Late pleistocene shrews and bats (Mammalia: Soricomorpha and Chiroptera) from Terapa, a neotropical-nearctic transitional locality in Sonora, Mexico.
Modern Environmental Setting--Terapa lies along the Rio Moctezuma, a tributary of the Rio Yaqui, in foothills of the Sierra Madre Occidental (29[degrees]41'N, 109[degrees]39'W; Fig. 1). Terapa is at a moderately low elevation, 605 m, where it is situated in the Sonoran Basin and Range subprovince of the Northwestern Plains and Sierras morphotectonic province (as described by Ferrusquia-Villafranca et al., 2005). Ecogeographically, Terapa exists today within a broad transitional area between the Nearctic and Neotropical biogeographic realms. Terapa is at the northeastern edge of the Sonoran-Sinaloan transition subtropical dry forest. This ecoregion was included in the Nearctic biogeographic realm (by Olson et al., 2001) and within the Mexican phylogenetic zoogeographic region of the Nearctic realm for mammals and other terrestrial vertebrates (Holt et al., 2013). Brown et al. (1998) called the same biotic community subtropical Sinaloan thornscrub and included it in the Neotropical realm. This ecosystem is now called Matorral Espinoso de Piedemonte (foothill thornscrub) and is considered tropical (Martinez-Yrizar et al., 2010; Van Devender et al., 2013). As is apparent from its being placed in either of the two biogeographic realms by various authors, the region around Terapa is in a transitional area between them. The "boundary" between Neotropical and Nearctic biogeographic regions is necessarily transitional rather than a hard line (e.g., Wallace, 1876; Good, 1974; Wiseman, 1980; Ceballos and Navarro, 1991; Brown and Lomolino, 1998; Ortega and Arita, 1998; Torres-Morales et al., 2010). For mammalian families, the transition in western Mexico is usually drawn along the Pacific Coast between the coastal lowlands and the highlands of the Sierra Madre Occidental to approximately the Rio Mayo and Rio Fuerte, river systems eroded into the Pacific versant of the Sierra Madre Occidental. Farther north along the coastal lowlands and central Sonora parallel ranges and basins, the region becomes more arid and becomes a barrier to humid-adapted tropical species. The deep canyons of the Rio Mayo and Rio Fuerte drainage basins afford dispersal corridors and filter barriers between the tropical coastal lowlands (in southern Sonora and northern Sinaloa) and the temperate uplands of the Sierras (in Chihuahua). The Rio Mayo is the next major drainage south of the Rio Yaqui with its tributaries including the Rio Moctezuma (formerly Rio Oposura) and Terapa. Given the potential vegetation and floristic changes during the Pleistocene, these drainages might have provided a corridor through the Sierras to the Mexican Central Plateau morphotectonic province.
Late Pleistocene Environmental Setting--As measured by global proxy data, the earth underwent numerous climatic fluctuations during the last 2.8 million y of geological time (Melles et al., 2012). The geographical position and topographic setting of the Terapa locality within the boundary zone between recent biogeographic regions enhances the likelihood that basins and ranges in the Terapa area underwent many ecological and environmental changes through Pleistocene time. At times during the last 2.5 million y, southwestern North America is thought to have experienced a climate that was cyclic but mostly wetter and cooler than now, associated with continental glaciers farther north, while it probably experienced drier and hotter climate during briefer interglacial periods. The Late Pleistocene sedimentary deposits of Terapa reflect fluvial sediments deposited by the Rio Moctezuma in a catchment basin formed by an early-medial Pleistocene (1.7 million-yr-old to 300,000-yr-old) basalt flow within the Moctezuma volcanic field (PazMoreno et al., 2003; Gonzalez-Leon, 2010). One study (Mead et al., 2006) described the areal geological context and stratigraphy of the Terapa deposits and reported a maximum age for the basalt flow, known as the Tonibabi basalt, of 440 [+ or -] 130 thousand y. Bright et al. (2010) used several methods to date sediments on either side of the basalt flow, and it was determined that the short-lived fossil deposition of the Terapa deposits began 43-40 thousand y ago. On a broader scale, four groups (Coblentz, 2005; Ferrusquia-Villafranca and Gonzales-Guzman, 2005; Ferrusquia-Villafranca et al., 2005; and Gonzalez-Leon, 2010) tried to reconstruct some of the geological and biological changes that have affected northern Mexico and led to its present-day biota. Some of the changes that occurred during the Pleistocene are reflected in the sedimentary rocks and fossils recovered at Terapa (Mead et al., 2006, 2007). The sediments, ostracodes, mollusks, and vertebrate fossils preserved along the Rio Moctezuma at Terapa suggest the presence of a wetter and more-tropical riparian corridor at 43-40 thousand y ago during the Late Pleistocene (Rancholabrean Land Mammal Age) than at present. The inferred paleohabitats include a slow-moving stream, ponded water, marsh, and savanna, or submerged to emergent grassland (Mead et al., 2006, 2007). To this list Oswald and Steadman (2011) added riparian forest as a concurrent habitat type. Stable isotope geochemistry indicates an adjacent woodland or forest and grassland habitat (Nuuez et al., 2010). Among the vertebrate fossils, the remains of a crocodylian, certain birds, and capybaras indicate the more-tropical nature of these habitats (Steadman, in litt 2004; Mead et al., 2006; Steadman and Mead, 2010; Oswald and Steadman, 2011). Yet other members of the paleofauna, such as bison, horse, mammoth, and Camelops species, are typical of temperate regions and presumed drier grassland or other open habitats farther north in the United States or eastward in northern and central Mexico (Kurten and Anderson, 1981; Arroyo-Cabrales et al., 2002).
