Petrified Forest National Park Research Articles

Re-evaluation of alleged bees' nests from the Upper Triassic of Arizona

Published records of supposed Triassic bees' nests are based on trace fossils in silicified wood and in sandstone in Upper Triassic strata of the Chinle Group in Petrified Forest National Park, Arizona. A critical, firsthand restudy of these trace fossils indicates that they lack diagnostic features of bees' nests, such as cells with smooth linings and spiral closure caps. Indeed, many of the observations claimed to identify these traces as bees' nests cannot be replicated. Instead, the putative Triassic bees' nests can be classified as: 1. Clavate borings in petrified wood, somewhat similar to Teredolites; these borings preferentially penetrate heart-rot fungus ( Polyporites) and are mostly likely larval chambers of wood-boring beetles. 2. Cylindrical, vertical burrows in sandstone assignable to Skolithos; these are almost certainly arthropod produced. The recognition that the Chinle Group trace fossils are not bees' nests eliminates them as evidence that decouples bee origins from the Cretaceous origin of angiosperms. The Triassic trace fossils in silicified wood are also a new and unique record of likely beetle borings in Triassic wood.

A Fly in the Amber: <i>Route 66 Architecture at Petrified Forest National Monument</i>

A Fly in the Amber:Route 66 Architecture at Petrified Forest National Monument Lillian Makeda (bio) Located in eastern Arizona, Petrified Forest National Park is renowned for its spectacular geography and outstanding paleontological resources. The area was set aside as one of the first national monuments created by President Theodore Roosevelt after the passage of the Antiquities Act of 1906.1 Living trees are few and far between in the rolling landscape of this bleak and desolate region, where the remains of ancient forests endure as some of the most important deposits of petrified wood in the world (Figure 1). The arrival of sightseers by way of the Thirty-Fifth Parallel Transcontinental Railroad Line and the National Old Trails Road (later to become Route 66) prompted both the National Park Service and private enterprise to develop architecture that would frame the touristic experience of Petrified Forest. Diverging objectives produced sharply contrasting designs for buildings. The National Park Service favored the Spanish-Pueblo Revival style from 1929 to 1942, and the International Style from 1958 through 1965.2 Private enterprise, along Route 66, built commercial vernacular buildings that epitomized the "flamboyant hucksterism" often found in contemporary roadside architecture.3 The Park Service at Petrified Forest viewed these types of ventures as "undesirable" and worked assiduously to remove them from the landscape. The most contentious business site was known as the Painted Desert Park or, alternatively, the Lion Farm, a small operation that sold gasoline, souvenirs, and snacks. Between the late 1950s and mid-1960s, archetypal examples of each of these three styles—Spanish-Pueblo Revival, the International Style, and commercial vernacular—comprised the only buildings on a plateau overlooking the Painted Desert in the northern part of the monument and were located a short distance from each other (Figure 2). This striking architectural juxtaposition would have been further heightened by the area's flat, barren terrain. In 1930, the National Park Service embarked on a lengthy campaign to take control of the architecture in and around Petrified Forest and eliminate the Lion Farm. The built environment of the park as it appears today reflects a plan conceived exclusively by the Park Service, which finally triumphed after a protracted battle that pitted federal and state governments against small-scale entrepreneurs who sought to make a living near the Painted Desert. The conflict at Petrified Forest represents only one instance of what has been an ongoing endeavor to assert government influence over the property within and around national parks and monuments. On a national level, these efforts have met with varying degrees of success, but when it came to Petrified Forest, the Park Service ultimately prevailed. Petrified Forest National Monument Accounts of petrified wood in eastern Arizona began to receive wide distribution after the completion of the Atlantic and Pacific railway line in 1883.4 The railroad furnished the primary means of approach for over thirty years, and the area became one of several attractions that would be packaged by the Atchison, Topeka, and Santa Fe as "the American Southwest." Charles Lummis, famous for Mesa, Cañon, and Pueblo and other publications describing his travels in the region, [End Page 53] Click for larger view View full resolution Figure 1. Petrified Forest National Monument, 1946. From 1906 to 1932, the boundaries of Petrified Forest National Monument were located south of the Thirty-fifth Parallel Transcontinental Railway Line; most visitors disembarked at Adamana or Holbrook. The development of Route 66 was followed by the addition of the Painted Desert to the monument in 1932. Detail from a map located in the Petrified Forest National Park Archives. [End Page 54] helped popularize the beauty of Petrified Forest National Monument. A 1912 article published in Santa Fe Employee's Magazine exclaimed: And the sight of them! The Titan trunks lying as they were felled by some unknown cataclysm, their chameleon chips paving an area half the size of the state of Rhode Island and shimmering at sunrise or at sunset as Sinbad never saw; their broken cross sections so radiant, bark and fiber, as no man ever before beheld outside his dreams!5 Tourism at Petrified Forest steadily increased during the early twentieth century as automobile...

