Gila Monsters and Kin
After the flood

Gila monster (Heloderma suspectum), Sonora, Mexico (CC BY-NC 2.0 Andrew DuBois)

The Helodermatidae is a family of largish, stocky lizards, armored dorsally with bead-like osteoderms and best known for being venomous. They are carnivorous, catching small mammals where they can, but with a predilection for bird and reptile eggs. Living species are New World, but one fossil genus is found in European deposits. There are five living species, comprised of the Gila monster (Heloderma suspectum) and four species of beaded lizard (H. alvarezi, H. charlesbogerti, H. exasperatum, and H. horridum). The beaded lizards range from Mexico to Guatemala, while the Gila monster is found in the southwestern U.S. and in Sonora, Mexico (Relserer et al. 2013).

Envenomation by Heloderma is rare (and venom is ‘chewed’ in by the large, grooved teeth, not injected), but while not usually life-threatening there are cases where immediate medical attention is necessary. There is no antivenom for Heloderma bites, so treatment primarily targets symptoms, whether respiratory, cardiac, or electrolytic issues (Chippaux and Amri 2021).

Rio Fuerte beaded lizard (H. exasperatum), Sonora, Mexico (CC BY-NC 2.0 Andrew DuBois)

The Helodermatidae consists of three genera, which are known only from the Cenozoic: Eurheloderma, Lowesaurus, and Heloderma. Below the Cenozoic, in the Cretaceous, which almost all creationists would consider Flood deposition, there are quite a few fossil lizards that appear to be related (more or less) to the Helodermatidae. These are found as North American and Asian fossils (Hamilton et al. 2023), and classified within the clade Monstersauria (typically denoted as those taxa within anguimorph lizards deemed closer to Heloderma than to the varanid lizards). The exact relationship of the Monstersauria to the Helodermatidae is still unresolved (Reeder et al. 2015); relationships within the Monstersauria are just as controversial (Yi and Norell 2013). All members of the Helodermatidae (including fossil genera) possess distinctive venom grooves, “a narrow slit or infolding in the tooth, at least as deep as it is wide, that runs the entire length of the tooth” (Nydam 2000). The Mongolian Estesia had distinct venom grooves (Yi and Norell 2013), but other monstersaurians, such as Primaderma, did not (Nydam 2000). Some genera, like Paraderma, may have had basal infoldings on teeth, similar to what is seen in certain varanids (Nydam 2000): venom glands have been found in varanid lizards like the Komodo dragon, while the extinct giant monitor lizard, Megalania priscus, has been suggested to be the largest venomous animal to have ever lived (Fry et al. 2009).

The earliest Cenozoic helodermatid was Eurheloderma from Eocene France (Hoffstetter 1957; Bolet and Augé 2014). Lowesaurus is known from several Oligocene deposits in Colorado and Nebraska (Gilmore 1928; Sullivan and Holman 1996). As-yet-undescribed helodermatid fossils, ?Heloderma, including dentition and osteoderms, have been found in Miocene deposits in Florida (Bryant 1991; Bhullar and Smith 2008). Heloderma texana, much smaller than living Heloderma, has been described from Miocene Texas (Stevens 1977). Helodermatid osteoderms have been found at the Miocene-Pliocene Gray Fossil Site in Tennessee (Mead et al. 2012): the presence of certain other animals, like alligators, at Gray Fossil Site suggest that the climate was a bit warmer during that period. Heloderma fossils from the Pleistocene have been reported from Arizona, California, and Oklahoma (Mead et al. 2015; Mead et al. 2021).