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A dromaeosaur from the Maastrichtian of James Ross Island and the Late Cretaceous Antarctic dinosaur fauna

DOI:10.3133/of2007-1047.srp083
Authors:
Judd A. Case at Eastern Washington University
Judd A. Case
James E. Martin at South Dakota School of Mines and Technology
James E. Martin
Marcelo A. Reguero at Instituto Antártico Argentino
Marcelo A. Reguero
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The recovery of material of a small theropod from the Early Maastrichtian, Cape Lamb Member of the Snow Hill Island Formation is an unusual occurrence from primarily marine sediments. The pedal morphology of the specimen that includes a Metatarsal II with a lateral expansion caudal to Metatarsal III, a third metatarsal that is proximally narrow and distally wide, a Metatarsal III with a distal end that is incipiently ginglymoidal and a second pedal digit with sickle-like ungual are all diagnostic of a theropod that belongs to the family of predatory dinosaurs, the Dromaeosauridae. Yet this Antarctic dromaeosaur retains plesiomorphic features in its ankle and foot morphology. As new dromaeosaur species are being recovered from the mid-Cretaceous of South America and the retention of primitive characters in the Antarctic dromaeosaur, a new biogeographic hypothesis on dromaeosaur distribution has been generated. Gondwanan dromaeosaurs are not North America immigrants into South America and Antarctica; rather they are the relicts of a cosmopolitan dromaeosaur distribution, which has been separated by the vicariant break up of Pangea and created an endemic clade of dromaeosaurs in Gondwana.
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U.S. Geologic al Survey and The National Academies; USGS OF-2007-1047, Short Research Paper 083; doi:10.3133/of2007-1047.srp083
A dromaeosaur from the Maastrichtian of James Ross Island and the Late
Cretaceous Antarctic dinosaur fauna
Judd A. Case,1 James E. Martin,2 and Marcelo Reguero3
1College of Science, Eastern Washington University, Cheney, WA 99004 USA (jcase@mail.ewu.edu)
2Museum of Geology, South Dakota School of Mines & Technology, Rapid City, SD 57701 USA (James.Martin@sdsmt.edu )
3Departmento Paleontologia de Vertebrados, Museo de La Plata, 1Paseo del Bosque 1990 La Plata, Argentina (mreguero@netverk.com.ar)
Abstract The recovery of material of a small theropod from the Early Maastrichtian, Cape Lamb Member of the Snow
Hill Island Formation is an unusual occurrence from primarily marine sediments. The pedal morphology of the
specimen that includes a Metatarsal II with a lateral expansion caudal to Metatarsal III, a third metatarsal that is
proximally narrow and distally wide, a Metatarsal III with a distal end that is incipiently ginglymoidal and a second
pedal digit with sickle-like ungual are all diagnostic of a theropod that belongs to the family of predatory dinosaurs, the
Dromaeosauridae. Yet this Antarctic dromaeosaur retains plesiomorphic features in its ankle and foot morphology. As
new dromaeosaur species are being recovered from the mid-Cretaceous of South America and the retention of primitive
characters in the Antarctic dromaeosaur, a new biogeographic hypothesis on dromaeosaur distribution has been
generated. Gondwanan dromaeosaurs are not North America immigrants into South America and Antarctica; rather
they are the relicts of a cosmopolitan dromaeosaur distribution, which has been separated by the vicariant break up of
Pangea and created an endemic clade of dromaeosaurs in Gondwana.
Citation: Case, J.A., J.E. Martin, and M. Reguero (2007), A dromaeosaur from the Maastrichtian of James Ross Island and the Late Cretaceous
Antarctic dinosaur fauna, in Antarctica: A Keystone in a Changing World – Online Proceedings of the 10th ISAES X, edited by A.K. Cooper and
C.R. Raymond et al., USGS Open-File Report 2007-1047, Short Research Paper 083, 4 p.; doi:10.3133/of2007-1047.srp083
Introduction
Relatively few dinosaurs have been collected from the
Late Cretaceous of Antarctica. Heretofore, only five
dinosaur species have been reported from the James Ross
Basin on the eastern side of the Antarctic Peninsula
(Figure 1).
Figure 1. James Ross Basin along the northeastern
Antarctic Peninsula. The numbered localities indicate
where dinosaur specimens have been recovered: 1) Cape
Lachman, a large theropod; 2) Santa Marta Cove, a
nodosaur; 3) The Naze, an iguantodontid and the
dromaeosaur reported here; 4) Cape Lamb, a
hypsilophodontid; and 5) Sandwich Bluff, a hadrosaur.
The principal reason for the paucity of dinosaurs is
because the source rocks were deposited in a shallow
marine environment. Therefore, any specimens recovered
represent specimens that had to have been derived from
terrestrial environments and floated from shore, to be
preserved against high odds in a marine setting.
Discovery of associated dinosaur remains are rare in such
circumstances, making the recovery reported herein
unusual.
The associated remains of a small theropod dinosaur
weathered from the lower portion of the Cape Lamb
Member of the Snow Hill Island Formation (Crame et al.,
2004) on the Naze of James Ross Island. This new
dinosaur occurrence is the second theropod from the Late
Cretaceous of Antarctica. The first is a large megalasaur-
like theropod represented by a femur from Santonian
rocks in Cape Lachman, James Ross Island (Molnar et al.,
1996). This femur represents a very large theropod
species, much larger than the gracile theropod discussed
here. Other dinosaur remains include a nodosaur, the first
dinosaur recovered from Late Cretaceous rocks in
Antarctica (Gasparini et al., 1987). The nodosaur was
recovered from Santa Marta Cove area on James Ross
Island from the Late Campanian Herbert Sound Member
of the Santa Marta Formation (Crame et al., 1991). From
the younger Cape Lamb Member of the Snow Hill Island
Formation on Vega Island, a partial skeleton of a
hysilophodontid dinosaur was recovered from these Early
Maastrichtian deposits (Hooker et al. 1992). From
similar-aged deposits on the James Ross Island, portions
of a hindleg and foot of an iguanodontid were recovered
(Cambiaso et al., 2002). However its exact stratigraphic
and geographic location are unsure, although field
evidence suggests that it came from Fortress Hill next to
Terrapin Hill. Finally, dental and pedal material of a
hadrosaurine hadrosaur, was recovered from the Late
Maastrichtian Sandwich Bluff Member of the Snow Hill
Island Formation on Vega Island (Case et al., 2000). As
can be observed, most specimens are fragmentary in
nature, so the recovery of an associated series of skeletal
U.S. Geologic al Survey and The National Academies; USGS OFR-2007-xxxx, Extended Abstract.yyy, 1-4 Ver. 1/25/07
Figure 2. Posing of the bones in life position of the left lower leg, ankle and foot of the dromaeosaur
from the Naze Peninsula on James Ross Island. In addition to the bones from the left hindlimb
illustrated here, the specimen also includes some elements from the right hindlimb including distal tibia,
and distal ends of metatarsals II and III.
