Editing Heloderma

{{Short description|Genus of reptiles}}
{{For|the dermatological condition|Knuckle pads}}
{{Italic title}}
{{Automatic taxobox
| name = ''Heloderma''
| image = Heloderma suspectum cinctum.jpg
| image_caption = [[Gila monster]], ''Heloderma suspectum''
| fossil_range = {{fossil_range|23|0|Early [[Miocene]] to Recent}}
| taxon = Heloderma
| authority = [[Arend Friedrich August Wiegmann|Wiegmann]], 1829
| type_species = ''[[Heloderma horridum]]''
| type_species_authority = [[Arend Friedrich August Wiegmann|Wiegmann]], 1829
| parent_authority = 
| display_parents = 3
| subdivision_ranks = Species
| subdivision = * ''[[Heloderma suspectum]]''
* ''[[Heloderma horridum]]''
* ''[[Heloderma exasperatum]]''
* ''[[Heloderma charlesbogerti]]''
* ''[[Heloderma alvarezi]]''
* ''[[Heloderma texana]]''†
}}

'''''Heloderma''''' is a [[genus]] of [[toxicofera]]n lizards that contains five species, all of which are [[venom]]ous.<ref>{{Cite web |url=http://herpetology.com/helobite.txt |title=POISINDEX(R) TOXICOLOGIC MANAGEMENTS Topic: GILA MONSTER (HELODERMA SUSPECTUM)}}</ref> It is the only extant genus of the family [[Helodermatidae]].

==Description==
The genus ''Heloderma'' contains the [[Gila monster]] (''H. suspectum'') and four species of beaded lizards. Their eyes are immobile and fixed in their heads.<ref>{{Cite book|url=https://books.google.com/books?id=ORptEAAAQBAJ&dq=Extraocular+muscles+Heloderma&pg=PA206|title=Wild and Exotic Animal Ophthalmology: Volume 1: Invertebrates, Fishes, Amphibians, Reptiles, and Birds|first1=Fabiano|last1=Montiani-Ferreira|first2=Bret A.|last2=Moore|first3=Gil|last3=Ben-Shlomo|date=April 27, 2022|publisher=Springer Nature|isbn=978-3-030-71302-7 |via=Google Books}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=SuKRyC1Q8W4C&dq=Gila+monster+eyes+fixed+in+their+head&pg=PA8|title=The Biology of the Eye|first=Jorge|last=Fischbarg|date=December 9, 2005|publisher=Elsevier|isbn=978-0-08-047609-4 |via=Google Books}}</ref> The Gila monster is a large, stocky, mostly slow-moving reptile that prefers arid deserts. Beaded lizards are seen to be more agile and seem to prefer more humid surroundings.<ref>{{Cite journal|last=C. M. Bogert, R. M. Del Campo|date=1956|title=The Gila Monster and its Allies. The relationships, habits, and behavior of the lizards of the family Helodermatidae|url=|journal=Bulletin of the American Museum of Natural History|volume=109|pages=1–238|via=}}</ref><ref>{{Cite book|last=Beck|first=D. D.|title=Biology of Gila Monsters and Beaded Lizards|publisher=University Press of California|year=2005|isbn=|location=|pages=}}</ref> The tails of all species of ''Heloderma'' are used as fat-storage organs. The scales of the head, back, and tail are bead-like, containing [[osteoderms]] for better protection. The scales of the belly are free from osteoderms. Most species are dark in color, with yellowish or pinkish markings.<ref>{{Cite book|last=Schwandt|first=Hans-Joachim|title=The Gila Monster Heloderma suspectum|publisher=Edition Chimaira|year=2019|isbn=978-3-89973-441-6|location=Frankfurt/Main|pages=}}</ref><ref name=EoR>{{cite book |editor1=Cogger, H.G. |editor2=Zweifel, R.G. |author = Bauer, Aaron M.|year=1998|title=Encyclopedia of Reptiles and Amphibians|publisher= Academic Press|location=San Diego|pages= 156|isbn= 0-12-178560-2}}</ref>

