gmane.science.dinosaurs.general

Kinematics of the Avian Wing and Shoulder during Ascending Flapping Flight and Uphill Flap-Running

Tim Williams — 2013-05-20T03:58:08

David B. Baier. Stephen M. Gatesy, Kenneth P. Dial (2013)
Three-Dimensional, High-Resolution Skeletal Kinematics of the Avian
Wing and Shoulder during Ascending Flapping Flight and Uphill
Flap-Running.  PLOS ONE 8: e63982

Abstract:

"Past studies have shown that birds use their wings not only for
flight, but also when ascending steep inclines.
Uphill flaprunning or wing-assisted incline running (WAIR) is used by
both flight-incapable fledglings and flight-capable
adults to retreat to an elevated refuge. Despite the broadly varying
direction of travel during WAIR, level, and descending
flight, recent studies have found that the basic wing path remains
relatively invariant with reference to gravity. If so, joints
undergo disparate motions to maintain a consistent wing path during
those specific flapping modes. The underlying
skeletal motions, however, are masked by feathers and skin. To improve
our understanding of the form-functional
relationship of the skeletal apparatus and joint morphology with a
corresponding locomotor behavior, we used XROMM (Xray
Reconstruction of Moving Morphology) to quantify 3-D skeletal
kinematics in chukars (_Alectoris chukar_) during WAIR
(ascending with legs and wings) and ascending flight (AF, ascending
with wings only) along comparable trajectories.
Evidence here from the wing joints demonstrates that the glenohumeral
joint controls the vast majority of wing
movements. More distal joints are primarily involved in modifying wing
shape. All bones are in relatively similar orientations
at the top of upstroke during both behaviors, but then diverge through
downstroke. Total excursion of the wing is much
smaller during WAIR and the tip of the manus follows a more vertical
path. The WAIR stroke appears ‘‘truncated’’ relative to
ascending flight, primarily stemming from ca. 50% reduction in humeral
depression. Additionally, the elbow and wrist
exhibit reduced ranges of angular excursions during WAIR. The
glenohumeral joint moves in a pattern congruent with
being constrained by the acrocoracohumeral ligament. Finally, we found
pronounced lateral bending of the furcula during
the wingbeat cycle during ascending flight only, though the phasic
pattern in chukars is opposite of that observed in
starlings (_Sturnus vulgaris_)."


Because it's a PLoS One paper, the main text is highly explanatory,
and the paper is replete with great figures.  These PLoS papers are a
joy to read.


One revelation is that uphill flap-running or WAIR (wing-assisted
incline running) requires extensive motion at the glenohumeral joint,
comparable to ascending flight. Although not directly addressed in
this particular study, WAIR has been proposed as an incipient flight
behavior in the ancestors of birds; this hypothesis has been advanced
in a number of publications (including in some especially high-impact
journals).  However, given the limited range of humeral elevation
inferred for non-avian maniraptorans and early birds, I very much
doubt that they were capable of WAIR.  If, as some people have
suggested, early flying theropods had a deltoideus-driven upstroke (to
compensate for limited humeral elevation), this would seem to be
incompatible with WAIR - and controlled flapping descent (CFD) too.


Although WAIR is a fascinating behavior exhibited by some modern
avians, there doesn't seem to be much to recommend it as an incipient
flight behavior in the evolution of flapping flight.  This conundrum
has been raised before.  WAIR is an "advanced" flight behavior, even
if it can be executed using incipient wings (such as present in
juvenile chukars).







Cheers

Tim

Cricosaurus (Thalattosuchia) postcranial skeleton from Jurassic of Argentina

Ben Creisler — 2013-05-19T17:34:36

From: Ben Creisler
bcreisler< at >gmail.com

A new online paper:

Yanina Herrera, Marta S. Fernández & Zulma Gasparini (2013)
Postcranial skeleton of Cricosaurus araucanensis (Crocodyliformes:
Thalattosuchia): morphology and palaeobiological insights.
Alcheringa 37 (advance online publication) 1–14
DOI: 10.1080/03115518.2013.743709
http://www.tandfonline.com/doi/full/10.1080/03115518.2013.743709#.UZkLobW1FcQ


The metriorhynchid crocodyliform Cricosaurus araucanensis (Gasparini &
Dellapé) has been documented from Tithonian (Upper Jurassic) strata of
the Vaca Muerta Formation exposed in the Neuquén Basin, northwest
Patagonia, Argentina. Postcranial components of this species were
mentioned but not described in the original analysis. Subsequently,
other authors described the forelimbs. The postcranial elements of
metriorhynchids are poorly documented in comparison with their skulls,
but new data from C. araucanensis reveal delayed ossification of the
caudal neurocentral sutures indicating skeletal paedomorphosis
affecting not only the appendicular skeleton but also the posterior
region of the vertebral column. The morphology of the caudal region
(transverse processes of the first caudal vertebrae ventrally
deflected) and the reduction in the femur of the fourth trochanter
suggest a reduction of the hypaxial musculature allowing increased
epaxial musculature. This pattern of musculoskeletal arrangement is
consistent with the swimming style and propulsion by lateral
undulation of the tail, as proposed by previous authors.