elements belonging to a carnivorous dinosaur is most
fortuitous.
Description
The dentition is poorly preserved except for two teeth
that were preserved in a fragment of concretion. The
teeth and the associated fragments all indicate long,
narrow biconvex teeth. This shape suggests that both
anterior and posterior carina were present; however, no
serrations were noted on the carina, thus it is impossible
to determine if serrations were present or absent. The
teeth are incipiently laterally compressed, but retain a
rounded outline, particularly anteriorly. The shape is
indicative of teeth from the anterior region of the jaw.
The left tibia is the most complete of the two tibia
fragments and most of the pedal elements are from the
left pes as well. The distal articular surface of the tibia is
planar and pentagonal in outline. The anterior face of the
distal tibia is only slightly concave to indicate the point of
articulation with the ascending process of the astragalus.
The astragalus is spool shaped with a thick semicircular
medial end and a thinner lateral end. The distal astragular
facet is curved from the anterior side to the posterior side.
The anterior surface is vertical, forming the base of the
ascending process of the astragalus. The ascending
process is broken at 1.1 cm above its base. The tibia is
locked into the astragalus with the planar tibioastragalar
facet and with the ascending process of the astragalus, but
the normally tight articulation between the ascending
process and the tibia seen in theropods is absent here. The
disc-shaped calcaneus is separate from the astragalus,
however, the calcaneus is fused to the fibula. The
calcaneus articulates with the Metatarsal IV (= MtIV) and
the distal fibula is ovoid in cross-section.
The proximal and distal ends of metatarsals II, III, and
IV are present for the left pes. The diaphyses for the
metatarsal have been highly fragmented by the freezing
and thawing conditions of the Antarctic climate and so far
only partial reconstruction of the diaphyses have been
possible. The proximal articular surface of MtII is
concave dorsally to accommodate the thick and curved
medial end of the astragalus. The distal MtII is condylar
in medial view, but triangular in ventral view. The distal
articular surface is narrow anteriorly and wide posteriorly,
Case et al.: A dromaeosaur from the Maastrichtian of James Ross Island and the Late Cretaceous Antarctic dinosaur fauna
3
as it forms a grooved and bitrochlear articular surface,
thus anteriorly the distal articular surface is convex while
posteriorly it is ginglymoidal.
MtIII retains a flattened distal tarsal element. This
outline in dorsal view of the proximal end of Mt III is
bullet-shaped with the sides being both convex.
Posteriorly, the MtIII is pinched into a long narrow ridge
resulting in the triangular cross-section for most of the
length of the diaphysis. MtII and MtIV are also triangular
in cross-section however in each case the apex is directed
towards the central metatarsal (MtIII). The triangular
shape is the result of a posterolateral expansion in MtII
and a posteromedial expansion in MtIV. These
expansions or flanges thus obscure much of the length of
MtIII in posterior view so that only the narrow posterior
ridge on MtIII can be seen. The distal end is wide and
ginglymoidal with prominent medial and lateral trochlea
bordering a wide sulcus.
The MtIV outline is an ovoid and the distal end of
MtIV resembles that of the distal end of MtII. The first
phalanx of digit II is large and tall as the proximal
articular surface is extended vertically. The articular
surface is not ginglymoidal, but it is highly cupped,
extended and asymmetrical to match the shape of the
distal articular surface of MtII. The ungual phalanx of
digit II is enlarged and trenchant, but the element is
incomplete with only the proximal third and a fragment
near the tip recovered. Here the proximal articular
surface is keeled and thus ginglymoidal. The lateral
groove is more dorsal than the medial groove and remains
the deeper of the two near to the tip of the ungual. The
distal portion of the ungual is tall and narrow and
symmetrical in cross-section.
Discussion
Morphology
The morphology of the pes is consistent with that of
members of the theropod family Dromaeosauridae, a
family that includes such predatory dinosaurs as
Velociraptor and Deinonychus, which have an enlarged
sickle-like claw on their hindfeet. Novas and Pol (2005)
presented a suite of diagnostic character states for the pes
of a dromaeosaurid, which are also present in this
Antarctic specimen: Mt II with a lateral expansion caudal
to Mt III; Mt III proximally narrow distally wide; distal
end of Mt III is incipiently ginglymoidal; pedal digit II
with trenchant ungual phalanx. These diagnostic features
clearly indicate that the theropod specimen from the Naze
on James Ross Island, is a dromaeosaur. However, the
Naze dromaeosaur is much less derived than
dromaeosaurs or the sister family Troodontidae of a
similar Late Cretaceous age from Laurasia, in that the
metatarsals are not long and slender and thus, generally
being longer than the length of the phalanges on digit III.
The metatarsal length may also be a function of size, but
Achillobatar, which is similar in size to the Naze
dromaeosaur also has elongate metatarsals. Two
additional plesiomorphic features of the Naze
dromaeosaur are the juxtaposition of the ascending
process of the astragalus and the anterior distal tibia
without a well-defined fossa on the tibia and the incipient
ginglymoidal MtII/digit II joint. Thus in many ways, the
Naze dromaeosaur more closely resembles Early
Cretaceous dromaeosaurs such as Deinonychus and
Utahraptor rather than contemporaneous dromaeosaurids,
Velociraptor and Dromaeosaurus or regional close (i.e.
