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6 FiguresSkeletal remains of a small theropod dinosaur with associated soft structures from the Lower Cretaceous Santana Formation of NE Brazil
Abstract
Associated well-preserved, uncrushed skeletal remains, comprising the pelvic girdle, partial sacrum, both femora, and parts of the right tibia and fibula, from the Romualdo Member of the Lower Cretaceous Santana Formation of northeastern Brazil record the presence of a previously unknown coelurosaurian theropod dinosaur in that formation. The pelvic girdle is noteworthy for the bilaterally asymmetrical development of various bony features. The specimen also preserves a segment of lithified intestinal tract. While still in the matrix, the fossil preserved a vacuity behind the pubic apron that may indicate the existence of a postpubic air sac.
Figures
Ecology, Systematics and Biogeographical Relationships of
Dinosaurs, Including a New Theropod, from the Santana
Formation (?Albian, Early Cretaceous) of Brazil
DARREN NAISH
a,
*, DAVID M. MARTILL
a
and EBERHARD FREY
b
a
School of Earth and Environmental Sciences, University of Portsmouth, Portsmouth PO1 3QL, UK;
b
Staatliches Museum fu
¨r Naturkunde Karlsruhe, Geowissenschaftliche Abteilung, Erbprinzenstra
b
e 13, D-76133 Karlsruhe, Germany
Although rare, dinosaurs are well preserved in calcare-
ous nodules of the Santana Formation (Early Cretace-
ous, ?Albian) of the Araripe Basin, in northeastern Brazil.
So far, including only a spinosauroid and three
coelurosaurs, the dinosaur fauna appears depauperate.
High theropod diversity in assemblages where other
dinosaurs are rare or absent is not unique to the Santana
Formation. It is seen also in several other assemblages,
including Solnhofen and the Maevarano Formation of
Madagascar. We consider several factors, including the
occurrence of intraguild predation, the possibility that
small theropods could subsist in marginal environments,
and reliance on coastal resources, that may have been
responsible for this apparent ecological imbalance.
A new coelurosaur from the Santana Formation, here
formally named Mirischia asymmetrica, is shown to be
distinct from Santanaraptor placidus [Kellner, A.W.A.
(1999) “Short note on a new dinosaur (Theropoda,
Coelurosauria) from the Santana Formation (Romualdo
Member, Albian) northeastern Brazil”, Boletim do Museu
Nacional, Nova Serie, Rio de Janeiro, Brasil 49, 1 – 8].
Other theropods from the Santana Formation are briefly
reviewed. Mirischia is a compsognathid, more similar to
the European Compsognathus than to the Asian Sino-
sauropteryx.
Keywords: Dinosaur; Theropoda; Compsognathidae; Mirischia;
Brazil; Santana Formation
INTRODUCTION
The calcareous nodule bearing Romualdo Member
of the Santana Formation, in the Araripe Basin of
northeastern Brazil, is the world’s premie
`re source
of Early Cretaceous pterosaurs. It has yielded a
diverse and exceptionally well preserved assem-
blage (Martill and Unwin, 1989; Kellner and Tomida,
2000). It is less well known that this deposit also
produces rare dinosaur remains (Campos and
Kellner, 1991; Frey and Martill, 1995; Kellner,
1996a). Crocodyliforms and turtles also occur
(Gaffney and Meylan, 1991; Martill, 1993; Hirayama,
1998), but these are rare. Perhaps surprisingly, the
initial discovery of these tetrapod remains was an
incidental result of commercial excavation of
Romualdo nodules for their abundant and diverse
fossil fishes. Previously, artisan fossil diggers had
disposed of tetrapod remains which they considered
to be of little or no commercial value. Since the 1980s
this situation has changed. Now, tetrapod-bearing
nodules, even those containing isolated or fragmen-
tary elements, have begun to attract high prices.
Several nodules containing dinosaur remains have
been documented, although not all have been
described in full, as noted by Kellner (2001).
Complete skeletons have not yet been reported, but
partial skeletons in exceptional states of preservation
are known (Kellner, 1996a,b; Martill et al., 2000).
Bones within the nodules are usually preserved in
three-dimensions, without flattening, sometimes in
articulation (Martill et al., 2000). Soft tissue preser-
vation has been reported (Kellner, 1996a,b; 1999) and
gut contents were discovered in the theropod
specimen described here (Martill et al., 2000).
The dinosaur fauna of the Romualdo Member is
incompletely known, due to the small data set so
far available, but the assemblage is clearly domi-
nated by theropods. The first report of a non-
crocodyliform, non-pterosaurian archosaur from the
nodules was an isolated bone, tentatively
identified as an ornithischian ischium (Leonardi
and Borgamanero, 1981). This identification is
ISSN 0891-2963 print/ISSN 1029-2381 online q2004 Taylor & Francis Ltd
DOI: 10.1080/08912960410001674200
*Corresponding author. E-mail: darren.naish@port.ac.uk
Historical Biology, June–December 2004 Vol. 16 (2–4), pp. 57–70
doubtful; Kellner (1996a; 1999) treated the specimen
as Dinosauria incertae sedis. To date, this specimen
is the only indication that ornithischians may
be represented in the Santana dinosaur assemblage.
However, apparently undiagnostic dinosaur
material has also been reported by Campos (1985).
More readily identifiable remains were figured by
Campos and Kellner (1991) in a short review of the
Santana Formation dinosaurs. These authors figured,
but did not describe, a number of new specimens.
Beginning in the mid-1990s, several theropods were
reported and described. Among the first of these was
the partial sacrum of a coelurosaur, described by
Frey and Martill (1995). They suggested, on the basis
of its pleurocoelous centra, that it had affinities
with Oviraptorosauria. With respect to this
identification, Makovicky and Sues (1998) noted
that pleurocoelous sacral centra occur in theropods
other than oviraptorosaurs. They argued that the
dorsally arched long axis and expanded intercentral
articulations of the Santana specimen suggest that it
is not an oviraptorosaur. Although there may be
insufficient grounds, at present, to refer this sacrum
to Oviraptorosauria with any degree of certainty, it
does resemble the sacrum of the caenagnathid
Chirostenotes (Currie and Russell, 1988; Sues, 1994).
