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367
DISTRIBUTION AND BIOCHRONOLOGY OF CAMARASAURIS
New Mexico Geological Society, 56th Field Conference Guidebook, Geology of the Chama Basin, 2005, p. 367-379.
INTRODUCTION
The stratigraphic correlation of the Morrison Formation (Late
Jurassic) has been studied for a long time (e.g., Owen et al., 1989;
Fishman et al., 1995; Demko et al. 1996; Turner and Peterson,
1999), and the presence of consistent regional isochronous marker
beds throughout Utah, Colorado, Wyoming, New Mexico, south-
ern Montana, northwestern Oklahoma, eastern South Dakota,
and northeastern Arizona is still debated. The main reasons for
uncertain stratigraphic correlation are: (1) relatively complicated
lithology, including various facies of fluvial and lacustrine sedi-
ments (e.g., Foster, 2003, tables 1, 2) and (2) physically isolated
exposures in a number of different plateaus and drainage basins
(Fig. 1).
The Morrison Formation is remarkably fossiliferious and, in
particular, it is known to contain abundant dinosaur remains.
Therefore, information on the relative age of the Morrison can
provide a better understanding of: (1) species occurrences (e.g.,
biochronology, paleobiogeography), (2) taxonomy (e.g., identifi-
cation of species), and (3) evolution (e.g., tempo of morphological
change) of some dinosaur taxa.
Turner and Peterson (1999) first proposed the biostratigraphy
of various dinosaurian taxa from the Morrison Formation. Their
correlation is mostly based on mineralogy and petrology, primar-
ily, the clay change. Above the clay change, claystones and mud-
stones contain abundant smectic-rich clays, altered from volcanic
ash and characterized by the absence of popcorn texture in soils
(Owen et al., 1989; Turner and Peterson, 1999). Significantly, the
clay change is thought to separate the Upper Morrison Formation
into the lower and upper members (Turner and Peterson, 1999).
Although Trujillo (2002, 2003) suggested that no significant
differences in the smectitic and non-smectic mudstone based on
X-ray diffraction are detectable in the Morrison Formation, her
data are primarily from the Wyoming area and do not cover the
entire Morrison Formation in the Rocky mountain region. In fact,
the clay change is thought to be present throughout the Colorado
Plateau (including Garden Park area), including the Dinosaur
National Monument Area, and in central, southern, and west-
ern Wyoming (e.g., Como Bluff, Thermopolis area) (Turner and
Peterson, personal communication, 2002), but is perhaps absent in
the eastern Wyoming and Black Hills (South Dakota) area (Turner
and Peterson, 1999). Therefore, in this study, I excluded data from
the eastern Wyoming and the Black Hills area for discussions of
the distribution of Camarasaurus. However, using clay minerals
is the only comprehensive method for stratigraphic correlation,
although, geographically, the feature is limited in the Rocky Moun-
tain region. The clay change can allow us to compare and correlate
biostratigraphy of the Morrison fossil taxa as in other previous
DISTRIBUTION AND BIOCHRONOLOGY OF CAMARASAURUS
(DINOSAURIA, SAUROPODA) FROM THE JURASSIC MORRISON
FORMATION OF THE ROCKY MOUNTAIN REGION
TAKEHITO IKEJIRI1,2
1Department of Geosciences, Fort Hays State University, 600 Park St., Hays, KS 67601;
2Wyoming Dinosaur Center, 110 Carter Ranch Road, Thermopolis, WY 82443
ABSTRACT.––The stratigraphic distribution of fossil remains of Camarasaurus (Dinosauria, Sauropoda) allows recognition
of five biozones in the upper Jurassic Morrison Formation: (1) no Camarasaurus Zone (early-mid Kimmeridgian), (2) Cama-
rasaurus grandis Zone (mid Kimmeridgian), (3) C. lentus Zone (late Kimmeridgian), (4) transition Zone (early Tithonian),
and (5) C. supremus Zone (Tithonian). Paleobiogeographically, C. grandis is known from south and central Wyoming, central
Colorado, and New Mexico; C. lentus occurs in Wyoming and Utah and C. supremus in south-central Colorado to western
Oklahoma. However, the geographic occurrences may only reflect stratigraphic distribution as locally appropriate beds may not
be exposed or were eroded. Camarasaurus might have a much wider distribution in the Rocky Mountain area than indicated by
its distribution of the fossil remains. Additionally, the data provide new insights into the taxonomy of Camarasaurus.
FIGURE 1. Geological features in the Rocky Mountain region and major
dinosaur quarries in the Morrison Formation. The map is modified from
King (1977, fig. 74). Areal definition of the Morrison Formation is based
on Turner and Peterson (1999).
368 IKEJIRI
studies that recognized six dinosaur biozones (Foster, 2003, fig. 6)
or four dinosaur biozones (Turner and Peterson, 1999).
In this paper, I review the stratigraphic distribution of Cama-
rasaurus (Dinosauria, Sauropoda) in the Morrison Formation
based on Turner and Peterson’s (1999) idea of stratigraphic cor-
relation of the Morrison dinosaur quarries. In Camarasaurus,
three significant features should be noted: (1) a wide geographic
distribution in the entire Rocky Mountain region, found in the
nearly entire area of Morrison outcrop, (2) a stratigraphic distri-
bution in the Morrison Formation from the upper member of the
lower Morrison to the top of the formation, and (3) perhaps, it is
the most common dinosaur in the formation. Therefore, a rela-
tively large sample size from the long vertical range in the Mor-
rison Formation allows me to establish biozones. I also examine
whether the broad geographic distribution provides enough data
to correlate stratigraphic positions among different areas of the
Morrison Formation.
