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12
Anuran Ilia from the Upper Cretaceous of
Utah – Diversity and Stratigraphic Patterns
Zbyneˇk Rocˇek, James D. Gardner, Jeffrey G. Eaton, and Tomáš Prˇikryl
-
tinctive structure, isolated ilia are among the most common-
ly recovered anuran bones from fossil micovertebrate sites.
Across the spectrum of known anurans, there is considerable
variation in features of the ilium. With some caveats, these
features may be useful for assigning anuran ilia to biologi-
cal taxa or, more conservatively, for estimating taxonomic
diversities in fossil assemblages. A stratigraphically extensive
sequence of microvertebrate sites, ranging in age from
the middle? Cenomanian–late Campanian (i.e., an interval
of about million years), in southwestern Utah, U.S.A., has
yielded a relatively large sample of about anuran ilia.
Three major groups of ilia can be identi ed in the Utah se-
quence: those with an oblique groove on the medial surface,
those with a dorsal tubercle, and those with neither structure.
Within each group, specimens further can be subdivided into
morphotypes based on other features (e.g., outline and rela-
tive size of acetabulum; extent and path of oblique groove;
shape and position of dorsal tubercle). Some of the iliac mor-
photypes are discrete and easily recognizable, whereas others
are less distinct. Certain of the iliac morphotypes (especially
the more distinct ones) undoubtedly represent biological spe-
cies, and the occurrence in many of the sampled localities
and horizons of multiple morphotypes implies the presence
in those areas of at least moderately diverse anuran assem-
blages. Only one iliac morphotype with an oblique groove
can be assigned to a named genus, Scotiophryne, and this
extends the temporal range for the genus back from the late
Maastrichtian into the late Campanian. Although anuran
ilia are not useful for stratigraphic correlations within the
Utah sequence, several interesting patterns are evident; for
example, the rarity both of specimens with a dorsal tubercle
in the early–middle Santonian and middle Campanian and
of specimens with an oblique groove in the late Santonian
or early Campanian. The Utah ilia are typical for Mesozoic
anurans in that none has a dorsal crest and only a minority
have a dorsal tubercle; this contrasts with the situation in
the Cenozoic, when most anurans have one or both of those
iliac structures.
Anurans (frogs) are the most diverse and widespread group
of living amphibians, consisting of about extant species
and occurring on every continent except Antarctica (Bossuyt
and Roelants, ). Anurans also were a characteristic com-
ponent of Late Cretaceous ecosystems in the North Ameri-
can Western Interior, judging by how common their remains
are in nonmarine deposits in that region (Estes, ; Sahni,
; Estes and Sanchíz, ; Brinkman, ; Gardner,
; Rocˇek et al., ). In contrast to the situation elsewhere
in the Western Interior, where Late Cretaceous anurans
are known from more limited stratigraphic intervals (e.g.,
Campanian and Maastrichtian of Wyoming and Montana;
Santonian and Campanian of Alberta, Canada), in Utah
anurans are known from every stage of the Late Cretaceous
(Cifelli et al., a, b; Rocˇek et al., ). Long-term
quarrying by one of us (J.G.E.) of Upper Cretaceous strata
in southwestern Utah, and subsequent processing of the rock
by wet screen washing, has recovered more than isolated
anuran bones from microvertebrate localities of middle?
Cenomanian–late Campanian age. This interval is about
million years, according to the timescale of Ogg, Agterberg,
and Gradstein (), and the Utah sequence represents
one of the most stratigraphically extensive records of Late
Cretaceous anurans from anywhere in the world. Recently
we presented a preliminary report on this collection (Rocˇek
et al., ). Ilia are the most commonly recovered bones
and account for about one quarter of the total collection
of anuran bones from southwestern Utah. Historically, ilia
have been important for identifying fossil anuran species.
To cite two examples: rst, in the most recent compendium
of fossil anurans, about % of the listed species had the
ilium as their holotype (Sanchiz, :); and second, four
of the ve anuran species recognized by Holman ()
from the North American Late Cretaceous had the ilium
as their holotype. In the past decade, justi able concerns
have been raised about the uncritical use of iliac features to
differentiate among anuran species (Jones, Evans, and Ruth,
; Bever, ; Gardner, ). Nevertheless, it is evident
that across the spectrum of extant and fossil anurans that
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Rocˇek et al.274
there is considerable variation in the structure of this bone
(Lynch, :gs. –; Trueb, :g. –; Tyler, :g.
) and that some of those features are phylogenetically and
taxonomically signicant. Although it is no longer accepted
practice to erect fossil anuran species solely on the basis of
subtle differences in iliac structure, especially when known
from only one isolated bone, anuran ilia remain useful for
estimating or gauging taxonomic diversities in fossil assem-
blages, especially ones in which isolated bones are the only
or a major source of information (Henrici, ; Prasad and
Rage, ; Gardner, ). As a follow-up to our article,
here we present more detailed identications, descriptions,
and comparisons of anuran iliac morphotypes from the Up-
per Cretaceous (middle? Cenomanian–upper Campanian)
of southwestern Utah, and we evaluate whether these mor-
photypes can be used for stratigraphic correlations.
All the ilia collected from southwestern Utah and used
for this study are curated in the vertebrate paleontological
collections of the Utah Museum of Natural History ()
in Salt Lake City, Utah. The complete list of those speci-
mens and their localities may be found in Rocˇek et al. ().
Examples of extant anuran ilia and important osteological
features are shown in Fig. ..
A thick succession of Upper Cretaceous sediments was de-
posited in the Sevier foreland basin of Utah. The anuran
specimens reported here are from three adjacent plateaus in
southwestern Utah (Figs. ., .). On these plateaus, the
Upper Cretaceous sequence unconformably overlies Juras-
sic rocks and in turn is overlain unconformably by lower
Cenozoic rocks. The youngest unit in the sequence, the
Kaiparowits Formation, is found only on the Kaiparowits
Plateau. With the exception of the Kaiparowits Formation,
the same units found on the Kaiparowits Plateau are found
on the next plateau to the west, the Paunsaugunt Plateau.
Units that are time equivalent to those on the Paunsaugunt
Plateau are present on the westernmost Markagunt Plateau,
but on the latter, the lithology is different enough that it has
been difcult to use the Paunsaugunt Plateau terminology
on the Markagunt sequence. Moore et al. () suggested
using the “Formation of Cedar Canyon” for rocks possibly
equivalent to the upper part of the Straight Cliffs Formation
and the Wahweap Formation until a more secure basis for
lithologic correlation has been established. The correlation
used for the Markagunt Plateau has been based on mam-
malian faunas (Eaton, ) and radiometric dates (Eaton,
Maldonado, and McIntosh, ; Eaton et al., ). Further
details about the anuran-bearing localities and formations
can be found in Rocˇek et al. ().
The anuran ilium consists of two portions: an expanded ac-
etabular portion and an anteriorly elongate shaft (Fig. .).
Compared to the more primitive tetrapod condition, anuran
ilia are distinctive in the following ways: () the left and right
ilia articulate with one another along the medial surface of
the acetabular region (primitively the ilia are separated by the
ischia and pubes); () the ilia and other bones of the pelvic
girdle are rotated posteriorward about °, so the iliac shaft
lies in the horizontal plane (primitively in a more vertical
plane); and () the iliac shaft is greatly elongate (primitively
12.1. Principal morphological features of the anuran ilium. (A) Right ilium with an oblique groove (group 1 ilia) in medial view, Pelobates fuscus (Recent).
(B) Pelvis, in right lateral view and with outlines of acetabulum marked by white dotted line, Pelobates fuscus (Recent). (C) Right ilium with a dorsal tubercle
(group 2 ilia) in lateral view, Bufo calamita (Recent). (D) Articulated anuran skeleton showing location of ilium, in dorsal view, Rana ridibunda (Recent).
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Anuran Ilia from the Upper Cretaceous of Utah 275
it is relatively shorter). Thanks to their distinctive structure,
anuran ilia can be easily recognized in fossil deposits, even
when they are isolated and broken. This is fortunate, because
all of the Upper Cretaceous ilia collected to date from
southwestern Utah are isolated and incomplete, with each
missing part of the shaft and some missing portions of the
acetabular region. For a more detailed description of anuran
ilia and features that are useful for identifying that bone, see
Gardner et al. (, and references therein).
