NEWS AND VIEWS
PA~EONTOLOGY------reassessments. Late extinctions of amphibians An example of this is the Triassic Jurassic boundary region in western North Andrew Milner America which is still in a state of strati graphic flux and may yet force further THE amphibian order Temnospondyli was Australia'·'. Because the fossil was found reconsideration of the timing of temno the main group of early amphibians from in an assemblage of dinosaur bones it was spondyl extinctions. Murry has recently the middle of the Carboniferous (315 briefly identified in an exhibition cata noted10 an assemblage of vertebrates from million years ago) to the end of the Triassic logue' as the mandible of an ankylosaurid a Dockum Formation horizon in Apache (215 million years ago). During this time, dinosaur! It has now been shown by Jupp Canyon, New Mexico, in which the these animals filled many of the niches and Warren' to belong to a large temno metoposaurid temnospondyl Anaschisma now occupied by salamanders, crocodiles spondyl. These authors are uncertain as to (supposedly restricted to the Upper Tri and even large freshwater fish. Until just its family position, but a comparison with assic) is associated with scales of the fish over 10 years ago, no post-Triassic Triassic specimens confirms that it Redfieldius (previously found only in the temnospondyls were known and it was belongs to the Plagiosauridae and that it Jurassic). The Metoposauridae is one of reasonably assumed that all had become has specific resemblances to Plagio- the last remaining temnospondyl families
extinct at the end of the Triassic. Con 100 sequently, they have been incorporated as components of supposed Triassic extinc ~ 1 w tion events -'. But a series of new, little II: publicized discoveries"-' extends the strati graphical range of several temnospondyl lineages beyond the Triassic (see figure) and suggests that, as at the Cretaceous .·~ Tertiary boundary event, amphibians ·:u; u- (/) I passed unscathed through the events <( which made many reptiles extinct. a: {j The first specimen to force a recon :::l...., sideration of temnospondyl chronology 0m:m was the huge complete skeleton from the 215 Lower Jurassic (200 million years ago) ui of Queensland which Warren and Hutch <( inson' named Siderops. This specimen II: 1- belongs to the Chigutisauridae, a family of !i:ii!ii 248 neotenous temnospondyls (in which the Br Ca Ch Mt PI larval body form is retained by the adult) previously known from the Triassic of South America and Australia. Before the Chronological distribution of some temnospondyl amphibian families during the Mesozoic. Br, significance of this single relict lineage Brachyopidae; Ca, Capitosauridae; Ch, Chigutisauridae; Mt, Metoposauridae; PI, Plagiosauridae. could be determined, several more fossils Numbers on the left are in millions of years. were found in east and central Asia. One sternum from the Middle Triassic of still believed to have contributed to a late of these is a well-preserved skull from the Germany. The plagiosaurs were wide Triassic extinction event. It is not yet clear Middle Jurassic ( 175-million-year-old) headed, neotenous forms superficially whether the fish represents an unprece dinosaur assemblage found at Zigong, resembling large flattened axolotls dentedly early record or the amphibian Sichuan, China' named Sinobrachyops, (salamanders). Within the past decade, a new late record. If the latter turns out a member of the widespread family therefore, it has become clear that up to be the case, then there will be little Brachyopidae. This specimen represents a to three temnospondyl families - the remaining evidence that amphibians were different lineage of neotenous temno Chigutisauridae, Brachyopidae and Capito involved in any Triassic global extinction spondyls not previously recorded later sauridae- survived into the Jurassic and event, at least at the family level. If, as than the Middle Triassic. Another is the one, the Plagiosauridae, into the Lower seems likely, there are patterns of extinc series of temnospondyl bones from the Cretaceous. tion and replacement among Triassic later Middle Jurassic ( 165-million-year In global terms, none of these families reptile families, it may be inadvisable to old) estuarine beds of the Kirgiz region of contributed to Triassic extinctions. But all dilute them with amphibian data. D Soviet central Asia just described by these discoveries have been made either in Nessov'. These bones seem to belong to Australia, which was at the end of an Andrew Milner is in the Department of Biology, the Capitosauridae, a family of crocodile Australasian-Antarctic peninsula by that Birkbeck College, University of London, Malet like forms. The associated fauna includes time, or in central and east Asia, which Street, London WC1E 7HX, UK. several fish more usually associated with was cut off from the other northern conti- 1. Benton. M.J. Spec. Pap. Palaeont. 33.185---202 (1985). the Triassic, together with typical Jurassic nents by the Turgai Straits in the Middle 2. Benton. M.J. in The Beginning of the Age of Dinosaurs Cretaceous reptiles. So at this locality, Jurassic. A conservative interpretation (ed. Padian. K.) 303--320 (Cambridge University Press. 1986). estuarine fish and amphibians seem to might be that temnospondyls did become 3. Olsen. P.E. &Sues. H.D. in TheBeginningoftheAgeof represent an entire relict ecosystem; extinct in the late Triassic in Europe, Dinosaurs (ed. Pad ian. K.) 321-351 (Cambridge Univer· sity Press. 1986). Nessov suggests that it would have been Africa and the Americas while persisting 4. Warren. A.A. & Hutchinson. M.N. Phil. Trans. R. Soc. difficult for other forms to replace families in partial or complete isolation in Asia and B303. 1-62 (1983). 5. Dong. Z. Vert. Palasiat. 23. 301-306 (1985). which had adapted to the osmotically Australasia, implying a regional rather 6. Nessov. L.A. Acta zoo/. cracov. 31. 475---486 (19881 demanding estuarine environment. than a global extinction event. But 7. Jupp. R & Warren. A.A. Alcheringa 10. 99-124 (1986) The most remarkable amphibian dis although a few Lower and Middle Jurassic 8. Flannery, T.F. & Rich, T.H. Aust. nat. hist. 20, 195---198 (1981). covery is that of a temnospondyl jaw from tetrapod assemblages in Europe and the 9. Smith, B.J. (ed.) Dinosaurs from China 1-52 (National the Lower Cretaceous (about 130-million A · h b d' d Museum of Victoria. 1982). mencas ave now een ISCOVere ' 10. Murry, P.A. J. Arizona-Nevada Acad. Sci. 22. 73--84 year-old) Strzelecki Formation of Victoria, there is plenty of potential for further (19871 NATURE ·VOL 338 · 9 MARCH 1989 117