Alamosaurus Research Articles

Phylogenetic relationships of a new titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous of Uruguay

The up to 200 m thick Upper Cretaceous deposits of Uruguay includes from base to top the Guichón, Mercedes, and Asencio formations, plus the lateral correlate of the latter, the Queguay Formation. In 2006, the most complete sauropod from the country was excavated from the Guichón Formation near Araújo, Paysandú Department. Augmented by new specimens reported here, the material includes sixty caudal vertebrae (all strongly procoelous, except for the biconvex first one), a partial coracoid, long bone fragments (proximal and distal portions of tibia, proximal portion of fibula), two astragali, and six metatarsals, as well as associated eggshell fragments. The Uruguayan titanosaur shows a unique combination of characters (biconvex first caudal centrum, pneumatic foramina in the anteriormost caudal centra, dorsal tuberosities on the transverse processes of the anterior caudal vertebrae, well developed fibular knob, pyramidal astragalus), as well as a potential autapomorphy – middle caudal centra condyles with hexagonal contour – allowing the proposition of new genus and species, Udelartitan celeste. Phylogenetic analyses were for the first time performed to assess the relations of that taxon, which was recovered either as a saltasaurine saltasaurid or a non-saltasaurid saltasauroid. Further, one of the analyses show Udelartitan celeste nested within a clade including Late Cretaceous titanosaurs with a biconvex first caudal vertebra, such as Alamosaurus sanjuanensis, Baurutitan britoi, and Pellegrinisaurus powelli. This contribution demonstrates that at least two titanosaur lineages were present in the Late Cretaceous of Uruguay: Saltasauroidea and Aeolosaurini, the latter recently recognized in the stratigraphically younger Asencio Formation.

Dinosaurs from the Late Cretaceous of the Ojinaga Basin in Northeastern Chihuahua, Mexico

The Ojinaga Basin is crucial for understanding the southern province of Laramidia because it contains a unique dinosaur fauna on the North American continent. The Upper Cretaceous Aguja and Javelina formations contain fossil remains of the dinosaur families Hadrosauridae, Ceratopsidae, Nodosauridae, Tyrannosauridae, and Saltasauridae. The latter is the first evidence for a saltasaurid taxon from Mexico identified as Alamosaurus sanjuanensis.

Osteology, paleohistology and phylogenetic relationships of Pellegrinisaurus powelli (Dinosauria: Sauropoda) from the Upper Cretaceous of Argentinean Patagonia

Pellegrinisaurus powelli is a large titanosaurian sauropod from the Upper Cretaceous of northern Patagonia (Río Negro Province, Argentina). The holotype of this species comprises an incomplete femur, four dorsal and 26 caudal vertebrae collected from the Lago Pellegrini locality. A single middle caudal vertebra from the nearby Cinco Saltos locality has been more recently referred to Pellegrinisaurus. With the purpose of increasing our knowledge about the titanosaur faunas of the Upper Cretaceous of Patagonia, here we provide a detailed redescription of the holotype and referred specimens of Pellegrinisaurus, reviewing its diagnosis and phylogenetic position. A histological analysis of the femur of the holotype is also carried out. The diagnostic characters originally proposed for Pellegrinisaurus are here considered invalid because they either correspond with diagenetic deformations of the specimen or are present in other titanosaurs. The new diagnostic features are related with the presence of large lateral blind fossae with distinct dorsal rims in the anterior caudal centra and with a low longitudinal ridge on the posterior side of the femur shaft originated from the trochanteric shelf and extending to the distal third of the shaft. The phylogenetic analysis recovers Pellegrinisaurus as a non-saltasaurid lithostrotian, closely related with Alamosaurus sanjuanensis. The bone histology indicates that the holotype corresponds to a subadult (i.e. sexually mature but still growing) individual. Finally, the caudal vertebra previously attributed to Pellegrinisaurus cannot be referred to this genus and is here assigned to Titanosauria indet.

Trends in embryonic and ontogenetic growth metabolisms in nonavian dinosaurs and extant birds, mammals, and crocodylians with implications for dinosaur egg incubation.

The embryonic metabolism of the saurischian dinosaur Troodon formosus and the ornithischian dinosaurs Protoceratops andrewsi and Hypacrosaurus stebingeri have been determined by using a mass growth model based on conservation of energy and found to be very similar. Embryonic and ontogenetic growth metabolisms are also evaluated for extant altricial birds, precocial birds, mammals, and crocodylians to examine for trends in the different groups of animals and to provide a context for interpreting our results for nonavian dinosaurs. This analysis reveals that the embryonic metabolisms of these nonavian dinosaurs were closer to the range observed in extant crocodylians than extant birds. The embryonic metabolisms of nonavian dinosaurs were in the range observed for extant mammals of similar masses. The measured embryonic metabolic rates for these three nonavian dinosaurs are then used to calculate the incubation times for eggs of 22 nonavian dinosaurs from both Saurischia and Ornithischia. The calculated incubation times vary from about 50 days for Archaeopteryx lithographica to about 150 days for Alamosaurus sanjuanensis.