==Venom==
The venom glands of ''Heloderma'' are located at the end of the lower jaws, unlike [[snake]]s' venom glands, which are located behind the eyes. Also, unlike snakes, the Gila monster and beaded lizards lack the musculature to inject venom immediately. They have to [[Mastication|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''.<ref name=EoR/><ref>Richard L. Cifelli, Randall L. Nydam. 1995. Primitive, helodermatid-like platynotans from the Early cretaceous of Utah. Herpetologica. 51(3):286-291.</ref> In general, one adult helodermatid has around 15 to 20&nbsp;mg of venom, while the estimated lethal dose for humans is 5 to 8&nbsp;mg.<ref>{{Cite book|last=Dart|first=Richard C.|url=https://books.google.com/books?id=BfdighlyGiwC&dq=gila+monster+estimated+lethal+dose+for+human&pg=PA1539|title=Medical Toxicology|date=2004|publisher=Lippincott Williams & Wilkins|isbn=978-0-7817-2845-4|language=en}}</ref>

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 [[snake]]s and 13 other families of lizards.<ref name="Fry2006">.
{{cite journal |author=Fry, B. |display-authors=etal |date=February 2006 |title=Early evolution of the venom system in lizards and snakes |journal=Nature |volume=439 |issue=7076 |pages=584–588 |bibcode=2006Natur.439..584F |doi=10.1038/nature04328 |pmid=16292255 |s2cid=4386245}}</ref> However, except for snakes, helodermatids, and possibly varanids, envenomation is not considered medically significant for humans.

==Diet==
Helodermatids are [[carnivorous]], [[preying]] on [[rodent]]s and other small [[mammal]]s, and eating the [[egg (biology)|eggs]] of [[bird]]s and reptiles.

==Reproduction==
All species of ''Heloderma'' are [[oviparous]]. The Gila monster typically lays six eggs, and the beaded lizards up to about 18 eggs .<ref name="EoR" /> Comparing the different species, all eggs have a similar size, as are their hatchlings.

==Taxonomy==
[[File:Kladoramm heloderma.jpg|alt=Cladogram of the heloderma species|thumb|Cladogram of the ''Heloderma'' species
{| class="wikitable"
! colspan="2" |Explanation of the numbers
|-
|1
|late Eocene (about 35 million years)
|-
|2
|late Miocene (about 10 million years)
|-
|3
|Pliocene (about 4.4 million years)
|-
|4
|Pliocene (about 3 million years)
|}
]]
'''Family Helodermatidae'''

