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Earliest dinosaur (Late Triassic ) taxonomic diversity and palaeobiogeography (free pdf)



From: Ben Creisler
bcreisler@gmail.com


A recent paper not yet mentioned on the DML--this was mentioned on
Green Tea and Velociraptors blog. The pdf is open access:

Martín D. Ezcurra (2012)
Comments on the taxonomic diversity and palaeobiogeography of the
earliest known dinosaur assemblages (Late Carnian-Earliest Norian)).
Historia Natural 2(1), 49-71
ISSN (impreso) 0326-1778 / ISSN (on-line) 1853-6581
http://www.fundacionazara.org.ar/Publicaciones/HN3/HN3_303.pdf

The beginning of dinosaur evolution is currently known based on a
handful of upper Carnian–lowermost Norian (232–225 Mya) localities
situated in a paleolatitudinal belt of approximately 40–50° S in
Argentina, Brazil, Zimbabwe and India. The taxonomic diversity of the
oldest known dinosaurbearing assemblages, included within the
Hyperodapedon Assemblage Zone, is reviewed here. The Brazilian
“Teyuwasu barberenarai” is reinterpreted as a nomen dubium
representing an indeterminate dinosauriform, the record of cf.
Saturnalia from Zimbabwe is considered a basal saurischian and only
one of the Indian specimens described by Huene can be unambiguously
assigned to Dinosauria. The highest early dinosaur species richness
sampled is concentrated in southwestern Pangean assemblages (Argentina
and Brazil), with 10 to 11 different described species. By contrast,
only one or two species can be currently recognized from the
approximately coeval beds of south–central Pangea (Zimbabwe and
India), which are much less well sampled. The oldest known dinosaur
assemblages appear to have been mostly restricted to subtropical to
cool temperate arid areas based on recent paleoclimatological
reconstructions. This observation agrees with the hypothesis that the
absence of dinosaurs in the upper levels of the Ischigualasto
Formation of Argentina is related to an increase in humidity in the
basin. Accordingly, climatic factors, with humidity as probably the
most important, may have controlled the paleobiogeographic
distribution of the oldest known dinosaur assemblages. The achievement
of a worldwide dinosaur distribution during the latest Triassic may
have occurred after a global climate change, such as the end of the
“Carnian Pluvial Event”, and/or the invasion of more tropical humid
climates by dinosaurs.


===

Also another earlier paper in Historia Natural that was not mentioned
on the DML:

Federico A. Gianechini, Gabriel Lio, and Sebastián Apesteguía (2012)
Isolated archosaurian teeth from “La Bonita” locality (Late
Cretaceous, Santonian-Campanian), Río Negro Province, Argentina.
Historia Natural 2(1): 5-16
ISSN (impreso) 0326-1778 / ISSN (on-line) 1853-6581
http://www.fundacionazara.org.ar/Publicaciones/HN3/HN3_101.pdf

The tetrapod assemblage of the Bajo de la Carpa Formation (Late
Cretaceous; Santonianearly Campanian) is dominated by archosaurs,
represented by saurischians, such as alvarezsaurid, enanthiornithine,
and abelisauroid theropods (e.g. Velocisaurus unicus Bonaparte, 1991)
and titanosaurs (e.g. Bonitasaura salgadoi Apesteguía, 2004), as well
as crocodyliform remains which are the most abundant specimens (e.g.
Notosuchus terrestris Woodward, 1896). Here we report new archosaur
remains from the Bajo de la Carpa Formation at the ‘La Bonita’
locality, consisting of isolated shed teeth. Two of these specimens
present a crown with a straight distal border and denticles with shape
and density similar to that observed in abelisaurid theropods. A third
tooth is more distally curved, without mesial denticles, and with a
figure eight-shaped basal cross-section, resembling the dental
features described for the basal tetanuran Orkoraptor burkei Novas,
Ezcurra and Lecuona, 2008, but differing from this theropod due to the
presence of parallel transversal wrinkles throughout the labial and
lingual surfaces of the crown. A fourth specimen is considered as
belonging to a neosuchian tooth, because it has a circular
cross-section, lack of labiolingual compression, and a serrated
carina. Although represented by isolated shed teeth, these findings
allow increasing the knowledge of the Cretaceous fauna of the Bajo de
la Carpa Formation.