Embryonic metabolism of the ornithischian dinosaurs Protoceratops andrewsi and Hypacrosaurus stebingeri and implications for calculations of dinosaur egg incubation times.

The embryonic metabolisms of the ornithischian dinosaurs Protoceratops andrewsi and Hypacrosaurus stebingeri have been determined and are in the range observed in extant reptiles. The average value of the measured embryonic metabolic rates for P. andrewsi and H. stebingeri are then used to calculate the incubation times for 21 dinosaurs from both Sauischia and Ornithischia using a mass growth model based on conservation of energy. The calculated incubation times vary from about 70 days for Archaeopteryx lithographica to about 180 days for Alamosaurus sanjuanensis. Such long incubation times seem unlikely, particularly for the sauropods and large theropods. Incubation times are also predicted with the assumption that the saurischian dinosaurs had embryonic metabolisms in the range observed in extant birds.

Remembering the Alamosaurus: Jensen Relocates Gilmore's Alamosaurus Quarry, USNM 15560, North Horn Formation, Emery County, Utah, and Discovers a Second Individual Alamosaurus

Alamosaurus sanjuanensis was originally described from a left scapula (USNM 10846) and right ischium (USNM 10847) discovered in the Late Cretaceous Ojo Alamo Formation of New Mexico in 1921 (USNM quarry 15560). In 1937 a second specimen was found in the North Horn Formation of Utah, consisting of a partial skeleton (USNM 15560), comprised of a mostly complete pelvis and caudal vertebral series, from the Late Cretaceous. A sacral complex with five vertebrae was observed in the field but was not collected. In 1966 James “Jim” Jensen of the Brigham Young University Earth Science Museum relocated the Gilmore quarry and found the sacrum, which, by then, had “rotted down into brown soil” and could not be recovered. Nearby, Jensen discovered the proximal heads of a humerus and femur and an isolated proximal caudal vertebra, none of which belonged to USNM 15560. Mike Morales and a team from the University of California at Berkeley discovered additional caudal vertebrae in the vicinity also, none of which belonged to the specimen collected by Gilmore. The specimens recovered by Jensen and Morales are significant because they indicate the presence of additional Alamosaurus specimens in the North Horn Formation. Additionally, the humerus is the most complete Alamosaurus humeral head yet discovered.

Incubation times of dinosaur eggs via embryonic metabolism.

The incubation times for the eggs of 21 dinosaurs are determined from an estimate of their embyronic metabolic rate and the mass of the hatchlings via a mass growth model based on conservation of energy. Embryos in extant birds and crocodiles are studied in order to determine the best model for embryonic metabolism and growth. These results are used to develop a theoretical model that predicts the incubation times of an egg. This model is applied to dinosaur eggs and provides a unique window into dinosaur reproduction. The dinosaurs studied come from both Saurischia and Ornithischia. The incubation times vary from about 28 days for Archaeopteryx lithographica to about 76 days for Alamosaurus sanjuanensis.

An articulated cervical series of Alamosaurus sanjuanensis Gilmore, 1922 (Dinosauria, Sauropoda) from Texas: new perspective on the relationships of North America's last giant sauropod

The sauropod dinosaur Alamosaurus sanjuanensis Gilmore, 1922 has been known from Maastrichtian deposits of south-western North America for nearly a century. Alamosaurus is the youngest sauropod taxon known in North America. Originally described from an isolated scapula and ischium from New Mexico, more of Alamosaurus was revealed by an incomplete skeleton from southern Utah. Additional referred specimens from western Texas provided the first few examples of cervical, dorsal and sacral vertebrae known for the taxon, but these came from relatively small and immature individuals. Here we describe an articulated series of cervical vertebrae of a large, mature titanosaur from Big Bend National Park, Texas, and provide evidence that the specimen can be referred to A. sanjuanensis. The specimen represents the first articulated cervical vertebral series described for the taxon, which clarifies aspects of cervical vertebral anatomy and provides at least one new diagnostic character for Alamosaurus. Many previous c...

