Chisos Mountains Research Articles

Environmental Correlates and Reproductive Capacity of Guadalupe Fescue (Festuca ligulata), an Endangered Grass of the Northern Sierra Madre Oriental

Guadalupe fescue (Festuca ligulata Swallen) is an endangered perennial grass species that is endemic to the Sky Island conifer-oak forests and piñonoak-juniper woodlands of the northern Sierra Madre Oriental. Little is known about the habitat requirements, population dynamics, or reproductive ecology of this species. We assessed aspects of the demography, habitat preferences, and germination rates of Guadalupe fescue in two Sky Island sites on each side of the US–Mexico border: the Chisos Mountains of Big Bend National Park (BIBE) in Texas, USA, and the Maderas del Carmen Protected Area (MCPA) in Coahuila, Mexico. Through field and greenhouse measurements, we evaluated the plant vigor, reproductive capacity, and environmental growing conditions of 422 plants (323 in BIBE and 99 in MCPA). Our results reveal that Guadalupe fescue is a very rare species growing within a narrow elevational range (2066–2394 m) on rocky microsites with relatively open canopy and forest floor conditions, compared to the range of available local habitats. For collected seeds, the mean fill rate was 54% (31% for BIBE and 61% for MCPA) and overall germination rate was 14% (8% at BIBE and 33% at MCPA). These results provide important baseline ecological data on Guadalupe fescue, which is critical for informing endangered species recovery planning and restoration activities aimed at bolstering this species' population size.

Endangered Nectar-Feeding Bat Detected by Environmental DNA on Flowers.

Leptonycteris nivalis (the Mexican long-nosed bat) is an endangered nectar-feeding bat species that follows "nectar corridors" as it migrates from Mexico to the southwestern United States. Locating these nectar corridors is key to their conservation and may be possible using environmental DNA (eDNA) from these bats. Hence, we developed and tested DNA metabarcoding and qPCR eDNA assays to determine whether L. nivalis could be detected by sampling the agave flowers on which it feeds. We sampled plants with known bat visitations in the Sierra Madre Oriental in Laguna de Sanchez (LS), Nuevo León, Mexico, and in the Chisos Mountains in Big Bend National Park, TX, USA (CB). A total of 13 samples included both swabs of agave umbels and cuttings of individual flowers. DNA metabarcoding was performed as a PCR multiplex that targeted bats (SFF-COI), arthropods (ANML-COI), and plants (ITS2 and rbcL). We targeted arthropods and plants in parallel with bats because future metabarcoding studies may wish to examine all the pollinators and plants within the nectar corridor. We developed and tested the sensitivity and specificity of two qPCR assays. We found that both DNA metabarcoding and qPCR were highly successful at detecting L. nivalis (11 of 13 for DNA metabarcoding and 12 of 13 for qPCR). Swabs and flower cuttings and both qPCR assays detected the species over four replicates. We suggest that L. nivalis leaves substantial DNA behind as it forages for nectar. We also suggest that future studies examine the time since sampling to determine its effect on detection success. The DNA metabarcoding multiplex will be useful for parallel questions regarding pollination ecology, while, with further testing, the qPCR assays will be effective for large-scale sampling for the detection of migration corridors and foraging areas. This work may be relevant to other nectar-feeding bat species, which can likely be detected with similar methodologies.

Sixty years on: birds of the Sierra del Carmen, Coahuila, Mexico, revisited

Summary. The rugged peaks of the Sierra del Carmen, Coahuila, visible from the Chisos Mountains in Texas, have tempted birdwatchers for decades, yet few have accessed the range, and its avifauna is poorly known. Based primarily on our own observations, supplemented by the literature, museum holdings and eBird records, we present an updated list of the region's avifauna. This list comprises 301 species, 137 of which breed in the region. As in previous surveys, we found bird species characteristic of both the intermontane West and tropical mountains to the south. We confirm that the Sierra del Carmen is slightly less speciose than sky islands of the Sierra Madre Occidental. Nevertheless, it is the northernmost outpost or migratory stopover of several regionally and globally rare species, and could serve as a stepping stone for species moving north with climate change. Although not a centre of endemism, the Sierra del Carmen is a vital and unique region for avian diversity.