The acetabular portion of the anuran ilium articulates
by immovable sutures with two other pelvic bones – ventrally
with the pubis, which typically is cartilaginous and thus not
capable of fossilization (the pubis is ossied in some anurans;
e.g., Pipidae) and posteriorly with the ischium. On its lateral
surface, the acetabular portion bears the anterior part of a
bowl-like cavity, termed the acetabulum, for articulation
with the femur; posteriorly, the acetabulum extends onto
the ischium. The shape, size, prominence, and position of
the acetabulum may differ considerably among species. The
posterior part of the acetabular region of the ilium may be
strongly extended both dorsally and ventrally, resulting in a
fan-like or triangular shape. As a result, when viewed in lat-
eral aspect, a considerable portion of the bone may be visible
below the acetabulum (termed the ventral acetabular or sub-
acetabular expansion) and above the acetabulum (termed the
dorsal acetabular or supraacetabular expansion). The medial
surface of the acetabular portion usually bears a rugosity that
is the contact area for attachment with the ilium on the op-
posite side (Fig. .A). The iliac shaft is anteriorly elongate,
and moderately convex dorsally and, to a lesser extent, also
laterally. Unlike in more advanced Cenozoic anurans, most
Mesozoic taxa have an iliac shaft that is suboval in cross sec-
tion and lacks a longitudinal dorsal crest.
The transition between the acetabular region and the
iliac shaft may be marked by a depression between the dorsal
margins of the supraacetabular expansion and the iliac shaft.
The dorsal margin of the supra-acetabular expansion slants
anteroventrally and continues onto the medial surface of the
shaft, thus producing a more or less prominent crista (Fig.
.A). As a result, an oblique groove (called the spiral groove
by some authors) that is delimited posteroventrally by that
crista crosses the dorsal margin of the ilium and extends onto
the medial surface, sometimes extending as far as the lower
margin of the shaft. On the lateral surface of the ilium, the
oblique groove may begin as a horizontal depression above
the acetabulum. The oblique groove is a typical feature of
many Mesozoic anurans.
In many extant anurans, the dorsal surface of the acetabu-
lar portion bears a raised outgrowth called the dorsal tu-
bercle. Although its base may be anteroposteriorly elongate,
the top of this tubercle is uniformly located at the level of
the anterior margin of the acetabulum. The dorsal tubercle
12.2. Location map showing Cretaceous outcrops in southwestern Utah from which anuran fossils were recovered. Most of the anuran specimens were
recovered from Cedar Canyon on the west side of the Markagunt Plateau, from Bryce Canyon National Park area on the east side of the Paunsaugunt Plateau,
and from the Kaiparowits Plateau, which is within the Grand Staircase–Escalante National Monument. P.F.Z., Paunsaugunt fault zone; S.F.Z., Sevier fault zone.
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Rocˇek et al.276
is the area of origin for three muscles that are functionally
important for the preparatory (crouching) and initial phases
of jumping. However, the same muscles also occur in those
taxa that lack a dorsal tubercle. In such cases, these muscles
originate on the lateral surface of the ilium (Prˇikryl et al.,
). It is not known whether the shift in the origin of these
muscles is associated with differences in jumping capabili-
ties. It is, however, important to emphasize that ilia with a
dorsal tubercle never have an oblique groove crossing their
dorsal margin onto the medial surface, so their medial sur-
face is mostly smooth. Some anurans, including some Meso-
zoic taxa, lack both an oblique groove and a dorsal tubercle
on their ilia.
To make comparisons easier and try to make some sense of
the diverse array of ilia, we created an informal classication
based on the morphotypes listed below. Such morphotypes
can be used to make limited inferences about the taxonomic
diversity of fossil assemblages, without erecting potentially
redundant biological taxa on the basis of isolated bones from
different parts of the skeleton that may be difcult to associ-
ate with each other. (For a similar approach using isolated
Upper Cretaceous sh elements, see Brinkman and Neu-
man, ; Brinkman et al., this volume, Chapter .) Three
principal groups of anuran ilia can be recognized easily in
the Utah samples: those with an oblique groove (group ),
those with a dorsal tubercle (group ), and those with neither
structure (group ). Within each group, many morphotypes
could be recognized, mostly on the basis of subtle differ-
ences. The main challenge we encountered in identifying
and dening those morphotypes was how to handle varia-
tion within each of the three principal groups. Especially
in the rst group, morphotypes that initially seemed to be
clearly dened often were bridged, as sample sizes increased,
by specimens with intermediate features. For instance, the
oblique groove in some ilia is delimited by sharp, promi-
nent cristae and in others by faint, rounded ridges; however,
there is a series of specimens that are intermediate between
those two extremes. That pattern could suggest extensive or
broad individual variation. However, other specimens exhibit
minimal or no obvious variation. For example, two group
specimens ( and ; Fig. ., upper part
of middle column) from the Santonian or Campanian Paul’s
locality in Cedar Canyon (Rocˇek et al., ) are right ilia
(and therefore from different individuals) that are identical
even in minor details.
The rst group consists of ilia with an oblique groove
but no dorsal tubercle. The oblique groove originates on
the lateral surface of the bone, above the dorsal margin of
the acetabulum, then it crosses over the dorsal edge of the
bone along a shallow depression between the acetabular re-
gion and iliac shaft, and continues onto the medial surface
of the posterior portion of the shaft where it may extend
as far as the ventral margin of the shaft. In Pelobates (Fig.
.A), Scaphiopus, and to a certain degree also Megophrys,
which are the only extant frogs in which the oblique groove
is known, the portion of the groove on the medial surface
of the shaft is the area of origin of muscles important for
locomotion (Prˇikryl at al., ). The second group consists
of ilia that have a dorsal tubercle but no oblique groove. The
dorsal tubercle is located on the upper margin of the ilium at
the level of the anterior margin of the acetabulum. In extant
anurans, the dorsal tubercle serves as the area of origin for
muscles responsible for extension and exion of the hind
limb (Prˇikryl at al., ). It should be noted that the earliest
anurans (Prosalirus; Early Jurassic) lacked the dorsal tubercle,
and that in the Early Triassic proanurans (Triadobatrachus
and Czatkobatrachus) there is a similar, prominent tubercle,
but it is located more anteriorly relative to the acetabulum.
The third group consists of ilia that have neither an oblique
groove nor a dorsal tubercle.
In the following accounts, each morphotype is briey
diagnosed, followed by information on stratigraphic oc-
currences and a list of voucher specimens. To allow for
better comparisons, key characters of all morphotypes are
12.3. Generalized Upper Cretaceous stratigraphic units on the Markagunt,
Paunsaugunt, and Kaiparowits Plateaus in southwestern Utah. Diagonal
lines indicate missing strata.
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Anuran Ilia from the Upper Cretaceous of Utah 277
illustrated in Figs. .–., and photographs of most of the
voucher specimens are presented in approximate stratigraph-
ic sequence in Figs. .–..
:
(. .–.; .
.–., )
Morphotype 1
Description The dorsal margin of the pars ascendens ex-
tends anteriorly as a distinct, oblique crista onto the medial
surface of the ilium and reaches the ventral margin of the
shaft; the iliac shaft is markedly convex dorsally, and conse-
quently there is a distinct concavity on the dorsal margin of
the bone in lateral view; an oblique groove passes the dorsal
margin of the bone from its lateral surface onto the medial
surface on the bottom of this concavity; the groove begins
in the horizontal depression above the acetabulum and ter-
minates on the lower margin of the iliac shaft; acetabulum
not extending beyond the anteroventral outline of the bone.
Distribution Dakota Formation, middle? Cenomanian:
.
Morphotype 2
Description Similar to , except the dorsal margin of the
pars ascendens continues anteroventrally onto the medial
surface of the bone as a prominent but gradually lowering
osseous lamina that disappears before reaching the lower
margin of the ilia shaft; the lamina may extend in an obtuse
point and may be paralleled by a shallow groove posteriorly;
the medial surface of the acetabular portion is depressed;
acetabulum does not reach the level of the anteroventral out-
line of the bone. These features correspond to those given by
Estes (:g. c, d) in his illustration of the holotype ilium
of Scotiophryne pustulosa.
