Gastropod Evidence Against the Early Triassic Lilliput Effect: COMMENT

Gastropod evidence against the Early Triassic Lilliput effect: COMMENT

COMMENT: doi: 10.1130/G31614C.1 and Bottjer, 2004). The authors are to be congratulated on discovering some of the largest Early Triassic gastropods, but a handful of specimens larger M.L. Fraiser1, R.J. Twitchett2, J.A. Frederickson1, B. Metcalfe3, than 1 cm from among thousands of Early Triassic fossils does not refute and D.J. Bottjer4 the hypothesis that Early Triassic gastropods exhibited the Lilliput effect. 1 Department of Geosciences, University of Wisconsin–Milwaukee, (3) Brayard et al.’s data set is defi cient. A meager data set of only Milwaukee, Wisconsin 53201, USA three collections was presented, with no details of sampling strategy. 2School of Geography, Earth and Environmental Sciences, University Fraiser and Bottjer’s (2004) fi nding that 99% of the Sinbad Limestone of Plymouth, Plymouth PL4 8AA, UK Member fauna (incorrectly stated as the “Sinbad Formation” in Brayard 3Faculty of Earth and Life Sciences, Free University, 1081 HV et al. [2010]) were less than 1 cm in height was based on mechanical Amsterdam, The Netherlands disaggregation of 27,200 cm3 of material from 120 m of strata exposed 4Department of Earth Sciences, University of Southern California, over a 3,750 km2 area, and its examination under a dissecting microscope. Los Angeles, California 90089, USA Brayard et al. did not report any gastropods smaller than 4 mm, in contrast to Fraiser and Bottjer (2004) and Bouchet et al. (2002) in which 66% of Brayard et al. (2010) assert that their study of late Early Triassic gastropods were <2 mm and 34% of mollusks were <4.1 mm in height, gastropods provides evidence against the post-extinction Lilliput effect. respectively. New data from the Griesbachian Dinwoody Formation reveal Regrettably, their data provide no such evidence. that 100% of examined gastropods are <1.60 mm in height. At least some The Lilliput effect as defi ned by Urbanek (1993) is a quantifi able, of the measured gastropods reported by Brayard et al. should have been temporary decrease in the size of surviving taxa in the immediate after- under 4 mm in height (e.g., juveniles). The absence of very small (<4 mm) math of an extinction event. Demonstrating that the Lilliput effect is or gastropods recorded by Brayard et al. suggests a sampling bias in their is not present in the aftermath of an extinction event requires the collec- analysis. Crucially, too, they neglected statistical testing to determine the tion and analysis of quantitative pre- and post-extinction body-size data signifi cance of perceived differences between their new data and previ- for those taxa that range through the crisis interval. A fundamental fl aw ously published data. of the Brayard et al. study is the lack of any quantitative size data from Brayard et al. have not reported evidence to refute the Lilliput effect the pre-extinction Late Permian and the immediate post-extinction Early among Early Triassic gastropods, or demonstrated that recovery occurred Triassic. Their data comprise only Olenekian (late Early Triassic) samples signifi cantly earlier than previously proposed. If the authors can demon- that signifi cantly post-date the extinction event (by at least 2 m.y.), and are strate, with quantitative data, no signifi cant difference in gastropod body inadequate for any discussion of the Lilliput effect. Furthermore, two of sizes from the pre-extinction Late Permian through to the post-recovery the fi ve genera in the study fi rst appear in the Early Triassic, and therefore Middle Triassic, then they will have refuted the Lilliput effect in one region. cannot have experienced Urbanek’s (1993) Lilliput effect. Other studies questioning the Lilliput effect also omit the fi rst 2 m.y. of REFERENCES CITED the Triassic (e.g., Nützel, 2005), while those working at high resolution all Bouchet, P., Lozouet, P., Maestrati, P., and Heros, V., 2002, Assessing the report small body size in the