South American) species like Neuquenraptor (Novas and
Pol, 2005) or Buitreraptor (Makovichy et al., 2005).
Biogeography
Dromaeosaurids were originally thought to have
originated in North America in the Early Cretaceous
(Barremian), dispersed to Asia and then into Europe
(Ostrom, 1990). The Asian record now extends back to
the Barremian (Xu et al., 2000) and the two new South
American (Gondwanan) species have now been recorded
from earlier time frames of Cenomanian and Coniacian
ages (Makovichy et al., 2005; Novas and Pol, 2005
respectively). By the middle of the Cretaceous,
dromaeosaurs are in Asia, North America and South
America. The plesiomorphic nature of the ankle and pes
of the Naze dromaeosaur is supportive of a hypothesis
that dromaeosaurs were in fact cosmopolitan in their
distribution and then fragmented vicariously into a
Gondwanan clade that was separate from the Laurasian
radiation (Makovichy et al., 2005; Novas and Pol, 2005).
Consequently, the Naze dromaeosaur may in fact be a
latest Cretaceous remnant of the Early Cretaceous,
cosmopolitan, basal stock of dromaeosaurids.
The majority of the dinosaur assemblage from the
Antarctic Peninsula (the megalasaur-like theropod, the
nodosaur, the iguanodontid and the hypsilophodontid) are
remnants of a cosmopolitan dinosaur fauna more typical
of other areas at earlier times (e.g. mid-Cretaceous of
North America and Australia; Case et al., 2003). The
recovery of a dromaeosaur from the Maastrichtian of
Antarctica up until recently would have been viewed in
much the same way as the hadrosaur is viewed, that is as
a North American immigrant into the Antarctic region.
However, the occurrences of dromaeosaurs in the mid-
Cretaceous of South America and the retention of
plesiomorphic characters in the Naze dromaeosaur tell a
different biogeographic tale. Rather, the dromaeosaurs,
like most of the Antarctic Peninsula dinosaur fauna, is a
relict of a cosmopolitan dinosaur distribution that is still
present in Antarctica until the end of the “Age of
Dinosaurs” at the end of the Cretaceous.
Acknowledgements. This work was supported by The National
Science Foundation Office of Polar Programs grants 0003844 (to J.
Case) and 0087972 (to J. Martin). Additionally, we would like to thank
Raytheon Polar Services for their logistical support for this project with
special thanks to Melissa Rider and John Evans. We would like to
thank Captain Mike Terminal and the crew of the RS Laurence M.
Gould for getting us there and getting us back.
10th International Symposium on Antarctic Earth Sciences
4
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... Upper Cretaceous deposits in Antarctica are restricted to the James Ross Basin at the northeastern tip of the Antarctic Peninsula ( Fig. 1), represented by primarily shallow marine sedimentary deposits ( Crame et al., 2004;Case et al., 2007;Reguero et al., 2013) and where the Late Cretaceous dinosaurian paleofauna is located. Lower Jurassic deposits are known from the Beardmore Glacier area of the Transantarctic Mountains on the main portion of the continent, and have produced the basal sauropodomorph Glacialisaurus ( Smith and Pol, 2007) and the theropod Cryolophosaurus (Hammer and Hickerson, 1994). ...
... The supposed dromaeosaur resembled North American eudromaeosaur taxa such as Deinonychus or Utahraptor (Case et al., 2007). The size of the new species, estimated to have been approximately 2 m in height, introduced a new case of gigantism in the Dromaeosauridae ( Case et al., 2007). ...
... Both troodontids and dromaeosaurids display hypertrophy of the digit II pedal ungual, although troodontids tend to have smaller digit II unguals than dromaeosaurids (Fowler et al., 2011). Case et al. (2007) introduced a description of the 'Naze Dromaeosaur.' An unambiguous synapomorphy of dromaeosaurids is the presence of ginglymoid articulation of the distal metatarsal II ( Turner et al., 2012), which is not present in the theropod from James Ross Island. ...
View
... Antarctica: Two isolated teeth associated with a partial left foot and fragments from the right foot from the Maastrichtian Snow Hill Island Formation of James Ross Island, Antarctica were referred to Dromaeosauridae (Case et al., 2007). These were subsequently reinterpreted as indeterminate deinonychosaurian material (Turner et al., 2012). ...
... Mei was first described on the basis of an exquisitelypreserved skeleton with a bird-like sleeping posture, which is arguably the most complete Early Cretaceous troodontid specimen known (Xu and Norell, 2004;Pan et al., 2013). Sinusonasus, Daliansaurus, and Liaoningvenator all have a similar size as Sinovenator, and each of them were reported from a single, near com- Hou et al., 1995Hou et al., , 1996Hou et al., , 1997bHou et al., , 1999aHou et al., , 1999bHou et al., , 2002Hou et al., , 2004Hou, 1996Hou, , 1997bChiappe et al., 1999Chiappe et al., , 2007Chiappe et al., , 2014Chiappe et al., , 2019bJi et al., 1999Ji et al., , 2002aJi et al., , 2002bZhang et al., 2006Zhang et al., , 2009Zhou and Zhang, 2005, 2006a, 2006bGao et al., 2008Gao et al., , 2012O'Connor et al., 2009O'Connor et al., , 2011aO'Connor et al., , 2013O'Connor et al., , 2016cWang et al., 2013dWang et al., , 2013e, 2019c;Zheng et al., 2007Zheng et al., , 2013Zheng et al., , 2014 Dames, 1884;Heller, 1959;Wellnhofer, 1974Wellnhofer, , 1988Wellnhofer, , 1993Wellnhofer, , 2009Mayr et al., 2005;Wellnhofer and Marsh, 1872Marsh, , 1877Marsh, , 1880Martin and Tate, 1976;Martin, 1984;Clarke, 2004;Bell and Chiappe, 2015;Field et al., 2018b Belly River Group Case et al., 2007;Turner et al., 2012;Ely and Case, 2019;Cordes-Person, 2020 ...