The main difference between them is the absence of a
neural spine lamina in the Santana specimen. The
suggestion that the Santana specimen represents an
alvarezsaurid (Marjanovic, 2000) is without founda-
tion. This specimen lacks the distinctive transversely
compressed, procoelous sacral centra that are
characteristic of that group.
The first named Santana theropod, Irritator
challengeri, was described by Martill et al. (1996) on
the basis of a partial skull, missing the end of its
snout. Irritator was initially referred to Bullatosauria,
a group erected by Holtz (1994) to include
troodontids and ornithomimosaurs, but not sup-
ported as monophyletic by more recent analyses
(Makovicky and Sues, 1998; Holtz, 2000). However,
the presence in Irritator of straight, conical, unser-
rated tooth crowns patterned with vertical ridges,
caudally located nares and other features indicate
that it is a spinosauroid (Kellner, 1996a; Charig and
Milner, 1997; Sereno et al., 1998). Further preparation
of this specimen has now been completed and
a more detailed description was recently published
(Sues et al., 2002).
Kellner and Campos (1996) described a second
Santana spinosauroid based only on a portion of
distal rostrum; they named it Angaturama limai.
While there is no overlap of corresponding structural
elements between the holotypes of Irritator and
Angaturama, they are similar in their degree of lateral
compression, both possess a dorsal midline crest,
and both have transversely round tooth crowns with
unserrated carinae (Kellner and Campos, 1996;
personal observations). Consequently, Charig and
Milner (1997) and Sereno et al. (1998) suggested that
Angaturama might be a junior synonym of Irritator.
Holtz (1998) even suggested that the distal rostrum
of Angaturama might fit on the end, as the missing
rostrum of the holotype of Irritator. The discovery of
another Santana spinosauroid specimen has recently
been announced (Kellner, 2001). This appears to be
the most complete Santana dinosaur yet discovered.
Reportedly, it includes a complete pelvis and
sacrum, caudal vertebrae, and incomplete front and
hindlimbs.
Another coelurosaur from the Santana Formation,
Santanaraptor placidus, was described by Kellner
(1999). The specimen consists of an associated partial
pelvis, hindlimb elements and vertebrae. It exhibits
extensive preservation of soft tissues, including
muscle fibres (Kellner, 1996b). As noted by Kellner
(1999), the proximodistally large, U-shaped obtura-
tor notch of Santanaraptor indicates that this is a
maniraptoriform coelurosaur. However, contra
Kellner (1999; 2001), this character is not diagnostic
for Santanaraptor. Similar ischial obturator notches
are widely distributed among other maniraptori-
forms, including oviraptorosaurs and deinonycho-
saurs. Similarly, the foramen on the base of the lesser
trochanter, regarded as diagnostic for Santanaraptor
by Kellner (1999), is not unique to this taxon (Naish,
2000). Other diagnostic characters of Santanaraptor
have been recognized, however, so we agree that this
is a distinct, diagnosable taxon. Kellner (2001) has
recently suggested inclusion of Santanaraptor within
Tyrannoraptora, a maniraptoriform group erected by
Sereno (1999) to include tyrannosauroids, oviraptoro-
saurs and paravians. This assignment is based on the
unfooted distal ischium of Santanaraptor. However,
the polarity of this character is undetermined at
present, as argued by Holtz (2000). It is possible that
the ischial foot was lost several times in the evolution
of maniraptoriforms. It is also clear from conflicting
coelurosaur phylogenies that Sereno’s (1999) group-
ings are controversial and at odds with results of
other studies (Makovicky and Sues, 1998; Padian
et al., 1999; Holtz, 2000).
Martill et al. (2000) described another small
coelurosaur from a Santana Formation nodule.
In this specimen, the nearly complete pelvis, both
femora, proximal parts of a tibia and fibula and
several gastralia are preserved in articulation.
In addition, the specimen included material filling
the gut and a post-pubic air sac may be preserved.
The osteology and soft tissues of this specimen were
described by Martill et al. (2000), but it was not
named, and neither its palaeoecological nor phylo-
genetic significance was discussed.
This specimen clearly represents a taxon, named
here as a new genus and species, that is distinct from
both previously described Santana coelurosaurs.
D. NAISH et al.58
The excellent preservation and intriguing osteology
of this specimen have caused it to become integral to
our understanding of theropod pelvic and hindlimb
morphology (Hutchinson, 2001a,b), soft tissue
biology and physiology (Paul, 2001) and the
interpretation of less complete remains representing
similar taxa (Naish et al., 2001).
Why Only Theropods?
The Santana Formation’s dinosaur assemblage is
unusual in that only theropods have been recorded.
There is evidence that ornithopods may have been
present in northeastern Brazil during the Early
Cretaceous. Footprints from the Rio de Peixe Basin of
Paraiba, some 100 km to the north-east of the Araripe
Basin, have been attributed to hypsilophodontids
(Leonardi, 1987; Leonardi et al., 1987).
The Romualdo Member was deposited under
brackish or quasi-marine conditions. It represents
either a lagoonal setting or a basin with only
restricted connections to waters of normal marine
salinity (Maisey, 1991; Martill, 1993). The dinosaur
fauna is allochthonous and may have been
derived from nearby shoreline environments. Trans-
port distances are likely to have been in the order
of tens of kilometres or less. The distance from
Santana do Cariri to the nearest mapable shoreline is
about 13 km. We infer that all the dinosaur
fossils represent remains of drifting carcasses,
derived from the shoreline or swept out to sea from
the mouths of rivers.
The environment surrounding the Araripe Basin is
generally considered to have been arid or semi-arid.
Thick sequences of evaporites occur in the Ipubi
Formation, immediately below the Santana For-
mation. By far the most abundant fossils in the
concretions of the Romualdo Member are fishes;
several mass mortality horizons are recorded
(Martill, 1988a; 1993). The flora consists largely of
plants of a xerophytic nature. It is dominated by the
gymnosperm Brachyphyllum, which had succulent
leaves, and cycadiales (Crane and Maisey, 1990). The
local terrestrial environment appears to have been
sparsely vegetated and thus unable to support large
numbers of herbivores. In these circumstances,
predatory theropods would have been able to gain
sustenance by scavenging along the shoreline, as
well as by foraging in shallow water. It has been
suggested that the spinosauroid Baryonyx was at
least in part piscivorous (Charig and Milner, 1997).
