Author Archives: LS

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

Let’s dry up a remnant ocean

http://www.nature.com/nature/journal/v480/n7377/full/nature10651.html

Garcia-Castellanos, D. & Villasenor, A., 2011: Messinian salinity crisis
regulated by competing tectonics and erosion at the Gibraltar arc.
–Nature: Vol. 480, #7377, pp. 359-363 [doi: 10.1038/nature10651]

The Messinian salinity crisis1, 2 (5.96 to 5.33 million years ago) was
caused by reduced water inflow from the Atlantic Ocean to the Mediterranean
Sea resulting in widespread salt precipitation and a decrease in
Mediterranean sea level of about 1.5 kilometres due to evaporation3. The
reduced connectivity between the Atlantic and the Mediterranean at the time
of the salinity crisis is thought to have resulted from tectonic uplift of
the Gibraltar arc seaway and global sea-level changes, both of which control
the inflow of water required to compensate for the hydrological deficit of
the Mediterranean1, 4. However, the different timescales on which tectonic
uplift and changes in sea level occur are difficult to reconcile with the
long duration of the shallow connection between the Mediterranean and the
Atlantic5 needed to explain the large amount of salt precipitated. Here we
use numerical modelling to show that seaway erosion caused by the Atlantic
inflow could sustain such a shallow connection between the Atlantic and the
Mediterranean by counteracting tectonic uplift. The erosion and uplift rates
required are consistent with previous mountain erosion studies, with the
present altitude of marine sediments in the Gibraltar arc6, 7 and with
geodynamic models suggesting a lithospheric slab tear underneath the
region8, 9, 10. The moderate Mediterranean sea-level drawdown during the
early stages of the Messinian salinity crisis3, 5 can be explained by an
uplift of a few millimetres per year counteracted by similar rates of
erosion due to Atlantic inflow. Our findings suggest that the competition
between uplift and erosion can result in harmonic coupling between erosion
and the Mediterranean sea level, providing an alternative mechanism for the
cyclicity observed in early salt precipitation deposits and calling into
question previous ideas regarding the timing of the events that occurred
during the Messinian salinity crisis1.

– Mikko

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

Stop the Press! – Energetics and the evolution of human brain size

http://www.nature.com/nature/journal/v480/n7375/full/nature10629.html

Energetics and the evolution of human brain size

Ana Navarrete
Carel P. van Schaik
Karin Isler

Journal name: Nature
Volume: 480
Pages: 91–93
Date published: 01 December 2011
DOI: 10.1038/nature10629

Abstract:

The human brain stands out among mammals by being unusually large. The
expensive-tissue hypothesis1 explains its evolution by proposing a trade-off
between the size of the brain and that of the digestive tract, which is
smaller than expected for a primate of our body size. Although this
hypothesis is widely accepted, empirical support so far has been equivocal.
Here we test it in a sample of 100 mammalian species, including 23 primates,
by analysing brain size and organ mass data. We found that, controlling for
fat-free body mass, brain size is not negatively correlated with the mass of
the digestive tract or any other expensive organ, thus refuting the
expensive-tissue hypothesis. Nonetheless, consistent with the existence of
energy trade-offs with brain size, we find that the size of brains and
adipose depots are negatively correlated in mammals, indicating that
encephalization and fat storage are compensatory strategies to buffer
against starvation. However, these two strategies can be combined if fat
storage does not unduly hamper locomotor efficiency. We propose that human
encephalization was made possible by a combination of stabilization of
energy inputs and a redirection of energy from locomotion, growth and
reproduction.

-Mikko

News Flash

This month’s Evolution & Development has several interesting articles (http://onlinelibrary.wiley.com/doi/10.1111/ede.2011.13.issue-6/issuetoc), in particular, an article on odontode evolution and another on digit development in pigs.

Teeth before jaws? Comparative analysis of the structure and development of the external and internal scales in the extinct jawless vertebrate Loganellia scotica
Martin Rücklin, Sam Giles, Philippe Janvier, Philip C. J. Donoghue
http://onlinelibrary.wiley.com/doi/10.1111/j.1525-142X.2011.00508.x/abstract

Developmental basis of mammalian digit reduction: a case study in pigs
Karen E. Sears, Allison K. Bormet, Alexander Rockwell, Lisa E. Powers, Lisa Noelle Cooper, Matthew B. Wheeler
http://onlinelibrary.wiley.com/doi/10.1111/j.1525-142X.2011.00509.x/abstract

Jackie

The End-Permian Mass extinction

http://www.sciencemag.org/content/early/2011/11/16/science.1213454

Shen, S.-z., Crowley, J. L., Wang, Y., Bowring, S. A., Erwin, D. H., Sadler, P. M., Cao, C.-q., Rothman, D. H., Henderson, C. M., Ramezani, J., Zhang, H., Shen, Y., Wang, X.-d., Wang, W., Mu, L., Li, W.-z., Tang, Y.-g., Liu, X.-l., Liu, L.-j., Zeng, Y., Jiang, Y.-f. & Jin, Y.-g., 2011: Calibrating the End-Permian Mass Extinction.
–ScienceExpress: [doi: 10.1126/science.1213454]

“The end-Permian mass extinction was the most severe biodiversity crisis in earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 Ma, following a decline of 2‰ in δ13C over 90,000 years, and coincided with a δ13C excursion of -5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years, and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.”

Have fun!

–Mikko

Derek D. Turner on “The Meaning of ‘Fossil’ and the Incompleteness of the Fossil Record”

Dear all,

Professor Derek D. Turner (Connecticut College)

will give a talk at the research seminar of the Helsinki Philosophy of Science Research Group on Monday 5 December on

“The Meaning of ‘Fossil’ and the Incompleteness of the Fossil Record”

Derek Turner is a philosopher of science who has specialized in evolutionary paleontology. He has studied philosophical questions on punctuated equilibrium, species selection, species sorting, large-scale directional changes in evolutionary history, and fossils and fossil record.

In the talk, he will explore some of the ways in which new techniques (for example, the study of chemofossils, molecular clocks, and ancient DNA) are changing the meaning of “fossil,” and thereby also forcing us to rethink the incompleteness of the historical record.

Turner has published two books on paleontology:
– Making Prehistory (2007, Cambridge University Press), and
– Paleontology: A Philosophical Introduction (2011, Cambridge University Press)

And articles on different aspects of paleontology, such as
–  (2009) “How much can we know about the causes of evolutionary trends.” Biology & Philosophy 24: 341- 357
– (2011) “Gould’s replay revisited” Biology & Philosophy 26: 65-79

Time: Monday 5 December, 12-14

Place: Unioninkatu 40 (“Forest House”), room A217 (A-wing, second floor)

Welcome!

———

Jani Raerinne, PhD
Department of Philosophy, History, Culture, and Art Studies
Univ. Helsinki