Neocavia pampeana, Madozzo-Jaén & Pérez & Montalvo & Tomassini, 2018

Madozzo-Jaén, M. Carolina, Pérez, M. Encarnación, Montalvo, Claudia I. & Tomassini, Rodrigo L., 2018, Systematic review of Neocavia from the Neogene of Argentina: Phylogenetic and evolutionary implications, Acta Palaeontologica Polonica 63 (2), pp. 241-260 : 250-253

Neocavia pampeana sp. nov.

Figs. 5C–E, G–I, 7, 8A.

2003 Neocavia cf. N. lozanoi ; Montalvo and Rocha 2003: 501–504, figs. 2, 3.

Etymology: In reference to the La Pampa Province, Argentina, where the holotype and other assigned specimens were collected.

Holotype: GHUNLPam 19559, fragment of left mandible with p4–m3 Figs. 5H, 7F).

Type locality: Caleufú, La Pampa Province, Argentina ( Fig. 1B ).

Type horizon: Cerro Azul Formation, late Miocene–early Pliocene, Huayquerian Stage/Age ( Montalvo and Rocha 2003; Verzi and Montalvo 2008).

Material.—GHUNLPam 19550: left mandibular fragment with posterior lobe of m1, m2, and anterior lobe of m3; GHUNLPam 19566: right mandibular fragment with m2– m3; GHUNLPam 19581:left mandibular fragment with broken i1 and p4; GHUNLPam 19582: left mandibular fragment with p4–m2 (Fig. 5G); GHUNLPam 19588: right mandibular fragment with m1–m2; GHUNLPam 19589: left mandibular fragment with m1–m2; GHUNLPam 19622: left mandibular fragment with p4–m1; GHUNLPam 21056: left mandibular fragment with p4–m1; GHUNLPam 21286: maxillary and palatine fragment with both dental series, complete left DP4–M3 (Fig. 5E) and right P4–M3; GHUNLPam 21288: right mandibular fragment with complete dental series (Fig. 5I); GHUNLPam 21330: right mandibular fragment with p4–m2; GHUNLPam 21332: right mandibular fragment with p4–m1; GHUNLPam 21351: fragment of maxilla with right P4–M3 and left P4–M1 (Fig. 5C); GHUNLPam 21353: maxillary and palatine fragment with left P4 and right P4, M2, and broken M1; GHUNLPam 21854: fragment of maxilla with complete dental series (Fig. 5D).

Diagnosis.— Neocavia pampeana sp. nov. differs from the other species of the genus because the primary internal flex is wider, and the anterior lobe of lower m1–m2 is proportionally anteroposteriorly longer than the posterior lobe, contrasting with the condition of N. lozanoi .

Description.— Palate: Several specimens include fragments of the palate with a portion of the maxilla and palatine. The most complete specimen (GHUNLPam 21351, Fig. 7A 1 ) has the posterior wall of the diastema with a wide posterior margin of the incisive foramina, similarly to M. australis and Dolicavia . The suture between Mx (in the posterior wall of the diastema) forms a small bulge as in N. lozanoi , M. australis , and Dolicavia . The anterior ventral root of the zygomatic arch begins anteriorly to P4 ( Fig. 7A 1 , B 2 , C). The Pt is more dorsally located than the Mx, forming a ridge in the palate, as in N. lozanoi , Microcavia , and Dolicavia ( Fig. 7A 1 , B 2 , C). In lateral view ( Fig. 7A 2 , B 1 ), the posterior border of the upper diastema has a vertical orientation, resembling M. australis and Dolicavia . The groove and ridge for the passage of the infraorbital nerve and artery is present, as in N. lozanoi , but is dorsoventrally shorter than in Cavia aperea , M. australis , and Dolicavia .

Dentary: The preserved fragments include mandibular bodies, lacking any portion of the diastema and the posterior process ( Fig. 7D–F ). In lateral view, the nMpi is located between m1 and m2, as in M. australis and N. lozanoi . The horizontal crest is only known by its anterior part in GHUNLPam 19559 ( Fig. 7F 3 ). The straight lateral crest originates at the level of the anterior lobe of m2 ( Fig. 7D 3 ), as in N. lozanoi , M. australis , and Dolicavia . In occlusal view ( Fig. 7D 3, F 3 ), the dorsal fossa for the insertion of the masseter medialis muscle is deeper than the nMpi, as in N. lozanoi , M. australis , Dolicavia , and C. aperea . In lingual view ( Fig. 7D 2, E 2, F 2 ), the lower incisor extends to the level of the anterior lobe of m1, as in N. lozanoi , and the mylohyoid crest is present, differing from M. australis .

Molariforms: The molariforms are euhypsodont, double heart-shaped, with a constriction in the apex of each lobe, and with a transverse dentine crest in the middle of the occlusal surface in each lobe, as in other caviines (Fig. 5C– E, G–I). The Hf/hf is funnel-shaped and has cement; the enamel is continuous around the entire crown, but is interrupted on the labial side in the upper molariforms and on the lingual side in the lower molariforms, except in H.S.E. and h.p.i., as in other caviines. The anteroposterior length of the molariforms increases posteriorly in the molariform series (P4/p4 are smaller than M1/m1, M1/m1 are smaller than M2/m2, and M2/m2 are smaller than M3/m3) as in N. lozanoi ; this pattern is shared with the lower molariforms of Microcavia , Galea , and Palaeocavia impar .