A NewCynepterisfrom the Upper Triassic of Arizona: Potential Implications for the Early Diversification of Schizaealean Ferns

Cynepteris bolichii is proposed as a new species of the monogeneric fern family Cynepteridaceae on the basis of a single, well‐articulated specimen from the Upper Triassic Chinle Formation in Petrified Forest National Park, Arizona. The specimen consists of an erect rhizome with at least eight attached fronds. As for the other three known Cynepteris species, C. bolichii pinnae exhibit reticulate venation and scattered, solitary, exindusiate sporangia on their abaxial surfaces. Each sporangium is ovoid to pyriform with a short, thick stalk and a complete, apical, caplike annulus consisting of a single row of cells surrounding a multicellular distal plate. These sporangial features are similar to those of several fossil and extant schizaealean ferns. Cynepteris bolichii differs from other Cynepteris species mainly in having once‐pinnate fronds with abundant, elongate hairs on the rachises and veins. Most recent estimates of fern phylogeny consider the Jurassic fossils Stachypteris, Klukiopsis, and Klukia as the oldest fossil representatives of the Schizaeales. It is here proposed that Cynepteris should be considered as a probable Late Triassic record of the order. Features such as reticulate venation, scattered sporangia, and lack of fertile/sterile frond dimorphism are rare and scattered among other fossil and extant ferns currently attributed to the Schizaeales, underscoring the importance of fossils for understanding the early divergence, ancestral morphology, and biogeography of ancient plants groups like the ferns.

Wood anatomy of Late Triassic trees in Petrified Forest National Park, Arizona, USA, in relation to Araucarioxylon arizonicum Knowlton, 1889

Wood anatomy of Late Triassic trees in Petrified Forest National Park, Arizona, USA, in relation to Araucarioxylon arizonicum Knowlton, 1889

Managing social norms for persuasive impact

In order to mobilise action against a social problem, public service communicators often include normative information in their persuasive appeals. Such messages can be either effective or ineffective because they can normalise either desirable or undesirable conduct. To examine the implications in an environmental context, visitors to Arizona's Petrified Forest National Park were exposed to messages that admonished against the theft of petrified wood. In addition, the messages conveyed information either about descriptive norms (the levels of others' behaviour) or injunctive norms (the levels of others' disapproval) regarding such thievery. Results showed that focusing message recipients on descriptive normative information was most likely to increase theft, whereas focusing them on injunctive normative information was most likely to suppress it. Recommendations are offered for optimising the impact of normative messages in situations characterised by objectionable levels of undesirable conduct. This research was partially funded through grants from the United States Forest Service (PSW‐96‐0022CA) and the Arizona Department of Environmental Quality (No.‐98‐154C/97‐0152AI). We are grateful to Claire Champion, Paul Story, Jessica Martin, and Lorraine Baumack for their valuable assistance in our data‐collection efforts.