Distribution Wahweap Formation, lower–middle Cam-
panian: , , , , perhaps also
, , (the last may be from a juvenile).
Morphotype 3
Description Similar to , except the pars ascendens is broad
and widely rounded on its dorsal margin, consequently the
crista delimiting the oblique groove is shifted onto the me-
dial surface of the bone; the oblique groove is wide and con-
tinues onto the medial surface of the shaft, consequently
the medial surface of the shaft is horizontally concave or
at; the oblique groove originates on the dorsal margin of
the bone, not on its lateral surface; on the lateral surface, a
faint oblique mound or groove runs anteroventrally from the
supraacetabular region.
Figure 12.4. Semidiagrammatic line drawings of the first 20 of 26 iliac
morphotypes with an oblique groove (group 1 ilia) left ilium in lateral
(left) and medial (right) views (continues onto Fig. 12.5. Morphotype
numbers are the same as in the text. Key characters are marked
by arrows. Full lines within the outlines of the bone denote crests,
broken lines denote rounded ridges, gray strips denote a broad shal-
low groove. See the text for diagnoses and voucher specimens.
12.5. Semidiagrammatic line drawings of the last six of 26 iliac
morphotypes with an oblique groove (group 1 ilia) left ilium in lateral (left)
and medial (right) views (continued from Fig. 12.4).
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Rocˇek et al.278
Distribution Straight Cliffs Formation, John Henry
Member, Coniacian: . Kaiparowits Forma-
tion, upper Campanian: .
Morphotype 4
Description Similar to , except the lateral surface of the
bone is uniformly convex and smooth, because the oblique
groove is conned to the medial surface.
Distribution Straight Cliffs Formation, John Henry
Member, upper Santonian: .
Morphotype 5
Description Similar to , except instead of the crista de-
limiting the oblique groove posteriorly there is only a faint
rounded ridge.
Distribution Straight Cliffs Formation, Smoky Hol-
low Member, Turonian: . Straight Cliffs
Formation, John Henry Member, upper Santonian:
. Wahweap Formation, lower–middle Campanian:
.
Morphotype 6
Description Similar to , except the margins of the acetabu-
lar region are markedly divergent from the longitudinal axis
of the bone; the shaft is slender; the anteroventral margin of
the acetabulum is markedly prominent; the medial surface
of the acetabular region is concave, consequently this part
of the bone is very thin.
Distribution Wahweap Formation, lower–middle Cam-
panian: .
Morphotype 7
Description Similar to , except the dorsal margin of the
pars ascendens joins the dorsal margin of the shaft by a short
crista shifted medially, which, however, does not continue
onto the medial surface; although this gives an impression
that there is a broad oblique groove crossing the dorsal sur-
face of the bone, it does not continue onto either the lateral
or medial surfaces.
Distribution Straight Cliffs Formation, John Henry
Member, lower Santonian: . Straight Cliffs
Formation, John Henry Member, upper Santonian:
, .
Morphotype 8
Description Similar to , except the oblique groove origi-
nates on the dorsal surface of the bone and continues as a
broad shallow depression toward the lower margin of the
bone.
Distribution Straight Cliffs Formation, John Henry
Member, lower Santonian: (note: spine pro-
jecting ventrally from anteroventral margin of the acetabu-
lum is considered a malformation). Kaiparowits Formation,
upper Campanian: , .
Morphotype 9
Description Similar to , except the tip of the pars ascen-
dens extends dorsally beyond the level of the shaft; the ac-
etabulum is prominent but shallow; the oblique groove deep,
with rounded margins; the dorsal part of the shaft is mark-
edly swollen medially.
Distribution Wahweap Formation, lower–middle Cam-
panian: .
Morphotype 10
Description Similar to , except the oblique groove is only a
faint depression on the medial surface of the shaft; the lateral
surface of the shaft is smooth; the dorsal margins of the shaft
and the pars ascendens meet in a shallow concavity.
Distribution Formation uncertain, lower–middle Cam-
panian: .
Morphotype 11
Description Similar to , except the oblique groove is de-
veloped only in the concavity on the rounded dorsal margin
of the bone; the medial surface of the acetabular portion is
moderately depressed; the acetabulum is in the middle of
the acetabular region.
Distribution Straight Cliffs Formation, John Henry
Member, middle Santonian: , perhaps also
, . Straight Cliffs Formation, John Henry
Member, upper Santonian: . Wahweap For-
mation, lower–middle Campanian: , .
Morphotype 12
Description Similar to , except the oblique groove carries
onto the medial surface of the shaft, extends anteriorly and
slightly ventrally, and is delimited ventrally by a short, faint
ridge; the acetabulum is extremely prominent ventrally.
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Anuran Ilia from the Upper Cretaceous of Utah 279
Distribution Straight Cliffs Formation, John Henry
Member, middle Santonian: .
Morphotype 13
Description Similar to , except the faint ridge deliminat-
ing the ventral margin of the oblique groove extends antero-
ventrally at a steeper angle and for a shorter distance along
the medial surface of the shaft.
Distribution Straight Cliffs Formation, John Henry
Member, middle Santonian: .
Morphotype 14
Description Similar to , except the acetabulum is ex-
tremely large, exceeding the anteroventral margin of the
bone.
Distribution Wahweap Formation, lower–middle Cam-
panian: .
Morphotype 15
Description Similar to , except the shaft is only slightly
convex and the pars ascendens only moderately declined
from the longitudinal axis of the bone; consequently, the dor-
sal margin of the bone has only a very shallow concavity; the
acetabulum is located in the middle of the acetabular region
and is not too extensive; lateral surface of the bone is smooth;
only a faint ridge runs down from the pars ascendens onto
the medial surface of the bone, but is not accompanied by
an obvious oblique groove. Although this morphotype lacks
an obvious oblique groove, we have retained it in the group
ilia because the faint ridge that typically accompanies that
groove is present and thus implies that the same muscle in-
serted in that region.
Distribution Straight Cliffs Formation, John Henry
Member, lower Santonian: .
Morphotype 16
Description Similar to in that a shallow oblique groove
begins on the dorsal margin of the bone, but the dorsal mar-
gin of the bone is straight; the oblique groove on the medial
surface of the bone is paralleled by another groove originat-
ing on the medial surface of the pars ascendens; the acetabu-
lum is shifted ventrally.
Distribution Straight Cliffs Formation, John Hen-
ry Member, lower Santonian: . Straight
Cliffs Formation, John Henry Member, upper Santonian:
, . Wahweap Formation, lower–middle
Campanian: , perhaps also .
Formation uncertain, lower–middle Campanian:
.
Morphotype 17
Description Similar to , except the groove that runs paral-
lel to the main oblique groove is faint and short; the dorsal
margin of the bone is shallowly concave; the acetabulum is
not extensive, located in the middle of the acetabular region.
Distribution Wahweap Formation, lower–middle Cam-
panian: .
Morphotype 18
Description Similar to , except the posterior margin of the
oblique groove is delimited by a prominent crista that may
appear, in lateral view, as a dorsal tubercle-like structure;
also the ridge coming from the medial surface of the pars
ascendens and delimiting the parallel groove on the medial
surface of the bone is better pronounced than in .
Distribution Straight Cliffs Formation, Smoky Hollow
Member, Turonian: .
Morphotype 19
Description Similar to , except the cristae are rounded
and the dorsal tubercle-like structure is less prominent.
Distribution Wahweap Formation, lower–middle Cam-
panian: .
Morphotype 20
Description Similar to , except the medial surface of the
bone is entirely smooth, because the oblique groove does not
extend onto that surface.
Distribution Straight Cliffs Formation, John Henry
Member, lower Santonian: . Straight Cliffs
Formation, John Henry Member, middle Santonian:
. Straight Cliffs Formation, John Henry Member,
upper Santonian: .
