East-central Arizona Research Articles

Stratigraphic evidence for culturally variable Indigenous fire regimes in ponderosa pine forests of the Mogollon Rim area, east-central Arizona – CORRIGENDUM

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Stratigraphic evidence for culturally variable Indigenous fire regimes in ponderosa pine forests of the Mogollon Rim area, east-central Arizona

AbstractThe impact of Indigenous populations on historical fire regimes has been controversial and beset by mismatches in the geographic scale of paleofire reconstructions and the scale of land-use behaviors. It is often assumed that anthropogenic burning is linearly related to population density and not different cultural practices. Here we take an off-site geoarchaeology strategy to reconstruct variability in historical fire regimes (<1000 years ago) at geographic scales that match the archaeological, ethnohistorical, and oral tradition evidence for variability in the intensity of Indigenous land use by two different cultural groups (Ancestral Pueblo and Western Apache). We use multiple, independent proxies from three localities in ponderosa pine (Pinus ponderosa) forests in east-Central Arizona to reconstruct fire regime variability during four phases of cultural use of different intensities. Elevated charcoal with domesticate pollen (Zea spp.) but otherwise unchanged forest pollen assemblages characterized intensive land use by Ancestral Pueblo people during an early phase, suggesting fire use to support agricultural activities. By contrast, a phase of intensive pre-reservation Western Apache land use corresponded to little change in charcoal, but had elevated ash-derived phosphorus and elevated grass and ruderal pollen suggestive of enhanced burning in fine fuels to promote economically important wild plants.

Cenozoic drainage reversal on the southern margin of the Colorado Plateau, east-central Arizona, USA

Laramide northeast-flowing streams from the ancestral Mogollon highland beveled gently northeast-dipping Late Proterozoic to Cretaceous strata across the southern Colorado Plateau Transition Zone. Late Eocene renewed uplift rejuvenated northeast-flowing streams incising paleocanyons. Apache paleocanyon was incised into the Mogollon highland, including the north-trending Laramide Apache uplift bounded by major reverse faults/monoclines. The Mogollon Rim sequence aggraded in Apache paleocanyon and on a broad alluvial plain to the east. Middle Cenozoic tectonic subsidence of the Transition Zone, aridification, and volcanism combined to aggrade Apache paleocanyon with sedimentary and volcanic rocks from 37.6 to 18.63 Ma. Emplacement of the Mogollon-Datil caldera complex and Chuska erg on the southeastern Colorado Plateau forced streamflow to northwest-dispersal of fluvio-eolian sediment from 34 to 26 Ma. Following erosion by northwest-flowing streams on the southern Colorado Plateau from ~26 to 16 Ma, lake sediments of the lower Bidahochi Fm were deposited. Southwestward reactivation of Laramide faults was underway by ~25 Ma coeval with extensive 25 to 20 Ma Natanes Plateau basalt flows and extreme crustal thinning southwest of the Transition Zone. As northeastward streamflow gradually diminished, a Superstition field ash flow tuff ended northeastward flow at 18.63 Ma and was followed by a period of sluggish southwest stream flow and ponding until after ~14.84 Ma. Southwestward structural subsidence and possible spillover from ancestral Lake Hopi on the Colorado Plateau southern margin caused incision of the southwest-directed Dagger Canyon paleovalley after 14.84, which followed the path of the earlier Apache paleocanyon and possibly to the Sespe delta on the California coast before opening of Gulf of California. Structural collapse of the Tonto Basin to the west induced deposition of the Dagger Canyon Conglomerate in the Dagger Canyon paleovalley before the modern Salt River incised all previous deposits and became integrated with the Gila River during the Plio-Pleistocene.

Systematics of the mountain-inhabiting cottontails (Sylvilagus) from southwestern United States and northern Mexico (Mammalia: Lagomorpha: Leporidae)