The Late Triassic pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs

A new discovery of skeletons of Revueltosaurus callenderi from the Upper Triassic Chinle Formation of Petrified Forest National Park, Arizona clearly shows that Revueltosaurus is not an ornithischian dinosaur as previously supposed. Features such as the presence of a postfrontal, crocodile-normal ankle and paramedian osteoderms with anterior bars place R. callenderi within the Pseudosuchia, closer to crocodylomorphs than to dinosaurs. Therefore, dental characters previously used to place Revueltosaurus within the Ornithischia evolved convergently among other archosaur taxa, and cannot be used to diagnose ornithischian dinosaur teeth. As a result, all other putative North American Late Triassic ornithischians, which are all based exclusively on teeth, are cast into doubt. The only reasonably well-confirmed Late Triassic ornithischians worldwide are Pisanosaurus mertii and an unnamed heterodontosaurid from Argentina. This considerably changes the understanding of early dinosaur diversity, distribution and evolution in the Late Triassic.

Vertebrate Burrows from Triassic and Jurassic Continental Deposits of North America and Antarctica: Their Paleoenvironmental and Paleoecological Significance

Comparisons of recently identified Triassic and Jurassic continental trace fossils in North America and Antarctica to modern mammal and reptilian burrows facilitate the identification and interpretation of the ancient burrows as vertebrate in origin, indicating advanced behaviors. Hollow, bowl-shaped depressions in the Petrified Forest Member of the Upper Triassic Chinle Formation in Petrified Forest National Park, Arizona, are interpreted as nest-holes constructed possibly by phytosaurs, aeotosaurs, turtles, or rauisuchians. Large-diameter, multiple-branching, and interconnected burrows in the Owl Rock Member of the Chinle Formation in southeastern Utah are tentatively interpreted as vertebrate burrows indicating communal behavior. Complex, large-diameter burrows in the Salt Wash Member of the Upper Jurassic Morrison Formation near the Henry Mountains in southern Utah are interpreted as burrow systems of fossorial mammals. Large-diameter, gently dipping, simple, subhorizontal burrows in the Salt Wash Member are interpreted as possible dwelling burrows of sphenodontids. Other vertebrate trace fossils, such as the large-diameter burrows from the Lower Triassic Fremouw Formation in the Queen Maud Mountains of Antarctica, are reinterpreted as vertebrate burrows and were likely constructed by small mammal-like reptiles. These burrows were thought to have been enigmatic in origin and different from very large-diameter burrows interpreted as therapsid dwelling burrows. Descriptions and interpretations of all these trace fossils are important because most vertebrate ichnology research to date has focused on trackways or locomotion experiments with modern reptiles and birds. These Triassic and Jurassic ichnofossils represent fossorial and nesting behavior of several different groups of vertebrates. The Fremouw Formation burrows indicate fossorial behavior in several sizes of vertebrates, including small and large therapsids. The burrows were likely used for shelter, giving birth, raising young, and hibernation. During the early Mesozoic, the Fremouw landscapes were thought to have had cold winters due to their high-paleolatitude position. The bowl-shaped depressions from the Petrified Forest Member of the Chinle Formation likely represent the earliest known structures excavated by reptilians for the sole purpose of reproduction. Basic nest-hole architecture in extant reptiles with early Mesozoic ancestry has changed minimally in nearly 220 million years. Large-diameter, multiple branching, and interconnected burrows in the Owl Rock Member of the Chinle Formation were likely constructed by fossorial vertebrates that had communal family groups. Simple, gently dipping, subhorizontal burrows in the Morrison Formation were used by crocodiles or sphenodontids as dwelling structures constructed in firm, subaerially exposed substrata close to open bodies of water. Complex, large-diameter burrows in the Salt Wash Member suggest subsocial behavior of fossorial mammals, where the burrow was used for raising young, storage and disposal of food and wastes, and coping with episodic water inundation. Research demonstrates that fossorial behavior of reptiles, therapsids, and mammals was established by the beginning of the Mesozoic and prior to the break-up of Pangea. The basic architecture of vertebrate nest construction has changed little in nearly 280 million years. Fossorial burrowing behavior likely evolved several times in different vertebrate groups during this time. These basic burrow architectures are also used by invertebrate groups. This overlap in burrow architectures between vertebrates and invertebrates suggests strongly that paleoenvironmental and paleoclimatic organism-substrate relationships dictate the architecture used by the organism. These burrow morphologies indicate particular physicochemical conditions in terrestrial and freshwater settings that are unique to the continental realm.

