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New Observations on the Skull of Pyrotherium (Pyrotheria, Mammalia) and New Phylogenetic Hypotheses on South American Ungulates

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Abstract

The Cenozoic South American endemic pyrotheres, mostly characterized by a bilophodont dentition, are one of the most mysterious ungulates ever known. Even though many specialists have investigated this group, the fascinating question of its origin is still unresolved after more than a century of study. This paper provides a new description of the only known pyrothere skull, that of Pyrotherium from the Deseadan of Patagonia. Detailed comparison of the cranial anatomy indicates strong similarities with the Notoungulata, especially in the auditory region, as already mentioned by some authors. Intriguing similarities are also detected in the anterior dentition of Pyrotherium and the Casamayoran notoungulate Notostylops. These resemblances suggest a unique relationship between Pyrotheria and Notoungulata, specifically between Pyrotheria and Notostylops. These hypotheses are tested through a series of phylogenetic analyses of South American ungulate craniodental anatomy, primarily focusing on Notoungulata and Pyrotheria. These phylogenetic analyses are the first to encompass such a diversity of South American ungulate taxa. When including the bunodont taxon Proticia usually attributed to the Pyrotheria, the strict consensus of the analysis does not present much resolution. When excluding it, the analysis supports the nesting of the pyrotheres within the Notoungulata via an exclusive relationship with Notostylops. This relationship is supported by both cranial and dental anatomy. The analysis also supports the position of Astrapotheria as the sister group of the Notoungulata. It does not support, however, the monophyly of the Litopterna. The clustering of Pyrotheria, Notoungulata, and Astrapotheria supports an isolated evolutionary history of these ungulates in South America similar to that of afrotherian mammals in Africa. These results give rise to new perspectives in research on South American endemic ungulate evolution.

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Acknowledgements

I am indebted to the following institutions and individuals for access to the specimens that form part of this study and for interesting discussions on notoungulates: Museo Argentino de Ciencias Naturales “Bernadino Rivadavia”, Buenos Aires, Argentina (MACN), Alejandro Kramarz; the Museo de La Plata, La Plata, Argentina (MLP), Marcelo Reguero and Mariano Bond; American Museum of Natural History, New York, US, Judith Galkin and Christopher Norris; Field Museum of Natural History, Chicago, Illinois, US, William Simpson; and Amherst College Museum, Amherst, Massachussets, US, Kate Wellspring. I am especially grateful to Kate Wellspring and ACM staff for kindly facilitating my access to the cumbersome skull of Pyrotherium. I warmly thank Jérémy Anquetin (Université de Rouen, France) for his friendly and invaluable practical help on the phylogenetic analysis and for helpful discussions and advices on the paper. I would also like to thank Jonathan Geisler (Georgia Southern University, US) for helpful discussions on the use of PAUP 4. Thanks are also due to Maëva Orliac (Université de Montpellier II, France), Rodolfo Salas (Museo de Historia Natural, Lima, Peru), Darin A. Croft (Case School of Medicine, Cleveland), Richard L. Cifelli (Oklahoma Museum), Pierre-Olivier Antoine (Université de Toulouse III, France), and Pascal Tassy and Christian de Muizon (Muséum national d’Histoire naturelle, Paris, France) for invaluable comments and discussions on systematics and pyrotheres. I thank also Manuel Martinez and Floréal Solé (Muséum national d’Histoire naturelle, Paris, France) for their friendly and efficient help when searching for articles and photos of specimens. I would also like to thank Javier Gelfo (MLP), John R. Wible (Carnegie Museum) and an anonymous reviewer for their very helpful comments and corrections.

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  1. Guillaume Billet

    Present address: IPHEP, CNRS UMR 6046, Faculté des Sciences Fondamentales et Appliquées, Université de Poitiers, 40, avenue du Recteur Pineau, 86022, Poitiers Cedex, France

Authors and Affiliations

  1. UMR 5143 (MNHN, CNRS, UPMC), Département histoire de la Terre (CP 38), Muséum national d’Histoire naturelle, 57, rue Cuvier, Paris, 75005, France

    Guillaume Billet

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  1. Guillaume Billet
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Correspondence to Guillaume Billet.