Plant dieback under exceptional drought driven by elevation, not by plant traits, in Big Bend National Park, Texas, USA.

In 2011, Big Bend National Park, Texas, USA, experienced the most severe single year drought in its recorded history, resulting in significant plant mortality. We used this event to test how perennial plant response to drought varied across elevation, plant growth form and leaf traits. In October 2010 and October 2011, we measured plant cover by species at six evenly-spaced elevations ranging from Chihuahuan desert (666 m) to oak forest in the Chisos mountains (1,920 m). We asked the following questions: what was the relationship between elevation and stem dieback and did susceptibility to drought differ among functional groups or by leaf traits? In 2010, pre-drought, we measured leaf mass per area (LMA) on each species. In 2011, the percent of canopy dieback for each individual was visually estimated. Living canopy cover decreased significantly after the drought of 2011 and dieback decreased with elevation. There was no relationship between LMA and dieback within elevations. The negative relationship between proportional dieback and elevation was consistent in shrub and succulent species, which were the most common growth forms across elevations, indicating that dieback was largely driven by elevation and not by species traits. Growth form turnover did not influence canopy dieback; differences in canopy cover and proportional dieback among elevations were driven primarily by differences in drought severity. These results indicate that the 2011 drought in Big Bend National Park had a large effect on communities at all elevations with average dieback for all woody plants ranging from 8% dieback at the highest elevation to 83% dieback at lowest elevations.

Tree mortality from a short-duration freezing event and global-change-type drought in a Southwestern piñon-juniper woodland, USA.

This study documents tree mortality in Big Bend National Park in Texas in response to the most acute one-year drought on record, which occurred following a five-day winter freeze. I estimated changes in forest stand structure and species composition due to freezing and drought in the Chisos Mountains of Big Bend National Park using permanent monitoring plot data. The drought killed over half (63%) of the sampled trees over the entire elevation gradient. Significant mortality occurred in trees up to 20 cm diameter (P < 0.05). Pinus cembroides Zucc. experienced the highest seedling and tree mortality (P < 0.0001) (55% of piñon pines died), and over five times as many standing dead pines were observed in 2012 than in 2009. Juniperus deppeana vonSteudal and Quercus emoryi Leibmann also experienced significant declines in tree density (P < 0.02) (30.9% and 20.7%, respectively). Subsequent droughts under climate change will likely cause even greater damage to trees that survived this record drought, especially if such events follow freezes. The results from this study highlight the vulnerability of trees in the Southwest to climatic change and that future shifts in forest structure can have large-scale community consequences.

Outlier Stands of Quaking Aspen in the Davis Mountains of West Texas: Clone or Clones?

Populus tremuloides (quaking aspen) is found from the Pacific to the Atlantic Ocean in the northern United States and Canada, and at higher elevations in the western United States and northern Mexico. While P. tremuloides can reproduce sexually or asexually, it is primarily a clonal species in the intermountain west, reproducing vegetatively via root sprouts, yielding genetically identical stems or ramets. In west Texas, isolated, outlier stands occur in the Guadalupe, Davis, and Chisos Mountains at an elevation of approximately 2300 m. This study utilized seven microsatellites or simple sequence repeats (SSRs) to examine leaf samples from 10 widely separated stems in 10 isolated P. tremuloides individual stands within the Davis Mountains to determine the level of clonal and genetic diversity. We then examined differentiation among stands. Each stem sampled within a stand was genetically identical to all stems examined in that stand or was part of a clone. There were eight genetically identical clones from these ten stands, with three stands being genetically identical or part of the same clone. Many of the genotypes shared several of the same alleles and the remaining alleles were only a few base pairs apart. Some of these alleles have been previously identified in other western North American P. tremuloides stands. Microsatellites identified several triploid patterns consistent with possible aneuploidy, which is concurrent with previous studies.

Oak bark allometry and fire survival strategies in the Chihuahuan desert Sky Islands, Texas, USA.

