (D), distally (E), and lingually (F). A small bump appears on the surface of the crown in the volume rendering (*). Cross sections confirm that it is not a cusp, but an artifact from denser material.
Fig 29.
Pseudotherium argentinus, tooth replacement.
Cross sections through left (left) and right (right) upper fourth postcanines (PC4) illustrating possible replacement teeth, indicated by arrows. Apparent replacement crowns are positioned near the distal margin and apex of the P4 roots.
Fig 30.
Strict consensus tree of all eight most parsimonious trees (tree length = 443, CI = 0.4695, RI = 0.7814) obtained using PAUP*4.0b10. Characters are unordered. The number to the left of the node is the decay index of that clade.
Table 1.
Postcanine morphology in derived probainognathians.
Fig 31.
Pseudotherium argentinus, the tall plesiomorphic vomer.
Line through Pseudotherium rostrum indicates position of cross sectional slice. Abbreviations: mx, maxilla; mxc, maxillary canal; mxpp, maxillary palatal process; na, nasal; pc IV, postcanine tooth IV; pc V, postcanine tooth V; rpc IV, replacement postcanine tooth IV; vo, vomer.