Trigonostylops wortmani, AMNH

MacPhee, R. D. E., Del Pino, Santiago Hernández, Kramarz, Alejandro, Forasiepi, Analía M., Bond, Mariano & Sulser, R. Benjamin, 2021, Cranial Morphology And Phylogenetic Relationships Of Trigonostylops Wortmani, An Eocene South American Native Ungulate, Bulletin of the American Museum of Natural History 2021 (449), pp. 1-185 : 7-15

TRIGONOSTYLOPS WORTMANI AMNH VP- 28700. Simpson (1933a: 1) described AMNH VP-28700 as being “nearly complete with preservation unusually favorable for study” (figs. 1A–E; 2A, B). This assessment is substantially correct, but it should be noted that, as was common practice at the time, a fair amount of reconstruction was undertaken to improve the fossil’s appearance. On the specimen’s left side (fig. 1D), much of the face, floor of the orbit, and rostral part of the zygomatic arch are reconstructed in plaster, their shapes based on the somewhat more intact right side. Plaster likewise holds together the nasal cavity’s surviving right wall, which is minutely fractured and crushed inward (fig. 24). The meso- and neurocranium are internally much fragmented, although the caudal cranium is in surprisingly good condition. Some sutures and plaster/bone contacts were traced in India ink, perhaps by Simpson (e.g., fig. 25). During the original preparation of the specimen, matrix was removed from all external surfaces; foramina were subjected to especially deep cleaning, with inevitable (if mostly minute) loss of bone as a result. Matrix lodged in the endocranium was removed by tunneling through the foramen magnum, which resulted in additional damage to some structures (e.g., to internal walls of extratympanic sinuses, so that they now artificially open into the cranial cavity; figs. 11, 12).

The basicranium as it appears at present (fig. 26) differs slightly from the illustration in Simpson’s (1933a: fig. 5) paper. This indicates that AMNH VP-28700 has undergone additional preparation by unknown hands since Simpson’s time, especially on the specimen’s right side where additional work on the auditory region has obviously occurred. Internally, the portion of the skull that housed the olfactory bulbs and adjacent parts of the forebrain are extensively damaged and could not be usefully reconstructed (fig. 8). The ubiquitous presence of mineral sinter on internal surfaces complicated endocast rendering (e.g., figs. 11, 12).

The skull may have been discovered in two or more parts, or perhaps it broke after collection or during preparation. In any case, the pieces were expertly glued together, albeit with a slight loss of bone as the pieces were fitted along fractures. The most obvious break can be seen ventrally, where the fracture line passes from side to side just caudal to the opening of the choanae. Large fractures were treated with a filler (?polyethylene glycol) at some stage of preparation.

OTHER TRIGONOSTYLOPS SPECIMENS. Three additional cranial fragments ascribed to T. wortmani were available for study: a partial face (MLP 52-X-5-98; fig. 21), a partial rostrum (MACN Pv 47 [cast of MNHN-CAS 187]), and another incomplete rostrum in poorer condition but preserving parts of the nasals and maxillae (MACN A 11078). A nearly complete jaw, MPEF PV 5483 (fig. 3), is also briefly described and illustrated in connection with the summary of dental features (see p. 69, Dentition and Upper Jaw).

MLP 52-X-5-98 is the only specimen of Trigonostylops discovered to date that substantially preserves the nasal aperture and rostral portion of the face. The rostrum has been distorted by lateral crushing, with the result that the left palatal process of the maxilla has been partly jammed under the right. There is also a significant fracture passing through the palate that principally affects the teeth, but has no other consequences for present purposes. There is some loss of bone on projecting margins, but the nasal aperture

TABLE 1 Comparative Set 1

Taxon Institution Accession No. Specimen(s) 2 Age/ Gender Geographical Origin 3 Geological Age/Fm