Trees may survive fire through persistence of above or below ground structures. Investment in bark aids in above-ground survival while investment in carbohydrate storage aids in recovery through resprouting and is especially important following above-ground tissue loss. We investigated bark allocation and carbohydrate investment in eight common oak (Quercus) species of Sky Island mountain ranges in west Texas. We hypothesized that relative investment in bark and carbohydrates changes with tree age and with fire regime: We predicted delayed investment in bark (positive allometry) and early investment in carbohydrates (negative allometry) under lower frequency, high severity fire regimes found in wetter microclimates. Common oaks of the Texas Trans-Pecos region (Quercus emoryi, Q. gambelii, Q. gravesii, Q. grisea, Q. hypoleucoides, Q. muehlenbergii, and Q. pungens) were sampled in three mountain ranges with historically mixed fire regimes: the Chisos Mountains, the Davis Mountains and the Guadalupe Mountains. Bark thickness was measured on individuals representing the full span of sizes found. Carbohydrate concentration in taproots was measured after initial leaf flush. Bark thickness was compared to bole diameter and allometries were analyzed using major axis regression on log-transformed measurements. We found that bark allocation strategies varied among species that can co-occur but have different habitat preferences. Investment patterns in bark were related to soil moisture preference and drought tolerance and, by proxy, to expected fire regime. Dry site species had shallower allometries with allometric coefficients ranging from less than one (negative allometry) to near one (isometric investment). Wet site species, on the other hand, had larger allometric coefficients, indicating delayed investment to defense. Contrary to our expectation, root carbohydrate concentrations were similar across all species and sizes, suggesting that any differences in below ground storage are likely to be in total volume of storage tissue rather than in carbohydrate concentration.

Mid-Tertiary magmatism in western Big Bend National Park, Texas, U.S.A.: Evolution of basaltic source regions and generation of peralkaline rhyolite

Tertiary magmatism in the Big Bend region of southwestern Texas spanned 47 to 17Ma and included representatives of all three phases (Early, Main and Late) of the Trans-Pecos magmatic province. Early phase magmatism was manifested in the Alamo Creek Basalt, an alkalic lava series ranging from basalt to benmoreite, and silicic alkalic intrusions of the Christmas Mountains. Main phase magmatism in the late Eocene/early Oligocene produced Bee Mountain Basalt, a lava series ranging from hawaiite and potassic trachybasalt to latite, widespread trachytic lavas of Tule Mountain Trachyte and silicic rocks associated with the Pine Mountain Caldera in the Chisos Mountains. Late main phase magmatism produced trachyte lava and numerous dome complexes of peralkaline Burro Mesa Rhyolite (~29Ma) in western Big Bend National Park. Late stage basaltic magmatism is sparsely represented by a few lavas in the Big Bend Park area, the adjacent Black Gap area and, most notably, in the nearby Bofecillos Mountains, where alkalic basaltic rocks were emplaced as lava and dikes concurrent with active normal faulting.Trace element modeling, Nd isotope ratios and calculated depths of segregation for estimated ancestral basaltic magmas suggest that Alamo Creek basalts (εNdt ~6.15 to 2.33) were derived from depths (~120 to 90km) near the lithosphere/asthenosphere boundary at temperatures of ~1600 to1560°C, whereas primitive Bee Mountain basalts (εNdt ~0.285 to −1.20) may have been segregated at shallower depths (~80 to 50km) and lower temperatures (~1520 to 1430°C) within the continental lithosphere. Nb/La versus Ba/La plots suggest that all were derived from OIB-modified continental lithosphere. Late stage basaltic rocks from the Bofecillos Mountains may indicate a return to source depths and temperatures similar to those calculated for Alamo Creek Basalt primitive magmas. We suggest that a zone of melting ascended into the continental lithosphere during main-phase activity and then descended as magmatism died out.Variation within Burro Mesa Rhyolite is best explained by fractional crystallization of a mix of alkali feldspar, fayalite and Fe–Ti oxide. Comendite of the Burro Mesa Rhyolite evolved from trachyte as batches in relatively small independent magma systems, as suggested by widespread occurrence of trachytic magma enclaves within Burro Mesa lava and results of fractionation modeling. Trachyte may have been derived by fractional crystallization of intermediate magma similar to that erupted as part of Bee Mountain Basalt. εNdt values of trachyte lava (0.745) and two samples of Burro Mesa Rhyolite (−0.52 and 1.52) are consistent with the above models. In all, ~5wt.% comendite may be produced from 100 parts of parental trachybasalt.Negative Nb anomalies in some Bee Mountain, Tule Mountain Trachyte and Burro Mesa incompatible element plots may have been inherited from lithospheric mantle rather than from a descending plate associated with subduction. Late phase basalts lack such a Nb anomaly, as do all of our Alamo Creek analyses but one. Even if some slab fluids partially metasomatized lithospheric mantle, these igneous rocks are much more typical of continental rifts than continental arcs.We relate Big Bend magmatism to asthenospheric mantle upwelling accompanying foundering of the subducted Farallon slab as the convergence rate between the North American and the Farallon plates decreased beginning about 50Ma. Upwelling asthenosphere heated the base of the continental lithosphere, producing the Alamo Creek series; magmatism climaxed with main phase magmatism generated within middle continental lithosphere, and then, accompanying regional extension, gradually died out by 18Ma.

