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Massetognathus ochagaviae (eucynodont) description + Permain Moradi Formation in Niger



Ben Creisler
bcreisler@gmail.com


New non-dino papers:





Ane Elise Branco Pavanatto, Rodrigo Temp Müller, Átila Augusto Stock
Da-Rosa & Sérgio Dias-da-Silva (2015)
New information on the postcranial skeleton of Massetognathus
ochagaviae Barberena, 1981 (Eucynodontia, Traversodontidae), from the
Middle Triassic of Southern Brazil.
Historical Biology (advance online publication)
DOI:10.1080/08912963.2015.1070148
http://www.tandfonline.com/doi/full/10.1080/08912963.2015.1070148#abstract

New postcranial remains of Massetognathus ochagaviae are described
based on a new specimen collected at the Dinodontosaurus Assemblage
Zone from the Middle Triassic of Southern Brazil. Several isolated
teeth collected together with the postcranial skeleton allowed a
taxonomic assignation of the specimen to M. ochagaviae. Its
postcranial morphology is quite similar to Massetognathus pascuali,
especially regarding the morphology of the transverse process of
presacral vertebrae (i.e. laminar in the anterior most and rounded in
the posterior most presacral vertebrae); humerus (i.e. the head is
dorsally deflected with a ‘fan-shaped’ distal end a deltopectoral
crest abruptly ending at the middle of shaft); and femur (with a
bulbous and dorsomedially inclined femoral head, lesser trochanter
which abruptly begins near the intertrochanteric fossa and extending
up to the middle of the femoral shaft and the medial condyle more
pronounced and ventrally projected than the lateral one). On the other
hand, the clavicle of M. ochagaviae is less lateromedially elongated
than in M. pascuali.

==


Roger M.H. Smith, Christian A. Sidor, Neil J. Tabor & J. Sébastien Steyer (2015)
Sedimentology and vertebrate taphonomy of the Moradi Formation of
northern Niger: A Permian wet desert in the tropics of Pangaea.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
doi:10.1016/j.palaeo.2015.08.032
http://www.sciencedirect.com/science/article/pii/S003101821500468X


Highlights

The Late Permian Moradi Formation of Niger accumulated in subtropical
central Pangaea
Monsoonal seasonality amplified by orographic rain-shadow promoted
species endemism in resident tetrapods
Fossils preserved in ephemeral distributaries, loessic plains and playa lakes.
Endpoint playa deposits preserve numerous tetrapod tracks of taxa that
have not been found as body fossils.
Pareaisaurian skeletons were commonly buried by wind-blown dust and sheetfloods
A much greater diversity of late Permian terrestrial life in
sub-equatorial Pangaea than previously thought

Abstract

Pangaean palaeogeographic models place the Tim Mersoi basin of
northern Niger in a 5000 km wide corridor between Gondwana and
Laurasia approximately 15 degrees south of the palaeoequator. Late
Permian palaeoclimate models position this basin between tropical
summerwet to the north and desert to the south. Recent investigations
of the fossil vertebrates and palaeosols in the late Permian
(Lopingian) Moradi Formation confirm that the climate was warm and
hyperarid with highly seasonal monsoonal rainfall. Possibly as a
result of these unusual “wet desert” conditions the tetrapod fauna
shows a high degree of endemism. This study tests existing
palaeoclimate models by providing additional data on sedimentary
environments and vertebrate taphonomic processes. The Moradi red bed
sequences accumulated in a gently subsiding sag basin to the west of
the tectonically active Massif de l'Aïr. Low angle gravelly alluvial
fans prograded westward from the massif and at times impinged on a
large stable northward flowing meandering channel system. The
interchannel mudrock sequences are over-thickened by the accumulation
of loessic silts and preserve isolated skull and post crania of
amphibians (Nigerpeton and Saharastega) as well as semi-articulated
captorhinids (Moradisaurus). Detailed surface mapping of a fossil-rich
exposure revealed an anastomosed network of loess-filled distributary
channels incised into the floodplain mudrocks. This provided a locus
for the accumulation and rapid burial of at least 15 associated
skeletons of the pareiasaurian Bunostegos. Semi-permanent ponds are
evidenced by patches of fissile red mudstone containing rare bivalves
and spiral coprolites. In the distal floodplains away from the main
river channels, the combination of a generally high groundwater table,
warm mean annual temperatures and deflation of fines from the
floodplain surface promoted the formation of gypsiferous palaeosols
and endpoint playa lakes. Carbonate-rich mud accumulated around the
lake margins and provided ideal conditions for the imprinting and
preservation of tetrapod trackways.