Institutional Abbreviations––AMNH, American Museum of
Natural History, New York; BHI, Black Hills Institute, Hill City,
South Dakota; BYU, Earth Science Museum, Brigham Young
University, Provo, Utah; CEU, College of Eastern Utah Prehis-
toric Museum, Price; CM, Carnegie Museum of Natural History,
Pittsburgh, Pennsylvania; DMNH, Denver Museum of Natural
History (now Denver Museum of Nature and Science), Denver,
Colorado; DNM, Dinosaur National Monument, Jensen, Utah;
FHSM, Fort Hays State University, Sternberg Museum of Natu-
ral History, Hays, Kansas; FMNH, Field Museum of Natural His-
tory, Chicago, Illinois; GMNH-PV, Gunma Museum of Natural
History Vertebrate Paleontology, Gunma, Japan; KUVP, Univer-
sity of Kansas Vertebrate Paleontology, Lawrence; NMMNH,
New Mexico Museum of Natural History & Science, Albuquer-
que; OMNH, Sam Noble Oklahoma Museum of Natural History,
Norman; SDSM, South Dakota School of Mines and Technology,
Rapid City; SMA, Sauriermuseum Aathal, Aathal, Switzerland;
UMMP, University of Michigan Museum of Paleontology, Ann
Arbor; USNM, National Museum of Natural History (formerly
United State National Museum), Washington DC; UUVP, Uni-
versity of Utah Natural History, Salt Lake City; WDC, Wyoming
Dinosaur Center, Thermopolis; YPM, Yale Peabody Museum,
New Haven, Connecticut.
GEOLOGICAL SETTING
The Morrison Formation is widely distributed in the Western
Interior (Fig. 1). Although outcrops of the Morrison Formation
are present in seven states, it also extends to western Kansas,
Nebraska, North Dakota, and northern Texas in the subsurface
(Foster, 2003). Most exposures are located near the edges of the
uplift and basin areas such as the Black Hills, Big Horn Basin,
Uinta Mountains, and Front Range (Fig. 1).
The age range of the Morrison Formation is estimated as
about 140-150 Ma (Currie, 1998) or 147-155 Ma (Kowallis et
al, 1998) and the end of the Jurassic is thought to be at about
141 Ma (Bralower et al, 1990; Gradstein and Ogg, 2004). Addi-
tionally, the Morrison Formation ranges from Kimmeridgian to
Tithonian in age and, probably, the very late Oxfordian and Early
Cretaceous in some areas (Foster, 2003). Stratigraphically, the
Morrison Formation consists of the lower and upper members.
However, several Cenozoic orogenic uplifts separated the Mor-
rison into different basins (Fig. 1), and the two members tend
to have different names in each basin; e.g., the Salt Wash and
Brushy Basin members on the Colorado Plateau, the upper and
lower members in the Bighorn Basin; and the Westwater Canyon
and upper part of Brushy Basin members near the San Juan Basin
(Foster, 2003, fig. 2; Peterson and Turner-Peterson, 1987; Turner
and Peterson, 1999).
SYSTEMATIC PALEONTOLOGY
REPTILIA
DINOSAURIA
SAUROPODA
CAMARASAURIDAE Cope, 1878
CAMARASAURUS Cope, 1877a
Apatosaurus Marsh, 1877:514 (in part).
Amphicoelias Cope, 1877b:2 (in part).
Caulodon Cope, 1877c:193.
Morosaurus Marsh, 1878a:242.
Pleurocoelus Marsh, 1888:90 (in part).
Astrodon Marsh, 1896:133 (in part).
Uintasaurus Holland, 1924:119.
Camarasaurus: McIntosh 1981:12.
Cathetosaurus Jensen, 1988:121.
Camarasaurus McIntosh 1990b:348.
Camarasaurus McIntosh et al. 1996b:74.
Range––Morrison Formation (Late Kimmeridgian-Titho-
nian, Late Jurassic) in Colorado, New Mexico, Oklahoma, South
Dakota, Utah, and Wyoming.
Emended Diagnosis––Massive lower and upper jaws; mas-
sive vomer; short basipterygoid process; 12 cervical and 12 dorsal
vertebrae; bifurcated neural spines in all mid- and posterior- cer-
vical vertebrae (but variable in the anterior cervical vertebrae);
U-shaped rather than V-shaped (e.g., diplodocids) neural spines
in some dorsal vertebrae; relatively short and massive neural
spine in posterior dorsal, sacral, and proximal caudal vertebrae;
relatively short tail with about 53 caudal vertebrae; distal end of
scapular blade broadly expanded; forelimbs more slender than
hindlimb; humero-femoral length ratio ~0.77; two carpal bones
(ulnare and radiae); metacarpal III to humerus length ratio ~0.33;
pubis massive with short shaft; very slender ischium, especially
the distal end; tibio-femoral length ratio ~0.60 (McIntosh 1990a,
b; Madsen et al., 1995).
CAMARASAURUS SUPREMUS Cope, 1877a
Amphicoelias latus Cope, 1877b:4.
Caulodon diversidense Cope, 1877c:193.
Caulodon leptoganus Cope, 1877c:193.
Camarasaurus leptodirus Cope, 1879:404.
Camarasaurus supremus: Osborn and Mook 1921:262.
369
DISTRIBUTION AND BIOCHRONOLOGY OF CAMARASAURIS
Holotype––AMNH 5760, composite of probably two (?) skel-
etons from near Cope’s Nipple, Garden Park, Colorado, very top
of the Morrison Formation (Carpenter, 1998; McIntosh, 1998;
Turner and Peterson, 1999).
Topotype––AMNH 5761, including at least a few partial skel-
etons from near Cope’s Nipple.
Range––Middle and upper Morrison Formation (Late Kim-
meridgian- Tithonian, Late Jurassic) in south-central and, pos-
sibly, southeastern Colorado and northwestern Oklahoma.
Referred specimens––DMNH 27228, axis, cervical vertebra
no. 4 (?), dorsal vertebra no. 3 (?), caudal vertebrae no. 1 and 3
(?), pubis from near Cope’s Nipple (Carpenter, 1998).
Emended Diagnosis––A species of Camarasaurus with a
large body, relatively short neural arch in dorsal vertebrae from
no. 3 to 8, T-shaped neural spine in caudal vertebrae from no. 1
to 5 or 6.
CAMARASAURUS GRANDIS (Marsh, 1877)
Apatosaurus Marsh, 1877:515 (in part).
Amphicoelias Cope, 1877b:2 (in part).
Morosaurus impar Marsh, 1878a:242.
Morosaurus robustus Marsh, 1878b:414.
Pleurocoelus montanus Marsh, 1896:184.
Camarasaurus grandis: Gilmore, 1925:352.
Holotype––YPM 1901, basioccipital, several dorsal verte-
brae, partial sacrum, caudal vertebrae 1 to 27, left pectoral girdle
and forelimb elements, right scapulocoracoid, left sternal plate,
femora, tibia, fibula, ribs from Como Bluff Quarry 1, Albany
County, Wyoming.