Genetic and Morphologic Variation in the Davis Mountains Cottontail (Sylvilagus robustus)

The Davis Mountains cottontail, Sylvilagus robustus, is an endemic species of the Trans-Pecos area of Texas. Although S. robustus previously was believed to be extirpated from the Chisos Mountains, we confirmed existence of a population. We examined intrapopulation and interpopulation variation in S. robustus, as well as the genetic relationship to the eastern cottontail (S. floridanus) using partial sequences of the mitochondrial cytochrome b and control region genes. Six morphometric traits relating to overall size and six cranial characters considered diagnostic for the two subspecies were used to confirm identification of specimens. Our morphological analysis suggested that specimens from the Chisos and Davis Mountains were S. robustus; however, low levels of genetic divergence between S. robustus and S. floridanus appeared inconsistent with species-level recognition for S. robustus.

Post-Grazing Changes of Vegetation in Big Bend National Park, Texas: A 50-Year Perspective

This research compared surveys of vegetation that were conducted in Big Bend National Park, Brewster County, Texas, during 1955–1960 and 1968–1969 with data collected in 2005 and 2006. Comparisons were based on percentages of cover and flora at five study sites. Results suggest some increases and decreases in certain types of vegetative cover since creation of the park, although no trend was consistent across elevations and years. Sites at lowest and highest elevations had significant increases in shrubs. Except for one, all sites had significant differences in total cover. Some species had changed in overall abundance. Lehmann lovegrass (Eragrostis lehmanniana) was becoming a dominant grass in foothills of the Chisos Mountains and surrounding Chihuahuan Desert. In contrast, leatherstem (Jatropha dioica), fragrant sumac (Rhus trilobata), tarbush (Flourensia cernua), four-wing saltbush (Atriplex canescens), desert hackberry (Celtis pallida), and Mexican mock vervain (Glandularia bipinnatifida) had disappeared from some, or all, locations where they were recorded previously.

Aeromagnetic mapping of the structure of Pine Canyon caldera and Chisos Mountains intrusion, Big Bend National Park, Texas

