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Brasilitherium (Triassic cynodont) digital endocast + Shandongemys, turtle from Cretaceous of China



From: Ben Creisler
bcreisler@gmail.com



Two recent non-dino papers that may be of interest:


Pablo Gusmão Rodrigues, Irina Ruf & Cesar Leandro Schultz (2013)
Study of a digital cranial endocast of the non-mammaliaform cynodont
Brasilitherium riograndensis (Later Triassic, Brazil) and its
relevance to the evolution of the mammalian brain.
Paläontologische Zeitschrift (advance online publication)
DOI: 10.1007/s12542-013-0200-6
http://link.springer.com/article/10.1007/s12542-013-0200-6


A digital cranial endocast of the specimen UFRGS-PV-1043-T,
Brasilitherium riograndensis, was obtained from high-resolution
computed tomography (μCT) scan images. This taxon is a small cynodont
from the Late Triassic of Brazil, and has been used as the
sister-group of the mammaliaforms in cladistic analyses. The digital
endocast of UFRGS-PV-1043-T is mostly complete, allowing the
description and collection of accurate linear and volumetric
measurements, which were taken and compared with other
non-mammaliaform cynodonts. Impressions of vessels were observed in
the inner walls of the braincase. Despite the lack of a cribiform
plate and the presence of a wide orbital vacuity, the endocast of
Brasilitherium shows olfactory bulb casts that are relatively larger
than in other non-mammaliaform cynodonts, suggesting a pattern of
gradual increase in size and improvement of the olfactory sense for
these structures toward the mammalian condition. The cerebral
hemispheres are elongated and clearly divided by a median sulcus. The
parafloccular casts are well defined, and their position corresponds
to the maximum width of the endocast. In the ventral view, a large
hypophyseal cast and a wide opening for the cavum epiptericum are
evident. The encephalization quotient (EQ) calculated for
Brasilitherium is greater than the range of EQs reported for most
non-mammaliaform cynodonts (although it may be similar to that of some
taxa, according to the equation used to estimate their body masses),
but it is smaller than that of the mammaliaforms and mammals. A
slighter increase in the brain size of Brasilitherium compared with
other non-mammaliaform cynodonts was observed, along with a more
significant increase in the size of the olfactory bulbs. This study
supports the proposition of an early evolution of the mammalian brain
associated with selective pressures for better sensorial acuity,
especially regarding improved olfaction, which began with small
Triassic mammaliamorphs.

Note an earlier article:
http://dml.cmnh.org/2013Jan/msg00183.html

=====

Lu Li, Haiyan Tong, Kebai Wang, Shuqing Chen & Xing Xu (2013)
Lindholmemydid turtles (Cryptodira: Testudinoidea) from the Late
Cretaceous of Shandong Province, China.
Annales de Paléontologie (advance online publication)
http://dx.doi.org/10.1016/j.annpal.2013.07.003
http://www.sciencedirect.com/science/article/pii/S0753396913000426


A new genus and new species of lindholmemydid turtle (Cryptodira:
Testudinoidea), Shandongemys dongwuica n. g. and n. sp. are described
on the basis of a partial skeleton with incomplete shell and skull,
complete lower jaws and disarticulated limb bones from the Upper
Cretaceous Wangshi Group of Zhucheng, Shandong Province, China. Among
Lindholmemydidae, the new species is closely related to Mongolemys
elegans from the Late Cretaceous of Mongolia. An incomplete shell from
the same locality is referred as Lindholmemydidae indet. Glyptops sp.
from the Upper Cretaceous Wang Group of Jingangkou, Laiyang, Shandong
is revised and assigned to Lindholmemydidae.