The skull morphology of four species of cottontails from the mountains and plateaus of southwestern United States and northern Mexico, currently recognized as Sylvilagus nuttallii, S. cognatus, S. robustus, and S. holzneri (=S. floridanus holzneri), was analyzed using multivariate statistics. Based on 26 or 30 measurements taken on each of 350 adult skulls, and formulation of 16 pooled samples, with each representing a different geographic population, the results show there are two species-level distinctions in skull type. Cottontails from southern Utah, northern and east-central Arizona, and northern New Mexico show morphological overlap among geographically adjacent samples and all have a highly arched skull. These are referable to S. nuttallii. Cottontails from central Arizona, central New Mexico, and western Texas southward along the Sierra Madre Occidental to Durango, Mexico, and Sierra Madre Oriental to central Coahuila, Mexico show morphological overlap among geographically adjacent samples and all have a relatively flat skull. These are referable to S. holzneri. Both S. nuttallii and S. holzneri are polytypic in the study area. Sylvilagus n. pinetis is restricted to the White Mountains of Arizona. Those north and west of the Colorado River in Arizona and Utah are referable to S. n. nuttallii and those from southeastern Utah, northeastern Arizona and northern New Mexico are referable to S. n. grangeri. The population of cottontails previously referred to S. cognatus from central New Mexico is indistinguishable from topotypical S. holzneri from southeastern Arizona as well as populations from southwestern New Mexico, Chihuahua, and Sonora, Mexico. Cottontails previously referred to S. robustus, from the Guadalupe Mountains of New Mexico and Texas, southward in the mountains of western Texas, and the Sierra Madre Oriental to central Coahuila, Mexico, average larger in overall size and, on average, have proportionately larger auditory bullae and are referable to S. holzneri robustus. The relationship of S. holzneri to other mountain/plateau-inhabiting taxa, outside the study area in central and southern Mexico remains to be resolved.

Remote Sensing Analysis to Quantify Change in Woodland Canopy Cover on the San Carlos Apache Reservation, Arizona, USA (1935 vs. 2017)

Since the late 1800s, pinyon–juniper woodland across the western U.S. has increased in density and areal extent and encroached into former grassland areas. The San Carlos Apache Tribe wants to gain qualitative and quantitative information on the historical conditions of their tribal woodlands to use as a baseline for restoration efforts. At the San Carlos Apache Reservation, in east-central Arizona, large swaths of woodlands containing varying mixtures of juniper (Juniperus spp.), pinyon (Pinus spp.) and evergreen oak (Quercus spp.) are culturally important to the Tribe and are a focus for restoration. To determine changes in canopy cover, we developed image analysis techniques to monitor tree and large shrub cover using 1935 and 2017 aerial imagery and compared results over the 82-year interval. Results showed a substantial increase in the canopy cover of the former savannas, and encroachment (mostly juniper) into the former grasslands of Big Prairie. The Tribe is currently engaged in converting juniper woodland back into an open savanna, more characteristic of assumed pre-reservation conditions for that area. Our analysis shows areas on Bee Flat that, under the Tribe’s active restoration efforts, have returned woodland canopy cover to levels roughly analogous to that measured in 1935.

Tracing the Circulation of Iconographic-style Red Ware in East-central Arizona

The appearance of Fourmile Polychrome in the AD 1320s signaled a shift in the decorative layout, use, and perhaps even value of red-slipped pottery in east-central Arizona. Bowls were often painted with iconographic-style designs that diverged from the geometric imagery of earlier White Mountain Red Ware. The type was circulated through the region and even copied in some localities. The provenance of Fourmile Polychrome has remained a mystery due to the lack of research at late Silver Creek villages. We integrate results of neutron activation analysis (NAA) with a large corpus of existing NAA data to shed light on the production and circulation of this iconographic-style pottery. The results illuminate the social networks of ceramic circulation in the Silver Creek drainage and surrounding areas during the fourteenth century.

Early Pueblo Period Population Aggregation and Dispersal in the Petrified Forest Region, East-Central Arizona

The Western Puerco region of east-central Arizona figured prominently in foundational studies of the Early Pueblo period (AD 650–950) yet remains on the periphery of recent research. This article presents new survey and chronometric data from three communities located in a densely occupied portion of the Western Puerco, the Petrified Forest. These data suggest that the Petrified Forest hosted the earliest known aggregated settlement in the region, ca. AD 700–800, before residents transitioned to a dispersed settlement pattern that remained in place through the Chaco era. Neighboring portions of the Western Puerco, however, only hosted settlements of a similar size from AD 840 forward. Chaco great houses were founded in these communities during the tenth and eleventh centuries. Unlike better known examples of aggregation in the northern San Juan region that unfolded within only a few generations, similar developments in the Petrified Forest were likely the culmination of hundreds of years of local population growth, increasing sedentism, and use of prominent natural features on the landscape. The lack of fit between the causal factors proposed for village formation in the northern San Juan and eighth-century aggregation in the Petrified Forest suggests alternative models are needed to explain the formation of early population aggregates in the Western Puerco and across much of the western portion of the northern Southwest more broadly.