Analysis of aeromagnetic and gravity data reveals new details of the structure, igneous geology, and temporal evolution of the prominent, enigmatic ca. 32 Ma Pine Canyon caldera and the Chisos Mountains (Big Bend National Park, Texas). The main caldera-fi lling Pine Canyon Rhyolite, the oldest member of the South Rim Formation, is reversely magnetized, allowing it to be used as a key marker bed for determining caldera fi ll thickness. Modeling of gravity and magnetic anomalies indicates that the Pine Canyon Rhyolite is probably thicker in the northeastern part of the caldera. Lineaments in the magnetic data suggest the presence of buried faults beneath the caldera that may have led to increased downdrop in the northeast versus the southwest, allowing a thicker section of caldera fi ll to accumulate there. The Pine Canyon caldera has been interpreted as a downsag caldera because it lacks surfi cial faulting, so these inferred faults are the fi rst mapped features there that could be responsible for caldera collapse. The caldera boundary correlates well with the margins of a gravity low. General features of the caldera match well with basic models of downsag calderas, meaning that the Pine Canyon caldera may be a classic example of downsagging, of which few well-described examples exist, in terms of a geophysical signature. The source of a long-wavelength magnetic high over the Chisos Mountains is interpreted as a previously unknown broad intrusion, the long axis of which trends parallel to a major crustal boundary related to the Ouachita orogeny or an even earlier Precambrian margin. This feature represents the largest intrusion (28‐ 34 km diameter, 1‐4 km thick, 700‐3000 km 3 in volume) in an area where relatively small laccoliths are ubiquitous. The intrusion most likely represents a long-lived (>1 m.y.) reservoir replenished by small batches of magma of varying composition, as refl ected in the variation of eruptive products from the Pine Canyon and Sierra Quemada calderas. The intrusion may represent the easternmost occurrence of voluminous Tertiary magmatism in the southwestern United States.

Structure of Isolated Populations of Populus tremuloides (Quaking Aspen) in the Davis Mountains of Far-West Texas

Abstract Populus tremuloides is one of the most widespread woody species in North America, occurring across Canada, the northern United States, and at higher elevations in the southwestern United States and parts of Mexico. In Texas, it is found only at the highest elevations in a few disjunct populations in the Guadalupe, Davis, and Chisos Mountains. We examined the structure of six isolated P. tremuloides stands in the Davis Mountains. Stand age ranged from 25 to 65 years. The density of tree-sized P. tremuloides was 429 to 15,520 stems/ha, average basal area was 8.2 to 305.9 cm2/plant, and total basal area 5.1 to 22.9 m2/ha. As stand age increased, density of P. tremuloides decreased and average basal area and total basal area increased. The highest density of seedlings and saplings was in the younger stands. Seventeen woody species were found, with four to 10 woody species in any one stand. While these stands were dominated by P. tremuloides, two stands had Quercus gambelii relative basal area of 34 a...

GEOCHEMICAL INDICATORS OF EXTERNAL ADDITIONS TO SOILS IN BIG BEND NATIONAL PARK, TEXAS

Soil genesis in semiarid climates must consider the influences of aeolian and other forms of sediment deposition, particularly the emplacement of dust and dissolved constituents in rain and sediment trapped by overland flow. The purpose of this study was to explore the possibility of using Ti-indexed elemental concentrations of the fine earth, whole clay fractions, and rock fragments extracted from the soil to propose that the soil’s elemental composition is incompatible with its development exclusively from the underlying igneous parent material. The soil, a member of the Brewster series (Loamy-skeletal, mixed, superactive, thermic Lithic Haplustolls), is located in the Chisos Mountains of Big Bend National Park, Texas. The soil profile descriptions, chemical properties and clay mineralogy are consistent with a limited degree of soil weathering. However the total Ti-indexed concentrations of the macro-elements and the rare earth elements indicate a substantial elemental depletion, suggesting that weathering has been prolonged and intensive. Titanium concentrations in the clay fraction are substantially greater than those of the whole soil, suggesting that external clay additions inflate both the Ti content of the whole soil and the elemental loss estimates. The evolution of these soils is, in part, predicated on external clay additions, with sediment accumulation caused by the trapping of overland flow the most plausible scenario.

SOIL GENESIS ON PERALKALINE FELSICS IN BIG BEND NATIONAL PARK, TEXAS

Soil genesis involving felsic rocks frequently involves understanding the roles of climate and time on the transformations of the primary minerals into secondary products. This study focuses on the weathering of peralkaline felsics in a semiarid climate. Soils and fresh parent materials were collected from different microclimate regimes in the Chisos Mountains of Big Bend National Park, Texas. Soils in the Chisos mountains generally have either a mollic-argillic-rock or a mollic-rock horizon sequence, whereas other sites at lower and drier locations have an ochric-rock horizon sequence. Atmospheric deposition of Ca and Sr and wind deflation of clay are important attributes of soil genesis. Elemental loss rates of Si, Al, K, Na, and other elements are appreciable, suggesting that leaching has been important to the soil formation. Iron oxide formation, which is related to the moisture regime, is greater in soils having wetter microclimates. Solution chemistry suggests that Mg concentrations are appropriate for smectite synthesis and maintenance, potassium concentrations reflect the presence of feldspar, sodium concentrations reflect their loss rates because of leaching, and calcium reflects the presence of calcite. The rare earth elements similarly demonstrate loss rates consistent with chemical weathering. In general, chemical weathering of feldspars, atmospheric deposition of Ca and Sr, and wind deflation are important pedogenic processes.