The Fossil Record of Mesozoic and Paleocene Pennaraptorans
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An unabated surge of new and important discoveries continues to transform knowledge of pen-naraptoran biology and evolution amassed over the last 150+ years. This chapter summarizes progress made thus far in sampling the pennaraptoran fossil record of the Mesozoic and Paleocene and proposes priority areas of attention moving forward. Oviraptorosaurians are bizarre, nonparavian pennaraptorans first discovered in North America and Mongolia within Late Cretaceous rocks in the early 20th century. We now know that oviraptorosaurians also occupied the Early Cretaceous and their unquestionable fossil record is currently limited to Laurasia. Early Cretaceous material from China preserves feathers and other soft tissues and ingested remains including gastroliths and other stomach contents, while brooding specimens and age-structured, single-species accumulations from China and Mongolia provide spectacular behavioral insights. Less specialized early oviraptorosaurians like Incisivosaurus and Microvenator remain rare, and ancestral forms expected in the Late Jurassic are yet to be discovered, although some authors have suggested Epidexipteryx and possibly other scansoriopterygids may represent early-diverging oviraptorosaurians. Long-armed scansoriopterygids from the Middle-Late Jurassic of Laurasia are either early-diverging oviraptorosaurians or paravians, and some have considered them to be early-diverging avialans. Known from five (or possibly six) feathered specimens from China, only two mature individuals exist, representing these taxa. These taxa, Yi and Ambopteryx, preserve stylopod-supported wing membranes that are the only known alternative to the feathered, muscular wings that had been exclusively associated with dinosaurian flight. Thus, scansoriopterygid specimens-particularly those preserving soft tissue-remain a key priority for future specimen collection. Dromaeosaurids and troodontids were first discovered in North America and Mongolia in Late Cretaceous rocks. More recent discoveries show that these animals originated in the Late Jurassic, were strikingly feathered, lived across diverse climes and environments, and at least in the case of dromaeosaurids, attained a global distribution and the potential for aerial locomotion at small size.
View
... Antarctica: Two isolated teeth associated with a partial left foot and fragments from the right foot from the Maastrichtian Snow Hill Island Formation of James Ross Island, Antarctica were referred to Dromaeosauridae (Case et al., 2007). These were subsequently reinterpreted as indeterminate deinonychosaurian material (Turner et al., 2012). ...
... Mei was first described on the basis of an exquisitelypreserved skeleton with a bird-like sleeping posture, which is arguably the most complete Early Cretaceous troodontid specimen known (Xu and Norell, 2004;Pan et al., 2013). Sinusonasus, Daliansaurus, and Liaoningvenator all have a similar size as Sinovenator, and each of them were reported from a single, near com- Hou et al., 1995Hou et al., , 1996Hou et al., , 1997bHou et al., , 1999aHou et al., , 1999bHou et al., , 2004Hou, 1996Hou, , 1997bChiappe et al., 1999Chiappe et al., , 2007Chiappe et al., , 2014Chiappe et al., , 2019bJi et al., 1999Ji et al., , 2002aJi et al., , 2002bZhang et al., 2006Zhang et al., , 2009Zhou and Zhang, 2005, 2006bGao et al., 2008Gao et al., , 2012O'Connor et al., 2009O'Connor et al., , 2011aO'Connor et al., , 2013O'Connor et al., , 2016cWang et al., 2013dWang et al., , 2013e, 2019c;Zheng et al., 2007Zheng et al., , 2013Zheng et al., , 2014 Dames, 1884;Heller, 1959;Wellnhofer, 1974Wellnhofer, , 1988Wellnhofer, , 1993Wellnhofer, , 2009Mayr et al., 2005;Wellnhofer and Marsh, 1872Marsh, , 1877Marsh, , 1880Martin and Tate, 1976;Martin, 1984;Clarke, 2004;Bell and Chiappe, 2015;Field et al., 2018b Belly River Group Case et al., 2007;Turner et al., 2012;Ely and Case, 2019;Cordes-Person, 2020 ...
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An unabated surge of new and important discoveries continues to transform knowledge of pen-naraptoran biology and evolution amassed over the last 150+ years. This chapter summarizes progress made thus far in sampling the pennaraptoran fossil record of the Mesozoic and Paleocene and proposes priority areas of attention moving forward. Oviraptorosaurians are bizarre, nonparavian pennaraptorans first discovered in North America and Mongolia within Late Cretaceous rocks in the early 20th century. We now know that oviraptorosaurians also occupied the Early Cretaceous and their unquestionable fossil record is currently limited to Laurasia. Early Cretaceous material from China preserves feathers and other soft tissues and ingested remains including gastroliths and other stomach contents, while brooding specimens and age-structured, single-species accumulations from China and Mongolia provide spectacular behavioral insights. Less specialized early oviraptorosaurians like Incisivosaurus and Microvenator remain rare, and ancestral forms expected in the Late Jurassic are yet to be discovered, although some authors have suggested Epidexipteryx and possibly other scansoriopterygids may represent early-diverging oviraptorosaurians. Long-armed scansoriopterygids from the Middle-Late Jurassic of Laurasia are either early-diverging oviraptorosaurians or paravians, and some have considered them to be early-diverging avialans. Known from five (or possibly six) feathered specimens from China, only two mature individuals exist, representing these taxa. These taxa, Yi and Ambopteryx, preserve stylopod-supported wing membranes that are the only known alternative to the feathered, muscular wings that had been exclusively associated with dinosaurian flight. Thus, scansoriopterygid specimens-particularly those preserving soft tissue-remain a key priority for future specimen collection. Dromaeosaurids and troodontids were first discovered in North America and Mongolia in Late Cretaceous rocks. More recent discoveries show that these animals originated in the Late Jurassic, were strikingly feathered, lived across diverse climes and environments, and at least in the case of dromaeosaurids, attained a global distribution and the potential for aerial locomotion at small size.