Cymatosaurus(?) pistosauroid material from Triassic of Netherlands

Ben Creisler — 2013-05-19T02:32:06

From: Ben Creisler
bcreisler< at >gmail.com


A new online paper:

P. Martin Sander, Nicole Klein, Paul C. H. Albers, Constanze
Bickelmann & Herman Winkelhorst (2013)
Postcranial morphology of a basal Pistosauroidea (Sauropterygia) from
the Lower Muschelkalk of Winterswijk, The Netherlands.
Paläontologische Zeitschrift (advance online publication)
DOI: 10.1007/s12542-013-0181-5
http://link.springer.com/article/10.1007/s12542-013-0181-5



Two partial postcranial skeletons from the Lower Muschelkalk (early
Anisian) of Winterswijk, The Netherlands, are described in detail. The
specimens were assigned to basal Pistosauroidea, presumably to cf.
Cymatosaurus or a closely related taxon. Cymatosaurus is currently the
earliest member of the Pistosauroidea and is only known from skull
material. Taxonomical assignment is based on humerus morphology and
histology, and on morphological differences from other Sauropterygia
(Nothosauria and Pachypleurosauria).

Ophthalmosaurian ichthyosaurs from Middle Jurassic of Argentina

Ben Creisler — 2013-05-17T15:15:58

From: Ben Creisler
bcreisler< at >gmail.com


A new online paper:


Marta S. Fernández and Marianella Talevi (2013)
Ophthalmosaurian (Ichthyosauria) records from the Aalenian–Bajocian of
Patagonia (Argentina): an overview.
Geological Magazine (advance online publication)
DOI: http://dx.doi.org/10.1017/S0016756813000058
http://128.232.233.5/action/displayAbstract?fromPage=online&aid=8920772&fulltextType=RA&fileId=S0016756813000058

The oldest ophthalmosaurian records worldwide have been recovered from
the Aalenian–Bajocian boundary of the Neuquén Basin in Central-West
Argentina (Mendoza and Neuquén provinces). Although scarce, they
document a poorly known period in the evolutionary history of
parvipelvian ichthyosaurs. In this contribution we present updated
information on these fossils, including a phylogenetic analysis, and a
redescription of ‘Stenopterygius grandis’ Cabrera, 1939. Patagonian
ichthyosaur occurrences indicate that during the Bajocian the Neuquén
Basin palaeogulf, on the southern margins of the Palaeopacific Ocean,
was inhabited by at least three morphologically discrete taxa: the
slender Stenopterygius cayi, robust ophthalmosaurian Mollesaurus
periallus and another indeterminate ichthyosaurian. Rib bone tissue
structure indicates that rib cages of Bajocian ichthyosaurs included
forms with dense rib microstructure (Mollesaurus) and forms with an
‘osteoporotic-like’ pattern (Stenopterygius cayi).

Largocephalosaurus (saurosphargid diapsid), new species from Triassic of China

Ben Creisler — 2013-05-17T15:14:23

From: Ben Creisler
bcreisler< at >gmail.com

A new online paper:


Chun Li, Da-Yong Jiang, Long Cheng, Xiao-Chun Wu and Olivier Rieppel (2013)
A new species of Largocephalosaurus (Diapsida: Saurosphargidae), with
implications for the morphological diversity and phylogeny of the
group.
Geological Magazine (advance online publication)
DOI: http://dx.doi.org/10.1017/S001675681300023X
http://128.232.233.5/action/displayAbstract?fromPage=online&aid=8920775&fulltextType=RA&fileId=S001675681300023X