If this was so, it is equally plausible that the
Santana spinosauroid Irritator was also facultatively
piscivorous. We favour the view that Irritator was a
generalist carnivore, preying on aquatic and terres-
trial vertebrates as well as carrion, around the
shoreline of the Santana lagoon. Theropods scaven-
ging at the shoreline and fishing in shallow water
would have stood a far greater chance of being
incorporated into the Santana sediments than any
herbivores feeding in the hinterland.
There are other dinosaur assemblages that are
notable for their abundance of theropods relative to
herbivorous taxa. The extreme case is that of the
Solnhofen Limestone (Kimmeridgian-Tithonian), in
which the only dinosaurs preserved are the small
theropods Archaeopteryx,Wellnhoferia (Elzanowski,
2001), Compsognathus and an unnamed form
(Viohl, 1999). The Aptian/Albian to Cenomanian
dinosaur-bearing sequences of North Africa yield
more theropod remains than herbivores, although
quantitative data are not available (Russell, 1996).
In the Gre
`s Rouges of Tafilalt, Morocco, theropods
outnumber sauropods and ornithischians are absent,
with the exception of a possible stegosaur (Russell,
1996). In the Wadi Milk Formation of Sudan,
iguanodontids and hypsilophodontids are present
but they appear to be rare compared with theropods
and sauropods (Rauhut, 1999). In both the Maeva-
rano Formation (Maastrichtian) of Madagascar and
the Sao Khua Formation (Lower Cretaceous) of
Thailand, the dinosaur assemblages are likewise
dominated by theropods and sauropods (Sampson
et al., 1998; Buffetaut and Suteethorn, 1999; Krause
et al., 1999), while ornithischians are absent. The
Santana dinosaur assemblage differs from those of
Tafilalt, Sudan, Madagascar and Thailand in that no
herbivores have yet been recorded. In this respect, it
recalls the Solnhofen fauna.
A number of speculative scenarios have been
advanced to explain the diversity of theropods in
some of these faunas. Russell (1996) suggested that
the Tafilalt deposit represents a trophically con-
trolled assemblage, in which fish represented the
primary food source for theropods. High theropod
diversity might be explained by the presence of a
large top predator, such as Carcharodontosaurus,
which was able to take large prey that were
otherwise unavailable to smaller theropods (cf.
Rauhut, 1999). Diverse carnivores can coexist in the
same environment, exploiting a paucispecific prey
assemblage. A modern analogue is provided by
African flamingo colonies, consisting of one or two
prey species (Phoenicopterus ruber and Phoeniconaias
minor), that are exploited by as many as nine
predator species. These include falconiforms, larids,
ciconiids, canids and hyaenids (Ogilvie and Ogilvie,
1986). Intraguild predation among carnivores can
also increase predator diversity. It is well documen-
ted in extant carnivorans (Palomares and Caro,
1999). Intraguild predation may well have existed
among theropods and could partly explain their
diversity in paucispecific assemblages. Theropod
abundance in an otherwise paucispecific assemblage
may in some cases be due to an abundance of
carrion. It is conceivable, for example that fish and
SANTANA THEROPOD DINOSAURS 59
pterosaur corpses were abundant on the Solnhofen
and Santana shorelines after storm events.
A possibility worth considering is that theropods
may be over-represented in marine or lagoonal
deposits because their size, which was often small,
and their pneumatic skeletons allowed their
carcasses to float and drift for longer times than
those of other dinosaurs. However, this hypothesis
is contradicted by the presence in many marine
deposits of non-theropod dinosaurs that outnum-
ber theropods in the number of taxa represented
(see below).
The fact that compsognathid theropods are found
in both the Santana and Solnhofen Formations
suggests that members of this group were
specifically adapted to inhabit semi-arid environ-
ments. Compsognathids may have been ecologically
similar to some varanid lizards, such as Varanus
griseus (see Kirschner et al., 1996), in being opportu-
nistic carnivores that also consumed some vegetation.
The preservation of gut and stomach contents in some
vertebrate fossils from the Santana Formation (Wilby
and Martill, 1992) holds out the hope that this may be
a testable hypothesis (cf. Munk and Sues, 1993).
SYSTEMATICS
DINOSAURIA Owen, 1842
SAURISCHIA Seeley, 1887
THEROPODA Marsh, 1881
COELUROSAURIA Huene, 1914
COMPSOGNATHIDAE Cope, 1875
Genus Mirischia gen. nov.
Type species:Mirischia asymmetrica gen. et sp. nov.
(Text– figures 1 –9)
Derivation of name:Mirischia, Mir, Latin, wonderful;
Ischia, Greek, pertaining to the pelvis (and not the
ischia alone).
Holotype: SMNK 2349 PAL
Locality: Region of Araripina (exact locality
unknown), Chapada do Araripe, Pernambuco,
northeastern Brazil.
Horizon and age: Romualdo Member of the Santana
Formation, Araripe Group. Lower Cretaceous
(Martill and Wilby, 1993). A ?late Albian age is
inferred by Pons et al. (1990).
Material: The holotype is the only known speci-
men. Prior to preparation, one dorsal vertebral
centrum with part of the neural arch, four sacral
vertebral centra with parts of neural arches, several
gastralia and lithified contents of the terminal part
of the intestinal tract, an articulated pelvis and
proximal parts of the hind limbs including partial
left and right ilia, left and right ossa pubis,
slightly damaged left and right ischia, partial
left and right femora, the proximal end of a
right tibia, and the proximal end of a right fibula
were contained in a single calcium carbonate
concretion.
Diagnosis:Compsognathus-like compsognathid coe-
lurosaur, probably reaching larger adult body size
than other compsognathids, pubic peduncle of ilium
with concave cranial surface, pubic boot with no
cranial expansion and 32% total length of pubis,
pedicular fossae located craniodorsal to neural canal
on caudal dorsal vertebra, distal tips of the neural
spines between 63% and 67% longer than their bases,
ventral surface of sacral centra bearing shallow
median depressions at either end, and extremely thin
bone walls to all known elements. For a complete
description see Martill et al. (2000).