earliest Early Triassic (e.g., Posenato, 2009). magnitude of species richness in tropical marine environments: Exceptionally Quantitative pre- and post-extinction size data have demonstrated that the high numbers of molluscs at a New Caledonia site: Biological Journal of the Lilliput effect (sensu Urbanek, 1993) is confi ned to the fi rst 1–2 conodont Linnean Society, Linnean Society of London, v. 75, p. 421–436, doi:10.1046/ zones of the Early Triassic (Twitchett, 2007). Fraiser et al. (2005) proposed j.1095-8312.2002.00052.x. Brayard, A., Nützel, A., Stephen, D.A., Bylund, K.G., Jenks, J., and Bucher, that small body size among gastropods was less pronounced by the Spath- H., 2010, Gastropod evidence against the Early Triassic Lilliput effect: ian, and was a primarily low-latitude phenomenon, perhaps related to pulses Geology, v. 38, p. 147–150, doi:10.1130/G30553.1. of deleterious environmental conditions that differed from ocean to ocean Fraiser, M.L., and Bottjer, D.J., 2004, The non-actualistic Early Triassic gastropod through the Early Triassic. That the largest early Induan Omphaloptycha fauna: A case study of the Lower Triassic Sinbad Limestone Member: Palaios, v. 19, p. 259–275, doi:10.1669/0883-1351(2004)019<0259:TNETGF>2.0 are recorded in East Greenland supports this hypothesis (Twitchett, 2007). .CO;2. Empirical data also demonstrate that body size in many marine groups Fraiser, M.L., Twitchett, R.J., and Bottjer, D.J., 2005, Unique microgastropod remained relatively low for much of the Early Triassic, beyond the earliest biofacies in the Early Triassic: Indicator of long-term biotic stress and the zones of the Induan (e.g., Fraiser et al., 2005; Twitchett, 2007): the Lilliput pattern of biotic recovery after the end-Permian mass extinction: Comptes Rendus. Palévol, v. 4, p. 543–552. effect sensu lato. Even using this broader defi nition of the Lilliput effect, Nützel, A., 2005, A new Early Triassic gastropod genus and the recovery of the Brayard et al. study still fails to provide the evidence needed to refute it. gastropods from the Permian/Triassic extinction: Acta Palaeontologica (1) Brayard et al. erroneously use a uniformitarian approach to argue Polonica, v. 50, p. 19–24. that the Lilliput effect did not affect Early Triassic gastropods by citing a Posenato, R., 2009, Survival patterns of macrobenthic marine assemblages during the end-Permian mass extinction in the western Tethys (Dolomites, Italy): study in which 60% of modern mollusk species are smaller than 10 mm Palaeogeography, Palaeoclimatology, Palaeoecology, v. 280, p. 150–167, (Bouchet et al., 2002). Small (<10 mm) gastropods are indeed found in all doi:10.1016/j.palaeo.2009.06.009. modern marine environments, but a key difference between modern and Taylor, J.D., and Glover, E., 2003, Food of giants—Field observations on the many Early Triassic ecosystems is that large gastropods are common to- diet of Syrinx aruanus (Linnaeus, 1758) (Turbinellidae) the largest living day (Fraiser and Bottjer, 2004). Brayard et al.’s largest gastropods, termed gastropod, in Wells, F.E., Walker, D.I., and Jones, D.S., eds., The Marine Flora and Fauna of Dampier, Western Australia: Perth, Western Australian “Gullivers” and reaching ~7 cm in size, are tiny compared to modern ex- Museum, p. 217–223. amples such as Syrinx aruanus which has a shell up to 910 mm in length Twitchett, R.J., 2007, The Lilliput effect in the aftermath of the end-Permian (Taylor and Glover, 2003). extinction event: Palaeogeography, Palaeoclimatology, Palaeoecology, (2) Despite these new specimens, gastropods are still much larger be- v. 252, p. 132–144, doi:10.1016/j.palaeo.2006.11.038. Urbanek, A., 1993, Biotic crises in the history of Upper Silurian graptoloids: fore and after the Early Triassic. The largest Permian and Middle Triassic A paleobiological model: Historical Biology, v. 7, p. 29–50, doi:10.1080/ gastropods reported are 12–15 cm and 20 cm in height, respectively (Fraiser 10292389309380442.

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