SYSTEMATIC PALEONTOLOGY--We collected specimens during trips in 2002-2008 by crawling the surface, searching for microvertebrates, and by digging and processing fossiliferous matrix from several informally named sub-localities of the main locality, Terapa. Sublocalities Betwixt, Eric Baez, Imhoff, and Organ Pipe yielded shrews and bats. The matrix was processed by screen-washing in the Rio Moctezuma through nylon and polyester screen bags of approximately 1-1.5-mm mesh. Some of the matrix that did not break down well was rewashed in water at the New Mexico Museum of Natural History and the Sam Noble Oklahoma Museum of Natural History using 0.6-mm wire-mesh screen boxes. The fossils from Terapa are temporarily cataloged and held at the Vertebrate Paleontology Laboratory of East Tennessee State University, Johnson City, Tennessee, United States, until a permanent repository in Mexico can be identified. Those fossils are preliminarily cataloged with the prefix "TERA-", used herein. Dental and morphological terminology for shrews follows Dannelid (1998) and Hutterer (2005b); terminology for bats follows Czaplewski (Czaplewski et al., 2007). Measurements of specimens are in millimeters; apl = anteroposterior length; tw = transverse width.
Genus and species indeterminate
Fossil Material--TERA-172, posterolabial portion of right upper molar, probably M1 (Fig. 2a), from Eric Baez sublocality.
Remarks--The ectoloph of this tooth is strongly pigmented on the faces of the shearing blades below the postparacrista, premetacrista, and postmetacrista, but the pigment stops before reaching the base of the paracone and metacone. It seems to represent a medium-sized shrew, much smaller than Megasorex and Blarina and about the size of Notiosorex crawfordi and Sorex trowbridgii. It is much-less extensively pigmented than in Blarina, which is heavily pigmented on the faces of the molar shearing crests and moderately pigmented within the trigon basin and part of the way across the talon basin. The distribution and density of pigment is about as in Sorex and Cryptotis, and much more than in Notiosorex, which is lightly pigmented only on the tips of the cusps of I1 through P4 and with molars unpigmented (George, 2012). The specimen probably represents a species of Sorex or possibly a large species of Cryptotis, but the molar fragment does not retain characters that allow firm allocation.
Notiosorex species indeterminate
Fossil material--TERA-173, left P4 from Betwixt sub-locality (Fig. 2b). This specimen has a slightly weaker hypocone and stronger postprotocrista than TERA-174. Measurements: apl (along labial border) 1.52 mm; tw 1.42 mm.
TERA-174, right P4 in a small fragment of maxilla from Organ Pipe sublocality (Fig. 2c). This specimen has a stronger hypocone than TERA-173 and lacks a postprotocrista. Measurements: apl (along labial border) 1.67 mm; tw 1.50 mm.
TERA-175, left dentary with i1-m2 from Betwixt (Fig. 2D-F). This specimen preserves all of the lower teeth except m3: i1, two lower unicuspids, and m1-m2. Measurements (partly following the method of Esteva et al., 2005): length of i1 from apex to posterior end of crown (enamelless, so measurement is somewhat less than it would have been in life), 3.42 mm; posterior height of i1 on labial side, 0.82 mm; length from the paraconid of p4 (posterior unicuspid) to the hypoconid of m2, 3.55 mm; length from the paraconid of m1 to the hypoconid of m2, 2.94 mm; length from the paraconid to the labial end of the labial reentrant valley of m1, 1.12 mm; width from the hypoconid to the entoconid of m1, 0.97 mm; length from the paraconid to the labial end of the labial reentrant valley of m2, 1.12 mm; width from the hypoconid to the entoconid of m2, 0.87 mm; labial depth of the dentary below middle of m1, 1.17 mm; lingual depth of the dentary below middle of m1, 1.32 mm.
Remarks--The P4s appear to have only light pigment on the tip of the paracone. Each has a deeply emarginated posterior border (a feature considered diagnostic of Notiosorex among North American shrews by Repenning, 1967). The partial lower jaw also appears to have the alveolus of i1 extending posteriorly beneath the paraconid of m1, a distinguishing feature of the genus Notiosorex (Carraway and Timm, 2000). The mental foramen is below the middle of m1. Enamel is damaged on the i1 and unicuspids, but the preserved portions of enamel of these teeth--the tip of the main cusp of each--are lightly pigmented. The tip of the protoconid of m1 also has a small pigmented area. The m1 has a weak entoconid and the m2 has no entoconid; neither tooth has an entoconid crest.
