Digit-only sauropod pes trackways from China - evidence of swimming or a preservational phenomenon?

For more than 70 years unusual sauropod trackways have played a pivotal role in debates about the swimming ability of sauropods. Most claims that sauropods could swim have been based on manus-only or manus-dominated trackways. However none of these incomplete trackways has been entirely convincing, and most have proved to be taphonomic artifacts, either undertracks or the result of differential depth of penetration of manus and pes tracks, but otherwise showed the typical pattern of normal walking trackways. Here we report an assemblage of unusual sauropod tracks from the Lower Cretaceous Hekou Group of Gansu Province, northern China, characterized by the preservation of only the pes claw traces, that we interpret as having been left by walking, not buoyant or swimming, individuals. They are interpreted as the result of animals moving on a soft mud-silt substrate, projecting their claws deeply to register their traces on an underlying sand layer where they gained more grip during progression. Other sauropod walking trackways on the same surface with both pes and manus traces preserved, were probably left earlier on relatively firm substrates that predated the deposition of soft mud and silt . Presently, there is no convincing evidence of swimming sauropods from their trackways, which is not to say that sauropods did not swim at all

Elevated extinction rates as a trigger for diversification rate shifts: early amniotes as a case study

Tree shape analyses are frequently used to infer the location of shifts in diversification rate within the Tree of Life. Many studies have supported a causal relationship between shifts and temporally coincident events such as the evolution of “key innovations”. However, the evidence for such relationships is circumstantial. We investigated patterns of diversification during the early evolution of Amniota from the Carboniferous to the Triassic, subjecting a new supertree to analyses of tree balance in order to infer the timing and location of diversification shifts. We investigated how uneven origination and extinction rates drive diversification shifts, and use two case studies (herbivory and an aquatic lifestyle) to examine whether shifts tend to be contemporaneous with evolutionary novelties. Shifts within amniotes tend to occur during periods of elevated extinction, with mass extinctions coinciding with numerous and larger shifts. Diversification shifts occurring in clades that possess evolutionary innovations do not coincide temporally with the appearance of those innovations, but are instead deferred to periods of high extinction rate. We suggest such innovations did not cause increases in the rate of cladogenesis, but allowed clades to survive extinction events. We highlight the importance of examining general patterns of diversification before interpreting specific shifts

A basal lithostrotian titanosaur (Dinosauria: Sauropoda) with a complete skull: Implications for the evolution and paleobiology of titanosauria

We describe Sarmientosaurus musacchioi gen. et sp. nov., a titanosaurian sauropod dinosaur from the Upper Cretaceous (Cenomanian - Turonian) Lower Member of the Bajo Barreal Formation of southern Chubut Province in central Patagonia, Argentina. The holotypic and only known specimen consists of an articulated, virtually complete skull and part of the cranial and middle cervical series. Sarmientosaurus exhibits the following distinctive features that we interpret as autapomorphies: (1) maximum diameter of orbit nearly 40% rostrocaudal length of cranium; (2) complex maxilla - lacrimal articulation, in which the lacrimal clasps the ascending ramus of the maxilla; (3) medial edge of caudal sector of maxillary ascending ramus bordering bony nasal aperture with low but distinct ridge; (4) ´tongue-like´ ventral process of quadratojugal that overlaps quadrate caudally; (5) separate foramina for all three branches of the trigeminal nerve; (6) absence of median venous canal connecting infundibular region to ventral part of brainstem; (7) subvertical premaxillary, procumbent maxillary, and recumbent dentary teeth; (8) cervical vertebrae with ´strut-like´ centroprezygapophyseal laminae; (9) extremely elongate and slender ossified tendon positioned ventrolateral to cervical vertebrae and ribs. The cranial endocast of Sarmientosaurus preserves some of the most complete information obtained to date regarding the brain and sensory systems of sauropods. Phylogenetic analysis recovers the new taxon as a basal member of Lithostrotia, as the most plesiomorphic titanosaurian to be preserved with a complete skull. Sarmientosaurus provides a wealth of new cranial evidence that reaffirms the close relationship of titanosaurs to Brachiosauridae. Moreover, the presence of the relatively derived lithostrotian Tapuiasaurus in Aptian deposits indicates that the new Patagonian genus represents a ´ghost lineage´ with a comparatively plesiomorphic craniodental form, the evolutionary history of which is missing for at least 13 million years of the Cretaceous. The skull anatomy of Sarmientosaurus suggests that multiple titanosaurian species with dissimilar cranial structures coexisted in the early Late Cretaceous of southern South America. Furthermore, the new taxon possesses a number of distinctive morphologies - such as the ossified cervical tendon, extremely pneumatized cervical vertebrae, and a habitually downward- facing snout - that have rarely, if ever, been documented in other titanosaurs, thus broadening our understanding of the anatomical diversity of this remarkable sauropod clade. The latter two features were convergently acquired by at least one penecontemporaneous diplodocoid, and may represent mutual specializations for consuming low-growing vegetation.Fil: Martínez, Rubén Darío. Universidad Nacional de la Patagonia; ArgentinaFil: Lamanna, Matthew C.. Carnegie Museum Of Natural History; Estados UnidosFil: Novas, Fernando Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "bernardino Rivadavia"; ArgentinaFil: Ridgely, Ryan C.. Ohio University College Of Osteopathic Medicine; Estados UnidosFil: Casal, Gabriel. Universidad Nacional de la Patagonia; ArgentinaFil: Martínez, Javier E.. Hospital Regional de Comodoro Rivadavia; ArgentinaFil: Vita, Javier R.. Resonancia Magnética Borelli; ArgentinaFil: Witmer, Lawrence M.. Ohio University College Of Osteopathic Medicine; Estados Unido