Phylogeny of Social Behavior in Aphelocoma Jays: A Role for Hybridization?

-The phylogeny of jays in the genus Aphelocoma describes the evolutionary appearance or disappearance of helping and other social behaviors that have been much studied in this genus. Using published allozyme data and new behavioral characters we reexamine the phylogeny of Aphelocoma. The best-fitting hypothesis is that the complex social system of the Mexican Jay (Aphelocoma ultramarina), including delayed maturation, helping, plural breeding, and loss of the rattle call, arose from a simpler state in a jay ancestor, perhaps one that already had occasional nonbreeding associates. The interpretation of phylogeny in eastern populations of the Mexican Jay may be complicated by hybridization with the Scrub Jay (A. coerulescens), suggesting the possibility of reticulate evolution in the genus. The Florida Scrub Jay (A. c. coerulescens) appears to be closely related to the population of Scrub Jays in southern Mexico, and together the two constitute a distinct clade within the Scrub Jay superspecies. Received 4 March 1994, accepted 28 January 1995. ALTHOUGH BEHAVIOR was used as a tool to study phylogeny in birds in the 1940s and 1950s (e.g. Lorenz 1941), the tables have turned recently; now phylogeny has become a tool to study the evolution of behavior (Brooks and McLennan 1991, Harvey and Pagel 1991, Harvey and Purvis 1991, Price 1991, Lanyon 1992, Richman and Price 1992). The evolution of social behavior in general and of helping behavior in particular can be studied in this way (Edwards and Naeem 1993). The genus Aphelocoma is a promising subject for such research because it spans the gamut from a complex, pluralbreeding system in the Mexican Jay (Aphelocoma ultramarina; Brown 1963), through a polyandrous system in the Unicolored Jay (A. unicolor; Webber and Brown 1994), to singular breeding in pairs with or without nonbreeding helpers in the Scrub Jay (A. coerulescens; Woolfenden 1975, Carmen 1989). The genus inhabits a wide range of habitats including Central American cloud forests (A. unicolor), pine-oak-juniper woodlands (A. ultramarina), and scrub vegetation (A. coerulescens). Some of the behavioral, phylogenetic, and taxonomic problems in this genus concern the populations of A. ultramarina that inhabit the Sierra Madre Oriental of eastern Mexico. This chain of montane populations includes two subspecies and extends from the Mexican state of Hidalgo (A. u. potosina) north to the Chisos Mountains on the Texas border (A. u. couchii). The Mexican Jay has two other groups of subspecies, a series of populations mainly in the mountains of western Mexico ranging from Arizona and New Mexico south through the Sierra Madre Occidental to Jalisco (arizonae, wollweberi, gracilis), and the populations crossing central Mexico in the Transvolcanic region (A. u. ultramarina, A. u. colimae). We refer to these geographic groups of subspecies as Orientalis, Occidentalis and Transvolcanic, respectively (Fig. 1). In this paper we survey the genus Aphelocoma with special reference to Orientalis. The Orientalis group may have been critical in the origin or loss of helping behavior in the genus (Brown and Horvath 1989, Peterson 1992b). Orientalis also has attracted the attention of behavioral ecologists because of the presence of certain Scrub-Jay-like behaviors and developmental patterns that are absent or weakly developed in other populations of the Mexican Jay. Three decades ago it was noticed that couchii, the population of Aphelocoma ultramarina in the border mountains of Texas and Coahuila, was in many respects somewhat intermediate between the Occidentalis group and the Scrub Jay (Brown 1963). Later, Orientalis was found to resemble the Scrub Jay in additional aspects of its social behavior (Brown and Horvath 1989). Northern populations of Orientalis possess a rattle call that is not found in the other groups (Strahl and Brown 1987 and earlier authors). In addition, sizes of territorial flocks in these populations are smaller, and the flocks appear to have only one breeding female each (singular

