Author Archives: LS

Dinosaur biomechanics – Power-walking tyrannosaurs

Nice!
–Mikko

An online article on the Nature site and the abstract from the SVP,
challenging Alexander’s calculations for theropod locomotion:

Tyrannosaurs were power-walkers
http://www.nature.com/news/2011/111107/full/news.2011.631.html

MALLISON, Heinrich, Museum fr Naturkunde – Leibniz Institute for Research
on Evolution and Biodiversity at the Humboldt University Berlin, Berlin,
Germany

FAST MOVING DINOSAURS: WHY OUR BASIC TENET IS WRONG

Locomotion speeds of dinosaurs are often calculated from ichnofossils, using Alexander’s  formula that is based on data mainly from mammals and birds. Results indicate that dinosaurs were rather slow compared to mammals. Inaccuracies due to errors in hip height  estimates and other factors are expected, but the method is generally accepted to deliver at least “ballpark figures”. However, in nearly all dinosaurs except theropods

the hind limbs differ significantly from both mammals and birds in the distribution of maximal joint torques possible. Is it biomechanically sound to apply the formula under these circumstances? A detailed assessment of dinosaur limbs, using musculoskeletal modeling in SIMM and Computer Aided Engineering (CAE) kinetic/dynamic modeling, taking gravity, mass distribution and inertia into account, indicates that a basic tenet of Alexander’s formula, the proportional relationship between stride length (SL) and stride frequency (SF) seen in mammals and birds, is unlikely to have existed in non-theropod dinosaurs, and may have had an unusually low slope in theropods. This means that speeds calculated from tracks are the slowest speeds at which the animals have moved, but may be significantly too low. We may therefore not expect to gain information on the top speeds of dinosaurs from tracks at all. Skeleton-based analyses can suffer from similar uncertainties, because large limb excursion angles as seen in quickly moving mammals create high forces in the limbs. Usually, similar limb kinematics are assumed for dinosaurs. However, if dinosaurs combined high SFs with short SLs, they were able to move far faster for given maximal forces in the joints than previous models suggest. The modeling results from SIMM and CAE suggest that dinosaurs used much higher SF/SL ratios than mammals, achieving absolute speeds in walking gaits that force same-size mammals into running gaits.

A new Mesozoic mammal from South America

All,

Say hello to _Cronopio dentiacutus_

Rougier, G. W., Apesteguia, S. & Gaetano, L. C., 2011: Highly specialized
mammalian skulls from the Late Cretaceous of South America.
–Nature: Vol. 479, #7371, pp. 98-102 [doi: 10.1038/nature10591]

http://www.nature.com/nature/journal/v479/n7371/abs/nature10591.html
http://www.nature.com/nature/journal/v479/n7371/abs/nature10591.html#supplem
entary-information

Abstract:
“Dryolestoids are an extinct mammalian group belonging to the
lineage leading to modern marsupials and placentals1,2. Dryolestoids
are known by teeth and jaws from the Jurassic period of North
America and Europe2,3, but they thrived in South America up to the
end of the Mesozoic era and survived to the beginnings of the
Cenozoic2,4–7. Isolated teeth and jaws from the latest Cretaceous of
South America provide mounting evidence that, at least in western
Gondwana, dryolestoids developed into strongly endemic groups by
the Late Cretaceous4–9. However, the lack of pre-Late Cretaceous
dryolestoid remains made study of their origin and early diversification
intractable. Here we describe the first mammalian remains
from the early Late Cretaceous of South America, including two
partial skulls and jaws of a derived dryolestoid showing dental
and cranial features unknown among any other group of
Mesozoic mammals, such as single-rooted molars preceded by
double-rooted premolars, combined with a very long muzzle,
exceedingly long canines and evidence of highly specialized
masticatory musculature. On one hand, the new mammal shares
derived features of dryolestoids1–3 with forms from the Jurassic of
Laurasia, whereas on the other hand, it is very specialized and
highlights the endemic, diverse dryolestoid fauna from the
Cretaceous of South America. Our specimens include only the
second mammalian skull known for the Cretaceous of Gondwana,
bridging a previous 60-million-year gap in the fossil record, and
document the whole cranial morphology of a dryolestoid, revealing
an unsuspected morphological and ecological diversity for nontribosphenic
mammals.”

