New Fossil Evidence on the Sister-Group of Mammals and Early Mesozoic Faunal Distributions Author(s): Neil H. Shubin, A. W. Crompton, Hans-Dieter Sues and Paul E. Olsen Source: Science, New Series, Vol. 251, No. 4997 (Mar. 1, 1991), pp. 1063-1065 Published by: American Association for the Advancement of Science Stable URL: http://www.jstor.org/stable/2875224 Accessed: 03-04-2017 21:50 UTC

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This content downloaded from 128.103.149.52 on Mon, 03 Apr 2017 21:50:59 UTC All use subject to http://about.jstor.org/terms This content downloaded from 128.103.149.52 on Mon, 03 Apr 2017 21:50:59 UTC All use subject to http://about.jstor.org/terms acteristic feature of undisputed Mesozoic cingulum; (iv) upper postcanines with a suchid crocodyliform archosaurs, reveal fur- mammals is unilateral occlusion. The lower buccal cingulum; (v) postcanine teeth with ther close similarities among continental te- jaw on the active side moves dorsomedially incipiently divided, massive roots. From trapod assemblages of Early Jurassic age. relative to the upper teeth during occlusion. these features, the family Tritheledontidae is The sphenodontian Clevosaurus is known This movement produces wear facets on the hypothesized to include the genera Diar- from Upper Triassic fissure-fillings in En- lingual face of the uppers and the buccal face thrognathus, Pachygenelus, and Tritheledon. gland (16), and closely related forms are of the lowers. In mammals this pattern of The dentition of Tritheledon is poorly known from the Forest Sandstone of Zim- jaw movement produces complex and con- known but dosely resembles that of Diar- babwe and the lower Lufeng Formation of sistent multiple wear facets on the molars. In thrognathus in the buccolingual expansion of Yunnan, China, both of which are Early these taxa the teeth are progressively added the upper postcanine teeth (1, 2, 11). The- Jurassic in age (17). The protosuchid Proto- from front to back and are not replaced. In rioherpeton does not possess any of the fea- suchus is known elsewhere from the Lower contrast to other nonmammalian cyn- tures above and cannot be considered to be Jurassic Glen Canyon Group of the south- odonts, Pachygenelus cf P. monus also pos- a tritheledontid. The phylogenetic status of western United States and the upper Storm- sesses unilateral occlusion but lacks precise, Chaliminia is uncertain because of the poor berg Group of southern Africa (18). Th,e matching wear facets. The matching facets preservation of the only known specimen. dinosaurian material from the McCoy on the teeth of Pachygenelus extend over the The newly discovered tritheledonts main- Brook Formation recovered to date is frag- entire lingual surface of the upper postca- ly support the cynodont phylogeny original- mentary but it includes an anchisaurid pro- nines and the buccal surface of the lower ly proposed by Hopson and Barghusen (1). sauropod and teeth of an ornithischian in- postcanines (Fig. 1A). Occlusal wear facets Dental characteristics such as the develop- distinguishable from Lesothosaurus from are also present on the incisors and canines ment of a buccal cingulum on the upper southern Africa. Both dinosaurian families of Pachygenelus cf. P. monus (Fig. 1F). In teetf, matching ocdusal wear on the buccal appear to have a worldwide distribution Pachygenelus cf. P. monus the postcanine surface of the lower postcanines and the during the Early Jurassic. teeth are replaced alternately and this pro- lingual surface of the upper postcanines, and The homogeneity of tetrapod distribu- cess appears to have continued throughout contact between the dentary and squamosal tions during the Early Jurassic represents the life. As new postcanines erupted, they con- bones apparently evolved only once among continuation of a trend toward increased tacted opposing teeth on the opposite jaw. cynodonts. cosmopolitanism that began in the late Pa- This resulted in the less well-defined facets The occurrence of Pachygenelus cf. P. mo- leozoic (19). Similar cosmopolitan distribu- on the postcanines of Pachygenelus cf. P. nus in Nova Scotia underscores a pattem of tions are also seen in Early Jurassic terrestrial monus. The other putative mammalian sister- wide, in many cases virtually cosmopolitan, floral assemblages that are dominated by group, the Trityledontidae, have postcanine distribution of Early Jurassic taxa of terres- cheirolepidaceous conifers (10). This trend wear facets that lack buccal-lingual postca- trial tetrapods. Other tetrapod taxa from the in terrestrial biotic cosmopolitanism is nine wear and do not suggest patterns of McCoy Brook Formation, particularly the broadly contemporaneous with the initial unilateral occlusion. Consequently, the tri- sphenodontian lepidosaurs and the proto- stages of the breakup of Pangaea. These tylodontid and mammal-tritheledontid oc- dusal patterns cannot be homologized as a single character as has been suggested (15). RPC WF EC In Pachygenelus cf. P. monus, there is a G close coupling of enamel distribution on the teeth to patterns of occlusal wear: enamel that borders on the occluding surfaces is A M~~~~~ thin whereas enamel on nonocduding sur- faces is thick (as seen on the apical portion of the principal postcanine cusp). Once the thin enamel is worn away the apical edge of thick enamel is exposed. This feature pro- vides a resistant cutting edge on the apical surface of the tooth. A :~ WF ;..3 . - A .

