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Modelling the Abundance of Megaherbivorous Dinosaurs of the Morrison Formation (Late Jurassic, Western USA) James O

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Modelling the Abundance of Megaherbivorous Dinosaurs of the Morrison Formation (Late Jurassic, Western USA) James O This article was downloaded by: [Dr Daniel Marty] On: 09 October 2012, At: 00:13 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Historical Biology: An International Journal of Paleobiology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ghbi20 Giants on the landscape: modelling the abundance of megaherbivorous dinosaurs of the Morrison Formation (Late Jurassic, western USA) James O. Farlow a , I. Dan Coroian b & John R. Foster c a Department of Geosciences, Indiana-Purdue University, 2101 East Coliseum Boulevard, Fort Wayne, IN, 46805, USA b Department of Mathematical Sciences, Indiana-Purdue University, 2101 East Coliseum Boulevard, Fort Wayne, IN, 46805, USA c Museum of Western Colorado, P.O. Box 20000, Grand Junction, CO, 81502, USA Version of record first published: 21 Jul 2010. To cite this article: James O. Farlow, I. Dan Coroian & John R. Foster (2010): Giants on the landscape: modelling the abundance of megaherbivorous dinosaurs of the Morrison Formation (Late Jurassic, western USA), Historical Biology: An International Journal of Paleobiology, 22:4, 403-429 To link to this article: http://dx.doi.org/10.1080/08912961003787598 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Historical Biology Vol. 22, No. 4, December 2010, 403–429 Giants on the landscape: modelling the abundance of megaherbivorous dinosaurs of the Morrison Formation (Late Jurassic, western USA) James O. Farlowa*, I. Dan Coroianb and John R. Fosterc aDepartment of Geosciences, Indiana-Purdue University, 2101 East Coliseum Boulevard, Fort Wayne, IN 46805, USA; bDepartment of Mathematical Sciences, Indiana-Purdue University, 2101 East Coliseum Boulevard, Fort Wayne, IN 46805, USA; cMuseum of Western Colorado, P.O. Box 20000, Grand Junction, CO 81502, USA (Received 11 December 2009; final version received 23 February 2010) The ecosystem impact of megaherbivorous dinosaurs of the Morrison Formation would have depended on their abundance (number of animals per unit of habitat area) on the landscape. We constrain Morrison megaherbivore abundance by modelling dinosaur abundance in terms of carrying capacity (K), average body mass (ABM) and animal’s energy needs. Two kinds of model are presented: ‘demand-side’ models that estimate K in terms of the aggregate energy demand of the dinosaur community, and ‘supply-side’ models that estimate K in terms of retrodicted primary productivity. Baseline values of K, ABM and energy needs for the models are further derived from comparisons with modern large herbivores, and from the composition of the megaherbivore fauna from a particular stratigraphic interval of the Morrison, but in all models a broad range of fractions and multiples of these baseline parameters are considered. ‘Best-guess’ estimates of Morrison megaherbivore abundance suggest an upper limit of a few hundred animals across all taxa and size classes per square kilometre, and up to a few tens of individuals of large subadults and adults. Keywords: Morrison Formation; terrestrial paleoecology; herbivorous dinosaurs Introduction: really big herbivores large-mammal faunas mostly are Plio-Pleistocene assem- Cenograms have become a standard tool in mammalian blages characterised by proboscideans, rhinos, horses, paleoecology (Legendre 1986, 1989; Gingerich 1989; hippos, cervids and bovids. The two dinosaur faunas come Ducrocq et al. 1994; Gunnell and Bartels 1994; Maas and from particular stratigraphic levels in the Late Cretaceous Kraus 1994; Montuire 1995, 1998, 1999; Morgan et al. Dinosaur Park Formation (Currie and Russell 2005) and 1995; Gibernau and Montuire 1996; Gunnell 1997; the Late Jurassic Morrison Formation (Foster 2003, 2007), Montuire and Desclaux 1997; Dashzeveg et al. 1998; selected to make them as comparable to the paleomammal faunas as possible by minimising time averaging. Wilf et al. 1998; Croft 2001; Montuire and Marcolini 2002; Several interesting observations can be made. The Storer 2003; Palombo et al. 2005; Tsubamoto et al. 2005; biggest members of the Australian faunas were small Geraads 2006; Go´mez Cano et al. 2006; Palombo and compared with other big herbivores, perhaps reflecting