Thecachampsa Temporal range:Miocene,15.97–5.3 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N
T. carolinense skeleton
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauria
Order:	Crocodilia
Superfamily:	Gavialoidea
Family:	Gavialidae
Subfamily:	Tomistominae
Genus:	†Thecachampsa Cope, 1867
Species
†T. sericodonCope, 1867 (type) †T. americana(Leidy, 1852) [originallyCrocodilus antiqua]) †T. antiqua(Leidy, 1851) [originallyCrocodilus antiquus]) †T. carolinense(Erickson and Sawyer, 1996 [originallyGavialosuchus carolinensis])

Thecachampsa is anextinctgenus ofgavialoidcrocodylian, traditionally regarded as a member of thesubfamilyTomistominae.^[2] Fossils have been found from the easternUnited States in deposits ofMiocene age. Those named in the 19th century were distinguished primarily by the shape of their teeth, and have since been combined withT. antiquus. More recently erected species were reassigned from other genera, although their assignment toThecachampsa has since been questioned.

Thecachampsa, like other "tomistomines" of the Oligocene and Miocene, was considerably larger than living crocodilians. Like livinggharials, it had a long, slender snout. The teeth were long and recurved. Unlike its living relatives,Thecachampsa was marine, inhabitingestuaries and shallow coastal waters. Other marine fossils such assea snail andbivalve shells,shark teeth, andbarnacles have been found alongside remains ofThecachampsa and similar taxa.^[3]

In 1852, American paleontologistJoseph Leidy describedCrocodylus antiquus from Miocene deposits in the Lee family's ancestral home in Virginia.^[4] The holotype was a tooth found in theCalvert Formation ofVirginia. Leidy also described additional material including several teeth andosteoderms, twovertebrae, a rib, and anungual phalanx or claw bone. The new genusThecachampsa was erected byEdward Drinker Cope in 1867, containing two species,T. sericodon andT. contusor, both also based on teeth, but no type species was designated.^[5] Cope (1882) designatedT. sericodon as theThecachampsa type species.^[6]T. sericodon was distinguished fromT. antiqua by its slender, curved teeth, each with a sharp edge near the base of the posterior margin (T. antiqua only possessed sharp edges along a small area near the tip of the posterior margin).^[3]

Crocodilian material found from Miocene deposits in the eastern United States has often been attributed toThecachampsa, even isolated teeth with few distinguishable features.^[7] In 1869, Cope named a fourth species,T. sicaria, from a jaw fragment and a dorsal vertebra. Unlike those of other species, the teeth ofT. sicaria were lenticular (lens-shaped) in cross section with sharp cutting edges.^[3] That year,Othniel Charles Marsh named another species ofThecachampsa, "T. squankensis", after the place of its discovery,Squankum,New Jersey, but that name is anomen nudum because Marsh provided no description, diagnosis, or type specimen.^[8] Cope named a new species,T. fastigiata, in 1870 as a reassignment ofCrocodylus fastigiatus, named by Leidy in 1852.^[9] These species were distinguished from one another primarily by differences in the shape of the teeth, the most common material found. The genus was synonymized withCrocodylus in 1973, but has since been regarded as valid.^[10]

A clear phylogenetic distinction between North AmericanGavialosuchus and the type species ofGavialosuchus,Gavialosuchus eggenburgensis Toula and Kail 1885^[11] from the Miocene of Austria, was clear once they were analyzed together in phylogenetic analyses.^{[12][13][14][15]} In 2001, A.C. Myrick synonymizedGavialosuchus americanus, another "tomistomine" from the eastern United States, withT. antiqua.^[16] Myrick also synonymizedTomistoma lusitanicum, a "tomistomine" fromPortugal, withThecachampsa, though this has not been supported by subsequent analyses that clearly distinguish them.^{[13][14][15][17]} The genus nameThecachampsa has priority over the other two, as it was erected earlier. A geologically younger species was first described from Florida asTomistoma americanus in 1915, with remains having been found from theKirkwood Formation inNew Jersey, theCalvert Formation inMaryland, theChesapeake Group ofVirginia, and thePungo River andYorktown Formations ofNorth Carolina. Remains have also been found fromFlorida,California,Baja California, and, more recently,Costa Rica. Fossils of the species are present in deposits that range in age from the lateEarly Miocene to the earlyPliocene.^[18] A few studies such as that of Jouveet al. (2008) have kept the species withinGavialosuchus, leavingT. antiqua as the only species withinThecachampsa,^[19] though they didn't testThecachampsa antiqua in their phylogenetic analysis, and most other analyses recover a clade including all North American forms that had previously been referredGavialosuchus with a broad phylogenetic separation between them andG. eggenburgensis.^{[14][15][20][21]}

The cladogram below follows from Brochu and Storrs (2012).

In addition to reassigningG. americanus andG. carolinensis toThecachampsa, Myrick combined all previously named species ofThecachampsa in a single species, with the oldest name beingT. antiqua. The different tooth shapes that distinguished the species were considered variations in the dentition of a single species.^[16] However, the variation in dentition could only be seen in complete skulls, all of which had been referred toGavialosuchus before the genus was synonymized withThecachampsa.

Weems (2018) agreed with Piras et al. (2007) and Brochu & Storrs (2012) thatTomistoma americana andGavialosuchus carolinensis belong toThecachampsa rather thanGavialosuchus, but treatedsericodon andantiqua as distinct species rather than one species, and suggested that theamericanus holotype is conspecific withT. sericodon, makingT. americana a synonym ofT. sericodon.

Most subsequent analyses have not accepted these suggestions based on clear differences betweenT. americana andT. antiqua and the lack of differences not explained by taphonomy betweenT. antiqua andT. sericodon.

Pairedδ¹⁸O andδ¹³C measurements suggest thatT. americana primarily fed on marine prey, in contrast to sympatricAlligator that ate freshwater prey.^[22]

• Crocodilia
• Prehistoric pseudosuchian genera
• Prehistoric marine crocodylomorphs
• Oligocene crocodylomorphs
• Oligocene reptiles of North America
• Taxa named by Edward Drinker Cope

• Articles with short description
• Short description is different from Wikidata
• Articles with 'species' microformats
• Taxonbars with multiple manual Wikidata items