An articulated cervical series of Alamosaurus sanjuanensis Gilmore, 1922 (Dinosauria, Sauropoda) from Texas: new perspective on the relationships of North America's last giant sauropod

The sauropod dinosaur Alamosaurus sanjuanensis Gilmore, 1922 has been known from Maastrichtian deposits of south-western North America for nearly a century. Alamosaurus is the youngest sauropod taxon known in North America. Originally described from an isolated scapula and ischium from New Mexico, more of Alamosaurus was revealed by an incomplete skeleton from southern Utah. Additional referred specimens from western Texas provided the first few examples of cervical, dorsal and sacral vertebrae known for the taxon, but these came from relatively small and immature individuals. Here we describe an articulated series of cervical vertebrae of a large, mature titanosaur from Big Bend National Park, Texas, and provide evidence that the specimen can be referred to A. sanjuanensis. The specimen represents the first articulated cervical vertebral series described for the taxon, which clarifies aspects of cervical vertebral anatomy and provides at least one new diagnostic character for Alamosaurus. Many previous cladistic analyses found Alamosaurus to be a saltasaurid titanosaur, sometimes closely related to the Asian taxon Opisthocoelicaudia skarzynskii. We present cladistic analyses incorporating new data from this and other specimens from Big Bend National Park. The first places Alamosaurus as a lithostrotian titanosaur outside Saltasauridae. The second analysis, with greater focus on South American titanosaurs, finds Alamosaurus allied to Lognkosauria, a clade of South American titanosaurs notable for giant size and exceptionally robust necks. This relationship may be more congruent with the fossil record than hypotheses of phylogeny that would require saltasaurid titanosaurs to inhabit northern Laramidia, Beringia and Central Asia through the late Campanian and Maastrichtian while leaving no record of their presence.

New specimens of a titanosaur sauropod from the Maastrichtian of Big Bend National Park, Texas

ABSTRACTNew specimens of a titanosaur sauropod from Maastrichtian strata in Big Bend National Park, Texas, include well-preserved dorsal vertebrae in association with pelvic elements. Anterior dorsal vertebrae are characterized by postspinal and centroprezygapophyseal laminae, with spinodiapophyseal laminae convergent on the anterior base of the neural spine. Posterior dorsal vertebrae are characterized by postzygodiapophyseal laminae and divided spinodiapophyseal laminae, with spinoprezygapophyseal laminae contributing to the prespinal lamina. The ilium and pubis differ from specimens previously collected, indicating a greater morphological disparity among titanosaurs in the Maastrichtian of West Texas than previously recognized. This disparity may be attributable to intraspecific variation or to the presence of multiple taxa. The new material is compatible with the only presently known North American titanosaur, Alamosaurus sanjuanensis, but is not formally referred due to lack of overlap with the hypodigm of that species. Comparison with other derived titanosaurs finds the closest affinities to Trigonosaurus pricei, Uberabatitan riberoi, and Baurutitan britoi of the Upper Cretaceous Brazilian Bauru Group, consistent with a South American immigration event at the end of the North American sauropod hiatus.

A complete titanosaur femur from West Texas with comments regarding hindlimb posture

An isolated titanosaur femur recovered from the Javelina Formation (Maastrichtian) of Big Bend National Park, Texas is the most complete example yet reported from North America. The specimen is likely referable to Alamosaurus sanjuanensis, the only titanosaur thus far known from Upper Cretaceous strata in North America, but cannot be attributed with certainty to that taxon. Compared to femora from other titanosaurs, the specimen has a relatively reduced abductor crest, a less elevated femoral head, and a distal joint surface that is orthogonal to the long axis of the shaft. These differences suggest that the Big Bend femur pertains to a species where hindlimb stance was closer to vertical, and with a comparatively narrower gait than other titanosaurids.

Carl Wiman's sauropods: The Uppsala Museum of Evolution's collection

The Museum of Evolution in Uppsala acquired a number of sauropod specimens under the tenure of Professor Carl Wiman. The most intensely studied of these are two partial skeletons, PMU 24705 (formerly PMU R 233) and PMU 24706 (formerly PMU R 234), excavated in Shandong (Shantung) Province, China, by Otto Zdansky, which form the basis for the species Euhelopus zdanskyi. These specimens were acquired by the Museum of Evolution in the 1920s and remain the subject of much interest among sauropod workers. The cranial anatomy, classification and the age of Euhelopus have been the subject of some debate. Other Chinese sauropod material in the Museum of Evolution collection includes three vertebrae (one cervical, one dorsal and one caudal) and an incomplete femur. The caudal vertebra has been recently referred to Diplodocoidea by some researchers and to Titanosauriformes by others. Incomplete sauropod remains, which may represent the topotype material of Alamosaurus sanjuanensis (the only named post-Cenomanian North American sauropod to date) in the Museum of Evolution collection from New Mexico, coupled with specimens from North American museums, may help resolve the validity of A. sanjuanensis as a taxon and the “sauropod hiatus” as either a real phenomenon or an artefact of the fossil record. The palaeontological significance of the Museum of Evolution's sauropod collection cannot be overstated. These important specimens continue to be a crucial resource for studies concerning sauropod taxonomy, phylogenetic systematics, evolution and functional morphology.

