PaleoBios,  Volume 15,  Number 2,  Pages 18-26, May 24,1993
Fossil Lizards from the Elsinore Fault Zone, Riverside County, California
Christopher J. Bell
Museum of Paleontology and Department of Integrative Biology,
University of California, Berkeley, CA 94720
INTRODUCTION
Recent salvage and mitigation efforts
conducted by the San Bernardino County Museum
Paleontologic Resource Assessment Program near
Murrieta, Riverside County, California produced a
significant number of fossil vertebrate remains
from sediments mapped by Kennedy (1977) as an
unnamed sandstone and conglomerate unit.
Kennedy (1977) indicates that this unit
uncomformably underlies the Pauba Formation
and may overlie the Temecula Arkose in the
Elsinore Fault Zone. A Pliocene age is assigned to
the Temecula Arkose based on the presence of
mammalian taxa indicative of the Blancan North
American Land Mammal Age (Golz et al., 1977;
Reynolds and Reynolds, 1993). Fossil vertebrates
have been reported from the Pauba Formation
(Mann, 1955; Reynolds and Reynolds, 1990b;
Bowden and Scott, 1992) and the unnamed
sandstone (Reynolds and Reynolds, 1990a;
Reynolds et al., 1990,1991; Scott and Cox, 1993).
Reynolds and Reynolds (1990a) and Reynolds
et al. (1991) tentatively proposed that an ash layer
present in the unnamed sandstone is
contemporaneous with the Bishop tuff dated at
700,000 yr BP (Dalrymple et al., 1965; Merriam and
Bischoff, 1975). Suggestions of a late Irvingtonian
age for the unnamed sandstone (Reynolds et al.,
1990, 1991) were based on this presumed ash
correlation and on the supposed presence of the
rodent Cleihrionomys. The ash from the unnamed
sandstone, however, remains undated and has not
conclusively been shown to correlate with the
Bishop tuff. In addition, specimens originally
identified as Cleihrionomys were recently
reexamined and determined to belong to the
species Mimomys (Ophiomys) parvus (C. A.
Repenning, pers. comm., 1993) of Blancan V age
(Repenning et al., 1990). A detailed review of the
biostratigraphy of the unnamed sandstone
indicates a late Blancan and/or early Irvingtonian
age for the sediments as a whole, however
individual vertebrate fossil collection localities
sampled from the unit appear to contain faunas of
one age or the other (Scott and Cox, 1993).
The lizard fossils reported here are from the
Morrison Homes parcel in the unnamed sandstone
(County of Riverside Tract 23110, accessioned
under San Bernardino County Museum # A2535).
A single tooth of the Pliocene rabbit Hypolagus was
recovered from this parcel, but appears to be
reworked (Scott and Cox, 1993). Apart from this,
no Blancan indicator taxa are known from the
unnamed sandstone at Morrison Homes.
A better understanding of the stratigraphic
relationships within and among the geologic units
along the Elsinore Fault Zone is necessary to
clarify the relationships of the recovered faunas,
and this report is a preliminary step towards
building an understanding of the herpetofaunas
from the region.
SYSTEMATIC PALEONTOLOGY
Class Reptilia Laurenti, 1768
Order Squamata Oppel, 1811
Suborder Sauria McCartney, 1802
Family Phrynosomatidae Fitzinger, 1843
Genus Phrynosoma Wiegmann, 1828
Phrynosoma coronatum (Blainville, 1835)
Referred Specimens: A2535-0257, left squamosal.
Description: This single specimen is assigned to
species based upon the diagnostic features of the
squamosal. There are two primary horns present,
the posterior larger than the anterior. The two
horns are connected at their base. Two accessory
horns are also present, one positioned posterior
and dorsal to the base of the posterior primary
horn, the second positioned dorsal to the junction
of the bases of the two primary horns. Although
the squamosal was not discussed as a diagnostic
element by Presch (1969) or Montanucci (1987),
Norell (1989) demonstrated that the horn
morphology of this bone may be used to
distinguish fossil and living species of the genus.