Largocephalosaurus polycarpon Cheng et al. 2012 was erected after the
study of the skull and some parts of a skeleton and considered to be
an eosauropterygian. Here we describe a new species of the genus,
Largocephalosaurus qianensis, based on three specimens. The new
species provides many anatomical details which were described only
briefly or not at all in the type species, and clearly indicates that
Largocephalosaurus is a saurosphargid. It differs from the type
species mainly in having three premaxillary teeth, a very short
retroarticular process, a large pineal foramen, two sacral vertebrae,
and elongated small granular osteoderms mixed with some large ones
along the lateral most side of the body. With additional information
from the new species, we revise the diagnosis and the phylogenetic
relationships of Largocephalosaurus and clarify a set of diagnostic
features for the Saurosphargidae Li et al. 2011. Largocephalosaurus is
characterized primarily by an oval supratemporal fenestra, an elongate
dorsal ‘rib-basket’, a narrow and elongate transverse process of the
dorsal vertebrae, and the lack of a complete dorsal carapace of
osteoderms. The Saurosphargidae is distinct mainly in having a
retracted external naris, a jugal–squamosal contact, a large
supratemporal extensively contacting the quadrate shaft, a leaf-like
tooth crown with convex labial surface and concave lingual surface, a
closed dorsal ‘rib-basket’, many dorsal osteoderms, a large
boomerang-like or atypical T-shaped interclavicle. Current evidence
suggests that the Saurosphargidae is the sister-group of the
Sauropterygia and that Largocephalosaurus is the sister-group of the
Saurosphargis–Sinosaurosphargis clade within the family.

Re: Psittacosaurus juvenile herd behavior

Ben Creisler — 2013-05-16T15:55:42

From: Ben Creisler
bcreisler< at >gmail.com

Since this has not been commented on on the DML (it's mentioned on
some blogs), I would point out an important fact revealed in this
paper--the fossil nest of psittacosaurs with a cluster of juveniles
"guarded" by an adult is in fact a fake (shades of Archaeoraptor!).
This doctored fossil find is cited in various places as supposed
evidence of direct parental care in dinosaurs.


"Our close inspection of this cluster of 34 juveniles (DNHM D2156)
shows that the ‘adult’ skull has been added with glue, and so was not
part of the original specimen; there is no sedimentary connection to
the main slab below, and the skull rests loosely on top of that slab,
and is not in any way part of the sedimentary layer in which the
juveniles all occur, intertwined with each other. The evidence is that
the ‘adult’ skeleton just contains a few postcranial bones without any
articulation, and the skull position is much higher than the juvenile
bone-bed plane. The juveniles all seem to belong together because they
are preserved at one level in the rock, and their limbs and tails
overlap each other in complex ways."



On Wed, May 15, 2013 at 8:31 AM, Ben Creisler <bcreisler< at >gmail.com> wrote:

Aw: Re: Layperson question on endothermic dinosaurs

David Marjanovic — 2013-05-16T13:13:11

So far, so good...


Hang on a second. Here it's you who suddenly jumps to conclusions without evidence. We don't even know that much!


I can't remember specific papers, but there are people who have vehemently disagreed with this piece of textbook wisdom.

Re: Layperson question on endothermic dinosaurs

Kelly Clowers — 2013-05-15T22:54:10

NP. It gets everyone now and then.

Re: Layperson question on endothermic dinosaurs

Jura — 2013-05-15T22:25:48

Thanks. I didn't even catch that it was truncated. Stupid Yahoo mail.

Jason


lation, but insulation hinders
es not
i, M. 2009. Metabolic Correlates of

Re: Layperson question on endothermic dinosaurs

Kelly Clowers — 2013-05-15T22:11:06

Rescued from truncation:

On Wed, May 15, 2013 at 12:17 PM, Jura <pristichampsus< at >yahoo.com> wrote:

The truth is that we are no closer to knowing the thermophysiology of
dinosaur now then we were in the 70's and 80's when this whole thing
was called into question. The biggest problem with metabolism is that
differences between groups are  often a question of grade rather than
of structure. For instance the cell membranes of crocodiles and cows
are almost exactly the same. However cows incorporate more
polyunsaturated fatty acids in their cell membranes than crocs do.
This makes the cell membrane less efficient at retaining certain ions
which forces the protein pumps in the membranes to work harder to keep
proper ionic concentrations, ultimately giving cow cells higher
metabolic rates than croc cells. Wu et al. (2004) actually "turned" a
croc cell into a cow cell by changing the unsaturated fatty acid ratio
in the membranes. All of this is soft-tissue related and differs only
in  ratios. None of it fossilizes which means we have no real way of
saying definitively anything about metabolic rate.