Cotypes––All paratypes from Como Bluff Quarry 1. YPM
1900 (holotype of Morosaurus impar), sacrum; YPM 1903, cora-
coids, right scapula, left pubis, ischia, left femur; YPM 1905, a
fairly complete skull, all cervical vertebrae, most or all dorsal
vertebrae, partial sacrum (formerly YPM 1900), 12 anterior-
mid caudal vertebrae, some chevrons, coracoids, scapulae, left
humerus, right ulna, right ischium, femora, tibiae, fibulae, some
pes elements.
Range––Middle and upper lower Morrison Formation (Late
Kimmeridgian, Jurassic) in south-central Wyoming, Colorado,
and New Mexico.
Referred specimens––DMNH 2850, three mid dorsal ver-
tebrae from DMNH Quarry 3, Garden Park, Colorado, FMNH
P25118 (paratype of Morosaurus grandis), right scapulocora-
coid (= FMNH P6670) from Riggs Quarry #12, Mesa County,
Colorado. This individual includes 20 (?) presacral vertebrae and
sacrum (=FMNH P6639, 7792, 7793, 7794, 7795, 7796, 7797,
7798, 7799, 7800, 7801), but two dorsal vertebrae were exchanged
to Professor Edward L. Holt at Mesa County Junior College in
Grand Junction, Colorado in 1947 (William E. Simpson, written
communication, 2004). GMNH-PV 101, nearly complete adult
skeleton (McIntosh et al., 1996a) from just northeast of Medi-
cine Bow, Wyoming; KUVP 1354, four dorsal vertebrae from
the Freezout Hills Quarry, Wyoming; NMMNH P-21094, partial
skull and jaw, isolated teeth, mid cervical vertebra, mid- and pos-
terior dorsal vertebrae, pubis, humerus from San Ysidro Quarry,
central New Mexico; YPM 1902, ilium [same individual as YPM
1905(?)] from Como Bluff Quarry 1; YPM 1907, premaxillae,
maxillae, left frontal and parietal, postorbitals, quadrates, ptery-
goids, ectopterygoid, supraoccipital, exoccipitals, opisthotics,
right prootic, right laterosphenoid, basioccipital, basisphenoid,
parasphenoid, dentary fragment, centra and neural arches of 22
(?) caudal vertebrae, ischia from Como Bluff Quarry 3; YPM
1908 (holotype of Pleurocoelus montanus), some neural arches
and centra of disarticulated anterior (and mid-?) dorsal vertebrae,
centra of proximal caudal vertebrae, humeri, partial right femur
from Como Bluff Quarry 1.
Emended Diagnosis––A species of Camarasaurus with a tall
neural arch in dorsal vertebrae from no. 3 to 8, T-shaped neural
spine from anterior view of caudal vertebrae from no. 1 to 5 or 6.
CAMARASAURUS LENTUS (Marsh, 1889)
Morosaurus lentus Marsh, 1889:331.
Uintasaurus douglassi Holland, 1924:119.
Camarasaurus annae Ellinger, 1950:225.
Camarasaurus lentus: McIntosh 1981:12.
Camarasaurus lentus McIntosh 1990b:348.
Holotype––YPM 1910, from Quarry 13 at Como Bluff,
Albany County, Wyoming. The specimen is mounted at YPM
and consists of the jaws, partial braincase, 11 cervical vertebrae,
12 dorsal vertebrae, five sacral vertebrae except neural arch of
sacral no. 5, 14 proximal and mid-caudal vertebrae, most (?)
distal caudal vertebrae, left scapula, right coracoid, humeri, left
ulna, ilia, right pubis, left ischium, left femur, tibiae, left fibula,
left pes, many chevrons. Plaster coats most presacral vertebrae,
and neural arches of most cervical and some dorsal vertebrae are
reconstructed. The mid–section of both ilia are lengthened by
plaster.
Range––Lower-middle Upper Morrison Formation (Late
Kimmeridgian, Late Jurassic) in Wyoming, and eastern and cen-
tral Utah.
Referred specimens––CEU 1694, semi-articulated composite
(?) partial skeleton, cervical vertebrae, dorsal vertebrae, sacrum,
many caudal vertebrae, scapulae, limb elements, and pelvic bones
(this specimen may include more than one individual) from Cleve-
land Lloyd Quarry, central Utah; CM 8492, dorsal vertebrae no.
1 to 4(?); CM 11069 (holotype of Uintasaurus douglassi), four
posterior cervical vertebrae and dorsal vertebra no. 1 (McIntosh,
1981); CM 11338, nearly complete articulated juvenile skeleton;
CM 11393, skull, two mid-cervical vertebrae [no. 7 and 8 (?)
belonging to UMMP V16995 (McIntosh, 1981)], some anterior-
mid dorsal vertebrae, right forelimb, right femur, left fibula, right
scapulocoracoid, pubis, ischium, ilium, some limb elements,
some elements are still unprepared at CM, all the CM specimens
above from DNM, Utah; DNM 28, an articulated skull, axis;
DNM 975, nearly complete skull on cliff; USNM 13786, nearly
complete articulated subadult skeleton from DNM; WDC A, jaw
fragments, right quadrate, all disarticulated presacral vertebrae
except dorsal vertebra no. 11(?), sacrum, some anterior caudal
370 IKEJIRI
vertebrae, scapulocoracoids, left humerus, left ulna, radius,
ischia, pubes, femora, fibula; WDC B, braincase, jaw fragments,
right quadrate, four anterior-mid- cervical vertebrae, four anterior
and a few posterior dorsal vertebrae, sacrum, several anterior and
mid-caudal vertebrae, left scapulocoracoid, left humerus, right
ulna, right radius, pubes, ischia, and femora; indeterminate WDC
specimens, both sides of upper and lower jaws, frontal, lacrimal,
jugal, many cranial fragments, two sternal plates, two carpals,
eight metacarpals, many cervical and thoracic ribs, and chevrons
(including the first chevron). All the WDC specimens from Ther-
mopolis, central Wyoming.
Emended Diagnosis––A species of Camarasaurus with rel-
atively short, massive neural arch in anterior dorsal vertebrae
(from about no. 3 to 8); gradually expanded top of neural spine in
anterior caudal vertebrae (from about no. 1 to 5 or 6).
CAMARASAURUS LEWISI (Jensen, 1988)
Cathetosaurus lewisi Jensen, 1988:121.