BRIEF ANATOMICAL DESCRIPTION
Vertebral Column
Five articulated vertebrae are known for Mirischia,
including a partial dorsal, a dorsosacral, and three
sacrals, the most caudal of which is incomplete
(Figs. 1– 3). The vertebrae all retain distinct neuro-
central sutures. Most of the cranial half of the
dorsal vertebra is missing; on its right side, a short
rib in articulation with its transverse process is
preserved. Pedicular fossae are located dorsal to
FIGURE 1 Preserved dorsal, dorsosacral and cranial sacral vertebrae of Mirischia asymmetrica in right lateral view. Magnification £3.
D. NAISH et al.60
the neural canal on the cranial surface of this
vertebra (Fig. 3). That on the left is a foramen linked
to the pneumatic interior of the neural arch while
that on the right is a fossa. The intervertebral
articulation between the second and third vertebrae
remains unfused, hence the identification of
the second as a dorsosacral (Martill et al., 2000).
The sacral vertebrae are fused and belong to
the cranial part of the sacrum, the total length of
which is unknown.
The sacral vertebrae of Mirischia are amphicoelous.
On the ventral surface of each there are both parallel
striations that run the length of the centrum and
shallow depressions located cranially and caudally
along the midline. On the second sacral vertebra, the
caudal depression continues onto the ventral surface
of the third centrum. To our knowledge, such
depressions have not been reported in any other
theropod. The more extensive ventral sulcus seen on
the sacral vertebrae of eumaniraptoran coelurosaurs
is clearly different.
The neural spines of Mirischia are cranially and
caudally concave, such that the apex of the spine is
between 63% and 67% longer than the base (Fig. 1).
Pelvis
The pelvis is nearly complete, with both ossa pubis,
both ischia and parts of both ilia present. The distal
ends of the ischia are missing, as are the caudal-most
portions of both ilia. The right ilium is better
preserved than the left. The width of the pelvis
shows that Mirischia had a very narrow body, being
approximately 30 mm wide across the sacrum. The
preacetabular process of the ilium terminates in a
square-ended process that is directed cranioven-
trally. The ventromedial part of this process is
slightly angled laterally with respect to the dorso-
medial part (Fig. 4). The ventral surface of the pubic
peduncle is convex craniocaudally, with a shallow
longitudinal groove; the peduncle is directed
cranioventrally and it has a concave cranial margin.
A cranially concave pubic peduncle also occurs in
the Tyrannosauroidea. However, since there is no
indication that Mirischia is a member of that clade,
we here regard this character as a diagnostic feature
of Mirischia. The pubis forms a long (145 mm) and
slender shaft, the distal end of which forms a
large pubic boot (Figs. 5 and 6). The length of
this boot (53 mm) extends 37% of the length
of the pubic shaft. Proximocaudally, the pubis bears
a caudally projecting rectangular flange. The angle
between the long axis of the sacrum and the pubis is
approximately 558.
Mirischia is remarkable in that it has an obturator
foramen on the caudally projecting rectangular
flange of the right pubis, but a ventrally open notch
in the corresponding position on the left pubis
(Martill et al., 2000). Conjoined medial laminae of
both ossa pubis together form a transverse pubic
apron that extends from the proximal third of the
pubis to the pubic boot (Fig. 7). An elongate pubic
FIGURE 3 Preserved vertebrae of Mirischia asymmetrica in cranial
view. Note the pedicular fossae dorsolateral to the neural canal.
Magnification £3.4.
FIGURE 2 Preserved dorsal, dorsosacral and cranial sacral vertebrae of Mirischia asymmetrica in dorsal view. Magnification £3.
SANTANA THEROPOD DINOSAURS 61
foramen is present distally and divides the cranial
third of the boot. As noted by Hutchinson (2001a),
Martill et al. (2000) proposed that this foramen may
have accommodated a ventral pneumatic duct,
leading to a post-pubic air sac (Fig. 8).
The ischia of Mirischia are asymmetrical, that on
the left being perforated by an oval foramen while
that on the right has an open notch in the same
position. The obturator flange on the right side is
similar in shape to those of Sinosauropteryx prima
(Currie and Chen, 2001) and Allosaurus fragilis
(Pe
´rez-Moreno et al., 1999). The caudal margin of
the ischium in Mirischia is evenly concave. The angle
between the pubis and ischium is approximately 608
(Figs. 5 and 6).
Femur
The femur of Mirischia exhibits a craniodorsally
curved shaft, a medially directed head set off at a
right angle to the shaft, and a bifid, craniodorsally
directed trochanter that is well separated from and
distal to the head (Fig. 9). Most of the distal condyles
are missing. Although the bifid trochanter was
identified by Martill et al. (2000) as the lesser (or
anterior) trochanter, it probably represents a fused
accessory and lesser trochanter (Hutchinson, 2001b).
Two small convexities caudolateral to the lesser
trochanter were interpreted by Martill et al. (2000)
as the insertion points of m. obturatorius and
m. iliotrochantericus. Hutchinson (2001b) has sugges-
ted that this area represents a reduced trochanteric
shelf and the attachment area for m. iliofemoralis
externus. The fourth trochanter in Mirischia is a low
ridge, located within the proximal third of the caudal
surface of the femur.
Tibia
The right tibia is represented only by its proximal
end. A shallow sulcus separates the cranial surface
of the lateral condyle from the proximal third of the
cnemial crest. The proximal condyles differ in
shape, as is typical for theropods; the medial
condyle is craniocaudally longer and mediolaterally
wider than the lateral condyle. The two condyles are
separated by a shallow flexor fossa. Only
the proximal part of the fibular crest is preserved.
FIGURE 4 Preserved fragment of right ilium of Mirischia asymmetrica in medial (A, above) and lateral (B, below) views.
Magnification £1.5.
D. NAISH et al.62
In distal cross-section, the shaft of the tibia is
subtriangular.