View
... Cretaceous theropod remains from Antarctica are all found within the James Ross Basin, along the Antarctic Peninsula (Acosta Hospitaleche et al., 2019;Lamanna et al., 2019). Remains from Campanian and Maastrichtian deposits on Seymour, James Ross, and Vega islands include isolated bones of non-avian and avian theropods (Acosta Hospitaleche et al., 2019;Lamanna et al., 2019) and partial skeletons of the paravian Imperobator antarcticus (Case et al., 2007;Ely and Case, 2019) and ornithurines V. iaai (Clarke et al., 2005(Clarke et al., , 2016 and P. gregorii (Chatterjee, 2002;Acosta Hospitaleche et al., 2019). Notably, populations during the latest Cretaceous of the Magallanes-Austral Basin and James Ross Basin would have been the last cross-continental Gondwanan populations to maintain connectivity during the end Cretaceous, as changes in sea level intermittently exposed connections to the Antarctic Peninsula (Poblete et al., 2016;Reguero and Goin, 2021), leading to similarities in the taxa found in both. ...
New records of Theropoda from a Late Cretaceous (Campanian-Maastrichtian) locality in the Magallanes-Austral Basin, Patagonia, and insights into end Cretaceous theropod diversity
Article
The end Cretaceous mass extinction was marked by a dramatic change in biodiversity, and the extinction of all non-avian dinosaurs. To understand the diversity of dinosaur clades prior to this event, as well as recovery by avian dinosaurs (birds), we need a better understanding of the global fossil record. However, the fossil record from southern localities, particularly southernmost (>60°S) South America, has only recently begun to be described. Discoveries from Patagonia are important to accurately assess global trends in dinosaur diversity, particularly during the latest Cretaceous before the Cretaceous/Paleogene (K/Pg) mass extinction event. Here we describe new theropod dinosaur specimens, representing both associated material and isolated elements, from Upper Cretaceous (Campanian-Maastrichtian) deposits of the Río de las Chinas Valley, Magallanes-Austral Basin, Chile. These discoveries include the southern-most known occurrences of several theropod clades outside of Antarctica, including megaraptorids, unenlagiines, enantiornithines and ornithurines. Notably, these remains provide much needed time-constrained records of smaller theropods, including birds, which are less often recovered from Upper Cretaceous deposits. While fragmentary, these fossils are the first records of theropods from Chilean Patagonia, and provide insight into the distribution of avian and non-avian theropods in southern high latitude ecosystems prior to the K/Pg mass extinction event. Sampling from this region is still sparse, and more fossils from age-controlled sections are needed to accurately assess global extinction dynamics through the end Cretaceous.
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... The lithology (Fig. 2) is dominated by fine-grained, laminated to massive, greenegray sandstones, interspersed with yellowegreen mudstone and clayey-siltstones, containing calcareous concretions and layers of bentonite (di Pasquo and Martin, 2013). This section contains the remains of a theropod paravian dinosaur and several vertebrates Case et al., 2007). Ely and Case (2019) described the paravian dinosaur collected at approximately 45 m of the base (red arrow; Fig. 2). ...
Dinoflagellate cysts from the Upper Cretaceous (Campanian–Maastrichtian) from The Naze Peninsula, James Ross Island, Antarctica
Article
We present the results of the quantitative and qualitative study of dinoflagellate cysts in outcrop samples from a section of the Snow Hill Island Formation (SHF) in James Ross Island, Antarctic. Dinoflagellate cysts assemblages are abundant and dominated by gonyaulacoid taxa. The last occurrence of the dinoflagellate cyst Kallosphaeridium? helbyi and Chatangiella granulifera, together with the first occurrence of Pterodinium cretaceum, indicates a probable late Campanian age (∼76.4 to ∼ 72.1 Ma) for the lower strata. Whereas the first occurrence of Manumiella bertodano and the last occurrence of Odontochitina operculata, Xenascus ceratioides, and Stiphrosphaeridium anthophorum indicate an early Maastrichtian (∼72.1 to ∼ 70.0 Ma) age for the upper strata. Our results, combined with paleobotanical and palynological published data, indicate medium-high continental and marine productivity with temperate paleoclimate free of glaciers for this interval. Lithological and paleontological data indicate mainly inner neritic marine depositional environments. The predominance of shales in the lower part of the lower Maastrichtian interval indicates a slightly deeper environment. In contrast, in the middle part of the lower Maastrichtian, a shallower, transitional environment is marked by the presence of theropod dinosaurs and decapod crustaceans.
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... The dinosaur record of the Upper Cretaceous of AP is composed by several clades (basal ornithopods, hadrosaurids, ankylosaurs, titanosaurs, basal paravians and birds (e.g., Molnar et al. 1996;Case et al., 2000;Chatterjee, 2002;Salgado and Gasparini, 2006;Clarke et al., 2005;Case et al., 2007;Cerda et al., 2012;Coria et al., 2013;Reguero et al., 2013b;Rozadilla et al., 2016;Ely and Case, 2019;Garcia-Marsá et al., 2020), most of them present in other Gondwanan continents. The majority of the non-avian dinosaurs from AP seem to be remnants of a cosmopolitan dinosaur fauna more typical of other areas, e.g. ...
Paleogeography and biogeography of the Gondwanan final breakup and its terrestrial vertebrates: New insights from southern South America and the “double Noah’s Ark” Antarctic Peninsula
Article
The Mesozoic plate tectonic and paleogeographic history of the final break up of West Gondwana had a profound effect on the distribution of terrestrial vertebrates in South America. As the supercontinent fragmented into a series of large landmasses (South America, Antarctica, Australia, New Zealand, the Indian subcontinent, and Madagascar), particularly during the Late Jurassic and Cretaceous, its terrestrial vertebrates became progressively isolated, evolving into unique faunal assemblages. The episodic nature of South American mammalian Cenozoic faunas became apparent in its modern formulation after George Gaylord Simpson’s seminal works on this topic. Two aspects add complexity to this generally accepted scheme: first, the fact that South America is not (and was not) a biogeographic unit, as the Neotropical Region does not include its southernmost tip (the Andean Region, including Patagonia and the southern Andes). Second, and intimately linked with the first one, that South America was not an island continent during the Late Cretaceous and the beginning of the Cenozoic, being its southernmost portion closely linked with West Antarctica up to the late Paleocene at least. Here we stress on this second aspect; we summarize a series of recent, detailed paleogeographical analyses of the continental breakup between Patagonia (including the Magallanes Region) and the Antarctic Peninsula crustal block, beginning with the opening of the Atlantic Ocean in the Early Cretaceous and running up to the Early Paleogene with the expansion of the Scotia Basin. In second place, we comment on the implications of these distinct paleogeographic and paleobiogeographic scenarios (before and after their geographic and faunistic isolation) for the evolution of South American terrestrial mammalian faunas. Summarizing, (1) we recognize a West Weddellian terrestrial biogeographic unit with the assemblage of the southern part of South America (Patagonia and the Magallanes Region) and the Antarctic Peninsula (and probably Thurston Island) crustal block of West Antarctica, spanning from the Late Cretaceous (Campanian) through the Early Paleogene (Paleocene); (2) we suggest that the Antarctic Peninsula acted as a double "Noah’s Ark” regarding, first, the probable migration of some non-therian lineages into southern South America; later, the migration of metatherians to Australasia.
