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Re: Evidence for gregarious behavior and age segregation in sauropod dinosaurs

A potential confounding factor relative to the interpretation of trapped herds 
is the fact that traps generally, including 'mud-based' traps, are usually 
size-selective. Relative to any given quality of mud, there will be a size 
threshold below which limb penetration will not be deep enough to cause miring. 
Much larger animals may have enough power to overcome the viscosity of the 
entrapping fluid, and/or long enough limbs to reach the 'bottom' of a given 

Given a very large intra-specific size range, these mechanisms could easily 
result in age-selective (ie, mid-size) entrapment and preservation episodes, 
giving the appearance of 100% entrapment of an age-segregated herd, whereas in 
reality the larger and smaller herd individuals escaped entrapment.

The presence of other fossils of a size-diverse range of species in the same 
stratigraphic position might lend support for an age-segregation interpretation 
of a given deposit, but the diverse and transitory (weather-related) nature of 
mud-trap conditions allows some doubt to be cast in this scenario as well.


--- On Fri, 3/6/09, Luis Azevedo Rodrigues <paleovouga@gmail.com> wrote:

> Cool!
> We have similar ichnological evidences here in Portugal:
> Lockley, M. G., Meyer, C. A. & Santos, V. F. 1994c.
> Trackway evidence for a herd of juvenile sauropods from the
> Late Jurassic of Portugal. Gaia: Revista de Geociencias,
> Museu Nacional de Historia Natural (Lisbon) 10, 27-36.
> Best
> Luis

> Original Message From: jigruiz@unizar.es
> To: <dinosaur@usc.edu>
> Sent: Friday, March 06, 2009 2:42 PM
> Subject: Evidence for gregarious behavior and age
> segregation in sauropoddinosaurs
> Timothy S. Myers & Anthony R. Fiorillo. 2009. Evidence
> for gregarious
> behavior and age segregation in sauropod dinosaurs.
> Palaeogeography,
> Palaeoclimatology, Palaeoecology 274, 96-104
> Both body fossil and ichnofossil evidence for gregarious
> behavior in
> sauropod dinosaurs is examined. Some localities suggest
> that herds
> were partitioned on the basis of age, whereas other sites
> reveal
> groups consisting of both adult and juvenile/subadult
> individuals. Two
> skeletal accumulations showing evidence of age segregation
> are
> examined in detail. The Mother's Day Quarry in the
> Upper Jurassic
> Morrison Formation of Montana contains the remains of
> several immature
> diplodocoid sauropods. An assemblage in the Upper
> Cretaceous Javelina
> Formation of Big Bend National Park in Texas consists
> entirely of
> juvenile Alamosaurus. Both the Mother's Day and Big
> Bend assemblages
> are interpreted here as remnants of age-segregated herds.
> The
> differences between skeletal accumulations composed
> entirely of
> immature animals and mixed-age ichnological assemblages
> imply that
> herd composition was variable. When age segregation is
> recognized, in
> both fossil and modern taxa, it is thought to minimize the
> fitness
> costs related to behavioral synchronization within social
> groups. Age
> segregation of herds also contraindicates extended parental
> care as
> typical of at least some sauropod taxa.
> © 2009 Elsevier B.V. All rights reserved.

> -------------------------------------------
> Jose Ignacio Ruiz-Omeñaca
> Museo del Jurásico de Asturias (MUJA)
> E-33328 Colunga, Spain
> www.dinoastur.com
> www.museojurasicoasturias.com
> www.aragosaurus.com
> -------------------------------------------