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FIGURE 1. A: Map showing late Eocene - early Miocene fossil localities of Alligator in North America, with Florida enlarged. B: Geologic timescale showing occurrences of fossil Alligator in different regions.





FIGURE 2. Right premaxilla of Alligator from the late Oligocene Brooksville 2 site in northern Florida (UF 422816). Element shown in dorsal (A, D), lateral (B, E), and ventral (C, F) views, with photos and interpretive sketches. Abbreviations: d4 o p, occlusal pit for the fourth dentary tooth; e n, external naris; i f, incisive foramen; pm 3-5, premaxillary alveoli 3-5; pmx-mx, premaxillary-maxillary; pmx-n, premaxillary-nasal; pmx-pmx, premaxillary-premaxillary.





FIGURE 3. Alligator fossils from the late Oligocene Brooksville 2 site in northern Florida. A, B: Dorsal view of parietal (UF 333984). C, D: Cranial fragment (UF 425424) in dorsal (C) and ventral (D) views; position is uncertain. E: Alligatorid tooth from posterior dentition (UF 422818). F: Alligatorid tooth from middle dentition (UF 422819). G: Alligatorid tooth from middle dentition (UF 422820). Fragment of right dentary (UF 425402) in lateral (H) and medial (I) views. Right articular (UF 422817) in dorsal (J), lateral (K), and medial (L) views. Dorsal osteoderm (UF 424647) in dorsal view (M) and left lateral view (N). Anterior portion of osteoderm (UF 425398) in dorsal view (O). Partial osteoderm (UF 422827) in dorsal view (P). Osteoderm (UF 425395) in dorsal view (Q). Neural arch of a dorsal vertebra (UF 424653) in posterior view (R). Ungual (UF 424655) in lateral view (S). Ungual (UF 425405) in lateral view (T). U, V: Caudal vertebra in left lateral view (UF 425435). Abbreviations: f-p, frontoparietal; i s, imbricating shelf; m k, median keel; nc, neurocentral; po-p, postorbital-parietal; sq-p, squamosal-parietal; stf, supratemporal fenestra.





FIGURE 4. Alligatorid fossils from the Live Oak fossil site. A: Isolated tooth, likely mid-rostral position (UF 424640) in lingual view. B: Isolated tooth, likely anterior position (UF 424639) in lingual view. C: Caudal vertebra exhibiting a fully fused neurocentral suture (UF 424637) in left lateral view. D: Caudal vertebra exhibiting a fully fused neurocentral suture (UF 424638) in left lateral view. E: Osteoderm (UF 424633) in dorsal view. F: Osteoderm (UF 424635) in dorsal view.





FIGURE 5. Isolated osteoderm fragment attributed to Alligatoridae from the I-75 fossil site (UF 16729) in dorsal view.





FIGURE 6. X-Y scatter plot of premaxillary-maxillary suture lengths compared to dorsal skull length of extant Alligator (n = 22). Linear regression is best-fit line (R2 = 0.9917).





FIGURE 7. Box and whisker plots of dorsal skull length of published fossil Alligator specimens and extant Alligator mississippiensis (this study). For data, see Table 3. Time shown in millions of years ago (MYA). UF 422816, an isolated right premaxilla, was estimated following methods outlined in the main document. Most notable is that the estimated dorsal skull length for UF 422816 is small, similar to ancestral forms such as Allognathosuchus, Procaimanoidea, and Wannaganosuchus. Global temperature curve from Zachos et al. (2001).

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