As in many relatively recently radiated, speciose mammalian genera, the species of Notiosorex are quite difficult (or presently impossible in the case of Notiosorex cockrumi) to distinguish by cranial morphological characters. George (2012) reviewed previously used morphological characters of North American Quaternary shrews with a phylogenetic approach to delimit apomorphic characters that could be used to identify specimens. George (2012) was able to distinguish three autapomorphic characters for Notiosorex (diagnostic only to genus): (1) lightly pigmented teeth, (2) posterior extent of alveolus of i1 in labial view reaching past paraconid to metaconid of m1, and (3) only one cusp, the hypoconid, present on talonid of m3. George (2012) also identified several synapomorphic characters of the dentary bone for the tribe Notiosoricini. Of these, the only characters available in the Terapa specimens were the first two. Assuming that the Terapa P4s and dentary represent the same genus of shrew, the weak pigment and extent of the i1 alveolus establish the Terapa fossils as Notiosorex.
The currently recognized extant species of Notiosorex include N. crawfordi, Notiosorex evotis, Notiosorex villai, and N. cockrumi. All are known in Mexico and the southwestern United States. In addition, N. crawfordi and four extinct species, Notiosorex dalquesti, Notiosorex harrisi, Notiosorex jacksoni, and Notiosorex repenningi are known as fossils in the late Neogene of North America (Harris, 1998; Carraway, 2010).
The only species of Notiosorex presently known in the Rancholabrean Land Mammal Age is N. crawfordi (although some of the specimens might pertain to other species currently recognized), which is recorded from fossil sites in Chihuahua and Tamaulipas, Mexico and Arizona, California, Kansas, New Mexico, Nevada, and Texas, United States (Harris, 1998). The species is also presently widespread in Baja California, northern and central mainland Mexico, and in the southwestern and central United States. Repenning (1967:55) noted that N. crawfordi has a strong entoconid and entoconid crest on m1. The Terapa lower jaw differs in having an exceedingly weak entoconid and no entoconid crest on the m1. The lower teeth are slightly smaller than in one specimen of N. crawfordi from Arizona.
Notiosorex evotis is presently known only by recent specimens from west-central Mexico including the states of Colima, Jalisco, Michoacan, Nayarit, and Sinaloa (Hutterer, 2005a). No specimens of N. evotis were available for comparison, but none of the morphological characters listed by Carraway and Timm (2000) are preserved in the Terapa fossils that would allow them to be referred to or distinguished from N. evotis.
Notiosorex villai is known only by modern specimens from central Tamaulipas (Carraway and Timm, 2000).The differential diagnosis for this species provided by Carraway and Timm (2000) uses qualitative features of the glenoid fossa and measurements of the cranium and coronoid process of the dentary that are not preserved in the Terapa specimens, so no comparisons can be made.
Notiosorex cockrumi was defined (by Baker et al., 2003) on genetic evidence but is indistinguishable morphologically from N. crawfordi (Carraway and Timm, 2000); the species occurs from central Sonora to southern Arizona. It is possible that the Terapa specimens could represent N. cockrumi, but until morphological characters distinguishing N. cockrumi from N. crawfordi or other species of Notiosorex are discerned, or until ancient DNA can be used to identify these fossils, they cannot be referred to nor distinguished from N. cockrumi.
Notiosorex dalquesti was recently described based on Late Quaternary fossils from Jimenez Cave in Chihuahua, San Josecito Cave in Nuevo Leon, and Municipio Panuco in Zacatecas as well as from many localities in Arizona, Kansas, New Mexico, Oklahoma, and Texas, United States. (Carraway, 2010). Previous, thorough studies did not reveal Notiosorex in San Josecito Cave (Findley, 1953; Esteva et al. 2005). Only some of the qualitative characters that Carraway (2010) used to diagnose N. dalquesti are preserved in the fragmentary Terapa fossils. Relative to those preserved characters, the Terapa fossils differ from N. dalquesti in having a mental foramen that is not situated within a slight depression, and the molar entoconids are not large on ml and m2. Additionally, Carraway's (2010) measurements numbered 22, 23, 24, 25, 28, 29, 30, 31, 32, and 34 are measurable in the single Terapa dentary fragment. In these measurements, the Terapa dentary falls within the range of variation of all species of Notiosorex, except N. cockrumi, in the width of m1; within the range of variation of all Notiosorex sp. in width of m2; and within the range of variation of most species except N. harrisi (in which the Terapa fossil is larger), N. jacksoni, N. villai, and N. evotis (in which it is smaller).
Notiosorex harrisi was recently named by Carraway (2010) for specimens from the Late Miocene and late Quaternary sites in Chihuahua and the southwestern United States. The specimens referred to this species came from the late Miocene (Hemphillian Land Mammal Age) White Cone local fauna on the Navajo (Dine) and Hopi Reservations (northeastern Arizona) and from Late Pleistocene to Holocene cave deposits in Jimenez Cave, Chihuahua, and several cave sites in New Mexico including a type locality at Big Manhole Cave (Carraway, 2010). Relative to the apomorphic characters of N. harrisi that can be assessed in the Terapa fossils, the Terapa specimens differ from N. harrisi in having the dentary bone deeper beneath the m1, the mental foramen is not located within a slight depression, and the entoconids on m1 and m2 are relatively small.