Camarasaurus lewisi McIntosh et al. 1996b:74.
Holotype––BYU 9047, consisting of one tooth, cervical ver-
tebrae (nearly complete cervical vertebrae from no. 1 to 8, but
largely damaged cervical vertebrae from no. 9 to 12), dorsal ver-
tebrae from no. 8 to12, sacrum, caudal vertebrae from no. 1 to
26, 18 chevrons; right humerus, radius, ulna, distal carpal, par-
tial right manus (metacarpals I-V, ungula phalanx I-2 and II-1),
partial left ilium, left pubis, both ischia from Dominguez-Jones
Quarry, Mesa County, Colorado.
Range––Middle Upper Morrison (Late Kimmeridgian-Titho-
nian, Jurassic) in western Colorado.
Diagnosis––A species of Camarasaurus with a very deep,
narrow bifurcation of spines of presacral vertebrae persist back
from cervical vertebra no. 3 through dorsal vertebra no. 11 with a
trace showing in dorsal vertebra no. 12 (McIntosh et al., 1996b).
CAMARASAURUS sp.
Referred specimens––AMNH 690, sacrum, ilium from Bone
Cabin Quarry, Como Bluff, Wyoming; AMNH 711, scapulo-
coracoid, femur, tibia, fibula, ulna, humerus from Reed’s Quarry,
Wyoming; AMNH 823, humerus, partial left manus from Bone
Cabin Quarry, Wyoming; BHI 6200, fairly complete skull, all (?)
cervical vertebrae (unprepared), some dorsal vertebrae, femora
from Black Hills, eastern Wyoming; BYU 8967, premaxilla;
BYU 13007, atlas; BYU 16953, atlas; BYU 17465, sacrum, all the
BYU specimens from the Dry Mesa Quarry, western Colorado;
CM 584, two cervical vertebrae, eight dorsal vertebrae, 31 caudal
vertebrae, ilium, pubis, ischium, scapulocoracoid, from Sheep
Creek, Albany County, Wyoming; FHSM VP-14850 (= Cama-
rasaurus supremus?), a few posterior dorsal vertebrae, ischium,
femur, and rib fragments from Comanche National Grasslands,
Colorado; uncatalogued GMNH-PV specimens (= C. grandis?)
from near the Bone Cabin Quarry Wyoming, 10 dorsal verte-
brae, sacral vertebrae, posterior caudal vertebrae, scapula, ulna,
ilium, femur, chevron, including perhaps from a few individuals;
KUVP 129714, a few dorsal vertebrae (centra and neural arches),
sacrum, some mid caudal vertebrae, right scapula, left coracoid,
ilia, chevrons; KUVP 129716 (= C. supremus?), partial skull ele-
ments, most cervical vertebrae, all dorsal vertebrae, sacrum, most
caudal vertebrae, all limb bones, all pectoral and pelvic bones,
many ribs, chevrons, both the KUVP specimens from Black Hills,
eastern Wyoming; all OMNH specimens (= C. supremus?) from
the Kenton area, western Oklahoma, including large isolated
skeletons of OMNH 1095, mid-cervical vertebra; OMNH 1141,
braincase; OMNH 1169, right maxillary; OMNH 1173, mid cer-
vical vertebra; OMNH 1174, intercentrum of atlas; OMNH 1321,
posterior cervical vertebrae; OMNH 1324, posterior dorsal ver-
tebra; OMNH 1239, cervical centrum; OMNH 1336, posterior
dorsal vertebra; OMNH 1367, DS 1(?); OMNH 1383, mid-cervi-
cal vertebra; OMNH 1457, axial centrum; OMNH 1465, proxi-
mal caudal vertebra; OMNH juvenile elements including OMNH
1226, neural arch of cervical; OMNH 1243, posterior cervical
cenrtum; OMNH 1245, posterior cervical centrum; OMNH 1246,
cervical centrum; OMNH 1247, mid-cervical centrum; OMNH
1249, mid- or posterior cervical centrum; OMNH 1252, cervical
centrum; OMNH 1253, axial centrum; OMNH 1329, posterior
dorsal vertebra; OMNH 1262, neural arch of cervical vertebra;
OMNH 1268, neural arch of posterior cervical vertebra; OMNH
1269, neural arch of sacral vertebra; OMNH 1273, posterior cer-
vical vertebra (see list in Carpenter and McIntosh, 1994); RTMP
83.35.03, sacrum with both ilia; RTMP 83.35.04, left femur;
RTMP 83.35.05, left fibula; RTMP 83.35.06, left tibia, all RTMP
specimens from Cleveland-Lloyd Quarry; SDSM 9234, a partial
ischium; SDSM 35924, ischium, both SDSM specimens are from
western South Dakota near the Black Hills; SMA 0002, fairly
complete disarticulated skull (cast at BHI) and nearly complete
articulated postcranial skeleton from the Howe Stephens Quarry,
Big Horn County, Wyoming; UUVP 1045, anterior caudal; UUVP
1555, axis; UUVP 1859, right maxilla; UUVP 1860, right max-
illa; UUVP 1984, quadrate; UUVP 3568, braincase; UUVP 3609,
left dentary; UUVP 3610, right dentary; UUVP 3638, quadrate;
UUVP 4273, axis; UUVP 4286, braincase; UUVP 4315, mid-
caudal vertebra with chevron; UUVP 5309, sacrum; UUVP 6341,
axis; UUVP 10070, braincase; UUVP 11626, left dentary; UUVP
10795, braincases; UUVP 22940, isolated anterior caudal verte-
brae; all UUVP specimens (= C. lentus?) from Cleveland-Lloyd
Quarry, central Utah; YPM 1904 (the type of Morosaurus agilis),
originally catalogued as USNM 5384, partial cranial elements,
first three cervical vertebrae from Quarry 1 in Garden Park, Colo-
rado.
NOTES ON TAXONOMY
Camarasaurus is one of the more common dinosaurs from the
Upper Jurassic in North America. Elements from this medium-
large sized sauropod are commonly found throughout the Mor-
rison Formation. However, even though hundreds of bones of
Camarasaurus have been found, a species-level identification of
individual elements is still problematic due to several factors: (1)
a significant degree of ontogenetic change between juvenile and
adult skeletons, (2) poor understanding of sexually dimorphic
371
DISTRIBUTION AND BIOCHRONOLOGY OF CAMARASAURIS
characters, (3) a wide degree of individual morphologic variation,
and (4) lack of accurate stratigraphic correlation of the widely
distributed localities of Camarasaurus (Ikejiri, 2004b; Ikejiri et
al., in press).
