Cardiatherium aff. orientalis Pascual and Bondesio, 1982

Vucetich, María Guiomar, Deschamps, Cecilia M., Vieytes, Emma Carolina & Montalvo, Claudia I., 2014, Late Miocene capybaras from Argentina: Skull anatomy, taxonomy, evolution, and biochronology, Acta Palaeontologica Polonica 59 (3), pp. 517-535 : 528-529

Cardiatherium aff. orientalis Pascual and Bondesio, 1982

Fig. 7 .

1982 Kiyutherium aff. orientalis ; Pascual and Bondesio 1982: 20; nec

Pascual and Bondesio 1985: 135. 1999 Kiyutherium orientalis ; Rocha and Montalvo 1999: 284. 2005 Kiyutherium orientalis ; Vucetich et al. 2005: 260.

Material.—GHUNLPam 139, extremely damaged skull fragment with both M1–3; GHUNLPam 2009, skull fragment with both P4–M3; GHUNLPam 5236, anterior fragment of palate of a juvenile specimen with anterior root of the zygomatic arch, both P4 and left M1; GHUNLPam 5274; skull with both P4–M3, rostrum, right orbital area and damaged skull roof; GHUNLPam 8978, small fragment of palate with left M1–2; GHUNLPam 14452, palate with both P4–M3 and posterior portion of rostrum; GHUNLPam 14661, distorted skull with both P4–M3; GHUNLPam 14985, damaged rostrum with right incisor, right P4–M2 and left P4; GHUNL- Pam 27389, skull with both P4–M3, incisors, a left mandible fragment with p4–m3, and six cervical vertebrae articulat- ed to skull; MLP 62-XII-4-17, left mandible fragment with p4–m3 and palatal fragment with left P4–M3 and right P4– M1 (the palatal fragment is currently lost). For mandibular remains, see Rocha and Montalvo (1999) and Vucetich et al. (2005). All specimens from Laguna Chillhué apart from GHUNLPam 139, 14985, and 27389, which are from Laguna Guatraché, La Pampa Province; lacustrine levels of the Cerro Azul Formation, Late Miocene.

Differential diagnosis.—No diagnosis can be provided given the present state of knowledge of C. orientalis Francis and Mones, 1965b . The occlusal morphology of the lower teeth is similar to that of C. paranense and the type of C. orientalis

Vucetich et al. 2005; Deschamps et al. 2007, 2009). However, some characters allow the differentiation of the taxon from the Cerro Azul Formation from C. chasicoense ( Pascual and Bondesio, 1968) , C. paranense ( Ameghino, 1883a) , and C. patagonicum Vucetich, Deschamps, Olivares, and Dozo, 2005 . Concerning potential morphological similarities with C. orientalis , the present specimens will need to be compared with as yet unpublished material from the type locality of the species in Uruguay.

Description

Skull.— The state of preservation of the skulls from the Cerro Azul Formation is generally poor, but they preserve the palatal region. None of the specimens has a snout with roll-shaped expansions, as seen in MLP 87-XI-1-27. The length of the diastema exceeds the combined length of P4–M3, especially in larger specimens (44.2/ 41.5 mm in GHUNL- Pam 5274, 6.5% longer; 58/ 53 mm in GHUNLPam 27389, 9.5% longer). The zygomatic arch is not preserved in any of the skulls.

Compared with H. hydrochaeris , the rostrum is wide transversely both anterior and posterior to the anterior root of the zygomatic arch, but not as wide as in C. paranensis . The bottom of the P4 alveolus is located further dorsally than in Cardiatherium paranense , and does not extend laterally beyond the occlusal surface of the tooth. The incisive foramen is long, but slender. The premaxillary-maxillary suture is straight and crosses the incisive foramen near its posterior border, rather than its centre as in C. paranense . The scar marking the origin of the masseter superficialis muscle begins at the posterior margin of the anterior root of the zygomatic arch, between prisms I and II of P4. It extends up to half the distance between the posterior margin of the incisive foramen and the anterior margin of P4, without extending anteriorly beyond the anterior margin of the anterior root of the zygomatic arch. The muscle scars are oval in shape, narrower than in C. paranense , and parallel to the maxillary symphysis. The palate is not as wide as in C. paranense because M3 does not follow the oblique orientation of P4–M2, and instead is oriented slightly medially towards the sagittal plane. The maxillo-palatine suture diverges from the alveolar margin at the level of prism III of M3, before gently curving towards the base of the small palatine foramina. Thus, the palatine occupies a larger area of the palate than in C. paranense . The anterior margin of the mesopterygoid fossa is deeper than in C. paranense , reaching the fourth prism from the last of M3.