Hybridization between Juniperus erythrocarpa Cory and Juniperus pinchotii Sudworth in the Chisos Mountains, Texas

Hybridization between Juniperus erythrocarpa Cory and Juniperus pinchotii Sudworth in the Chisos Mountains, Texas

Systematics of Vaejovis dugesi Pocock, with Descriptions of Two New Related Species (Scorpiones, Vaejovidae)

Vaejovis dugesi Pocock, previously recognized as a subspecies of Vaejovis mexicanus Koch, is redescribed and elevated to specific status. Two new species are described: Vaejovis chisos, from the Chisos Mountains in Big Bend National Park, Texas, and Vaejovis sprousei, from the Mexican states of Tamaulipas and Nuevo Le6n. RESUMEN--Vaejovis dugesi Pocock, reconocido previamente como una subespecie de Vaejovis mexicanus Koch, es redescrito y elevado a estado especifico. Se describen dos nuevas especies: Vaejovis chisos, de Chisos Mountains en el Parque National Big Bend, Texas, y Vaejovis sprousei, de los estados mexicanos de Tamaulipas y Nuevo Le6n. The scorpion Vaejovis mexicanus dugesi Pocock was described from the mountains of Guanajuato (Pocock, 1902), and the type remains the single known specimen referable to this taxon. Vaejovis m. dugesi has rarely been mentioned in subsequent systematic works, and its identity has remained enigmatic. Hoffmann (1931) listed the taxon but indicated he had not seen any material referable to it. He suggested that it was similar to Vaejovis granulatus, especially in color pattern, but did not propose a synonymy. Diaz Naijera (1975) did not mention V. m. dugesi in a revised list of Mexican scorpions. I had the opportunity to study the type of V. m. dugesi. It is clear that its closest relative is not V. mexicanus and that it should be regarded as a valid species. Examination of considerable vaejovid material collected throughout mainland Mexico has uncovered only one additional specimen of this species, but new related species from northeastern M6exico and the Chisos Mountains in the Big Bend area in Texas have been found. These species have obvious affinities with certain members of the V. mexicanus group. They have dusky markings on the dorsum (faint in the species from Big Bend), are similar in metasomal carinal structure, have weak dorsointernal carinae on the pedipalp chelae, and have trichobothrium et of the chela fixed finger situated very close to the third enlarged primary row denticle. They differ from other species in the V. mexicanus group as follows: (1) the pedipalps are relatively long and slender, with chela length: width ratios exc eding 4.0, (2) the chela fingers end in moderately to distinctly enlarged, clawlike terminal denticles. These latter features are suggestive of pecies of the Vaejovis nitidulus group. However, e species of that group have trichobothrium et situated at the level of or distal to the second enlarged primary row denticle and a well developed, crenulate to serrate dorsointernal chela carina. Because Vaejovis dugesi and the new species lack these characters, it seems best to retain them in the V. mexicanus group. Vaejovis dugesi Pocock, new combination

Occurrences of the Millipeds Thrinaxoria lampra (Chamberlin) and Stenodesmus tuobitus (Chamberlin) in Eastern and Southern Texas (Polydesmida: Xystodesmidae)

