geosciences Article Stratigraphic Changes in the Pliocene Carnivoran Assemblage from Hagerman Fossil Beds National Monument, Idaho Dennis R. Ruez Jr. 1,2,3 1 Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712, USA 2 Current affiliations: Department of Environmental Studies, University of Illinois at Springfield, Springfield, IL 62703, USA; [email protected]; Tel.: +1-217-206-8425 3 Research and Collections Center, Illinois State Museum, Springfield, IL 62703, USA Academic Editor: Olaf Lenz Received: 2 January 2016; Accepted: 26 February 2016; Published: 4 March 2016 Abstract: At least 17 carnivoran taxa occur in the Pliocene Glenns Ferry Formation at Hagerman Fossil Beds National Monument (HAFO), Idaho. This assemblage was examined for stratigraphic changes in species distribution, specimen abundance, and species diversity. Three relatively common mustelids, Trigonictis cookii, Trigonictis macrodon, and Mustela rexroadensis, occur at most stratigraphic levels, but are absent during an interval coinciding with the coolest time segment at HAFO. It is within this gap that two less-common mustelids, Ferinestrix vorax and Buisnictis breviramus, first appear at HAFO; they persist up-section with the more common mustelids listed above. Specimens of Borophagus hilli are restricted to the warm intervals at HAFO, irrespective of the relative abundance of surface water. The other canid at HAFO, Canis lepophagus, is more abundant during the dry intervals at HAFO, regardless of the estimated paleotemperature. Most remarkable is the recovery of many taxa impacted by abrupt climate change, although a notable change is the much higher relative abundance of carnivoran species following a return to warm temperatures. Keywords: Glenns Ferry; Blancan; paleoclimate 1. Introduction Hagerman Fossil Beds National Monument (HAFO) in southern Idaho (Figure1) is internationally significant because it is one of the richest sources of Pliocene vertebrates. Hundreds of localities within the exposed beds of the Glenns Ferry Formation have produced many thousands of fossil mammals housed at museums across the United States [1]. These localities range in age from about 4.2 to 3.1 Ma [2]. This is the first in a series of notes that document the stratigraphic distribution of fossil mammals at HAFO. Comparisons are here made with the estimated paleoclimate during the Pliocene represented in the Glenns Ferry Formation. This study examines the distribution of carnivorans at HAFO, but the relative paucity of those fossils, compared to some other groups, means that future studies may have important implications for the interpretations below. There are at least 54 species of mammals at HAFO, including 17 species of carnivorans [1]. Eight species of carnivorans were named on holotypes from HAFO; of these, six are still valid. Publication on these specimens began in the 1930s [3–5], but comprehensive description of the carnivorans from HAFO was completed much later [6]. The taxonomy of these species is reviewed elsewhere with a discussion on their geographic distributions [1]. Geosciences 2016, 6, 15; doi:10.3390/geosciences6010015 www.mdpi.com/journal/geosciences Geosciences 2016, 6, 15 2 of 9 Geosciences 2016, 6, 15 2 of 9 FigureFigure 1. Location of Hagerman Fossil Beds National MonumentMonument withinwithin Idaho.Idaho. Dotted red lineline outlinesoutlines thethe SnakeSnake RiverRiver Plain-YellowstonePlain-Yellowstone PlateauPlateau sensusensu LeemanLeeman [[7],7], butbut excludesexcludes thethe OwyheeOwyhee PlateauPlateau inin southwesternsouthwestern Idaho. Idaho. Inset Inset map map shows shows the the boundaries boundaries of HAFO of HAFO (in green) (in green) to the to west the westof the of Snake the SnakeRiver, River,city of cityHagerman of Hagerman (yellow), (yellow), paved pavedroads (black roads (blacklines), lines),and Oregon and Oregon Trail (purple Trail (purple lines—dashed lines—dashed where whereinferred). inferred). Topographic Topographic map is adapted map isadapted from the fromDigital the Atlas Digital of Idaho Atlas [8] of in Idaho accordance [8] in accordance with their usage with theirpolicy. usage policy. 