Upper teeth: The anterior lobes have a round posterolabial extension that reaches the anterior margin of the posterior lobe (Fig. 5C–E), as in N. lozanoi , but different from M. australis and Dolicavia , in which the projection is posteriorly pointed. The anteroposterior length of the anterior lobes is smaller than that of the posterior lobes ( Table 2). The M3 is the largest molariform and has an elongated posterior projection, with an orientation similar to that of Dolicavia .

Lower teeth: The h.p.i. of the molariforms is wider than that of N. lozanoi , “ N. depressidens ”,and Neocavia sp. ; it has the same depth as in N. lozanoi ( Table 3). The anterior lobe of p4 has an incipient anterior projection (Fig. 5G–I), differing from N. lozanoi , which has a well-developed projection when it is present. In addition, it seems that the hypoflexid of p4 is more obliquely oriented, posterolaterally, than in the latter species. A unique characteristic of N. pampeana sp. nov. is that the anteroposterior length of the anterior lobe of m2 is larger than that of the posterior lobe; differing from N. lozanoi , in which both lobes are similar in length. The difference between the surfaces of the anterior and posterior lobe in m1–m 2 in N. pampeana sp. nov. is smaller than in N. lozanoi and Neocavia sp. ( Fig. 6B), but we cannot corroborate this condition in “ N. depressidens ”.

Ontogeny: Molariforms of caviines have a simplified occlusal surface, so in the absence of deciduous teeth or other attributes that provide clues for the ontogenetic stage, such as exposed areas of trabecular bone (see Montalvo 2004), it is difficult to estimate the age of the individuals.

The sample from Caleufú includes two juvenile individuals. GHUNLPam 19581 is a mandible fragment with immature bone, a fragment of incisive, and p4. The p4 is slightly conical and the h.p.i. is anteroposteriorly wider than in adult individuals. GHUNLPam 21286 includes maxilla and palatine fragments with complete molariform series; a fragment of right deciduous premolar (DP4), and emergent P4 (Figs. 5E, 7C, 8A). The DP4 is bilobed with cement in the hypoflexus, and the enamel is continuous around the entire crown but is interrupted on the labial side, except in H.S.E., as in the DP4 of juvenile M. australis ( Fig. 8B ). These molariforms probably developed roots, as in “eocardiids” (e.g., Luantus , Eocardia ; Kraglievich 1930; Pérez 2010a, b). The lobes of DP4 are smaller and anteroposteriorly more compressed than molars, as in the DP4 of

LAP p4 (mm) C PLS–ALS (mm) B APB

1.50 1.70 1.90 2.10 2.30 2.50 2.70 2.90 3.10 3.30 MACN-Pv 8400 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 M. M N.. australis lozanoi 15.0 20.0 25.0

chapalmalensis

MACN-Pv 8415 D. minuscula

MD-FM-17-01 G.

GHUNLPam musteloides G.

19559 spixii

GHUNLPam C. O.

aperea

chapadmalense

GHUNLPam

19582 19622 D. patagonum

GHUNLPam 21056 H.

D K.. salinicola rupestris

GHUNLPam hydrocharis

21330

1.10 1.30 1.50 1.70 1.90 2.10 2.30 LAP m1 (mm)

juvenile M. australis . The base of the DP4 is smaller than the occlusal surface. On the labial side, the partially broken anterior lobe of DP4 has a subtle square projection. The

H.S.E. is very shallow and is located a little anteriorly in the posterior lobe, respect to adult individuals. The emerging P4 is cone-shaped, a common condition in erupting euhypsodont cheek teeth, with their apices conspicuously smaller than the bases ( Vucetich et al. 2005). GHUNLPam 21286 has a shallower H.S.E., and the posterior projection of M3 is shorter than in adult individuals. Others characteristics e.g., wide margin of incisive foramina) are similar to the conditions of adult individuals.

In addition, GHUNLPam 21288 is a right dentary fragment with p4–m3 (Figs. 5I, 7D). The p4 is smaller than molars, and its anterior lobe has a rounded outline and a poorly developed apex. The posterior lobe is heart-shaped but the h.p.i. is incipiently developed. Due to the absence of dp4 (confirmed with X-rays analysis) and the presence of immature bone, this specimen would correspond to a subadult individual.

Most of the caviids are born with all cheek teeth already erupted, even with occlusal wear ( Kraglievich 1930; Vucetich et al. 2005). Until now, Microcavia was the only identified Caviinae with postnatal dental replacement ( Kraglievich 1930; Cabrera 1953; Contreras 1964), but the specimens here reported confirm that Neocavia would have a later replacement of premolars.