Fibula
The right fibula is also represented only by a
proximal fragment. On its medial surface, this bears
a deep, parallel-sided sulcus. This is separated by a
raised area from a more caudally situated depression
(Fig. 10).
COMPARISONS
Mirischia closely resembles compsognathid theropods
from the Late Jurassic of Europe (Compsognathus
longipes) and the Early Cretaceous of Europe
(Aristosuchus pusillus) and China (Sinosauropteryx
prima)(Bidaret al., 1972; Ostrom, 1978; Chen et al.,
1998; Naish et al., 2001; Currie and Chen, 2001).
However, it has proven difficult to find convincing
derived characters that unite compsognathids,
setting them apart from all other theropods. Currie
and Chen (2001) suggested the presence of a
proportionally large skull, unserrated premaxillary
but serrated maxillary teeth, slender cervical ribs,
short forelimbs, limited cranial expansion of the
pubic boot, a prominent ischial obturator process,
fan-shaped dorsal neural spines, a prominent ulnar
olecranon process and a powerful manual phalanx I-1
as characters indicating a monophyletic Compso-
gnathidae. However, they noted that some of these
characters are widely distributed within Theropoda.
Pending further study we provisionally accept
compsognathid monophyly, regarding neural spines
on the dorsal vertebrae that are craniocaudally
FIGURE 5 Pubis and ischium of Mirischia asymmetrica in right lateral view. Note enclosed foramen on proximal pubis and ventrally open
obturator notch on ischium. Magnification £1.2.
SANTANA THEROPOD DINOSAURS 63
longer at the dorsal apex than at the base (“fan-
shaped” of Chen et al., 1998) and limited cranial
expansion of the pubic boot (Martill et al., 2000; Naish
et al., 2001) as diagnostic features indicating member-
ship of this group (Fig. 11).
Like Sinosauropteryx,Mirischia exhibits “fan-
shaped” neural spines. This character is also seen
in the dorsal neural spines of ornithomimosaurs,
where the spine may be 55% longer at its tip than at
its base (Makovicky, 1995). It is also reported in a
basal troodontid, Sinovenator changii (Xu et al., 2002).
The distal expansion of the neural spines appears
greater in Mirischia than in other compsognathids
and ornithomimosaurs. The neural spines of
Mirischia are between 63% and 67% longer at their
distal tips than at their bases. Since compsognathids,
ornithomimosaurs and troodontids are almost
certainly not close relatives (Holtz, 2000; Xu et al.,
2002), it appears likely that any feature which is held
in common among these groups represents conver-
gence. Distal expansion of the neural spine therefore
stands as a possible compsognathid character.
However, we note that ossification of the dorsal tip
and of the cranial and caudal surfaces of the neural
spine may vary during ontogeny. “Fan-shaped”
neural spines may yet prove to be more widespread
among theropods than has so far been recognized.
A prominent pubic boot with only moderate
cranial expansion is present in Mirischia,Compso-
gnathus,Sinosauropteryx and Aristosuchus. This could
also be a derived compsognathid character. How-
ever, similar boot morphologies occur in other
coelurosaurs (Currie and Chen, 2001), and it is
difficult to quantify this character. We here compare
FIGURE 6 Pubis and ischium of Mirischia asymmetrica in left lateral view. Note the absence of the enclosed foramen present on the right
pubis and the enclosed obturator foramen on the ischium. Magnification £1.2.
D. NAISH et al.64
Mirischia directly with the other compsognathid taxa
and with the contemporaneous coelurosaur Santa-
naraptor (Kellner, 1999).
Sinosauropteryx prima
The holotype of Sinosauropteryx prima and at least
one of the referred specimens (NIGP 127587) exhibit
the same derived forelimb characters, including the
proximomedial flange on the first metacarpal (Currie
and Chen, 2001). Hence, we provisionally regard
NIGP 127587 as a representative of S. prima. A third
specimen (GMV 2124) differs from the type speci-
men and from NIGP 127587 in its skeletal pro-
portions and other anatomical features. On the basis
of a cladistic analysis, Longrich (2000) concluded
thatthetypespecimenandGMV2124might
represent two unrelated taxa.
In S. prima, the preacetabular process of the ilium
has near-parallel dorsal and ventral margins; it does
FIGURE 8 Conjoined ossa pubis and ischia of Mirischia
asymmetrica in caudal view. Magnification £2.4.
FIGURE 7 Conjoined ossa pubis of Mirischia asymmetrica in
cranial view with intestinal infill preserved between the pubes.
Magnification £2.4.
SANTANA THEROPOD DINOSAURS 65
not exhibit marked ventral curvature at its cranial
tip. In contrast, in Mirischia the preacetabular process
curves ventrally, exhibiting a notably convex dorsal
margin and a concave ventral margin. While S. prima
has distally expanded neural spines on its dorsal
vertebrae, these are not as expanded as those of
Mirischia (Chen et al., 1998). The pubic boot in S. prima
is proportionally smaller (approximately 27% of total
pubis length) than that of Mirischia, but the two taxa
are similar in the morphology of their femora, tibiae
and ischia. In S. prima, the lesser trochanter appears
similar in form and size to that of Mirischia, although
a distinct accessory trochanter is not evident in
S.prima (Chen et al., 1998; Currie and Chen, 2001).
While in Mirischia and Compsognathus the angle
between the long axis of the sacrum and the pubis is
approximately 558, this angle is larger (about 758)in
S.prima, where the pubis is more vertical.
This character is obviously correlated with the
inclination of the pubic peduncle.
Aristosuchus pusillus
The holotype of Aristosuchus, long confused with
Calamospondylus oweni (see Naish et al., 2001; Naish,
2002), more resembles Compsognathus in the form of
its pubis than any other theropod, so it is regarded
as an ostensible compsognathid. The concavities
and parallel striations present on the ventral
surfaces of the sacral vertebrae in Mirischia are not
present in Aristosuchus. The most cranial of the
vertebrae in Aristosuchus also lacks the pedicular
FIGURE 9 Right femur of Mirischia asymmetrica in A, cranial; B, medial; C, lateral; and D, caudal views. The caput is absent in these
figures. Magnification £1.1.
