Thecachampsa is an extinct genus of gavialoid crocodylian, traditionally regarded as a member of the subfamily Tomistominae.

Other marine fossils such as sea snail and bivalve shells, shark teeth, and barnacles have been found alongside remains of Thecachampsa and similar taxa.

[3] In 1852, American paleontologist Joseph Leidy described Crocodylus antiquus from Miocene deposits in the Lee family's ancestral home in Virginia.

Leidy also described additional material including several teeth and osteoderms, two vertebrae, a rib, and an ungual phalanx or claw bone.

[3] Crocodilian material found from Miocene deposits in the eastern United States has often been attributed to Thecachampsa, even isolated teeth with few distinguishable features.

Unlike those of other species, the teeth of T. sicaria were lenticular (lens-shaped) in cross section with sharp cutting edges.

[16] Myrick also synonymized Tomistoma lusitanicum, a "tomistomine" from Portugal, with Thecachampsa, though this has not been supported by subsequent analyses that clearly distinguish them.

[18] A few studies such as that of Jouve et al. (2008) have kept the species within Gavialosuchus, leaving T. antiqua as the only species within Thecachampsa,[19] though they didn't test Thecachampsa antiqua in their phylogenetic analysis, and most other analyses recover a clade including all North American forms that had previously been referred Gavialosuchus with a broad phylogenetic separation between them and G.