A reliable species-level identification of Camarasaurus is
needed to examine the stratigraphic distributions of its species
in the Morrison Formation. The taxonomy of Camarasaurus
has been discussed previously: Ikejiri (2004b), Ikejiri et al. (in
press), Madsen et al. (1995), McIntosh (1990a), and McIntosh
et al. (1996a, b). Therefore, I briefly review the taxonomy of the
four species here. Two morphological characteristics are thought
to be significant for discussions of the taxonomy of Camarasau-
rus (Ikejiri et al, in press; McIntosh, 1990a). First, the relatively
short, massive base of the neural arches in the dorsal vertebrae of
Camarasaurus lentus (Fig. 2A) and C. supremus (Fig. 2B) can
be easily distinguished from the elevated neural peduncle in C.
grandis (Fig. 2, C) (McIntosh, 1990a). Additionally, this mor-
phology is applied to only no. 2 or 3 to 6 or 7 dorsal vertebrae, but
the posterior dorsal vertebrae are similar and are not diagnostic
enough to separate them into the three species (Ikejiri, 2004b).
Furthermore, based on four growth stages for Camarasaurus, the
diagnostic feature of C. grandis appears in post-juvenile stages
(from stage 2 to 4), but is never found in stage 1.
Second, the degree of transverse expansion of the neural spine
of the anterior caudal vertebrae can also separate Camarasaurus
lentus from C. supremus and C. grandis (Ikejiri et al., in press)
(Fig. 3). This morphology is particularly important to separate
C. lentus and C. supremus because both of these species share
the massive and relatively short base of the neural arches in the
anterior and mid-dorsal vertebrae (Fig. 2). In C. lentus, the top of
the neural spine is gradually expanded transversely (Fig. 3A-B);
however, the two latter species exhibit a T-shaped spine, charac-
terized by a rapid transverse expansion with a constricted mid-
spinal shaft (Fig. 3C,D). Generally, the different morphology is
FIGURE 2. Comparison of anterior dorsal vertebrae (no. 3?) among Camarasaurus. A, Camarasaurus lentus, WDC A (BS-346); B, C. supremus,
AMNH 5760 (D-X-132); C, C. grandis, YPM 1905. Anterior views. Scale bar = 10 cm.
372 IKEJIRI
found from the caudal vertebrae no.1 to 5 or 6, but is not apparent
in the more posterior caudal vertebrae (Ikejiri, 2004b).
The very large body size of Camarasaurus supremus is diag-
nostic with the genus (McIntosh, 1990a). However, a significant
question is whether or not C. supremus is an adult form of C.
lentus so that they are the same species. Four growth stages are
established in Camarasaurus based on a number of morphologi-
cal features (Ikejiri, 2003, 2004a, b; Ikejiri et al., in press), and
body size of individuals of relatively similar ontogenetic age can
be directly compared. Based on one of the largest individuals of
C. grandis and C. lentus, belonging to the oldest ontogenetic stage
(stage 4; see Ikejiri et al., in press), exhibits about the same body
size, and C. supremus is, at least, 20 % larger than C. grandis
and C. lentus (see also Morphological Variation and Its Relation-
ship to Stratigraphic Position in DISCUSSION). Therefore, the
possibility that C. lentus and C. grandis are the ontogenetically
younger forms of C. supremus is rejected.
Only a single specimen is known of Camarasaurus lewisi, and
this condition makes comparisons with other species or individu-
als difficult. The most diagnostic character of the species is the
bifurcated neural spines from cervical vertebra no. 3 to the last
dorsal vertebrae (McIntosh et al., 1996b). However, intraspe-
cific variation is found in the occurrence of the bifurcated neural
spines of C. lentus; e.g., the last occurrence is dorsal vertebra
FIGURE 3. Comparison of neural spines in anterior caudal vertebrae of Camarasaurus. A, Camarasaurus lentus, WDC A (BS-152); B, C. lentus (?),
UUVP 1045; C. C. grandis, YPM 1905; D, C. supremus, AMNH 5761. Posterior view. Scale bar = 10 cm. C and D modified from Ikejiri et al (in
press).
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DISTRIBUTION AND BIOCHRONOLOGY OF CAMARASAURIS
no. 6 in CM 11338 and YPM 1910 and dorsal vertebra no. 7 in
USNM 13786, and dorsal vertebra no. 8 in WDC A. Further-
more, none of the specimens of C. grandis and C. lewisi exhib-
its articulated mid- and posterior dorsal. Thus, the question still
remains whether the character is diagnostic in C. lewisi or how
much intra- and interspecific variation is present. Well developed
enthesis (ossified ligaments) in the posterior dorsal and particu-
larly the sacral vertebral regions, linking the spine of one verte-
bra with the diapophyses of the succeeding vertebra, is suggested
to be another significant character of C. lewisi (McIntosh et al.,
1996b). However, a similar enthesis is also found in the sacra of
the fully grown individuals of C. lentus (WDC A) and C. supre-
mus (AMNH 5761), suggesting this feature results from ontogeny
(Ikejiri et al., in press). Thus, the taxonomy of C. lewisi seems to
be problematic, and, perhaps, it may be a synonym of C. grandis
(see further discussion below).
RESULTS
Biostratigraphy of Camarasaurus
Turner and Peterson (1999) presented a comprehensive
study of the biostratigraphy of Morrison dinosaurs, including
the vertical distribution of the four species of Camarasaurus.
Stratigraphically, Camarasaurus is found in the upper two-thirds
of the Morrison Formation. Camarasaurus grandis is the oldest
known species of the genus, with the first appearance placed
about 20 m below the clay change, based on a correlation to the
Carnegie Quarry at Dinosaur National Monument (Turner and
Peterson, 1999, figs. 7, 10) (Fig. 4). To my knowledge, the geo-
logically youngest record of the species is NMMNH P-21094,
which is thought to occur about 20 m below the Kimmeridgian/
Tithonian boundary.
The occurrence of Camarasaurus lentus is concentrated in
the upper Kimmeridgian. All specimens seem to appear above
the highest occurrence of C. grandis, with the exception of the
holotype of C. lentus (YPM 1910), which is found about 10 m
above the lowest appearance of C. grandis (Fig. 4). The highest
occurrence of C. lentus (WDC A, B) appears slightly above the
Kimmeridgian/Tithonian boundary.
