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Reptilia, Archosauria, Crocodylomorpha, Crocodylia, Alligatoridae, Alligatorinae


ALLIGATOR MISSISSIPPIENSIS (DAUDIN, 1802)


Common Name: American alligator

Alternate Scientific Names: Crocodilus mississippiensis, Crocodilus luicus, Crocodilus cuvieri, Alligator luicus, Alligator helois, Champsa lucia, and possibly Alligator mefferdi and Alligator thomsoni

Source of Species Name: named for the Mississippi River region of North America, which is part of the modern range of the species.

Age Range: Fossils regarded as representing the living species Alligator mississippiensis range from the early Pliocene to the latest Pleistocene in Florida, or Hemphillian 4 through the end of the Rancholabrean land mammal ages; about 5 million to 11,000 years ago. Fossils of a species of alligator very close in morphology to Alligator mississippiensis are known from the middle and late Miocene (Clarendonian and early Hemphillian land mammal ages); about 12 to 6 million years ago. Some specialists refer such specimens to an extinct species, either Alligator thomsoni and/or Alligator mefferdi, both described from the Miocene of Nebraska. However, on this web page, the term “cf. Alligator mississippiensis” will be used for these Miocene fossils, as the differences with the living species do not appear sufficient to place them in a separate species. See below for further discussion.


Florida Fossil Occurrences:

Florida map with occurrences indicated

Figure 1. Map of Florida, with black circles indicating counties where fossils of Alligator mississippiensis have been found and grey circles where fossils of cf. Alligator mississippiensis have been found (the circles do not necessarily indicate a specific location within the county where the fossils were found, and some counties may have more than one different locality from which fossils of this species has been found).


Florida Fossil Sites with Alligator mississippiensis and cf. Alligator mississippiensis:

cf. Alligator mississippiensis (middle to late Miocene localities):

Alachua County—Haile 19A; Love Site; McGehee Farm Site; Tyner Farm
Hamilton County—Swift Creek Mine
Levy County—Mixson's Bone Bed
Marion County—Emathela; Moss Acres Racetrack Site; Withlacoochee River 4A
Polk County—Agricola Road Site, Hookers Prairie Mine; Stream Matrix Site, Nichols Mine

Alligator mississippiensis (Pliocene to late Pleistocene localities):

Alachua County—Arredondo 1; Arredondo 2; Haile 1A; Haile 7A; Haile 7C; Haile 7G; Haile 13A; Haile 13E; Haile 13F; Haile 15A; Haile 16B; Haile 20B; Haile 21A; Hornsby Springs; Hornsby Sink; Pareners Branch; Wall Company Pit
Brevard County—Melbourne; Melbourne 1A; Tucker Borrow Pit
Charlotte County—Copely Road Shell Pit; D&M Shell Pit; Florida Shell And Fill; Pelican Road Shell Pit; Port Charlotte Area; Punta Gorda
Citrus County—Bone Cave; Crystal River Power Plant; Inglis 1C
Columbia County—Ichetucknee River; Santa Fe River; Devil's Eye Spring
De Soto County—Peace River 3; Peace River 3A; De Soto Shell Pit 5
Dixie County—Suwannee River
Duval County—Jacksonville Beach; St. Johns River Dredge
Hardee County—Fort Green Mine; Harrison Ranch Site
Hendry County—Big Cypress Indian Reservation; La Belle Highway Pit; Tri-Britton Site
Highlands County—Brighton Canal
Hillsborough County—Leisey Shell Pit 1; Leisey Shell Pit 1A; Leisey Shell Pit 1B; Leisey Shell Pit 2; Leisey Shell Pit 3; Leisey Shell Pit 3A; Four Corners Mine
Indian River County—Luther Locality; Vero Canal Site; Winter Beach
Jefferson County—Aucilla River 1B; Aucilla River 1E; Wacissa River 1A; Wacissa River 2B
Lee County—Bedman Creek Site; Hickey Creek; Lehigh Acres Pit
Levy County—Devil's Den; Waccasassa River; Waccasassa River 6; Wekiva Springs; Williston 3A
Manatee County—Bradenton 51st Street; Fort Green Mine
Marion County—Cullins River Mine; Meffert Lime Company Mine; Oklawaha River 2; Orange Lake 2A; Rainbow River; Reddick 1A; Reddick 1B; Reddick 1C; Withlacoochee River 1A; Zuber
Nassau County—North Fernandina Beach
Okeechobee County—DRK-Davis Pit; Kissimmee 6
Orange County—Rock Springs
Palm Beach County—West Palm Beach
Pinellas County—Catalina Gardens; Millennium Park; Oldsmar 1; Seminole Field; St. Petersburg Times; Zeta Pond Site
Polk County—Achan Mine; Amalgamated Phosphate Company Mine; Chicora Mine; Fort Green Mine; Fort Meade Mine (Gardinier); Whidden Creek Site, Fort Meade Mine (Gardinier); Fish Locality, Fort Meade Mine (Mobil); Kingsford Mine; Nichols Mine (Mobil); Palmetto Mine; Micro Site, Palmetto Mine; Pleistocene Bog Site, Payne Creek Mine, TRO Quarry, Payne Creek Mine; Pool Branch Site, Peace River Mine
Putnam County—St. Johns Lock; Murphy Island
Sarasota County—C.C.E. Trailer Park; North Havana Road; Macasphalt Shell Pit 1A; Richardson Road Shell Pit 6A; Big Slough; Warm Mineral Springs
Seminole County—Wekiwa River 1
Saint Johns County—Wilson Quarry
Saint Lucie County—Dickerson Coquina Pit; Port St. Lucie
Sumter County—Coleman 2A
Suwannee County—Santa Fe River 13A; Denali Limerock Mine 1B; Branford 2A
Taylor County—Aucilla River 1A; Aucilla River 2; Aucilla River 2C; Aucilla River 2E; Aucilla River 3C; Aucilla River 3J; Fitch Site
Wakulla County—Wakulla Springs