The four [[subspecies]] of beaded lizards were elevated to full species in 2013.<ref>http://www.redlist-arc.org/Article-PDFs/Special%20Mexico%20Issue_ARC_7(1)_74-96_low_res.pdf {{Webarchive|url=https://web.archive.org/web/20131023060725/http://www.redlist-arc.org/Article-PDFs/Special%20Mexico%20Issue_ARC_7%281%29_74-96_low_res.pdf |date=2013-10-23 }} Reiserer & al., 2013, ''Taxonomic reassessment and conservation status of the beaded lizard, ''Heloderma horridum'' (Squamata: Helodermatidae)''</ref>
{| class="wikitable"
! Image
! Species
! Taxon author
! Common name
! Geographic range
|-
|[[File:Heloderma alvarezi.jpg|190px]]
|''[[Heloderma alvarezi|H. alvarezi]]''
|[[Charles Mitchill Bogert|Bogert]] and Martin del Campo, 1956
|Chiapan beaded lizard
| style="width:40%" |[[Mexico]]: northern Chiapas to extreme northwestern [[Guatemala]]
|-
|[[File:HelodermaHCharlesbogerti.JPG|190px]]
|''[[Heloderma charlesbogerti|H. charlesbogerti]]''<span style="font-size:100%;"><sup>T</sup></span>
|[[Jonathan Atwood Campbell|Campbell]] and Vannini, 1988
|Guatemalan beaded lizard
|[[Guatemala]]: the Motagua Valley
|-
|[[File:Heloderma exasperatum exposé au Palais de la Découverte en août 2019.jpg|190px]]
|''[[Heloderma exasperatum|H. exasperatum]]''
|[[Charles Mitchill Bogert|Bogert]] and Martin del Campo, 1956
|Rio Fuerte beaded lizard
|[[Mexico]]: Rio Fuerte, Rio Mayo, southern Sonora, northern Sinaloa, western Chihuahua and the Sierra Madre Occidental
|-
|[[File:Heloderma horridum -Zurich Zoo-8a.jpg|190px]]
|''[[Mexican beaded lizard|H. horridum]]''<span style="font-size:100%;"><sup>T</sup></span>
|Wiegmann, 1829
|Mexican beaded lizard
|[[Mexico]]: southern Sinaloa to Oaxaca
|-
|[[File:Gila monster2.JPG|190px]]
|''[[Gila monster|H. suspectum]]''
|[[Edward Drinker Cope|Cope]], 1869
|Gila monster
|[[Southwest United States]], [[Sonora]]
|}
[[File:Fossil Florida Heloderma FLMNH.jpg|thumb|A partial ''Heloderma'' skull from the [[Miocene]] of [[Florida]] ([[Florida Museum of Natural History|FLMNH]]). These lizards are no longer found in the region.]]


Members of the genus ''Heloderma'' have many extinct relatives in the Helodermatidae, whose evolutionary history may be traced back to the [[Cretaceous]] period, such as ''[[Estesia]]''. The genus ''Heloderma'' has existed since the [[Miocene]], when ''H. texana'' lived, and fragments of [[osteoderm]]s from the Gila monster have been found in late [[Pleistocene]] (8,000-10,000 years ago) deposits near [[Las Vegas, Nevada]]. Because the helodermatids have remained relatively unchanged [[Morphology (biology)|morphologically]], they are occasionally regarded as [[living fossil]]s.<ref name="varanoid">{{cite book |author1=King, Ruth Allen |author2=Pianka, Eric R. |author3=King, Dennis |title=Varanoid Lizards of the World |publisher=Indiana University Press |location=Bloomington |year=2004 |isbn=0-253-34366-6 }}</ref> Although the beaded lizards and the Gila monster appear closely related to the [[monitor lizard]]s (varanids) of Africa, Asia, and Australia, the wide geographical separation and unique features not found in the varanids indicate they are better placed in a separate family.<ref name="mattison">{{cite book |author=Mattison, Chris |title=Lizards of the World |publisher=Blandford |location=London |year=1998 |isbn=0-7137-2357-2 |url-access=registration |url=https://archive.org/details/lizardsofworld00matt }}</ref>
[[File:Beaded Lizard Skeleton.jpg|thumb|Mexican beaded lizard skeleton ([[Museum of Osteology]])|left]]
The [[type species]] is ''Heloderma horridum'', which was first described in 1829 by [[Arend Friedrich August Wiegmann|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)&mdash;the head of a nail or stud&mdash;and ''derma'' (δερμα), meaning skin.<ref>{{cite journal | last = Wiegmann| first = A.F.A.| author-link = Arend Friedrich August Wiegmann| title = Über die Gesetzlichkeit in der geographischen Verbreitung der Saurier| journal = Isis| volume =22 | issue =3–4 | pages = 418&ndash;428| publisher =Oken | year = 1829 }}</ref>

