18. Crampin, S. Geological and industrial implications of extensive-dilatancy anisotropy. Nature 328, 491–496 (1987). 19. Sobolev, S. V., Babeyko, A. Y. & Garfunkel, Z. Desert Group. Thermo-mechanical model of the Dead Sea Transform. Earth Planet. Sci. Lett. (submitted). 20. Wolfe, C. J., Vernon, F. L. III & Al-Amri, A. Shear-wave splitting acrosswestern Saudi Arabia: The pattern of upper mantle anisotropy at a Proterozoic shield. Geophys. Res. Lett. 26, 779–782 (1999). 21. Reinecker, J., Heidbach O. & Mu ¨ller, B.The 2003 release of the World Stress Map khttp://www.world- stress-map.org/l (2003). 22. Bartov, Y., Avni, Y., Calvo, R. & Frieslander, U. The Zofar fault — A major intra-rift feature in the Arava Rift Valley. Geol. Surv. Israel Curr. Res. 11, 27–32 (1998). 23. Savage, M. K. Seismic anisotropy and mantle deformation: What have we learned from shear wave splitting? Rev. Geophys. 37, 65–106 (1999). 24. McNamara, D. E., Owens, T. J., Silver, P. G. & Wu, F. T. Shear wave anisotropy beneaththe Tibetan Plateau. J. Geophys. Res. 99, 13655–13665 (1994). 25. Hirn, A. et al. Seismic anisotropy as an indicator of mantle flow beneath the Himalayas and Tibet. Nature 375, 571–574 (1995). 26. Herquel, G., Tapponnier, P., Wittlinger, G., Mei, J. & Danian, S. Teleseismic shear wave splitting and lithospheric anisotropy beneath and across the Altyn Tagh fault. Geophys. Res. Lett. 26, 3225–3228 (1999). 27. Nicolas, A. & Christensen, N. I. in Composition, Structure and Dynamics of the Lithosphere- Asthenosphere System (eds Fuchs, K. & Froidevaux, C.) Geodyn. Ser. 16, 111–1123 (1987). Supplementary Information accompanies the paper on www.nature.com/nature. Acknowledgements We are grateful to the Geophysical Institute of Israel, the National Ministry of Infrastructure of Israel, the Natural Resources Authority of Jordan, and the An-Najah University in Nablus, Palestine Authority, for their support. The instruments were provided by the Geophysical Instrument Pool of the GeoForschungsZentrum Potsdam. The experiment was supported by the Deutsche Forschungsgemeinschaft, the GeoForschungsZentrum Potsdam, and the Minerva Dead Sea Research Centre. Competing interests statement The authors declare that they have no competing financial interests. Correspondence and requests for materials should be addressed to G.R. (rumpker@gfz-potsdam.de). Desert Seismology Group M. Weber 1,2 , K. Abu-Ayyash 3 , Z. Ben-Avraham 4 , R. El-Kelani 5 , Z. Garfunkel 6 , C. Haberland 1 , A. Hofstetter 7 , R. Kind 1 , J. Mechie 1 , A. Mohsen 1 , I. Qabbani 3 , K. Wylegalla 1 1 GeoForschungsZentrum, Telegrafenberg, 14473 Potsdam, Germany; 2 University of Potsdam, Potsdam, Germany; 3 Natural Resources Authority, Amman, Jordan; 4 Tel Aviv University, Tel Aviv, Israel; 5 Ah-Najah National University, Nablus, Palestine Authority; 6 Hebrew University, Jerusalem, Israel; 7 Geophysical Institute of Israel, Lod, Israel .............................................................. The oldest articulated chondrichthyan from the Early Devonian period Randall F. Miller 1 , Richard Cloutier 2 & Susan Turner 1,3 1 Steinhammer Palaeontology Laboratory, New Brunswick Museum, Saint John, New Brunswick E2K 1E5, Canada 2 Laboratoire de Biologie e´volutive, Universite ´ du Que ´bec a ` Rimouski, Rimouski, Quebec G5L 3A1, Canada 3 School of Geosciences, Monash University, Clayton, Victoria 3088, and Queensland Museum, South Brisbane, Queenland 4101, Australia ............................................................................................................................................................................. Chondrichthyans (including living sharks, skates, rays and chi- maeras) have a fossil record of scales and dermal denticles perhaps dating back to the Late Ordovician period, about 455 million years ago 1,2 . Their fossil tooth record extends to the earliest Devonian period, almost 418 million years ago 3 , whereas the oldest known articulated shark remains date from the Early Devonian period 4 , about 394 million years ago 5 . Here we report the discovery of an articulated shark that is almost 409 million years old 5 from the Early Devonian (early Emsian) period of New Brunswick, Canada. The specimen, identified as Doliodus problematicus (Woodward) 6 , sheds