Wedel, Mathew J., and Michael P. Taylor. 2013. Neural spine bifurcation in sauropod dinosaurs of the Morrison Formation: ontogenetic and phylogenetic implications. Palarch’s Journal of Vertebrate Palaeontology 10(1):1-34. ISSN 1567-2158.
SV-POW! posts – pre-publication
This paper is a departure for us in that we wrote it as a series of blog posts first, and then turned those posts into the submitted manuscript. Here are the original posts, from April, 2012:
And posts about the VertFigure software that we wrote and used to create figure 9:
and the post that started it all:
SV-POW! posts – post-publication
The Nexus files we used to run the phylogenetic analyses in the paper are available on FigShare:
Figure 1. A cervical vertebra of Apatosaurus ajax YPM 1860 showing complete bifurcation of the neural spine into paired metapophyses. In dorsal (top), anterior (left), left lateral (middle), and posterior (right) views.
Figure 2. Consensus phylogeny of sauropods based on the strict consensus trees of Taylor (2009), Ksepka & Norell (2010) and Whitlock (2011). The first of these provides the skeleton of the tree including outgroups, basal sauropods and macronarians; the second gives the positions of Erketu and Qiaowanlong; the last provides a detailed phylogeny of Diplodocoidea. Taxa with bifid neural spines are highlighted in blue. Haplocanthosaurus and Suuwassea, whose positions are disputed by Woodruff & Fowler (2012) are shown in bold.
Figure 3. A middle cervical vertebra of a human in cranial view showing paired bony processes for the attachment of dorsal muscles to the neural spine. Uncatalogued specimen from the anthropology teaching collection at the University of California, Santa Cruz.
Figure 4. Cervical vertebrae of Camarasaurus supremus AMNH 5761 cervical series 1 in anterior view, showing different degrees of bifurcation of the neural spine. Modified from Osborn & Mook (1921: plate 67).
Figure 5. Sacra of Apatosaurus excelsus holotype YPM 1980 (left) and A. ajax holotype YPM 1860 (right) in ventral view and at the same scale, modified from Ostrom & McIntosh (1966: plates 27 and 29).
Figure 6. From left to right: Apatosaurus sp. OMNH 1670 D?5 in anterior view, A. louisae CM 3018 D5 in anterior view, and A. sp. OMNH 1382 in posterior view. Total heights of the vertebrae are 1350 mm, 1060 mm, and 950 mm, respectively, although OMNH 1382 would have been somewhat taller when the spine was intact. The arrow next to OMNH 1382 points to the unfused neurocentral synchondrosis.
Figure 7. BYU 12613, a posterior cervical of Diplodocus, in dorsal (top), left lateral (left), and posterior (right) views. It compares most favourably with C14 of D. carnegii CM 84/94 (Hatcher, 1901: plate 3) despite being only 42% as large, with a centrum length of 270 mm compared to 642 mm for C14 of D. carnegii.
Figure 8. Third and fifteenth cervical vertebrae of Diplodocus carnegii CM 84/94 in posterior view. The cotyle diameters of the vertebrae are 69 and 245 mm, respectively. Modified from Hatcher (1901: plate 6).
Figure 9. Degree of neural spine bifurcation of presacral vertebrae in well-preserved Morrison Formation sauropod specimens representing several taxonomic groups. In all taxa with deep bifurcations, these are concentrated around the cervico-dorsal transition. ‘No data’ markers may mean that the vertebrae are not preserved (e.g., posterior dorsals of Suuwassea emilieae ANS 21122), that the degree of bifurcation cannot be assessed (e.g., anterior cervicals of Barosaurus lentus AMNH 6341), or that the serial positions of the vertebrae are uncertain so they contribute no information on serial changes in bifurcation (e.g., the four cervical vertebrae known for Barosaurus lentus YPM 429). The Camarasaurus specimens are roughly in ontogenetic order: C. lentus CM 11338 is a juvenile, C. grandis YPM 1905 and GMNH-PV 101/WPL 1995, and C. supremus AMNH 5761 are adults, and C. lewisi BYU 9047 is geriatric. See text for sources of data.
Figure 10. Apatosaurus parvus UWGM 15556 (formerly A. excelsus CM 563) cervicals 7, 5, 4 and 3 in anterior (top) and right lateral views, showing that neural spines of anterior cervicals are unsplit even in adult diplodocids. From Gilmore (1936: plate 31).
Figure 11. Apatosaurus parvus UWGM 15556 D4 (left) and D3 (right) in anterior (top), right lateral, and posterior views, showing that neural spine bifurcation generally does not persist farther back than the mid-dorsals even in adult diplodocids. From Gilmore (1936: plate 32).
Figure 12. Serially comparable dorsal vertebrae in different Camarasaurus species or ontogenetic stages. Left: dorsal vertebra 7 (top) and dorso-sacral (= D11) (bottom) of C. supremus AMNH 5760 and 5761 “Dorsal Series II” both in posterior view, with unsplit neural spines. Modified from Osborn & Mook (1921: plate 71). Right: dorsal vertebrae 7-11 of C. lewisi holotype BYU 9047 in posterodorsal view, with split spines. From McIntosh, Miller et al. (1996: plate 5). Scaled so that the height of D11 is roughly equivalent in the two specimens.
Figure 13. Cervical vertebrae of Diplodocus carnegii CM 84/94 in right lateral view. Note the increasing complexity of the laminae and pneumatic cavities in successively posterior cervicals. From Hatcher (1901: plate 3).
