Oldest skeleton of a fossil flying squirrel casts new light on the phylogeny of the group

Accession numbers for all the species considered in total evince analysis and/or node dating analysis. We retrieved the four genes more frequently used in previous phylogenetic studies of the Sciuridae: 12S, 16S, cytochrome b, and irbp (Mercer and Roth, 2003).

See Appendix 2 for character description and coding.

Cheek tooth measurements of Miopetaurista neogrivensis from localities ACM/C5-D1, ACM/C8-Af, ACM/C6-A5, as well as sector ACM/C8-B (material is listed in Tables 1–2). Measurement method follows Casanovas-Vilar et al., 2015: L, mesiodistal length; W, buccolingual width; w1, buccolingual width measured at the mesial margin of the tooth (only for m1 and m2); w2, buccolingual width measured at the distal margin of the tooth (only for m1 and m2). Estimated measurements (due to minor damage to the cheek teeth) are within parentheses. Abbreviations for dental elements follow Smith and Dodson, 2003. IPS, acronym for the collections of the Institut Català de Paleontologia Miquel Crusafont. All measurements are in mm.

Cranial measurements for Miopetaurista neogrivensis and some extant flying squirrels. The specimens of the extant species are housed in the Naturalis Biodiversity Center (Leiden, the Netherlands), except for Glaucomys sabrinus, which comes from the collections of the Institut Català de Paleontologia Miquel Crusafont. Cranial measurements for the virtually reconstructed skull of M. neogrivensis are also included. Estimated measurements are in parentheses. Acronyms and definitions of the measurements follow Bertrand et al., 2016 and Nicolas et al., 2008: BNAS, maximum breadth of the nasals; BRCA, maximum breadth of the braincase; BULL, maximum length of the auditory bulla; CTL, length of the upper cheek tooth row; DIA, length of the diastema (from the alveolus of the incisor to the alveolus of the P3); HEBA, henselion–basion length; HEPA, henselion–palation length; IF, length of the incisive foramen; INTE, smallest interorbital breadth; LNAS, maximum length of the nasals; PALA, smallest palatal breadth; RB, maximum rostrum breadth; RH, mediosagittal projection of rostrum height at the anterior border of the M1; SL, maximum length of the skull. The virtual reconstruction of the cranium of M. neogrivensis is shown in Figure 6, for the original crania see Figure 6—figure supplements 1–2. All measurements are in mm.

Mandibular material of Miopetaurista neogrivensis is listed in Tables 1–2. The specimens of the extant species are housed in the Naturalis Biodiversity Center (Leiden, the Netherlands), except for Glaucomys sabrinus which comes from the collections of the Institut Català de Paleontologia Miquel Crusafont. Estimated measurements are in parentheses. Acronyms and definitions of the measurements are as follows: DIA1, length of the diastema measured from the alveolus of the incisor to the anterior alveolus of the p4; DIA2, length of the diastema from the anterior alveolus of the p4 to the projection of the incisor; DDIA, depth of the mandibular corpus at the lowermost point of the diastema; DM1, depth of the mandibular corpus below the anterior border of the m1; DM3, depth of the mandibular corpus below the anterior border of the m3; LAJ, length from the most ventral point of the angular apophysis to the anterior margin of the articular condyle; LCJ, length from the tip of the coronoid apophysis to the anterior margin of the articular condyle; LTL, length of the lower cheek tooth row; ML, maximum length of the mandible; RH, maximum height of the mandibular ramus. The mandibular remains of M. neogrivensis are shown in Figure 3. All measurements are in mm.

Postcranial measurements for Miopetaurista neogrivensis (for material list see Table 1) and some extant squirrels. The specimens of the extant species are housed in the Naturalis Biodiversity Center (Leiden, the Netherlands), except for Glaucomys sabrinus and Sciurus carolinensis which come from the collections of the Institut Català de Paleontologia Miquel Crusafont. Only right elements were measured. Acronyms and definitions of the measurements are based in Samuels and Van Valkenburgh, 2008: BI, brachial index (RL/HL), indicating the proportions of the distal and proximal elements of the forelimb; CI, crural index (TL/FL), indicating the proportions of the distal and proximal elements of the forelimb; FEB, epicondylar mediolateral breadth of the distal femur; FGT, mediolateral breadth of the greater trochanter of the femur; FL, femoral length from the tip of the femoral head to the tip of the medial epicondyle; FMD, greater diameter of the femur at midshaft; FRI, femoral robusticidty index (FMD/FL); HEB, epicondylar mediolateral breadth of the distal humerus; HL, humeral length from the tip of the head to the tip of the most distal point of the trochlea; HMD greater diameter of the humerus at midshaft; HRI, humeral robusticity index (HMD/HL); IM, intermembral index [(HL +RL)/(FL +TL)], indicating the length of the forelimb relative to the hindlimb; TL, tibial length from the medial condyle to the tip of the medial malleolus; TMD, greater diameter of the tibia at midshaft; TRI, tibial robusticity index (TMD/TL); RL, radius lenght. All measurements are in mm. Specimens shown in Figure 5 are: Miopetaurista neogrivensis IPS56468; Petaurista petaurista RMNH.MAM.130; Hylopetes sagitta 056.054.b; Callosciurus prevostii 056.099 .j; Urocitellus paryii 065.238a; Xerus erythropus 26483.