1064 SCIENCE, VOL. 251

This content downloaded from 128.103.149.52 on Mon, 03 Apr 2017 21:50:59 UTC All use subject to http://about.jstor.org/terms patterns suggest that the persistence of Pan- Bioestratigr. 1 Congr. Latinoam. Paleonttol. (Buenos 14. D. Stern and A. W. Crompton, J. Dent. Res. 67, Aires) 2, 123 (1980). 231 (1988); D. Stern, thesis, Harvard University gaea throughout the Triassic provided few 5. S. Chatterjee, Science 220, 1151 (1983). (1989). barriers for the migration of terrestrial ver- 6. J. A. Hopson and A. W. Crompton, in preparation. 15. T. Rowe, J. Vertebr. Paleontol. 8, 241 (1988). tebrates. The initial stages of rifling in the 7. F. E. Grine, C. E. Gow, J. W. Kitching, Proc. 16. N. C. Fraser, Philos. Trants. Roy. Soc. London Ser. B Electron Microsc. Soc. S. Afr. 9, 99 (1979). 321, 125 (1988). Late Triassic resulted in no corresponding 8. A. W. Crompton, Proc. Zool. Soc. London Ser. B 17. H.-D. Sues et al., in preparation. provinciality of terrestrial vertebrate distri- 130, 183 (1958). 18. J. M. Clark, thesis, University of Chicago, Chicago, 9. P. E. Olsen, N. H. Shubin, M. H. Anders, Science bution by the Early Jurassic. IL (1986). 237, 1025 (1987). 19. N. H. Shubin and H.-D. Sues, in preparation.

REFERENCES AND NOTES 10. P. E. Olsen and P. M. Galton, Palaeonttol. Afr. 25, 21. W. W. Amaral, W. A. Clemens, N. Greenwald, J. A. 87 (1984). Hopson, K. Padian, M. Russell, and M. Seidl pro- 1. J. A. Hopson and H. Barghusen, in The Ecology and 11. C. E. Gow, Proc. R. Soc. London Ser. B 208, 461 vided helpful discussion and comments on the Biology of Mammal-like Reptiles, N. Hotton, P. D. (1980). manuscript. F. A. Jenkins, Jr., and W. W. Amaral MacLean, J. J. Roth, E. C. Roth, Eds. (Smithsonian 12. A. W. Crompton, Annt. S. Afr. Mus. 46, 479 provided facilities and extraordinary expertise for Institution Press, Washington, DC, 1986), pp. 83- (1963); Proc. Zool. Soc. London Ser. B 140, 697 laboratory and field investigation. Field permits and 106; T. S. Kemp, Mammal-like Reptiles and the (1963); ..and F. Ellenberger, Atin. S. Afr. logistical support were provided by the Nova Scotia Origin of Mammals (Academic Press, New York, Mus. 44, 1 (1957). Museum, Halifax, Nova Scotia. Supported by grants 1982). 13. A. W. Crompton and F. A. Jenkins, Jr., Annui. Rev. from the National Geographic Society, the Museum 2. J. A. Hopson and J. W. Kitching, Palaeontol. Afr. Earth Planet. Sci. 1, 131 (1973); in Mesozoic Matn- of Comparative Zoology of Harvard University, and 14, 71 (1972). mals: The First Two- Thirds of Mammalian History, J. the Department of Biology of the University of 3. J. F. Bonaparte and M. C. Barberena, J. Paleontol. Lillegraven, Z. Kielan-Jaworowska, W. Clemens, Pennsylvania. 49, 931 (1975). Eds. (Univ. of California Press, Berkeley, 1979), pp. 4. J. F. Bonaparte, Actas 2 Congr. Argent. Paleontol. 59-73. 10 September 1990; accepted 29 November 1990

