






































Iguana_11.2_text.ps


78 IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 HOLLINGSWORTH

Distribution of Chuckwallas. Illustration by John Binns.

Sauromalus ater, Rancho Los Tepetates, Sierra La Libertad, Baja California.

Sauromalus ater, Mountain Springs, San Diego County,
California. This population and all of those in the United States
were previously assigned to S. obesus. Chuckwallas typically
inhabit arid regions with moderate low-lying shrub cover and
usually are found on or near rocky outcrops with plenty of
crevices for use as retreats.



Among iguanid lizards, members in the genus Sauromalus rep-
resent some of the most divergent forms in the family.

Among the 45 species in the family Iguanidae, Chuckwallas rep-
resent a modest radiation of five currently recognized species
(Hollingsworth 2004, Pregill 2004). Sauromalus ater is found in
the southwestern United States, adjacent regions in México, much
of the Baja California peninsula, and on islas Willard, Tiburón,
San Marcos, El Coyote, Danzante, San Cosme, Santa Cruz, San
Diego, San José, San Francisco, Ballena, Gallo, Partida Sur, and
Espíritu Santo in the Gulf of California. The other four species

are restricted to islands in the Gulf of California. Sauromalus
hispidus occurs on islas Ángel de La Guarda, Granito, Mejía, Pond,
San Lorenzo Norte, San Lorenzo Sur, Cabeza de Caballo, La
Ventana, Piojo, Flecha, Mitlán, and Smith; S. varius on islas San
Esteban and Roca Lobos; S. klauberi only on Isla Santa Catalina;
and S. slevini on islas Carmen, Los Coronados, and Monserrate.

Over the past few years, a sometimes heated nomenclatural
debate has raged regarding the best way in which to represent the
species-level diversity within the genus (Montanucci et al. 2001,
McDiarmid et al. 2002; see also Iguana Times 9(1–2):18–26,

Understanding the Diversity of Chuckwallas
(Genus Sauromalus)

and a Debate Over Names
Bradford D. Hollingsworth

Department of Herpetology, San Diego Natural History Museum
San Diego, CA 92112

All photographs by the author.

IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 79UNDERSTANDING THE DIVERSITY OF CHUCKWALLAS

�

Sauromalus varius, Isla San Esteban, Sonora. This large species is commonly found in both the arroyo bottoms and on the rocky hillsides.



which includes the text of the Montanucci et al. petition). The
debate has focused on the choice of names for the widespread
populations that inhabit the deserts of the southwestern United
States, northwestern México, peninsular Baja California, and
numerous islands in the Gulf of California. The root cause of this
controversy was the synonymy of three species found to inter-
grade with one another and which lacked diagnosable characters
(Hollingsworth 1998). The recent ruling by the International
Commission of Zoological Nomenclature (ICZN) brought this
specific matter to a close (ICZN 2004; see also p. 10) — but for

80 IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 HOLLINGSWORTH

Sauromalus ater, Sierra Vizcaíno, Baja California Sur. This population
was previously assigned to S. australis.

A speckled juvenile Sauromalus hispidus, Isla La Ventana, Baja
California. Note the faint cross-barring remnant of the juvenile pattern.

Sauromalus klauberi, Isla Santa Catalina, Baja California Sur. 

Adult male Sauromalus slevini, Isla Monserrate, Baja California Sur. 

Sauromalus varius, Isla San Esteban, Sonora.



IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 81UNDERSTANDING THE DIVERSITY OF CHUCKWALLAS

biologists studying these lizards, understanding this nomenclat-
ural debate, the process of nomenclatural decision-making, and
the species diversity within Sauromalus is important.

As many as ten different species of Chuckwallas have been
recognized since Duméril (1856) first described Sauromalus ater,
but today, only half are considered valid. Evaluating how best to
represent biodiversity is the primary motivation of systematic
biologists. Since species are regarded as hypotheses to be contin-
ually tested, taxonomies inevitably and naturally will change as
new information is evaluated. Unfortunately, when systematists
modify taxonomies, confusion often develops. Among the users
of these taxonomies, the first concern usually centers on the
adoption of the new naming system and how to recover infor-
mation from previously published works that may have used one
or more different names. Secondary to these immediate responses
is how the new naming system changes previous ideas on diver-
sity, distributional limits, and levels of variance in ecological pref-
erences.

Prior to the synonymy of the three formerly recognized
species of Chuckwallas, the name Sauromalus obesus was used to
describe populations from Arizona, California, Nevada, and
Utah. Sauromalus obesus also was applied to populations found
in western Sonora, northern Baja California, and some islands in
the Gulf of California. In the more remote regions of Baja
California, the name S. australis was used to describe populations
inhabiting the southern portion of the peninsula, and the name
S. ater described populations on islands off its southern peninsu-
lar coastline in the Gulf of California. Each of these names had

Sauromalus ater, Sierra Vizcaíno, Baja California Sur. This population was previously assigned to S. australis.

