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TABLE 1. Measurements of the premaxilla UF 422816 from the Brooksville 2 fossil site. All measurements given in mm. Note: Measurements of the 3rd premaxillary alveolus are not provided here because it is incomplete.

4th Premaxillary Alveolus Length 4.28
  Width 3.92
5th Premaxillary Alveolus Length 2.78
  Width 2.63
Premaxillary-Maxillary Suture Length 19.74
Premaxillary-Premaxillary Suture Length 10.91
Premaxillary-Nasal Suture Length 12.05


TABLE 2. Length measurements of the premaxillary-maxillary suture in Alligator. When possible, these were measured on both the left (L) and right (R) sides. In these cases, the value is an average of those two measurements. All A. mississippiensis specimens were from wild populations. Institutional abbreviations: ETMNH-Z, East Tennessee State University Museum of Natural History - Zoology Collection; UF, Vertebrate Paleontology Collection at the University of Florida, Florida Museum of Natural History.

Taxon Catalog Number Premax-Max
Suture Length (mm)
Side Dorsal Skull Length
A. mississippiensis ETMNH-Z 7217 37.72 L 271.00
A. mississippiensis ETMNH-Z 507 22.71 R 177.46
A. mississippiensis ETMNH-Z 265 76.21 L/R 506.00
A. mississippiensis ETMNH-Z 7207 41.23 L/R 291.00
A. mississippiensis ETMNH-Z 3036 65.35 L/R 438.00
A. mississippiensis ETMNH-Z 7203 45.92 L/R 315.00
A. mississippiensis ETMNH-Z 6920 53.85 L/R 390.00
A. mississippiensis ETMNH-Z 7208 63.50 L/R 420.00
A. mississippiensis ETMNH-Z 7205 54.11 L/R 375.00
A. mississippiensis ETMNH-Z 5025 22.59 L/R 181.00
A. mississippiensis ETMNH-Z 2957 51.53 L/R 362.00
A. mississippiensis ETMNH-Z 509 39.51 L/R 286.00
A. mississippiensis ETMNH-Z 3024 45.89 L 328.00
A. mississippiensis ETMNH-Z 3366 48.28 L/R 357.00
A. mississippiensis ETMNH-Z 487 38.88 L/R 285.00
A. mississippiensis ETMNH-Z 17916 19.81 L/R 163.00
A. mississippiensis ETMNH-Z 5289 21.98 L/R 172.00
A. mississippiensis ETMNH-Z 3371 38.93 L/R 296.00
A. mississippiensis ETMNH-Z 10937 18.27 L/R 149.00
A. mississippiensis ETMNH-Z 7144 30.31 L/R 220.00
A. mississippiensis ETMNH-Z 266 75.31 L/R 480.00
Alligator sp. UF 422816 19.74 R See Table 3



TABLE 3. Dorsal skull lengths used as a proxy for body size in basal Alligator and its ancestors. Alligator mississippiensis with locations specified are from wild populations; specimens with “No Data” may be from either wild or captive populations. ETMNH-Z 10937 and 17916 are known captive specimens. Data are plotted in Figure 7. Institutional Abbreviations: AMNH, American Museum of Natural History, New York, New York, USA; CM, Carnegie Museum of Natural History, Pittsburg, Pennsylvania, USA; ETMNH-Z, East Tennessee State University Museum of Natural History - Zoology Collection, Johnson City, Tennessee, USA; FMNH, Field Museum of Natural History, Chicago, Illinois, USA; MCZ, Museum of Comparative Zoology, Vertebrate Paleontology Collection, Harvard University, Cambridge, Massachusetts, USA; SDSM, South Dakota School of Mines Museum of Natural History, Rapid City, South Dakota, USA; SMM P, Science Museum of Minnesota Paleontology Collection, Saint Paul, Minnesota, USA; UF, Vertebrate Paleontology Collection at the University of Florida, Florida Museum of Natural History, Gainesville, Florida, USA; USNM; United States National Museum of Natural History, Vertebrate Paleontology Collection, Washington, D.C., USA; YPM-PU, Yale Peabody Museum and Princeton University Vertebrate Paleontology Collection, New Haven, Connecticut, USA.