D. NAISH et al.66
fossae seen on the cranial surface of the dorsal
vertebra of Mirischia.
Two elements provisionally referred to Aristo-
suchus are strikingly similar to corresponding
elements in Mirischia. Galton (1973) described
a fragmentary proximal femur from the Wessex
Formation of the Isle of Wight (specimen BMNH
R5194), referring it to Aristosuchus (see Naish et al.,
2001). Like the femur of Mirischia, BMNH R5194 has
fused lesser and accessory trochanters that exhibit a
shallow V-shaped notch at their point of fusion. This
morphology is probably primitive for coelurosaurs,
however, and not a shared derived similarity
(Hutchinson, 2001b). The reduced fourth trochanter
in BMNH R5194 indicates that it is from a
coelurosaur, and its similarity to the femora of
Mirischia further suggests that it belongs to a
compsognathid (Naish et al., 2001). This inference is
provisional in the absence of further material,
however. If this specimen is from Aristosuchus, this
taxon differs from Mirischia in having thicker bone
walls. An isolated ischium that has provisionally
been referred to Aristosuchus (Naish, 2002) resembles
that of Mirischia, but differs from it in that the
obturator process is triangular and thus more like the
ischia of Compsognathus.
Compsognathus longipes
Mirischia closely resembles Compsognathus in having
a pubic boot that lacks a cranial projection and that is
almost flat ventrally. The pubic boot of Mirischia is
virtually identical in shape to that of the Nice
specimen of Compsognathus (Bidar et al., 1972).
However, the pubic boot of Compsognathus is
proportionally larger than that of Mirischia. In the
Nice Compsognathus, the length of the pubic boot is
approximately 41% the total length of the shaft of the
pubis (Bidar et al., 1972) while in the German
specimen (based on the cast BMNH R49159) it is
approximately 45%. In Mirischia, the boot represents
32% of the total length of the pubis. There appear to
be other differences between Compsognathus and
Mirischia, including a triangular ischial obturator
process in Compsognathus.However,theseare
difficult to validate because of poor or incomplete
preservation of skeletal material (Bidar et al., 1972;
Ostrom, 1978; personal observations).
Santanaraptor placidus
Mirischia is not synonymous with Santanaraptor.As
pointed out above, Santanaraptor has a proportion-
ally larger ischial obturator notch that fully separates
the pubic peduncle from the obturator process
(Kellner, 1999). In Santanaraptor the femur bears a
large sulcus that is not present in Mirischia.
DISCUSSION: THE SANTANA DINOSAUR
FAUNA
Referral of Mirischia to Compsognathidae has
implications for the palaeobiogeographic affinities
of the Santana dinosaur fauna. All previously known
compsognathids are from Eurasia (Bidar et al., 1972;
Ostrom, 1978; Ji and Ji, 1997; Zinke, 1998; Chen et al.,
FIGURE 10 Skeletal reconstruction of the compsognathid Compsognathus with known elements of Mirischia asymmetrica stippled.
Diagram by kind courtesy of Gregory S. Paul.
FIGURE 11 Tentative proposal of phylogenetic relationships of
compsognathid taxa with compsognathid monophyly and choice
of outgroups based on previous studies (Holtz, 1994; 2000).
Characters defining relationships in the cladogram are as follows:
(1) Unserrated premaxillary teeth; (2) Reduced/absent cranial
process on pubic boot; (3) “Fan-shaped” dorsal neural spines;
(4) Proportionally large pubic boot (,32% total pubis length);
(5) Dorsal/sacral neural spines proportionally longer than those of
Sinosauropteryx; (6) Angle between long axis of sacrum and shaft of
pubis about 558; (7) Triangular obturator process.
SANTANA THEROPOD DINOSAURS 67
1998; Rauhut, 2000; Naish et al., 2001; Currie and
Chen, 2001). If compsognathids first evolved as an
endemic Laurasian group, Mirischia constitutes
evidence of an interchange of dinosaurs between
Europe and South America, probably via Africa,
during the Early Cretaceous. Alternatively, the geo-
graphic distribution of compsognathids may reflect
vicariance following the fragmentation of Pangaea.
The referral of a theropod sacrum from the
Santana Formation to Oviraptorosauria by Frey and
Martill (1995) is also biogeographically significant, if
this assignment proves to be correct. Thus far, there
are only two other reports of members of Oviraptoro-
sauria from Gondwana: a surangular and a dorsal
vertebra from the Early Cretaceous of Australia
(Currie et al., 1996), and an isolated cervical vertebra
from the Late Cretaceous of Argentina (Frankfurt
and Chiappe, 1999).
The spinosauroid Irritator challengeri (Martill et al.,
1996) indicates that the dinosaur fauna of
the Santana Formation includes elements at the
suprageneric level that also are found in the Early
and mid-Cretaceous of Africa. Other similarities
between the Santana tetrapod assemblage and North
African Cretaceous assemblages are well known
(Buffetaut and Taquet, 1979; but see Kellner, 1994;
Ortega et al., 2000), suggesting that Eurasian
dinosaurs could have spread to South America by
way of Africa.
As noted above, Kellner (1999) suggested that
Santanaraptor may belong to Maniraptoriformes. This
coelurosaur clade is now well documented in the
Cretaceous of South America, where it is represented
by Unenlagia, oviraptorosaurs, alvarezsaurids and
avialians (Novas, 1996; 1997; Novas and Puerta,
1997; Frankfurt and Chiappe, 1999). Maniraptori-
form dinosaurs were evidently widely distributed;
they appear to have had an almost global geographic
range in the Cretaceous.
In conclusion, the presence in the Santana
Formation of spinosauroids, compsognathids and
maniraptoriforms casts further doubt on sugges-
tions (Bonaparte, 1996) that Gondwana had a
distinct, endemic tetrapod fauna during the
Cretaceous.
Acknowledgements
We thank Marie-Celine Buchy and an anonymous
referee for critical reading of the manuscript and
Oliver Rauhut, Nick Longrich and Hans-Dieter Sues
for discussion. Ben Creisler provided assistance with
the name of the new taxon. Greg Paul kindly allowed
use of his updated Compsognathus reconstruction.