The number of squamosal horns varies in the 12
living species recognized by Montanucci (1987)
and among fossil species preserving squamosals.
P. solare and P. josecitensis have 4; P. ditmarsi and P.
modestum have 3 or 4; P. anzaense, P. braconnieri, P.
cornutum, P. mcallii, P. orbiculare, and P. platyrhinos
have 3; P. coronatum and P. douglassti have 2 or 3;
P. asio has 2; P. taurus has 1 enlarged horn
(Brattstrom, 1955; Presch, 1969; Montanucci, 1987;
in New Additions to the Pleistocene Vertebrate Record of California (R. G. Dundas and D. J. Long, eds.), PaleoBios v.15.
Bell
Fossil Lizards from the Eisinore Fault Zone
Page 19
Norell, 1989). The squamosal horn patterns of the
extinct species P. adinognathus (Rickart, 1976) and
P. holmani (Eshelman, 1975; Van Devender and
Eshelman, 1979) are unknown. Two forms, P.
cerroense and P. boucardii, not included in
Montanucci's (1987) treatment were recognized by
Presch (1969). The former is an endemic species
(closely related to P. coronation) on Cedros Island
off the west coast of Baja California, and has 3
squamosal horns, the latter has been synonymized
under P. orbiculare (Montanucci, 1979). P. cerroense
was not included in Norell's (1989) analysis of
squamosal horn, morphology, and specimens were
not available for comparisons with the Morrison
Homes fossil. In P. asio, the two squamosal horn
bases are separate and an accessory horn, when
present, is located at the anterior base of the
anterior horn. The horns of P. douglassii are not as
large as the horns in the Morrison Homes
specimen.
The presence of 2 primary squamosal horns
and the relative position of these and the accessory
horns on the fossil are the characters used to
identify the specimen to P. coronation. This species
lives in the Murrieta area today (Stebbins, 1985).
The phylogenetic reconstructions of Phrynosoma by
Presch (1969) and Montanucci (1987) both place P.
orbiculare as the most primitive living member of
the genus, with P. coronatum or its sister species
being an early derivitive form which gave rise in
the Pliocene and Pleistocene to the more xeric
adapted species P. cornutum,P. mcallii,P.
modestum, P. platyrhinos, and P. solare. Although P.
coronatum is considered to be an early derivation
within the genus, the fossil record for this species
is extremely limited. P. coronatum is known from
late Pleistocene/early Holocene deposits at
Rancho La Brea and Maricopa, and from
?Irvingtonian to late Pleistocene sediments in the
Emery Borrow Pit in Orange County, California
(Brattstrom, 1953; Jefferson, 1991). This specimen
from Morrison Homes represents the earliest
known fossil of this species.
Phrynosoma sp.
Referred Specimens: A2535-0254, A2535-0838c,
right maxillae; A2535-0255, right maxilla
fragment; A2535-0253, left maxilla fragment;
A2535-0256, left squamosal fragment.
Description: The dorsal portion of the maxillae of
Phrynosoma species typically show a narrow,
dorsally projecting, anteriorly directed ramus. The
crowns of the posterior teeth of Phrynosoma are
typically simple, blunt, and peglike, but may be
tricuspid with very small secondary cusps
(Etheridge and de Queiroz, 1988). The fossil
maxillae above show the typical morphological
characters for the genus.
Robinson and Van Devender (1973) provide a
brief discussion of the morphology of the maxillae
of seven species of Phrynosoma. They use a
combination of total maxillary tooth space counts
and general morphology to distinguish some
species. They note a prominent ridge on the labial
surface of the maxilla of P. coronatum, but do not
comment on the presence or absence of this feature
in other species. In order to determine whether
this character remains valid with a larger sample
size and across taxa, I examined 9 additional
specimens of P. coronatum and available specimens
of other species (Figure 1, Table 1). The ridge is
strongly developed to moderately well developed
in specimens of P. coronatum, P. platyrhinos, and P.
solare, and is weakly developed in some specimens
of P. cornutum, P. coronatum, and P. solare. No ridge
was found on available specimens of P. douglassii.