A number of large individuals of Camarasaurus supremus
from near Cope’s Nipple, Garden Park, including AMNH 5760,
5761, and DMNH 27228, come from the very upper Morrison
Formation (Carpenter, 1998; McIntosh, 1998) (Fig. 4). Many
isolated skeletons of Camarasaurus from Kenton, Oklahoma
(OMNH specimens listed in Systematic Paleontology) and FHSM
VP-14850 from the Comanche National Grasslands, southeast-
ern Colorado seem to be assignable to C. supremus. The OMNH
specimens are from near the Kimmeridgian/Tithonian boundary,
which is thought to occur slightly below the Besides Sauropod
(BS) Quarry, Thermopolis, Wyoming (Turner and Peterson,
1999). Thus, the stratigraphic occurrence of C. lentus (WDC A
and B) and C. supremus (OMNH specimens) slightly overlaps
(Fig. 4). The stratigraphic position of the FHSM specimen is
about 20 m below the Jurassic-Cretaceous boundary. According
to Turner and Peterson (1999), this would place the specimen
approximately between the BS Quarry and Cope’s Nipple, near
the very top of the upper Morrison.
BYU 9047 is the only known specimen of Camarasaurus
lewisi. Stratigraphically, the specimen was found near the clay
change about 10 m above the base of the Brushy Basin Member
(Fig. 4) (Jensen, 1988, p. 122; Turner and Peterson, 1999).
FIGURE 4. Stratigraphic distribution of Camarasaurus in the Mor-
rison Formation. Stratigraphic positions are based on Turner and
Peterson (1999) and Ikejiri (2002). Numbers for quarries; 1, Howe
Stephens Quarry, Big Horn County; 2, WPL Camarasaurus Quarry,
Albany County; 3, Reed’s Quarry 13, East Como Bluff; 4, Lindsey’s
1977 Quarry, Garden Park; 5, Dominguez-Jones Quarry, Mesa County;
6, Reed’s Quarry 1 & 3, West Como Bluff; 7, San Ysidro Camarasaur
Quarry, Sandoval County; 8, Cleveland Lloyd Quarry, Emery County; 9,
DNM, Vernal; 10, Stovall Pits near Kenton; 11, BS Quarry, Thermopolis;
12, Cope’s Nipple, Garden Park.
374 IKEJIRI
Biochronology of Camarasaurus
No Camarasaurus Zone––No record of Camarasaurus
has been reported in the lower member of the lower Morrison
Formation (early-mid Kimmeridgian in age), which is assigned
to a No Camarasaurus Zone (Fig. 5). This zone overlaps Foster’s
(2003) Zone 1 and Turner and Peterson’s (1999) Dinosaur Zone
1. For sauropods, only Haplocanthosaurus is known in this zone
(Turner and Peterson, 1999).
Camarasaurus grandis Zone––The C. grandis Zone occurs in
the upper Kimmeridgian, and this zone reflects the stratigraphic
occurrence of the species (Fig. 4). The uppermost boundary of
the C. grandis Zone is slightly higher than Foster’s (2003) Zone
4, because his definition of the zone is based on various dinosaur
taxa. Camarasaurus has a slightly different distribution. How-
ever, it should be noted that, geologically, the youngest record of
C. grandis is NMMNH P-21904 (Fig. 4) was previously assigned
to C. supremus (Rigby, 1982; Lucas and Hunt, 1985; Turner and
Peterson, 1999, appendix 3). However, I observed that an anterior
(or mid) dorsal vertebra of the specimen has a very tall base of
the neural arch with an elevated neural peduncle, which is one of
the most diagnostic characters of C. grandis (McIntosh, 1900a,
fig. 4.3; Ikejiri, 2004b). In contrast, C. supremus has a relatively
short massive base of the neural arch. The mis-identification of
the specimen may be one of the explanations for its odd occur-
rence in the C. grandis Zone.
Another significant argument about this zonation is the holo-
type of Camarasaurus lentus (YPM 1910) which is found in the
middle of the C. grandis Zone. The occurrence is obviously too
low for C. lentus. However, it should be noted that the identifica-
tion of YPM 1910 seems to be problematic, and this datum may
have to be excluded from the C. lentus Zone (See further discus-
sion in Interpretation of Taxonomy below).
Camarasaurus lentus Zone––The C. lentus Zone occurs in
the upper Kimmeridgian to the very lower Tithonian. This zona-
tion is placed above the clay change in the upper member of the
upper Morrison. A number of UUVP specimens (see Systematic
Paleontology) from the Cleveland Lloyd Quarry in central Utah
and CM 8492, 11383, and 11393 from the Carnegie Quarry in
the DNM, eastern Utah, are known in the zone (Appendix I). The
uppermost boundary is placed at the same horizon in the C. lentus
Zone, Foster’s (2003) Zone 5, and Turner and Peterson’s (1999)
Dinosaur Zone 3 (Fig. 5).
Transitional Zone––The stratigraphic distributions of Cama-
rasaurus lentus and C. supremus overlap in the upper Morrison
ranged near the Kimmeridgian/Tithonian boundary (Fig. 4). The
lowest stratigraphic occurrence of C. supremus (OMNH speci-
mens; see Systematic Paleontology) is just below the Tithonian-
Kimmeridgian boundary, which is slightly lower than the highest
occurrence of C. lentus (WDC A, B). Therefore, an additional
biozone, the Transitional Zone, is established between the C.
lentus and C. supremus zones to recognize this overlap (Fig.
5). The lowest occurrence of C. supremus is shared with the No
Camarasaurus Zone, Foster’s (2003) Zone 6, and Turner and
Peterson’s (1999) Dinosaur Zone 4 (Fig. 5).
Camarasaurus supremus Zone––The C. supremus Zone
occurs near the top of the upper member of the Morrison For-
mation (Tithonian in age). Only C. supremus is known from
this biozone, including AMNH 5760, 5761, and DMNH 27228
(Fig. 4; see also Systematic Paleontology, Appendix I). Addition-
ally, Bakker (1990) defined the Medium-Size Camarasaur Zone
(the middle to upper Morrison) and the Giant-size Allosaur and
Camarasaur zone (top of the formation). I suspect that his zonal
FIGURE 5. Dinosaur biozones in the Morrison Formation. The Cama-
rasaurus Zones are modified from Ikejiri (2002, 2004b).