2.2. Materials Materials and and Methods Methods InIn spitespite ofof thethe species-levelspecies-level diversitydiversity andand overalloverall numbernumber ofof mammalianmammalian fossilsfossils atat HAFO,HAFO, thethe numbernumber ofof specimensspecimens referablereferable toto carnivoranscarnivorans isis low;low; onlyonly 361361 fossilsfossils werewere recognizedrecognized duringduring thethe preparationpreparation of this manuscript. Only Only specimens specimens with with well-established well-established locality locality data data were were included included in inthis this study. study. Additionally, Additionally, only only specimens specimens that that could could be be identified identified to to species, species, or or as as Taxidea sp.sp. oror HomotheriumHomotherium sp.sp. (the(the sparsesparse materialmaterial doesdoes notnot allowallow forfor moremore specificspecific identification),identification), werewere used.used. TheThe 256256 specimensspecimens usedused herehere areare listedlisted inin SupplementarySupplementary filefile (List(List S1).S1). (Collections(Collections ofof fossilsfossils atat HAFOHAFO have continued since the data in this manuscript were collected, resulting in additional specimens, particularly mustelids [9], and the possible addition of two carnivoran taxa [10].) Geosciences 2016, 6, 15 3 of 9 have continued since the data in this manuscript were collected, resulting in additional specimens, particularlyGeosciences 2016 mustelids, 6, 15 [9], and the possible addition of two carnivoran taxa [10].) 3 of 9 Although a Minimum Number of Individuals (MNI) is commonly preferred in analysis of Although a Minimum Number of Individuals (MNI) is commonly preferred in analysis of abundance in a fauna (e.g., Lyman [11]), it is not an empirical observational unit such as the number abundance in a fauna (e.g., Lyman [11]), it is not an empirical observational unit such as the number of identifiable specimens (NISP). In fact, the MNI must be calculated from the NISP, and the method of identifiable specimens (NISP). In fact, the MNI must be calculated from the NISP, and the method involved can include various criteria [12]. In the case of a single locality with abundant fossils, involved can include various criteria [12]. In the case of a single locality with abundant fossils, comparisonscomparisons of of MNI MNI instead instead of of NISP NISP cancan give significantly significantly different different results. results. However, However, at atHAFO HAFO there there areare hundreds hundreds of of localities, localities, soso thethe MNIMNI wouldwould have to to be be calculated calculated for for each each locality locality because because it is it is unlikelyunlikely that that different different localities localities willwill containcontain specimensspecimens from from the the same same individual. individual. Because Because the the ratio ratio ofof localities localities to to specimens specimens is is so so high, high, aboutabout two to on one,e, and and no no localities localities are are especially especially abundant abundant with with carnivorans,carnivorans, the the MNI MNI and and NISP NISP ofof carnivoranscarnivorans at HAFO are are similar. similar. In In fact, fact, Bjork Bjork [6] [6 examined] examined 196 196 carnivorancarnivoran fossils, fossils, but but calculated calculated anan MNIMNI ofof 173. In In this this particular particular case, case, use use of of NISP NISP instead instead of ofMNI MNI hashas little little impact impact on on the the results. results. ProxyProxy data data for for paleoecological paleoecological interpretationsinterpretations for HAFO HAFO (Figure (Figure 2)2) follow follow Ruez Ruez [13]. [ 13 Stratigraphic]. Stratigraphic distributiondistribution of of specimens specimens isis basedbased onon placementplacement of localities localities on on the the Hagerman Hagerman Horse Horse Quarry Quarry (HHQ) (HHQ) datumdatum (sensu (sensu Ruez Ruez [ 2[2]).]). ThisThis facilitatesfacilitates comparisoncomparison of of sites sites across across HAFO HAFO.. Specimen Specimen and and species species abundancesabundances were were plotted plotted atat 1-m1-m intervalsintervals with a sliding window window of of 20 20 m m for for the the stratigraphic stratigraphic span span encompassingencompassing the the majoritymajority of localities localities at at HAFO: HAFO: 900 900 to to1005 1005 m on m the on theHHQ HHQ datum, datum, or about or about 4.0 to 4.03.2 to 3.2Ma. Ma By. By using using a asliding sliding window window some some detail detail may may be be lost, lost, but but the the pattern pattern will will more more accurately accurately reflect reflect overalloverall trends trends and and not not be be as as subject subject to to distorting distorting spikesspikes from particularly fossili fossiliferousferous localities. localities. Further, Further, the sliding window acknowledges that there is difficulty in placing some localities stratigraphically. the sliding window acknowledges that there is difficulty in placing some localities stratigraphically. FigureFigure 2. 2.Pliocene Pliocene paleoecological paleoecological interpretations at at HAFO. HAFO. Temperature Temperature trend trend is isadjusted adjusted to tothe the chronologychronology of of deposits deposits at at HAFO HAFO [2[2].]. SolidSolid line indicatesindicates the the temperature temperature