–Mikko

Hagfish as predators

Bloody hell!!

http://www.nature.com/srep/2011/111027/srep00131/full/srep00131.html

Zintzen, V., Roberts, C. D., Anderson, M. J., Stewart, A. L., Struthers, C.
D. & Harvey, E. S., 2011:
Hagfish predatory behaviour and slime defence mechanism.
–Nature Scientific Reports: Vol. 1, #131, [doi: 10.1038/srep00131]

Received
24 August 2011
Accepted
12 October 2011
Published
27 October 2011

Abstract:
“Hagfishes (Myxinidae), a family of jawless marine pre-vertebrates, hold a
unique evolutionary position, sharing a joint ancestor with the entire
vertebrate lineage. They are thought to fulfil primarily the ecological
niche of scavengers in the deep ocean. However, we present new footage from
baited video cameras that captured images of hagfishes actively preying on
other fish. Video images also revealed that hagfishes are able to choke
their would-be predators with gill-clogging slime. This is the first time
that predatory behaviour has been witnessed in this family, and also
demonstrates the instantaneous effectiveness of hagfish slime to deter fish
predators. These observations suggest that the functional adaptations and
ecological role of hagfishes, past and present, might be far more diverse
than previously assumed. We propose that the enduring success of this oldest
extant family of fishes over 300 million years could largely be due to their
unique combination of functional traits.”

One just started to wonder about conodonts…

Cheers!

–Mikko

Ancestral woolly rhino

Dear Kurtenians,

You may wish to explore:

http://www.sciencemag.org/content/333/6047/1285.abstract

Science 2 September 2011:
Vol. 333 no. 6047 pp. 1285-1288
DOI: 10.1126/science.1206594

REPORT

Out of Tibet: Pliocene Woolly Rhino Suggests High-Plateau Origin of Ice Age Megaherbivores

Tao Deng, Xiaoming Wang, Mikael Fortelius, Qiang Li, Yang Wang, Zhijie J. Tseng, Gary T. Takeuchi, Joel E. Saylor, Laura K. Säilä, Guangpu Xie

Regards,

Mikael

Juramaia, Jurassic eutherian from China

This message was seen in DINOSAUR mailing list… Of all things…

–Mikko

—–Original Message—–

A Mesozoic mammal of interest:

Zhe-Xi Luo, Chong-Xi Yuan, Qing-Jin Meng & Qiang Ji (2011)
Jurassic eutherian mammal and divergence of marsupials and placentals.
Nature 476: 442-445
doi:10.1038/nature10291
http://www.nature.com/nature/journal/v476/n7361/full/nature10291.html

Placentals are the most abundant mammals that have
diversified into every niche for vertebrates and
dominated the world’s terrestrial biotas in the Cenozoic.
A critical event in mammalian history is the divergence
of eutherians, the clade inclusive of all living
placentals, from the metatherian-marsupial clade. Here we
report the discovery of a new eutherian of 160 Myr from
the Jurassic of China, which extends the first appearance
of the eutherian-placental clade by about 35 Myr from the
previous record, reducing and resolving a discrepancy
between the previous fossil record and the molecular
estimate for the placental-marsupial divergence. This
mammal has scansorial forelimb features, and provides the
ancestral condition for dental and other anatomical
features of eutherians.

News Stories:
http://www.carnegiemnh.org/press/11-jul-sep/082511fossil.htm
http://www.eurekalert.org/pub_releases/2011-08/cmon-doa081911.php
http://www.pittsburghlive.com/x/pittsburghtrib/news/pittsburgh/s_753170.html

Diversity of hypsodont teeth in mammalian dentitions

Just in case somebody finds this interesting… 🙂

http://www.schweizerbart.de/papers/pala/detail/294/76206

Diversity of hypsodont teeth in mammalian dentitions – construction and
classification

von Koenigswald, Wighart

Palaeontographica Abteilung A Band 294 Lieferung 1-3 (2011)
p. 63-94, published: 8/22/2011
9 figures 3 tables