375
DISTRIBUTION AND BIOCHRONOLOGY OF CAMARASAURIS
definitions assign Camarasaurus supremus to the Giant-size
Camarasaur Zone and C. grandis and C. lentus to the Medium-
Size Zone. Therefore, the Medium-Size Camarasaur Zone could
be further sub-divided into C. grandis Zone (lower) and C. lentus
Zone (higher) (Fig. 5).
Distribution of Camarasaurus
Specimens of Camarasaurus are known from Colorado, Utah,
Wyoming, Montana, New Mexico, Oklahoma, and South Dakota
(Ikejiri, 2004b). Although some species of Camarasaurus over-
lap in their geographic ranges, there is a suggestion that the taxa
may be somewhat restricted (Fig. 6). For example, Camarasaurus
supremus is found in southern Colorado and, probably, western
Oklahoma. In contrast, no C. lentus has been identified from this
area, indicating a geographic separation between C. supremus
and C. lentus. Remains of C. lentus have been identified from
a wide area extending from northern Wyoming to eastern and
central Utah. C. grandis has been identified from south-central
Wyoming, central Colorado, and New Mexico. Although several
fragmentary specimens have been recovered from eastern Wyo-
ming, western South Dakota, and Montana (Fig. 6), none have
been identified at the species level. C. lewisi is known only from a
single specimen recovered from the Dominguez-Jones Quarry of
western Colorado, so, further discussion of its range is difficult.
DISCUSSION
Morphological Variation and Its Relationship
to Stratigraphic Position
Body size among species of Camarasaurus is variable (Ike-
jiri, 2002, 2004b; McIntosh, 1990a). Based on one of the larg-
est known skeletons in each species, Camarasaurus lewisi (BYU
9047: ontogenetically, very old individual) is the smallest taxon,
about 26 % smaller than C. supremus (AMNH 5761). Relative
to C. supremus, C. lentus is 20 % smaller based on the length of
axial centra. The body mass of C. supremus is estimated to reach
up to 47000 kg, which is up to 50 % larger than an average Cama-
rasaurus (Foster, 2003, p. 38).
Only a few minor trends of morphological change are found in
the skeletons of Camarasaurus through the stratigraphic section
of the Morrison Formation (Ikejiri, 2002, 2004b). First, the neural
spines of the anterior-mid dorsal vertebrae tend to increase in the
degree of massiveness. For example, Camarasaurus grandis,
which is from an earlier period, has slender spines. Furthermore,
C. lentus (WDC A, B), C. lentus (?) (UUVP 5461), and C. grandis
(YPM 1905, KUVP 1354) exhibit a large centrum relative to over-
all vertebral size (Fig. 7A, B). In contrast, earlier forms (C. gran-
dis) tend to have small centra in the anterior dorsal vertebrae (Fig.
7C, D). For example, C. lentus (USNM 13786, CM 8492) and
C. grandis (DMNH 2850) have remarkably small centra. Because
the difference cannot be explained by ontogenetic, taxonomic, or
sexual dimorphic variation, and they are commonly found among
individuals of both C. lentus and C. grandis, this type of variation
is possibly due to population variation (Ikejiri, 2004b).
Interpretation of Distribution
It appears that the biostratigraphic zones of Camarasaurus
are correlated with their geographic distribution. The early group
(Camarasaurus grandis) is only found in south-central Wyo-
FIGURE 6. Geographic distribution of Camarasaurus in Morrison
Formation (From Ikejiri et al., in press). Dot mark = identified species.
X = Camarasaurus sp. Abbreviations for quarries: 1, Howe Stephens
Quarry, Big Horn County; 2, BS/S Quarry in Thermopolis; 3, Reed’s
Quarry 13, East Como Bluff; 4, Reed’s Quarry 1 & 3, West Como Bluff;
5, DNM, Uintah County; 6, CLL Quarry in Emery County; 7, Grand
Valley, Mesa County; 8, Dominguez-Jones Quarry, Mesa County; 9,
San Ysidro Camarasaur Quarry, Sandoval County; 10; Cope’s Nipple
and Lindsey’s 1977 Quarry, Garden Park; 11, Comanche National
Grasslands, Otero County, and 12, Stovall Pits near Kenton (Modified
from Ikejiri, 2002; Turner and Peterson, 1999).
376 IKEJIRI
ming, central Colorado, and New Mexico. The middle biozone
(C. lentus) is distributed in central Wyoming and eastern and cen-
tral Utah. C. supremus from the very upper Morrison has been
found only in southern Colorado-western Oklahoma.
Moreover, evidence of the distribution (Fig. 6) of Camarasau-
rus indicates that a single quarry produces only one species of
Camarasaurus. I suspect the present geographic distribution does
not represent the paleobiogeography of the species of Cama-
rasaurus. It is more likely that each species was distributed over
a much larger area than the data because populations of extant,
large-bodied animals have a relatively wide distribution. Because
the species of Camarasaurus are seemingly restricted in space
and time, perhaps the rocks containing other species have been
eroded away or are not yet exposed, or there was something in the
biology of Camarasaurus that restricted its distribution.
Interpretation of Taxonomy
Based on the data on the distribution and geologic occurrences
of Camarasaurus, I suggest a few new insights into the taxon-
FIGURE 7. Variation in centrum size of anterior dorsal vertebrae of Camarasaurus. A, Camarasaurus lentus (WDC A, dorsal vertebra no. 4) and B,
C. grandis, (KUVP 1354, dorsal vertebra no. 2 or 3) from central and southern Wyoming show a relatively large centrum. In contrast, C, C. lentus
(CM 8492, dorsal vertebra no. 3) from the Dinosaur National Monument and D, C. grandis (DMNH 2850, dorsal vertebra no. 4?) from Garden Park,
Colorado tend to have a relatively small centrum in the anterior dorsal vertebrae.
