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New Miocene caimans Gnatusuchus, Kuttanacaiman + perching bird feet (free pdf)

Ben Creisler

New non-dino papers that may be of interest:

Rodolfo Salas-Gismondi, John J. Flynn, Patrice Baby, Julia V.
Tejada-Lara, Frank P. Wesselingh & Pierre-Olivier Antoine (2015)
A Miocene hyperdiverse crocodylian community reveals peculiar trophic
dynamics in proto-Amazonian mega-wetlands.
Proceedings of the Royal Society B: 2015 282 20142490 (advance publication)
DOI: 10.1098/rspb.2014.2490

Amazonia contains one of the world's richest biotas, but origins of
this diversity remain obscure. Onset of the Amazon River drainage at
approximately 10.5 Ma represented a major shift in Neotropical
ecosystems, and proto-Amazonian biotas just prior to this pivotal
episode are integral to understanding origins of Amazonian
biodiversity, yet vertebrate fossil evidence is extraordinarily rare.
Two new species-rich bonebeds from late Middle Miocene proto-Amazonian
deposits of northeastern Peru document the same hyperdiverse
assemblage of seven co-occurring crocodylian species. Besides the
large-bodied Purussaurus and Mourasuchus, all other crocodylians are
new taxa, including a stem caiman—Gnatusuchus pebasensis—bearing a
massive shovel-shaped mandible, procumbent anterior and globular
posterior teeth, and a mammal-like diastema. This unusual species is
an extreme exemplar of a radiation of small caimans with crushing
dentitions recording peculiar feeding strategies correlated with a
peak in proto-Amazonian molluscan diversity and abundance. These
faunas evolved within dysoxic marshes and swamps of the long-lived
Pebas Mega-Wetland System and declined with inception of the
transcontinental Amazon drainage, favouring diversification of
longirostrine crocodylians and more modern generalist-feeding caimans.
The rise and demise of distinctive, highly productive aquatic
ecosystems substantially influenced evolution of Amazonian
biodiversity hotspots of crocodylians and other organisms throughout
the Neogene.

News stories:





In open access:

Spencer B. Backus, Diego Sustaita, Lael U. Odhner & Aaron M. Dollar (2015)
Mechanical analysis of avian feet: multiarticular muscles in grasping
and perching.
Royal Society Open Science: 2015 2 140350;
DOI: 10.1098/rsos.140350

The grasping capability of birds' feet is a hallmark of their
evolution, but the mechanics of avian foot function are not well
understood. Two evolutionary trends that contribute to the mechanical
complexity of the avian foot are the variation in the relative lengths
of the phalanges and the subdivision and variation of the digital
flexor musculature observed among taxa. We modelled the grasping
behaviour of a simplified bird foot in response to the downward and
upward forces imparted by carrying and perching tasks, respectively.
Specifically, we compared the performance of various foot geometries
performing these tasks when actuated by distally inserted flexors
only, versus by both distally inserted and proximally inserted
flexors. Our analysis demonstrates that most species possess relative
phalanx lengths that are conducive to grasps actuated only by a single
distally inserted tendon per digit. Furthermore, proximally inserted
flexors are often required during perching, but the distally inserted
flexors are sufficient when grasping and carrying objects. These
results are reflected in differences in the relative development of
proximally and distally inserted digital flexor musculature among
‘perching’ and ‘grasping’ taxa. Thus, our results shed light on the
relative roles of variation in phalanx length and digit flexor muscle
distribution in an integrative, mechanical context.