Notiosorex jacksoni is recognized in the Late Pliocene and possibly Middle Pleistocene (Irvingtonian Land Mammal Age) of the United States (Harris, 1998). Notiosorex jacksoni is differentiated from N. crawfordi by having extremely emarginated posterior borders of the P4 and upper molars. In this feature of the P4, the Terapa fossils are not so deeply emarginated and thus differ from N. jacksoni.
Notiosorex repenningi is a Late Pliocene (Blancan) species known from La Concha, Chihuahua (Lindsay and Jacobs, 1985) and is known only by its lower jaw; it was diagnosed on characters of the m3, which is not preserved in the available specimens from Terapa. Comparison of the Terapa lower jaw fragment with a cast of the type specimen of N. repenningi revealed muchweaker entoconids and absent entoconid crests in the m1 and m2 of the Terapa specimens. The Terapa lower teeth are also slightly smaller.
Two species, N. cockrumi and N. crawfordi, lived in Sonora in historic times (Maldonado, 1999; Baker et al., 2003). Previous Rancholabrean fossil records for the genus were all reported as N. crawfordi but actually are diagnosable only to the genus according to George (2012), although many of them were assigned to N. harrisi and N. dalquesti by Carraway (2010). Fossils of Notiosorex are numerous and scattered from southern California to western Oklahoma and southwestern Texas (Harris, 1993; Faunmap Working Group, 1994). Those records nearest to Terapa include Baldy Peak, Howell's Ridge, U-Bar, and Pendejo caves in New Mexico, Deadman and Papago Springs caves in Arizona, and woodrat middens in Arizona and New Mexico (Harris, 1987, 1993, 2003; Faunmap Working Group, 1994; Mead et al., 2005). There are also Holocene records from woodrat middens in Arizona and Texas (Mead et al., 1983; Faunmap Working Group, 1994). As noted above, the Terapa fossils clearly differ from N. crawfordi (and presumably also the morphologically identical species N. cockrumi), N. jacksoni, N. dalquesti, N. harrisi, and N. repenningi; they cannot presently be distinguished from N. evotis and N. villai on the basis of the elements preserved. Because of this, the Terapa fossils cannot certainly be assigned to a species.
Extant species of Notiosorex are found in a wide variety of habitats, in sites described by various collectors as desert scrub, oak-pine forest, yellow pine forest, grassland with oak (Quercas species) chaparral and oak woodland habitats nearby, alkaline marsh, sandy flats, arid grassland with scattered catclaw acacia (Acacia greggii), juniper (Juniperus species), and mesquite (Prosopis species), tropical forest, riparian vegetation, scattered cacti and dense thornbush, abandoned agricultural fields bordered by scattered cacti, thornbush, and mesquite, damp spots under rocky ledges, and semidesert (Carraway and Timm, 2000; Carraway, 2007). Notiosorex species occur at low-tomoderate elevations from 3 m above sea level to 2,317 m in the Sierras and are known from an area of southwestern North America spanning from Baja California (both ends of peninsula) and Sonora to southwestern Mexico (Michoacan and Colima), northeast to Tamaulipas and the Ozark Highland of Arkansas of the United States, and westward to southern Nevada and southern California (Maldonado, 1999; Carraway and Timm, 2000). Their broad habitat tolerance does not contribute to an interpretation of the paleoenvironment of Pleistocene central Sonora nor does it refute previous interpretations (Mead et al., 2006, 2007).
Lasiurus species indeterminate
Fossil Material--TERA-176, right proximal radius-ulna from Betwixt sublocality (Fig. 3b). Measurements: greatest proximal width, 2.8 mm; proximal projection of olecranon process beyond proximal rim of semilunar notch, 0.75 mm; proximodistal length of semilunar notch, 2.0 mm.
TERA-177, left proximal radius-ulna (ulna mostly broken off) from Organ Pipe sublocality (Fig. 3a). Measurement: greatest proximal width, 2.85 mm.
Remarks--These specimens have the remnant ulna completely fused to the radius at their proximal ends. The olecranon process is much reduced when compared with typical mammals but is recognizable as an olecranon and much-better developed than in most bats (Fig. 3b). The olecranon process is partly broken in one of the fossils. On the posterior edge, the portion of the ulnar shaft just distal to the level of the semilunar notch becomes free of the posterior side of the radius, but the shaft is thin and broken in both specimens at this point.