Paleobiology of titanosaurs: reproduction, development, histology, pneumaticity, locomotion and neuroanatomy from the South American fossil record

Fil: García, Rodolfo A.. Instituto de Investigación en Paleobiología y Geología. Museo Provincial Carlos Ameghino. Cipolletti; ArgentinaFil: Salgado, Leonardo. Instituto de Investigación en Paleobiología y Geología. General Roca. Río Negro; ArgentinaFil: Fernández, Mariela. Inibioma-Centro Regional Universitario Bariloche. Bariloche. Río Negro; ArgentinaFil: Cerda, Ignacio A.. Instituto de Investigación en Paleobiología y Geología. Museo Provincial Carlos Ameghino. Cipolletti; ArgentinaFil: Carabajal, Ariana Paulina. Museo Carmen Funes. Plaza Huincul. Neuquén; ArgentinaFil: Otero, Alejandro. Museo de La Plata. Universidad Nacional de La Plata; ArgentinaFil: Coria, Rodolfo A.. Instituto de Paleobiología y Geología. Universidad Nacional de Río Negro. Neuquén; ArgentinaFil: Fiorelli, Lucas E.. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica. Anillaco. La Rioja; Argentin

Body Size Distribution of the Dinosaurs

The distribution of species body size is critically important for determining resource use within a group or clade. It is widely known that non-avian dinosaurs were the largest creatures to roam the Earth. There is, however, little understanding of how maximum species body size was distributed among the dinosaurs. Do they share a similar distribution to modern day vertebrate groups in spite of their large size, or did they exhibit fundamentally different distributions due to unique evolutionary pressures and adaptations? Here, we address this question by comparing the distribution of maximum species body size for dinosaurs to an extensive set of extant and extinct vertebrate groups. We also examine the body size distribution of dinosaurs by various sub-groups, time periods and formations. We find that dinosaurs exhibit a strong skew towards larger species, in direct contrast to modern day vertebrates. This pattern is not solely an artefact of bias in the fossil record, as demonstrated by contrasting distributions in two major extinct groups and supports the hypothesis that dinosaurs exhibited a fundamentally different life history strategy to other terrestrial vertebrates. A disparity in the size distribution of the herbivorous Ornithischia and Sauropodomorpha and the largely carnivorous Theropoda suggests that this pattern may have been a product of a divergence in evolutionary strategies: herbivorous dinosaurs rapidly evolved large size to escape predation by carnivores and maximise digestive efficiency; carnivores had sufficient resources among juvenile dinosaurs and non-dinosaurian prey to achieve optimal success at smaller body size. © 2012 O'Gorman, Hone

Diversity of diapsid fifth metatarsals from the Lower Triassic karst deposits of Czatkowice, southern Poland —functional and phylogenetic implications

Three morphotypes of the fifth metatarsal (MttV), one of the most informative bones of the postcranium, have been described herein from the Early Triassic karst deposits of the Czatkowice locality (Southern Poland). Two of them have been assigned to a basal archosauriform Osmolskina czatkowicensis and a basal lepidosauromorph, Sophineta cracoviensis, respectively, while one is undetermined saurian. Two morphological categories of the hooked fifth metatarsals recognized from this assemblage account for two different solutions to the problem of improvement of locomotion. A strongly inflected (sensu Robinson 1975) MttV shaft consists of two parts, a distal one lying on the ground in a plantigrade manner and a proximal one bent at an angle to get align with the ventral surface of the crus and proximal tarsus. In contrast, a straight shaft of the hooked MttV, suggests its subvertical life position and thus a digitigrade foot stance. The hooking of the fifth metatarsal, that is currently accepted saurian synapomorphy, appeared in phylogeny in a primitive state referred to herein as a neckless type: with neither a neck-shaped articular protrusion for the fourth distal tarsal nor a directly medial orientation of the articular facet. A derived long-necked type with protruding arricular part and more directly medial orientation of the articular facet appeared, at various stages of further phylogeny. A strong plantar–dorsal inflexion of the fifth metatarsal associated with a protrusion of lateral plantar tubercle, dates from a directly pre-lepidosaurian stage of evolution