Abstract

“Hypsodonty, as used here, describes a specific type of tooth with the crown
elongated parallel to the growing axis, a condition which can occur in any
tooth position. Hypsodonty is interpreted as the elongation of specific
ontogenetic phases during tooth development at the cost of all others in a
heterochronic mode. Three parameters are used for differentiation: the
specific elongated ontogenetic phase or phases; the degree of hypsodonty
(increasing hypsodont and euhypsodont); and the kind of abrasion (balanced
wear by an antagonist or free growth). The first parameter is regarded as
the most important one. Although the separation of the four ontogenetic
phases (I – cusps, II – sidewalls, III – dentine surface, and IV –
differentiated roots) is artificial, it allows characterization of the great
diversity of hypsodont teeth in six categories: 1) multicusped hypsodonty
(extended phase I); 2) unicuspid hypsodonty (confluent phases I+II); 3)
sidewall hypsodonty (extended phase II); 4) enamel band hypsodonty (phases
II+III synchronous); 5) partial hypsodonty (phases II+III+IV synchronous);
and 6) dentine hypsodonty (phase III dominant). A synopsis with previously
defined types of hypsodonty is given. The new classification is
comprehensive, opens the view to the construction of hypsodont teeth, and
allows a comparison under evolutionary aspects.”

Too bad that we don’t have rights to download it…

–Mikko

Columbian mammoth interbreeding with woolly mammoth

Complete Columbian mammoth mitogenome suggests interbreeding with woolly mammoths

Jacob Enk*, Alison Devault, Regis Debruyne, Christine E King, Todd Treangen, Dennis O’Rourke, Steven L Salzberg,Daniel Fisher, Ross MacPhee and Hendrik Poinar*

Late Pleistocene North America hosted at least two divergent and ecologically distinct species of mammoth: the periglacial woolly mammoth (Mammuthus primigenius) and the subglacial Columbian mammoth (Mammuthus columbi). To date, mammoth genetic research has been entirely restricted to woolly mammoths, rendering their genetic evolution difficult to contextualize within broader Pleistocene paleoecology and biogeography. Here, we take an interspecific approach to clarifying mammoth phylogeny by targeting Columbian mammoth remains for mitogenomic sequencing. We sequenced the first complete mitochondrial genome of a classic Columbian mammoth, as well as the first complete mitochondrial genome of a North American woolly mammoth. Somewhat contrary to conventional paleontological models, which posit that the two species were highly divergent, the M. columbi mitogenome we obtained falls securely within a subclade of endemic North American M. primigenius. Though limited, our data suggest that the two species interbred at some point in their evolutionary histories. One potential explanation is that woolly mammoth haplotypes entered Columbian mammoth populations via introgression at subglacial ecotones, a scenario with compelling parallels in extant elephants and consistent with certain regional paleontological observations. This highlights the need for multi-genomic data to sufficiently characterize mammoth evolutionary history. Our results demonstrate that the use of next-generation sequencing technologies holds promise in obtaining such data, even from non-cave, non-permafrost Pleistocene depositional contexts.

Genome Biology 2011, 12:R51 doi:10.1186/gb-2011-12-5-r51
http://genomebiology.com/2011/12/5/R51/abstract

____________________________________
Laura

Fossil Evidence on Origin of the Mammalian Brain

Timothy B. Rowe, Thomas E. Macrini, Zhe-Xi Luo

ABSTRACT

Many hypotheses have been postulated regarding the early evolution of the mammalian brain. Here, x-ray tomography of the Early Jurassic mammaliaforms Morganucodon and Hadrocodium sheds light on this history. We found that relative brain size expanded to mammalian levels, with enlarged olfactory bulbs, neocortex, olfactory (pyriform) cortex, and cerebellum, in two evolutionary pulses. The initial pulse was probably driven by increased resolution in olfaction and improvements in tactile sensitivity (from body hair) and neuromuscular coordination. A second pulse of olfactory enhancement then enlarged the brain to mammalian levels. The origin of crown Mammalia saw a third pulse of olfactory enhancement, with ossified ethmoid turbinals supporting an expansive olfactory epithelium in the nasal cavity, allowing full expression of a huge odorant receptor genome.

Science 20 May 2011: Vol. 332 no. 6032 pp. 955-957 DOI: 10.1126/science.1203117

http://www.sciencemag.org/content/332/6032/955.full

http://beta.news.yahoo.com/ancient-furry-mammals-had-big-brains-smell-191357916.html
__________________________________
Laura