These specimens pertain to a member of the Vespertilionidae and are distinguishable from the same element in Molossidae. In molossids (at least in Tadarida, Nyctinomops, and Molossus), the ulna is fused with the radius only distally (about at the midshaft of the radius) and not at the proximal end. In some vespertilionids (such as Eptesicus, Perimyotis, Myotis, Lasionycteris), the ulna has a small or absent olecranon process, is unfused at the semilunar notch but fused slightly more distally along the shaft beneath or just distal to the semilunar notch, and contributes its own separate, small articular facet to the semilunar notch. In Parastrellus the ulna is weakly fused to the radius proximally and is not fused distally but occurs as a hair-thin, free shaft; it has a small facet contributing to the semilunar notch that is separate from the articular surface of the radius. In Corynorhinus the ulna is fused proximally but maintains its own separate articular facet in the semilunar notch; the ulnar shaft occurs as an exceedingly thin, hair-like flange fused to the posterior surface of the radius along its short length except for a short, free section directly beneath the semilunar notch. In Nycticeius the ulna is weakly fused to the radius proximally, where it is connected by a thin flange of bone and then becomes a separate, unfused, hair-thin shaft that rejoins the radius distally; it has its own separate articular facet in the semilunar notch. In Antrozous the ulna is completely fused to the radius and appears as a flange running along the posterior side of the radius for a short distance before terminating where the free portion of the shaft begins in other vespertilionids and molossids; there is no relatively large olecranon process, only a small, flat, proximally directed point at the posterior end on the semilunar notch. In Lasiurus the ulna retains a small but relatively prominent olecranon process and is completely fused proximally to the radius; it has a free, thin shaft that is fused to the radius distally at a point about one third of the length of the radius from the articular end. No specimens of yellow bats (Lasiurus xanthinus, Lasiurus intermedius, or Lasiurus ega) or of Rhogeessa were available for comparison.
The preserved portions of the fossils match exactly the morphology of the radius-ulna in Lasiurus. In size they match the radius-ulna in small species such as Lasiurus xanthinus, Lasiurus blossevillii, Lasiurus seminolus, and Lasiurus borealis, but ulnar features and size are not diagnostic among these species (NJ Czaplewski, pers. obser.).
Lasiurus are solitary, tree-roosting bats. Three species, L. xanthinus, L. blossevillii, and L. cinereus are known in central Sonora in historic times, and four others are known elsewhere in Mexico (Bogan, 1999; Medellin et al., 2008). Lasiurus xanthinus roost sometimes in palms, especially beneath the dead leaves that form a skirt around the trunk beneath the living leaves, whereas red bats (L. blossevillii and L. borealis) often roost in deciduous broadleaf trees, usually in transitional areas (edge habitat) or sometimes in leaf litter on the ground in colder temperate areas when foliage is lacking (Mager and Nelson, 2001; Mormann and Robbins, 2007). Bogan (1999) noted that both L. blossevillii and L. xanthinus in Sonora probably inhabit riparian areas where large trees are available for roosting and where foraging is possible along waterways. The coloration of these bats camouflages them because it matches the color of dead leaves and tree bark. The presence of a small species of Lasiurus indicates the presence of trees in the paleoenvironment of Terapa but does not disclose the type of trees, or whether they were associated with riparian or marshy habitat or occurred at some distance from the water.
Previous Quaternary occurrences of smaller species of Lasiurus are from Lolthn Cave in Yucatan, Mexico, and Lagoa Santa in Brazil (as L. ega, which formerly included L. xanthinus as a subspecies; Winge, 1893; Paula Couto, 1946; Arroyo-Cabrales, 1992; Arroyo-Cabrales and Alvarez, 1990), the Balcony Room of Dry Cave (Lasiurus sp.) and Carlsbad Caverns in New Mexico (L. borealis), and several localities in the eastern United States (L. borealis and L. cf. seminolus, Morgan, 1985).
Fossil Material--TERA-178, left maxilla fragment with M2-M3 from Betwixt site (Fig. 3c). Measurements: apl of M1, 2.10 mm; tw of M1, 2.40 mm; apl of M2, 0.74 mm; tw of M2, 2.15 mm.
Remarks--The specimen retains a small portion of the anterior root of the zygomatic arch and floor of the orbit. The M2 and M3 have slight damage to the enamel of the cusps but are otherwise complete. The specimen is of a relatively large bat. The M2 lacks a talon and hypocone, and the postprotocrista runs from the protocone to the base of the metacone. The M3 is extremely reduced, with a tiny protocone, only a single commissure (the preparacrista) associated with the paracone, and no hint of a second commissure (postparacrista). This matches the condition in A. pallidus and differs from Bauerus dubiaquercus, which also has a reduced M3. In Bauerus M3 retains a small postparacrista, terminated with a small cusp (mesostyle?), creating a prominent bulge on the posterior edge of the tooth.
Antrozous pallidus has a broad distribution in western North America from extreme southwestern Canada southward to the Trans-Mexican Volcanic Belt and throughout the Baja California peninsula. The species is known as a Quaternary fossil at Cueva de Jimenez in Chihuahua (Arroyo-Cabrales, 1992), at Dark Canyon, Dry, Muskox, Howell's Ridge, U-Bar, and Pendejo caves in New Mexico, at Bida, Deadman, Papago Springs, and Sandblast caves in Arizona, at Fowlkes Cave in Texas (Dalquest and Stangl, 1984; Mead et al. 1984, 2005; Harris, 1987, 1993, 2003; Emslie, 1988; Czaplewski et al., 1999), and in an 8,720 [+ or -] 330-y-old woodrat midden in the Castle Mountains in Arizona (Mead et al., 1983).
Myotis species indeterminate
Fossil Material--TERA-179, right maxilla with P4, M2, and alveoli for all upper teeth from Organ Pipe site (Fig. 3d).
TERA-277, left partial scapula from Imhoff site. Measurements: alveolar length from I1-M3, 5.85 mm; alveolar length of maxillary toothrow (C1-M3), 4.90 mm; apl of P4, 0.92 mm; tw of P4, 0.97 mm; apl of M2, 1.21 mm; tw of M2, 1.47 mm.
