ABSTRACT We report the discovery of a new species of the snake Madtsoia from infratrappean horizons of Late Cretaceous age in Pisdura, central India. Recovered vertebrae are large (1.83 cm long; 4.35 cm tall) and pertain to a snake that was ca. 5 m long. Discovery of Madtsoia in India extends the geographic distribution of the genus and represents only the second species known from the Cretaceous. Vertebrae of Madtsoia pisdurensis sp. nov. are strikingly similar to those of M. bai and M. camposi (South America) and M. madagascariensis (Madagascar), but can be distinguished from them by a unique process on the hemal keel, which is low, flat, and triangular in outline. Whereas the eastern Gondwanan species of Madtsoia (M. madagascariensis, M. pisdurensis) are Late Cretaceous in age, the western Gondwanan species (M. bai, M. camposi) are Paleogene in age. Geophysical evidence suggests that land connections between South America, Madagascar, and Indo-Pakistan were severed by at least 100–90 Ma, which implies that Madtsoia achieved its broad geographic distribution either by (1) origin and dispersion before the end of the Turonian; or (2) the presence of an unrecognized land connection persisting into the latest Cretaceous. Both hypotheses predict that Madtsoia will be discovered in Mesozoic strata of South America, where it survived the Cretaceous-Paleogene mass extinction.
Sauropod dinosaurs achieved the largest body sizes and the most elongate necks and tails of any terrestrial vertebrate. The elongate, cantilevered necks of sauropods comprised opisthocoelous vertebrae joined at concavo-convex joints. Opisthocoelous centra also occurred in the dorsal region of sauropods and procoelous centra in the tails of certain lineages. Concavo-convex intercentral joints have been hypothesized to increase the flexibility of the vertebral column or to stabilize intervertebral joints against shear stresses. Using Alligator as an extant analog, condyle convexity and range of motion were measured at every intervertebral joint in an individual, with the latter measured in situ. Results reveal that convexity is greatest in the alligator presacral column where flexibility is low; amphiplatyan vertebrae occur in the distal caudal region where flexibility is highest. The negative relationship between convexity and flexibility is not significant, indicating that flexibility is independent of centrum articular morphology. Convexity is greatest in regions in which high shear stresses are predicted to result from terrestrial locomotion and tail flexion. The evolution of opisthocoelous cervical vertebrae in early sauropods likely strengthened the long and massive neck against catastrophic dislocations without compromising joint mobility. The stabilization provided by dorsal opisthocoely and caudal procoely may relate to clade-specific specializations such as the “whiplash” tails of flagellicaudatans and the “wide-gauge” limb stance in titanosaurs. The study of opisthocoely and procoely provides a means to understand the loading regimes of the vertebral column in sauropods and other vertebrates, with implications for the behavior and ecology of fossil taxa.
JASON J. HEAD,*' DHANANJAY M. MOHABEY,2 and JEFFREY A. WILSON3; 1Department of Biology, University of Toronto at Mississauga, 3359 Mississauga Road, Mississauga ON, L5L 1C6, Canada; 2Geological Survey of India (Central Region), Palaeontology Division, Seminary Hills, Nagpur 440 010, India; 3Museum of Paleontology and Department of Geological Sciences, The University of Michigan, 1109 Geddes Rd., Ann Arbor MI 48109-1079, U.S.A.
This chapter reports the current view of sauropod phylogeny and shows that sauropods were successful in terms of their geographic and temporal distributions, biomass, morphological complexity, and diversity at both higher and lower levels. It reviews the difficulties in tracing two major parts of the sauropod phylogeny. The main topological disagreement among early cladistic analyses of Sauropoda centered on the relationships of broad- and narrow-crowned sauropods. Additionally, the evolutionary events diagnosing several major sauropod clades (Sauropoda, Eusauropoda, Neosauropoda, Diplodocoidea, Macronaria) are described. The chapter outlines the major specializations relating to herbivory, neck elongation, and locomotion for each of five major sauropod clades. The stratigraphic distribution of the first representatives of Sauropoda and of their sister-taxon Prosauropoda implies a 10 million to 15-million year missing lineage during which the score of features diagnosing sauropods evolved. Despite advances in understanding of the group, substantial gaps in the knowledge of sauropod history still exist.
