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Posted by 08 Apr 2013 at 00:30 GMTon
1) Georgi et al. take skull length data for AMNH 6810, a specimen they list as Plateosaurus longiceps, from Sereno et al. (2007) (Georgi et al. 2013., table S1). Georgi et al. (2013, p. 4) detail that "the value used is the basicranial length", with two exceptions, neither of which is Plateosaurus.
Sereno et al. (2007, table 2) list a skull length of 36 cm for an individual of Plateosaurus engelhardti*, based on data in Galton (1985), combined with the mass of AMNH 6810 taken from Seebacher (2001).
However, for AMNH 6810, Galton (1985, table 2) lists the maximum length from premaxilla to basicranium as 312 mm, and that from premaxilla to paroccipital as 342 mm (left) and 345 mm (right). Measurements on the figures of AMNH 6810 in Galton (1985, figures 3, 8) result in nearly identical measurements (scaling from the scale bar, not from the scale factor in the figure caption). None of the specimens listed in Galton (1985, table 2) has a basicranial length of 360 mm, or a value that could be rounded to 36 cm.
Thus, the basicranial length given by Sereno et al. (2007) apparently differs from that in the very source it was supposedly taken from. Georgi et al. (2013) therefore copied erroneous data, inflating the skull size of AMNH 6810.
2) Georgi et al. claim that "wherever possible (21 of 29 specimens), preference was given to body masses estimated using Seebacher's polynomial estimation approach" (Georgi et al. 2013, p. 4).
However, although Seebacher (2001, table 2) lists AMNH 6810, with a total length of 6.5 m and a calculated mass of 1,072.6 kg, Georgi et al. (2013, table S1) list Sander (1992) and Sereno et al. (2007) as the sources for their data. Of these, Sereno et al. (2007) was used as the source for skull length (see above), but not as the source for mass, although the same table 2 in Sereno et al. (2997) lists the mass estimate of 1,072.6 kg Sereno et al. (2007) took from Seebacher (2001). Instead, Georgi et al. (2013, table S1) use a mass of 2179.0 kg for an individual with a body length of 8 m. This mass estimate can indeed be found in Sander (1992), based on a generic scale model (i.e., not for AMNH 6810, nor for an individual of that size). Georgi et al. (2013) therefore greatly inflated the mass of AMNH 6810 by using a mass estimate for a different animal at a different size, although a mass estimate for the very specimen they use for their skull data is available from Seebacher (2001).
*Note that the differing species names are likely synonyms (Moser 2003; although others disagree without addressing Moser's work).
3) Georgi et al. (2013) follow Galton and Upchurch (2004) in assuming that Plateosaurus was a facultative biped. That article, in turn, relies on Christian and Preuschoft (1996), who analysed the resistance of the vertebral column to bending, and concluded that Plateosaurus was a "habitual quadruped", but was capable of a slow bipedal run. Since then, a number of articles were published, including a study of the pronation capability of the manus of Plateosaurus (Bonnan and Senter 2007) and several papers studying the body proportions, range of motion and centre of mass position of Plateosaurus (Mallison 2010a, 2010b, 2011), that all conclude that Plateosaurus was incapable to locomote quadrupedally. Georgi et al. (2013) make no mention of these studies.
A. Christian and H. Preuschoft are by now convinced that above mentioned studies are correct, and that the intermediate resistance to bending of the shoulder region of the vertebral column of Plateosaurus found by Christian and Preuschoft (1996) was likely caused by other actions that locomotion (Christian and Preuschoft, various pers. comm. between 2007 and 2011).
Therefore, the assertion that Plateosaurus was facultatively bipedal seems highly questionable, and Georgi et al.'s (2013) interpretations regarding basal sauropodomorphs thus rest on a single data point, from a taxon (Anchisaurus) for which the detailed analyses that Bonnan and Senter (2007) and Mallison (2010a, 2010b, 2011) performed for Plateosaurus have not been attempted. Furthermore, Bonnan and Senter (2007) analysed not only Plateosaurus, but also Massospondylus, a basal sauropodomorph of similar size, body and limb proportions as Anchisaurus, and also concluded that it was an obligate biped as an adult. Their conclusion further weakens the interpretations presented by Georgi et al. (2013) with regards to basal sauropodomorphs.
Bonnan, M.F., Senter, P. 2007. Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadrupeds? In: Barrett, P.M., Batten, D.J., editors. Evolution and Palaeobiology of Early Sauropodomorph Dinosaurs. Special Papers in Palaeontology 77:139–155
Christian, A., Preuschoft, H. 1996. Deducing the body posture of extinct large vertebrates from the shape of the vertebral column. Palaeontology 39: 801–812
Galton, P.M. 1985. Cranial anatomy of the prosauropod dinosaur Plateosaurus from the Knollenmergel (Middle Keuper, Upper Triassic) of Germany. II. All the cranial material and details of soft−part anatomy. Geologica et Palaeontologica 19:119–159
Galton, P.M., Upchurch, P. 2004. Prosauropoda. In: Weishampel, D.B., Dodson, P., Osmólska, H., editors. The Dinosauria. Berkeley, California: University of California Press. pp. 232–258
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Mallison, H. 2010b. The digital Plateosaurus II: an assessment of the range of motion of the limbs and vertebral column and of previous reconstructions using a digital skeletal mount. Acta Palaeontologica Polonica 55(3):433-458. doi:10.4202/app.2009.0075, http://www.app.pan.pl/art...
Mallison, H. 2011. Plateosaurus in 3D: how CAD models and kinetic-dynamic modeling bring an extinct animal to life. In: Klein, N., Remes, K., Gee, C., Sander M., editors, Biology of the Sauropod Dinosaurs: Understanding the life of giants. Life of the Past (series ed. Farlow, J.). Indiana University Press. pp. 219-236
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