Journal of Paleontology, 91(3), 2017, p. 512–547 Copyright © 2017, The Paleontological Society 0022-3360/15/0088-0906 doi: 10.1017/jpa.2017.5
Late Miocene chondrichthyans from Lago Bayano, Panama: Functional diversity, environment and biogeography
Victor J. Perez,1,2 Catalina Pimiento,3,4 Austin Hendy,4,5 Gerardo González-Barba,6 Gordon Hubbell,7 and Bruce J. MacFadden1,2
1Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA ⟨
victorjperez@ufl.edu⟩; ⟨
bmacfadd@flmnh.ufl.edu⟩ 2Department of Geological Sciences, University of Florida, Gainesville, FL 32611, USA 3Paleontological Institute and Museum, University of Zürich, Ch-8006 Zürich, Switzerland ⟨
catalina.pimientohernandez@pim.uzh.ch⟩ 4Smithsonian Tropical Research Institute, Center for Tropical Paleoecology and Archaeology, Box 2072, Panama, Republic of Panama 5Natural History Museum of Los Angeles, Los Angeles, CA 90007, USA ⟨
ahendy@nhm.org⟩ 6Museo de Historia Natural, Area de Ciencias del Mar, La Paz, Universidad Autonoma de Baja California Sur, AP 23080, Mexico
⟨
gerardo@uabcs.mx⟩ 7Jaws International, Gainesville, FL, USA ⟨
jawsint@aol.com⟩
Abstract.—This newly described chondrichthyan fauna from the late Miocene Chucunaque Formation of Lago Bayano reveals a prolific and highly diverse assemblage from Panama, and one of the richest shark faunas from the Neotropics. Strontium geochronology indicates an age of 10–9.5Ma for the chonrichthyan-bearing strata. Field efforts resulted in 1429 identifiable specimens comprising at least 31 taxa, of which at least eight are new to the documented fossil record of Panama. With this information an analysis of functional diversity was conducted, indicating ecosystems dominated by generalist species feeding upon a wide range of organisms, from plankton to marine mammals. A probabilistic approach of paleobathymetric estimation suggests a neritic environment. Previous studies based on foraminifera have suggested that the Chucunaque Formation had a greater Pacific Ocean affinity, making this the first Miocene chondrichthyan fauna described from the Pacific shelf of Panama. However, our geographic comparisons show that this fauna has mixed Caribbean and Pacific biogeographic affinities, which likely supports the previously purported connection between chondrichthyan faunas during the lateMiocene.
Introduction
LagoBayano in Panama Province, Panama is an artificial lake that contains an extraordinarily rich assemblage of chondrichthyans. Hundreds of shark and ray teeth erode from host sediments and concentrate on the shorelines of emerged lake islands as a result of annual water-level fluctuations. Prior to the damming of the Rio Bayano drainage that created Lago Bayano, Stewart (1966) made a geological reconnaissance of this region and mapped what is nowLago Bayano as the Chucunaque Formation (Shelton, 1952). Chondrichthyan remains were noted to be common in the marine mudstones and sandstones of the deeply incised river valleys, although no collections were
retained.More recently, Coates et al. (2004) mapped the Chucunaque Formation throughout the Darien Province of Panama. Even though marine vertebrates were not reported, this study confirmed a late Miocene age for the unit, and noted a foraminiferal assemblage indicating a Pacific Ocean affinity. In the present study, new biostratigraphic and Sr-isotope analyses derived from marine invertebrate fauna yield ages of 10–9.5 Ma for chondrichthyan-bearing strata in Lago Bayano. The closure of a Central American Seaway (CAS) and
consequent formation of the Isthmus of Panama during the Neogene extremely affected tropical American (=Neotropical)
marine communities and increased the biogeographic complexity of the region (e.g., Coates and Obando, 1996). Miocene chondrichthyan faunas are fundamental to understand these processes because they were: (1) abundant and widely distributed during this time, and (2) have been proven to be good paleobathy- metry indicators of the deposits adjacent to the CAS (e.g., Pimiento et al., 2013a; Carillo-Briceño et al., 2015a). However, previous studies onMiocene chondrichthyans of Panama have been limited to Caribbean faunas (e.g., the Gatun Formation, Gillette, 1984; Pimiento et al., 2010; Pimiento et al., 2013a; theCulebra Formation, Pimiento et al., 2013b; and theChagres Fromation, Carrillo-Briceño et al., 2015a). Hence, the chondrichthyan fauna of Lago Bayano is the first Miocene fauna from the Pacific shelf of Panama to be described. The only other chondrichthyan fauna described from the PacificofPanamawas theEocene TonosiFormationfromthe Azuero Peninsula (Vasquez and Pimiento, 2014). Other late Miocene shark assemblages from the region include Ecuador (Longbottom, 1979; Carrillo-Briceño et al., 2014), Venezuela (Sánchez-Villagra et al., 2000; Aguilera andRodrigues deAguilera, 2001; Carrillo-Briceño et al., 2015b), Jamaica (Donovan and Gunter, 2001), Costa Rica (Laurito and Valerio, 2008), and Grenada (Portell et al., 2008). All of these studies have provided a better understanding on the composition of marine communities during a time of rapid change.
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