Sauropod dinosaurs achieved the largest body sizes and the most elongate necks and tails of any terrestrial vertebrate. The elongate, cantilevered necks of sauropods comprised opisthocoelous vertebrae joined at concavo-convex joints. Opisthocoelous centra also occurred in the dorsal region of sauropods and procoelous centra in the tails of certain lineages. Concavo-convex intercentral joints have been hypothesized to increase the flexibility of the vertebral column or to stabilize intervertebral joints against shear stresses. Using Alligator as an extant analog, condyle convexity and range of motion were measured at every intervertebral joint in an individual, with the latter measured in situ. Results reveal that convexity is greatest in the alligator presacral column where flexibility is low; amphiplatyan vertebrae occur in the distal caudal region where flexibility is highest. The negative relationship between convexity and flexibility is not significant, indicating that flexibility is independent of centrum articular morphology. Convexity is greatest in regions in which high shear stresses are predicted to result from terrestrial locomotion and tail flexion. The evolution of opisthocoelous cervical vertebrae in early sauropods likely strengthened the long and massive neck against catastrophic dislocations without compromising joint mobility. The stabilization provided by dorsal opisthocoely and caudal procoely may relate to clade-specific specializations such as the "whiplash" tails of flagellicaudatans and the "wide-gauge" limb stance in titanosaurs. The study of opisthocoely and procoely provides a means to understand the loading regimes of the vertebral column in sauropods and other vertebrates, with implications for the behavior and ecology of fossil taxa.
Fossil vertebrate distributions are typically based on body fossils, which are often poorly sampled at the margins of their true temporal and spatial ranges.Because vertebrate ichnofossils can be preserved in great abundance and in different environments than vertebrate body fossils, inclusion of ichnofossil data may improve sampled ranges.However, if ichnofossils are to serve as an independent source of distributional data, then their attribution to a body fossil group (i.e., trackmaker identification) cannot rely on temporal and spatial coincidence.Ichnofossils identified by synapomorphies can act as an independent source of distributional data that can modify spatial, temporal, and character distributions, which in turn may influence hypotheses of locomotor evolution.In this paper I evaluate the spatial, temporal, and character distributions of early sauropod dinosaurs by using a combined ichnofossil and body fossil data set.Sauropod ichnofossils supplement the spatiotemporal distributions of early sauropods and provide important information on early sauropod foot posture that is rarely preserved or can only be inferred from body fossils.The presence of derived features in early-appearing ichnofossils challenges previous hypotheses of character transformation, implying either parallelism, reversal, or ghost lineages.Stratocladistics can be used to resolve conflicting character and temporal distributions from body fossils and ichnofossils.Stratocladistic analysis of a combined ichnofossil and body fossil data set suggests a richer, more widely distributed diversity of early sauropods than currently recognized in body fossils and suggests that several locomotor characters originated much earlier than implied by body fossils.
Background Temnospondyls are one of the earliest radiations of limbed vertebrates. Skeletal remains of more than 190 genera have been identified from late Paleozoic and early Mesozoic rocks. Paleozoic temnospondyls comprise mainly small to medium sized forms of diverse habits ranging from fully aquatic to fully terrestrial. Accordingly, their ichnological record includes tracks described from many Laurasian localities. Mesozoic temnospondyls, in contrast, include mostly medium to large aquatic or semi-aquatic forms. Exceedingly few fossil tracks or trackways have been attributed to Mesozoic temnospondyls, and as a consequence very little is known of their locomotor capabilities on land. Methodology/Principal Findings We report a ca. 200 Ma trackway, Episcopopus ventrosus, from Lesotho, southern Africa that was made by a 3.5 m-long animal. This relatively long trackway records the trackmaker dragging its body along a wet substrate using only the tips of its digits, which in the manus left characteristic drag marks. Based on detailed mapping, casting, and laser scanning of the best-preserved part of the trackway, we identified synapomorphies (e.g., tetradactyl manus, pentadactyl pes) and symplesiomorphies (e.g., absence of claws) in the Episcopopus trackway that indicate a temnospondyl trackmaker. Conclusions/Significance Our analysis shows that the Episcopopus trackmaker progressed with a sprawling posture, using a lateral-sequence walk. Its forelimbs were the major propulsive elements and there was little lateral bending of the trunk. We suggest this locomotor style, which differs dramatically from the hindlimb-driven locomotion of salamanders and other extant terrestrial tetrapods can be explained by the forwardly shifted center of mass resulting from the relatively large heads and heavily pectoral girdles of temnospondyls.
We report a complete left fourth metatarsal collected from rocks of the Upper Cretaceous (Campanian) "El Gallo" Formation exposed along the Pacific Ocean near El Rosario, Baja California, México.The metatarsal IV was part of an arctometatarsalian metatarsus, as evidenced by a deep medial notch proximally and extensive articulation for metatarsal III.This condition, along with the U-shape of the proximal end, supports identification as tyrannosauroid.It is assigned to Tyrannosauridae based on features on the posterior surface of the shaft, but finer taxonomic resolution is not possible.Compared to other tyrannosauroids, the metatarsal is relatively short, closely resembling the proportions of the gracile Albertosaurus sarcophagus rather than the much more massive, robust metatarsals of Tyrannosaurus rex.The Baja tyrannosaurid metatarsal is shorter than almost all other tyrannosauroid fourth metatarsals, raising the possibility that it pertains to an immature individual.North American tyrannosauroids are best known from the northern coast of the Western Interior Seaway, as well as less frequently on the southern coast of the seaway in Utah and New Mexico.The new record in Baja marks the first unambiguous skeletal material of a tyrannosaurid both in México and along the Pacific coast.