So we typically turn to proxies for metabolism, which is a problem.
Forty years of tackling thermophysiological questions and we are still
not sure what makes for a good proxy for automatic endothermy (i.e.,
mammal and bird-style endothermy in which the metabolism is always
revved up. Contrast this with the myriad of other endothermic critters
out there that use muscle power to become endothermic and only do so
when they need it). The presence of filamentous integument on some
dinosaurs (and full on feathers in others) has recently been cited as
a good proxy, but it is a just-so assumption with no real empirical
basis (i.e., endothermy requires insulation, but insulation hinders
ectothermy). The closest test of this came from a paper in 1958 by
Raymond Cowles. The paper briefly mentioned a student experiment
involving placing lizards in a crude covering of mink (spared no
expense there). The paper doesn't list much in the way of materials
and methods. It doesn't cover anything on acclimation period between
trials (how long were the lizards allowed to get used to their new
coats), or really how long the trial was performed. Hell, the paper
doesn't even deal with this study. It just mentions it in passing. The
other problem with the integument argument is that we only have two
vertebrate groups that have filamentous integument today. That's two
data points or a line. It might be a requirement or it might be a
coincidence. If we expand our search out to other animals with
integument we can incorporate arthropods. If we do that then the
support of integument and endothermy weakens (e.g., tarantulas aren't
endothermic, nor are fuzzy geometer moths). Seebacher (2003) used a
mathematical model to show how even an ectothermic, 3.8 kg,
_Sinosauropteryx_ could maintain thermal stability in a cool
environment. There also cases of observed ectothermy in roadrunners
and vultures. Both taxa are known to sun themselves in the morning to
get their metabolisms up and running. That filamentous integument is
dynamic and adjustable (rather than a flat mink coat) no doubt plays
an important role in how these animals are able to get past the
thermal barrier caused by their feathers.

Many other proxies (growth rate, activity levels, limb ratios) are
based on the aerobic capacity model for the origin of automatic
endothermy (Bennett and Ruben 1979). The argument goes that basal
metabolic rate (the minimum amount of energy necessary to survive) is
intrinsically linked to how active one can be. Thus the more active
one is the higher the standard/basal metabolic rate needs to be to
match these needs. Despite the popularity of this hypothesis (and it
is BY FAR the most cited origin for automatic endothermy) it does not
have a lot of empirical support. Not to get too off track about this
but in brief: the organs responsible for increasing endurance (heart,
lungs, skeletal muscle) are not the same organs that are responsible
for the majority of our metabolic rates (intestines, liver, kidneys,
brains). Studies that have bred mice with higher endurance capacities
have found no concomitant increase in basal metabolic rate (Gebczynski
and Konarzewski 2009) whereas mice bred for low basal metabolism were
actually found to have higher endurance capacities (Ksiazek et al.
2004).

Getting back on track, in the past forty years we have learned much
more about how dinosaurs lived and looked. We have gained a better
understanding of their potential behaviours, and as a side-effect of
wanting to know about their metabolisms, the field of comparative
physiology has actually learned a lot about how complicated and
variable metabolic rates (and thermophysiology) are. Unfortunately
none of this has brought us any closer to knowing what kind of
metabolism dinosaurs had. It is generally accepted that dinosaurs were
diverse enough that one size did not fit all. Thus there was likely a
spectrum of metabolic regimes employed throughout the Mesozoic. It's
also becoming increasingly more accepted that the biggest differences
between "cold-blooded" animals and "warm blooded" animals occur at the
small body sizes. Once one reaches the size of your average dinosaur
those differences become vanishingly small. So a "cold-blooded"
_T.rex_ probably acted near identically to a "warm-blooded" _T.rex_.

Lastly I think it's worth keeping in mind that the data also aren't
there for cold-blooded mosasaurs, or warm-blooded therapsids. This is
not a problem limited to dinosaurs. It's true for all prehistoric
life.

Jason


References

Bennett, A. and Ruben, J. 1979. Endothermy and Activity in
Vertebrates. Science. Vol.206:649-654.