Adult male Sauromalus ater, South Mountain, Maricopa County,
Arizona. Some isolated populations of S. ater may yet reveal species-
level diversity within the genus.



82 IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 HOLLINGSWORTH

Sauromalus hispidus, Isla San Lorenzo Norte, Baja California. A gravid adult female excavating a burrow.

An adult Sauromalus hispidus basking outside a burrow on Isla Ángel de La Guardia, Baja California.



IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 83UNDERSTANDING THE DIVERSITY OF CHUCKWALLAS

been in use since Charles Shaw revised the genus in 1945, and
his taxonomy had provided stability for nearly a half century.

The synonymy of Sauromalus obesus and S. australis with S.
ater was based on an analysis of additional specimens and previ-
ously used diagnostic characters, as well as a search for new char-
acters that could help delimit the species boundaries within the
genus (Hollingsworth 1998). With evidence of intergrades and
the overlap of diagnostic characters, the species limits between
the three could not be determined. Consequently, the familiar
name of S. obesus was subsumed into S. ater, because the former
now was considered a junior synonym of the latter.

Decisions regarding the application of zoological names are
governed by the ICZN and the rules established in the Code
(ICZN 1999). Here, the decision to select Sauromalus ater to rep-
resent the combined species was based on the Principle of Priority
(Article 23). Since S. ater was the oldest of the three names, the
Principle of Priority gives it precedence over the others. Without
the overseeing body of the ICZN and the Code, the authority of
researchers who first describe taxa could be undermined at the
will of subsequent authors. In extreme cases, a new name could
be applied to the same population every year, which would result
in taxonomic instability.

Petitions to the ICZN can be submitted when clarification
is needed on the validity of names or exceptions to the Code are
requested. Montanucci et al. (2001) petitioned the ICZN and
requested that the long-used and well-known name, Sauromalus

obesus, be given precedence over the little-used and older name,
S. ater. For two years, the ICZN received and published com-
ments on the petition. One of the greatest concerns was the tax-
onomic stability of Sauromalus obesus and its abundant use in the
scientific literature. In opposition to the petition, McDiarmid et
al. (2002) commented that the discrepancy in usage between S.
obesus and S. ater reflected the large number of papers published
on S. obesus in the United States, which could not have been
expected to mention S. ater. In addition, the name S. ater has
been used regularly for the last 145 years and should not be
regarded as a name infrequently used. In its recent decision
(Opinion 2072), the ICZN ruled that the priority of the name
Sauromalus ater should be maintained (ICZN 2004). In their
comments, commissioners stated that publication capacity
should not be given precedence over the Principle of Priority and
reversing priority does not achieve stability.

During the intervening period, when petitions, comments,
and opinions are published, confusion often develops as to which
nomenclature to follow. Many invoke a section of the Code
(Article 82.1) that requires that the prevailing usage of names be
maintained while a case is under consideration. In this instance,
authors have chosen to use either Sauromalus obesus or S. ater.
Because different interpretations of prevailing usage can result,

Sauromalus ater, Isla Espirítu Santo, Baja California Sur. This popu-
lation served as the type locality for many years.

Sauromalus ater, Bahía Kino, Sonora. This population and all of those
in mainland Sonora were previously assigned to S. obesus.

Adult male Sauromalus hispidus, Isla San Lorenzo Sur, Baja California. 



84 IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 HOLLINGSWORTH

Adult male Sauromalus hispidus, Isla San Lorenzo Sur, Baja California.

Sauromalus varius, Isla San Esteban, Sonora.



IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 85UNDERSTANDING THE DIVERSITY OF CHUCKWALLAS

both names have appeared in the literature. Deciding which
name best reflected the populations under consideration was sub-
jective, because the petition did not question the synonymy of
the three species. However, now that Opinion 2072 has been
issued, Sauromalus ater should be used.

Before the time of formal taxonomies, the understanding of
biodiversity was based on common names. The inherent insta-
bility of common names provides insights into the importance
of the ICZN and the Code. Stability is relative and our judgment
on acceptable levels of change should be gauged against informal
versus formal taxonomies. For example, the Indian origin for the
name Chuckwalla appears to be derived from as many as four dif-
ferent variants used by tribes in the southwestern United States.
Merriam (1979) recorded Chah´ch wahl from the Cahuilla,
Chah-kwar´-rah from the Southern Paiute, Chuk-war´-rah from
the Mono Paiute, and Cha-gwar´-rah from the Kawaiisu.
English-speaking peoples most likely adopted the word
“Chuckwalla” from one or more of these variations. Other names
for Chuckwallas recorded by Merriam (1979) include Hum-
sooth´ (Kamia), Hum-sool´ (Yuma), Um thool´ya (Mohave),
Tsah-wahr´ (Southern Paiute), Sow-wahr´(Chemehuevi), Sow-
war´-rah (Panamint Shoshone), Sah-gwar´-rah (Southern Nevada
Shoshone), Sahk-war´-rah (Shivwits), and Chakt´-tch (Serrano).
Without the use of scientific names and the guidance of the

ICZN rules, names describing the same animals could be as
diverse as regional differences in dialects and languages.

