Tag Archives: Dinosaurs

Microraptor plumage, pterosaur eating fish

http://www.sciencemag.org/content/335/6073/1215.short

Reconstruction of Microraptor and the Evolution of Iridescent Plumage
Quanguo Li, Ke-Qin Gao, Qingjin Meng, Julia A. Clarke, Matthew D. Shawkey, Liliana D’Alba, Rui Pei, Mick Ellison, Mark A. Norell, Jakob Vinther

You have to see the figures.
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031945

The Late Jurassic Pterosaur Rhamphorhynchus, a Frequent Victim of the Ganoid Fish Aspidorhynchus?
Eberhard Frey, Helmut Tischlinger

– Jacqueline

Body-size transitions and trait evolution in therapsids and archosauromorphs

(Notice the clever use of the word ‘dinosaur’ in the title, even if dinosaurs are only a small part of the study)

Rise of dinosaurs reveals major body-size transitions are driven by passive processes of trait evolution

Roland B. Sookias, Richard J. Butler and Roger B. J. Benson

A major macroevolutionary question concerns how long-term patterns of body-size evolution are underpinned by smaller scale processes along lineages. One outstanding long-term transition is the replacement of basal therapsids (stem-group mammals) by archosauromorphs, including dinosaurs, as the dominant large-bodied terrestrial fauna during the Triassic (approx. 252– 201 million years ago). This landmark event preceded more than 150 million years of archosauromorph dominance. We analyse a new body-size
dataset of more than 400 therapsid and archosauromorph species spanning the Late Permian– Middle Jurassic. Maximum-likelihood analyses indicate that Cope’s rule (an active within-lineage trend of body-size increase) is extremely rare, despite conspicuous patterns of body-size turnover, and contrary to proposals that Cope’s rule is central to vertebrate evolution. Instead, passive processes predominate in taxonomically and ecomorphologically more inclusive clades, with stasis common in less inclusive clades. Body-size limits are clade-dependent, suggesting intrinsic, biological factors are more important than the external environment. This clade-dependence is exemplified by maximum size of Middle–early Late Triassic archosauromorph predators exceeding that of contemporary herbivores, breaking a widelyaccepted ‘rule’ that herbivore maximum size greatly exceeds carnivore maximum size. Archosauromorph
and dinosaur dominance occurred via opportunistic replacement of therapsids following extinction, but were facilitated by higher archosauromorph growth rates.

Keywords: evolutionary trends; body size; Cope’s rule; Archosauromorpha; Therapsida; Permo-Triassic

http://rspb.royalsocietypublishing.org/content/early/2012/01/31/rspb.2011.2441

__________________________________
Laura

Deinonychus

http://www.plosone.org/article/info:doi/10.1371/journal.pone.0028964

The Predatory Ecology of Deinonychus and the Origin of Flapping in Birds

Denver W. Fowler, Elizabeth A. Freedman, John B. Scannella, Robert E. Kambic

Abstract
Most non-avian theropod dinosaurs are characterized by fearsome serrated teeth and sharp recurved claws. Interpretation of theropod predatory ecology is typically based on functional morphological analysis of these and other physical features. The notorious hypertrophied ‘killing claw’ on pedal digit (D) II of the maniraptoran theropod Deinonychus (Paraves: Dromaeosauridae) is hypothesized to have been a predatory adaptation for slashing or climbing, leading to the suggestion that Deinonychus and other dromaeosaurids were cursorial predators specialized for actively attacking and killing prey several times larger than themselves. However, this hypothesis is problematic as extant animals that possess similarly hypertrophied claws do not use them to slash or climb up prey. Here we offer an alternative interpretation: that the hypertrophied D-II claw of dromaeosaurids was functionally analogous to the enlarged talon also found on D-II of extant Accipitridae (hawks and eagles; one family of the birds commonly known as “raptors”). Here, the talon is used to maintain grip on prey of subequal body size to the predator, while the victim is pinned down by the body weight of the raptor and dismembered by the beak. The foot of Deinonychus exhibits morphology consistent with a grasping function, supportive of the prey immobilisation behavior model. Opposite morphological trends within Deinonychosauria (Dromaeosauridae + Troodontidae) are indicative of ecological separation. Placed in context of avian evolution, the grasping foot of Deinonychus and other terrestrial predatory paravians is hypothesized to have been an exaptation for the grasping foot of arboreal perching birds. Here we also describe “stability flapping”, a novel behaviour executed for positioning and stability during the initial stages of prey immobilisation, which may have been pivotal to the evolution of the flapping stroke. These findings overhaul our perception of predatory dinosaurs and highlight the role of exaptation in the evolution of novel structures and behaviours.