EXTANT TAXA

Tapiridae

Tapirus indicus AMNH M-77875 skull young juvenile ND Holocene

Tapirus indicus AMNH M-130108 skull adult (M) ND Holocene

Tapirus indicus 4 AMNH M-200300 skull subadult ND Holocene

Tapirus terrestris AMNH M-77576 skull adult (M) Venezuela Holocene

Tapirus terrestris MACN Ma 24.30 skull adult Alto Amazonas, Brazil Holocene

Tapirus terrestris MACN Ma 27200 skull adult ND Holocene

Tapirus terrestris MACN Ma 52.77 skull juvenile Misiones, Argentina Holocene Rhinocerotidae

Ceratotherium simum AMNH M-51882 skull juvenile (F) Democratic Republic of Congo Holocene Dicerorhinus sumatrensis AMNH M-81892 skull adult (M) Malaysia Holocene Rhinoceros unicornis AMNH M-274636 skull perinatal ND Holocene

Equidae

Equus asinus AMNH M-204141 skull adult ND

Equus caballus AMNH M-204155 skull young juvenile (F) ND

Bovidae

Saiga tatarica AMNH M-85305 skull adult Kazakhstan

FOSSIL TAXA

Astrapotheria

Trigonostylops wortmani AMNH VP-28700 skull young adult Colhué-Huapí, Argentina Trigonostylops wortmani MLP 52-X-5-98 partial rostrum adult Pampa de María Santísima, Argentina

Holocene

Holocene

Holocene

M. Eocene; Sarmiento Fm. M. Eocene; Sarmiento Fm. Taxon Institution Accession No. Specimen(s) 2 Age/ Gender Geographical Origin 3 Geological Age/Fm

Trigonostylops wortmani MACN Pv 47 partial rostrum adult Punta Casamayor, Argentina M. Eocene; Sarmiento Fm.

Trigonostylops wortmani MACN A 11078 partial rostrum? Colhué-Huapí, Argentina M. Eocene; Sarmiento Fm.

Trigonostylops wortmani MPEF PV 5483 jaw adult Valle Hermoso, Argentina M. Eocene; Sarmiento Fm.

Tetragonostylops apthomasi DGM 355-M partial skull adult Itaboraí, Brazil E. Eocene; Itaborai Fm.

Tetragonostylops apthomasi DGM 216-M left maxilla adult Itaboraí, Brazil E. Eocene; Itaborai Fm.

Granastrapotherium snorki IGM SCG MGJRG- 2018 V4 skull adult La Venta, Colombia M. Miocene; Villavieja Fm.

Astraponotus sp. MPEF PV 1279 skull adult Gran Hondonada, Argentina L. Eocene; Sarmiento Fm.

Astraponotus sp. MPEF PV 1084 skull adult Gran Hondonada, Argentina L. Eocene; Sarmiento Fm.

Astraponotus sp. MPEF PV 1296 right maxilla juvenile Gran Hondonada, Argentina L. Eocene; Sarmiento Fm.

Astrapotherium magnum YPM PU 15117 skull, jaw adult Güer Aike , Argentina E. Miocene ; Santa Cruz Fm. Astrapotherium magnum YPM PU 15261 skull adult Güer Aike , Argentina E. Miocene ; Santa Cruz Fm. Astrapotherium magnum MACN A 8580 skull adult Corrigue Kaik , Argentina E. Miocene ; Santa Cruz Fm. Astrapotherium magnum MACN A 3208 skull 5 adult Corrigue Kaik , Argentina E. Miocene ; Santa Cruz Fm. Astrapotherium magnum YPM PU 15332 skull adult Coy Inlet , Argentina E. Miocene ; Santa Cruz Fm. Astrapotherium magnum AMNH VP-9278 skull, jaw adult Río Gallegos , Argentina E. Miocene ; Santa Cruz Fm. Astrapotherium sp. MLP 38 -X-30-1 partial skull juvenile Río Coyle , Argentina E. Miocene ; Santa Cruz Fm. Astrapotherium magnum FMNH P14259 skull, jaw, LE adult Río Coyle , Argentina E. Miocene ; Santa Cruz Fm. Astrapotherium guillei MAPBAR 5322 skull, jaw adult Comallo , Argentina M. Miocene ; Collon Cura Fm. Parastrapotherium sp. AMNH VP-29596 skull juvenile Las Cascadas , Argentina L. Oligocene ; Sarmiento Fm. Parastrapotherium sp. AMNH VP- 295756 skull adult Las Cascadas , Argentina L. Oligocene ; Sarmiento Fm. Parastrapotherium martiale MACN A 52-604 partial skull, jaw adult Argentina? L. Oligocene

Scaglia kraglievichorum MMP M 207 skull juvenile Cañadón Vaca, Argentina M. Eocene; Sarmiento Fm.