Taxon Geologic Age Skull Length (mm) Location Reference Specimen Number
Allognathosuchus wartheni early Eocene 106 Wyoming Miller-Camp, 2016 YPM-PU 8357
Allognathosuchus wartheni early Eocene 163 Wyoming Miller-Camp, 2016 YPM-PU 8449
Allognathosuchus wartheni early Eocene 136 Wyoming Miller-Camp, 2016 MCZ 4367
Allognathosuchus polyodon early Eocene 172 Wyoming Mook, 1961 AMNH 60491
Procaimanoidea kayi early Eocene 98 Wyoming Mook, 1941 CM 9600
Procaimanoidea utahensis middle Eocene 115 Utah Gilmore, 1946 USNM 159962
Wannaganosuchus brachymanis Paleocene 144 North Dakota This Study SMM P76.28.247
Alligator prenasalis early Oligocene 198 South Dakota This Study MCZ 1014
Alligator prenasalis Eocene/Oligocene 215 South Dakota This Study MCZ 1015
Alligator prenasalis Eocene/Oligocene 223 South Dakota Miller-Camp, 2016 YPM 13799
Alligator prenasalis Eocene/Oligocene 215 South Dakota Miller-Camp, 2016 YPM 14063
Alligator prenasalis late Eocene 278 South Dakota Miller-Camp, 2016 YPM 16273
Alligator prenasalis Eocene/Oligocene 218 South Dakota Miller-Camp, 2016 SDSM 243
Alligator olseni early Miocene 257 Florida This Study MCZ 1899
Alligator olseni early Miocene 223 Florida This Study MCZ 1887 [Type]
Alligator olseni early Miocene 299 Florida This Study MCZ 101578
Alligator mcgrewi middle Miocene 157 Nebraska Miller-Camp, 2016 AMNH 7905
Alligator mcgrewi middle Miocene 150 Nebraska Miller-Camp, 2016 FMNH P 26242
Alligator mississippiensis Modern 149 No data This Study ETMNH-Z 10937
Alligator mississippiensis Modern 163 No data This Study ETMNH-Z 17916
Alligator mississippiensis Modern 172 No data This Study ETMNH-Z 5289
Alligator mississippiensis Modern 177 No data This Study ETMNH-Z 507
Alligator mississippiensis Modern 181 Georgia This Study ETMNH-Z 5025
Alligator mississippiensis Modern 220 Georgia This Study ETMNH-Z 7144
Alligator mississippiensis Modern 271 Georgia This Study ETMNH-Z 7217
Alligator mississippiensis Modern 285 Georgia This Study ETMNH-Z 487
Alligator mississippiensis Modern 286 No data This Study ETMNH-Z 509
Alligator mississippiensis Modern 291 Georgia This Study ETMNH-Z 7207
Alligator mississippiensis Modern 296 Louisiana This Study ETMNH-Z 3371
Alligator mississippiensis Modern 315 Georgia This Study ETMNH-Z 7203
Alligator mississippiensis Modern 328 Georgia This Study ETMNH-Z 3024
Alligator mississippiensis Modern 357 Louisiana This Study ETMNH-Z 3366
Alligator mississippiensis Modern 362 South Carolina This Study ETMNH-Z 2957
Alligator mississippiensis Modern 375 Georgia This Study ETMNH-Z 7205
Alligator mississippiensis Modern 390 No data This Study ETMNH-Z 6920
Alligator mississippiensis Modern 420 Georgia This Study ETMNH-Z 7208
Alligator mississippiensis Modern 438 Georgia This Study ETMNH-Z 3036
Alligator mississippiensis Modern 480 Arkansas This Study ETMNH-Z 266
Alligator mississippiensis Modern 506 Arkansas This Study ETMNH-Z 265
Alligator sp. Oligocene 158.97 Florida This Study UF 422816

1Estimated from Mook (1961; figure 1) using the preserved craniomandibular joint to approximate distal end of skull.
2Determined from Plate 11, figure 3 of Gilmore, 1946.




TABLE 4. Statistical support for linear regressions of different premaxillary measurements against dorsal skull length for study set of extant Alligator mississippiensis specimens (n = 22; see Table 2). R2 values are calculated for a ‘best fit’ line. Due to its higher congruence with the data, we selected the premaxillary-maxillary suture length as the best proxy for estimating dorsal skull length.

Premaxillary Measurement R2 Value
Overall Width 0.9125
Length of premaxillary-maxillary suture 0.9917
Length of left-right premaxillary suture 0.7712
Width of 4th Premaxillary Alveolus 0.9221
Length of 4th Premaxillary Alveolus 0.9149
Length of 5th Premaxillary Alveolus 0.9101

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