Overall Geographic Range: The modern American alligator ranges throughout the southeastern United States, and most definitive fossil localities for this species also exist in the same region, from Texas to Florida (Preston, 1979; Brochu, 1999; Meylan et al., 2001). In warmer climatic periods such as the middle–late Miocene, the American alligator (or its close relatives/possible synonyms Alligator thomsoni and Alligator mefferdi) ranged farther north and west than today (Mook, 1923, 1946).

Comments: Fossils of the American alligator are found throughout much of Florida (Fig. 1). Not surprisingly, given the species’ preferred habitats today, swamps, lakes, and rivers, its fossils are most common at sites formed in fresh-water habitats and are typically found together with species having similar ecologic preferences, such as aquatic turtles, wading birds and ducks, and frogs. Alligators will move across land from one body of water to another, so their fossils do end up in fossil deposits not associated with water, such as dry sinkholes and caves, but typically not in large numbers. Alligators also are not very salt tolerant, especially compared to crocodiles, so are rare or absent in nearshore marine deposits. The most common fossils found are isolated teeth and osteoderms (bony dermal elements found on the backs of crocodylians and used for thermoregulation and protection) (Fig. 2). Alligators are both homodont (most teeth are identical in shape and structure) and polyphyodont (meaning they constantly replace lost teeth, unlike diphyodont mammals which are typically limited to only two sets of teeth throughout their lifespan) and so they can easily produce hundreds or thousands of teeth during their lifespan which commonly become fossilized. For more discussion and comparisons of fossil crocodylian teeth and osteoderms from Florida, see species accounts of Alligator olseni and Thecochampsa americana.

 tooth and osteoderm

Figure 2. Typical fossils of Alligator mississippiensis; an osteoderm in dorsal (A), ventral (B), and lateral (C) views, and an isolated tooth in side view (D). Osteoderm is UF 56386, North Havana Road Site; tooth is UF 56705, C.C.E. Trailer Park Site. Both are late Pleistocene localities in Sarasota County, Florida.

