This may be helpful:
TRANSACTIONS OF THE SAN DIEGO SOCIETY OF NATURAL HISTORY
Volume 21 Number 11 pp. 167-202 5 December 1986
The evolution of helodermatid squamates, with description of a
new taxon and an overview of Varanoidea.
Pregill et al.
http://www.archive.org/stream/transacti ... d_djvu.txt
"McDowell and Bogert (1954) were the first to place helodermatids in a systematic
framework that combined them with Varanus and Lanthanotus as a group distinct
from other extant anguimorph squamates. McDowell and Bogert ( 1954) altered Romer's
(1956) classification by removing Lanthanotus from Helodermatidae and placing it
closer to Varanidae. They assigned Helodermatidae to Varanoidea instead of Anguioi-
dea (Diploglossa), and recommended the designation "Varanoidea" over "Platynota."
Hence, Varanoidea included Varanidae, Lanthanotidae, Helodermatidae, and the ex-
tinct families Dolichosauridae, "Aigialosauridae" and Mosasauridae. With some mod-
ifications, Rieppel (1 980a) corroborated their conclusions, but used the name Platynota
for this taxon. In that paper and in a companion study on the postcranial osteology of
Lanthanotus (Rieppel 1980Z?), he regarded the three extant families as a monophyletic
assemblage within the more inclusive Platynota. Elsewhere, Gauthier (1982) discussed
Varanoidea with reference to the articulation between the dentary and post-dentary
bones, a character complex providing insight into anguimorph phylogeny.
The evolutionary history becomes cluttered, however, in consideration of several
fossils from the late Cretaceous of North America and Asia, and the Paleogene of
Europe that can be interpreted as at or near the base of helodermatid and varanoid
phylogeny. For example, Estes (1964) proposed Parasaniwidae to accommodate two
taxa from the late Cretaceous Lance Formation of Wyoming: Parasaniwa wyomingensis
Gilmore and Paraderma bogerti Estes. More recently Estes (1983a) synonymized Par-
asaniwidae with the more inclusive designation Necrosauridae Hoffstetter, a family
constituted by Estes to include Necrosaurus, Parasaniwa, Eosaniwa, Provaranasaurus,
Paraderma bogerti is in ways similar to necrosaurids but remains even more
problematical, primarily because it is so poorly represented by fossils. We regard it as
the earliest known member of Helodermatidae.
Borsuk-Bialynicka (1984) described several new anguimorphs collected from Up-
per Cretaceous deposits of Mongolia. Two of these, Proplatynotia longirostrata and
Gobidenna pulchrum, she referred to as "necrosaurian grade lizards," primitive platy-
notans whose relationships among anguimorphs remain problematic. Furthermore,
Gobidenna possesses a few features described as Hcloderma-\ike. Besides these taxa,
Borsuk-Bialynicka (1984) reported the first known remains of a fossil lanthanotine,
Cherminotus longifrons, a new varanine, Saniwides mongoliensis, as well as additional
material of the enigmatic varanid Tel masaurus granger! Gilmore. These new varanoids,
though difficult to place unambiguously, do suggest that the lineages represented by
Heloderma, Lanthanotus and Varanus are of considerable antiquity. The incomplete
nature of the Cretaceous fossils makes their early history difficult to resolve.
The discovery of these new helodermatid and varanid fossils, and our interpretation
of novel characters, inspired this review of helodermatid phylogeny. The paper is
organized into three parts. Part I reviews the diagnosis of Varanoidea in an attempt to
clarify those characters that have been troublesome and ambiguous. We then (Part II)
describe the new helodermatid fossils from the early Miocene of Nebraska, and discuss
another from the latest Paleocene of Wyoming. In light of these we reinterpret Helo-
derma texanum and those fossils previously assigned to H. matthewi in a discussion
of the diagnostic features of Helodermatidae. A phylogeny based on this evidence is
presented. Having this background, together with information from Part III on their
natural history, we propose that the principal specialization of helodermatid squamates
is a distinctive feeding mode. This is readily observed in the stout jaws and sturdily
constructed skull architecture designed for crushing large prey. Venom delivery occurs
in the more derived species as a superimposed specialization. For these reasons we will
argue for the inclusion of Paraderma bogerti in Helodermatidae. We conclude our
presentation of helodermatid phylogeny based on morphology by demonstrating (Part
III) some concomitant associations with the natural history, behavior, and feeding
biology of captive and wild animals."
On another note, I have heard of them being found in fish traps set in rice paddies at the edge of forest and in recently cleared forest plots. Cool critters.