Remarks.— Montalvo and Rocha (2003) described several fossil remains recorded in the Cerro Azul Formation (Caleufú) and they assigned the sample to Neocavia cf. N. lozanoi . In the present revision, we reassign some of this material (see above) to N. pampeana sp. nov. Among the other specimens of the sample, we have identified? Microcavia (GHUNLPam 21346), Palaeocavia sp. (GHUNLPam 19568), and two indeterminate caviids (GHUNLPam 21355 and 21356).

GHUNLPam 21346 consists in a maxillary fragment with left and right P4–M3. The molariforms are similar in morphology to those of Microcavia and the posterolabial extension of the anterior lobe is posteriorly more pointed than in Neocavia ; however, the palatine is located approximately at the same level to the maxilla, differing from Microcavia which has a well-marked unevennes. GHUNLPam 19568 is a maxillary fragment with left and right P4–M2. The molariforms are similar to those of Palaeocavia , the shape of the anterior lobe is more lanceolate than in Neocavia , and it has no a posterolabial extension of anterior lobes (synapomorphy of Neocavia ); the hypoflexus is similar to that of Palaeocavia , anteroposteriorly wider than in Neocavia , and the labial apex of hypoflexus has a bevel contour similar to that of Palaeocavia . The specimens GHUNLPam 21355 and 21356 consist in maxillary fragments with M3 and they have not enough characters to be identified at generic or specific level.

Stratigraphic and geographic range.—Late Miocene–early Pliocene, Cerro Azul Formation, Caleufú locality, La Pampa Province, Argentina.

Figures

Fig. 1. A. Location map indicating the geographic distribution of Neocavia localities in Argentina. B. Encalilla and Andalhuala localities, Santa María Valley, Tucumán, and Catamarca provinces, respectively. C. Caleufú locality, La Pampa Province. D. Farola Monte Hermoso locality, Buenos Aires Province.

Fig.7. Caviid rodent Neocavia pampeana sp. nov.from CerroAzul Formation,late Miocene–early Pliocene, Caleufú locality,La Pampa Province,Argentina. A. GHUNLPam 21351, fragment of palate. B. GHUNLPam 21854, fragment of palate. C. GHUNLPam 21286, fragment of palate. D. GHUNLPam 21288 reflected), fragment of mandible. E. GHUNLPam 19622 (reflected), fragment of mandible. F. GHUNLPam 19559, holotype (reflected), fragment of mandible. In ventral (A1, B2, C), lateral (A2, B1), labial (D1, E1, F1), lingual (D2, E2, F2), and occlusal (D3, E3, F3) views. Abbreviation: nMpi, notch for the insertion of the tendon of the masseter medialis pars infraorbitalis muscle.

Fig. 2. Measurements used in the comparative analysis A. Skull of Microcavia australis, Recent. B. Third left upper molar (M3) C. First right lower premolar (p4; anterior to left). Abbreviations: Cranial measurements: APB, anteromedial-posterorlateral length of tympanic bullae; APL, length of premaxillary-maxillary suture to anterior border of foramen magnum; BO, width of the anterior half of the basioccipital; BP, anteroposterior length of the posterior part of the diastema; IF, length of incisive foramina; MXL, length from the premaxillary-maxillary suture to the posterior portion of the M3 projection; UDL, upper diastema length from alveolar posterior margin of incisor to alveolar anterior margin of P4; WBc, width of basicranial. Dental measurements: LAP, anteroposterior length of molariforms; LLA, anteroposterior length of anterior lobe of molariforms; LPL, anteroposterior length of posterior lobe of molariforms; PLE, posterolabial extension of anterior lobes; WAL, mediolateral length of anterior lobe of molariforms; WPL, mediolateral length of posterior lobe of molariforms.

Fig. 3. Caviid rodent Neocavia lozanoi Kraglievich, 1932 from the late Miocene–early Pliocene of northwest Argentina, Andalhuala Formation, “Araucanense”: Andalhuala locality, Santa María Valley, Catamarca Province, Argentina (A, C) and Encalilla locality, Santa María Valley, Tucumán Province (B). A. MACN-Pv 8400, skull with left P4–M3 and right P4–M2 (A1–A4), right mandibular fragment with incisor p4–m2, and m3 broken (A5–A7). B. PVL 7057, maxillary fragment with left and right P4–M2. C. MACN-Pv 8415, left mandibular fragment with p4–m2. In dorsal (A1), ventral (A2, B1), lateral (A3, A4, B2), labial (A5, C1), lingual (A6, C2), and occlusal (A7, C3) views. Abbreviations: nMpi, notch for the insertion of the tendon of the masseter medialis pars infraorbitalis muscle. Scale bars 5 mm.

Fig. 8. Juvenile caviid rodents; molariforms (DP4 and P4) in occlusal views. A. Neocavia pampeana sp. nov. (GHUNLPam 21286) from Cerro Azul Formation, late Miocene–early Pliocene, Huayquerian Stage/Age, Calufú locality, La Pampa Province, Argentina. B. Microcavia australis Gervais and Ameghino, 1880 (MACN-Ma.34-12, reversed), Recent, from La Rioja Province. Photographs (A1, B1) and explanatory drawings (A2, B2). Scale bars 0.5 mm.