Complete skulls are very important for species diagnoses within the genus Alligator, and as such are highly valued fossil finds no matter their age or origin. But these are relatively rare, as the individual bones tend to separate easily from each other after death, so isolated skull bones are found more commonly (Fig. 3). The mandible consists of separate bones, the long, tooth-bearing dentary (Fig. 4), the splenial which inserts along the ventral margin of the medial side of the dentary, and three found at the posterior end of the mandible, the angular, surangular, and articular.

maxilla of Alligator mississippiensis

Figure 3. UF 56384, left maxilla of Alligator mississippiensis in dorsal (A), ventral or occlusal (B), and lateral (C) views. Specimen is from the North Havana Road Site, Sarasota County, Florida; late Pleistocene. The outer surface of many cranial bones of Alligator mississippiensis have irregularly shaped pits; these can be seen in A. Although it is clear from B and C that the teeth varying in size, they all are similar, but those in the posterior of the jaw tend to be blunter and used more for crushing, while those in the front of the jaw are sharper, for grasping and holding onto prey.



lower jaw of Alligator mississippiensis

Figure 4. UF 80669, left dentary of Alligator mississippiensis in lateral (A), dorsal or occlusal (B), and medial (C) views. Specimen is from Leisey Shell Pit 1A, Hillsborough County, Florida; early Pleistocene.

Taxonomic issues plague the systematics of the genus Alligator, largely due to the high degree of similarity between currently recognized fossil species and a wide degree of intraspecific morphological variation in both extant and extinct species. The diagram in Figure 5 shows the results of one recent analysis on the evolutionary relationships of fossil and modern species in the family Alligatoridae. In this analysis, the early Miocene Alligator olseni of Florida falls outside a group that includes the two living species, the Chinese alligator, Alligator sinensis, and the American alligator. The middle Miocene species Alligator mefferdi came out as the closest relative of Alligator mississippiensis. Alligator mefferdi has a shorter, blunter snout and a somewhat greater degree of cranial ornamentation around the orbits than most modern and Pleistocene Alligator mississippiensis. However, the high degree of intraspecific morphological variation in American alligators for these features could account for the morphology seen in the middle Miocene species, thus making to a junior synonym of Alligator mississippiensis (Malone, 1979). Others favor recognizing Alligator mefferdi as a valid species distinct from Alligator mississippiensis based on these characters of the skull (Brochu, 1999; Snyder, 2007).


Alligator phylogeny

Figure 5. Hypothesis of the evolutionary relationships of selected species of Alligator, after Hastings et al. (2013).


In this account, a conservative approach has been taken towards classification of fossil specimens of Alligator. There are few Barstovian (early middle Miocene) records of Alligator in Florida, and the known fossils are not diagnostic at the species level. Snyder (2007) described relatively complete specimens of Alligator from the late Miocene (Hemphillian) Moss Acres Racetrack locality in Marion County, Florida, but could not make a definitive assignment to Alligator mefferdi due to a lack of the preserved feature(s). No Alligator specimens from any Florida locality have thus far been shown to exhibit the diagnostic features of Alligator mefferdi. Assignment of middle and late Miocene Florida specimens of Alligator to the extinct species is discouraged until the requisite diagnostic characteristics are observed. An equally valid argument can also be made that they represent early members of Alligator mississippiensis

In an unpublished thesis, Stout (2009) suggested that a new species be named for Alligator fossils from the early Pleistocene (Blancan) Haile 7C and 7G sites in Alachua County, Florida. But he never fully described the specimens or suggested diagnostic characters in sufficient detail. Observation and analyses of the same specimens and others from Haile 7C and 7G do not support his conclusion that a new species is apparent. Instead, the relatively complete Haile 7C and 7G specimens provide a more definitive lower chronologic boundary for the occurrence of Alligator mississippiensis in the Florida fossil record (extending it to the late Blancan, roughly 2 million years ago). These Haile 7C and 7G alligators appear to have attained quite large sizes at maturity, and Alligator mississippiensis may have indeed reached lengths of up to seven meters during the Pleistocene, several meters longer than the largest modern American alligators (Meylan et al. 2001). The Haile 7C and 7G Alligator mississippiensis sample is also unique in that it includes individuals that were likely hatchlings at the time of death, and they exhibit a few characteristics allying them with modern alligators. The Haile 7C and 7G fossils provide a nearly unprecedented glimpse into a thriving American alligator population living nearly 2 million years ago in a large sinkhole lake (Morgan and Hulbert 1995; Hulbert et al., 2006; Hulbert, 2010).