A new species of Hypoprepia from the mountains of central Arizona (Lepidoptera, Erebidae, Arctiinae, Lithosiini).

A new firefly-mimicking lichen moth of the genus Hypoprepia, H.lampyroides Palting & Ferguson, sp. n., is described from the mountains of east-central Arizona and the Sierra Madre Occidental of Mexico. Hypoprepia Hübner, 1831 is a North American genus of lithosiine tiger moths, previously consisting of five species: H.fucosa Hübner, 1831 and H.miniata (Kirby, 1837), both of eastern and central North America; H.cadaverosa Strecker, 1878 from the Rocky Mountains into New Mexico and west Texas; H.inculta H. Edwards, 1882, a widespread western USA species and H.muelleri Dyar, 1907 from the vicinity of Mexico City. The latter is herein synonymized under H.inculta (= H.muellerisyn. n.), resulting in the total number of taxa in the genus unchanged at five.

Basaltic magmatic mapping: A suggested methodology and the resulting petrologic and volcanic hazard implications from the Springerville Volcanic Field, east central Arizona

The magmatic mapping methods we describe from the recently completed map of the Pleistocene Springerville Volcanic Field (SVF) provide a robust organizational model for detailed mapping of similar monogenetic continental fields. Results from this work offer a unique temporal and physical assessment of the lavas and their volcanic hazards from this field for comparison with other similar volcanic occurrences on all terrestrial-like planets.Magmatic mapping focuses on recognizing each individual magmatic event or unit. It involves delineating contacts between units, characterizing the units, placing them into a stratigraphically controlled temporal framework and organizing the data for analysis based on these recognized units.The ~3000 km2 SVF contains 501 units comprised of lava flows and cinder (scoria) cones. Of the 12 lithologic classes we defined, olivine phyric lavas are most abundant (244 units), comprising nearly 45% of the mapped areal extent of volcanic outcrop. The next most extensive are diktytaxitic (7 units) and olivine-plagioclase (48 units) units, each making up approximately 15% of the outcrop area. Younger units trend towards more evolved lithologies ranging from aphyric to feldspathic basalts; these 5 lithologic classes (106 total units, 16.7% areal extent) have smaller average areas. Similarly, lava geochemistry trends towards more alkalic products in younger units. The largest geochemical class is basalt with tholeiitic affinities (>24% areal extent), followed by transitional basalts (23.7%), alkali-olivine basalts (20.5%) and hawaiites (12.9%) with lesser amounts of the five more evolved classes (15.5% combined) and basanites (3.7%). Eruptions progressed from large volumes of tholeiites (21.6% observed, 36% interpreted) early in its lifespan (2–1.5 Ma), to an intermediate period (1.5–1.0 Ma) characterized by AOB (11.3%) and transitional basalts (8.9%), with increasing evolved alkali rocks (EAR, 12.5%). Its most recent phase (1.0 to 0.3 Ma) was dominated by more alkalic eruptions (EAR comprising 12.3%, with AOB and transitional basalt totaling 7.4%), a field-wide trend mimicked locally by seven temporal-vent clusters defined by Condit and Connor (1996).This pattern, from early high volume tholeiitic to lower volume alkalic eruptions, provides some predictability as to the types of volcanic hazards inherent in these fields. In terms of lava-flow hazards, the most destructive events of this field come from eruptions of fluid-high-volume-lavas with tholeiitic affinities, which are the least predictable because they initiate volcanism both field-wide, and within spatial temporal-vent clusters, and they affect the largest areal extent of any magma type. The later stage, lower volume alkalic eruptions pose a greater explosive threat, although their timing in the chemo-temporal patterns observed in the SVF suggest a higher degree of predictability.

Evaluating and monitoring forest fuel treatments using remote sensing applications in Arizona, U.S.A.