Scaglia cf. kraglievichorum MPEF PV 5478 skull adult Cañadón Vaca, Argentina M. Eocene; Sarmiento Fm.

Eoastrapostylops riolorense PVL 4216 skull, jaw young adult Río Loro, Argentina?L. Paleocene; Rio Loro Fm. Eoastrapostylops riolorense PVL 4217 skull, jaw young adult Río Loro, Argentina?L. Paleocene; Rio Loro Fm. Taxon Institution Accession No. Specimen(s) 2 Age/ Gender Geographical Origin 3 Geological Age/Fm

Notoungulata

Nesodon imbricatus YPM PU 16012 skull adult Corpen Aike, Argentina E. Miocene; Santa Cruz Fm. Nesodon imbricatus YPM PU 15000 skull adult Güer Aike, Argentina E. Miocene; Santa Cruz Fm. Nesodon imbricatus YPM PU 15336 skull adult Güer Aike, Argentina E. Miocene; Santa Cruz Fm. Nesodon imbricatus YPM PU 15492 skull adult Güer Aike, Argentina E. Miocene; Santa Cruz Fm. Nesodon sp. YPM 33847 partial skull?

Adinotherium ovinum YPM PU 15986 skull adult Güer Aike, Argentina E. Miocene; Santa Cruz Fm. Adinotherium ovinum YPM PU 15114 skull adult Güer Aike, Argentina E. Miocene; Santa Cruz Fm. Piauhytherium sp. MCL 5191 partial skull adult Procedência, Toca dos Ossos, Brazil Pleistocene

Toxodon sp. MCL 5192 partial skull adult Procedência, Toca dos Ossos, Brazil Pleistocene

Toxodon sp. MCL 5194 partial skull juvenile Procedência, Toca dos Ossos, Brazil Pleistocene

Toxodon sp. MACN Pv 16615 skull juvenile Río Carcarañá, Argentina L. Pleistocene

Puelia coarctatus MLP 67-II-27-27 skull adult Gran Hondonada, Argentina L. Eocene; Sarmiento Fm.

Homalodotherium sp. MPM PV 17490 skull adult Cañadon de la Vacas , Argentina E. Miocene, Santa Cruz Fm. Homalodotherium segoviae FMNH P 13092 LE adult Cape Fairweather, Argentina E. Miocene ; Santa Cruz Fm. Homalodotherium sp. MACN A 32068 skull adult Monte Observacion , Argentina E. Miocene ; Santa Cruz Fm. Rhynchippus equinus FMNH P 13410 skull, LE adult Cabeza Blanca , Argentina L. Oligocene ; Sarmiento Fm. Oldfieldthomasia debilitata AMNH VP-28600 skull adult Cerro Blanco , Argentina M. Eocene ; Sarmiento Fm.

Notopithecus adapinus AMNH VP-28949 skull adult Colhué-Huapí, Argentina M. Eocene; Sarmiento Fm.

Cochilius volvens AMNH VP-29651 skull adult Colhué-Huapí, Argentina E. Miocene; Sarmiento Fm.

Cochilius volvens FMNH P 13424 skull adult Colhué-Huapí, Argentina E. Miocene; Sarmiento Fm.

Interatherium robustum FMNH P 13057 skull, jaw adult Estancia Felton, Argentina E. Miocene; Santa Cruz Fm. Campanorco inauguralis MLP 79-IV-16-1 skull adult Cerro Campanorco , Argentina M. Eocene; Lumbrera Fm.

Protypotherium sp. FMNH P13234 skull, jaw adult Güer Aike , Argentina E. Miocene; Santa Cruz Fm. Typotheriopsis internum FMNH P 14420 skull adult Puerta de Corral Quemado , Argentina L. Miocene ; Chiquimil Fm.