Now that this specific nomenclatural debate has come to a
close, we can move on to evaluating the consequences of lump-
ing the three species into one. Chuckwalla diversity and their
overall biology should be reevaluated in light of our new inter-
pretation of their relationships. The widespread Sauromalus ater
is found across an extensive range of arid habitats with different
plant communities and climatic cycles. Well-known populations
should be compared to populations in more remote regions.
Many populations are continuously distributed, whereas others
are isolated in mountain ranges or on islands. Of the five recog-
nized species of Chuckwallas, four are insular endemics in the
Gulf of California. Sauromalus varius, S. hispidus, S. slevini, and
S. klauberi were each described as a distinct insular species and
little controversy has surrounded their recognition (see Grismer
2003 for a review). Since the greatest diversity of Chuckwallas
occurs in relatively small, isolated islands or groups of islands, fur-
ther diversity may be found in isolated populations of Sauromalus
ater. This wide-ranging species will likely be the source of many
more fascinating discoveries.

Literature Cited
Duméril, A. 1856. Descriptions des Reptiles Nouveaux et Imparfaitement

Connus de la Collection du Museum d’Histoire Naturelle et Remarques
sur la Classification et les Caracteres des Reptiles. Arch. Mus. Hist. Nat.
8:437–589.

Grismer, L.L. 2003. Amphibians and Reptiles of Baja California, including its
Pacific Islands and the Islands in the Sea of Cortés. University of California
Press, Berkeley and Los Angeles, California.

Hollingsworth, B.D. 1998. The systematics of Chuckwallas (Sauromalus) with
a phylogenetic analysis of other iguanid lizards. Herpetol. Monogr.
12:38–191.

Hollingsworth, B.D. 2004. The evolution of iguanas: An overview of rela-
tionships and a checklist of species, pp. 19–44. In: A.C. Alberts et al.
(eds.), Iguanas: Biology and Conservation. University of California Press,
Berkeley and Los Angeles, California.

International Commission of Zoological Nomenclature. 1999. International
Code of Zoological Nomenclature. 4th ed. The International Trust for
Zoological Nomenclature, London.

International Commission of Zoological Nomenclature. 2004. Opinion
2072. Euphryne obesa Baird, 1858 (currently Sauromalus obesus Reptilia,
Squamata): Proposal to give the specific name precedence over that of
Sauromalus ater Duméril, 1856 not approved. Bull. Zool. Nomencl.
61:74–75.

McDiarmid R.W., K. de Queiroz, K. Beaman, B. Crother, R. Etheridge, O.
Flores-Villela, D. Frost, L.L. Grismer, B.D. Hollingsworth, M.
Kearney, J.A. McGuire, J. Wright, G. Zug. 2002. Comment on the pro-
posed precedence of the specific name of Euphryne obesus Baird 1859 over
that of Sauromalus ater Duméril, 1856 (Reptilia, Squamata). Bull. Zool.
Nomencl. 59:45–48.

Merriam, C.H. 1979. Indian Names for Plants and Animals among Californian
and other Western North American Tribes. Ballena Press, Socorro, New
Mexico.

Montanucci R.R., H.M. Smith, K. Adler, D.L. Auth, R.W. Axtell, T.J. Case,
D. Chiszar, J.T. Collins, R. Conant, R. Murphy, K. Petren, R.C.
Stebbins. 2001. Case 3143. Euphryne obesus Baird, 1858 (Reptilia,
Squamata): Proposed precedence of the specific name over that of
Sauromalus ater Duméril, 1856. Bull. Zool. Nomencl. 58:37–40.

Pregill, G.K. and D.W. Steadman. 2004. South Pacific iguanas: Human
impacts and a new species. J. Herpetol. 38:15–21.

Shaw, C. E. 1945. The Chuckwallas, genus Sauromalus. Trans. San Diego Soc.
Nat. Hist. 10:269–306.

Chuckwallas from Isla Acatraz, Sonora represent hybrids among two
or even three species, all or some of which are probably introduced.