Appendices

Appendix 1

List of characters used in the cladistic analysis (ordered characters are followed by an asterisk)

Teeth

  1. 1.

    Diastema between adjacent anterior teeth (I2-P1): 0, absent; 1, present

  2. 2.

    I2-C labio-lingually compressed: 0, absent; 1, present

  3. 3.

    I1: 0, smaller or subequal to other incisors; 1, enlarged relatively to other incisors

  4. 4.

    I1 crown highly curved: 0, absent; 1, present

  5. 5.

    I1 comma-shaped in section: 0, absent; 1, present

  6. 6.

    I1 hypsodont to hypselodont and chisel-like: 0, absent; 1, present

  7. 7.

    I1 obliquely implanted, meeting at tips: 0, absent; 1, present

  8. 8.

    Procumbent I1-2, occluding in an angle of 90° (or less) with procumbent i1-2? (wear forms a bevel on upper incisors): 0, absent; 1, present

    The nature of the proclive lower incisor of Pyrotherium cannot be determined. It is likely however to be either i1 or i2. This type of occlusion is associated with wear in a long bevel of the upper incisor occluding with the proclivous lower incisor.

  9. 9.

    I1 tusk-like and straight: 0, absent; 1, present

  10. 10.

    (I1-)I2 caniniform, circular in cross-section: 0, absent; 1, present

  11. 11.

    I2 hypertrophied, trigonal, and diverging: 0, absent; 1, present

  12. 12.

    I2 position relatively to I1: 0, I2 lateral or posterolateral to I1; 1, I2 immediately posterior to I1 (I1 and I2 brought into line anteroposteriorly)

  13. 13.

    Subequal and hypsodont incisors, disposed in a close horseshoe-shaped (U-shaped) series: 0, absent; 1, present

  14. 14.

    I3 (+-i3): 0, present; 1, absent

  15. 15.

    Lingual cingulum on upper incisors forms a fossa: 0, absent; 1, present

  16. 16.

    I1-2 dental arcade transverse: 0, absent; 1, present

  17. 17.*

    Canine (upper and lower): 0, present; 1, vestigial, often absent; 2, always absent

  18. 18.

    Tusk-like upper and lower canines: 0, absent; 1, present

  19. 19.

    Canine (upper and lower): 0, caniniform; 1, incisiform and subequal to other incisors

  20. 20.*

    Cheek teeth: 0, brachyodont; 1, hypsodont; 2, hypselodont

  21. 21.

    Distal cingulum isolating a deep fossette (post-cingulum fossette) on upper cheek teeth: 0, absent; 1, present

  22. 22.

    Mesial cingulum on upper molars: 0, absent; 1, present

  23. 23.

    Continuous cingulum around lingual margin of upper cheek teeth and labial and lingual cingulum on lower cheek teeth: 0, absent; 1, present

  24. 24.

    Protoloph (loph joining paracone and protocone) on upper molars (and premolars): 0, absent; 1, present

    Proterotherium is coded “0” as its anterior loph is not a protoloph in the sense used here, as it does not join the paracone and protocone but only the paraconule to the latter.

  25. 25.

    Ectoloph (loph joining paracone and metacone) on upper molars (and premolars): 0, absent; 1, present

  26. 26.

    Metaloph (loph joining metacone and hypocone) on M1-2 (and premolars): 0, absent; 1, present

  27. 27.

    Long crochet on upper cheek teeth connected to the ectoloph, thus isolating a posterolabial fossette: 0, absent; 1, present

  28. 28.

    Anterolabial fossette on upper cheek teeth: 0, absent; 1, present

    For this character and other similar ones dealing with fossettes isolated by lophs, those taxa that do not present lophs or lophids are coded as ‘-‘ = non applicable.

  29. 29.

    Central fossette on upper cheek teeth: 0, absent; 1, present

    Proterotherium is coded ‘1’ because it isolates a central fossette in late wear stages even if it does not possess protoloph and ectoloph.