Conrad, 2008 and Estes et al., 1988 (using morphological data) place the Helodermatidae within [[Varanoidea]] along with [[Earless monitor lizard|''Lanthanotus borneensis'']] and ''[[Varanus]]''.<ref>{{Cite journal|last1=Conrad|first1=Jack L.|last2=Ast|first2=Jennifer C.|last3=Montanari|first3=Shaena|last4=Norell|first4=Mark A.|date=2011|title=A combined evidence phylogenetic analysis of Anguimorpha (Reptilia: Squamata)|journal=Cladistics|language=en|volume=27|issue=3|pages=230–277|doi=10.1111/j.1096-0031.2010.00330.x|pmid=34875778|s2cid=84301257|issn=1096-0031|doi-access=free}}</ref><ref>{{Cite journal|last=Estes|first=Richard|date=1988|title=Phylogenetic relationships within squamata|url=https://repository.si.edu/handle/10088/6457|journal=Phylogenetic Relationships of the Lizard Families: Essays Commemorating Charles L. Camp|pages=119–281|hdl=10088/6457|isbn=9780804714358}}</ref> However, Estes et al., 1988 understood the 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 the Anguioidea along with Anguidae and Xenosauridae, but specifically sister to Anguidae.<ref>{{Cite journal|last1=Vidal|first1=Nicolas|last2=Marin|first2=Julie|last3=Sassi|first3=Julia|last4=Battistuzzi|first4=Fabia U.|last5=Donnellan|first5=Steve|last6=Fitch|first6=Alison J.|last7=Fry|first7=Bryan G.|last8=Vonk|first8=Freek J.|last9=Rodriguez de la Vega|first9=Ricardo C.|last10=Couloux|first10=Arnaud|last11=Hedges|first11=S. Blair|date=2012-10-23|title=Molecular evidence for an Asian origin of monitor lizards followed by Tertiary dispersals to Africa and Australasia|url= |journal=Biology Letters|volume=8|issue=5|pages=853–855|doi=10.1098/rsbl.2012.0460|pmc=3441001|pmid=22809723}}</ref><ref>{{Cite journal|last1=Townsend|first1=Ted M.|last2=Larson|first2=Allan|last3=Louis|first3=Edward|last4=Macey|first4=J. Robert|date=2004-10-01|title=Molecular Phylogenetics of Squamata: The Position of Snakes, Amphisbaenians, and Dibamids, and the Root of the Squamate Tree|journal=Systematic Biology|language=en|volume=53|issue=5|pages=735–757|doi=10.1080/10635150490522340|pmid=15545252|issn=1063-5157|doi-access=free}}</ref>[[File:Heloderma suspectum skull with dentition.jpg|alt=Heloderma suspectum skull with dentitio|thumb|''Heloderma suspectum'' skull with dentition, Photo by A. Laube]]

== In captivity ==
[[File:Heloderma hatchling sizes.jpg|alt=Hatchling sizes of H. exasperatum and H. suspectum (taxidermy)|thumb|Hatchling sizes of ''H. exasperatum'' (top) and ''H. suspectum'' (taxidermy)]]
''H. horridum'', ''H. exasperatum'', and ''H. suspectum'' are frequently found in [[captivity (animal)|captivity]] and are well represented in [[zoo]]s 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 ==
<gallery mode="nolines" widths="220" caption="''Heloderma suspectum'' in captivity">
File:Heloderma Eiablage.jpg|alt=Helderema suspectum with 4 eggs|''Heloderma suspectum'' with four eggs
File:Gila-monster-6-eggs.jpg|alt=Helderema suspectum with 6 eggs|''Heloderma suspectum'' with six eggs
File:Schluepfendes-jungtier-OS6.jpg|alt=Gila monster hatching|Gila monster hatching
File:Group of young gila monster.jpg|alt=Group of young Gila monsters|Group of young Gila monsters
</gallery>[[File:Heloderma Skin.jpg|alt=Heloderma Skin|thumb|''Heloderma'' skin]]

==References==
[[File:Heloderma suspectum captured.jpg|alt=Captured Gila monster|thumb|Captured Gila monster]]
[[File:H-horridum.jpg|alt=Heloderm horridum captive bred|thumb|Heloderm horridum captive bred]]
{{Reflist}}[[Image:Heloderma_alvarezi2.jpg|thumb|right|A Chiapan beaded lizard in captivity.]]