Thanks to Sandra Chapman (Natural History
Museum, London) for allowing us to examine
material in her care. DMM was supported by a
University of Portsmouth Fellowship. Special thanks
to Dr Paulo Brito (Rio) and Dr Artur Andrade (Crato)
for their invaluable help in Brazil.
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179–189.
APPENDIX: A COMMENT ON SMALL DATA
SETS
The tetrapod assemblage of the Santana Formation
is similar to that of the Jurassic Solnhofen Lime-
stone, at least in terms of the reconstructed
terrestrial palaeoenvironment and the presence of
carnivorous terrestrial tetrapods. The hinterland of
the Solnhofen lagoons, like that of the Santana
lagoon, is thought to have been semi-arid (Barthel
et al., 1990). One might argue that this is an
unusual deposit in that it represents a marine,
lagoonal environment with many fossils of terres-
trial origin. However, allochthonous dinosaur
assemblages are well-known from several fully
marine deposits, including the Callovian to
Oxfordian (Middle to Late Jurassic) Oxford Clay
and the Kimmeridgian (Late Jurassic) Kimmeridge
Clay, both in England (Martill, 1988b). Dinosaurs
are known from both of these organic-rich
mudrocks and, although the data sets are small,
dinosaurs are represented in both cases by most of
the major groups (Martill, 1988b). Similar numbers
of dinosaur specimens have been recorded from
these Jurassic marine mudrock formations, the
Santana Formation, and the Solnhofen Limestone.
Thus, it is surprising that all the approximately ten
dinosaur specimens collected from Solnhofen, even
after 150 years, are theropods. Similarly, we know
of about eight specimens, all of them theropods,
from the Santana Formation. The Oxford Clay of
Peterborough, England has yielded about ten
dinosaur specimens, representing seven taxa, only
two of which are theropods. The Kimmeridge Clay
of southern England has yielded nine taxa (total
specimen count is not known) of which only two
are theropods. One of these theropods is an
undescribed partial skeleton. In all cases, these
faunas are considered allochthonous, the dinosaurs
probably having drifted into marginal marine
environments from river systems draining local
hinterlands. Despite the small numbers of speci-
mens, the terrestrial environments adjacent to the
Santana Formation and the Solnhofen Limestone
do appear to have supported at most limited
numbers of herbivorous dinosaurs.
ADDENDUM
After this paper had been accepted for publication,
two published studies appeared which included
discussions of compsognathid systematics and
phylogeny (Rauhut, 2003; Hwang et al., 2004).
While both employed a more thorough analysis of
character distribution within Coelurosauria than the
present study, both supported compsognathid
monophyly and inclusion within the clade of the
same taxa included here. Though Rauhut (2003)
argued that the holotype of Mirischia should be
regarded as Compsognathinae indet., he also noted
that it probably represented a distinct taxon. Hwang
et al. (2004) described the new compsognathid
Huaxiagnathus orientalis from the Yixian Formation
(probably the most basal compsognathid) and
agreed that Mirischia is a compsognathid, albeit one
too incomplete to include in their analysis.
D. NAISH et al.70
- ... 'rauisuchians', Dutuit, 1979;crocodylomorphs, Walker, 1970;Crush, 1984;Hutchinson, 2001;extant crocodylians, Hutchinson, 2001;Schachner et al. 2011) as well as avemetatarsalians (e.g. pterosaurs, sauropodomorphs, early saurischians, Hutchinson, 2001;theropods, Andrews, 1921;Raath, 1977;Martill et al. 2000;neornithines, Ballman, 1969;Hutchinson, 2001). In birds, a scar, ridge or groove, known as the 'obturator ridge', marks insertion of the OM. ...
- ... However, Frey and Martill (1995) considered the matrix surrounding the specimen as typical of early diagenetic carbonate concretions of the Araripe Basin. Many of these concretions are fossiliferous and often preserve threedimensional fossils (e.g., Martill, 1988;Maisey, 1991;Fara et al., 2005); some of them even preserve soft tissues (e.g., Martill, 1988;Kellner, 1996;Martill et al., 2000). The beds bearing these concretions crop out mainly in the slopes of the Chapada do Araripe (¼Araripe Plateau) and are characterized by greenish shales and some marls and limestones. ...... Despite being rare, all non-avian dinosaur specimens from the Araripe Basin have been discovered within the carbonate concretions of the Romualdo Member. Besides SMNS 58023, they include the holotype of the spinosaurids Irritator challengeri and Angaturama limai, the possible tyrannosauroid Santanaraptor placidus, and the possible compsognathid Mirischia asymmetrica, together with other postcranial remains of indeterminate theropods ( Maisey, 1991;Kellner, 1996Kellner, , 1999Kellner and Campos, 1996;Martill et al., 1996Martill et al., , 2000Naish et al., 2004;Kellner, 2007, 2008). This non-avian dinosaur assemblage is unusual because consists only of theropods so far ( Naish et al., 2004). ...... Tyrannosaurus: Brochu, 2003). Conversely, proportionally lower sacral neural arches in comparison to their respective centrum occur in oviraptorosaurs (e.g., Chirostenotes: Currie and Russell, 1988;Nomingia: Barsbold et al., 2000) and Mirischia ( Martill et al., 2000;Naish et al., 2004). The ventral surface of the sacral centra is transversely convex and without a longitudinal keel contrasting with the condition, in at least, some oviraptorosaurs, in which there is a pair of longitudinal ridges on the ventral surface of the sacral centra (e.g., Chirostenotes: Currie and Russell, 1988;Osm olska et al., 2004). ...
- ... Specimens like BP/1/4885 suggest that possible asymmetry occurs between the left and right ischia of some smaller specimens. Skeletal asymmetry is rare but has been documented in dinosaurs, including the theropod Mirischia asymmetrica (Martill et al., 2000 ). Asymmetry of the skeleton could be sexually dimorphic, or may simply reflect a common tetratological lack of ossification either on one or both sides of the pelvis. ...