  30. 30.

    Deep labial extension of central fossette between the protoloph (-crista 1) and the crochet (-crista 2) on upper molars: 0, absent; 1, present

  31. 31.

    Multiple cristae individualized mesially to the crochet on upper cheek teeth: 0, absent; 1, present

  32. 32.

    Crista intermedia running lingually from the ectoloph between the protoloph and the crochet on upper cheek teeth: 0, absent; 1, present

  33. 33.*

    Crista intermedia: 0, not-well individualized but suggested by a bulge; 1, clearly individualized but connected lingually to the crochet; 2, completely individualized

  34. 34.

    Posterolabial fossette on upper molars: 0, co-occurs with the central fossette; 1, disappears before the closure of the central fossette

  35. 35.

    Crochet originating lingually at mesial edge of hypocone: 0, absent; 1, present

  36. 36.

    Para- and metaconule: 0, absent; 1, present

    The taxa that present cusps strongly embedded within lophs are scored ‘-’ for this character.

  37. 37.

    Parastyle-paracone sulcus on upper cheek teeth: 0, absent; 1, present

  38. 38.

    Parastyle-paracone sulcus on upper premolars: 0, shallow; 1, deep

    The depth of the parastyle-paracone sulcus varies only on premolars for the taxa considered here. This explains why the ch. 38 deals only with upper premolars whereas ch. 37 deals with the whole upper cheek teeth.

  39. 39.

    Metacone fold on upper premolars: 0, absent; 1, present

    Proterotherium is coded as ‘-‘= non applicable because of the presence of styles in that region.

  40. 40.

    Deep mesial valley on P2-3 (-4) due to incomplete development of protoloph: 0, absent; 1, present

  41. 41.

    Strong thickening of the cingulum at mesiolingual base of protocone on P2-4: 0, absent; 1, present

  42. 42.

    P3-4 molariform, elongated mesiodistally: 0, absent; 1, present

  43. 43.

    Persistent sulcus (enamel infolding) between protoloph and metaloph strictly located on the lingual face on upper premolars: 0, absent; 1, present

  44. 44.

    Persistent lingual sulcus after the isolation of the central fossette on upper molars: 0, absent; 1, present

  45. 45.

    Small persistent lingual sulcus (enamel infolding) between protoloph and metaloph on upper molars: 0, absent; 1, present

  46. 46.*

    Upper molars trilobed when little worn, with large and rounded median lobe: 0, absent; 1, present but disappears with wear; 2, trilobation persists throughout all wear stages

  47. 47.

    Lingual vertical ridge on lower incisors and canine: 0, absent; 1, present

  48. 48.*

    Lingual face of i1-2: 0, without vertical sulcus; 1, with a shallow vertical sulcus; 2, with a deep vertical sulcus (bifid incisors)

  49. 49.

    Lower incisors: 0, implanted subvertically; 1, procumbent

  50. 50.*

    First lower incisor: 0, well developed; 1, reduced relative to other incisors; 2, absent

  51. 51.

    Third lower incisor large and canine-like: 0, absent; 1, present

  52. 52.

    Tusk-like third lower incisor: 0, absent; 1, present

  53. 53.

    Mesial lophid (paralophid?) in a paraconid position on lower cheek teeth: 0, absent (or just a faint cristid); 1, present

  54. 54.

    Lower cheek teeth with short mesiodistal protolophid, transverse metalophid and mesiodistal hypolophid slightly convex labially: 0, absent; 1, present

  55. 55.

    Lower cheek teeth with entoconid transversely expanded into entolophid: 0, absent; 1, transversely expanded; 2, less transverse and attached to the trigonid

  56. 56.

    Isolated cuspid in front of the metalophid on lower cheek teeth: 0, absent; 1, small mesiodistal crest running mesially from the distolingual extremity of the metalophid; 2, completely isolated cusp

  57. 57.