the Giovinazzo 2006; Costeur and Legendre 2008), albeit with small land area and/or harsh conditions of Australia some reservations expressed (Rodrı´guez 1999). Graphs (Farlow et al. 1995; Burness et al. 2001; Murray and that plot the natural logarithm of body mass (in grams) of Vickers-Rich 2004). There is a broad overlap in the sizes each species of non-volant, non-predatory mammal in a of the larger members of most of the remaining Downloaded by [Dr Daniel Marty] at 00:13 09 October 2012 fauna against the decreasing rank order of each species’ mammalian faunas and the Dinosaur Park assemblage body mass in the fauna (Figure 1) are thought to reflect the (although comparison is complicated by the different ways structure of the vegetation and climate, but what interests in which body masses were estimated, with dental us here is what cenograms show about the structure of measurements usually used for Eurasian mammals, and large-herbivore faunas. Figure 1 plots cenograms of the postcranial dimensions or scale models used for other biggest [body mass ¼ 8000 g (natural log ca. 9) or larger] groups). Some of the Pleistocene mammalian herbivores herbivores in a selection of Cenozoic large-mammal (and seem to have been substantially bigger animals than the bird) faunas and two dinosaur faunas. Marsupials and hadrosaurs, ceratopsians and ankylosaurs of the Dinosaur dromornithid birds comprise the large herbivores in the two Park Formation (cf. Christiansen 2004). Australian faunas (Murray and Vickers-Rich 2004). The But one assemblage stands out as being especially Argentinian fauna not only includes edentates, litopterns characterised by giants. The trend defined by the nine largest and notoungulates, but also large rodents, a horse, a plant-eating dinosaur species (in this conservative tabulation peccary, camelids, deer and a gomphothere. The remaining of valid species and their estimated body masses) from Zone *Corresponding author. Email: [email protected] ISSN 0891-2963 print/ISSN 1029-2381 online q 2010 Taylor & Francis DOI: 10.1080/08912961003787598 http://www.informaworld.com 404 J.O. Farlow et al. Figure 1. Comparative cenograms of paleofaunas of ‘large’ (estimated body mass ¼ 8000 g or more) herbivorous mammals, birds and dinosaurs. As the mammal body sizes are conventional allometric estimates based on skeletal or dental parameters, the body masses of the larger taxa may be somewhat off (?too large). The Morrison dinosaur body-size estimates are based on the version of an allometric equation relating body mass to propodial circumferences presented by Packard et al. (2009); estimating dinosaur masses this way probably minimises differences in mass estimates between the Morrison dinosaurs and the megamammals. Data from Croft (2001 and personal communication); Montuire and Desclaux (1997), Montuire and Marcolini (2002), and Montuire personal communication; Morgan et al. (1995); P. Murray personal communication; Currie and Russell (2005); Palombo et al. (2005), Palombo and Giovinazzo (2006), and Palombo personal communication; Tsubamoto et al. (2005); Geraads (2006) and personal communication. 5 of the Morrison Formation (updated from Foster 2007) and (ultimately) decomposer organisms. So, if we could shows no overlap with the other faunas. Most of these constrain how common the herbivorous giants were, we dinosaurs were sauropods, and their sizes are comparable to could better reconstruct the nature of interactions between Downloaded by [Dr Daniel Marty] at 00:13 09 October 2012 those seen in other sauropod faunas (cf. Paul 1998; the dinosaurs and their environment. This paper, by Henderson 1999; Seebacher 2001; Aberhan et al. 2002; modelling the interaction of physiological and ecological Mazzetta et al. 2004; Carpenter 2006; Foster 2007; Lovelace parameters we consider most likely to have affected the et al. 2007; Gunga et al. 2008; Sander and Clauss 2008; maximum abundance of Morrison plant-eating dinosaurs, Royo-Torres et al. 2009; Taylor 2009; Klein et al. in press). attempts to set reasonable limits on how common these Body mass is related to numerous aspects of organism giants could have been. physiology and ecology (Peters 1983), including the Some proportion of the secondary productivity of abundance of animals in ecological communities Morrison megaherbivores was undoubtedly consumed by (Damuth 1987, 1993, 2007; White et al. 2007), and carnivores (cf.
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