Morphotype 21
Description Similar to , except the medial surface of the
bone is entirely smooth, because the oblique groove does not
extend onto that surface, and the acetabulum is extensive
and shifted to the lower part of the acetabular region.
Distribution Straight Cliffs Formation, John Henry
Member, lower Santonian: , .
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Rocˇek et al.280
Morphotype 22
Description Similar to , except the oblique groove (which
is restricted to the dorsal margin of the bone) is accompanied
by a similar, short groove posteriorly.
Distribution Straight Cliffs Formation, John Henry
Member, upper Santonian: .
Morphotype 23
Description Similar to , except the acetabulum extends
beyond the anteroventral margin of the bone; a rounded
ridge runs down from the medial surface of the dorsal mar-
gin of the acetabular region onto the medial surface of the
iliac shaft, where it soon disappears.
Distribution Formation uncertain, upper Santonian or
lower Campanian: . Wahweap Formation,
lower–middle Campanian: .
Morphotype 24
Description Similar to in that the dorsal margin of the
shaft arises on the lateral margin of the bone above the ante-
rior margin of the acetabulum, and that a shallow concavity
between the shaft and the pars ascendens continues onto the
medial surface of the bone, delimited posteriorly by a faint
ridge; the shaft is widely convex dorsally; however, the pars
ascendens is low, producing a moderate convexity and not
terminating in a posterodorsally directed point; the lateral
surface of the proximal section of the shaft bears faint, an-
teroventrally directed grooves and longitudinal elevations; a
posteroventrally directed crista splits off from the anteroven-
tral margin of the acetabulum and the ventral margin of the
acetabulum continues posteriorly and even posterodorsally;
consequently, a triangular eld occurs between the crista
and margin of the acetabulum. (Note that although this
crista is a distinctive structure, it is too small to be depicted
in the corresponding drawing in Fig. ..)
Distribution Straight Cliffs Formation, Smoky Hollow
Member, Turonian: .
Morphotype 25
Description Similar to , except the oblique groove is only
on the dorsal margin of the bone, delimited posteriorly by
a rounded ridge coming from the margin of the pars ascen-
dens; posteriorly, the oblique groove is paralleled by another
groove, delimited by a crista; on the lateral surface of the
bone is a shallow horizontal depression.
Distribution Wahweap Formation, lower–middle Cam-
panian: .
Morphotype 26
Description Similar to , except the acetabulum is large
and shifted ventrally, with its anteroventral margin mark-
edly prominent; a horizontal mound derives from the dor-
sal portion of the acetabulum, and another, less prominent
mound is directed anteroventrally; a distinct depression is
developed between them; the crista delimiting posteroven-
trally the oblique groove is rather prominent, accompanied
by a parallel groove that is delimited by only a faint ridge.
Distribution Kaiparowits Formation, upper Campan-
ian: .
:
(. .; . .–
., )
Morphotype 1
Description The iliac shaft is moderately convex and its
dorsal margin widely rounded; the dorsal margin of the pars
ascendens is continuous with the dorsal margin of the shaft;
the dorsal tubercle is mediolaterally compressed, triangular
in lateral view, with its upper part widely rounded and slight-
ly declined anteriorly; the dorsal margin of the acetabulum is
markedly prominent; consequently, the dorsal surface of the
pars ascendens is horizontal or even concave; a broad mound
runs from the anterior margin of the acetabulum anteriorly;
a broad shallow groove extends from the base of the tubercle
onto the posterior section of the shaft where it disappears.
Distribution Straight Cliffs Formation, Smoky Hollow
Member, Turonian: . Formation uncertain,
upper Santonian or lower Campanian: ,
.
Morphotype 2
Description Similar to , except the dorsal tubercle is knob-
like, not compressed mediolaterally, and is slightly squarish
in lateral outline.
Distribution Straight Cliffs Formation, John Henry
Member, upper Santonian: . Formation un-
certain, upper Santonian or lower Campanian:
, .
Morphotype 3
Description Similar to , except the dorsal tubercle is knob-
like, not compressed mediolaterally, and the medial surface
of the bone is smooth.
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Anuran Ilia from the Upper Cretaceous of Utah 281
Distribution Dakota Formation, upper Cenomanian:
. Straight Cliffs Formation, Smoky Hollow
Member, Turonian: .
Morphotype 4
Description Similar to , except the dorsal tubercle is rather
quadrangular in lateral view and the acetabulum is promi-
nent but shallow; because of the prominent dorsal margin of
the acetabulum, there is a groove between the acetabulum
and the dorsal tubercle.
Distribution Straight Cliffs Formation, Smoky Hollow
Member, Turonian: .
Morphotype 5
Description Similar to , except the acetabulum is deeply
concave with a raised edge along the entire margin and
it extends from the level of the dorsal margin of the pars
ascendens to beyond the anteroventral margin of the bone;
the medial surface of the bone is smooth.
Distribution Straight Cliffs Formation, Smoky Hollow
Member, Turonian: .
Morphotype 6
Description Similar to , except the dorsal tubercle is not
compressed laterally and the dorsal margin of the acetabu-
lum is not prominent.
Distribution Formation uncertain, upper Santonian or
lower Campanian: .
Morphotype 7
Description The posterior section of the iliac shaft is
straight;; the dorsal tubercle has an anteroposteriorly extend-
ed base but is low, with its upper part rather swollen; in cross
section, the dorsal surface of the pars ascendens is a broadly
rounded, nearly horizontal plane extending onto the dorsal
margin of the acetabulum; the acetabulum extends from
nearly the level of the dorsal surface of the pars ascendens
almost to the anteroventral margin of the bone; the medial
surface of the bone is at and almost smooth, except for a
faint crista running from the medial surface of the pars as-
cendens to the lower margin of the iliac shaft.
Distribution Dakota Formation, upper Cenomanian:
.
Morphotype 8
Description Similar to , except the dorsal tubercle is a low,
anteroposteriorly elongate crista; the iliac shaft is moderately
convex dorsally; the medial surface of the bone is smooth.
Distribution Dakota Formation, upper Cenomanian:
. Wahweap Formation, lower–middle Cam-
panian: .
Morphotype 9
Description Similar to in size and lateral shape of the
tubercle; however, the upper part of the tubercle is sharp (not
swollen) and its lateral surface slants down toward the promi-
nent dorsal margin of the acetabulum; the medial surface
of the tubercle is vertical, continuous without any distinct
border with the at and smooth medial surface of the bone;
the anteroventral margin of the acetabulum reaches the level
of the bone; the iliac shaft is straight.
Distribution Straight Cliffs Formation, John Henry
Member, middle Santonian: .
12.6. Semidiagrammatic line drawings of the 21 iliac morphotypes with
a dorsal tubercle (group 2 ilia) left ilium in lateral (left) and medial (right)
views. Symbols are the same as in Fig. 12.4.
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Rocˇek et al.282
Morphotype 10
Description Similar to , except the dorsal tubercle is more
extensive anteroposteriorly, and slightly declined anteriorly;
the medial surface of the bone is smooth.
Distribution Straight Cliffs Formation, John Henry
Member, upper Santonian: .
Morphotype 11
Description Similar to , except the dorsal tubercle is small
and declined anteriorly; the acetabulum extends to the dorsal
margin of the bone.
Distribution Straight Cliffs Formation, John Henry
Member, upper Santonian: .
Morphotype 12
Description Similar to , except the acetabulum extends
beyond the anteroventral margin of the bone.
Distribution Wahweap Formation, lower–middle Cam-
panian: , .
Morphotype 13
Description Similar to , except the dorsal margin of the
pars ascendens is above the level of the dorsal margin of the
iliac shaft.
Distribution Wahweap Formation, lower–middle Cam-
panian: .
Morphotype 14
Description Similar to , except the dorsal margin of the
pars ascendens is slightly concave and the acetabular region
of the bone is low.
Distribution Wahweap Formation, lower–middle Cam-
panian: .
Morphotype 15
Description Similar to , except the dorsal tubercle is only
a faint though extensive elevation; a shallow groove extends
on the medial surface of the bone as in morphotype .
Distribution Formation uncertain, upper Santonian or
lower Campanian: .