Euphryne obesa Baird, 1858 (currently Sauromalus obesus
Reptilia, Squamata): proposal to give the specific name
precedence over that of Sauromalus ater Duméril, 1856 not
approved

Abstract. The Commission has ruled that the priority of the
name Sauromalus ater Duméril, 1856 should be maintained.
Sauromalus ater is the senior name for the chuckwalla (family
IGUANIDAE) from the southwest of North America. A proposal
had been made to give precedence to a junior subjective syn-
onym S. obesus (Baird, 1858).

Keywords. Nomenclature; taxonomy; Reptilia; Squamata;
IGUANIDAE; Sauromalus ater; Sauromalus obesus; chuckwal-
las; southwestern North America.

Ruling
(1) The name obesa Baird, 1858 (specific name corrected

under Article 34.2 of the Code), as published in the
binomen Euphryne obesus, is not to be given priority over
Sauromalus ater Duméril, 1856, as published in the
binomen Sauromalus ater, whenever the two names are
considered to be synonyms. The Principle of Priority is
upheld and S. ater Duméril, 1856 has priority over
Euphryne obesa Baird, 1858 whenever the two names are
considered to be synonyms.

(2) The name Sauromalus Duméril, 1856 (gender: masculine),
type species by monotypy Sauromalus ater Duméril, 1856,
is hereby placed on the Official List of Generic Names in
Zoology.

(3) The following names are hereby placed on the Official List
of Specific Names in Zoology:
(a) ater Duméril, 1856, as published in the binomen
Sauromalus ater (specific name of the type species of
Sauromalus Duméril, 1856);
(b) obesa Baird, 1858, as published in the binomen
Euphryne obesus.

History of Case 3143
An application to conserve the specific name of Euphryne obesa
Baird, 1858 (specific name corrected to agree in gender with
the feminine generic name under Article 34.2 of the Code) for
the chuckwalla (family IGUANIDAE) from the southwest of
North America by giving it precedence over its junior subjec-
tive synonym Sauromalus ater Duméril, 1856 was received from
Richard R. Montanucci (Clemson University, South Carolina),
Hobart M. Smith and David Chiszar (University of Colorado),
Kraig Adler (Cornell University, Ithaca, New York), David L.
Auth (University of Florida, Gainesville), Ralph W. Axtell
(Southern Illinois University, Edwardsville), Ted J. Case

(University of California at San Diego), Joseph T. Collins (The
Center for North American Amphibians and Reptiles, Lawrence,
Kansas), Roger Conant (Albuquerque, New Mexico), Robert
Murphy (Royal Ontario Museum, Ontario, Canada), Kenneth
Petren (University of Cincinnati, Ohio) & Robert C. Stebbins
(Kensington, California) on 10 September 1999. After corre-
spondence the case was published in BZN 58: 37-40 (March
2001). The title, abstract and keywords of the case were pub-
lished on the Commission’s website. Comments opposing the
application were published in BZN 58: 307-308; BZN 59: 45-
48 and 205. Comments in support of the application were
published in BZN 58: 229; 307-308.

Decision of the Commission
On 1 December 2002 the members of the Commission were
invited to vote on the proposals published in BZN 58: 39. At
the close of the voting period on 1 March 2003 the votes were
as follows: 12 Commissioners voted FOR the proposals, 12
Commissioners (Alonso-Zarazaga, Bouchet, Brothers, Calder,
Halliday, Kraus, Lamas, Macpherson, Minelli, Patterson,
Rosenberg and van Tol) voted AGAINST, no votes were
received from Cogger, Dupuis and Mahnert. Ng was on leave
of absence.

Voting against, Alonso-Zarazaga commented that stability
is not better achieved by reversing priority. A junior name
should not be given precedence because of preference by a par-
ticular school, or as a result of the publication capacity by a
given set of researchers. Also voting against, Halliday com-
mented that the case rests on two arguments. First, that there
is uncertainty surrounding the type locality of S. ater. This is
irrelevant to the nomenclatural issue. Second, it is argued that
S. obesus should be preferred because it is used in a greater num-
ber of papers than S. ater. There is no Article in the Code that
invites the use of this argument, nor do the authors invoke any
particular Article to support their case. The nearest relevant
Article would be 23.9.3, however, both S. ater and S. obesus
have been in continuous use for over 100 years. Therefore, the
Principle of Priority should be upheld and the proposals should
be rejected.

Original References
The following are the original references to the names placed
on Official Lists by the ruling given in the present Opinion:

ater, Sauromalus, Duméril, 1856, Archives du Muséum d’Histoire
Naturelle, Paris, 8: 536.
obesa, Euphryne, Baird, 1858, Proceedings of the Academy of
Natural Sciences of Philadelphia, 10: 253.
Sauromalus Duméril, 1856, Archives du Muséum d’Histoire
Naturelle, Paris, 8: 536.

86 IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 OPINION 2072 (CASE 3143)

OPINION 2072 (Case 3143)