Cowles, R.B. 1958. Possible Origin of Dermal Temperature Regulation.
Evolution Vol.12(3):347-357

Gebczynski, A.K., Konarzewski, M. 2009. Metabolic Correlates of
Selection on Aerobic Capacity in Laboratory Mice: A Test of the Model
for the Evolution of Endothermy. J. Exp. Biol. Vol. 212:2872-2878

Ksiazek, A., Konarzewski, M., Lapo, I.B. 2004. Anatomic and Energetic
Correlates of Divergent Selection for Basal Metabolic Rate in
Laboratory Mice. Physiol. Biochem. Zool. Vol. 77(6): 890-899

Seebacher, F. 2003. Dinosaur Body Temperatures: The Occurrence of
Endothermy and Ectothermy. Paleobiology. Vol.29(1):105-122

Wu, B.J., Hulbert, A.J., Storlien, L.H., Else, P.L. 2004. Membrane
Lipids and Sodium Pumps of Cattle and Crocodiles: An Experimental Test
of the Membrane Pacemaker Theory of Metabolism. Am. J. Physiol. Regul.
AIntegr. Comp. Physiol. Vol. 287:R633-R641

http://reptilis.net

"I am impressed by the fact that we know less about many modern
[reptile] types than we do of many fossil groups." - Alfred S. Romer

Evolution of Theropod Tail into Stiff Aerodynamic Surface

Ben Creisler — 2013-05-15T21:34:59

From: Ben Creisler
bcreisler< at >gmail.com


New in PLoS ONE:

Michael Pittman, Stephen M. Gatesy, Paul Upchurch, Anjali Goswami &
John R. Hutchinson (2013)
Shake a Tail Feather: The Evolution of the Theropod Tail into a Stiff
Aerodynamic Surface.
PLoS ONE 8(5): e63115.
doi:10.1371/journal.pone.0063115
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0063115



Theropod dinosaurs show striking morphological and functional tail
variation; e.g., a long, robust, basal theropod tail used for
counterbalance, or a short, modern avian tail used as an aerodynamic
surface. We used a quantitative morphological and functional analysis
to reconstruct intervertebral joint stiffness in the tail along the
theropod lineage to extant birds. This provides new details of the
tail’s morphological transformation, and for the first time
quantitatively evaluates its biomechanical consequences. We observe
that both dorsoventral and lateral joint stiffness decreased along the
non-avian theropod lineage (between nodes Theropoda and Paraves). Our
results show how the tail structure of non-avian theropods was
mechanically appropriate for holding itself up against gravity and
maintaining passive balance. However, as dorsoventral and lateral
joint stiffness decreased, the tail may have become more effective for
dynamically maintaining balance. This supports our hypothesis of a
reduction of dorsoventral and lateral joint stiffness in shorter
tails. Along the avian theropod lineage (Avialae to crown group
birds), dorsoventral and lateral joint stiffness increased overall,
which appears to contradict our null expectation. We infer that this
departure in joint stiffness is specific to the tail’s aerodynamic
role and the functional constraints imposed by it. Increased
dorsoventral and lateral joint stiffness may have facilitated a
gradually improved capacity to lift, depress, and swing the tail. The
associated morphological changes should have resulted in a tail
capable of producing larger muscular forces to utilise larger lift
forces in flight. Improved joint mobility in neornithine birds
potentially permitted an increase in the range of lift force vector
orientations, which might have improved flight proficiency and
manoeuvrability. The tail morphology of modern birds with tail fanning
capabilities originated in early ornithuromorph birds. Hence, these
capabilities should have been present in the early Cretaceous, with
incipient tail-fanning capacity in the earliest pygostylian birds.

Mapusaurus (Theropoda) bonebed pathology survey

Ben Creisler — 2013-05-15T21:31:07

From: Ben Creisler
bcreisler< at >gmail.com

New in PLoS ONE:

Phil R. Bell & Rodolfo A. Coria (2013)
Palaeopathological Survey of a Population of Mapusaurus (Theropoda:
Carcharodontosauridae) from the Late Cretaceous Huincul Formation,
Argentina.
PLoS ONE 8(5): e63409.
doi:10.1371/journal.pone.0063409
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0063409



Paleoepidemiology (the study of disease and trauma in prehistoric
populations) provides insight into the distribution of disease and can
have implications for interpreting behavior in extinct organisms. A
monospecific bonebed of the giant carcharodontosaurid Mapusaurus
(minimum number of individuals = 9) from the Cañadón del Gato site,
Neuquén Province, Argentina (Cenomanian) provides a rare opportunity
to investigate disease within a single population of this important
apex predator. Visual inspection of 176 skeletal elements belonging to
a minimum of nine individuals yielded a small number of abnormalities
on a cervical vertebra, two ribs, pedal phalanx, and an ilium. These
are attributed to traumatic (two cases), infectious (two cases) and
anomalous (one case) conditions in a minimum of one individual. The
emerging picture for large theropod (abelisaurids, allosaurids,
carcharodontosaurids, tyrannosaurids) populations suggests that 1)
osseous abnormalities were relatively rare (7–19% of individuals) but
consistently present, and 2) trauma was a leading factor in the
frequency of pathological occurrences, evidence of an active, often
perilous lifestyle.