Morphotype 16
Description Similar to , except the dorsal tubercle is com-
paratively large and prominent; the dorsal margin of the pars
ascendens is horizontal, continuous with that of the iliac
shaft.
Distribution Formation uncertain, upper Santonian or
lower Campanian: .
Morphotype 17
Description Similar to , except the dorsal tubercle is a
triangular, comparatively thin lamella with its rounded tip
slightly declined anteriorly; the tubercle is well delimited,
both laterally and medially, from the surrounding horizontal
surface of the bone.
Distribution Formation uncertain, upper Santonian or
lower Campanian: , , .
Morphotype 18
Description Similar to , except the dorsal tubercle is more
prominent; the medial surface of the bone is smooth.
Distribution Wahweap Formation, lower–middle Cam-
panian: , , .
Morphotype 19
Description Similar to , except the medial surface of the
dorsal tubercle is continuous with the medial surface of the
bone, the latter of which is smooth.
Distribution Wahweap Formation, lower–middle Cam-
panian: .
Morphotype 20
Description Similar to , except the dorsal tubercle is com-
paratively large, triangular in lateral view, compressed me-
diolaterally either only in its posterior part or in the whole of
its extent, with a rugosity in its lateral side; the medial surface
of the tubercle is continuous with the medial surface of the
bone, which is at and smooth; the acetabulum extends up
to the dorsal margin of the bone.
Distribution Formation uncertain, upper Santonian or
lower Campanian: . Wahweap Formation,
lower–middle Campanian: , .
Morphotype 21
Description Large ilium; the dorsal margin of the pars as-
cendens is declined posteroventrally from the longitudinal
axis of the bone; the acetabulum is comparatively small and
shifted ventrally; the iliac shaft is strongly compressed me-
diolaterally but not bearing a dorsal crest; the dorsal tubercle
is small, declined dorsolaterally, separated from the dorsal
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Anuran Ilia from the Upper Cretaceous of Utah 283
edge of the shaft by a shallow depression; both the lateral
and medial surfaces of the bone are smooth.
Distribution Formation uncertain, upper Santonian or
lower Campanian: .
:
(.
.; . .–., )
Morphotype 1
Description Between the pars ascendens and shaft is only a
very faint concavity on the dorsal surface of the bone; the ac-
etabulum is cup-like, located in the middle of the acetabular
region; on the lateral surface of the posterior section of the
shaft are longitudinal, anteroventrally directed elevations,
well delimited posteroventrally; the medial surface of the
acetabular portion is depressed.
Distribution Straight Cliffs Formation, John Henry
Member, Coniacian: .
Morphotype 2
Description Similar to , except the lateral surface bears a
moderately well-developed (i.e., not too prominent) crista.
Distribution Wahweap Formation, lower–middle Cam-
panian: .
Morphotype 3
Description Similar to , except the lateral surface of the
shaft bears no elevations.
Distribution Straight Cliffs Formation, John Henry
Member, middle Santonian: , . Straight
Cliffs Formation, John Henry Member, upper Santonian:
. Formation uncertain, ?Campanian:
, possibly also . Wahweap Formation,
lower–middle Campanian: .
Morphotype 4
Description Similar to , except there are no longitudinal
elevations on the lateral surface of the shaft; the pars ascen-
dens is extensive and produces a robust posterodorsal point;
the posterior section of the shaft is comparatively slender; the
acetabulum is shifted ventrally.
Distribution Straight Cliffs Formation, John Henry
Member, middle Santonian: , ; Forma-
tion uncertain, upper Santonian or lower Campanian:
, , possibly also and . Formation
uncertain, ?Campanian: .
Morphotype 5
Description Similar to , except the posterior section of the
shaft is not slender; the acetabulum is large, exceeding the
anteroventral margin of the bone.
Distribution Straight Cliffs Formation, John Henry
Member, upper Santonian: . Perhaps also
Wahweap Formation, lower–middle Campanian:
, .
Morphotype 6
Description Similar to , except the margins of the acetabu-
lar portion are moderately divergent; the dorsal margin of
the shaft is straight and meets the dorsal margin of the pars
12.7. Semidiagrammatic line drawings of the 18 iliac morphotypes
lacking both an oblique groove and a dorsal tubercle (group 3 ilia)
left ilium in lateral (left) and medial (right) views. Morphotypes 17
and 18 are cf. Nezpercius sp. (Caudata) each depicted with long axis
rotated about 90° from life orientation (i.e., iliac shaft would have
extended vertically) to emphasize similarities between isolated ilia
of anurans and caudates. Symbols are the same as in Fig.12.4.
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Rocˇek et al.284
12.8. Stratigraphic distribution of representative anuran ilia from middle? Cenomanian through lower Santonian localities in south–western Utah (continues
onto Figs. 12.9–12.11). Left column is group 1 ilia (with an oblique groove); center column is group 2 ilia (with a dorsal tubercle); and right column is group
3 ilia (lacking both an oblique groove and a dorsal tubercle). Most of the voucher specimens listed in the text are depicted here. For each specimen, the
accompanying five-digit number is its formal UMNH catalog number; a, b, and c indicate lateral, medial, and dorsal views, respectively. Specimens shown at
same magnification (see scale bar at lower right).
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Anuran Ilia from the Upper Cretaceous of Utah 285
12.9. Stratigraphic distribution of representative anuran ilia from middle Santonian through upper Santonian or lower Campanian localities in southwestern
Utah (continued from Fig. 12.8; see Fig. 12.8 caption for details).
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Rocˇek et al.286
12.10. Stratigraphic distribution of representative anuran and caudate ilia from upper Santonian or lower Campanian through lower or middle Campanian
localities in southwestern Utah (continued from Figs. 12.8 and 12.9; see Fig. 12.8 caption for details). Four examples of group 3 ilia (UMNH VP 18303, 18319,
18105, and 18109; all in upper right) are cf. Nezpercius sp. (Caudata) each depicted with long axis rotated about 90° from life orientation (i.e., iliac shaft
would have extended vertically) to emphasize similarities between isolated ilia of anurans and caudates.
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Anuran Ilia from the Upper Cretaceous of Utah 287
12.11. Stratigraphic distribution of representative anuran ilia from lower or middle Campanian through upper Campanian localities in southwestern Utah
(continued from Figs. 12.8–12.10; see Fig. 12.8 caption for details).
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Rocˇek et al.288
ascendens in a shallow depression; the acetabulum is promi-
nent but shallow; the medial surface of the bone is concave
and smooth.
Distribution Formation uncertain, upper Santonian or
lower Campanian: , .
Morphotype 7
Description Similar to , except the dorsal margin of the
bone is straight.
Distribution Straight Cliffs Formation, Smoky Hollow
Member, Turonian: .
Morphotype 8
Description Similar to , except there are two elongate and
anteriorly divergent mounds on the lateral surface of the
posterior section of the shaft; the medial surface of the pars
ascendens is concave.
Distribution Straight Cliffs Formation, John Henry
Member, middle Santonian: , , possibly
also .
Morphotype 9
Description Acetabulum large, extending closer to the dor-
sal margin of the acetabular region than to the ventral one;
on the dorsal margin of the bone, the transition between the
pars ascendens and the iliac shaft is marked by a moderate
indentation; the shaft seems to be comparatively slender; the
medial surface of the bone is at or even slightly concave
posteriorly.
Distribution Kaiparowits Formation, upper Campan-
ian: .
Morphotype 10
Description Acetabulum small, its anterodorsal part is a
mere depression in the bone; the shaft is comparatively ro-
bust; a prominent though rounded ridge runs horizontally
on the dorsal part of the medial surface.
Distribution Kaiparowits Formation, upper Campan-
ian: .
Morphotype 11
Description Similar to , except the acetabulum is well
delimited and located in the middle of the acetabular re-
gion; the acetabular region is comparatively small; the shaft
is only moderately convex dorsally; the medial surface of the
acetabular region is smooth and at.
Distribution Kaiparowits Formation, upper Campan-
ian: .