    Lingual connection of lophids of the trigonid and talonid (entolophid connects to metalophid with wear) on lower cheek teeth: 0, absent; 1, isolating a trigonid-talonid fossettid in conjunction with the preceding more labial connection of hypolophid with trigonid; 2, lingual connection trigonid-talonid precedes the labial connection and isolation of fossettid; 3, single lingual connection, producing a deep labial sulcus between trigonid and talonid

  58. 58.

    Fossettid of entolophid: 0, absent; 1, present

  59. 59.

    Trigonid of lower molars with a tiny trigonid fossettid partially or entirely isolated lingually by a crest (premetacristid) running mesially from metalophid: 0, absent; 1, present

  60. 60.

    Transversely elongated fossettid isolated between entolophid (mesially) and hypolophid (labially and distally) with advanced wear: 0, absent; 1, present

  61. 61.

    Distolabial crest on trigonid of lower premolars made by a distolabial extension of protolophid: 0, absent; 1, present

  62. 62.

    Talonid extending well distal to entolophid on lower molars: 0, absent; 1, present

  63. 63.

    Deep labial and lingual sulci dividing trigonids and talonids on lower cheek teeth at all wear stages: 0, absent; 1, present

  64. 64.

    Flat and straight lingual face on lower molars at all wear stages (on all the crown height): 0, absent; 1, present

  65. 65.

    Trigonid and talonid of lower molars with angulate (pointed) labial edge: 0, absent; 1, present

  66. 66.

    M1-3 trigonid shape: anterior margin short producing a triangular appearing lobe: 0, absent; 1, present

  67. 67.

    Small rounded fossettid between m3 entolophid and hypolophid: 0, absent; 1, present

See also ch. 137 to 141, which concern teeth. These were added to deal with pyrothere systematics whereas the above characters of the matrix (issued from Billet ( 2008 )) are essentially focused on notoungulates.

Skull

  1. 68.

    Rostrum length/braincase length < 0.5 (braincase more than two times larger than rostrum): 0, absent; 1, present

  2. 69.

    Premaxillaries defining a strong and long ridge connecting the narial processes to the anterior alveolar border (the nares open much higher than the alveolar border): 0, absent; 1, present

  3. 70.

    Palatal premaxillary extension almost restricted to lateral parts, with the premaxillary-maxillary suture running strongly forward medially: 0, absent; 1, present

  4. 71.

    Development of incisive foramina: 0, small; 1, large (=anteroposteriorly elongated)

  5. 72.

    Triangular incisive foramina (distal extremities converging): 0, absent; 1, present

  6. 73.

    Medial platform of palatines expanding palate posteriorly and fully continuous with it: 0, absent; 1, present

  7. 74.

    Strong and diverging ectopterygoid crests formed exclusively by palatines/alisphenoids: 0, absent; 1, present

    Pyrotherium is coded ‘0’ notably because there is a large maxillary contribution in its ectopterygoid crests.

  8. 75.

    Choanae divided by a vomerian/palatine process: 0, absent; 1, present

  9. 76.*

    Premaxillary-maxillary suture course on palate: 0, medially: directed anteriorly; 1, medially: grossly transverse; 2, medially: directed posteriorly; 3, directed posteriorly in its entire course

  10. 77.

    Narial processes of the premaxillaries: 0, absent; 1, present

  11. 78.*

    Posterodorsal extremity of maxillary contacting nasal: 0, does not reach posterior extremity of nasals; 1, does approximately reach posterior extremity of nasals; 2, reaches much further than posterior extremity of nasals

  12. 79.

    Infraorbital foramen in adult: 0, above premolars; 1, above molars

  13. 80.

    Strong vertical descending process of maxillary: 0, absent; 1, present

  14. 81.

    Descending process of maxillary developed as a horizontal spine lateral to infraorbital foramen: 0, absent; 1, present

  15. 82.

    Numerous accessory foramina perforating maxillary in front of infraorbital foramen: 0, absent; 1, present

  16. 83.

    Anterior tips of nasals: 0, extends anterior to ascending process of premaxillary; 1, does not extend anterior to ascending process of premaxillary

  17. 84.