Remarks--The worldwide genus Myotis is diverse in southwestern North America, where many species (Myotis auriculus, Myotis californicus, Myotis evotis, Myotis fortidens, Myotis melanorhinus, Myotis occultus, Myotis thysanodes, Myotis velifer, Myotis vivesi, Myotis volans, and Myotis yumanensis) occurred within 500 km of Terapa in historic times (Bogan, 1999; Lopez-Gonzales and Garcia-Mendoza, 2006; Medellin et al. 2008). In addition, the extinct Pleistocene species Myotis rectidentis is known from Dry Cave, New Mexico (Harris, 1993). The Terapa specimen shows alveoli for two small upper premolars and thus cannot represent M. fortidens, which has only one small upper premolar anterior to the large P4.
The Terapa fossils represent a small Myotis, much smaller than M. auriculus, M. evotis, M. occultus, M. thysanodes, M. velifer, and M. volans. The maxilla and scapula are slightly smaller, or about the same size as individuals of the smallest southwestern North American species M. californicus, M. melanorhinus, and M. yumanensis. Maxillary toothrow (alveolar) length for TERA-179 is 4.90 mm and falls at the low end of the range of this measurement for M. melanorhinus (overall range of observed measurements 4.9-5.9 mm; van Zyll de Jong, 1984; Constantine, 1998; Lopez-Gonzales and GarciaMendoza, 2006) and in the middle of the range for M. californicus (overall range 4.5-5.4 mm; Bogan, 1975; Constantine, 1998; Lopez-Gonzales and Garcia-Mendoza, 2006) and M. yumanensis (4.7-5.6 mm; Harris, 1974; Lopez-Gonzales and Garcia-Mendoza, 2006) for specimens from northwestern Mexico and southwestern United States. Morphologically, these small species are difficult to differentiate osteologically when complete skulls or skeletons are available (Bogan, 1974, 1975; van Zyll de Jong, 1984); the species at Terapa cannot be distinguished on the basis of the available fragmentary material.
The scapula fragment consists of the glenoid head and proximal portion of the blade. Adjacent to the glenoid facet is a relatively large dorsal articular facet for the greater tuberosity of the humerus. The acromion process is completely broken off, but there is a portion of the base of the coracoid process present. There is a prominent infraglenoid tubercle (see Strickler, 1978 for terminology) and another equally prominent tubercle just dorsal to the infraglenoid tubercle and distal to the glenoid on a ridge on the dorsal surface below the anterior base of the acromion process and scapular spine. Morphologically the bone matches the scapula in Myotis and differs from the other bats in the Terapa fauna. It has a rounded prominence at the anterior edge of the glenoid near the dorsal articular facet, as in Myotis, rather than a pointed one as in Lasiurus and Tadarida. The dorsal articular facet is relatively smaller in the fossil than in Tadarida and other molossids. The preserved portion of the coracoid process curves ventrolaterally as in Myotis and other vespertilionids rather than curving ventromedially as in molossids. Like the maxilla, the scapula also is from a small species of Myotis. It is the same size as the scapula in M. yumanensis, M. californicus, and M. melanorhinus; it is far smaller than the scapula in other bats in the Terapa fauna, (e.g., Lasiurus species and Tadarida brasiliensis.)
Fossils of Myotis of several species (some undifferentiated) have been reported widely, reflecting the worldwide distribution of the genus. Late Quaternary Myotis fossils in the Terapa region include at least Cueva de Jimenez in Chihuahua (Arroyo-Cabrales, 1992), Carlsbad Caverns, UBar, Pendejo, Muskox, Isleta no. 1, Algerita Blossom, and Dry caves in New Mexico (Harris, 1987, 1993, 2003) and Arkenstone, Bida, Deadman, Papago Springs, and Stanton's caves in Arizona (Skinner, 1942; Czaplewski et al., 1999; Mead et al., 2005).
Genus and species indeterminate
Fossil Material--TERA-180, proximal left metacarpal III from Betwixt site. Measurements: greatest proximal diameter, 1.15 mm; proximal shaft diameter, 0.45 mm.
Remarks--The bone is smaller than in T. brasiliensis and much-more slender and delicate than in the long, narrow-winged molossids in which the third metacarpal is the stoutest metacarpal. The bone resembles that in other vespertilionids but is much too small to represent A. pallidus, Lasiurus cinereus, or Eptesicus fuscus. It is smaller than in M. velifer and Corynorhinus townsendii but about the same size as in the small species M. californicus, M. yumanensis, and Parastrellus hesperus. No attempt was made to identify the taxon to which it belongs beyond the family.
Fossil Material--TERA-181, right M1 from Organ Pipe site (Fig. 3e). Measurements: apl, 1.65 mm; tw, 2.05 mm.
