Gila Monsters and Kin
After the flood
Chad Arment (2024)
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).
The secular model suggests that living Heloderma evolved in North America directly from Cretaceous ancestors, with the Asian Cretaceous monstersaurians dying off after that period. A North America-to-Europe dispersal scenario through Greenland is proposed for the appearance of European Cenozoic helodermatids (Yi and Norell 2013; Van Devender et al. 2017).
For a creationist, that model clearly does not work. The widespread Cretaceous fossils in North America and Asia were deposited during the Flood, and there is likely little correlation to their original pre-Flood locations. We have no way to determine the Ark kind, other than to suggest that it was a single pair of monstersaurian that had already developed venom grooves on its teeth. (The specific monstersaurian may have never been fossilized.)
A creation model would argue that in the Cenozoic helodermatids spread out from the Ark, not North America. Given the early appearance (Eocene) of Eurheloderma, it seems likely that this genus was closer in lineage to the Ark kind. Interestingly, Eurheloderma fossils are found in the French Phosphorites with several other herpetological taxa that have New World relatives (Rage 2006). Does this indicate an early viable pathway (via land bridges, rafting, or combination) to the New World?
Just as interesting is the as-yet-unnamed helodermatid fossil from early Miocene Florida that appears to be a morphological bridge between the “numerous, shorter teeth” of Eurheloderma and the “fewer, taller teeth” of modern Heloderma (Bhullar and Smith 2008). Osteoderms in Eurheloderma and Lowesaurus were “large, low, and granular . . . separated by shallow grooves,” while they are much smaller and more pustulate in living Heloderma (Stevens 1977). Interestingly, the Miocene Heloderma texanum was not intermediate in osteoderm morphology, but rather its osteoderms were “more pustulate and more tuburculate” with deeper grooves separating them, than are found in modern Heloderma species (Stevens 1977).
More helodermatid fossils are required before any solid conclusions can be made about the post-Flood diversification and dispersal of this lineage, but it seems reasonable to assume (based on current evidence) that the Family Helodermatidae is a monobaramin, but probably not a holobaramin. Its early dispersal may have taken a Europe-to-North America pathway, where the lineage diversified into Lowesaurus and Heloderma. Climatic change likely constricted the lineage’s biogeographic distribution to its present day range.
A Post-Flood View of the Helodermatidae
references
Bhullar, B.-A. S., and K. T. Smith. 2008. Helodermatid lizard from the Miocene of Florida, the evolution of the dentary in Helodermatidae, and comments on dentary morphology in Varanoidea. Journal of Herpetology 42(2): 286-302.
Bolet, A., and M. Augé. 2014. A new miniaturized lizard from the late Eocene of France and Spain. The Anatomical Record 297: 505-515.
Bryant, J. D. 1991. New early Barstovian (middle Miocene) vertebrates from the Upper Torreya Formation, eastern Florida Panhandle. Journal of Vertebrate Paleontology 11(4): 472-489.
Chippaux, J.-P., and K. Amri. 2021. Severe Heloderma spp. envenomation: A review of the literature. Clinical Toxicology 59(3): 179-184.
Fry, B. G., et al. 2009. A central role for venom in predation by Varanus komodoensis (Komodo dragon) and the extinct giant Varanus (Megalania) priscus. PNAS 106(22): 8969-8974.
Gilmore, C. W. 1928. Fossil lizards of North America. Memoirs of the National Academy of Sciences 22: 1-201. 1978 rpnt., The National Academies Press, Washington, D.C.
Hamilton, S. M., et al. 2023. New lizard specimens from the Campanian Wapiti Formation of Alberta, Canada. Geosciences 12: 337.
Hoffstetter, R. 1957. Un saurien Hélodermatidé (Eurheloderma gallicum nov. gen. et sp.) dans le faune fossile des phosporites du Quercy. Bulletin de la Société Géologique de France S6-VII(6): 775-786.
Mead, J. I., et al. 2012. Helodermatid lizard from Mio-Pliocene oak-hickory forest of Tennessee, eastern USA, and a review of monstersaurian osteoderms. Acta Palaeontologica Polonica 57(1): 111-121.
Mead, J. I., et al. 2015. Early Pleistocene (Blancan) helodermatid lizard from Arizona, USA. Journal of Herpetology 49(2): 295-301.
Mead, J. I., et al. 2021. Heloderma (Helodermatidae; Squamata) from the Apache Local Fauna, Pleistocene, southwestern Oklahoma. Journal of Herpetology 55(1): 70-76.
Nydam, R. L. 2000. A new taxon of helodermatid-like lizard from the Albian-Cenomanian of Utah. Journal of Vertebrate Paleontology 20(2): 285-294.
Rage, J.-C. 2006. The lower vertebrates from the Eocene and Oligocene of the Phosphorites du Quercy (France): An overview. Strata 1(13): 161-173.
Reeder, T. W., et al. 2015. Integrated analyses resolve conflicts over squamate reptile phylogeny and reveal unexpected placements for fossil taxa. PLoS One 10(3): e0118199.
Relserer, R. S., et al. 2013. Taxonomic reassessment and conservation status of the beaded lizard, Heloderma horridum (Squamata: Helodermatidae). Amphibian & Reptile Conservation 7(1): 74-96.
Stevens, M. S. 1977. Further study of Castolon Local Fauna (early Miocene) Big Bend National Park, Texas. The Pearce-Sellards Series (Texas Memorial Museum) (28): 1-69.
Sullivan, R. M., and J. A. Holman. 1996. Squamata. in: Prothero, D. R., and R. J. Emry, eds. The Terrestrial Eocene-Oligocene Transition in North America. Cambridge University Press, Cambridge.
Van Devender, T. R., et al. 2017. The Gila monsters (Heloderma suspectum) of Cajón Bonito and the southern Four Corners area. Sonoran Herpetologist 30(2): 43-46.
Yi, H.-Y., and M. A. Norell. 2013. New materials of Estesia mongoliensis (Squamata: Anguimorpha) and the evolution of venom grooves in lizards. American Museum Novitates (2767): 1-31.