Table 1 also provides total tooth space counts
of examined specimens and the range for tooth
spaces is expanded for 3 species: P. cornutum, P.
coronatum, and P. platyrhinos (Table 2). I found no
consistently reliable means of distinguishing
isolated maxillae of all species of Phrynosoma,
although the extremely reduced dentition of P.
solare noted by Robinson and Van Devender (1973)
Figure 1. Left maxilla of two modern Phrynosoma
solare showing the weak (A) and strong (B)
development of a ridge on the labial surface. Scale
bar = 1 mm.
Page 20
Fossil Lizards from the Elsinore Fault Zone
Bell
Table 1. Total maxillary tooth space counts for specimens of five species of Phrynosoma housed in the
UCMP collections. The relative development of a ridge on the labial surface of the maxilla is noted,
rt. = right; It. = left; n.a. = not observed.
Species	Specimen #	Total tooth	Development of
		spaces	labial ridge
P. cornutum	118979	12	weak
	118980	14	weak
	137775	14	n.a.
	137776	14	weak
	137779	16	weak
	137782	19 rt., 16 It.	absent
P. coronatum	117136	14	weak
	117165	14	weak
	117164	15	weak
	118982	16	weak
	118981	17	weak
	137781	17	moderate
	123059	19	moderate
P. douglassii	118983	17	absent
	137791	19	absent
P. platyrhinos	117137	13	strong
	113138	16	strong
	85186	17	n.a.
	118978	17	moderate
P. solare	137783	15	strong
	137777	16	strong
	137785	16	strong
	137784	17	weak
is present in all specimens of this species I
examined, and is probably a taxonomically useful
character.
Only the anterior two thirds or so of A2535-
0256 is preserved and does not display any
characters which may be used to definitively place
it within any species of Phrynosoma. There are two
horns preserved, the anterior horn being the
smaller and very reduced in size. The posterior
preserved horn is also quite small and the bases of
the two horns do not connect.
There are three species of horned lizards living
in California, P. coronatum, P. mcallii, and P.
platyrhinos, but only P. coronatum lives in the
Murrieta area today (Stebbins, 1985). The extinct
species P. anzaense is known only from the Palm
Springs Formation in the Anza Borrego Desert
(Norell, 1989). Phrynosoma fossils are relatively
common in fossil lizard faunas in the southwestern
United States (Mead and Bell, in press; Jefferson,
1991).
BeU
Fossil Lizards from the Elsinore Fault Zone
Page 21
Table 2. Summary table of total maxillary tooth space counts for seven species of Phrynosoma. Mean
dumber and observed range of total tooth spaces, and number of specimens examined (N) are provided,
h.a. = no specimens observed; R&VD = data from Robinson and Van Devender (1973); Bell = data
summarized from Table 1.
Species	Mean total tooth spaces	Observed range	N
P. cornutum R&VD BeU	14 15	12-18 12-19	15 6
P. coronatum R&VD BeU	17 16	17 14-19	2 7
P. douglassii R&VD BeU	17.3 18	13-23 17-19	47 2
P. mcallii R&VD BeU	14 n.a.	14 n.a.	2 n.a.
P. modestum R&VD BeU	17 n.a.	16-18 n.a.	6 n.a.
P. platyrhinos R&VD BeU	14 15.75	12-16 13-17	28 4
P. solare R&VD Bell	14.3 16	12-17 15-17	22 4
Sceloporine, sp. indet.
(sensu Etheridge and de Queiroz, 1988)
Referred Specimens: A2535-0287, A2535-0838b,
right maxillae; A2535-0245, A2535-0248, left
maxilla fragments; A2535-0250, right dentary;
A2535-0246, left dentary; A2535-0247, 2 left
dentary fragments; A2535-0249, left dentary
fragment; A2535-0430b, 2 left dentary fragments.