Remarks--The tooth has a relatively large talon that is rather triangular in occlusal outline and pointed posteriorly; it bears an indistinct hypocone on a strong hypoconal crest that runs posteriorly from the postprotocrista across the talon. The preprotocrista runs from the protocone to the parastyle, forming a wide shelf anterior to the paracone and preparacrista. There is a strong paraloph at the base of the paracone and moderately developed metaloph in the trigon basin just anterior to the base of the metacone, as in Tadarida. The paraloph and metaloph are weaker and shorter than in Nyctinomops, in which the two prominent lophs converge and nearly reach the protocone.
In size and shape, TERA-181 matches the M1 of Tadarida brasiliensis; it is also similar to the extinct species Tadarida constantinei but has a weaker hypocone and is somewhat smaller. TERA-181 is about the same size as the same tooth in Nyctinomops femorosaccus and Nyctinomops aurispinosus but differs in having a much shorter and weaker paraloph and metaloph and a weaker hypocone. It is much smaller than M1 in Nyctinomops macrotis and differs morphologically from the other species of Nyctinomops.
Tadarida brasiliensis is widespread in the western hemisphere, ranging from roughly the southern half of the United States in North America, southward across Mexico and the Caribbean Basin, through western and southern South America (excluding the Orinoco and Amazon river basins) to central Chile and Argentina (Wilkins, 1989). Like many species of Molossidae, these bats are strong fliers and wander widely. Fossil records of T. brasiliensis are not particularly common, despite the species' widespread modern distribution. Wilkins (1989) listed fossil records known prior to 1989; only one record in North America was outside the present distribution of the species (in the eastern state of Kentucky, United States). The fossil record from Terapa is well within the modern distribution and is not distant from other Late Pleistocene fossils of the species at Cueva de Jimenez in Chihuahua (as Tadarida; Arroyo-Cabrales, 1992), Carlsbad Caverns, Muskox, Dry, and U-Bar caves in New Mexico (Harris, 1987, 1993) and Papago Springs Cave in Arizona (Skinner, 1942; Czaplewski et al., 1999).
The habitat preferences of T. brasiliensis are equally broad, both for roosting and foraging. During the 20th Century, migratory populations varying between 1,500 in winter and 4 million in summer were estimated at Cueva del Tigre, Sonora (Arroyo-Cabrales, 1999). These bats tend to forage at high altitudes in open air, where the habitat below affects them mostly indirectly through factors that affect insect variety and abundance. These bats sometimes feed opportunistically on swarms of migrating moths and other agricultural pests (Russell et al., 2011).
DISCUSSION AND CONCLUSIONS--The shrews and bats identified in the Terapa fauna still have living representatives in the general area of southwestern North America today (Alvarez-Castaueda and Patton, 1999; Castillo-Gamez et al., 2010). Closely related or identical modern mammals in Sonora include two species of Notiosorex shrews, the pallid bat A. pallidus, three species of hairy-tailed bats, genus Lasiurus, several species of mouse-eared bats, genus Myotis, and the Mexican free-tailed bat T. brasiliensis. The Terapa specimens are the first fossil bats to be reported from Sonora.
Interestingly, the paleofauna of Terapa includes no phyllostomids, mormoopids, emballonurids, or natalids, even though these are known today nearby or only slightly farther south in Sonora. The Terapa fossil bats are mostly temperate zone species (three) with one tropical-subtropical species. The absence from the Terapa paleofauna of mormoopids and phyllostomids is perhaps surprising given the modern-day presence of three species of mormoopids and at least one migratory phyllostomid in lava tube caves of the Moctezuma volcanic field near Divisadero and Tepache merely 12 km to the southeast (G. S. Morgan and N. J. Czaplewski, pers. obser.) These present-day bats are cave dwellers and their remains might be considered less likely to become deposited in a marshy or lacustrine setting, as proposed for ancient Terapa. However, the same could be said of the likelihood of preservation of modern relatives of the vespertilionid and molossid bats that are known as fossils at Terapa.
Fossils of bats are always rare in open depositional settings such as fluvial and lacustrine sedimentary deposits (Sige and Legendre, 1983; Kowalski, 1995). In Mexico, as elsewhere, bats are far more common as fossils in cave deposits (Arroyo-Cabrales et al., 2010). No modern taphonomic studies have been made (and would be exceedingly difficult) comparing the likelihood of preservation of bat remains in an open setting (that is, in potential foraging habitat or site away from their roosts) relative to local bats with a variety of roosting preferences.