American alligators are important to modern ecosystems, and act as keystone predators that are essential for keeping prey populations in check. In addition to their ecological importance, American alligators are also major components of certain economies that exploit them for their meat and skin. They are also crucial study subjects in a multitude of different scientific disciplines ranging from dentistry to immunology, and are utilized in various research projects. The significance of these reptiles across such a wide variety of topics is almost unmatched, and warrants their protection and conservation. American alligators have recovered from once being endangered, and their populations have exploded in certain areas of the Southeastern United States. This iconic reptile is also the beloved mascot for the University of Florida, and occupies a unique cultural niche in the fabric of Floridian society.

Alligator mississippiensis is one of the most widely-studied and well-known reptiles in the world, and yet it still offers a diverse array of research avenues for new scientists. The American alligator is an incredibly adaptable crocodylian, has lived for millions of years with little morphologic change, and has survived numerous instances of climate and sea level change relatively unaffected.


Scientific Publications and Other References Cited:

Brochu, C. A. 1999. Phylogenetics, taxonomy, and historical biogeography of Alligatoroidea. Society of Vertebrate Paleontology Memoir 6:9-100. http://www.jstor.org/stable/10.2307/3889340

Brochu, C. A. 2004. Alligatorine phylogeny and the status of Allognathosuchus Mook, 1921. Journal of Vertebrate Paleontology 24(4):857-873. http://www.jstor.org/stable/10.2307/4524781

Hastings, A. K., J. I. Bloch, C. A. Jaramillo, A. F. Rincon, and B. J. MacFadden. 2013. Systematics and biogeography of crocodylians from the Miocene of Panama. Journal of Vertebrate Paleontology 33(2):239-263. http://dx.doi.org/10.1080/02724634.2012.713814

Hulbert Jr., R. C. 2010. A new early Pleistocene tapir (Mammalia: Perissodactyla) from Florida, with a review of Blancan tapirs from the state. Bulletin of the Florida Museum of Natural History 49(3):67-126. http://www.flmnh.ufl.edu/bulletin/vol49no3/vol49no3lores.pdf

Hulbert Jr., R. C., J. I. Bloch, and A. R. Poyer. 2006. Exceptional preservation of vertebrates from Haile 7G, a new late Pliocene site from Florida. Journal of Vertebrate Paleontology 26(3, supplement):78A-79A.

Malone, B. 1979. The systematics, phylogeny and paleobiology of the genus Alligator. Ph.D. dissertation, City University of New York. http://search.proquest.com/docview/302917454

Meylan, P. A., W. A. Auffenberg, and R. C. Hulbert, Jr. 2001. Reptilia 2: Lizards, Snakes, and Crocodilians. Pp. 137-151 in R. C. Hulbert (ed.), The Fossil Vertebrates of Florida. University Press of Florida, Gainesville.

Mook, C. C. 1923. A new species of Alligator from the Snake Creek beds. American Museum Novitates 73:1-13. http://digitallibrary.amnh.org/dspace/handle/2246/4668

Mook, C. C. 1946. A new Pliocene Alligator from Nebraska. American Museum Novitates 1311:1-12. http://digitallibrary.amnh.org/dspace/handle/2246/2307

Morgan, G. S., and R. C. Hulbert, Jr. 1995. Overview of the geology and vertebrate biochronology of the Leisey Shell Pit local fauna, Hillsborough County, Florida. Bulletin of the Florida Museum of Natural History 37:1-92. http://ufdcweb1.uflib.ufl.edu/UF00095791/00001

Snyder, D. 2007. Morphology and systematics of two Miocene alligators from Florida, with a discussion of Alligator biogeography. Journal of Paleontology 81(5):917-928. http://www.jstor.org/stable/10.2307/4498848

Stout, B. 2009. Cranial morphology and systematics of late Pliocene Alligator from Florida, with notes on Alligator evolution and distribution. M.S. Thesis, East Tennessee State University.


Original Author(s): Evan T. Whiting

Original Completion Date: September 8, 2013

Editor(s) Name(s): Richard C. Hulbert Jr.

Last Up-dated On: October 9, 2013

This material is based upon work supported by the National Science Foundation under Grant Number CSBR 1203222, Jonathan Bloch, Principal Investigator. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Copyright © 2013 by Florida Museum of Natural History, University of Florida