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::: Info Dinosauria :::

Noticias, resúmenes e información

viernes, febrero 10, 2006

Huevos y comportamiento de nidificación


Dinosaur eggs and nesting behaviors: A paleobiological investigation
Gerald Grellet-Tinner a,b,*, Luis Chiappe b, Mark Norell c, David Bottjer a a Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089-0740, USA b Department of Vertebrate Paleontology, Natural History Museum of, Los Angeles County, CA 90007, USA c Department of Vertebrate Paleontology, American Museum of Natural History, New York, New York 10024-5192, USA Received 8 February 2005; received in revised form 19 October 2005; accepted 28 October 2005

Abstract:
Although dinosaur eggs were first discovered and identified in the late 1800s, limited attention was given to the scientific value of zoological fossils in contrast to observations based on skeletal features. Here, we offer a review of Mesozoic saurischian egg materials,
in comparison with extant crocodilians and avians, and their paleobiological interpretation based either on the presence of embryos in ovo or brooding adults on egg clutches. Our study focuses on the eggs of the oviraptorid Citipati osmolka (Mongolia), the troodontid
Troodon formosus (North America), the theropod oospecies Macroelongatoolithus xixiaensis (China), the ornithothoracine bird (Argentina), an indeterminate theropod (Thailand), and titanosaurs (Argentina). Results show that (1) many oological characters and reproductive behaviors associated with modern birds are rooted among non-avian theropods, (2) there is a reproductive evolutionary cline from crocodilians to modern birds with (3) a noticeable pattern of coeval development between the accretion of eggshell layers,
origination and size increased of larger air cells (inferred from egg polar asymmetry), and brooding/incubating behaviors. Most of these pre-adaptations are grouped in two main clades of the saurischian cladogram: one at the level of Oviraptorosauridae and the
other at Troodontidae. Although undeniably these two theropod taxa seem to represent two important phases for the evolution of avian reproduction, the phylogenetic distance between these clades and Titanosauria cannot be ignored. As such, the reproductive features
that appeared in concert in oviraptorids might have gradually evolved across more basal theropod clades. Although Troodon formosus by its egg shape and nesting behavior seems to be in this study the precursors of modern avian reproduction, the importance of smallbodied
theropods such as those who laid the Phu Phok eggs cannot be dismissed and the eggs of such dinosaurs could suggest a closer phylogenetic ties to Aves than troodontids. At a higher level of inferences, there is a strong possibility that the evolution of these reproductive features is concurrent with profound physiological and metabolic changes that occurred in saurischian dinosaurs throughout their evolution.

Huellas de dinosaurio en Korea

Dinosaur-dominated footprint assemblages from the Cretaceous Jindong Formation, Hallyo Haesang National Park area, Goseong County, South Korea: Evidence and implications

Martin G. Lockley a,*, Karen Houck a, Seong-Young Yang b, Masaki Matsukawa c, Seong-Kyu Lim d a Dinosaur Tracks Museum, University of Colorado at Denver, PO Box 173364, Campus Box 172, Denver, CO 80217-3364, USA b 706-010, 5-45 Beomeodong, Suseong-gu, Taegu, South Korea c Department of Science Education, Tokyo Gakugei University, Koganei, Tokyo 184-8501, Japan d Earth Science Department, Kyungpook National University, Taegu, South Korea Received 12 March 2005; accepted in revised form 20 October 2005

Abstract:
The track-rich Cretaceous Jindong Formation comprises part of an intra-arc basin, fluvio-lacustrine succession that represents a late stage in the evolution of the Kyongsang Basin. This formation is replete with track-bearing levels indicating the activity of many generations of dinosaurs and birds. The track-rich beds occur in the upper part of the Hayang Group (Kyongsang Supergroup), which also contains other, underlying dinosaur-track-bearing formations. However the Jindong Formation and underlying formations have produced few age-diagnostic body fossils.

Altered volcaniclastic sediments such as are found the Jindong Formation complicate interpretation of the age of the tracks as discussed in the accompanying companion paper. Nonetheless such settings provided near optimal conditions for the formation and preservation of abundant track assemblages (ichnofaunas), and the Jindong Formation has become an ichnological ‘‘cause celebre’’ producing impressive statistics on
the number of track-bearing sites, number of track-bearing levels and number of measured trackways. These data allow various inferences about certain aspects of the population structure, behavior and distribution of the dinosaurian track makers in these dinosaur-dominated paleocommunities.
The Jindong Formation and underlying Haman Formation have also yielded many bird tracks. The complete lack of avian body fossils in Korea and the rarity of dinosaur skeletal remains means that the footprint record currently provides the vast majority of the Mesozoic vertebrate evidence available for the entire Korean peninsula. Thus, the tracks represent a highly significant addition to the national paleontological heritage of Korea, as well as being a very important component of the East Asian and global footprint records. Detailed studies of a 100e200-m-thick succession at the Sangjok Dinosaur Tracksite National Monument in the Hallyo Haesang National Park area in Kosong County reveal an average
of about two track-bearing levels per meter, making it one of the richest track-bearing sections on record and providing evidence of the activity of hundreds of individuals. Many other track sites are found locally in the Jindong Formation in Kosong County (about 500 km2) including one described herein from near Gohyeon village where the Jindong Formation type section is situated. Other track sites can be traced laterally over larger distances within the Gyeongsang Basin. The composition of ichnofaunas throughout this region appears remarkably consistent.
The Jindong Formation is one of the few localities where sauropod, ornithopod, and bird tracks all occur in abundance, probably due to latitudinal/ climatic controls. The sauropod tracks, which include wide-gauge forms allied to Brontopodus, form the largest brontosaur trackway sample yet reported but are characterized by a high proportion of small individuals. Such unusual size-frequency distributions raise interesting ecological and taphonomic questions about the biasing of the body fossil record towards large individuals by various physical (preservational) or biological/ ecological controls.
The most abundant dinosaur trackways are those of iguanodontids (cf. Caririchnium or Iguanodontipus) that often traveled in herds. By contrast, sauropod tracks show little or no evidence of gregarious behavior and rarely occur on the same bedding planes as ornithopod trackways.