Abstract The practice of fire suppression across the western United States over the past century has led to dense forests, and when coupled with drought has contributed to an increase in large and destructive wildfires. Forest management efforts aimed at reducing flammable fuels through various fuel treatments can help to restore frequent fire regimes and increase forest resilience. Our research examines how different fuel treatments influenced burn severity and post-fire vegetative stand dynamics on the San Carlos Apache Reservation, in east-central Arizona, U.S.A. Our methods included the use of multitemporal remote sensing data and cloud computing to evaluate burn severity and post-fire vegetation conditions as well as statistical analyses. We investigated how forest thinning, commercial harvesting, prescribed burning, and resource benefit burning (managed wildfire) related to satellite measured burn severity (the difference Normalized Burn Ratio – dNBR) following the 2013 Creek Fire and used spectral measures of post-fire stand dynamics to track changes in land surface characteristics (i.e., brightness, greenness and wetness). We found strong negative relationships between dNBR and post-fire greenness and wetness, and a positive non-linear relationship between dNBR and brightness, with greater variability at higher severities. Fire severity and post-fire surface changes also differed by treatment type. Our results showed harvested and thinned sites that were not treated with prescribed fire had the highest severity fire. When harvesting was followed by a prescribed burn, the sites experienced lower burn severity and reduced post-fire changes in vegetation greenness and wetness. Areas that had previously experienced resource benefit burns had the lowest burn severities and the highest post-fire greenness measurements compared to all other treatments, except for where the prescribed burn had occurred. These results suggest that fire treatments may be most effective at reducing the probability of hazardous fire and increasing post-fire recovery. This research demonstrates the utility of remote sensing and spatial data to inform forest management, and how various fuel treatments can influence burn severity and post-fire vegetation response within ponderosa pine forests across the southwestern U.S.

Canyon Creek revisited: New investigations of a late prehispanic turquoise mine, Arizona, USA

Turquoise has been used in the American Southwest since “time immemorial,” and remains an important material for contemporary indigenous groups of the region. Detailed studies of ancient turquoise mines are few, however, and inferences of turquoise procurement and provenance have been limited. Our intensive investigation of one mine, the Canyon Creek locale in Arizona, integrates archaeology and geochemistry to enhance understanding of the mine and its output. A detailed description of the mine's morphology and geologic setting lays foundations for interpreting an isotopic analysis of specimens from the mine's four localities. The analysis reveals extremely radiogenic Pb isotope ratios, which distinguish Canyon Creek turquoise from that of other known sources in the American Southwest. Its distinctive isotopic signature makes Canyon Creek turquoise readily identifiable in archaeological assemblages. The presence of turquoise from Canyon Creek at late prehispanic settlements in east-central Arizona helps clarify the mine's chronology of use and regional distribution. Our observations suggest the mine was larger than previously supposed, and that it provided an important source of turquoise for inhabitants of the region during the thirteenth and fourteenth centuries AD.

High-Temporal Resolution Photography for Observing Riparian Area Use and Grazing Behavior

Observation is a simple method of acquiring information and is a critical step in the scientific method for both developing and investigating testable hypotheses. Cameras have long played a role in observation, and as technology advances, new tools and methods for collecting, interrogating, and displaying large quantities of high-resolution images have evolved. We describe an automated digital time-lapse camera system and present an example field deployment to observe the temporal and spatial patterns of riparian use by humans and animals during a 3-mo period. We also describe software tools for image interrogation and visualization, as well as new information gathered through their use. The system was tested in 2014, in a 2.4-ha site within the Apache-Sitgreaves National Forest in east central Arizona, United States where elk (Cervus elaphus nelsoni) and cattle grazed. Photographs were taken every 30 sec for 38 d, after which an electric fence was installed to restrict cattle access and the time step was increased to every 3 min. We observed that elk exhibited the unique behavior of standing in and traveling within the stream channel while grazing and tended to graze and lie in close proximity to the channel. Cattle drank from, but typically did not enter, the stream channel and tended to lie away from the channel. Recreational use by people had the distinct impact of dispersing elk from the riparian corridor. Zoomable time-lapse videos allowed us to observe that in contrast to the cattle, elk grazed while lying down. High-temporal resolution photography is a practical tool for observing phenomena that are important for local resource management.

