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Dromaeosaurid material from Bayan Gobi Formation, China + dinosaur tails + dinosaur numbers

Ben Creisler

A number of recent papers in preprint form:

Michael Pittman, Rui Pei & Xing Xu  (2015)
The first dromaeosaurid (Dinosauria: Theropoda) from the Early
Cretaceous Bayan Gobi Formation of Nei Mongol, China.
PeerJ PrePrints 3:e1654
doi: https://dx.doi.org/10.7287/peerj.preprints.1340v1

The first dromaeosaurid theropod from the Early Cretaceous Bayan Gobi
Formation is identified based on an incompletely preserved
partially-articulated left leg, increasing the known diversity of its
understudied ecosystem. The leg belongs to specimen IVPP V22530 and
includes a typical deinonychosaurian pedal phalanx II-2 with a
distinct constriction between the enlarged proximal end and the distal
condyle as well as a typical deinonychosaurian enlarged pedal phalanx
II-3. It possesses a symmetric metatarsus and a slender and long MT V
that together suggest it is a dromaeosaurid. Two anatomical traits
suggest the leg is microraptorine-like, but a more precise taxonomic
referral was not possible: metatarsals II, III and IV are closely
appressed distally and the ventral margin of the medial ligament pit
of phalanx II-2 is close to the centre of the rounded distal condyle.
This taxonomic status invites future efforts to discover additional
specimens at the study locality because - whether it is a
microraptorine or a close relative - this animal is expected to make
important contributions to our understanding of dromaeosaurid
evolution and biology. IVPP V22530 also comprises of an isolated
manual ungual, a proximal portion of a right dorsal rib and an
indeterminate bone mass that includes a collection of ribs. However,
these specimens cannot be confidently referred to Dromaeosauridae,
although they may very well belong to the same individual from whom
the left leg belongs.


Heinrich Mallison, Michael Pittman & Daniela Schwarz (2015)
Using crocodilian tails as models for dinosaur tails.
PeerJ PrePrints 3:e1653
doi:  https://dx.doi.org/10.7287/peerj.preprints.1339v1

The tails of extant crocodilians are anatomically the closest
approximation of the tails of non-avian dinosaurs, and therefore a
good starting point for any reconstruction of non-avian dinosaur tail
muscles. However, we here demonstrate some methodological problems
using crocodile tails, firstly regarding the general reconstruction of
tail mobility from osteology, secondly for the reconstruction of tail
musculature for the quantification of muscle forces, especially the m.
caudofemoralis longus, and thirdly with respect to the anatomical
differences between crocodilians and non-avian dinosaurs, especially
in relation to the reconstruction of m. caudofemoralis brevis. Our
results show that, given the current limited knowledge of crocodilian
tails, volumetric reconstructions should be created on the basis of
more gross morphological data than is usually used, and that
biomechanical studies should include sensitivity analysis with greater
parameter ranges than often applied.


Jostein Starrfelt & Lee Hsiang Liow (2015)
How many dinosaurs were there? True richness estimated using a Poisson
sampling model (TRiPS).
bioRxiv (advance online publication)
doi: http://dx.doi.org/10.1101/025940

The fossil record is a rich source of information about biological
diversity in the past. However, the fossil  record is not only
incomplete but has inherent biases due to geological, physical,
chemical and biological factors such that not all individuals or
species are equally likely to be discovered at any point in time or
space. In order to use the fossil record to reconstruct temporal
dynamics of diversity, biased sampling must be explicitly taken into
account. Here, we introduce an approach that utilizes the variation in
the number of times each species is observed in the fossil record to
estimate both sampling bias and true richness. We term our technique
TRiPS (True Richness estimated using a Poisson Sampling model) and
explore its robustness to violation of its assumptions via simulations
before applying it to an empirical dataset. We then venture to
estimate sampling bias and absolute species richness of dinosaurs in
the geological stages of the Mesozoic. Using TRiPS, we present new
estimates of species richness trajectories of the three major dinosaur
clades; the sauropods, ornithischians and theropods, casting doubt on
the Jurassic-Cretaceous extinction event and demonstrating that all
dinosaur groups are subject to  considerable sampling bias throughout
the Mesozoic.