Fig 1.
Geographic and stratigraphic context of the localities in San Miguel de Allende Basin.
Location of San Miguel de Allende Basin in central Mexico and stratigraphy columns of the localities GTO 6 “Arrastracaballos” and GTO 12 “La Pantera”.
Fig 2.
Maxillaries and upper teeth of Sigmodon minor from the early Blancan of San Miguel de Allende Basin, Mexico.
a-c) MPGJ 2670, left maxillary with M1 and M2, occlusal (a), lingual (b) and labial (c) views; d-f) MPGJ 2692 right maxillary with M1 and M2; occlusal (d), lingual (e) and labial (f) views; g-i) MPGJ 2674 left maxillary with M1 and M2, occlusal (g), lingual (h), and labial (i) views; j, k) MPGJ 2667 left maxillary with M2 and M3, occlusal (j) and lingual (k) views; l, m) MPGJ 2653, right maxillary with M1-M3, occlusal (l) and lingual (m); n, o) MPGJ 2672, right maxillary with M1 and M2, occlusal (n) and labial (o) views; p, q) MPGJ 2675, left maxillary with M1 and M2, occlusal (p) and lingual (q) views; r) MPGJ 2689, right maxillary with M1; s) MPGJ-1908, left maxillary with M1, occlusal view; t, u) MPGJ 2716, left upper M1, occlusal (t) and labial (u) views. Anatomical abbreviations: apm, alveolar process of maxillary; ar, accessory root; M1, first upper molar; M2, second upper molar; M3 third upper molar; if, incisive foramen; zpm, zygomatic plate of maxillary. Scale bar is 1 mm.
Fig 3.
Lower jaws and lower teeth of Sigmodon minor from the early Blancan of San Miguel de Allende Basin, Mexico.
a-c) MPGJ 6007, left lower jaw with m1 and m2, occlusal (a), labial (b), and lingual (c) views; d-f) MPGJ 2650, left lower jaw with m1-m3, occlusal (d), labial (e) and lingual (f) views; g-i) MPGJ 2673 left lower jaw with m1-m3, occlusal view (g), labial (h) and lingual (i) views; j-l) MPGJ 2668, right lower jaw with i1, m2 and m3, j) occlusal view, k) labial view, l) lingual view; m-o) MPGJ 2669, right lower jaw with m1-m3, m) occlusal view, n) labial view, o) lingual view; p) MPGJ 1907, right lower m1; q-r) MPGJ 2736, right lower m1, p) occlusal view, q) labial view;. Anatomical abbreviations: alf, alveolar foramen; cap, capsular process of the lower incisor alveolus; cor, coronoid process; con, condyloid process; m1, first lower molar; m2, second lower molar; m3, third lower molar; mf, mental foramen; mpm, medioventral process of mandibular ramus; sn, sigmoid notch. Scale bar is 1 mm.
Fig 4.
Left lower jaw of Sigmodon minor from San Miguel de Allende Basin (MPGJ 2681).
a) stereo photos in occlusal view; b) labial view. The dashed line shows the ridges of the masseteric crest. Scale bar is 1 mm.
Table 1.
Dental measurements (in mm) of Sigmodon minor from the early Blancan of San Miguel de Allende Basin, central Mexico. Abbreviations: M1-M3) upper molars; m1-m3) lower molars; N, number of specimens.
Fig 5.
Map of distribution and stratigraphic record of Sigmodon minor in North America.
A, map of distribution of S. minor that includes the previous records obtained from the Paleobiology Database (Paleodbd.org, revision January 6 of 2025, see S2 Table) in grey and the new records from SMA basin in blue. B, chronologic ranges of S. minor in the principal localities of North America. The columns are ordered in direction east-west, the grey color are previous records and in blue the new records in this study. Code of the numbers refer the following formations, basins and localities: 1, Palm Spring Formation; 2 San Timoteo Formation; 3, Verde Formation; 4, St. David Formation; 5, Gila Conglomerate; 6, Blanco Formation; 7, Beck Ranch Fauna; 8, GTO 6 “Arrastracaballos”; 9, GTO 12 “La Pantera”; 10, GTO 19 “Pecos”; 11, Meade Basin; 12, White Rock Fauna; 13, Pinecrest Beds. Abbreviations: Hh) Hemphillian; Irving) Irvingtonian; Ma) millions of years before the present; NALMA) North American Land Mammal Ages;?) doubts in the record.
Fig 6.
Body mass estimation in cotton rats from Meade Basin, Kansas and San Miguel de Allende Basin, central Mexico.
The values and graph of Meaden Basin was taken from Martin [15] and was modified to include the records in central Mexico. Abbreviations: GPTS) Geomagnetic Polarity Time Scale; NALMA) North American Land Mammal Ages; Ma) millions of years; W est) body mass estimated.