Vegetative response to water availability on the San Carlos Apache Reservation

On the San Carlos Apache Reservation in east-central Arizona, U.S.A., vegetation types such as ponderosa pine forests, pinyon-juniper woodlands, and grasslands have significant ecological, cultural, and economic value for the Tribe. This value extends beyond the tribal lands and across the Western United States. Vegetation across the Southwestern United States is susceptible to drought conditions and fluctuating water availability. Remotely sensed vegetation indices can be used to measure and monitor spatial and temporal vegetative response to fluctuating water availability conditions. We used the Moderate Resolution Imaging Spectroradiometer (MODIS)-derived Modified Soil Adjusted Vegetation Index II (MSAVI2) to measure the condition of three dominant vegetation types (ponderosa pine forest, woodland, and grassland) in response to two fluctuating environmental variables: precipitation and the Standardized Precipitation Evapotranspiration Index (SPEI). The study period covered 2002 through 2014 and focused on a region within the San Carlos Apache Reservation. We determined that grassland and woodland had a similar moderate to strong, year-round, positive relationship with precipitation as well as with summer SPEI. This suggests that these vegetation types respond negatively to drought conditions and are more susceptible to initial precipitation deficits. Ponderosa pine forest had a comparatively weaker relationship with monthly precipitation and summer SPEI, indicating that it is more buffered against short-term drought conditions. This research highlights the response of multiple, dominant vegetation types to seasonal and inter-annual water availability. This research demonstrates that multi-temporal remote sensing imagery can be an effective tool for the large scale detection of vegetation response to adverse impacts from climate change and support potential management practices such as increased monitoring and management of drought-affected areas. Different vegetation types displayed various responses to water availability, further highlighting the need for individual management plans for forest and woodland, especially considering the projected drier conditions in the Southwest U.S. and other arid or semi-arid regions around the world.

The White Mountain Recreational Enterprise: Bio-Political Foundations for White Mountain Apache Natural Resource Control, 1945–1960

Among American Indian nations, the White Mountain Apache Tribe has been at the forefront of a struggle to control natural resource management within reservation boundaries. In 1952, they developed the first comprehensive tribal natural resource management program, the White Mountain Recreational Enterprise (WMRE), which became a cornerstone for fighting legal battles over the tribe’s right to manage cultural and natural resources on the reservation for the benefit of the tribal community rather than outside interests. This article examines how White Mountain Apaches used the WMRE, while embracing both Euro-American and Apache traditions, as an institutional foundation for resistance and exchange with Euro-American society so as to reassert control over tribal eco-cultural resources in east-central Arizona.

Evaluating Lidar Point Densities for Effective Estimation of Aboveground Biomass

The U.S. Geological Survey (USGS) 3D Elevation Program (3DEP) was recently established to provide airborne lidar data coverage on a national scale. As part of a broader research effort of the USGS to develop an effective remote sensing-based methodology for the creation of an operational biomass Essential Climate Variable (Biomass ECV) data product, we evaluated the performance of airborne lidar data at various pulse densities against Landsat 8 satellite imagery in estimating above ground biomass for forests and woodlands in a study area in east-central Arizona, U.S. High point density airborne lidar data, were randomly sampled to produce five lidar datasets with reduced densities ranging from 0.5 to 8 point(s)/m 2 , corresponding to the point density range of 3DEP to provide national lidar coverage over time. Lidar-derived aboveground biomass estimate errors showed an overall decreasing trend as lidar point density increased from 0.5 to 8 points/m 2 . Landsat 8-based aboveground biomass estimates produced errors larger than the lowest lidar point density of 0.5 point/m 2 , and therefore Landsat 8 observations alone were ineffective relative to airborne lidar for generating a Biomass ECV product, at least for the forest and woodland vegetation types of the Southwestern U.S. While a national Biomass ECV product with optimal accuracy could potentially be achieved with 3DEP data at 8 points/m 2 , our results indicate that even lower density lidar data could be sufficient to provide a national Biomass ECV product with accuracies significantly higher than that from Landsat observations alone.

John Beach Rinaldo: Quintessential Culture Historian

During an archaeological career that spanned four decades, John Beach Rinaldo (1912-1999) made substantive contributions to the delineation and definition of the Mogollon Culture, the culture history of west-central New Mexico and east-central Arizona, and the identification of material relationships between precolumbian cultures and modern-day Zuni. For a variety of reasons, Rinaldo is overshadowed by his Field Museum collaborator Paul Sidney Martin. As a result, historians of archaeology have failed to critically evaluate Rinaldo's career and contributions. This paper offers a controlled analysis and comparison of data in unpublished archives, artifact collections at the Field Museum, and the published record to illuminate previously unrecognized but important aspects of Rinaldo's many contributions to archaeological knowledge, method, and theory.