    Anterior edge of ascending process of premaxillary shifted posteriorly: 0, absent; 1, present

  18. 85.

    Length of nasals reduced relative to width: 0, absent; 1, present

  19. 86.

    Large facial extent of lacrimal toward nasal bone: 0, absent; 1, present

  20. 87.

    Post-orbital constriction: 0, strong; 1, weak

  21. 88.

    Jugal excluded from anterior orbital border: 0, absent; 1, present

  22. 89.

    Squamosal contacts with frontal at level of post-orbital apophysis: 0, absent; 1, present

  23. 90.

    Zygomatic arches in dorsal view: 0, parallel to anteroposterior axis; 1, semi-circular and well-expanded laterally

  24. 91.

    Zygomatic plate below and in front of orbit: 0, absent; 1, present

  25. 92.

    Anterior root of zygomatic arch grossly situated at level of M1 anteriorly (removed from M3 posteriorly): 0, absent; 1, present

  26. 93.

    Orbit shape: 0, round; 1, oval (higher than long, dorsal edge of zygomatic arch excavated below orbit)

  27. 94.

    Jugal-squamosal suture curved anteriorly: 0, absent; 1, present

  28. 95.

    Dorsal edge of posterior root of zygomatic arch: 0, weak relief; 1, strong relief, continuous with lambdoid crests, with medial face of arch deeply excavated

  29. 96.

    Sphenopalatine foramen: 0, well individualized at limit between medial orbital wall and orbital floor; 1, poorly individualized, within a groove at limit between medial orbital wall and orbital floor

  30. 97.

    Position of sphenopalatine foramen: 0, in posterior part of orbit roof; 1, at level of middle of orbit roof antero-posterior length

  31. 98.

    Very large orbit (the orbit occupies almost all the orbitotemporal fossa): 0, absent; 1, present

  32. 99.*

    Temporal lines (forming sagittal crest): 0, fused temporal lines, sagittal crest well-developed; 1, fusion of temporal lines only in most posterior part; 2, no fusion between temporal lines

  33. 100.

    Auditory region (basicranium) large and short (= auditory region much wider than longer, from level of anterior edge of squamosal root of zygomatic process to posterior border of paroccipital processes): 0, absent; 1, present

  34. 101.

    Well-marked notch posterior to squamosal root of zygomatic process: 0, absent; 1, present

  35. 102.

    Narrow and shallow fossa posterior to squamosal root of zygomatic arch: 0, absent; 1, present

  36. 103.

    External aperture of Eustachian (auditory) tube: 0, lateral to foramen ovale or sphenotympanic fissure; 1, at same level (and ventral to) or medial to foramen ovale or sphenotympanic fissure

  37. 104.

    Postglenoid foramen: 0, posterior (or postero-medial) to the postglenoid process; 1, anterior to the post-glenoid process

  38. 105.

    Postglenoid foramen piercing deeply postglenoid process postero-dorsally and defining a large sinus within its base: 0, absent; 1, present

  39. 106.

    Foramen ovale: 0, entirely within alisphenoid; 1, mandibular branch of V3 passes through sphenotympanic fissure and/or piriform fenestra.

  40. 107.

    Inflated ossified auditory bulla well attached to basicranium: 0, absent; 1, present

  41. 108.

    Position of hypoglossal foramen relative to posterior lacerate (jugular) foramen: 0, well separated from it; 1, in a common depression

  42. 109.

    Posterior lacerate (jugular) foramen: 0, transversally elongated and posterior to posterior wall of bulla; 1, rounded and medial to posterior wall of bulla

  43. 110.

    Strong relief of medial crest and condyles on basioccipital and exoccipital: 0, absent; 1, present

  44. 111.

    Medial wall of auditory bulla: 0, attached to basioccipital medially; 1, not attached to basioccipital medially defining a long posterior lacerate foramen

  45. 112.

    Posterior carotid foramen shifted anteriorly, medial to auditory bulla: 0, absent; 1, present

  46. 113.

    Large quadrangular auditory bulla with an anterior border grossly transverse and a medial border defining a long straight line: 0, absent; 1, present

  47. 114.