377
DISTRIBUTION AND BIOCHRONOLOGY OF CAMARASAURIS
omy: (1) Camarasaurus supremus differs from C. lentus, (2) C.
lewisi (BYU 9047) may be C. grandis, and (3) the holotype of C.
lentus (YPM 1910) is possibly C. grandis. The larger body size
of C. supremus is thought to be the only feature that distinguishes
it from C. lentus (McIntosh, 1990a). Additionally, C. supremus
has a transversely wider (T-shaped) top of the neural spine in the
anterior caudal vertebrae than C. lentus (Ikejiri, 2004b; Ikejiri et
al., in press). This character also allows us to separate the two spe-
cies more accurately and give us a better understanding of their
biostratigraphic and paleobiogeographic occurrences. Although
both species seem to co-exist in the Transitional Zone (Figs. 4, 5),
no C. lentus is known from the C. supremus Zone. This evidence
also supports the idea that these are indeed two species.
Camarasaurus lewisi cannot seemingly be clearly separated
from C. grandis (Ikejiri, 2004b). A relatively tall neural arch
on the anterior-mid dorsal vertebrae is thought to be the most
diagnostic character in C. grandis (McIntosh, 1990a), but they
are missing in the holotype of C. lewisi (BYU 9047). The most
diagnostic feature of C. lewisi is a bifurcated neural spine through-
out the last dorsal vertebrae (McIntosh et al., 1996a). However,
this morphology possibly results from an intraspecific variation
(Ikejiri, 2004b). The anterior caudal vertebrae of BYU 9047 have
T-shaped neural spines, which infers as one of the diagnostic fea-
tures of C. grandis (Ikejiri, 2004b; Ikejiri et al., in press). Further-
more, BYU 9047 is found near the middle of the C. grandis Zone
(Fig. 5), and C. grandis is common in northern-central Colorado
(Fig. 6). Therefore, both morphological and biostratigraphic data
indicate that BYU 9047 is C. grandis, but more data are needed
to be certain of this.
It should be noted that the holotype of Camarasaurus lentus
(YPM 1910) is a juvenile (stage 1 in my previous study) (see Ike-
jiri, 2002, 2004b; Ikejiri et al., in press), and, in Camarasaurus,
juveniles do not contain diagnostic characteristics in any species
that are found in mature individuals (Ikejiri, 2004b). This evi-
dence raises the question of whether or not the identification of
YPM 1910 is correct. Because the holotype of C. lentus is found
in the C. grandis Zone (the upper lower Morrison Formation; Fig.
4), the holotype of C. lentus may be a juvenile C. grandis.
CONCLUSIONS
Paleobiogeographically, Camarasaurus lentus occurs in Wyo-
ming and Utah and Camarasaurus supremus in south-central Col-
orado to western Oklahoma; C. grandis is known from south and
central Wyoming, central Colorado, and New Mexico. However,
the geographic distribution may be due to stratigraphic occur-
rences, as appropriate beds may not be exposed or were eroded.
Camarasaurus might have had a much wider distribution in the
Rocky Mountain area than indicated by its distribution.
Camarasaurus forms five biozones in the upper Morrison: (1)
no Camarasaurus Zone (early-mid Kimmeridgian), (2) Cama-
rasaurus grandis Zone (mid Kimmeridgian), (3) C. lentus Zone
(late Kimmeridgian), (4) transitional Zone (early Tithonian), and
(5) C. supremus Zone (Tithonian). Because juveniles do not con-
tain diagnostic characteristics in any species of Camarasaurus,
the holotype of C. lentus may be a juvenile C. grandis.
Three suggestions can be important for the taxonomy of Cama-
rasaurus: (1) Camarasaurus supremus differs from C. lentus, (2)
C. lewisi may be the same taxon as C. grandis or C. lentus, and
(3) the holotype of C. lentus (YPM 1910) may be a C. grandis.
ACKNOWLEDGMENTS
This is a part of my M.S. thesis, and I greatly thank my thesis
advisor Richard J. Zakrzewski at FHSU and other committee:
Greg H. Farley, John S. McIntosh, Kenneth R. Neuhauser, and
William Stark. Valuable comments and discussions by Kenneth
Carpenter, John Foster, Spencer G. Lucas, John S. McIntosh,
Virginia Tidwell, and William E. Simpson are greatly appreci-
ated. Spencer G. Lucas and Kate E. Zeigler provided construc-
tive reviews of the original manuscript. I also thank the staff at
the following institutions for access to specimens: AMNH, BHI,
BYU, CM, CEU, Dino Depot (Cañon City, Colorado), DMNH,
FHSM, FMNH, GMNH-PV, KUVP, NMMNH, OMNH, SDSM,
SMA,USNM, UMMP, UUVP, WDC, and YPM. The Jurassic
Foundation (2002, 2003) and a WDC research grant (2005) sup-
ported this project.
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DISTRIBUTION AND BIOCHRONOLOGY OF CAMARASAURIS
APPENDIX I. List of selected specimens of Camarasaurus in each biozone (See also Figure 4).
Biozone Species Specimen* Remarks
C. Supremus Zone C. supremus AMNH 6760, 5761
C. supremus Zone C. supremus DMNH 27228
C. supremus Zone C. sp. FHSM VP-14850 Possibly, C. supremus
C. supremus Zone? C. sp. KUVP 129714, 129715, 129716 Possibly, C. supremus
C. supremus Zone? C. sp. SDSM 9234, 35924
Transitional Zone C. sp. OMNH specimens Possibly, C. supremus
Transitional Zone C. lentus WDC A, B
Transitional Zone? C. sp. BHI 6200
C. lentus Zone C. lentus CM 8492, 11069, 11338, 11393
C. lentus Zone C. lentus UUVP specimens
C. lentus Zone C. lentus RTMP specimens
C. lentus Zone C. lentus UMMP V16995
C. lentus Zone C. lentus DNM 28, 965
C. lentus Zone C. lentus USNM 13786
C. grandis Zone C. grandis NMMNH P-21904
C. grandis Zone C. sp. CM 584
C. grandis Zone C. grandis FMNH P25118
C. grandis Zone C. lentus YPM 1910 Possibly, C. grandis
C. grandis Zone C. grandis YPM 1901, 1902, 1904, 1905, 1908
C. grandis Zone C. sp. BYU 13007, 16953, 17465
C. grandis Zone C. lentus DMNH 2850
C. grandis Zone C. sp. USNM 5384
C. grandis Zone C. grandis KUVP 1354
C. grandis Zone C. grandis GMNH-PV 101
C. grandis Zone C. sp. AMNH 620, 690, 711
C. grandis Zone C. sp. SMA 0002
* See additional information for the listed specimens in Systematic Paleontology.
Note: The list ordered by stratigraphic position from younger (top) to older (bottom).