In the past 2 years, knowledge of the xystodesmid milliped fauna of Texas has increased dramatically. Before 1987, only two species were known from the state: Rhysodesmus texicolens (Chamberlin), in the lower Rio Grande Valley (records summarized by Hoffman (1970)) and Pachydesmus clarus (Chamberlin), in eastern counties near Louisiana (Hoffman, 1958; Stewart, 1969). The first xystodesmid from western Stenodesmus tuobitus (Chamberlin), discovered in McKittrick Canyon, Guadalupe Mountains National Park, Culberson Co., and additional sites for the previous species were reported in 1987 (Shelley, 1987). Rhysodesmus chisosi Shelley was described from the Chisos Mountains, Big Bend National Park, Brewster Co., Texas (Shelley, 1989). An unidentifiable juvenile with retrorse coxal spines was also recorded (Shelley, 1989), thus representing an additional genus and species, from Three Mile Cave, Williamson Co., Texas. A sixth xystodesmid can now be reported from as I recently discovered a male and female of Thrinaxoria lampra (Chamberlin) from Longview, Gregg Co., in the private collection of R. L. Hoffman. The specimens were collected by H. F. Loomis on 13 May 1931, and the gonopods agree closely with published illustrations (Shelley, 1984:Figs. 25 and 26), except for a shorter, stouter prefemoral process. This record, the westernmost for T. lampra and some 80 km from the closest known localities in western Louisiana, confirms statements that the milliped probably occurs in eastern Texas (Shelley, 1984, 1987), and, indeed, Wood (1864, 1865) reported its congener, Thrinaxoria bifida (Wood), from Texas, although this species actually is found in Tennessee, North Carolina, and Georgia (Shelley, 1984). At least one more xystodesmid is expected in eastern since Pleurolomaflavipes Rafinesque inhabits adjoining parts of Oklahoma, Arkansas, and Louisiana (Shelley, 1980). Another recent discovery is that of a male of S. tuobitus from Edinburg, Hidalgo Co., at the National Museum of Natural History, Smithsonian Institution (NMNH). The closest known locality, McKittrick Canyon, is about 936 km to the northwest. The new locality seems accurate because the specimen was mixed with eurymerodesmids known to occur in southern Texas and because it was collected by S. Mulaik in April 1935, a time when he sampled other millipeds in the Rio Grande Valley. The male from Hidalgo Co. is fragmented and unmeasurable but is larger than those from Culberson Co. and subequal to ones in Otero Co., New Mexico. The gonopods conform closely to published illustrations (Hoffman, 1966:Fig. 7; Shelley, 1987:Fig. 2b), and the only noteworthy variation concerns the sharply triangular sternal spines subtending the posterior leg coxae on segments 10 through 18, which are much sharper and more pronounced than the minute lobes on western males. Thus, S. tuobitus is now known from three allopatric populations, two relatively close ones in western Texas and southern New Mexico, and one far to the southeast in the lower Rio Grande Valley. This distribution reflects fragmentation of an ancestral range that probably covered much of southern, central, and western Texas. The milliped may also have extended south of the Rio Grande River and isolated pockets may survive today in remote corners of Nuevo Leon and Tamaulipas Provinces, Mexico. Figure 1 shows the known distributions of the six xystodesmids in Texas. I thank my colleagues R. L. Hoffman and J. A. Coddington for loaning the samples of T. lampra and S. tuobitus, respectively. The latter was located in 1986 while I was working at the NMNH on a Smithsonian Short-Term Visitor Award.

Geographic Variation of Group Size, Ontogeny, Rattle Calls, and Body Size in Aphelocoma ultramarina

Geographic Variation of Group Size, Ontogeny, Rattle Calls, and Body Size in Aphelocoma ultramarina

Stratigraphy of the Cretaceous-Tertiary and Paleocene-Eocene Transition Rocks of Big Bend National Park, Texas

The marine to terrestrial transition in the Big Bend area falls within the Late Cretaceous Aguja Formation, and, in light of new biostratigraphic data resulting from screening for small vertebrates and magneto-stratigraphic data, the Cretaceous-Tertiary boundary falls within the Javelina Formation, which includes the first red banding produced by oxidation of overbank fluvial mudstones. No record of a catastrophic event is apparent in the Javelina Formation. The Javelina, Black Peaks, and Hannold Hill Formations and the Big Yellow Sandstone Member of the Canoe Formation record increasing uplift in the region, culminating in uplift and volcanism in the Chisos Mountains, the source for upper Canoe Formation sediments. The sequence of changes produced by this trend and by unroofing in source highlands to the west is sufficiently gradual that the Javelina through Black Peaks units are not lithostratigraphically distinct at the formation level and therefore are reduced to member status, and placed, along with ...