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Agnolin, F.L., and Martinelli, A.G. 2008. Fossil birds from the Late
Cretaceous Los Alamitos Formation, Río Negro Province, Argentina. Journal of
South American Earth Sciences. doi: 10.1016/j.jsames.2008.09.003.
ABSTRACT: In this note we report new avian remains from the Late Cretaceous
Los Alamitos Formation (Campanian-Maastrichtian) at the Los Alamitos
locality, Río Negro province, Argentina. Isolated remains referable to
indeterminate Aves, ?Patagopterygiformes, indeterminate Ornithurae, cf.
Hesperornithes and cf. Neornithes are described and discussed. The new genus
and species Alamitornis minutus is erected to include a minute-sized and
gracile bird, probably related to the non-volant ratite-like bird
Patagopteryx. If correctly identified, the record of Hesperornithes may be
the first for this group in the Southern Hemisphere. The Los Alamitos
paleoavifauna represents one of the most diverse fossil bird assemblage from
the Mesozoic of Gondwana known to date.
Brusatte, S.L., Benton, M.J., Ruta, M., and Lloyd, G.T. 2008. The first 50
Myr of dinosaur evolution: macroevolutionary pattern and morphological
disparity. Biology Letters. doi: 10.1098/rsbl.2008.0441.
ABSTRACT: The evolutionary radiation of dinosaurs in the Late Triassic and
Early Jurassic was a pivotal event in the Earth's history but is poorly
understood, as previous studies have focused on vague driving mechanisms and
have not untangled different macroevolutionary components (origination,
diversity, abundance and disparity). We calculate the morphological
disparity (morphospace occupation) of dinosaurs throughout the Late Triassic
and Early Jurassic and present new measures of taxonomic diversity.
Crurotarsan archosaurs, the primary dinosaur ?competitors?, were
significantly more disparate than dinosaurs throughout the Triassic, but
underwent a devastating extinction at the Triassic?Jurassic boundary.
However, dinosaur disparity showed only a slight non-significant increase
after this event, arguing against the hypothesis of ecological
release-driven morphospace expansion in the Early Jurassic. Instead, the
main jump in dinosaur disparity occurred between the Carnian and Norian
stages of the Triassic. Conversely, dinosaur diversity shows a steady
increase over this time, and measures of diversification and faunal
abundance indicate that the Early Jurassic was a key episode in dinosaur
evolution. Thus, different aspects of the dinosaur radiation (diversity,
disparity and abundance) were decoupled, and the overall macroevolutionary
pattern of the first 50Myr of dinosaur evolution is more complex than often
Fitzpatrick, B.M., Fordyce, J.A., and Gavrilets, S. 2008. What, if anything,
is sympatric speciation? Journal of Evolutionary Biology. doi:
ABSTRACT: Sympatric speciation has always fascinated evolutionary
biologists, and for good reason; it pits diversifying selection directly
against the tendency of sexual reproduction to homogenize populations.
However, different investigators have used different definitions of
sympatric speciation and different criteria for diagnosing cases of
sympatric speciation. Here, we explore some of the definitions that have
been used in empirical and theoretical studies. Definitions based on
biogeography do not always produce the same conclusions as definitions based
on population genetics. The most precise definitions make sympatric
speciation an infinitesimal end point of a continuum. Because it is
virtually impossible to demonstrate the occurrence of such a theoretical
extreme, we argue that testing whether a case fits a particular definition
is less informative than evaluating the biological processes affecting
divergence. We do not deny the importance of geographical context for
understanding divergence. Rather, we believe this context can be better
understood by modelling and measuring quantities, such as gene flow and
selection, rather than assigning cases to discrete categories like sympatric
and allopatric speciation.
Collin, R., and Miglietta, M.P. 2008. Reversing opinions on Dollo's Law.
Trends in Ecology and Evolution. doi: 10.1016/j.tree.2008.06.013.
ABSTRACT: Dollo?s Law, the idea that the loss of complex features in
evolution is irreversible, is a popular concept in evolutionary biology.
Here we review how application of recent phylogenetic methods, genomics and
evo-devo approaches is changing our view of Dollo?s Law and its underlying
mechanisms. Phylogenetic studies have recently demonstrated cases where
seemingly complex features such as digits and wings have been reacquired.
Meanwhile, large genomics databases and evo-devo studies are showing how the
underlying developmental pathways and genetic architecture can be retained
after the loss of a character. With dwindling evidence for the law-like
nature of Dollo?s Law, we anticipate a return to Dollo?s original focus on
irreversibility of all kinds of changes, not exclusively losses.
Jerry D. Harris
Director of Paleontology
Dixie State College
225 South 700 East
St. George, UT 84770 USA
Phone: (435) 652-7758
Fax: (435) 656-4022
"I have made this letter longer
than usual because I lack the
time to make it shorter."
-- Blaise Pascal