light on the earliest chondrichthyans and their interrelationships with basal jawed vertebrates. This species has been truly problematic 7 . Previously known only from isolated teeth 2,6,8 , it has been identified as an acanthodian and a chondrichthyan. This specimen is the oldest shark showing the tooth families in situ, and preserves one of the oldest chondrichthyan braincases. More notably, it shows the presence of paired pectoral fin-spines, previously unknown in cartilaginous fishes. Isolated and articulated Early to Middle Devonian shark speci- mens are rare 1,9 . Until now, the oldest partial articulated shark, consisting of the braincase articulated with parts of the visceral skeleton, was Pucapampella from the Early Devonian of South Africa 4 . Significant Middle Devonian partially articulated speci- mens include Pucapampella from Bolivia 10,11 , Antarctilamna prisca from Antarctica and Australia 7,12 , and Gladbachus adentatus from Germany 13 . Specimen NBMG (New Brunswick Museum, Geology) 10127/ 1a,b-4 consists of the anterior part of D. problematicus, forward of the mid-trunk region (Fig. 1). It is preserved dorsoventrally, oriented dorsal side up with exo- and endoskeletal elements pre- served, including characteristic prismatic calcified cartilage, teeth, scales and large fin-spines. The specimen is cleaved in five parts, providing a series of transverse sections through the head and branchial region. The preserved length is 23 cm, suggesting a body length of perhaps 50–75 cm on the basis of shark comparative anatomy. Prismatic calcified cartilage, considered to be a chondrichthyan synapomorphy 1,14 , compose the neurocranium and splanchnocra- nium. The articulated jaws confirm that D. problematicus possessed tooth families and provide early evidence in chondrichthyans of the relationship of teeth to the dental lamina 1,15 . Most teeth are partially buried; however, tooth families that are visible have teeth stacked in a row, with newer teeth sitting in a space representing the position of the dental lamina groove. Tooth bases abut a prominent dark- brown concave surface, interpreted as preserved basal connective tissue. The dentition shows weak dignathic and disjunct mono- gnathic heterodonty, suggesting revision of earlier opinions about the evolution of shark teeth 16 . Functional upper and lower teeth, offset anteriorly, oppose one another with sharp lateral edges of principal cusps connecting in a scissors movement. The functional teeth show the asymmetry and range of variation previously recognized 2,6,8 , and verify the position and number of tooth types in the jaw. Teeth are not seen in the symphysial and parasymphysial portions of the lower jaw. The right side of the lower jaw shows about 15 tooth families; the left side has only 11 tooth families preserved, with bases of at least three anterior rows present in the cartilage. Tooth families expose up to three teeth each. Near the posterior jaw articulation, flat basal pads might represent the most posterior teeth. Lower tooth families are seen in cross-section, showing the apparently highly vascular- ized lower edge and new tooth germs. The last three to four posterior tooth families do not show dental membranes and thus are more like modified dermal scales. In a few teeth, two large divergent lateral outer cusps with two to four intermediate small cusps can be seen in cross-section. These and a thin section of a D. problematicus tooth from the National Museums of Scotland (RSM1897.51.46) show that the cusps are formed of orthodentine 2 . Bases are rounded and cap-like with a row of five to six large foramina in the slightly concave foot. Cross-sections show osteodentine with a basal lamellar tissue, which directly abuts the dental membrane. The difference between the structure of the smaller posterior teeth (equivalent to type specimen BMNH (Brit- ish Museum, Natural History) P.6540) and that of branchial denticles is still strong, contrary to one hypothesis on the origin of teeth 17 . Woodward 6 diagnosed the taxon “Diplodus” problematicus on an isolated tooth (BMNH P.6540), concluding that the diplodont (xenacanth) tooth type was present by Early Devonian. Traquair 8 letters to nature NATURE | VOL 425 | 2 OCTOBER 2003 | www.nature.com/nature 501