One genus, Lasiurus, is tree-roosting, some species of which utilize riparian habitats and ecotones for foraging. Antrozous pallidus is a rock-crevice-roosting species that forages in a variety of mostly arid to semiarid habitat types. Myotis species are extremely varied in both roosting and foraging habitat. Tadarida brasiliensis in Mexico, and most other parts of its broad range, roosts in caves and forage high over various habitat types. Except for largely migratory species (such as nectar-feeding phyllostomids), most members of the Neotropical families Phyllostomidae, Mormoopidae, Emballonuridae, and Natalidae reach their northwestern limits in Mexico at about the lower Rio Yaqui, or along the lower rios Mayo and Fuerte, and help define the Neotropical-Nearctic boundary (Anderson, 1960; Koopman, 1961; Findley and Jones, 1965). Lopez-Gonzales and Garcia-Mendoza (2006) noted that the chasms of the Sierra Tarahumara in the Sierra Madre Occidental act as vertical barriers to bats but can also provide avenues of dispersal. Lowland Neotropical species can move upward and Nearctic species can move downward if habitat heterogeneity and conditions changed during pluvial-interpluvial cycles of the Pleistocene. Species of shrews might do the same, but are much less mobile than bats, and any change in their distribution might occur more slowly. Terapa is on the Rio Moctezuma, a south-flowing tributary of the Rio Yaqui, which could have acted as a north-south corridor rather similar to, but wider than, the corridors farther south in the Sierras. As noted by Torres-Morales and associates in discussing the bats of the Neotropic-Nearctic transition zone in Durango (Torres-Morales et al., 2010), the Terapa bats include two species with Nearctic affinities, Lasiurus and A. pallidus, one species with primarily Neotropical affinities, T brasiliensis, and one genus with a global distribution, Myotis. The number of Late Pleistocene bats for Terapa is small, and almost certainly more species occurred there than are preserved as fossils. However, it is worthy of note that no bat of Neotropical affinities other than T. brasiliensis, whose range actually extends well into the northern temperate zone, are preserved despite the presence of other Neotropical vertebrates in the paleofauna such as a crocodylian, pampathere, and capybara (Mead et al., 2006, 2007).
In the present day, about 34 species of bats occur in northeastern Sonora (Medellin et al., 2008), and many more bat species would be expected if the Terapa area was more tropical in the Late Pleistocene because their modern geographic limits are not far south of the area. During our fieldwork near Terapa, in a brief visit to a lava tube cave ("Cueva de Chmeros") in the Moctezuma lava field in March 2008, we observed and photographed four species of two families, Pteronotus davyi, Pteronotus parnellii, Mormoops megalophylla (Mormoopidae), and Leptonycteris yerbabuenae (Phyllostomidae). These mormoopids are near the northwestern limits of their present-day ranges, but neither family was found in the Pleistocene deposit. Possibly additional specimens of bats, including forms with Neotropical affinities, would come to light if more fossiliferous matrix could be processed for microvertebrates. Alternatively, the bats and shrews indicative of a mostly temperate-zone fauna, taken together with the tropical faunal indicators of the crocodile, capybara, and some birds, might reflect a no-analog (or "disharmonious") vertebrate fauna at Terapa as at other Late Pleistocene faunas in Mexico and elsewhere in North America (Graham et al., 1996; Stafford et al., 1999; Ceballos et al., 2010). Perhaps the Terapa fauna reflects a dynamic in Sonora between the Sonora-Central America Pacific lowlands tropical corridor and Rocky Mountains-Sierra Madre Occidental temperate corridor, as has been described (Ceballos et al., 2010).
For facilitating and directly participating in our fieldwork at Terapa, we thank A. Baez, and S. Swift. F. Tapia Grijalva and E. Villalpando of Instituto Nacional de Antropologia e Historia, INAH Sonora assisted J. I. Mead and A. Baez with obtaining permits. We greatly appreciate the hospitality and aid, and mourn the passing, of the late S. Garcia Lopez, Opata elder of Terapa. Similarly, we thank H. Ruiz Durazo and E. M. Aruna Moore and their families and friends of Moctezuma for support and hospitality while we did the fieldwork. Digging and hauling matrix, and sediment field-processing, were aided by several of the (Opata boys and girls of Terapa as well as by A. Al-Aryan, V. Black, C. Bomberger, J. Bright, M. C. Carpenter, A. Cartwright, F. Croxen, B. Haist, D. Kaur, P. Gensler, M. Hollenshead, M. Imhof, R. Irmis, S. Jenkins, A. Kelly, M. Kropf, C. McCracken, J. Meyers, B. Schmeisser, and D. Sherrat. W. May, C. Baker, and especially S. Swift sorted much of the screen-washed concentrate. We appreciate the many discussions about the paleosetting and paleofauna of Terapa with T. R. Van Devender and R. S. White. We also are grateful for the constructive comments of two anonymous reviewers.
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Submitted 21 October 2013.
Acceptance recommended by Associate Editor, Troy A. Ladine, 11 February 2014.
NICHOLAS J. CZAPLEWSKI, * GARY S. MORGAN, JOAQUIN ARROYO-CABRALES, AND JIM I. MEAD
Oklahoma Museum of Natural History, 2401 Chautauqua Avenue, University of Oklahoma, Norman, OK 73072 (NJC) New Mexico Museum of Natural History and Science, 1801 Mountain Road NW, Albuquerque, NM 87104 (GSM) Laboratorio de Arqueozoologia "M. en C. Ticul Alvarez Solorzano," Subdireccion de Laboratorios y Apoyo Academico, Instituto Nacional de Antropologia e Historia, Moneda #16, Col. Centro, 06060 Moxico, Mexico (JAC) Vertebrate Paleontology Laboratory, Department of Geosciences, and Sundquist Center of Excellence in Paleontology, East Tennessee State University, Johnson City, TN37614 (JIM)
* Correspondent: firstname.lastname@example.org
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|Author:||Czaplewski, Nicholas J.; Morgan, Gary S.; Arroyo-Cabrales, Joaquin; Mead, Jim I.|
|Date:||Dec 1, 2014|
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