    Posterior bulla laps up onto paraoccipital process: 0, absent; 1, present

  48. 115.

    Crista meatus: 0, absent; 1, present

  49. 116.

    Crista meatus: 0, small; 1, well developed

  50. 117.

    Ossified tubular external auditory meatus strongly attached to the basicranium: 0, absent; 1, present

  51. 118.

    Ossified tubular external auditory meatus: 0, short, does not reach lateral edge of skull (especially lateral edge of postglenoid process); 1, long, reaches lateral edge of skull

  52. 119.

    Postglenoid process appressed or almost fused on all its length to crista meatus and/or to external auditory meatus and defining a channel for postglenoid foramen: 0, absent; 1, present

  53. 120.

    Crista meatus and post-tympanic process of squamosal: 0, widely separated; 1, very close to or appressed against each other

  54. 121.

    Tympanohyal recess defined as a fossa isolated anteriorly and laterally by the crista meatus (or by an adjacent tympanic extension (Billet et al. 2009)) at posterolateral corner of bulla: 0, absent; 1, present

  55. 122.

    Posterior border of tympanohyal recess: 0, formed by paroccipital process; 1, formed by a tympanic extension and/or post-tympanic process

  56. 123.

    Very small tympanohyal recess located on posterolateral slope of bulla: 0, absent; 1, present

  57. 124.

    Epitympanic sinus in posterodorsal part of squamosal: 0, absent; 1, present

  58. 125.

    Hypertrophied epitympanic sinus, prominent in dorsal view: 0, absent; 1, present

  59. 126.

    Epitympanic sinus in a large swollen triangular area delimited by a medial crest continuous with posterior root of zygomatic arch and with lambdoid crest: 0, absent; 1, present

  60. 127.

    Expanded and fanlike medial margin of tympanic face of petrosal, well demarcated from the bean-shaped promontory: 0, absent; 1, present

  61. 128.

    Subarcuate fossa: 0, well marked and deep; 1, shallow or trifling and reduced in surface

  62. 129.

    Vertical septum bullae: 0, absent; 1, present

  63. 130.

    Crista tympanica surrounding the tympanic sulcus at internal aperture of external auditory meatus: 0, in relief and external auditory meatus protrudes within the tympanic cavity; 1, faint crista tympanica and external auditory meatus aperture in retreat within tympanic cavity

  64. 131.

    Pars mastoidea of petrosal: 0, well extended; 1, reduced to a thin strip of bone appearing between squamosal and exoccipital, disrupted in surface from non-mastoid portion of petrosal

  65. 132.*

    Mastoid foramen: 0, opening medial to petrosal bone; 1, opening within petrosal; 2, opening lateral to petrosal

  66. 133.

    Paroccipital process and post-tympanic process define a blade-like extension on posteroventral part of bulla: 0, absent; 1, present

  67. 134.

    Very high sagittal and lambdoid crests, this latter crest being inclined backward: 0, absent; 1, present

  68. 135.

    Coronoid process of dentary: 0, rectilinear; 1, bent medially

  69. 136.

    Mandibular foramen: 0, below alveolar border; 1, at level of alveolar border

Dental Pyrotheres Characters

  1. 137.

    I2 tusk-like: 0, absent; 1, present

  2. 138.*

    Bilophodont structure of upper and lower cheek teeth, two loph/lophids in strict parallel lines: 0, absent; 1, suggested by aligned bunodont cusps; 2, buno-bilophodont; 3, bilophodont

  3. 139.

    Shape of lower cheek teeth: 0, elongated, longer than wide; 1, square, length and width approximately equal

  4. 140.

    Loph/lophid with denticles, crenulated mesial and distal cingulae on cheek teeth: 0, absent; 1, present

  5. 141.

    Lower tusk (i2?): 0, absent; 1, present

Appendix 2

Data matrix

Appendix 3

List of taxa and sources used for the phylogenetic analysis

The species used to score each genus are precised immediately after the dashes.

Leptictis—Leptictis spp., AMNH 80213; Novacek (1986).

