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Re: Kaatedocus, new diplodocid sauropod from Jurassic Morrison Formation, Wyoming



Rescued from truncation, Michael Lange wrote: I haven't seen the
paper, but isn't Barosaurus rather common at the Howe Quarry and isn't
the skull of Barosaurus only barely known? So, why can't this be a
Barosaurus? Just wondering.

I could not help wondering the same thing. Quoting from the paper
(Tschopp and Mateus, 2012), with my comments (>>) below:

"[Kaatedocus siberi is a] Diplodocid sauropod with the following
features not found in other sauropods:U-shaped notch separating the
frontals anteriorly (Fig. 5); a rugose tuberosity that marks the
anterodorsal corner of the lateral surface of the posterior cervical
vertebrae (Fig. 10); posterior margin of the prezygapophyseal
articular facet of posterior cervical vertebrae bordered posteriorly
by a conspicuous transverse sulcus, separating the facet from the
prezygapophyseal process (Fig. 10)." (p. 4)
"Comparison of Kaatedocus siberi with Barosaurus lentus and Tornieria
africana is hampered due to little overlap in the incomplete reported
specimens" (p. 26)
"K. siberi differs from the more derived Barosaurus, Tornieria and
Diplodocus in the absence of a small, anteroposteriorly elongate fossa
posteroventral and separate from the main pleurocoel, relatively short
mid-cervical vertebrae, and the lack of a vertical accessory lamina
posterior to the sprl of posterior cervical vertebrae (unknown in
Tornieria)" (p. 26)

>> The only elements which are represented in the type specimen of Barosaurus 
>> lentus (YPM 429) that overlap with the holotype of Kaatedocus siberi are 
>> three-and-a-half cervical vertebrae (McIntosh, 2005) - these are the most 
>> posterior (Lull 1919) and, depending on the number of cervicals present, may 
>> actually not overlap with K. siberi. AMNH 6341 has cervicals 10-16(?) 
>> (McIntosh, 2005), CM 11984 has cervicals 7-16(?) (McIntosh, 2005), and CM 
>> 1198 has four cervicals (serial position not given; McIntosh, 2005).

"It [Kaatedocus] can be distinguished from Diplodocus, Tornieria and
Barosaurus due to its relatively short mid-cervical centra (Elongation
Index (EI) = centrum length/height of posterior cotyle < 4)" (p4)

>> The neck of Kaatedocus, which is represented by cervicals III-XIV, measures 
>> 3.192m based on addition of the lengths given in Table 1. In contrast, the 
>> total length of cervicals III-XIV in Diplodocus carnegii is 5.975m (Hatcher, 
>> 1901). Barosaurus' neck is, of course, longer still (Lull, 1919; McIntosh, 
>> 2005).

"With a mean EI of 3.5, the mid-cervical vertebrae constitute the most
elongated centra of the series, which lies between the values reported
for Apatosaurus or Diplodocus and Barosaurus" (p17)

>> The vertebrae were divided into anterior (III-V), middle (VI-X) and 
>> posterior (XI-XIV), which is interesting - I wonder how comparisons of the 
>> EIs of each vertebra in the series would have compared.

"...A very young age for SMA 0004 can be excluded due to the complete
neurocentral fusion" (p. 26)
"A separation of Kaatedocus siberi from Barosaurus lentus is equally
[compared to separation from Tornieria] well supported. Apart from the
improbable enormous allometric growth necessary for the cervical
vertebrae of SMA 0004 to reach the elongation index of B. lentus
(McIntosh 2005), three more morphological characters can be put
forward to distinguish these two taxa (plus the unambiguous
autapomorphies of K. siberi). B. lentus YPM 429 exhibits a bifurcate
anterior end of the pcdl, and postzygapophyses that terminate anterior
to the posterior margin of the posterior cervical centra (Lull 1919;
pers. obs. 2011). Furthermore, the ventral keels in the cervical
vertebrae of the B. lentus holotype YPM 429 show a quite different
morphology from the single anterior ridge in SMA0004: in YPM429 two
crests extend obliquely from between the parapophyses posterolaterally
to unite with the posteroventral flanges (Lull 1919; pers. obs. 2011).
Adding the recovered autapomorphies of K. siberi, a generic
distinction from Barosaurus can be justified." (p. 27)

>> But how mature is it, and how good an indicator is neurocentral fusion of 
>> age? I've seen this brought up on SV-POW 
>> (http://svpow.com/2008/01/26/tutorial-5-neurocentral-fusion/), in a paper on 
>> Camarasaurus (Ikejiri et al., 2005) and one on crocodiles (Brochu, 1996), 
>> and Ikejiri et al. (p. 173) confirm Britt & Naylor's (1994) hypothesis that 
>> Camarasaurus neck length increased through ontogeny. I don't see why the 
>> same would not be true for Barosaurus. The laminae may be more valid 
>> characters, but I would again have to more carefully assess this.

I am more inclined to think that Kaatedocus probably does represent a
pre-existing taxon, but in all honesty I'd be basing that more on a
gut feeling (i.e. "already enough diplodocid genera in the Morisson
Formation") and the questions / cursory observations listed above than
from careful scrutiny of their paper; I would not dismiss it a priori.
Regardless of whether or not it truly is a new genus and/or species,
the specimen is beautiful, the photography is excellent, the
measurements plentiful, and the descriptions clear.

Steve

References:
Britt, B. B., and B. G. Naylor. 1994. An embryonic Camarasaurus
(Dinosauria, Saruopoda) from the Upper Jurassic Morrison Formation
(Dry Mesa Quarry, Colorado); pp. 256-264 in K. Carpenter, K. F.
Hirsch, and J. R. Horner (eds.), Dinosaur Eggs and Babies. Cambridge
University Press, Cambridge.
Brochu, C. A. 1996. Closure of neurocentral sutures during crocodilian
ontogeny: implications for maturity assessment in fossil archosaurs.
Journal of Vertebrate Paleontology 16:49-62.
Hatcher, J. B. 1901. Diplodocus (Marsh): its osteology, taxonomy and
probable habits, with a restoration of the skeleton. Memoirs of the
Carnegie Museum 1:1-63.
Ikejiri, T., V. Tidwell, and D. L. Trexler. 2005. New adult specimens
of Camarasaurus lentus highlight ontogenetic variation within the
species; pp. 154-179 in V. Tidwell, and K. Carpenter (eds.),
Thunder-lizards: The Sauropodomorph Dinosaurs. Indiana University
Press, Bloomington & Indianapolis.
Lull, R. S. 1919. The sauropod dinosaur Barosaurus Marsh:
redescription of the type specimen in the Peabody Museum, Yale
University. Memoirs of the Connecticut Academy of Arts and Sciences
6:1-42.
McIntosh, J. S. 2005. The genus Barosaurus Marsh (Sauropoda,
Diplodocidae); pp. 38-77 in V. Tidwell, and K. Carpenter (eds.),
Thunder-lizards: The Sauropodomorph Dinosaurs. Indiana University
Press, Bloomington & Indianapolis.
Tschopp, E., and O. Mateus. In press. The skull and neck of a new
flagellicaudatan sauropod from the Morrison Formation and its
implication for the evolution and ontogeny of diplodocid dinosaurs.
Journal of Systematic Palaeontology.

On Sat, Dec 15, 2012 at 7:45 PM, Michael Lange <Michael.Lange@gmx.ch> wrote:
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--
Dr. Stephen Poropat

Postdoctoral Research Fellow
Uppsala University
Villavägen 16
SE-752 36 Uppsala
Sweden

Research Associate
Australian Age of Dinosaurs
PO Box 408
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Australia