This suggests a pattern of mutual exclusion or geological segregation between these two herbivore groups, which indicates that they probably frequented the area at different times. Sauropod and ornithopod track size-frequency distributions are also fundamentally different, suggesting that the ornithopods were mainly sub-adults and adults, whereas the sauropods were predominantly juveniles. Theropod tracks are uncommon suggesting a low predator:prey ratio of 1:20.

Bird tracks including the large ichnospecies Jindongornipes kimi, an intermediate-sized form, Goseongornipes markjonesi ichnosp. and ichnogen.
nov., and a small ichnospecies Koreanaornis hamanensis occur at several dozen stratigraphic levels in association with nematode trails (Cochlichnus) and other invertebrate traces. These three ichnospecies are assigned to the respective ichnofamilies Koreanornipodidae ichnofam.
nov., Ignotornidae, and Jindongornipodidae ichnofam. nov. All these avian footprints are typical of bird track assemblages in lake shoreline deposits, and indicate the activity of many generations of waders or shorebirds. We also recognize other, much less common, small footprint types tentatively attributed to a perching bird or a diminutive theropod. Collectively the bird tracks indicate the considerable potential of avian ichnites to provide insight into avian paleoecology at an early stage in the evolution of Class Aves.

Tiranosaurio basal de China

A basal tyrannosauroid dinosaur from the Late Jurassic of China.
2006. Xing Xu, James M. Clark, Catherine A. Forster, Mark A. Norell, Gregory M. Erickson, David A. Eberth, Chengkai Jia and Qi Zhao. Nature 439: 715-718

Abstract: The tyrannosauroid fossil record is mainly restricted to Cretaceous sediments of Laurasia, although some very fragmentary Jurassic specimens have been referred to this group. Here we report a new basal tyrannosauroid, Guanlong wucaii gen. et sp. nov., from the lower Upper Jurassic of the Junggar Basin, northwestern China. G. wucaii is the oldest known tyrannosauroid and shows several unexpectedly primitive pelvic features. Nevertheless, the limbs of G. wucaii share several features with derived coelurosaurs, and it possesses features shared by other coelurosaurian clades. This unusual combination of character states provides an insight into the poorly known early radiation of the Coelurosauria. Notably, the presumed predatory Guanlong has a large, fragile and highly pneumatic cranial crest that is among the most elaborate known in any non-avian dinosaur and could be comparable to some classical exaggerated ornamental traits among vertebrates.

Antiguo Tiranosaurio crestado

La especie llamada Dragón con Corona, de tres metros de altura es el ancestro del Tiranosaurio Rex.
Paleontólogos chinos descubrieron una nueva especie de dinosaurio denominada Dragón con Corona, que vivió hace 160 millones de años y era el ancestro del Tiranosaurio Rex, uno de los más feroces predadores que habitó la Tierra hace 67 millones de años. De acuerdo a un informe de la revista Nature, fue hallado por científicos del Instituto de Vertebrados y Paleontología de Pekín en el desierto de Gobi, en el oeste de China.

El nuevo ejemplar pertenece a la especie Wucaii que en chino significa cinco colores, en referencia a los colores de las rocas donde fue encontrado el ejemplar. La denominación en chino es Guanlong, que deriva de una palabra empleada para denominar corona y dragón.

Este ejemplar de dinosaurio medía tres metros de altura, se paraba en dos patas y al parecer podría haber estado cubierto enteramente de plumas. Los científicos señalaron que el Dragón con Corona precedió al Tiranosaurio Rex que es físicamente muy parecido, pero medía 13 metros de alto y vivió hace 67 millones de años.

Ambos dinosaurios tenían igual ferocidad, pero a diferencia del Tiranosaurio Rex, el Guanlong poseía una cresta ósea en su nariz. Los expertos consideraron que esa cresta le servía al animal como "ornamento sexual", como lo es el plumaje del pavo real. Xing Xu, uno de los paleontólogos que descubrió al nuevo dinosaurio, calificó el hallazgo de "histórico".

El investigador indicó que "la cresta craneana del Guanlong provee una evidencia crucial para explicar la exagerada ornamentación sexual entre los dinosaurios predadores".

En tanto, el paleontólogo italiano Cristiano Dal Sasso, comprobó que el Spinosaurus fue el dinosaurio predador más grande del mundo, superando al temible Tiranosaurio Rex y al Giganotosaurus Carolini, que habitó la patagonia argentina. Dal Sasso, investigador del Museo de Historia Natural de Milán, en Italia, destacó que el Spinosaurus medía 17 metros de altura, se paraba en dos patas y poseía una cola de gran tamaño.