- ... Unequivocal evidence of structures linked to sexual dimorphism has not yet been documented; however, there are some cases of exceptional preservation that allow artists to go beyond the simple skeletal reconstruction (e.g. Horner 1984b; Martill 1991; Kellner 1996; Briggs et al. 1997; Benton 1998; Chiappe et al. 1998; Chen et al. 1998; Monasterski 1999; Xu et al. 1999a Xu et al. , 1999b Martill et al. 2000a Martill et al. , 2000b Gatesy 2001; Norell et al. 2001; Mayr et al. 2002; Schweitzer et al. 2007; reconstructed and placed in a virtual aquatic environment, where they interact with each other. The use of digital technologies is extended to the preparation of the sculptures, whose base is modelled digitally, and then printed in real size into several mountable parts. ...
- ... To date, the fossil record of Laurasian coelurosaurs provides the most complete and informative resource for understanding the clade's anatomy and evolution. However, documentation of coelurosaurian theropods from the southern continents has increased considerably since 1990, yielding valuable evidence regarding their diversification in Gondwana (e.g., Kellner, 1999;Novas, 1997aNovas, , 2009Novas and Puerta, 1997;de Klerk et al., 2000;Martill et al., 2000;Makovicky et al., 2005;Novas et al., 2009Novas et al., , 2012Agnolín et al., 2012;Choiniere et al., 2012). Remains of at least 13 non-avian coelurosaur nominal species have been recovered from different Cretaceous beds in South America, Africa, Madagascar, and Australia. ...
- ... Bidar et al. (1972) referred a specimen to a new species, Compsognathus corrallestris, but the synonomy of this specimen with C. longipes, which was suggested by Ostrom (1978), has been nearly universally accepted (Glut 1997; Norman 1990). Aristosuchus pusillus from the Wealden Group of England (Owen 1876; Naish 1999 ) and a fragmentary unnamed theropod (SMNK 2349 Pal) from the Santana Formation of Brazil (Martill et al. 2000) are probably also compsogathids, but both specimens are too incomplete to include in a phylogenetic analysis. Here we describe a new compsognathid, Huaxiagnathus orientalis gen. ...... Aristosuchus pusillus from the Wealden Group of England (Owen 1876; Naish 1999) and a fragmentary unnamed theropod (SMNK 2349 Pal) from the Santana Formation of Brazil (Martill et al. 2000) are probably also compsogathids, but both specimens are too incomplete to include in a phylogenetic analysis. Here we describe a new compsognathid, Huaxiagnathus orientalis gen. ...... Distally, a well-developed pubic boot that is anteroposteriorly longer than the proximal end is present. There is no anterior expansion of the pubic boot, as in Compsognathus (Ostrom 1978), Aristosuchus (Owen 1876; Naish 1999), SMNK 2349 Pal (Martill et al. 2000) and some other maniraptorans (Gauthier 1986). ...
- ... Note, however, that it is not known to what extent even small coelurosaurian theropod dinosaurs displayed anatomical features, such as airsacks, seen in modern birds (Ruben et al., 1997). The only evidence for the existence of airsacks comes from soft-tissue preservation in fossils of two small coelurosaurs (Dal Sasso and Signore, 1998; Martill et al., 2000), so that my argument here must be treated as speculative with respect to airsacks, although theropods undoubtably share numerous characteristics with Aves (Feduccia, 1999). Nonetheless, in order to explore a possible differences in scaling exponents between different groups of theropods, I repeated the regression analysis for theropods after dividing the data into ''small coelurosaurs'' (Alxasaurus, Archaeopteryx, Avimimus, Compsognathus, Deinonychus, Ornitholestes, Sinornithoides and Velociraptor) and ''other'' theropods. ...
- ... Early Cretaceous dinosaurs have been reported from the Hauterivian-Barremian of the La Amarga Formation of Neuquén, from which the dicraeosaurid sauropod Amargasaurus, the small, probable abelisaurian theropod Ligabueno, and an undetermined stegosaur have been described ( Salgado & Bonaparte, 1991;Bonaparte, 1996). Several theropods have recently been reported from the Santana Formation (Aptian) of Brazil, including spinosaurids ( Kellner & Campos, 1996;Martill et al., 1996) and coelurosaurs ( Frey & Martill, 1995;Kellner, 1999;Martill et al., 2000). Some theropod material of Aptian age, including two partial skeletons of an undescribed carcharodontosaurid, have also been reported from the Chubut Group of Argentina ( Rich et al., 2000). ...
- ... Whereas the anterior margin of the pubic peduncle is straight or even slightly convex in nontetanuran theropods and basal tetanurans (e.g. Madsen 1976; Currie and Zhao 1993), it is concave and shows an expansion ventrally in basal coelurosaurs (Martill et al. 2000), ornithomimosaurs (Archaeornithomimus: AMNH 21790), dromaeosaurids (Saurornitholestes: MOR 660), tyrannosaurids (Osborn 1916), Stokesosaurus, and Aviatyrannis. 4. Obturator process of ischium clearly offset from the pubic peduncle and con¯uent with ischial shaft distally. ...
- ... If reliable form-function relationships exist for a given muscle-tendon complex, anatomical changes can be used to reconstruct locomotor evolution. In contrast, the attachments of muscles and thin aponeuroses are more diffuse and subtle (Bryant and Seymour, 1990), and thus harder to distinguish in fossils, although recent discoveries of soft tissue fossils are promising (Kellner, 1996; Sasso and Signore, 1998; Martill et al., 2000). ...... Right proximal femur in lateral view with approximate orientation of surface fibers indicated (striations). (a) Herrerasaurus (Herrerasauridae; PVSJ 373); (b) Santana coelurosaur (Martill et al., 2000; reversed left side); (c) Microvenator (Oviraptorosauria; AMNH 3041); (d) Deinonychus (Deinonychosauria; MCZ 4371; reversed left side); (e) Sinornithoides (DeinonychosauriayTroodontidae; IVPP V9612); (f) Meleagris (Neognathae; personal collection). Abbreviations: 4T, fourth trochanter; AT, accessory trochanter; GT, greater trochanter; LT, lesser (anterior) trochanter; PT, posterior trochanter; TC, trochanteric crest; TS, trochanteric shelf. ...
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