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RE: Torosaurus NOT Triceratops

  It's purpose is to show 1) that there is overlap in the morphology across a 
range of ontogenetic stages, but more specifically that 2) there are 
non-"adult" specimens with clear "Torosaurus" morphologies.


  Jaime A. Headden
  The Bite Stuff (site v2)

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 

> Date: Thu, 1 Mar 2012 00:45:12 +0000
> From: Michael.OSullivan@port.ac.uk
> To: bcreisler@gmail.com; dinosaur@usc.edu
> Subject: Re: Torosaurus NOT Triceratops
> Am I the only one who thinks that the dataset used for the determination
> of Torosaurus as a valid genus, or something synonymous with
> Triceratops, is capable of being used to support either view, depending
> on who's analysing the data. I think there's a real danger of
> subjectivity obscuring the reality. Whatever the hell that is...this
> rate, Torosaurus will be revealed to be a late living Stegosaur
> ---
> Michael O'Sullivan
> Palaeobiology Research Group
> Postgraduate Student
> School of Earth & Environmental Sciences
> Burnaby Building
> Burnaby Road
> Portsmouth
> PO1 3QL
> Email:michael.osullivan@port.ac.uk
> >>> Ben Creisler 01/03/12 12:10 AM >>>
> From: Ben Creisler
> bcreisler@gmail.com
> A new paper in PLoS ONE:
> Longrich, N.R. & Field, D.J. (2012)
> Torosaurus Is Not Triceratops: Ontogeny in Chasmosaurine Ceratopsids
> as a Case Study in Dinosaur Taxonomy.
> PLoS ONE 7(2): e32623.
> doi:10.1371/journal.pone.0032623
> http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0032623
> Background
> In horned dinosaurs, taxonomy is complicated by the fact that the
> cranial ornament that distinguishes species changes with age. Based on
> this observation, it has been proposed that the genera Triceratops and
> Torosaurus are in fact synonymous, with specimens identified as
> Torosaurus representing the adult form of Triceratops. The hypothesis
> of synonymy makes three testable predictions: 1) the species in
> question should have similar geographic and stratigraphic
> distributions, 2) specimens assigned to Torosaurus should be more
> mature than those assigned to Triceratops, and 3) intermediates should
> exist that combine features of Triceratops and Torosaurus. The first
> condition appears to be met, but it remains unclear whether the other
> predictions are borne out by the fossil evidence.
> Methodology/Principal Findings
> We assessed the relative maturity of Torosaurus and Triceratops
> specimens by coding skulls for characters that vary with maturity, and
> then using a clustering analysis to arrange them into a growth series.
> We found that a well-defined sequence of changes exists in horned
> dinosaurs: development of cranial ornament occurs in juveniles,
> followed by fusion of the skull roof in subadults, and finally, the
> epoccipitals, epijugals, and rostral fuse to the skull in adults.
> Using this scheme, we identified mature and immature individuals of
> both Torosaurus and Triceratops. Furthermore, we describe the ventral
> depressions on the frill of Triceratops, and show that they differ in
> shape and position from the parietal fenestrae of Torosaurus. Thus, we
> conclude that these structures are not intermediates between the solid
> frill of Triceratops and the fenestrated frill of Torosaurus.
> Conclusions/Significance
> Torosaurus is a distinct genus of horned dinosaur, not the adult of
> Triceratops. Our method provides a framework for assessing the
> hypothesis of synonymy through ontogeny in the fossil record.