Morphotype 12
Description The dorsal margin of the pars ascendens is
declined posterodorsally and its posterior tip is swollen and
slightly declined laterally above the acetabulum; the iliac
shaft is laterally compressed; the posterior section of the dor-
sal margin of the iliac shaft is widely convex; consequently,
it meets the dorsal margin of the pars ascendens in a shallow
concavity; an oblique rounded ridge splits from the dorsal
margin of the pars ascendens and runs down anteroventral-
ly onto the lateral surface of the shaft where it terminates
abruptly at the level of the anterior margin of the acetabu-
lum; the acetabulum is a mere depression in the bone, ex-
cept for a well-delimited anterior part that is prominent; the
medial surface of the bone is moderately convex and smooth.
Distribution Dakota Formation, upper Cenomanian:
. Formation uncertain, lower or middle Cam-
panian: .
Morphotype 13
Description Similar to , except the margins of the acetab-
ular region are strongly divergent from the longitudinal axis
of the bone; the shaft is relatively stout; the acetabulum is a
mere depression in the bone, except for the anterior margin,
which is slightly prominent; a rounded ridge coming from
the dorsal margin of the pars ascendens terminates abruptly
above the anterior acetabular margin; the medial surface of
the bone is moderately convex and smooth.
Distribution Formation uncertain, upper Santonian or
lower Campanian: .
Morphotype 14
Description The iliac shaft is convex in its posterior section,
whereas its anterior part is straight; the acetabulum is a mere
depression with rounded margins; the medial surface of the
bone is moderately convex and smooth.
Distribution Formation uncertain, upper Santonian or
lower Campanian: .
Morphotype 15
Description The pars ascendens is not developed, conse-
quently the dorsal margin of the acetabulum extends to the
dorsal margin of the bone; the acetabulum is large, exceed-
ing beyond the anteroventral margin of the bone; the shaft
is comparatively slender; a very shallow convexity is present
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Anuran Ilia from the Upper Cretaceous of Utah 289
on the dorsal surface of the acetabular region, above the
anterior margin of the acetabulum (although this convexity
occurs in the same position as the dorsal tubercle, we hesitate
to identify it as such because it is very shallow and it is not
prominently developed as the knob- or ridge-like structure
seen in most group ilia); the medial surface of the acetabu-
lar portion is concave.
Distribution Straight Cliffs Formation, John Henry
Member, upper Santonian: .
Morphotype 16
Description The dorsal margin of the bone is straight; the
acetabulum is small but markedly prominent; a posteroven-
trally directed crista splits from the anteroventral margin of
the acetabulum.
Distribution Formation uncertain, ?Campanian:
.
Morphotype 17
Description The posterior part of the acetabular portion is
strongly extended both dorsally and ventrally so it has a fan-
like, triangular shape; the posterior, articular surface of the
bone is thick but concave (it was probably lled with carti-
lage in the living animal); the anterior part of the acetabulum
is convex and extremely prominent, so the acetabulum is
strongly declined posteriorly and very shallow; the acetabu-
lum does not reach the level of the anteroventral outline of
the bone; the medial surface of the acetabular portion is
smooth; there is a distinct rugosity on the lateral surface of
the iliac shaft. Those features are similar (but not all iden-
tical) to those of Nezpercius dodsoni (Blob et al., ), so
referral to Nezpercius is justied.
Distribution Wahweap Formation, lower–middle Cam-
panian: .
Morphotype 18
Description Same as in (and also referable to Nezpercius),
except there is no rugosity on the lateral surface of the iliac
shaft. The surface of the anterior, convex margin of the ac-
etabulum may be abraded.
Distribution Wahweap Formation, lower–middle Cam-
panian: , , .
Group 1 ilia
For the rst group of ilia, namely those with an oblique
groove, we dened our morphotype on the basis of a typi-
cal ilium with an oblique groove ( ) from the
lowest locality in our stratigraphic sequence (middle? Ceno-
manian). On the basis of its stratigraphic occurrence, this
morphotype can be postulated as the basic or most primi-
tive iliac morphotype, from which others in the same group
could have been derived. Interestingly, morphotype or its
slight modications persisted throughout the entire strati-
graphic sequence, as indicated by morphotype (represented
by , which differs from morphotype only in
that there is a shallow depression instead of a groove) in the
upper Campanian portion of the sequence.
Morphotype could have been derived from morphot-
ype . It also is one of the few morphotypes in our samples
that corresponds with ilia from elsewhere in the Western
Interior that have been assigned to a named anuran spe-
cies. Estes () chose an ilium having an oblique groove
delimited posteriorly by an expanded crista from the Bug
Creek Anthills (mixed upper Maastrichtian and lower Paleo-
cene), Hell Creek Formation of Montana, as the holotype of
Scotiophryne pustulosa. Estes () also referred to the spe-
cies some distinctive skull bones (maxillae and squamosals),
humeri, and several ilia in which the oblique groove was
less strongly marked than in the holotype. Gardner ()
described additional, isolated bones and presented a revised
diagnosis for S. pustulosa. Because the holotype ilium (Estes,
:g. c, d) of S. pustulosa appears virtually identical to
our morphotype ilium, we assign the Utah specimens to
Scotiophryne. In our samples, this morphotype occurs in the
lower–middle Campanian Wahweap Formation, at both the
Campbell Canyon and White Flats Road localities. These
Utah occurrences extend the range for Scotiophryne from
the late Maastrichtian/early Paleocene (Estes, ; Gardner,
) back to the early–middle Campanian.
Morphotype mainly differs from the previous two in
that its crista delimits a broad depression in the medial sur-
face of the iliac shaft and bears an oblique depression on its
lateral surface. It was recorded by only two specimens, one
( ) from the Coniacian and one (
) from the upper Campanian. Morphotype , represent-
ed by from the upper Santonian, is similar
and differs only in that its lateral surface is smooth. If these
differences express individual variation and morphotypes
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Rocˇek et al.290
and belong to a single taxon, then its stratigraphic range is
from the Coniacian to late Campanian.
Morphotypes , , and are also similar to each other
and vary only in different expressions of the oblique groove.
Considering that the oblique groove is an area for attachment
of the medial head of the iliacus externus muscle (Prˇikryl et
al., ), variation in the groove may indicate differences
in how well developed this muscle was in individuals of the
same or closely related taxa. These three morphotypes were
recorded from the Turonian to the uppermost level (upper
Campanian) in our stratigraphic sequence. This lengthy
stratigraphic range supports the view that morphotypes –,
, and are generalized ilia with an oblique groove, from
which only morphotype is markedly derived by its peculiar
morphology of having a prominent lamina delimiting the
groove posteriorly, which is a feature that substantiates the
taxonomic distinctiveness of the genus Scotiophryne (Estes,
). Morphotypes , , and may also be derived from
the generalized scheme, as are morphotypes –, , and ,
in that their oblique groove is poorly developed (i.e., very
shallow or entirely absent). Morphotypes , , and have
a more restricted range and are known from the middle San-
tonian through middle Campanian.
In contrast to the previously discussed ilia, morphotype
( ) differs in that the margins of its pars
ascendens and pars descendens are strongly divergent from
the longitudinal axis of the bone (they form an angle of more
than °) and that its shaft is straight and comparatively slen-
der. The only example of this morphotype was recovered
from the lower–middle Campanian Barker Reservoir Road
locality.
Morphotype ( ) also is markedly differ-
ent in having a massive pars ascendens and an acetabulum
that is shifted to the anteroventral margin of the acetabular
region and is markedly prominent from the surface of the
bone, but with a at acetabular surface. It also was recovered
only from the lower–middle Campanian Barker Reservoir
Road locality.
Nine morphotypes (–, –, , and ) still maintain
the basic morphology of the oblique groove, especially on the
medial surface of the bone; however, there is some variation,
especially in the position and size of their acetabula.
Morphotypes and are characterized by their large
and ventrally shifted acetabula, which resembles the condi-
tion in morphotype . However, morphoptypes and
are older (middle Santonian) and thus provide the earliest
evidence for expansion and ventral shift of the acetabulum
in ilia with an oblique groove from Utah. Otherwise, the two
morphotypes are typical for ilia with an oblique groove and
differ from each other only in minor details, most notably
the course of the oblique groove on the medial surface of
the bone. Morphotype could also be included with the
previous two morphotypes, but it differs from them in hav-
ing a larger acetabulum and a stratigraphically higher (lower
Campanian) occurrence.