– Jacqueline

Microraptor

http://www.pnas.org/content/108/49/19662.abstract?etoc

Additional specimen of Microraptor provides unique evidence of dinosaurs preying on birds

Jingmai O’Connor, Zhonghe Zhou, and Xing Xu

Abstract

Preserved indicators of diet are extremely rare in the fossil record; even more so is unequivocal direct evidence for predator–prey relationships. Here, we report on a unique specimen of the small nonavian theropod Microraptor gui from the Early Cretaceous Jehol biota, China, which has the remains of an adult enantiornithine bird preserved in its abdomen, most likely not scavenged, but captured and consumed by the dinosaur. We provide direct evidence for the dietary preferences of Microraptor and a nonavian dinosaur feeding on a bird. Further, because Jehol enantiornithines were distinctly arboreal, in contrast to their cursorial ornithurine counterparts, this fossil suggests that Microraptor hunted in trees thereby supporting inferences that this taxon was also an arborealist, and provides further support for the arboreality of basal dromaeosaurids.

– Jacqueline

Dinosaur biomechanics – Power-walking tyrannosaurs

Nice!
–Mikko

An online article on the Nature site and the abstract from the SVP,
challenging Alexander’s calculations for theropod locomotion:

Tyrannosaurs were power-walkers
http://www.nature.com/news/2011/111107/full/news.2011.631.html

MALLISON, Heinrich, Museum fr Naturkunde – Leibniz Institute for Research
on Evolution and Biodiversity at the Humboldt University Berlin, Berlin,
Germany

FAST MOVING DINOSAURS: WHY OUR BASIC TENET IS WRONG

Locomotion speeds of dinosaurs are often calculated from ichnofossils, using Alexander’s  formula that is based on data mainly from mammals and birds. Results indicate that dinosaurs were rather slow compared to mammals. Inaccuracies due to errors in hip height  estimates and other factors are expected, but the method is generally accepted to deliver at least “ballpark figures”. However, in nearly all dinosaurs except theropods

the hind limbs differ significantly from both mammals and birds in the distribution of maximal joint torques possible. Is it biomechanically sound to apply the formula under these circumstances? A detailed assessment of dinosaur limbs, using musculoskeletal modeling in SIMM and Computer Aided Engineering (CAE) kinetic/dynamic modeling, taking gravity, mass distribution and inertia into account, indicates that a basic tenet of Alexander’s formula, the proportional relationship between stride length (SL) and stride frequency (SF) seen in mammals and birds, is unlikely to have existed in non-theropod dinosaurs, and may have had an unusually low slope in theropods. This means that speeds calculated from tracks are the slowest speeds at which the animals have moved, but may be significantly too low. We may therefore not expect to gain information on the top speeds of dinosaurs from tracks at all. Skeleton-based analyses can suffer from similar uncertainties, because large limb excursion angles as seen in quickly moving mammals create high forces in the limbs. Usually, similar limb kinematics are assumed for dinosaurs. However, if dinosaurs combined high SFs with short SLs, they were able to move far faster for given maximal forces in the joints than previous models suggest. The modeling results from SIMM and CAE suggest that dinosaurs used much higher SF/SL ratios than mammals, achieving absolute speeds in walking gaits that force same-size mammals into running gaits.

Stop the Press!! – A Pterosaur with an Egg 

http://www.sciencemag.org/content/331/6015/321.full

Junchang Lü, David M. Unwin, D. Charles Deeming, Xingsheng Jin, Yongqing Liu
and Qiang Ji

An Egg-Adult Association, Gender, and Reproduction in Pterosaurs

Science 21 January 2011:
Vol. 331 no. 6015 pp. 321-324
DOI: 10.1126/science.1197323

Abstract:

A sexually mature individual of Darwinopterus preserved together with an egg
from the Jurassic of China provides direct evidence of gender in pterosaurs
and insights into the reproductive biology of these extinct fliers. This new
find and several other examples of Darwinopterus demonstrate that males of
this pterosaur had a relatively small pelvis and a large cranial crest,
whereas females had a relatively large pelvis and no crest. The ratio of egg
mass to adult mass is relatively low, as in extant reptiles, and is
comparable to values for squamates. A parchment-like eggshell points to
burial and significant uptake of water after oviposition. This evidence for
low parental investment contradicts the widespread assumption that
reproduction in pterosaurs was like that of birds and shows that it was
essentially like that of reptiles.

--Mikko

News-flash: A new basal theropod from the Valley of the Moon 

Hi,

review: http://www.sciencemag.org/content/331/6014/134.full

article: http://www.sciencemag.org/content/331/6014/206.full

Ricardo N. Martinez, Paul C. Sereno, Oscar A. Alcober, Carina E. Colombi,
Paul R. Renne, Isabel P. Montañez and Brian S. Currie:
A Basal Dinosaur from the Dawn of the Dinosaur Era in Southwestern Pangaea.

Science 14 January 2011:
Vol. 331 no. 6014 pp. 206-210
DOI: 10.1126/science.1198467

--Mikko