Description: The extant Phrynosomatids (sensu
Frost and Etheridge, 1989) can be divided into four
generic groups: 1) Pertrosaurus group, 2) Sator -
Sceloporus - Urosaurus - Uta group (the "Sceloporus
group"), 3) sand lizard group including
Callisaurus, Cophosaurus, Holbrookia, and Uma, and
4) Phrynosoma group (Etheridge and de Queiroz,
1988). The problems of distinguishing isolated
skeletal elements from taxa within a group are
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Fossil Lizards from the Elsinore Fault Zone
Bell
discussed elsewhere (see Etheridge, 1964; Larsen
and Tanner, 1974; Gauthier, 1982; Wellstead, 1982;
Norell, 1989). The general dental characteristics of
each group are presented by Norell (1989), and the
specimens recovered from the Morrison Homes
parcel most closely resemble the "Sceloporus
group" in general morphology. The teeth are
tricuspid and high-crowned with expanded bases.
The teeth of some specimens have well defined
cusps, in others the lateral cusps are merely
weakly developed shoulders on the edges of the
crown. All the specimens here are of small sized
lizards within the size range of Urosaurus, Ufa and
the smaller species of Sceloporus. Representatives
of all three of these genera live in the Murrieta area
today (Stebbins, 1985). Sceloporines are an
important component of Pleistocene
herpetofaunas throughout the southwestern U.S.
(Mead and Bell, in press; Jefferson, 1991).
Family Teiidae Gray, 1827
Genus Cnemidophorus Wagler, 1830
ct. Cnemidophorus sp.
Referred Specimens: A2535-0267a, A2535-0267b,
A2535-0268, right maxillae; A2535-0270, right
maxilla fragment; A2535-0269, 2 right maxilla
fragments; A2535-0261, A2535-0262, A2535-0263,
left maxillae; A2535-0265, A2535-0266, left maxilla
fragments; A2535-0264, 2 left maxilla fragments;
A2535-0156b, 2 right dentaries; A2535-0280,5 right
dentaries; A2535-0279, 2 right dentaries; A2535-
0278, right dentary; A2535-0281, 2 right dentary
fragments; A2535-0271, A2535-0272, A2535-0273,
A2535-0274, A2535-0275, A2535-0276, left
dentaries; A2535-0277, 3 left dentaries; A2535-
0156c, left dentary fragment; A2535-0282, A2535-
0283, frontal; A2535-0284, frontal fragment;
A2535-0285, left quadrate.
Descripton: Teeth of Cnemidophorus are
asymmetrically bicuspate, with an anteriorly
directed smaller cusp. The dorsal portion of the
maxilla forms an anteroposteriorly broad-based
triangle which displays no distinct dorsal ramus.
The Meckelian canal of the dentary is open
ventrally for its entire length. The frontal has a
rugose dorsal surface and three anterior processes,
the longest in the middle for insertion between the
nasals. There is no pineal foramen. The frontal
narrows posterior to the mid point, but widens to
reach its greatest width at the posterior margin
where it contacts the parietal. Mead (1988)
demonstrates the potential for using quadrates to
distinguish lizard taxa and the quadrate of teiids is
unlike that of any other North American lizards I
examined. The lateral border is slightly expanded
and strongly recurved, forming an anterior
tympanic recess (Fisher and Tanner, 1970). There
are several extant species of Cnemidophorus in
western North America (Stebbins, 1985) and
individual skeletal elements cannot be reliably
identified to the specific level. In addition, Presch
(1974) found that there were no significant
osteological differences between Cnemidophorus
and Ameiva. These two genera can be
distinguished from Kentropyx by their concave
parietal-frontal roof (Presch, 1974). Because these
specimens could potentially represent Ameiva, they
are only tentatively referred to Cnemidophorus, and
are not assigned with certainty. Although the
specimens are most likely from the more northern
genus Cnemidophorus, it is possible that the
southern Ameiva may have ranged further North
during Irvingtonian time. There are two extant
species of Cnemidophorus in California, C.
hyperythrus and C. tigris, and both occur in the
Murrieta area (Stebbins, 1985). Fossil specimens of
Cnemidophorus have been recovered from
numerous Pleistocene localities in the
southwestern United States (Mead and Bell, in
press; Jefferson, 1991).
