Paleobiology, 46(1), 2020, pp. 41–57 DOI: 10.1017/pab.2020.7 Article Extinction of North American Cuvieronius (Mammalia: Proboscidea: Gomphotheriidae) driven by dietary resource competition with sympatric mammoths and mastodons Gregory James Smith and Larisa R. G. DeSantis Abstract.—The gomphotheres were a diverse and widespread group of proboscideans occupying Eurasia, North America, and South America throughout the Neogene. Their decline was temporally and spatially heterogeneous, and the gomphotheres ultimately became extinct during the late Pleistocene; however, the genus Cuvieronius is rarely represented in late Pleistocene assemblages in North America. Two alternative hypotheses have been invoked to explain this phenomenon: (1) competitive exclusion by sympatric mam- moths and mastodons or (2) ecologic displacement due to an environmental transition from closed forests to open grasslands. To test whether competition for resources contributed to the demise of North Ameri- can Cuvieronius, we present herein a large collection of stable isotope and dental microwear data from populations occupying their Pleistocene refugium in the Atlantic Coastal Plain. Results suggest that Cuvieronius consumed a wide range of resources with variable textural and photosynthetic properties and was not specialized on either grasses or browse. Further, we document evidence for the consumption of similar foods between contemporaneous gomphotheres, mammoths, and mastodons. The generalist feeding strategy of the gomphotheres likely facilitated their high Miocene abundance and diversity. How- ever, this “jack of all trades and master of none” feeding strategy may have proved challenging following the arrival of mammoths and likely contributed to the extirpation of Cuvieronius in North America. Gregory James Smith. Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, Tennessee 37240, U.S.A. E-mail: [email protected] Larisa R. G. DeSantis. Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37232, U.S.A.; and Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, Tennessee 37240, U.S.A. E-mail: [email protected] Accepted: 4 January 2020 Data available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.6djh9w0x1 Introduction (ca. 0.3–0.012 Ma sensu Bell et al. 2004) (Car- Gomphotheres (subfamily Gomphotheriinae rasco et al. 2005). The success of the mammoth sensu lato) are temporally and spatially prolific; radiation and its temporal correlation with the the clade became dominant in North America demise of the gomphotheres in North America in the Miocene and emigrated to South Amer- has led some to argue that competition from ica from North America after the closure of early mammoths caused the extirpation of the the Isthmus of Panama between 2.5 and 0.125 gomphotheres (i.e., competitive exclusion; Ma (Webb 1985; Reguero et al. 2007; Wood- Kurtén and Anderson 1980). However, others burne 2010; Mothé et al. 2017). Their dietary have argued that cooling climates and the flexibility is hypothesized to have facilitated emergence of steppe/prairie habitats would their successful migration in contrast to mam- have displaced the gomphotheres from North moths and mastodons, which remained in Cen- America even in the absence of competition tral and North America despite the continental (i.e., ecological displacement; Dudley 1996). connection (Pérez-Crespo et al. 2016). On the These two competing hypotheses have yet to other hand, gomphothere abundance, diver- be fully tested or resolved. sity, and geographic range in North America The competitive exclusion principle attests rapidly drops off after the arrival of mam- that when closely related species with similar moths, and the gomphotheres are rarely repre- niches coexist, one of these taxa will either out- sented in Rancholabrean faunal assemblages compete the other or they will partition their © 2020 The Paleontological Society. All rights reserved. This is an Open Access article, distributed under the terms of the DownloadedCreative from https://www.cambridge.org/core Commons Attribution licence. IP address: (http://creativecommons.org/licenses/by/4.0/), 170.106.40.139, on 26 Sep 2021 at 22:06:40, subject to the Cambridge which permits Core terms unrestricted of use, available at https://www.cambridge.org/core/termsre-use, distribution, and reproduction. https://doi.org/10.1017/pab.2020.7 in any medium, provided the original work is properly cited. 