Morphotypes through share two features: () the
oblique groove is paralleled posteriorly by another groove
arising on the medial surface of the pars ascendens, and ()
the nearly straight dorsal margin of the bone. Morphotype
is characterized by a large and ventrally shifted acetabu-
lum; its stratigraphic occurrence is lower Santonian through
lower–middle Campanian. Morphotypes through differ
from morphotype and resemble one another in having
the acetabulum smaller and located in the middle of the
acetabular region, but they differ from each other in how
prominently developed is the crista that posteriorly delimits
the oblique groove. In morphotype , represented by
, this crista is so prominent that where it crosses the
dorsal margin of the bone it resembles a small tubercle. How-
ever, because morphotype occurs in the Turonian and the
similar morphotype ( ) occurs much later
in the lower–middle Campanian, it appears that these two
morphotypes (and probably also other morphotypes with two
parallel grooves) are just variations of the basic morphotype
with a single oblique groove and, judging by their strati-
graphic occurrence, they have no stratigraphic value.
Morphotypes and are characterized by having the
oblique groove restricted to the dorsal margin of the bone
and by the smooth medial surface of the bone. These mor-
photypes differ from one another only in the position of their
acetabula. Both occur only in the Santonian.
The remaining two morphotypes, and , are notable
for their large and ventrally located acetabula. Besides
from the upper Santonian or lower Campanian
Pinto Flats locality; this is the only example of an ilium with
an oblique groove recovered from this locality, even though
the other two principal groups of ilia are well represented at
that locality.
Although ilia with an oblique groove have a continuous
distribution throughout the stratigraphic sequence in south-
ern Utah and we have recognized different morphotypes,
we were not able to recognize correlations between any par-
ticular morphotype and stratigraphic intervals. Even if there
were morphotypes restricted to certain stratigraphic units,
those would be difcult to recognize on the basis of our small
sample sizes, which, in some cases, constituted only a single
specimen for a particular morphotype. Moreover, because
the morphotypes in this group of ilia generally differ only
subtly from one another, it is difcult to decide whether those
differences are taxonomically signicant or simply reect
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Anuran Ilia from the Upper Cretaceous of Utah 291
individual variation; regardless, most of the morphotypes
appear to have no stratigraphic value. The only exception
seems to be morphotype (Scotiophryne), which is clearly
dened by a prominent lamina that posteriorly delimits the
oblique groove and, in the Utah samples, is stratigraphically
restricted to the lower–middle Campanian. Elsewhere in the
Western Interior, Scotiophryne is known from the late Maas-
trichtian and early Paleocene of Montana and Wyoming
(Estes, ; Gardner, ).
Group 2 ilia
The second principal group consists of ilia with a dorsal
tubercle. The most generalized morphotype (morphotype
) is characterized by having a slightly convex shaft, by a
dorsal tubercle that is triangular, laterally compressed, has a
rounded apex and is slightly declined anteriorly, and by the
prominent dorsal margin of the acetabulum. This morphot-
ype occurs in the Turonian and upper Santonian or, possibly,
lower Campanian.
Morphotype is similar, except its dorsal tubercle is not
laterally compressed. It occurs in the upper Cenomanian
and Turonian. The relatively early (Turonian) co-occurrence
and the overall similarity of morphotypes and might sug-
gest that the generalized morphotype for this group of ilia
was one in which the dorsal tubercle could vary in its me-
diolateral compression. In other words, it could include ilia
with both compressed and knob-like dorsal tubercles. If this
is correct, then morphotypes and could both represent
the generalized morphotype for this group of ilia.
Morphotype from the upper Santonian or lower Cam-
panian is similar to morphotypes and , except the outline
of its dorsal tubercle tends to be a more squarish and it is
not laterally compressed. A squarish outline of the dorsal
tubercle is also characteristic of morphotypes , , and ;
these vary only in the shape and location of their acetabula.
However, they occur in the Turonian ( and
in Fig. .) and upper Santonian or lower Campan-
ian ( in Fig. .). It is unknown why there is
a gap between these stratigraphic occurrences and whether
the squarish outline of the dorsal tubercle indicates the ilia
are from closely related taxa. If the squarish outline of the
dorsal tubercle arose independently more than once, then
at least some of the ilia with that feature might be from un-
related taxa.
Morphotype differs from the previous six in that its ac-
etabular region is declined ventrally (i.e., the dorsal margin
behind the tubercle is declined posteroventrally, whereas
the dorsal margin of the shaft is located horizontally; conse-
quently, the dorsal tubercle is a protuberance located at the
point where both meet together). It is represented by a single
specimen ( ) from the upper Cenomanian.
Morphotype is similar, except its dorsal tubercle is com-
pressed laterally and elongated anteroposteriorly, so it is more
a crista than a tubercle. This morphotype is very characteris-
tic, and therefore it is rather surprising that examples occur
in the upper Cenomanian ( in Fig. .) and
Campanian ( in Fig. .).
Morphotype possibly could be related to morphotype
(there are only minor differences between them); how-
ever, they are separated by a large stratigraphic gap (upper
Cenomanian versus middle Santonian). On the other hand,
morphotype likely is related to morphotypes , , and
, represented by , , and and
, respectively. All (including morphotype ) are from
the middle Santonian to lower or middle Campanian and
all are characterized by a massive acetabular region that is
declined posteroventrally from the longitudinal axis of the
shaft. Morphotype , which also is from the lower or middle
Campanian, differs from morphotype only by having the
posterior margin of its dorsal tubercle being conuent with
the dorsal margin of the pars ascendens. Consequently, the
dorsal tubercle is only slightly prominent.
Morphotypes and (represented by
and , respectively) are similar to each other in their
acetabular region being shallow and slender, and their dorsal
tubercle is not prominent. These two morphotypes are also
restricted to the upper Santonian or lower Campanian (mor-
photype ) and lower–middle Campanian (morphotype ).
Morphotype is characterized by an extensive acetabu-
lar region (the dorsal margin of which is continuous with the
dorsal margin of the shaft) and by a prominent dorsal tuber-
cle. It occurs in the upper Santonian or lower Campanian.
Morphotypes – are all characterized by a dorsal tu-
bercle that is large and triangular in lateral aspect and by an
extremely large acetabulum. All are restricted to the upper
Santonian–middle Campanian.
Morphotype strongly deviates from all other ilia in that
the dorsal margin of the shaft is a comparatively sharp edge.
This morphotype is similar to ilia of Enneabatrachus hechti
Evans and Milner, , from the Upper Jurassic Morrison
Formation, in that the dorsal tubercle is declined laterally
and that its shaft has a medially declined dorsal crest. How-
ever, in from the upper Santonian or lower
Campanian, the dorsal tubercle is separated from the dorsal
crest by a deep depression, which argues against assigning
this specimen to Enneabatrachus.
To sum up the situation in the group of the ilia with a
dorsal tubercle, one can conclude that although there are
intriguing irregularities in the occurrences of this type of
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Rocˇek et al.292
ilia (e.g., their complete absence or relative scarcity in the
lower and middle Santonian and in the upper Campanian),
it is not possible to recognize any morphotypes that can be
correlated with a particular stratigraphic interval. Even those
morphotypes that seemingly are well dened (i.e., those with
squarish tubercle, such as morphotypes , , , and ) occur
in the upper Santonian or lower Campanian, but also in the
Turonian. If differences in the size and shape of the dorsal
tubercle are ignored, one might argue that ilia with an en-
larged acetabular region (morphotypes –) are typical of
the upper Santonian–middle Campanian.
Group 3 ilia
Within the third group – ilia lacking both the oblique groove
and dorsal tubercle – morphotypes to differ from each
other only in presence or absence of rounded ridges on the
lateral surface of the iliac shaft. Their shafts are rather stout.
However, their stratigraphic range spans the Coniacian to
lower–middle Campanian. Morphotype from the middle
Santonian is similar in general proportions, but differs in
having two rounded and slightly divergent mounds on the
lateral surface of the iliac shaft.