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... This may indicate a vicariance event due to the separation of Laurasia and Gondwana during the Middle Jurassic (Makovicky et al., 2005;Novas and Pol, 2005). Antarctic occurrences of dromaeosaurids were also inferred from some pedal fossil fragments, which, together with other Gondwanan taxa, might imply a cosmopolitan distribution of the clade before the breakup of Pangea (Case et al., 2007). Although Jurassic teeth from Laurasia have been referred to Dromaeosauridae (Goodwin et al., 1999;Vullo et al., 2014), more substantial fossil evidence is needed to confirm this important early record. ...
The Biogeography of Coelurosaurian Theropods and Its Impact on Their Evolutionary History
Conference Paper
Full-text available
  • Aug 2020
The Coelurosauria are a group of mostly feathered theropods that gave rise to birds, the only dinosaurians that survived the Cretaceous-Paleogene extinction event and are still found today. Between their first appearance in the Middle Jurassic up to the end Cretaceous, coelurosaurians were party to dramatic geographic changes on the Earth’s surface, including the breakup of the supercontinent Pangaea, and the formation of the Atlantic Ocean. These plate tectonic events are thought to have caused vicariance or dispersal of coelurosaurian faunas, influencing their evolution. Unfortunately, few coelurosaurian biogeographic hypotheses have been supported by quantitative evidence. Here, we report the first, broadly sampled quantitative analysis of coelurosaurian biogeography using the likelihood-based package BioGeoBEARS. Mesozoic geographic configurations and changes are reconstructed and employed as constraints in this analysis, including their associated uncertainties. We use a comprehensive time-calibrated coelurosaurian evolutionary tree produced from the Theropod Working Group phylogenetic data matrix. Six biogeographic models in the BioGeoBEARS package with different assumptions about the evolution of spatial distributions are tested against geographic constraints. Our results statistically favor the DIVALIKE+J and DEC+J models, which allow vicariance and founder events, supporting continental vicariance as an important factor in coelurosaurian evolution. Ancestral range estimation indicates frequent dispersal events via the Apulian route (connecting Europe and Africa during the Early Cretaceous) and the Bering land bridge (connecting North America and Asia during the Late Cretaceous). These quantitative results are consistent with commonly inferred Mesozoic dinosaurian dispersals and continental-fragmentationinduced vicariance events. In addition, we recognize the importance of Europe as a dispersal center and gateway in the Early Cretaceous, as well as other vicariance events such as those triggered by the disappearance of land bridges.
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... This may indicate a vicariance event due to the separation of Laurasia and Gondwana during the Middle Jurassic (Makovicky et al., 2005;Novas and Pol, 2005). Antarctic occurrences of dromaeosaurids were also inferred from some pedal fossil fragments, which, together with other Gondwanan taxa, might imply a cosmopolitan distribution of the clade before the breakup of Pangea (Case et al., 2007). Although Jurassic teeth from Laurasia have been referred to Dromaeosauridae (Goodwin et al., 1999;Vullo et al., 2014), more substantial fossil evidence is needed to confirm this important early record. ...
Chapter 4: The Biogeography of Coelurosaurian Theropods and Its Impact on Their Evolutionary History
Chapter
Full-text available
  • Aug 2020
The Coelurosauria are a group of mostly feathered theropods that gave rise to birds, the only dinosaurians that survived the Cretaceous-Paleogene extinction event and are still found today. Between their first appearance in the Middle Jurassic up to the end Cretaceous, coelurosaurians were party to dramatic geographic changes on the Earth's surface, including the breakup of the supercontinent Pangaea, and the formation of the Atlantic Ocean. These plate tectonic events are thought to have caused vicariance or dispersal of coelurosaurian faunas, influencing their evolution. Unfortunately , few coelurosaurian biogeographic hypotheses have been supported by quantitative evidence. Here, we report the first, broadly sampled quantitative analysis of coelurosaurian biogeography using the likelihood-based package BioGeoBEARS. Mesozoic geographic configurations and changes are reconstructed and employed as constraints in this analysis, including their associated uncertainties. We use a comprehensive time-calibrated coelurosaurian evolutionary tree produced from the The-ropod Working Group phylogenetic data matrix. Six biogeographic models in the BioGeoBEARS package with different assumptions about the evolution of spatial distributions are tested against geographic constraints. Our results statistically favor the DIVALIKE+J and DEC+J models, which allow vicariance and founder events, supporting continental vicariance as an important factor in coelurosaurian evolution. Ancestral range estimation indicates frequent dispersal events via the Apulian route (connecting Europe and Africa during the Early Cretaceous) and the Bering land bridge (connecting North America and Asia during the Late Cretaceous). These quantitative results are consistent with commonly inferred Mesozoic dinosaurian dispersals and continental-fragmentation-induced vicariance events. In addition, we recognize the importance of Europe as a dispersal center and gateway in the Early Cretaceous, as well as other vicariance events such as those triggered by the disappearance of land bridges.
