Heloderma

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Heloderma
Temporal range: Early Miocene to Recent
Gila monster, Heloderma suspectum
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Infraorder: Neoanguimorpha
Clade: Monstersauria
Family: Helodermatidae
Genus: Heloderma
Wiegmann, 1829
Type species
Heloderma horridum
, 1829
Species

Heloderma is a genus of toxicoferan lizards that contains five species, all of which are venomous.[1] It is the only extant genus of the family Helodermatidae.

Description

The genus Heloderma contains the

osteoderms for better protection. The scales of the belly are free from osteoderms. Most species are dark in color, with yellowish or pinkish markings.[6][7]

Venom

The venom glands of Heloderma are located at the end of the lower jaws, unlike

chew the venom into the flesh of a victim. Heloderma venom is used only in defense. Venom glands are believed to have evolved early in the lineage leading to the modern helodermatids, as their presence is indicated even in the 65-million-year-old fossil genus Paraderma.[7][8] In general, one adult helodermatid has approximately 15 to 20 mg of venom, while the estimated lethal dose for humans is 5 to 8 mg.[9]

Diet

Helodermatids are

and reptiles.

Reproduction

All species of Heloderma are

oviparous. The Gila monster typically lays 6 eggs, the beaded lizards up to about 18 eggs .[7]
Comparing the different species, all eggs have a similar size, and the same holds true for their hatchlings.

Taxonomy

Cladogram of the heloderma species
Cladogram of the Heloderma species
Explanation of the numbers
1 late Eocene (approx. 35 million years)
2 late Miocene (approx. 10 million years)
3 Pliocene (approx. 4.4 million years)
4 Pliocene (approx. 3 million years)

Family Helodermatidae

Members of the genus Heloderma have many extinct relatives in the Helodermatidae whose evolutionary history may be traced back to the

Las Vegas, Nevada. Because the helodermatids have remained relatively unchanged morphologically, they are occasionally regarded as living fossils.[10] Although the beaded lizards and the Gila monster appear closely related to the monitor lizards (varanids) of Africa, Asia, and Australia, the wide geographical separation and unique features not found in the varanids indicates they are better placed in a separate family.[11]

Mexican beaded lizard skeleton (Museum of Osteology)

The type species is Heloderma horridum, which was first described in 1829 by Arend Wiegmann. Although he originally assigned it the generic name Trachyderma, he changed it to Heloderma six months later, which means "studded skin", from the Ancient Greek words hêlos (ηλος)—the head of a nail or stud—and derma (δερμα), meaning skin.[12]

Conrad, 2008 and Estes et al., 1988 (using morphological data) places Helodermatidae within

Varanus.[13][14]
However, Estes et al., 1988 understood Helodermatidae as having split earlier from Lanthanotus and Varanus, whereas Conrad, 2008 groups them at the same branch point.

In contrast, molecular studies have identified Heloderma as being within Anguioidea along with Anguidae and Xenosauridae, but specifically sister to Anguidae.[15][16]

Venom

Venom production among lizards was long thought to be unique to this genus, but researchers studying venom production have proposed many others also produce some venom, all placed in the clade Toxicofera, which includes all snakes and 13 other families of lizards.[17] However, except for snakes, helodermatids, and possibly varanids, envenomation is not considered medically significant for humans

Heloderma suspectum skull with dentitio
Heloderma suspectum skull with dentition, Photo by A. Laube

In captivity

Hatchling sizes of H. exasperatum and H. suspectum (taxidermy)
Hatchling sizes of H. exasperatum (top) and H. suspectum (taxidermy)

H. horridum, H. exasperatum, and H. suspectum are frequently found in captivity and are well represented in zoos throughout much of the world. The other two species of Heloderma, H. alvarezi and H. charlesbogerti, are extremely rare, and only a few captive specimens are known.

Gallery

  • Heloderma suspectum in captivity
  • Helderema suspectum with 4 eggs
    Heloderma suspectum with 4 eggs
  • Helderema suspectum with 6 eggs
    Heloderma suspectum with 6 eggs
  • Gila monster hatching
    Gila monster hatching
  • Group of young Gila monsters
    Group of young Gila monsters
Heloderma Skin
Heloderma skin

References

Captured Gila monster
Captured Gila monster
Heloderm horridum captive bred
Heloderm horridum captive bred
  1. ^ "POISINDEX(R) TOXICOLOGIC MANAGEMENTS Topic: GILA MONSTER (HELODERMA SUSPECTUM)".
  2. – via Google Books.
  3. – via Google Books.
  4. ^ C. M. Bogert, R. M. Del Campo (1956). "The Gila Monster and its Allies. The relationships, habits, and behavior of the lizards of the family Helodermatidae". Bulletin of the American Museum of Natural History. 109: 1–238.
  5. ^ Beck, D. D. (2005). Biology of Gila Monsters and Beaded Lizards. University Press of California.
  6. .
  7. ^ .
  8. ^ Richard L. Cifelli, Randall L. Nydam. 1995. Primitive, helodermatid-like platynotans from the Early cretaceous of Utah. Herpetologica. 51(3):286-291.
  9. .
  10. .
  11. .
  12. ^ Wiegmann, A.F.A. (1829). "Über die Gesetzlichkeit in der geographischen Verbreitung der Saurier". Isis. 22 (3–4). Oken: 418–428.
  13. S2CID 84301257
    .
  14. .
  15. .
  16. .
  17. ^ . Fry, B.; et al. (February 2006). "Early evolution of the venom system in lizards and snakes". Nature. 439 (7076): 584–588.
    S2CID 4386245
    .
A Chiapan beaded lizard in captivity.

Notes

Heloderma exasperatum near Los Alamos
Heloderma exasperatum near Los Alamos

External links

Schwandt, Hans- Joachim www.heloderma.net 2006 in 6 languages

Further reading

  • C. M. Bogert, R. M. Del Campo (1956). The Gila Monster and its Allies. The relationships, habits, and behavior of the lizards of the family Helodermatidae. Vol. 109. Bulletin of the American Museum of Natural History. pp. 1–238.
  • Beck, D. D. (2005). Biology of Gila Monsters and Beaded Lizards. London: University Press of California.
  • Schwandt, Hans-Joachim (2019). The Gila Monster Heloderma suspectum. Frankfurt/Main: Edition Chimaira. .
Wikispecies has information related to Heloderma suspectum