Salicornia bigelovii Torr.: An Oilseed Halophyte for desert environment at the northern Gulf of California. Seeds were collected near Puerto Seawater Irrigation Peniasco in Estero Morua. Trials in 1982 were conducted in the same 1-ha field and EDWARD P. GLENN, JAMES W. O'LEARY,* M. CAROLYN WATSON, with the same methods previously described T. LEWIS THOMPSON, ROBERT 0. KUEHL for other halophytes (6). Trials from 1984 to 1988 were conducted in a 0.5-ha field The terrestrial halophyte, Salicornia bigelovii Torr., was evaluated as an oilseed crop nearby. Both fields had sandy soils typical of for direct seawater irrigation during 6 years of field trials in an extreme coastal desert light agricultural soils in the region and were environment. Yields of seed and biomass equaled or exceeded freshwater oilseed crops divided into individually irrigated, 200 m2 such as soybean and sunflower. The seed contained 26 to 33 percent oil, 31 percent flood plots. At both sites irrigation water protein, and was low in fiber and ash (5 to 7 percent). The oil and meal were extracted with a salinity range of 38 to 42 per mil was by normal milling equipment, and the oil was high in linoleic acid (73 to 75 percent) supplied daily from seawater wells. In field and could replace soybean oil in chicken diets. The meal had antigrowth factors, 1, seawater that passed through a shrimp attributed to saponins, but could replace soybean meal in chicken diets amended with aquaculture facility, which added nitrogen the saponin antagonist, cholesterol. Salicornia bigelovii appears to be a potentially and other nutrients to the water, was used, valuable new oilseed crop for subtropical coastal deserts. and no supplemental fertilizer was needed. Field 2 was irrigated with unenriched sea- T HERE ARE TWO APPROACHES TO DE- of the seed spikes on the upper one-third water, of and plots received fertilizer additions veloping crops tolerant of seawater- the plant. The seeds are approximately 1 equivalentmg to 200 kg of N per hectare or concentration salinity. One is to in- and germinate directly on seawater. Salicor- more, as urea, diammonium phosphate, or crease the tolerance of present crops (1), but nia bigelovii emerged as a potential seawater ammonium nitrate. Rainfall was less than 90 the difference between the upper limit of salt oilseed crop from a screening of wild halo- mm annually and the soil in the root zone tolerance currently exhibited by crop plants phytes (5-7) and was selected for seawater was at seawater salinity or higher at all times and that required to tolerate seawater salin- field trials including determination of seed (6). ity is great (2). An alternative is to select yield and seed analyses. The standard seeding rate of 25 kg ha-' from the large pool of halophytes, plants The trials were conducted at Puerto Pe- produced a mean plant density at harvest of which already have the requisite salt toler- niasco, Sonora, Mexico, in an extreme coastal 323 plants/m2 (SD, 249; n = 49; observa- ance, those that might make desirable crops (3). Salicornia bigelovii Torr. is a leafless, an- Table 1. Summary of annual Salicornia bigelovii seed and biomass yields at field 2, Puerto Pefiasco, nual salt-marsh plant with green, jointed, Sonora, Mexico (n, number of plots). Crops were sown during a 2- to 3-week period during the succulent stems that ultimately form termi- months indicated and were harvested the following September or October in the year indicated. In nal fruiting spikes in which seeds are borne 1986 12 plots were planted in February and 12 in April. (4). In subtropical regions it may grow to be a large, upright plant, 50 cm tall, with most Month Year Biomass SE n Seed SE n sown (kg m2) (g m2)

E. P. Glenn, J. W. O'Leary, M. C. Watson, T. L. December 1984 2.46 0.18 9 233 13 9 Thompson, Environmental Research Laboratory, 2601 April 1985 1.39 0.04 15 208 11 15 East Airport Drive, Tucson, AZ 85706. 1986 1.27 0.05 12 177 5 12 R. 0. Kuehl, Statistical Support Unit, College of Agri- February 1986 1.51 0.08 12 193 10 12 culture, University of Arizona, Tucson, AZ 85721. 1987 1.98 0.04 15 246 7 15 *Present address: Bioresources Research Facility, 250 1988 1.44 0.09 20 139 11 20 East Valencia Road, Tucson, AZ 85706.

1 MARCH 1991 REPORTS 1065

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