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... Salgado and Gasparini (2006) reviewed the presence of Campanian ankylosaurian dinosaurs from the Antarctic Peninsula, but refrained from proposing a South American connection, which is comparable to Agnolin et al. (2010). Case et al. (2007) recorded the early Maastrichtian presence of an Antarctic Peninsula dromaeosaur, considered it to be endemic and of Gondwanan origin, comparable to the Santonian megalasaurid theropod, a late Campanian nodosaur, and early Maastrichtian hypsilophodontid and a similarly aged Lawver et al. (2013: Fig. 4a) iguanodontid also known from the James Ross Island area of the Antarctic Peninsula (4, Fig. 3.3). The lambeosaurine (Powell 1987) was included in a new hadrosaur genus, Willinakage, by Juárez- , so the presence of lambeosaurs in South America is not supported. ...
A Brief History of South American Metatherians
Article
  • Jan 2016
This book summarizes major aspects of the evolution of South American metatherians, including their epistemologic, phylogenetic, biogeographic, faunal, tectonic, paleoclimatic, and metabolic contexts. A brief overview of the evolution of each major South American lineage ("Ameridelphia", Sparassodonta, Didelphimorphia, Paucituberculata, Microbiotheria, and Polydolopimorphia) is provided. It is argued that due to physiological constraints, metatherian evolution closely followed the conditions imposed by global temperatures. In general terms, during the Paleocene and the early Eocene multiple radiations of metatherian lineages occurred, with many adaptive types exploiting insectivorous, frugivorous, and omnivorous adaptive zones. In turn, a mixture of generalized and specialized types, the latter mainly exploiting carnivorous and granivorous-folivorous adaptive zones, characterized the second half of the Cenozoic. In both periods, climate was the critical driver of their radiation and turnovers.
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The cranial osteology of Buitreraptor gonzalezorum Makovicky, ApesteguÍa, and AgnolÍn, 2005 (Theropoda, Dromaeosauridae), from the Late Cretaceous of Patagonia, Argentina
Article
  • Jan 2017
Buitreraptor gonzalezorum is a paravian theropod from the Late Cretaceous of Patagonia that has been recovered as an unenlagiine dromaeosaurid in several phylogenies. It was preliminarily described in a brief article, but a detailed osteology has not been published to date. Here we provide a thorough osteological description of the skull of the holotype, which preserves the maxillae, nasals, frontals, parietals, postorbitals, quadrates, and many mandibular bones, together with some in situ and isolated teeth. The isolated occipital condyle is the only element preserved from the braincase. Diagnostic cranial characters of this taxon include elongate skull; maxillary fenestra not dorsally displaced; posteriorly expanded postantral wall; quadrate with expanded lateral flange and a posterior pneumatic foramen; straight anterior border of the supratemporal fossa; nutrient foramina within a well-marked lateral groove on the dentary; and small, fluted teeth without denticles. Buitreraptor shares traits with Austroraptor cabazai, the only other unenlagiine to preserve cranial remains, although they also differ in the morphology of the maxillary fenestra and the presence/absence of interdental plates. A phylogenetic analysis was performed, recovering Buitreraptor as an unenlagiine dromaeosaurid, in agreement with previous works. The phylogenetic implications of some characters are discussed, including characters not previously considered for this taxon, such as the presence of the mylohyoid foramen. The distribution and codings of some characters are reconsidered, with an evaluation of how they influence the phylogenetic position of Buitreraptor and paravian relationships overall. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Gianechini, F. A., P. J. Makovicky, and S. Apesteguía. 2017. The cranial osteology of Buitreraptor gonzalezorum Makovicky, Apesteguía, and Agnolín, 2005 Makovicky, P. J., S. Apesteguía, and F. L. Agnolín. 2005. The earliest dromaeosaurid theropod from South America. Nature 437:1007–1011.[CrossRef], [PubMed], [Web of Science ®] (Theropoda, Dromaeosauridae), from the Late Cretaceous of Patagonia, Argentina. Journal of Vertebrate Paleontology. DOI: 10. 10.1080/02724634.2017.1255639.
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The first duck-billed dinosaur (Family Hadrosauridae) from Antarctica
Article
Full-text available
  • Jan 2000
Department of Earth Sciences, University of California, Riverside, California 92521Duck-billed dinosaurs or hadrosaurs are a very common family ofdinosaurs in the Late Cretaceous of North America and Eurasia withrare occurrences in South America. Here, we report the first hadrosaurrecovered in Antarctica from sandstones of late Maastrichtian age, VegaIsland, Antarctic Peninsula (Fig. 1) during a joint U.S.-Argentinian geo-logical and paleontological field expedition to the island. This discoverysupports the hypothesis of a dispersal route between southern SouthAmerica and Antarctica in the Maastrichtian.Dinosaurs are extremely rare in the dominantly marine deposits ofLate Cretaceous age in Antarctica, so the discovery of a single hadro-saur tooth (Fig. 2) by the third author (DSC) was unexpected. Hadro-saurs are not the first dinosaurs from Late Cretaceous deposits in theJames Ross Basin. Theropod, ornithopod, and ankylosaur specimenshad been previously recorded (Gasparini et al., 1987; Hooker et al.,1991; Molnar et al., 1996). However, these dinosaur groups representeither cosmopolitan taxa or native Gondwanan taxa, thus the duck-billeddinosaur represents a new immigrant family of dinosaurs into this south-ernmost continent.The fossil-bearing deposit occurs at 61 51 S and 53 33 W, at Sand-wich Bluff on Cape Lamb, Vega Island, Antarctic Peninsula. The ‘‘Rep-tile Horizon,’’ named for the numerous mosasaur and plesiosaur spec-imens recovered from this stratigraphic level, is in the upper third ofthe Sandwich Bluff Member (Crame et al., 1991; Pirrie et al., 1991) orUnit C (Olivero, 1992) of the Lopez de Bertodano Formation. Thismember is a nearshore marine deposit of composed of fine-grained,ferruginous, loosely consolidated sandstones that are latest Maastrich-tian age (approximately 66–68 million years ago), based on correlationsof ammonite and palynological taxa (Crame et al., 1991; Pirrie et al.,1991).In addition to the hadrosaur, at least four different bird species (whichcan be referred to modern avian orders, including charadriiform andgaviid birds, based on the morphology of their respective tarsometatar-sals), have been recovered from this same stratigraphic level. Addition-ally, numerous specimens of plesiosaurs and mosasaurs were collectedfrom this same horizon, as well as the 5-meter horizon immediatelybelow (Martin et al., 1999a, b). At least five taxa of marine reptiles arerepresented on Vega Island, and numerous specimens of juvenile indi-viduals were collected, concentrations of which are relatively rare inthe North American marine reptile record.SYSTEMATIC PALEONTOLOGYREPTILIAA
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New evidence on deinonychosaurian dinosaurs from the Late Cretaceous of Patagonia
Article
Full-text available
Most of what is known about the evolution of deinonychosaurs (that is, the group of theropods most closely related to birds) is based on discoveries from North America and Asia1. Except for Unenlagia comahuensis 2, 3 and some fragmentary remains from northern Africa4, no other evidence was available on deinonychosaurian diversity in Gondwana. Here we report a new, Late Cretaceous member of the clade, Neuquenraptor argentinus gen. et sp. nov., representing uncontroversial evidence of a deinonychosaurian theropod in the Southern Hemisphere. The new discovery demonstrates that Cretaceous theropod faunas from the southern continents shared greater similarity with those of the northern landmasses than previously thought. Available evidence suggests that deinonychosaurians were probably distributed worldwide at least by the beginning of the Cretaceous period. The phylogenetic position of the new deinonychosaur, as well as other Patagonian coelurosaurian theropods, is compatible with a vicariance model of diversification for some groups of Gondwanan and Laurasian dinosaurs.