The Late Triassic Schilderia Adamanica and Woodworthia Arizonica Trees of the Petrified Forest National Park, Arizona, Usa

Two fossil tree species, both with unusual characteristics, occur in the Upper Triassic of the Petrified Forest National Park, Arizona, USA and adjacent areas. The first, Schilderia adamanica, has a highly idiosyncratic secondary xylem structure which contains normal uniseriate and broad complex multiseriate ‘herring‐bone’ rays. The trunk cross‐section of the secondary xylem may be either of a normal pycnoxylic type with a central pith and rays radiating from that or it may consist of appressed ‘xylem masses’ with rays curving towards one another at their extremities. The second, Woodworthia arizonica, has narrow, horizontal vascular traces traversing the entire radial width of the secondary xylem. By analogy with extant tree species, these traces would have terminated on preventitious buds deeply embedded in the bark which, in the case of these fossil trunks, have failed to be silicified. Such buds have the capacity to develop into epicormic shoots when the crown foliage of the tree is damaged. A further specimen of W. arizonica is recorded for the first time from the Permian of southern Brazil. Reconstruction drawings of both trees are produced.

Understanding Park Visitors’ Response to Interventions to Reduce Petrified Wood Theft

This study examined why theft of petrified wood at Petrified Forest National Park occurred and how designed interventions worked to inhibit the performance of that behavior. This evaluation was based on semi-structured interviews with observed thieves and non-thieves. Subjective responses revealed that theft was not a thoughtless act, but instead occurred because thieves rationalized that their particular act of theft was acceptable. The primary rationalization given by thieves was that their piece of stolen wood was so small that taking it would not hurt anything. It appeared as though anti-theft messages were received by all of those interviewed, but that thieves only applied these messages to the larger pieces of wood. In addition, most thieves did not view taking a little chip as stealing. There was not one primary message from the interventions processed by respondents, but instead many different messages were received and may have been impacting behavior.

Isotopic age of the Black Forest Bed, Petrified Forest Member, Chinle Formation, Arizona: An example of dating a continental sandstone

Zircons from the Black Forest Bed, Petrified Forest Member, Chinle Formation, in Petrified Forest National Park, yield ages that range from Late Triassic to Late Archean. Grains were analyzed by multigrain TIMS (thermal-ionization mass spectrometry), single-crystal TIMS, and SHRIMP (sensitive, high-resolution ion-microprobe). Multiple-grain analysis yielded a discordia trajectory with a lower intercept of 207 6 2 Ma, which because of the nature of multiple-grain sampling of a detrital bed, is not considered conclusive. Analysis of 29 detrital-zircon grains by TIMS yielded UPb ages of 2706 6 6M a to 2066 6 Ma. Eleven of these ages lie between 211 and 216 6 6.8 Ma. Our statistical analysis of these grains indicates that the mean of the ages, 213 6 1.7 Ma, reflects more analytical error than geologic variability in sources of the grains. Grains with ages of ca. 1400 Ma were derived from the widespread plutons of that age exposed throughout the southwestern Cordillera and central United States. Twelve grains analyzed by SHRIMP provide 206 Pb*/ 238 U ages from 214 6 2M a to 200 6 4 Ma. We use these data to infer that cores of inherited material were present in many zircons and that single-crystal analysis provides an accurate estimation of the age of the bed. We further propose that, even if some degree of reworking has occurred, the very strong concentration of ages at ca. 213 Ma provides a maximum age for the Black Forest Bed of 213 6 1.7 Ma. The actual age of the bed may be closer to 209 Ma. Dating continental successions is very difficult when distinct ash beds are not clearly identified, as is the case in the Chinle Formation. Detrital zircons in the Black Forest Bed, however, are dominated by an acicular morphology with preserved delicate terminations. The shape of these crystals and their inferred environment of deposition in slow-water settings suggest that the crystals were not far removed from their site of deposition in space and likely not far in time. Plinian ash clouds derived from explosive eruptions along the early Mesozoic Cordilleran margin provided the crystals to the Chinle basin, where local conditions insured their preservation. In the case of the Black Forest Bed, the products of one major eruption may dominate the volcanic contribution to the unit. Volcanic detritus in the Chinle Formation was derived from multiple, distinct sources. Coarse pebble- to cobble-size material may have originated in eastern California and/or western Arizona, where Triassic plutons are exposed. Fine-grained detritus, in contrast, was carried in ash clouds that derived from caldera eruptions in east-central California or western Nevada.