0094-8373/20 42 GREGORY JAMES SMITH AND LARISA R. G. DESANTIS niches to exploit different resources (Hardin (Hulbert 2001). Mastodons, represented by the 1960). Niche partitioning studies in fossil ungu- genus Zygolophodon, and gomphotheres, lates are commonly carried out through a including the genus Gomphotherium,have reconstruction of diet using methods similar been recovered from Miocene sites in both Flor- to those implemented here and often show ida and Texas (Lambert and Shoshani 1998). the alteration of dietary preference by one or Later representatives of these clades, including multiple organisms to facilitate coexistence the mastodon Mammut and the gomphothere with other organisms (e.g., in bovids, camelids, Rhynchotherium, are found extensively in the and horses; MacFadden et al. 1999; Bibi 2007; southern latitudes of North America and Cen- DeSantis et al. 2009; Yann and DeSantis 2014). tral America beginning in the early Pliocene Similarly, studies of proboscidean dietary (Lambert and Shoshani 1998; Lucas and Alvar- niche partitioning often indicate high dietary ado 2010; Pasenko 2012). Cuvieronius—the only flexibility among focal taxa (e.g., Calandra gomphothere genus found in North America, et al. 2008; Rivals et al. 2015; Pérez-Crespo South America, and Central America—appears et al. 2016). Most paleoecological studies on in Florida by ca. 2 Ma (Arroyo-Cabrales et al. gomphotheres suggest that they were already 2007; Lucas 2008; Lucas and Alvarado 2010). highly flexible in their dietary choices, capable The mammoth specimens recovered from the of fluctuating between grazing, browsing, and ACP are coeval with some of the earliest Mam- mixed-feeding habits (e.g., MacFadden and muthus records in North America from the Rio Cerling 1996; Koch et al. 1998, 2004; MacFad- Grande valley of southern New Mexico (Lucas den 2000; Fox and Fisher 2001, 2004; Sánchez et al. 2017). Cuvieronius is known in Florida et al. 2004; Calandra et al. 2008; DeSantis et al. until ca. 0.5 Ma (Lucas 2008); however, some 2009; Rivals et al. 2015; Pérez-Crespo et al. of the youngest Cuvieronius records known in 2016; Zhang et al. 2017; González-Guarda North America come from the Big Cypress et al. 2018). However, on a smaller spatial and Creek site of east Texas (Lundelius et al. 2013, temporal scale, gomphotheres tended to restrict 2019). Mammuthus and Mammut are last their dietary preferences due to abiotic (cli- known from North America in late Pleistocene matic) or biotic (competitive) factors; for sites between 14 and 10 ka (Bell et al. 2004; Bar- example, South American populations of Notio- nosky et al. 2014). Thus, the samples used in mastodon showed an adaptive trend toward this study include some of the earliest and latest either grazing or browsing habits in the late examples of these proboscidean taxa in the Pleistocene due to habitat differentiation (Sán- ACP. chez et al. 2004; Mothé and Avilla 2015), This study aims to fill an important spatial South China populations of Sinomastodon and temporal gap in the paleoecological record were restricted to the consumption of browse of proboscideans. In this paper, we present a due to competition with co-occurring Stegodon quantitative analysis of dietary differences (Zhang et al. 2017), and the East Asian gom- among Pleistocene proboscideans in North photherid Protanancus was competitively dis- America using the integration of stable isotope placed by the amebelodont Platybelodon geochemistry and dental microwear texture (Wang et al. 2015). Recognizing this pattern of analysis (DMTA). The design of this study dietary restriction in smaller populations, we allows for both a regional comparison over therefore limit our analysis herein to Pleisto- time (from the early to late Pleistocene) and cene populations of gomphothere (Cuvieronius local, site-based assessments. Specifically, mul- hyodon), mammoth (Mammuthus columbi), and tiproxy data are used to test the following mastodon (Mammut americanum) occupying hypotheses: (1) North American Cuvieronius the Atlantic Coastal Plain (ACP) physiogeo- consumed similar resources as sympatric Mam- graphic province of North America (Fig. 1A). muthus and/or Mammut; and (2) Cuvieronius, While both the mastodon and the gom- Mammuthus, and Mammut altered their dietary phothere families were present in the ACP habits in the ACP throughout the Pleistocene. since the middle Miocene, the earliest mam- Evidence for the consumption of similar moths did not arrive until the early Pleistocene resources by Cuvieronius and Mammuthus or Downloaded from https://www.cambridge.org/core. IP address: 170.106.40.139, on 26 Sep 2021 at 22:06:40, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/pab.2020.7 DIETARY RESOURCE COMPETITION IN PROBOSCIDEANS 43 Downloaded from https://www.cambridge.org/core. IP address: 170.106.40.139, on 26 Sep 2021 at 22:06:40, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.