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The earliest dromaeosaurid from South America
Article
Full-text available
The evolutionary history of Maniraptora, the clade of carnivorous dinosaurs that includes birds and the sickle-clawed Dromaeosauridae, has hitherto been largely restricted to Late Jurassic and Cretaceous deposits on northern continents. The stunning Early Cretaceous diversity of maniraptorans from Liaoning, China, coupled with a longevity implied by derived Late Jurassic forms such as Archaeopteryx, pushes the origins of maniraptoran lineages back to Pangaean times and engenders the possibility that such lineages existed in Gondwana. A few intriguing, but incomplete, maniraptoran specimens have been reported from South America, Africa and Madagascar. Their affinities remain contested, however, and they have been interpreted as biogeographic anomalies relative to other faunal components of these land-masses. Here we describe a near-complete, small dromaeosaurid that is both the most complete and the earliest member of the Maniraptora from South America, and which provides new evidence for a unique Gondwanan lineage of Dromaeosauridae with an origin predating the separation between northern and southern landmasses.
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An Antarctic cretaceous theropod
Article
  • Dec 1996
The distal part of a theropod tibia has been recovered from the Coniacian-Santonian Hidden Lake Fm. near Cape Lachmann, James Ross Island. The piece closely resembles the corresponding region in Megalosaurus and, more closely, in Piatnitzkysaurus. This suggests that a persistently plesiomorphic tetanuran lineage inhabited the Antarctic. The relatively small size of the animal argues against a mean annual temperature below 15°C in its environment.
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Campanian-Maastrichtian (Cretaceous) stratigraphy of the James Ross Island area, Antarctica
Article
  • Dec 1991
One of the most important outcrops of uppermost Cretaceous (Campanian-Maastrichtian) sedimentary rocks in the southern high latitudes occurs within the James Ross Island group, northeastern Antarctic Peninsula. These rocks comprise a 1500-2000 m thick sequence of predominantly shallow marine clastic sediments that were deposited within a retro-arc basin. They are virtually undeformed and have yielded prolific invertebrate and vertebrate faunas, and a wide range of plant taxa. Campanian-Maastrichtian strata are contained within two component formations of the Upper Cretaceous-lower Tertiary Marambio Group. The lower Santa Marta Formation is approximately 1100 m thick and has three constituent members. Ammonites within the Santa Marta Formation indicate an early to late Campanian age assignment. Dinoflagellates suggest that the lower levels of the formation may range into the Santonian Stage. In the northern James Ross Island to Vega Island region there is a conformable transition into the overlying Lopez de Bertodano Formation. Here the basal Cape Lamb Member is unconformably overlain by the Sandwich Bluff Member. Although there are some lithological and faunal discrepancies, which are attributed to marked lateral facies changes across the basin, it is believed that the Cape Lamb Member can be correlated with the lower to middle regions of the 1200 m thick sequence of undifferentiated Lopez de Bertodano Formation lithologies exposed on Seymour Island. Molluscan data indicate a late Campanian-Palaeocene age range for this upper formation. Dinoflagellates again suggest that the lowest beds may be slightly older. The correlation presented provides the basis for a formal subdivision of the Campanian and Maastrichtian stages in the southern high latitudes. It has also revealed two major basin shallowing events (in the late Campanian-early Maastrichtian and latest Maastrichtian, respectively) and the existence of a major fault/fault zone across southeastern James Ross Island. The improved temporal framework will aid late Cretaceous palaeoclimatic and palaeobiological studies in Antarctica.
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An ornithopod dinosaur from the Late Cretaceous of West Antarctica
Article
In February 1989, the partial skeleton of an ornithopod dinosaur was discovered during a British Antarctic Survey (BAS) expedition, supported by RRS John Biscoe , to the James Ross Island area, east of the Antarctic Peninsula. This was only the second dinosaur to be found in the continent of Antarctica, the first being an ankylosaur collected three years earlier (Olivero et al. 1986, Gasparini et al. 1987, Gasparini 1988, Gasparini & Olivero 1989, Olivero et al. 1991).
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The smallest known non-avian theropod dinosaur
  • Jan 2000
  • 705-708
  • X Xu
  • Z Zhou
  • X Wang
Xu, X., Z. Zhou and X. Wang. 2000. The smallest known non-avian theropod dinosaur. Nature 408:705-708.
Dromaeosauridae The Dinosauria
  • Jan 1990
  • 269-279
  • J H Ostrom
Ostrom, J.H. 1990. Dromaeosauridae. In D.B. Weishampel, P. Dodson and H. Osmolska (eds.), The Dinosauria. University of Claifornia Press, Berkeley, p. 269-279.