Internal anatomy of the Late TriassicEquisetocaulisgen. nov., and the evolution of modern horsetails

Abstract The occurrence of permineralized stem fragments with diagnostic equisetophyte anatomy in Petrified Forest National Park, east-central Arizona provides an opportunity to characterize the internal structure of a Late Triassic (Norian Stage) equisetophyte. Features of Equisetocaulis muirii gen. et sp. nov. constitute the first evidence for internal anatomy of a Triassic equisetophyte from the Northern Hemisphere. Anatomically preserved stem fragments occur in pyrite nodules and are revealed on etched surfaces of nodule wafers. Stems range 7–16 mm in diameter, with a large hollow pith and 24–40 cauline bundles, each with a distinct carinal canal and several rows of radially aligned secondary tracheids. Cauline bundles converge at nodes to produce a ring of tracheids within the nodal diaphragms. Leaf traces and branch bases occur at nodes on alternating radii. These features confirm a close relationship between at least one of the equisetophytes from the Chinle Formation and modern species, amplify ou...

The Lives of Painted Bowls at Ancestral Pueblos in East-Central Arizona

AbstractThe appearance of iconographic-style pottery at fourteenth-century Pueblo villages in east-central Arizona marked an important shift in the decoration of pottery. These polychrome containers were painted with elaborate imagery that contrasts with earlier geometric-style traditions. Remarkably, though the type was circulated and copied throughout the region, we still know very little about how it was used. This paper addresses that issue by analyzing surface abrasions on a large corpus of White Mountain Red Ware whole vessels. Our research not only examines changes in the uses of Ancestral Pueblo ceramics during the late prehispanic period, but underscores the importance of use-alteration studies to interpreting the biographies of ancient objects.

Identifying the Origin of Southwestern Shell: A Geochemical Application to Mogollon Rim Archaeomolluscs

Archaeological marine shell artifacts moving over long distances may reveal the remnants of social networks, social currency, and the nuances of exchange. For the southwestern United States and northern Mexico, potential sources of marine shell are predominantly the Gulf of California and Pacific Ocean. There exists some taxonomic overlap between molluscan communities of these regions and the Gulf of California, necessitating non-biogeographic methods to distinguish their origins. Combined oxygen and carbon stable isotope ratio measurements demonstrate that modern shells from these water bodies have distinct isotopic ranges. Molluscan isotopie composition within the Gulf of California varies, which allows for the identification of distinct source regions. Archaeological marine shell from Pueblo III and IV sites in the Mogollon Rim region of east-central Arizona are sourced, demonstrating that archaeological shell was obtained from a northeastern subregion of the Gulf of California. This is the closest source for the Puebloan communities, but it is not consistent with previous hypotheses concerning the origin of marine shell in the Colorado Plateau and Mogollon Highlands, which suggested an exchange route via Paquime originating south of Isla Tiburon. We discuss the implications of these results in the context of previous research and draw conclusions about the meaning of shell use in the region.

Identifying the Origin of Southwestern Shell: A Geochemical Application to Mogollon Rim Archaeomolluscs

Archaeological marine shell artifacts moving over long distances may reveal the remnants of social networks, social currency, and the nuances of exchange. For the southwestern United States and northern Mexico, potential sources of marine shell are predominantly the Gulf of California and Pacific Ocean. There exists some taxonomic overlap between molluscan communities of these regions and the Gulf of California, necessitating non-biogeographic methods to distinguish their origins. Combined oxygen and carbon stable isotope ratio measurements demonstrate that modern shells from these water bodies have distinct isotopic ranges. Molluscan isotopie composition within the Gulf of California varies, which allows for the identification of distinct source regions. Archaeological marine shell from Pueblo III and IV sites in the Mogollon Rim region of east-central Arizona are sourced, demonstrating that archaeological shell was obtained from a northeastern subregion of the Gulf of California. This is the closest source for the Puebloan communities, but it is not consistent with previous hypotheses concerning the origin of marine shell in the Colorado Plateau and Mogollon Highlands, which suggested an exchange route via Paquime originating south of Isla Tiburon. We discuss the implications of these results in the context of previous research and draw conclusions about the meaning of shell use in the region.