Aniksosaurus (Theropoda) bonebed found in Upper Cretaceous Bajo Barreal Formation, Argentina

Ben Creisler — 2013-05-15T21:26:07

From: Ben Creisler
bcreisler< at >gmail.com


New in open-access PLoS ONE:

Lucio M. Ibiricu, Rubén D. Martínez,  Gabriel A. Casal & Ignacio A. Cerda (2013)
The Behavioral Implications of a Multi-Individual Bonebed of a Small
Theropod Dinosaur.
PLoS ONE 8(5): e64253
doi:10.1371/journal.pone.0064253
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0064253


Background

Central Patagonia, Argentina, preserves an abundant and rich fossil
record. Among vertebrate fossils from the Upper Cretaceous Bajo
Barreal Formation of Patagonia, five individuals of the small,
non-avian theropod dinosaur Aniksosaurus darwini were recovered. Group
behavior is an important aspect of dinosaur paleoecology, but it is
not well-documented and is poorly understood among non-avian
Theropoda.

Methods/Principal Findings

The taphonomic association of individuals from the Bajo Barreal
Formation and aspects of their bone histology suggest gregarious
behavior for Aniksosaurus, during at least a portion of the life
history of this species. Histology indicates that the specimens were
juvenile to sub-adult individuals. In addition, morphological
differences between individuals, particularly proportions of the
appendicular bones, are probably related to body-size dimorphism
rather than ontogenetic stage.

Conclusions/Significance

Gregarious behaviour may have conferred a selective advantage on
Aniksosaurus individuals, contributing to their successful
exploitation of the Cretaceous paleoenvironment preserved in the Bajo
Barreal Formation. The monospecific assemblage of Aniksosaurus
specimens constitutes only the second body fossil association of
small, coelurosaurian theropods in South America and adds valuable
information about the paleoecologies of non-avian theropod dinosaurs,
particularly in the early Late Cretaceous of Patagonia.

Aw: RE: Layperson question on endothermic dinosaurs

David Marjanovic — 2013-05-15T21:14:45

Two things:

1) You, or your sbelchequer, wrote "monospecific boneheads". :-D :-D :-D

2) Crocodiles have "leaky" mitochondria!?! I'd say that clinches it! Reference, please!

Re: Layperson question on endothermic dinosaurs

Jura — 2013-05-15T19:17:48

The truth is that we are no closer to knowing the thermophysiology of dinosaur now then we were in the 70's and 80's when this whole thing was called into question. The biggest problem with metabolism is that differences between groups are often a question of grade rather than of structure. For instance the cell membranes of crocodiles and cows are almost exactly the same. However cows incorporate more polyunsaturated fatty acids in their cell membranes than crocs do. This makes the cell membrane less efficient at retaining certain ions which forces the protein pumps in the membranes to work harder to keep proper ionic concentrations, ultimately giving cow cells higher metabolic rates than croc cells. Wu et al. (2004) actually "turned" a croc cell into a cow cell by changing the unsaturated fatty acid ratio in the membranes. All of this is soft-tissue related and differs only in ratios. None of it fossilizes which means we have no real way of saying
definitively anything about metabolic rate.

So we typically turn to proxies for metabolism, which is a problem. Forty years of tackling thermophysiological questions and we are still not sure what makes for a good proxy for automatic endothermy (i.e., mammal and bird-style endothermy in which the metabolism is always revved up. Contrast this with the myriad of other endothermic critters out there that use muscle power to become endothermic and only do so when they need it). The presence of filamentous integument on some dinosaurs (and full on feathers in others) has recently been cited as a good proxy, but it is a just-so assumption with no real empirical basis (i.e., endothermy requires insulation, but insulation hinders ectothermy). The closest test of this came from a paper in 1958 by Raymond Cowles. The paper briefly mentioned a student experiment involving placing lizards in a crude covering of mink (spared no expense there). The paper doesn't list much in the way of materials and methods. It
doesn't cover anything on acclimation period between trials (how long were the lizards allowed to get used to their new coats), or really how long the trial was performed. Hell, the paper doesn't even deal with this study. It just mentions it in passing. The other problem with the integument argument is that we only have two vertebrate groups that have filamentous integument today. That's two data points or a line. It might be a requirement or it might be a coincidence. If we expand our search out to other animals with integument we can incorporate arthropods. If we do that then the support of integument and endothermy weakens (e.g., tarantulas aren't endothermic, nor are fuzzy geometer moths). Seebacher (2003) used a mathematical model to show how even an ectothermic, 3.8 kg, _Sinosauropteryx_ could maintain thermal stability in a cool environment. There also cases of observed ectothermy in roadrunners and vultures. Both taxa are known to sun
themselves in the morning to get their metabolisms up and running. That filamentous integument is dynamic and adjustable (rather than a flat mink coat) no doubt plays an important role in how these animals are able to get past the thermal barrier caused by their feathers.