Family Scincidae Gray, 1825
Genus Eumeees Wiegmann, 1834
Eumeces sp.
Referred Specimens: A2535-0259, A2535-0260, left
dentaries; A2535-0709b, left dentary fragment.
Description: Posteriorly, the Meckelian groove in
the dentary of Eumeces is broadly open and
directed lingually. The groove narrows and
becomes ventrally directed as it nears the
symphysis. The teeth are unicuspate, generally
closely and regularly spaced, with lingually
concave, striated crowns, of a uniform height
above the dentary parapet (Estes, 1963; Norell,
1989). Individual skeletal elements of Eumeces can
be extremely difficult to distinguish at the species
level (Estes, 1963; Nash and Tanner, 1970; Norell,
1989) and no characters have been found to
identify these specimens beyond generic rank.
There are two species extant in California, E.
gilberti and E. skiltonianus, and both occur in the
general region of the Morrison Homes deposits
(Stebbins, 1985). The fossil specimens are relatively
small and are within the size range of a young E.
Bell
Fossil Lizards from the Elsinore Fault Zone
Page 23
gilberti or of an adult E. skiltonianus. Eutneces is a
fairly common component of fossil lizard faunas
in California (Jefferson, 1991; Norell, 1989).
Family Anguidae Gray, 1825
Subfamily Gerrhonotinae Tihen, 1949
gen. et sp. indet.
Referred Specimens: A2535-0838d, A2535-0838e,
right dentaries; A2535-0838f, left dentary; A2535-
0838g, frontal.
Description: The difficulties in assigning
gerrhonotine fossil elements to genus or species
are discussed at length by Gauthier (1982) and
Good (1987,1988). The dental characteristics listed
by Gauthier (1982) as diagnostic for Anguidae are
present in these dentary specimens. These include
chisel-shaped teeth which form an inwardly
pointing V in occlusal view, with striae on the
medial face of the crown. The Gerrhonotinae is
diagnosed by only two character states: elongate
supratemporals and fused, hourglass shaped
frontals (Good, 1988). The dentaries above are
assigned to this subfamily based on their
association with the frontal. Identification beyond
the subfamily is not possible based on the material
preserved. The only extant gerrhonotine in the
Murrieta area is Elgaria multicarinata (Stebbins,
1985). Fossil gerrhonotines are fairly common in
California (Jefferson, 1991; Good, 1988).
Subfamily Anniellinae Nopsca, 1928
Genus Anniella Gray, 1852
Anniella sp.
Referred Specimens: A2535-0430c, 2 dorsal
vertebrae; A2535-0430d, 3 dorsal vertebrae; A2535-
0709c, 2 anterior dorsal vertebrae; A2535-0840b, 1
dorsal vertebra; A2535-0840c, 1 dorsal vertebra.
Description: The anguimorphan affinities of the
osteology of Anniella are discussed by Gauthier
(1980, 1982). There are two extant species of
Anniella, but there are no characteristics of isolated
vertebrae which may serve to distinguish them
(Gauthier, 1980). Members of the genus Anniella
are small, fossorial lizards whose modern
distribution includes coastal and near-coastal
California and Baja California del Norte, Mexico
(Stebbins, 1985). Anniella fossils were recovered
from Qarendonian (Miocene) sediments in Contra
Costa County, California (Gauthier, 1980) and
Reynolds et al. (1990, 1991) include Anniella in
faunal lists from other localities within the
unnamed sandstone. The larger, extinct
Apodosauriscus from the Early Eocene of
Sweetwater County, Wyoming (Gauthier, 1982) is
the only other member of the Anniellinae, and is
known only from the type locality.
COMPARISON OF FAUNA
The Plio-Pleistocene Palm Springs Formation
in the Anza Borrego Desert (Norell, 1989)
produced the nearest roughly contemporaneous
fossil lizard fauna. Taken as a whole, the Morrison
Homes and Anza Borrego lizard faunas are similar
in some respects, yet differ in a few significant
ways. Both include Phrynosoma (though different
species), Eutneces, a teiid (Atneiva or Cnemidophorus)
and indeterminate sceloporine and gerrhonotine
taxa. Although no extinct taxa are recognizable
among the Morrison Homes lizards, the Anza
Borrego Fauna includes several extinct taxa,
including the iguanid Putnilia novaceki*, the
crotaphytid Gatnbelia corona, and the xantusiid
Xantusia downsi* (the asterisk denotes a
metaspecies, sensu Norell, 1989).
