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Re: Kosmoceratops, Utahceratops & Vagaceratops: the paper

Are the ages right? 

Sampson et al (2010) PLoS article:

"Laser-fusion 40Ar/39Ar ages indicate a late Campanian range for the formation, 
spanning 76.6â74.5 Ma and corresponding to the Judithian land vertebrate age 
(Fig. 7) [29]"

[29] is Roberts et al (2005) who state in their abstract:

"Laser-fusion 40Ar/39Ar analysis of four bentonite horizons produces the first 
absolute ages for the 860-m-thick Kaiparowits
Formation and resolves previous age uncertainty caused by ambiguous 
biostratigraphy. A late Campanian (Judithian) age of ca.
76.1-74.0 Ma is determined, resulting in a high-resolution temporal framework 
for the richly fossiliferous formation."

The Roberts et al (2005) radiometric dates are 75.96 (+/-0.14), 75.02 (+/-0.15) 
(twice), and 74.21 (+/- 0.18). If the 76.6-74.5Ma cited age in Sampson et al is 
a new extrapolation, then it isn't mentioned in the paper, and has not been 
reviewed for accuracy. A radiometric date of 74.21 in the upper Kaiparowits 
would seem to falsify the statement that the Kaiparowits ranges only to 74.5Ma, 
especially considering that this is still 70m from the top of the ~860m thick 
formation. Sampson et al do not provide precise stratigraphic positions of 
specimens (relative to the radiometrically dated horizons) described in the 
study, yet this is critical to their interpretation of the biogeography.

Still, the authors are entitled to their opinion on their (fantastic) 
I would interpret the specimens and stratigraphy differently.

Denver Fowler

----- Original Message ----
From: "Thomas R. Holtz, Jr." <tholtz@umd.edu>
To: dinosaur@usc.edu
Sent: Wed, 22 September, 2010 9:41:14
Subject: Kosmoceratops, Utahceratops & Vagaceratops: the paper


Sampson SD, Loewen MA, Farke AA, Roberts EM, Forster CA, et al. (2010) New
Horned Dinosaurs from Utah Provide Evidence for 
Endemism. PLoS ONE 5(9): e12292. doi:10.1371/journal.pone.0012292



During much of the Late Cretaceous, a shallow, epeiric sea divided North
America into eastern and western landmasses. The western landmass, known as
Laramidia, although diminutive in size, witnessed a major evolutionary
radiation of dinosaurs. Other than hadrosaurs (duck-billed dinosaurs), the
most common dinosaurs were ceratopsids (large-bodied horned dinosaurs),
currently known only from Laramidia and Asia. Remarkably, previous studies
have postulated the occurrence of latitudinally arrayed dinosaur
"provinces," or "biomes," on Laramidia. Yet this hypothesis has been
challenged on multiple fronts and has remained poorly tested.
Methodology/Principal Findings

Here we describe two new, co-occurring ceratopsids from the Upper Cretaceous
Kaiparowits Formation of Utah that provide the strongest support to date for
the dinosaur provincialism hypothesis. Both pertain to the clade of
ceratopsids known as Chasmosaurinae, dramatically increasing representation
of this group from the southern portion of the Western Interior Basin of
North America. Utahceratops gettyi gen. et sp. nov.-characterized by short,
rounded, laterally projecting supraorbital horncores and an elongate frill
with a deep median embayment-is recovered as the sister taxon to
Pentaceratops sternbergii from the late Campanian of New Mexico.
Kosmoceratops richardsoni gen. et sp. nov.-characterized by elongate,
laterally projecting supraorbital horncores and a short, broad frill adorned
with ten well developed hooks-has the most ornate skull of any known
dinosaur and is closely allied to Chasmosaurus irvinensis from the late
Campanian of Alberta.

Considered in unison, the phylogenetic, stratigraphic, and biogeographic
evidence documents distinct, co-occurring chasmosaurine taxa north and south
on the diminutive landmass of Laramidia. The famous Triceratops and all
other, more nested chasmosaurines are postulated as descendants of forms
amidia. Results further
suggest the presence of latitudinally arrayed evolutionary centers of
endemism within chasmosaurine ceratopsids during the late Campanian, the
first documented occurrence of intracontinental endemism within dinosaurs.

Vagaceratops is the former "Chasmosaurus" irvinensis.

A kick-ass (technical term) phylogeny is presented:

It's PLoS ONE, so everyone has access.

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu    Phone: 301-405-4084
Office: Centreville 1216            
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Fax: 301-314-9661        

Faculty Director, Science & Global Change Program, College Park Scholars
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