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Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 Annual Scientific Session “Ion Popescu Voiteşti”. Cluj University Press, Cluj-Napoca, 2008: 57- 59. Raath M.A. Fossil vertebrate studies in Rhodesia: a new dinosaur(Reptilia: Saurischia) from near the Trias-Jurassic boundary. Arnoldia, 1972, 5: 1-37. Scotese C.R. Palaeomap Project. www.scotese.com, 2002. Upchurch P. The Anatomy, Phylogeny, and Syste- matics of the Sauropod Dinosaurs. Ph.D. Thesis, Univ. Cambridge, 1993: 489. 196 Upchurch P. Sauropod Phylogeny and Palaeoecology. Gaia, 1994, 10: 249-260. Wild R. Ein Sauropoden-Rest (Reptilia, Saurischia) aus dem Posidonienschiefer (Lias, Toarcium) von Holzmaden. Stuttgart. Beitr. Natur., (B), 1978, 41: 1-15. Wilson J.A., Sereno P.C. Early Evolution and higher- level phylogeny of sauropod dinosaurs. Journal of Vertebrate Paleontology, 1998, 18: Supplement (2): 1-68.
Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 Ammonoid Morphology Changes Across the Triassic-Jurassic Boundary L.M. Longridge, P.L. Smith * , J. Zhang, B. Liang Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia, V6T 1Z4, Canada (E-mail: llongridge@eos.ubc.ca; psmith@eos.ubc.ca; jzhang@jinshanmines.com; bo.liang@mckesson.com) The end-Triassic mass extinction was the last severe bottleneck in ammonoid evolution before their final demise at the end of the Cretaceous (e.g. Raup and Sepkoski, 1982; Dommergues et al., 1996). The ammonoid diversity collapse was prolonged in the Late Triassic and only one earliest Hettangian genus served as the ‘root stock’ for the spectacular adaptive radiation that followed (Guex, 2001, 2006). We use bivariate and simple multivariate techniques to examine changes in shell geometry and suture style from the Carnian to the Bajocian. Based on simple shell geometry, this interval has three phases: 1) the Late Triassic pre-extinction phase which includes diverse shell shapes and heteromorph genera with four types of shell geometry (Figs.1, 2.1); 2) the Hettangian through Aalenian post- extinction phase, where expansion rate is negatively correlated with volution and involute, slowly expanding forms are lacking (Figs.1, 2.2); and 3) the Bajocian recovery phase in which shell shape diversity increases and heteromorphs of a single shell geometry reappear (Figs.1, 2.3). Correlations between umbilical width and expansion rate versus whorl shape vary from negligible to moderately strong. The most depressed shells are usually located in slowly expanding or evolute regions of morphospace. In ammonoids with nearly equidimensional whorls, there is a trend towards greater hydrodynamic efficiency with time. In the Late Triassic, ammonoids with the simplest suture style tend to be evolute whereas ammonoids with the most complex suture style are usually more involute. In nearly all cases, Hettangian ammonoids are chara- cterized by complex sutures and more evolute mor- phologies. Key words: Morphospace; Ammonoids; Triassic- Jurassic; Extinction References: Dommergues J.L., Laurin B., Meister C. Evolution of ammonoid morphospace during the Early Jurassic radiation. Paleobiology, 1996, 22: 219-240. Guex J. Environmental stress and atavism in ammonoid evolution. Eclogae Geologicae Helvetiae, 2001, 94: 321-328. Guex J. Reinitialization of evolutionary clocks during sublethal environmental stress in some inverte- brates. Earth and Planetary Science Letters, 2006, 242: 240-253. Raup D.M. Geometric analysis of shell coiling: Coiling in ammonoids. Journal of Paleontology, 1967, 41: 43-65. Raup D.M., Sepkoski J.J.Jr. Mass extinction in the marine fossil record. Science, 1982, 215: 1501- 1502. Smith P.L. The implications of data base management systems to paleontology: A discussion of Jurassic ammonoid data. Journal of Paleontology, 1986, 60: 327-340. Fig.1 Schematic of shell morphology of ammonoids in W-U morphospace W = expansion rate; U = umbilical ratio (Smith, 1986). The W=1/U line indicated on the figure is the off-lap line (Raup, 1967), which separates coiled forms where consecutive whorls are in contact from those where whorls are uncoiled. Modified from Raup (1967) 197
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