The First Giant Titanosaurian Sauropod from the Upper Cretaceous of North America

Argentinosaurus (Cenomanian, Argentina) is generally accepted as being the largest dinosaur so far discovered and is one of several giant titanosaurian sauropods known from the Upper Cretaceous of South America and Asia, but surprisingly not from North America. Here we present the first evidence of giant titanosaurian sauropods from the Upper Cretaceous of North America: two enormous vertebrae and a partial femur, from the Naashoibito Member of the Ojo Alamo Formation, New Mexico, and referred to Alamosaurus sanjuanensis. One of the new vertebrae, a posterior cervical, is comparable in size to a posterior cervical described for Puertasaurus: an Argentinosaurus-sized titanosaurian from the Maastrichtian of Argentina. This makes A. sanjuanensis the largest dinosaur from North America, and among the largest in the world. These findings indicate that A. sanjuanensis is diagnosed based on immature remains, which may have implications for cladistic analyses.

First sauropod (Dinosauria: Saurischia) remains from the Guichón Formation, Late Cretaceous of Uruguay

We report the first sauropod remains recorded in the Guichón Formation, western Uruguay. The materials belong to a middle-sized sauropod represented by more than one individual, and among other remains include more than fifty caudal centra. Close to the bones, several eggshell fragments resembling Sphaerovum erbeni Mones, 1980 were found. We discuss the biostratigraphic implications of these findings, which for the first time allow us to confidently refer the Guichón Formation to the Late Cretaceous. The combination of several synapomorphies such as a biconvex first caudal centrum, strongly procoelous middle and distal caudal centra, and a pyramidal astragalus suggests that the sauropod remains belong to a derived lithostrotian, probably related to Pellegrinisaurus powelli, Baurutitan britoi and Alamosaurus sanjuanensis. A few isolated teeth (now lost) referred by Frederich von Huene in 1934 to ornithomimid theropods and ornithischians are herein reinterpreted as belonging to indeterminate theropods and basal iguanodontians.

A sauropod dinosaur pes from the latest Cretaceous of North America and the validity of Alamosaurus sanjuanensis (Sauropoda, Titanosauria)

ABSTRACT Complete sauropod pedes are rare in the fossil record, which has limited their use in systematics. We describe a nearly complete, large sauropod pes from the Maastrichtian-age Naashoibito Member of the Kirtland Formation of New Mexico, U.S.A., that bears synapomorphies of some eusauropod clades, such as the presence of metatarsal I with a wide shaft and laterally deflected pedal unguals. Novel pedal characters presented herein, such as the presence of an embayment on the proximomedial corner of metatarsal IV, suggest that the Naashoibito specimen likely belongs to a titanosauriform. Based on its provenance, the Naashoibito specimen likely belongs to the derived titanosaur Alamosaurus sanjuanensis, which is the only recognized Late Cretaceous titanosaur in North America. However, formal referral to Alamosaurus awaits discovery of overlapping materials with the holotype or definitively referred remains. The holotypic scapula of Alamosaurus sanjuanensis is diagnostic, providing a basis for referral of some other Maastrichtian North American titanosaur specimens to the genus. Confirmation of these referrals and the description of the pes presented herein augment the data relevant to the systematic problems that have historically surrounded Alamosaurus.

Bone histology of the titanosaur Lirainosaurus astibiae (Dinosauria: Sauropoda) from the Latest Cretaceous of Spain

The titanosaur Lirainosaurus astibiae is the only sauropod species known from the Late Cretaceous of the Iberian Peninsula. Lirainosaurus did not reach a gigantic body size and is one of the smallest sauropods discovered to date. Histological analysis of Lirainosaurus bones, focused on diaphyseal transverse sections of appendicular elements, reveals that Lirainosaurus did not exhibit the osseous microstructure typical for large sauropods, but is comparable with that of the coeval titanosaurs Alamosaurus sanjuanensis, Ampelosaurus atacis, and Magyarosaurus dacus, and also shares histological traits with other small to medium-sized sauropodomorph dinosaurs. Lirainosaurus limb bones exhibit a laminar fibrolamellar bone microstructure interrupted by growth marks, fully obliterated in adulthood by intense secondary remodeling processes which tend to replace completely the primary cortex. Lirainosaurus attained smaller sizes than typical sauropods reducing the rate of primary periosteal osteogenesis and developing an extensive secondary remodeling well before the adult size was reached. Histological organization of Lirainosaurus long bones is more mature than observed in basal neosauropods at similar ontogenetic stage, documenting a case of peramorphosis by pre-displacement. This heterochronic growth would be a reversal of the accelerated pattern of bone deposition typical for the sauropod lineage.