Globaura venusta gen. et sp.n. i Eoxanta lacertifrons gen. et sp. n.- nieteiidowe lacertoidy z póznej kredy Mongolii

Two Late Cretaceous Mongolian lizards Eoxanta lacertifrons gen. et sp. n. (?middle Campanian) and Globaura venusta gen. et sp. n. (?late Santonian-?middle Campanian) are assigned to Lacertoidea (sensu Estes et al. 1988). Eoxanta is considered the sister group of the Xantusiidae, and, thus, the oldest known representative of the xantusiid line. Globaura is the sister group of the Lacertiformes (sensu Estes et al. 1988). The paper also considers the polarity of some scincomorphan characters. Formation of the anteroventral border of orbit by maxilla is considered synapomorphic for the Scincomorpha.Opracowany materiał pochodzi z kolekcji Polsko-Mongolskich Wypraw na Pustynię Gobi z lat 1963—1971. W pracy opisano dwa nowe rodzaje i gatunki jaszczurek: Globaura venusta gen. et sp. n. (pl. 1: 1; 2: 1; 3; 4; 6: 2; 7: 6, oraz tabele 1 i 2) z ?gómego santonu—?środkowego kampanu oraz Eoxanta lacertifrons gen. et sp. n. (pl. 1: 2; 2: 2; 5: 1—3; 6: 3, 4; 7: 4, 5; 8: 2 oraz tabele 1 i 2) ze ?środkowego kampanu i zaliczono je do Lacertoidea (sensu Estes i in. 1988). Globaura jest siostrzaną grupą taksonu obejmującego Lacertidae, Gymnophtalmidae i Teiidae, nazwanego Lacertiformes przez Estesa i in. (l. c.), Eoxanta siostrzaną grupą Xantusiidae. Globaura i Eoxanta są to pierwsze nieteiidowe lacertoidy opisane z górnej kredy Mongolii, a Eoxanta jest najwcześniejszym przedstawicielem linii xantusiidowej jaszczurek i jedynym przedstawicielem tej linii znanym z Azji. Globaura dzieli z Lacertiformes swoisty szew czołowo-ciemieniowy lecz poza tym zachowuje cechy wspólnego przodka Scincomorpha, plezjomorficzne i synapomorficzne dla tego podrzędu, które ulegają unowocześnieniu u Lacertiformes. Są to cechy przedoczodołowej części czaszki i podniebienia. Cechy wspólnego przodka Scincomorpha zachowały się także u Eoxanta i Slavoia Sulimski, 1984, a także u rodzin Scincidae, Xantusiidae i Cordylidae żyjących i obecnie. Świadczą one o dużej stabilności morfotypu odziedziczonego po wspólnym przodku, który jedynie u Lacertiformes uległ zasadniczym zmianom (patrz tabela 3). Ten rys ewolucji Scincomorpha został podkreślony przez wprowadzenie nieformalnej jednostki — wczesnoscynkomorfowego gradu. Pod względem metodologicznym praca opiera się na kladystyce (Henning 1966, Eldredge i Cracraft 1980). Dla uściślenia języka przyjęto terminologię i skróty za Maddisonem i in. (1984) rozróżniając wśród stanów wyjściowych (ancestralnych) danego taksonu stany jego wyłącznego przodka, odpowiadającego węzłowi grupy wewnętrznej (ingroup node IN) oraz stany przodka wspólnego z grupą zewnętrzną (outgroup node ON). Unika się w ten sposób dwuznaczności terminu ancestralny który obejmuje wszystkie stany wyjściowe, zarówno synapomorfie jak i plezjomorfie danego etapu filogenezy. W pracy przedyskutowano rozmaite wersje sekwencji cech w filogenezie Squamata zawierające się w najbardziej aktualnym kladogramie tej grupy gadów zaczerpniętym z Estesa i in. (1988), posługując się zasadą globalnej oszczędności (Maddison’a i in. 1984) oraz prostymi hipotezami dotyczącymi sposobu transformacji cech. Te ostatnie hipotezy (patrz np. fig. 7), oparte na danych innych niż rozprzestrzenienie taksonomiczne i innych niż rozprzestrzenienie stratygraficzne, a głównie na bliskości morfologicznej stanów cech, odpowiadają najlepiej pierwotnej koncepcji morfokliny (Maslin 1952, Eldredge i Cracraft 1980: 54) jako sekwencje stanów cech nie osadzone w czasie geologicznym ani w filogenezie. W wyniku przedyskutowania następujących cech: obrzeżenia oczodołu (fig. 2), kontaktów kości w części przedoczodołowej czaszki (fig. 3, 4), kontaktu kości żuchwy (fig. 5, 6, 7) oraz pewnych cech podniebienia (fig. 1), uznano szczękowe (zamiast jarzmowego) brzuszne obrzeżenie oczodołu za cechę synapomorficzną Scincomorpha. Wniosek ten nie jest zgodny z wnioskiem Estesa i in. (1988). Praca została wykonana w ramach CPBP 04.03