Late Triassic charcoal from Petrified Forest National Park, Arizona, USA

Fossil charcoal has been found in the Late Triassic Chinle Formation in Petrified Forest National Park, a location that is world famous for its silicified tree trunks. The material consists of charcoalified secondary wood, and has sufficiently well preserved plant anatomy to show it may be described as ‘araucarian type’, although it does display some minor differences from the anatomies described for the silicified gymnosperm trunks in the park. The presence of the charcoal proves that on occasion natural wildfires, most probably ignited by lightning, must have occurred in the Chinle Triassic palaeoenvironments, with resulting impacts on the biota of those times. It is currently impossible to estimate how often these fires occurred, as the incidence of charcoal here and in the whole fossil record apart from the frequency of ancient fires also reflects the preservation and burial conditions of the material. There is scant mention of Triassic charcoal in the literature, a notable absence given the abundance of charcoal that has been recorded in the Carboniferous, Jurassic, and Cretaceous periods. This lack of charcoal may support the theory that atmospheric oxygen levels were lower during the Triassic than in the Carboniferous.

Mapping sedimentary and volcanic units within and surrounding Petrified Forest National Park, Arizona, using Landsat-5 and SPOT panchromatic data

Landsat Thematic Mapper (TM) and SPOT panchromatic data were analysed to determine the lateral variation of the sedimentary and volcanic formations within and surrounding the Petrified Forest National Park in northeastern Arizona. Detailed geological mapping of portions of Petrified Forest National Park allowed for a correlation between TM images and the geological formations that aided in identifying these formations in unmapped areas outside and inside the park. A variety of image processing techniques, including band ratios, RGB composite images, selective principal component analysis and Brovey transformations were used in distinguishing these geological formations. Newly determined regions of the Lower and Upper parts of the Petrified Forest Member of the Chinle Formation were identified south of Pilot Rock and east of the Blue Mesa region. A final spectral reflectance-based geological map created by a maximum likelihood supervised classification algorithm provides a first-order approximation to the ...

Mapping sedimentary and volcanic units within and surrounding Petrified Forest National Park, Arizona, using Landsat-5 and SPOT panchromatic data

Landsat Thematic Mapper (TM) and SPOT panchromatic data were analysed to determine the lateral variation of the sedimentary and volcanic formations within and surrounding the Petrified Forest National Park in northeastern Arizona. Detailed geological mapping of portions of Petrified Forest National Park allowed for a correlation between TM images and the geological formations that aided in identifying these formations in unmapped areas outside and inside the park. A variety of image processing techniques, including band ratios, RGB composite images, selective principal component analysis and Brovey transformations were used in distinguishing these geological formations. Newly determined regions of the Lower and Upper parts of the Petrified Forest Member of the Chinle Formation were identified south of Pilot Rock and east of the Blue Mesa region. A final spectral reflectance-based geological map created by a maximum likelihood supervised classification algorithm provides a first-order approximation to the location of numerous sedimentary and volcanic units within and surrounding Petrified Forest National Park.

The Gunnison's prairie dog structures a high desert grassland landscape as a keystone engineer

The influence of landscape spatial structure on ecological processes has recently received much attention. Comparisons are made here between the spatial structure of grasslands, and active and extirpated Gunnison's prairie dog (Cynomys gunnisoni Hollister) towns at the Petrified Forest National Park, Arizona, U.S.A. The spatial structure of bare ground was quatified using a box-counting technique to extract landscape fractal dimensions, D, and bare-ground patch size. These landscapes are fractal, and active prairie dog towns had higher fractal dimensions, i.e. a more homogeneous spatial structure as D approaches 2, than inactive towns, which had higher fractal dimensions than unmodified grasslands. Morisita's index suggested that shrubs were more randomly distributed on prairie dog towns and more aggregated on grassland habitats. The different spatial distributions of bare ground and shrubs have the potential to influence resource distributions between these habitats for both prairie dogs and other fauna. Consequently, the presence of prairie dogs in these grasslands increases grassland landscape heterogeneity at large spatial scales, potentially enhancing beta diversity.