Bone histology and microanatomy of Alamosaurus sanjuanensis (Sauropoda: Titanosauria) from the maastrichtian of Big Bend National Park, Texas

ABSTRACT Bones of Alamosaurus sanjuanensis were collected from the Upper Cretaceous Javelina and Black Peaks formations in Big Bend National Park, Texas, for use in the first extensive histological study of a titanosaurian sauropod dinosaur. Samples include cervical, dorsal, and caudal vertebrae; ribs; a scapula; humeri; an ulna; a metacarpal; an ischium; femora; a tibia; fibulae; and a metatarsal, representing a minimum of twenty two individuals between 35% and 100% maximum length. In elements of less than 60% maximum length, cortical tissue is primarily reticular or plexiform fibro-lamellar, often with modulations. Resorption in some specimens appears to have proceeded as outwardly expanding bands. In larger specimens (70–79% maximum length), primary tissue is only visible interstitially as either fibro-lamellar or parallel-fibered with low vascularity and annuli. Secondary osteons are in many places linearly arranged. Haversian systems are so pervasive in many of the largest specimens (80–100% maximum length) that virtually no primary tissue remains. However, one adult sized femur possesses laminar fibro-lamellar tissue in its outer cortex, suggesting that the adult size for Alamosaurus may have been underestimated. Camellae typical of titanosaur dorsal vertebrae are present in Alamosaurus but absent in caudal vertebrae. Although pneumatic dorsal ribs characterize Titanosauriformes, sections of ribs analyzed in this study show the cavities in Alamosaurus are much more extensive than most previously described. Overall, Alamosaurus bone histology combines characteristics found in less derived sauropods, such as an early onset of secondary reconstruction, with novel characters such as extensively pneumatic ribs and longer retention of juvenile tissue.

A JUVENILE SPECIMEN OF THE SAUROPOD DINOSAUR ALAMOSAURUS SANJUANENSIS FROM THE UPPER CRETACEOUS OF BIG BEND NATIONAL PARK, TEXAS

A juvenile specimen of the titanosaurid sauropod Alamosaurus sanjuanensis, recovered from just below the Cretaceous/Tertiary boundary horizon in Big Bend National Park, Texas, is from an individual less than half the size of adult specimens referred to this species. The disarticulated skeleton was preserved in deposits of a shallow flood-plain pond and includes elements not previously described, allowing for an improved diagnosis for this species. The elongate opisthocoelous cervical vertebrae have non-bifid posteriorly deflected neural spines with deep postspinal fossae. The dorsal vertebrae have wide spatulate neural spines with strong prespinal laminae, and lack hyposphene-hypantrum articulations. Alamosaurus sanjuanensis exhibits a unique morphology of the ischium, evident even in this juvenile specimen. Comparison with other titanosaurid species suggests that A. sanjuanensis is most closely related to an unnamed titanosaur from Peiropolis, Brazil and Neuquensaurus australis from Argentina.

A juvenile specimen of the sauropod dinosaur Alamosaurus sanjuanensis from the Upper Cretaceous of Big Bend National Park, Texas

A juvenile specimen of the titanosaurid sauropod Alamosaurus sanjuanensis, recovered from just below the Cretaceous/Tertiary boundary horizon in Big Bend National Park, Texas, is from an individual less than half the size of adult specimens referred to this species. The disarticulated skeleton was preserved in deposits of a shallow flood-plain pond and includes elements not previously described, allowing for an improved diagnosis for this species. The elongate opisthocoelous cervical vertebrae have non-bifid posteriorly deflected neural spines with deep postspinal fossae. The dorsal vertebrae have wide spatulate neural spines with strong prespinal laminae, and lack hyposphene-hypantrum articulations. Alamosaurus sanjuanensis exhibits a unique morphology of the ischium, evident even in this juvenile specimen. Comparison with other titanosaurid species suggests that A. sanjuanensis is most closely related to an unnamed titanosaur from Peiropolis, Brazil and Neuquensaurus australis from Argentina.