Octodontoidea rodents (Hystricognathi) are particularly useful for analysing evolution of diversity and derived biochronological patterns. Despite its significance, our knowledge of the systematics of octodontoids from the late Miocene–early Pliocene, a key time interval in the evolution of this group in South America, is still partial. Here, we analyse the taxonomic status and diversity of the late Miocene octodontoid Cercomys primitiva and related samples, a taxon known hitherto only by the holotype specimen. New findings associated with an extensive review of late Miocene rodents, has allowed us to recognise the occurrence of this and other related species in several localities of central and western Argentina, and in southcentral Bolivia. We discuss the invalidity of Cercomys, and propose the new genus Metacaremys, which includes the type species Metacaremys primitiva comb. nov and two new species, Metacaremys calfucalel sp. nov. and Metacaremys dimi sp. nov. Osteological, brain, and dental morphology shows that the new genus is not related to Brasilian Echimyidae, as previously considered, but to the southern family Octodontidae. Although the molar morphology within this genus is quite conservative, the comparison among samples shows variation in size. We discuss the plausible evolutionary pattern explaining this variation and the implied biochronological and biostratigraphical information. It is recognised as an anagenetic lineage in which an increase in size occurs from the oldest M. primitiva comb. nov. (lower late Miocene, c. 9.23 Ma) to the youngest M. dimi sp. nov. (Miocene–Pliocene boundary, c. 5.28 Ma). Metacaremys calfucalel is intermediate in size and age between the two latter. The polarity of this pattern of change is consistent with that shown by other partially synchronous independent lineages of octodontoids, thus providing new evidence for the biochronological-biostratigraphic scheme of the late Miocene–early Pliocene of southern South America.

Pinero_etal_2020_SUPPLEMENTAL_DATA_S1

SUPPLEMENTAL DATA S1. Referred material and occurrence of Metacaremys primitiva comb. nov., Metacaremys calfucalel sp. nov., and Metacaremys dimi sp. nov.

Pinero_etal_2020_SUPPLEMENTAL_FIGURES_S1–S3

FIGURE S1. Upper and lower teeth of Metacaremys primitiva comb. nov. A, GHUNLPam 5088, left maxillary fragment with DP4–M3, Laguna Chillhué; B, GHUNLPam 6924, left M1, Cerro La Bota; C, GHUNLPam 6926, left DP4, Cerro La Bota; D, GHUNLPam 5233, left M1 or M2, Laguna La Amarga; E, GHUNLPam 6927, right DP4 (reversed), Cerro La Bota; F, GHUNLPam 8081, left M1 or M2, Estancia Quiñi Malal; G, PVSJ-LT30, fragment of palate with left DP4–M1 and right DP4 and M2, Loma de las Tapias; H, CRILAR Pv 431, right dp4–m1 (reversed), El Degolladito Site 2; I, PVSJ-LT30, right m1–3 (reversed), Loma de Las Tapias; J, GHUNLPam 307, left m1–3, Laguna Chillhué; K, GHUNLPam 5234, left dp4–m2, Laguna Chillhué; L, GHUNLPam 2227, right m1–2 (reversed), Laguna Chillhué; M, MMH-CH 88-6-90, right dp4–m1 (reversed), Arroyo Chasicó; N, MD-CH-06-246, right dp4–m2 (reversed), Arroyo Chasicó; O, MMP 983-M, right m1–3 (reversed), Arroyo Chasicó; P, GHUNLPam 21987, left dp4, Cerro La Bota; Q, MLP 58-IX-3-24, left m1, Arroyo Chasicó; R, GHUNLPam 21986, left dp4, Cerro la Bota; S, GHUNLPam  5969, left m1 or m2, Cerro La Bota; T, GHUNLPam 6923, right m3 (reversed), Cerro La Bota; U, GHUNLPam 303, left m1–3, Laguna Chillhué; V, MLP 55-IV-28-3, right m1–2 (reversed), paratype of Chasichimys bonaerense, Arroyo Chasicó; W, MMH-CH 85-4-126, left m2–3, Arroyo Chasicó; X, PVSJ-LT11, right m1–3 (reversed), Loma de las Tapias; Y, MD-CH-06-251, left dp4–m2, Arroyo Chasicó. Scale bar represents 2 mm.

FIGURE S2. Upper and lower teeth of Metacaremys calfucalel sp. nov. A, GHUNLPam 14374, left M1, Quehué; B, GHUNLPam 14773, right DP4–M1 (reversed), Loventué; C, GHUNLPam 14127, right m1 (reversed), Loventué; D, GHUNLPam 19119, left m1, Quehué; E, GHUNLPam 8547, right m1–3 (reversed), Bajo Giuliani; F, GHUNLPam 14372, right m2–3 (reversed), Quehué; G, GHUNLPam 6314, left dp4–m2, Telén; H, GHUNLPam 8494, left m1–3, Telén: I, GHUNLPam 2338, left m1–2, Bajo Giuliani; J, GHUNLPam 22760, left dp4–m1, Quehué; K, GHUNLPam 6947, right dp4–m1 (reversed), Salinas Grandes de Hidalgo; L, GHUNLPam 27058, right dp4–m1 (reversed), Bajo Giuliani; M, GHUNLPam 8552, right m2–3 (reversed), Quehué. Scale bar represents 2 mm.

FIGURE S3. Plot of fitted model of APL dp4–m3 versus group (species). The middle lines show the 95% confidence limits for the means and the outer lines show the 95% prediction limits for new observations. Abbreviations: CHA, Chasicó; CHL, Laguna Chillhué; EDM, Estancia Don Mariano; GT, Guatraché; MHU, Muyu Huasi; SH, Salinas Grandes de Hidalgo; TL, Telén.

Pinero_etal_2020_SUPPLEMENTAL_TABLE_S1

TABLE S1. Dental measurements, in millimeters. Abbreviations: APL, antero-posterior length; AW, anterior width; Dm, depth of mandible below m1; PW, posterior.

Pinero_etal_2020_SUPPLEMENTAL_TABLE_S2

TABLE S2. Parameters of X-ray micro-computed tomography.

Morphosource_DOIs