The dorsal margin of the masseteric fossa appears to be more horizontally oriented than in C. paranense , thus more closely resembling that of Hydrochoerus hydrochaeris . The anterior root of the zygomatic arch is inclined anterodorsally-posteroventrally with respect to the alveolar plane, at an angle greater than 20º. The posterior portion of the skull is preserved, but damaged, in GHUNLPam 27389. The temporal fossa is large and there is a moderately developed sagittal crest, unlike in Hydrochoerus and Neochoerus in which the latter is absent. The posterior wall of the skull is proportionally narrower than in Hydrochoerus , although this feature may be exaggerated as the posterior portion of the skull has been deformed by slight lateral compression. The paroccipital process is robust, laterally compressed, and long (the preserved fragment is more than 30 mm), extending well ventral to the ventral border of the bulla. These features of the paroccipital process characterise capybaras, and are also found in Hydrochoerus , C. patagonicum Vucetich, Deschamps, Olivares, and Dozo, 2005 , and “ Chapalmatherium ” novum Ameghino, 1908 . By contrast, the paroccipital process is slender and scarcely extends beyond the ventral border of the bulla in Kerodon and in other large cavioids such as Dolichotis . Both bullae have been partially preserved in this specimen, and contribute new data to those originally provided by Mones (1974). The bulla is more spherical and larger than in C. patagonicum ( Dozo et al. 2010: fig. 4), Neochoerus ( Deschamps 1998) , and H. hydrochaeris ( Linnaeus, 1766) . The epitympanic sinus is large, and the external acoustic meatus appears to be doubled, as also seen in other hydrochoerids, with the inferior portion being enlarged anteroposteriorly.

Upper teeth ( Fig. 6M, N ).—Incisors: Only the largest specimen (GHUNLPam 27389) preserves the incisors. They are subcircular rather than subtriangular in cross section and lack a longitudinal furrow.

P4: The premolar resembles that of C. paranense , but in the juvenile specimen both the primary and secondary external flexi are shallower. The labial flexus of prism Ib is very shallow.

PC 1 PC 2 PC 3

1 -0 0 -0 Cardiatherium

2 -0 -0 0 paranense

3 -0 -0 0

M1–2: These molars differ from those of C. paranense in lacking a labial flexus on prism Ib. The primary external flexus extends along up to 50% of the total transverse width of prism I, whereas the secondary external flexus is shorter, especially in the young specimen (GHUNLPam 5236).

4 -0 -0 -0 C. paranense

5 -0 0 0

(Tupungato)

6 -0 -0 -0

7 -0 -0 0

8 -0 0 -0 Cardiatherium

9 0 -0 -0 aff. orientalis Eigenvalue 7 0 0 Hydrochoerus Explained 78 10 4 hydrochaeris variance %

M3: The third molar differs from that of C. paranense in comprising seven prisms, plus an incipient last one (the left M3 of GHUNLPam 14452 lacks this incipient prism; Fig. 6N ). Only prisms II to VI have labial flexi. The transverse width of the prisms increases up to prism IV, whereas prisms VI to VIII decrease in size.

Figures

Fig. 7. Late Miocene capybara Cardiatherium aff. orientalis Pascual and Bondesio, 1982, GHUNLPam 14452 from Laguna Chillhué, Huayquerian SALMA, in ventral (A) and lateral (B) views (anterior to the left). Dotted area, sediment.

Fig. 6. Occlusal view of the right upper teeth of Late Miocene capybaras Cardiatherium paranense (Ameghino, 1883a) (A–L) and C. aff. orientalis (M, N). C–E, H, N, reversed. A. MACN 3353, M3. B. MLP 71-VI-16-1, P4–M2. C. MLP 69-XII-2-19, P4–M1. D. MLP 87-XI-1-2, M3. E. MLP 40-XI-15- 2, P4–M3. F. MLP 87-XI-1-3, P4–M1. G. MLP 41-XII-13-153, P4–M3. H. MLP 87-XI-1-1, P4–M1. I. MLP 87-XI-1-3a, P4–M2. J. MLP 87-XI-1-27, P4–M3. K. MACN 13434, P4–M1. L. MLP 41-XII-13-161, M3. M. GHUNLPam 5236, P4–M1. N. GHUNLPam 14452, P4–M3.