Figure 14. Plateosaurus engelhardti (originally P. trossingensis) SMNS 13200 cervical vertebrae 3-8 in left lateral view, showing the gradual acquisition of diapophyseal laminae in successively posterior cervicals. The PODL becomes strongly developed in the dorsal vertebrae. C8 is roughly 15 cm long. Abbreviations (after Wilson, 1999): PCDL, posterior centrodiapophyseal lamina; PODL, postzygodiapophyseal lamina; PRDL, prezygodiapophyseal lamina.
Figure 15. An isolated cervical of cf. Diplodocus MOR 790 8-10-96-204 (A) compared to D. carnegii CM 84/94 C5 (B), C9 (C), and C12 (D), all scaled to the same centrum length. Actual centrum lengths are 280 mm, 372 mm, 525 mm, and 627 mm for A-D respectively. MOR 790 8-10-96-204 modified from Woodruff & Fowler (2012: figure 2B), reversed left to right for ease of comparison; D. carnegii vertebrae from Hatcher (1901: plate 3).
Figure 16. Diplodocid anterior dorsal vertebrae. Left and right, dorsal vertebrae 3 and 4 of adult Apatosaurus louisae holotype CM 3018, from Gilmore (1936: plate 25). Center, juvenile neural arch MOR 790 7-17-96-45, modified from Woodruff & Fowler (2012: figure 5B), corrected for shearing and scaled up.
Figure 17. Apatosaurus parvus CM 563/UWGM 15556 caudals 8 and 7 in right lateral (top) and posterior view, from Gilmore (1936: plate 33). Arrows highlight shallow antero-posterior notches in the tips of the neural spines.
Figure 18. Middle cervical vertebrae of Barosaurus AMNH 6341 (top) and Supersaurus BYU 9024 (bottom) in left lateral view, scaled to the same centrum length. The actual centrum lengths are 850 mm and 1380 mm, respectively. BYU 9024 is the longest single vertebra of any known animal.
Figure 19. The sixth cervical vertebrae of Diplodocus carnegii CM 84/94, Suuwassea emilieae ANS 21122, and Apatosaurus sp. CM 555 in left lateral view, scaled to the same centrum length. Actual centrum lengths are 442 mm, 258 mm, and 327 mm, respectively. Diplodocus carnegii modified from Hatcher (1901: plate 3), reversed left to right for ease of comparison. Suuwassea emilieae from a photo provided by Jerry Harris; the same photo also appears as Harris (2006c: text-figure 7B). Apatosaurus photographs by Mathew Wedel, digitally composited by Michael Taylor.
Figure 20. Pelves of diplodocids and Haplocanthosaurus. From left to right: Apatosaurus excelsus CM 568, Diplodocus carnegii CM 84/94, and Haplocanthosaurus priscus CM 572. All in left lateral view. From Hatcher (1903: plate 4).
Figure 21. Posterior, mid and anterior cervical vertebrae, in right lateral view, of (top to bottom), Haplocanthosaurus, Apatosaurus louisae CM 3018 (from Gilmore, 1936: plate 24, reversed for ease of comparison) and Diplodocus carnegii CM 84/94 (from Hatcher, 1901: plate 3), scaled to roughly the same size. For the diplodocids, we illustrate C13, C9 and C4. For Haplocanthosaurus, we illustrate C14 of H. priscus (from Hatcher, 1903: plate 1) and C9 and C4 of H. utterbacki (from plate 2).
Figure 22. Posterior cervical vertebrae C15 and C14, in posterior view, of (top to bottom), Haplocanthosaurus priscus CM 572 (from Hatcher, 1903: plate 1), Apatosaurus louisae CM 3018 (from Gilmore, 1936: plate 24) and Diplodocus carnegii CM 84/94 (from Hatcher, 1901: plate 6), scaled to the same centrum-to-neural-spine height (these are the only Haplocanthosaurus cervical vertebrae that Hatcher illustrated in posterior view.)
Figure 23. Posterior, middle and anterior dorsal vertebrae, in right lateral view, of (top to bottom), Haplocanthosaurus, Apatosaurus louisae CM 3018 (from Gilmore, 1936: plate 25, reversed for ease of comparison) and Diplodocus carnegii CM 84/94 (from Hatcher, 1901: plate 7), scaled to roughly the same size. For the diplodocids, we illustrate D9, D5 and D2. For Haplocanthosaurus, which has four more dorsals, we illustrate D13 and D7 of H. priscus (from Hatcher, 1903: plate 1) and D2 of H. utterbacki (from plate 2).
Figure 24. Posterior, mid and anterior dorsal vertebrae, in posterior view, of (top to bottom), Haplocanthosaurus priscus CM 572 (from Hatcher, 1903: plate 1), Apatosaurus louisae CM 3018 (from Gilmore, 1936: plate 25) and Diplodocus carnegii CM 84/94 (from Hatcher, 1901: plate 7), scaled to the same height of the mid dorsal. For the diplodocids, we illustrate D9, D5 and D1. For Haplocanthosaurus, which has four more dorsals, we illustrate D13, D6 and D1.
Figure 25. Neurocentral fusion in Haplocanthosaurus. A, B. Posterior cervical vertebra C?12 of sub-adult H. utterbacki holotype CM 879: A, X-ray in right lateral view; B, transverse CT slice showing separate ossificaton of centrum and neural arch. C, D. Mid-dorsal vertebra D6 of adult H. priscus holotype CM 572: X-rays in (C) right lateral and (D) posterior view, showing fully fused neural arch. Modified from Wedel (2009: figure 6).