==Notes==
* {{cite journal|last1=Ariano-Sánchez|first1=Daniel|title=Envenomation by a wild Guatemalan beaded lizard ''Heloderma horridum charlesbogerti''|url=|journal=Clinical Toxicology|date=2008|volume=46|issue=9|pages=897–899|doi=10.1080/15563650701733031|pmid=18608297|s2cid=22173811|doi-access=free}}
*Ariano-Sánchez, D. & G. Salazar. 2007. Notes on the distribution of the endangered lizard, ''Heloderma horridum charlesbogerti'', in the dry forests of eastern Guatemala: an application of multi-criteria evaluation to conservation. Iguana 14: 152–158. [https://www.scribd.com/doc/11116925/Ariano-D-y-G-Salazar-2007-Notes-on-the-Distribution-of-the-Endangered-Lizard-Heloderma-horridum-charlesbogerti-in-the-Dry-Forests-of-Eastern-Gu]
*Ariano-Sánchez, D. 2006. The Guatemalan beaded lizard: endangered inhabitant of a unique ecosystem. Iguana 13: 178–183. [https://www.scribd.com/doc/11117893/Ariano-D-2006-The-Guatemalan-beaded-lizard-Endangered-inhabitant-of-a-unique-ecosystem-Iguana-133-178183]
*[http://www.ssn.org/Meetings/cop/cop14/Other/CoP14_results.pdf CONVENTION ON INTERNATIONAL TRADE IN ENDANGERED SPECIES OF WILD FAUNA AND FLORA] {{Webarchive|url=https://web.archive.org/web/20180930041659/http://www.ssn.org/Meetings/cop/cop14/Other/CoP14_results.pdf |date=2018-09-30 }}. 2007. Resume of the 14th Convention of the Parts. The Hague. The Netherlands.
[[File:Heloderma exasperatum.jpg|alt=Heloderma exasperatum near Los Alamos|thumb|''Heloderma exasperatum'' near Los Alamos]]

==External links==
{{Wikispecies|Helodermatidae}}
Schwandt, Hans- Joachim [https://www.heloderma.net/en/ www.heloderma.net] 2006 in 6 languages

== Further reading ==
{{Commons category|Heloderma}}
* {{Cite book|last=C. M. Bogert, R. M. Del Campo|title=The Gila Monster and its Allies. The relationships, habits, and behavior of the lizards of the family Helodermatidae|publisher=Bulletin of the American Museum of Natural History|year=1956|isbn=|volume=109|location=|pages=1–238}}
* {{Cite book|last=Beck|first=D. D.|title=Biology of Gila Monsters and Beaded Lizards|publisher=University Press of California|year=2005|isbn=|location=London|pages=}}
* {{Cite book |last=Schwandt |first=Hans-Joachim |title=The Gila Monster Heloderma suspectum - Natural History, Husbandry & Propagation |publisher=Edition Chimaira |year=2019 |isbn=978-3-89973-441-6 |location=Frankfurt/Main |pages=}}

{| class="wikitable"
|
|[[Wikispecies]] has information related to '''''Heloderma suspectum'''''
|}

* [http://www.helodermahorridum.com/beaded_lizard.php About Beaded Lizards] {{Webarchive|url=https://web.archive.org/web/20150215024644/http://www.helodermahorridum.com/beaded_lizard.php |date=2015-02-15 }}
* [http://herpetology.com/heloderma.html Heloderma information]
* [http://www.jcvi.org/reptiles/families/helodermatidae.php Family Helodermatidae (Gila Monsters)] {{Webarchive|url=https://web.archive.org/web/20100715164854/http://www.jcvi.org/reptiles/families/helodermatidae.php |date=2010-07-15 }}

{{Squamata families}}
{{Varanoidea}}
{{Taxonbar|from=Q729412}}
{{Authority control}}

[[Category:Helodermatidae|*]]
[[Category:Extant Miocene first appearances]]
[[Category:Lizard genera]]
[[Category:Taxa named by Arend Friedrich August Wiegmann]]