Phenacodus—Phenacodus spp., Thewissen (1990).

Meniscotherium—Meniscotherium spp., AMNH 48083, 48123, 48122; Williamson and Lucas (1992).

Proterotherium—Proterotherium spp., AMNH 9245 and uncatalogued specimens from the MNHN-SCZ collection from the Santa Cruz Beds of Patagonia, and Scott (1910).

Protolipterna—P. ellipsodontoides, Cifelli (1983).

Trigonostylops—T. wortmani, AMNH 28700; MNHN-CAS 187, 188, 1200.

Astrapotherium—Astrapotherium spp., MNHN-SCZ 8; AMNH 9278; other uncatalogued specimens from the MNHN-SCZ collection (from the Santa Cruz Beds of Patagonia); Scott (1928).

Pyrotherium—P. romeroi, ACM 3207; FMNH 13515; MNHN-DES 1238, 1239, 1240, 1243.

Notostylops—N. murinus, N. pendens, and N. pigafettai, MNHN-CAS 96, 97, 637 and 647; MACN A-10499 and 10498; FMNH P13319; AMNH 28581, 28604, 28614, 28634, 28758 and 28956.

Henricosbornia—H. lophodonta, MACN A-10717, 10808 (holotype), and 10792.

Simpsonotus—S. praecursor and S. major, MLP 73-VII-3-11, 73-VII-3-12 and 73-VII-3-13.

Pleurostylodon—P. modicus, P. similis, MLP 74-IV-27-1, 82-V-1-51; MACN A-10554; FMNH P13528, P13296, P13309 and P13620; AMNH 28644, 28646, 28830, 28878 and 28880.

Thomashuxleya—T. externa, MNHN-CAS 844; AMNH 28698 and AMNH 28447; Simpson (1967).

Pampahippus—P. arenalesi, photographs (send by Daniel Garcia López, University of Tucumán) of PVL-S-4192; Bond and López (1993).

Periphragnis—P. harmeri, P. exauctus, MLP 82-V-7-1, 12-1708, 12-1716, 69-III-24-286 and an uncatalogued skull from the MLP collections; AMNH 29420.

Ryphodon—R. lankesteri, MLP 12-1719, 12-1718, 12-1717, 12-2186, 12-1749; AMNH 29414.

Puelia—Puelia sp., MLP 67-II-27-27.

Leontinia—L. gaudryi, FMNH P 13284, P 13412, and P 13285; ACM 3335, 3290, and 3293; MNHN-DES 461, 462 and 514.

Colpodon—C. distinctus, C. propinquus, MNHN-COL 13 and MNHN-COL uncatalogued specimens.

Ancylocoelus—A. frequens, FMNH P 13494, P 14715, and P 13342; many MNHN-DES uncatalogued specimens.

Scarittia—S. canquelensis, AMNH 29613 and 29612; Chaffee (1952).

Homalodotherium—Homalodotherium spp., MNHN-SCZ 2; FMNH P 13092; Patterson (1934).

Asmodeus—A. osborni, MLP 82-V-6-1; FMNH P 12381.

Rhynchippus—R. equinus, FMNH P 13420, P 13287, and P 13410.

Eurygenium—E. pacegnum, MNHN-SAL 12, 13, and 14; Shockey (1997).

Pascualihippus—P. boliviensis, MNHN-SAL 15 and 190; Shockey (1997).

Eomorphippus—E. obscurus, E. pascuali, AMNH 29474 and 29405; MLP 12-1508; Simpson (1967).

Morphippus—M. imbricatus, MNHN-DES 375; FMNH P 13282, P 13378, P 13411, and P 13283.

Argyrohippus—A.s fraterculus, A. praecox, MNHN-DES 336; MNHN-COL uncatalogued crushed skull; AMNH 29685; Patterson (1935).

Nesodon—Nesodon spp., MNHN-SCZ 34, 36, 38, and 52; Scott (1912).

Adinotherium—Adinotherium spp., MNHN-SCZ 5, 13, and 14; FMNH P 13110; Scott (1912).