Typotheriopsis internum FMNH P 14477 skull adult Puerta de Corral Quemado, Argentina L. Miocene; Chiquimil Fm.

Taxon Institution Accession No. Specimen(s) 2 Age/ Gender Geographical Origin 3 Geological Age/Fm

Mesotherium angustirostrum MACN Pv 6040 skull adult General Alvarado, Argentina E. Pleistocene; “Pampean Fm.” Paedotherium chapadmalense AMNH VP-45914 skull adult Chapadmalal, Argentina L.Pliocene; Chapadmalal Fm. Argyrohyrax proavus FMNH P 13415 skull adult Cabeza Blanca, Argentina L. Oligocene; Sarmiento Fm.

Pyrotheria

Pyrotherium romeroi ACM 3207 partial skull adult Cabeza Blanca, Argentina Pyrotherium romeroi FMNH P 13515 incomp. rostrum adult Pico Truncado, Argentina

Litopterna

Diadiaphorus majusculus AMNH VP-9270 skull adult Santa Cruz, Argentina Tetramerorhinus mixtum MACN A 8970 skull adult Corrigue Kaik, Argentina Tetramerorhinus cingulatum MACN A 5971 skull adult La Cueva, Argentina Tetramerorhinus cingulatum MACN A 8666 skull adult Corrigue Kaik, Argentina Tetramerorhinus lucarius AMNH VP-9245 9 skull adult Río Gallegos, Argentina Tetramerorhinus sp. YPM PU 153689 skull adult Killik Aike, Argentina Tetramerorhinus mixtum YPM PU 151079 skull, jaw adult Lago Pueyrredón, Argentina Neobrachytherium morenoi MACN Pv 8428 skull adult Andalhualá, Argentina Thoatherium minusculum YPM PU 15721 skull adult Río Gallego, Argentina Scalabrinitherium bravardi MACN Pv 13082 caudal cranium adult Paraná, Argentina Promacrauchenia antiquua MACN Pv 7986 skull adult Monte Hermoso, Argentina Huayqueriana cf. cristata IANIGLA Pv 29 skull adult Huayquerías del Este, Argentina Macrauchenia patachonica MACN Pv 2 skull adult Salto, Argentina

Perissodactyla (Palaeotheriidae)

Palaeotherium siderolithicum MNHN GY- 52310 skull adult Montmartre, France Palaeotherium crassum MACN A 11538 maxilla adult France L. Oligocene; Sarmiento Fm. L. Oligocene; Sarmiento Fm.

E. Miocene; Santa Cruz Fm.

E. Miocene; Santa Cruz Fm.

E. Miocene; Santa Cruz Fm.

E. Miocene; Santa Cruz Fm.

E. Miocene; Santa Cruz Fm.

E. Miocene; Santa Cruz Fm.

E. Miocene; Santa Cruz Fm.

L. Miocene; Corral Quemado Fm. E. Miocene; Santa Cruz Fm.

L. Miocene; Ituzaingó Fm.

E. Pliocene; Monte Hermoso Fm.

L. Miocene; Huayquerias Fm.

L. Pleistocene; “Pampean Fm.”

Eocene

Eocene

1 Scanned specimens in bold.

2 LE, latex endocast (FMNH Patterson collection); F, female; M, male.

3 ND, no locality data (zoo specimens in the case of extant species). For fossils lacking locality data, only country of origin is listed.

4 Accessioned as “ Tapirus sp. ” in AMNH Mammalogy catalog, but cranial characters are those of T. indicus (cf. Moyano and Giannini, 2017).

5 Left petrosal scanned.

6 Specimen extensively reconstructed.

7 Temporary accession number.

8 Type of Diorotherium aegregium .

9 Specimens usually included in Protertotherium (e.g., Billet et al., 2015, App. S1), but here placed in Tetramerorhinus following Soria (2001). YPM PU 15107 is type of Proterotherium dodgei .

10 Examined for pneumatization-related features; other Palaeotherium specimens used for scoring discrete traits.

11 Cast of YPM PU 14864.

and the pillarlike projections in which the tusks were socketed are relatively well preserved.