Many other proxies (growth rate, activity levels, limb ratios) are based on the aerobic capacity model for the origin of automatic endothermy (Bennett and Ruben 1979). The argument goes that basal metabolic rate (the minimum amount of energy necessary to survive) is intrinsically linked to how active one can be. Thus the more active one is the higher the standard/basal metabolic rate needs to be to match these needs. Despite the popularity of this hypothesis (and it is BY FAR the most cited origin for automatic endothermy) it does not have a lot of empirical support. Not to get too off track about this but in brief: the organs responsible for increasing endurance (heart, lungs, skeletal muscle) are not the same organs that are responsible for the majority of our metabolic rates (intestines, liver, kidneys, brains). Studies that have bred mice with higher endurance capacities have found no concomitant increase in basal metabolic rate (Gebczynski and
Konarzewski 2009) whereas mice bred for low basal metabolism were actually found to have higher endurance capacities (Ksiazek et al. 2004).

Getting back on track, in the past forty years we have learned much more about how dinosaurs lived and looked. We have gained a better understanding of their potential behaviours, and as a side-effect of wanting to know about their metabolisms, the field of comparative physiology has actually learned a lot about how complicated and variable metabolic rates (and thermophysiology) are. Unfortunately none of this has brought us any closer to knowing what kind of metabolism dinosaurs had. It is generally accepted that dinosaurs were diverse enough that one size did not fit all. Thus there was likely a spectrum of metabolic regimes employed throughout the Mesozoic. It's also becoming increasingly more accepted that the biggest differences between "cold-blooded" animals and "warm blooded" animals occur at the small body sizes. Once one reaches the size of your average dinosaur those differences become vanishingly small. So a "cold-blooded" _T.rex_ probably
acted near identically to a "warm-blooded" _T.rex_.

Lastly I think it's worth keeping in mind that the data also aren't there for cold-blooded mosasaurs, or warm-blooded therapsids. This is not a problem limited to dinosaurs. It's true for all prehistoric life.

Jason

References

Bennett, A. and Ruben, J. 1979. Endothermy and Activity in Vertebrates. Science. Vol.206:649-654.

Cowles, R.B. 1958. Possible Origin of Dermal Temperature Regulation. Evolution Vol.12(3):347-357

Gebczynski, A.K., Konarzewski, M. 2009. Metabolic Correlates of
Selection on Aerobic Capacity in Laboratory Mice: A Test of the Model
for the Evolution of Endothermy. J. Exp. Biol. Vol. 212:2872-2878

Ksiazek, A., Konarzewski, M., Lapo, I.B. 2004. Anatomic and Energetic Correlates of Divergent Selection for Basal Metabolic Rate in Laboratory Mice. Physiol. Biochem. Zool. Vol. 77(6):890-899

Seebacher, F. 2003. Dinosaur Body Temperatures: The Occurrence of Endothermy and Ectothermy. Paleobiology. Vol.29(1):105-122

Wu, B.J., Hulbert, A.J., Storlien, L.H., Else, P.L. 2004. Membrane
Lipids and Sodium Pumps of Cattle and Crocodiles: An Experimental Test
of the Membrane Pacemaker Theory of Metabolism. Am. J. Physiol. Regul.
Integr. Comp. Physiol. Vol. 287:R633-R641

http://reptilis.net

"I am impressed by the fact that we know less about many modern [reptile] types than we do of many fossil groups." - Alfred S. Romer

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Re: Layperson question on endothermic dinosaurs

Kelly Clowers — 2013-05-15T19:13:55

Thanks a lot, and thanks to everyone for the replies so far!

Kelly

RE: Layperson question on endothermic dinosaurs

Thomas R. Holtz, Jr. — 2013-05-15T17:43:26

Here are some lecture notes: http://www.geol.umd.edu/~tholtz/G204/lectures/204endo.html

Thomas R. Holtz, Jr.
Email: tholtz< at >umd.eduPhone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661

Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:Thomas R. Holtz, Jr.
Department of Geology
Building 237, Room 1117
University of Maryland
College Park, MD 20742 USA

RE: Layperson question on endothermic dinosaurs

Allan Edels — 2013-05-15T17:33:11

[Speaking as another layperson:] 

The likelihood is that the large sauropods and the larger of the ornithischians would feel warm to the touch.   The bigger problem for these creatures would need help reducing the heat retained by the large mass, as well as that generated by the muscles as they moved.