Hoffstetterius—H. imperator, MNHN-ACH 1; Saint-André (1999).

Ponanskytherium—P. vicachense, P. desaguaderoi, MNHN-AYO 191; MNHN-VIZ 38; MNHN-BOL-VGB-004.

Toxodon—T. platensis, AMNH 11169; MNHN-PAM uncatalogued specimens.

Colbertia—C. magellanica, C. lumbrerense, AMNH 49873, 49867, 49868, 49874, 49871, and 49887; photographs of PVL-5-11 and PVL-5-2 (sent by Daniel Garcia-López University of Tucumán, Argentina); Bond (1981); Paula Coulo (1952).

Oldfieldthomasia—O. debilitata, O. parvidens, MNHN-CAS 393; MACN 10376, A-10772, and 10400; AMNH 28780, 28691, 28896, 28680, and 28730; Simpson (1967).

Campanorco—C. inauguralis, not formally described; MLP 79-IV-16-1.

Acropithecus—A. rigidus, AMNH 28782; Simpson (1967).

Ultrapithecus—U. rutilans, MNHN-CAS 387; AMNH 28583, 28706, 28749, 28853, 28828, and 28679 ; Simpson (1967).

Notopithecus—Notopithecus spp., MNHN-CAS 1037-1039; MACN A-10787, A-10790; AMNH 28949, 28673, 28627, and 28894.

Archaeophylus—A. patrius, MACN A-52-483 and MACN A-52-484.

Cochilius—C. volvens, MNHN-COL uncatalogued specimens; Simpson (1932b).

Plagiarthrus—P. clivus, MACN A-52-472 and MACN A-52-474; FMNH P 13415.

Protypotherium—Protypotherium spp., MNHN-SCZ 178, 179, and 184; MACN A-4001; FMNH P13002; AMNH 9534.

Miocochilius—M. anomopodus, AMNH 45882; Stirton (1953).

Interatherium—Interatherium spp., MNHN-SCZ 170-173, 177, and 188; MACN A-9859; FMNH P 13057.

Federicoanaya—F. sallaensis, MNHN-SAL 418; Hitz et al. (2008).

Trachytherus—T. alloxus, Billet et al. (2008).

Plesiotypotherium—P. achirense, MNHN-ACH 23 and 26.

Mesotherium—M. cristatum, MNHN-PAM 2 and 344.

Eohyrax—Eohyrax spp., MNHN-CAS 56, 94, 95, and 480; MACN 10-53; Simpson (1967).

Pseudhyrax—Pseudhyrax spp., MLP 67-II-27-359 and 61-IV-9-1; Simpson (1967).

Archaeotypotherium—A. tinguiriricaense, Croft et al. (2003).

Archaeohyrax—A. suniensis, Billet et al. (2009).

Prohegetotherium—P. schiaffinoi, MNHN-SAL 5, 6, 1003, and 1009; MNHN-BOL-V 00-39-40.

Hegetotherium—H. mirabile, MNHN-SCZ 189 and other MNHN-SCZ uncatalogued specimens; MACN 11198; FMNH P13194.

Prosotherium—P. triangulidens, P. garzoni, MACN A52-464; AMNH 14154; ACM 3730 and 3731.

Paedotherium—P. bonaerense, MNHN-MHR 45; Cerdeño and Bond (1998).

Proticia—P. venezuelensis, FMNH cast of Museo de Historia Natural, Caracas, Venezuela, n°237.

Colombitherium—C. tolimense, MNHN-CLB 15.

Baguatherium—B. jaureguii; Salas et al. (2006).

Propyrotherium—P. saxeum; Simpson (1967).

Carolozittelia—C. tapiroides; Simpson (1967).

Gryphodon—G. peruvianus, AMNH 17724.

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Billet, G. New Observations on the Skull of Pyrotherium (Pyrotheria, Mammalia) and New Phylogenetic Hypotheses on South American Ungulates. J Mammal Evol 17, 21–59 (2010). https://doi.org/10.1007/s10914-009-9123-0

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