Morphotype is similar to the previous four in general
shape of the bone; however, it differs in the relatively larger
size of its acetabulum. It was recorded from the upper San-
tonian and lower–middle Campanian.
Morphotype is clearly different from morphotypes –
in its slender shaft and in having the acetabulum shifted
toward the anteroventral margin of the bone. It is restricted
to the middle Santonian through lower Campanian.
Morphotype is similar to morphotypes –, but differs
in that its acetabular region is symmetrical, with the acetabu-
lum in the middle. Its stratigraphic record is from the upper
Santonian or lower Campanian.
Morphotype is well distinguished from all others in this
group by a thin shaft, a straight dorsal margin terminated
by a point, and by its ventrally shifted acetabulum. It was
recorded from the Turonian.
Morphotype clearly differs from all others (irregardless
of the size of the bone) by its large acetabulum extending
almost to the dorsal margin of the bone and by its slender
iliac shaft. Unfortunately, it is represented by only a single
specimen ( ), from the upper Campanian.
This specimen is also notable because it documents the pres-
ence of large anurans in the upper Campanian.
Morphotypes and resemble one another, and differ
only in the size and position of the acetabulum and in the
presence or absence of a horizontal rounded ridge. Both are
from the upper Campanian.
Morphotypes and are similar to one another in the
shape of the anterodorsal margin of the acetabulum, which
is unusual in being discontinuous. Morphotype is known
from the upper Cenomanian ( ) and also the
lower or middle Campanian ( ).
(morphotype ) is from the upper Santonian or lower
Campanian and it differs in the shape of the acetabular re-
gion and the iliac shaft.
Morphotype is based on one fragmentary specimen,
, but it is distinct in having a dorsal mar-
gin that is moderately depressed at the level of the anterior
margin of the iliac shaft. It was recovered from the upper
Santonian or lower Campanian Paul’s locality.
Morphotype , although also based on a fragmentary
specimen ( ), is profoundly different from all
others in having an extremely large acetabulum and by the
unusual shape of its acetabular region. It is known only from
the upper Santonian.
Morphotype is dubious, but it seems to be character-
ized by its straight and horizontal dorsal margin. It is from the
upper Santonian or lower Campanian Pinto Flats locality.
The remaining two morphotypes ( and ) generally
resemble the other morphotypes, but differ in that the ac-
etabular surface closest to the iliac shaft is broadly convex,
but the rest of the surface is steeply declined in the opposite
direction. Such an acetabular morphology is characteristic
of Nezpercius, as described by Blob et al. () from the
Campanian age Judith River Formation in Montana. One of
the Utah morphotypes () bears an elevated rugosity on the
dorsolateral side of its shaft, which is a key diagnostic char-
acter of Nezpercius. All our specimens referable to these two
morphotypes (and thus to the genus Nezpercius) are from the
lower or middle Campanian, which is in agreement with the
stratigraphic occurrence of the three specimens described by
Blob et al. (). Although Nezpercius was described as an
anuran, its distinctive ilia (which are the only bones known
for the taxon) have recently been reinterpreted as belong-
ing to a caudate amphibian (Gardner et al., ). We have
retained the Nezpercius-like ilia from Utah here to highlight
their presence in the Utah sequence and to emphasize that
these problematic ilia are similar in many respects to, and
thus may easily be mistaken for, ilia of unequivocal anurans.
For a more detailed list of similarities and differences be-
tween ilia of anurans and caudates, see Gardner et al. ().
The collection used in this study from the Upper Cretaceous
of southwestern Utah is the largest sample of anuran ilia yet
reported from a comparable area and stratigraphic interval
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Anuran Ilia from the Upper Cretaceous of Utah 293
in North America. Even a cursory glance at Figs. .–.
and .–. indicates a diversity of ilia were recovered. The
question naturally arose whether these ilia could be used for
stratigraphic correlations. Unfortunately, this is not feasible
at present. Although we have identied iliac morphotypes
among the nearly specimens used in this study, there are
several problems with using those morphotypes for biostrati-
graphic correlation. Many of the morphotypes differ only
subtly from one another. From a practical standpoint, these
morphs may be challenging for nonspecialists to identify
in their screen-wash samples. Equally importantly, some of
these morphotypes may simply be variants within a broader
range of biologically distinct taxa. What we have recognized
here as different morphotypes could conceivably be some
combination of ontogenetic, sexually dimorphic, temporal,
or individual variants of a lesser number of temporally lon-
ger-ranging species. The very real possibility that some of
those iliac morphotypes are from conspecic individuals is
difcult to evaluate, because many of the morphotypes are
known by just one or only a few specimens and from only one
or a few localities. It is possible that certain iliac morphotypes
had a broader stratigraphic range than what is suggested by
our current, relatively small samples. Some morphotypes
admittedly are more distinctive (e.g., group , morphotypes
and ), yet their utility remains limited because they are
known by a single specimen each from just one locality. For-
tunately, collecting and processing of previously sampled and
new microvertebrate localities in the study area continues. As
sample sizes of anuran ilia increase, it should be possible to
rene identications of anuran iliac morphotypes (perhaps
even assign some of those to biological taxa) and better re-
solve their stratigraphic ranges.
At a general morphological level, however, we were able
to record some potentially interesting patterns in the strati-
graphic occurrences of the three groups of ilia. The most re-
markable is the relatively poor record of the ilia with a dorsal
tubercle in the lower and middle Santonian and in the upper
Campanian. Another peculiarity is the relative absence of
ilia with an oblique groove in the upper Santonian or lower
Campanian. Although these patterns may accurately reect
the presence or absence (or relative abundances) of taxa at
different times, they may simply be an artifact of sample sizes
(which generally were small; i.e., less than a dozen ilia per lo-
cality) or particular depositional conditions in the localities.
The predominance of ilia without a dorsal tubercle in
Mesozoic anurans is surprising, and it contrasts with the
situation in the Cenozoic when most anurans have a dorsal
tubercle. It is interesting that almost all known Mesozoic
frogs also lack a dorsal crest on the iliac shaft (in life, this
crest separates the origins of the iliacus externus and coc-
cygeoiliacus muscles from each other; Prˇikryl et al., ).
A notable exception from North America is Paradiscoglos-
sus americanus Estes and Sanchíz, , which is known by
two ilia from the upper Maastrichtian Lance Formation of
Wyoming that each bear a relatively tall and anteriorly elon-
gate dorsal crest (Estes and Sanchíz, ; Gardner, );
no examples of this kind of ilia were identied from any of
our older Utah localities. It is not clear whether the dorsal
tubercle and the dorsal crest appeared at the same or differ-
ent times during the evolution of anurans as a consequence
of a shift in locomotor behavior or whether the widespread
occurrence of these structures in Cenozoic anurans is as-
sociated with the appearance and diversication during the
Paleogene and Neogene of more derived groups (e.g., Bu-
fonidae, Ranidae, and Hylidae) that now dominate most
contemporary anuran faunas (Rage and Rocˇek, ). We
do not even know whether the dorsal tubercle in the Early
Triassic proanurans Triadobatrachus and Czatkobatrachus
(Rage and Rocˇek, ; Evans and Borsuk-Białynicka, )
is homologous with those in true anurans. Additional mate-
rial is needed to resolve these kinds of problems. Further
collection and study of specimens from stratigraphically
extensive sequences of localities – such as the sequence in
southwestern Utah used for this study – should help establish
when key iliac features appeared during the evolution of an-
urans and may allow us to better understand how signicant
those novelties might have been to the success of particular
anuran groups.
This research was funded by the Ministry of Education,
Youth and Sports of the Czech Republic (grant )
through the American Science Information Center, Prague.
Funds for collecting in Utah were provided by grants to Ea-
ton from the National Park Service and the Bryce Canyon
Natural History Association, the Petroleum Research Fund
(-# -; -# -), the National
Science Foundation (-), and the National Geo-
graphic Society. We thank J.-C. Rage for his constructive
review and A. L. Titus for his helpful suggestions and edito-
rial help.
©2013 by Indiana University Press. All rights reserved. Do not reproduce.
Rocˇek et al.294
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