(Long necks and tails might have facilitated some thermal reduction, as might the plates on stegosaurs, etc).

I've often wondered what a good Finite Element Analysis (FEA) of the movement of sauropods might shine on their heat production.

Allan Edels

Re: Layperson question on endothermic dinosaurs

Vivian Allen — 2013-05-15T17:05:57

Theropods, yeah. You've got several lines of evidence that make that
one pretty solid. Off the top of my head:

Feathers. I know feathers have other functions (display,
water-proofing, flying eventually) but I'm going to go out on a limb
and say one of the main things feathers do is insulate the body. Why
would you need to insulate yourself if you were not warm-blooded?

Extensive, bird-like lungs.  Most theropods had very large, complex
breathing structures similar to those seen in birds. In birds, these
lung complexes are very efficient at extracting a lot of oxygen from
the air (http://en.wikipedia.org/wiki/Bird_anatomy#Respiratory_system),
and you need a lot of oxygen to power a high metabolism. So again, why
have these complex lung structures unless you need a lot of oxygen?

Relationship with birds. Less concrete, but the fact is that birds are
living theropod dinosaurs, and they are endothermic. You may argue
that this is just because they fly, but many species of birds have
become more-or-less terrestrial, and they still maintain endothermy.

Long legs. The biomechanics behind it may be a little above layperson
level (paper here if you are interested:
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0007783 ,
but fairly simple put, moving around on long legs requires quite a lot
of consistent effort from quite large muscles, and to provide
consistent energy for a lot of large muscles you need a high metabolic
rate, i.e. are in the 'warm-blooded' part of the metabolic spectrum.

I'm sure other list members will be happy to add to the list (and
correct me if I am wrong), but yeah, I think there is a very good case
for endothermy in theropod dinosaurs.

In other dinosaurs (the long-necked sauropods and the very diverse
ornithischians) it is difficult to be sure - they do not have living
representatives, so it is more difficult to make inferences about
their biology. But, a lot of ornithischians have similar body
proportions to theropods, again with these long legs, which does
indicate that they were pretty active, high-metabolism creatures.

Viv

On 15 May 2013 17:34, Kelly Clowers <kelly.clowers< at >gmail.com> wrote:

Layperson question on endothermic dinosaurs

Kelly Clowers — 2013-05-15T16:34:01

Hi, I am hoping that I could get sense of  what the consensus, if any,
is on endothemry. I try to stay up to date and knowledgeable on all
things dino-related, but I just want to be clear on this to help
settle a discussion on the Ars Technica forums.

I believe that it pretty solidly accepted for therapods, but maybe
somewhat less so for the rest? Or am I all wrong?

Thanks very much,

Kelly Clowers

Psittacosaurus juvenile herd behavior

Ben Creisler — 2013-05-15T15:31:48

From: Ben Creisler
bcreisler< at >gmail.com


A new online open-access paper:


Qi Zhao, Michael J. Benton, Xing Xu, and Martin J. Sander (2013)
Juvenile-only clusters and behaviour of the Early Cretaceous dinosaur
Psittacosaurus.
Acta Palaeontologica Polonica (in press)
doi: http://dx.doi.org/10.4202/app.2012.0128
http://app.pan.pl/article/item/app20120128.html


It has hitherto been hard to prove that any association of juvenile
dinosaurs represents original behaviour rather than sedimentary
accumulation, and it has been hard also to determine the ages of such
juveniles. A previously described specimen, which consists of an
‘adult’ Psittacosaurus with 34 fully articulated juveniles, turns out
to be a composite: the ‘adult’ skull has been added, and in any case
it is below breeding age. Other juvenile-only clusters have been
reported, but the best examples that likely reflect behaviour rather
than sedimentary accumulation are specimens from the Early Cretaceous
Lujiatun beds in NE China, which were entombed beneath pyroclastic
flow deposits. A remarkable juvenile-only cluster of Psittacosaurus
shows clear evidence of different ages (five 2-year olds and one
3-year old) based on bone histological analysis. These juveniles may
have associated together as a close knit, mixed-age herd either for
protection, to enhance their foraging, or as putative helpers at the
parental nest.