There is some faunal evidence suggesting that
the Morrison Homes lizards were living in
relatively more mesic conditions than found at
Anza Borrego. Two taxa are particularly
suggestive. The desert iguana, Dipsosaurus dorsalis,
from Anza Borrego is today a desert dwelling
lizard with a high thermal tolerance and a
preferred body temperature (38.5°C) near the
maximum level tolerated by Anniella (Miller, 1944;
DeWitt, 1967). The two taxa are currently almost
entirely allopatric, although Klauber (1932) reports
Anniella from the base of the desert foothills in
eastern San Diego County, in possible association
with Dipsosaurus dorsalis. The two taxa are not
found in association in the fossil record. Both
genera favor sandy substrates, but the distribution
of Anniella is at least in part controlled by soil
moisture content (Stebbins, 1985; Norris, 1953;
Miller, 1944).
The other lizard taxa from the two faunas do
not provide much information regarding
paleoenvironments at the two localities because
they are extinct, are relatively cosmopolitan taxa
(eg: Cnemidophorus), or cannot be identified to a
level at which ecological information can be
inferred.
Comparisons of the faunas are hindered by the
lack of tight chronological control in the unnamed
sandstone deposits. An examination of the
stratigraphic distributions of the lizard taxa in the
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Fossil Lizards from the Elsmore Fault Zone
Bell
Palm Springs Formation (Norell, 1989-27) indicates
that some taxonomic changes took place through
the depositional sequence. Norell (1989) does not
provide stratigraphic data for Gambelia corona,
Phrynosoma, or the gerrhonotine, but an increase in
sceloporine taxa concurrent with the
disappearance of Dtpsosaurus and Putnilia just
before the Plio-Pleistocene boundary is evident.
Xantusia is present in both the Blancan and
Irvingtonian components of the Palm Springs
Formation, but is found in greater abundance in
the Irvingtonian. The teiid and Eutneces are present
fairly consistently throughout the section. If an
Irvingtonian age for the Morrison Homes parcel is
correct, then this fauna postdates the
disappearance of Dipsosaurus from the Anza
Borrego locality and indicates a greater taxonomic
similarity between the two faunas. This may
suggest that during the late Pliocene and early
Pleistocene the two regions were not as
significantly segregated environmentally as they
are today.
The Soboba fossil flora from near San Jacinto,
California (North and East of the Morrison Homes
project area) is roughly contemporaneous with the
Morrison Homes deposits. Analysis of this fossil
flora suggests an increased effective precipitation
in the region at the time, with a slightly lower
mean annual temperature, but a seasonality
similar to that of today (Axelrod, 1966).
The two faunas suggest a modernization of the
lizard fauna of southern California (at the generic
and subfamilial level) by the beginning of the
Pleistocene, and support the hypothesis that the
squama te faunas in this region have a long history
essentially in place as they are today (Savage, 1960;
Norell, 1989).
ACKNOWLEDGEMENTS
I thank Robert E. Reynolds, Richard L.
Reynolds, Alois Pajak, Charles Repenning and
especially Eric Scott for many enlightening
discussions regarding the faunas from the
Murrieta area and the geology and chronology of
the unnamed sandstone. Kathleen Springer and
Robert E. Reynolds provided access to the
specimens in their care. Scott Springer provided
help in synthesizing locality information and
Mamie Crook curated the lizard fossils. Special
thanks to J. Howard Hutchison for preparing the
illustrations. Many helpful comments on an early
version of this paper were provided by Drs. J.
Howard Hutchison and Jim I. Mead. This is
contribution #1601 from the University of
California Museum of Paleonotology.
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Fossil Lizards from the Elsinore Fault Zone
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