EVIDENCE OF ORIBATID MITE HERBIVORY IN THE STEM OF A LATE TRIASSIC TREE FERN FROM ARIZONA

Small coprolite-bearing borings occur in the stem of the filicalean tree fern Itopsidema vancleaveii Daugherty from the Chinle Formation of Late Triassic Age (Carnian Stage) in Petrified Forest National Park, Arizona. These borings are restricted to parenchyma within the leaf petioles and among the adventitious roots of the root mantle. Although they are not lined by wound tissue, some of the borings in the leaf petioles contain small discontinuous masses of wound-tissue at a few places along some of the walls, indicating that the plant was alive when it was attacked. Coprolites within the borings generally are small (mostly about 40–50 μm in diameter and 85–100 μm in length) and oval in longitudinal section and round to weakly hexagonal in transverse section; they consist of very small particles of unidentifiable plant matter. Although the weakly hexagonal coprolites are similar to those produced by termites but they are an order of magnitude smaller. Furthermore, the borings are much smaller than those produced by known extant termites. It is likely that oribatid mites produced the coprolite-bearing borings and coprolites. This occurrence is significant because it bridges the Late Permian to Early Jurassic gap in the geologic record of endophagous mites and also contributes new data on arthropod activity during the Late Triassic in southwestern North America.

Evidence of oribatid mite herbivory in the stem of a Late Triassic tree fern from Arizona

Small coprolite-bearing borings occur in the stem of the filicalean tree fern Itopsidema vancleaveii Daugherty from the Chinle Formation of Late Triassic Age (Carnian Stage) in Petrified Forest National Park, Arizona. These borings are restricted to parenchyma within the leaf petioles and among the adventitious roots of the root mantle. Although they are not lined by wound tissue, some of the borings in the leaf petioles contain small discontinuous masses of wound-tissue at a few places along some of the walls, indicating that the plant was alive when it was attacked. Coprolites within the borings generally are small (mostly about 40–50 μm in diameter and 85–100 μm in length) and oval in longitudinal section and round to weakly hexagonal in transverse section; they consist of very small particles of unidentifiable plant matter. Although the weakly hexagonal coprolites are similar to those produced by termites but they are an order of magnitude smaller. Furthermore, the borings are much smaller than those produced by known extant termites. It is likely that oribatid mites produced the coprolite-bearing borings and coprolites. This occurrence is significant because it bridges the Late Permian to Early Jurassic gap in the geologic record of endophagous mites and also contributes new data on arthropod activity during the Late Triassic in southwestern North America.

Paleoenvironments of Early Theropods, Chinle Formation (Late Triassic), Petrified Forest National Park, Arizona

Abstract Three localities in the Chinle Formation (Late Triassic), Petrified Forest National Park (PEFO), Arizona, provide insights into the paleoenvironments frequented by primitive North American theropods. At the Dinosaur Wash locality, an undetermined theropod is preserved in paleosols that indicate a transition from wet to dry conditions on the floodplain. Coelophysis bauri remains from the Dinosaur Hill locality are preserved in a filled channel scour. The paleosols at this locality contain carbonate nodules intimately associated with Fe and Mn oxides, indicative of alternating alkaline/acidic conditions around roots in response to a semi-arid climate with strong seasonal precipitation. At the Dinosaur Hollow locality, Chindesaurus bryansmalli is preserved in a setting similar to those encountered at Dinosaur Hill. The paleosols exhibit vertic features, such as pseudoanticlines, and are indicative of water-deficit periods during the year. The most complete theropod remains at PEFO are predominantly ...

Paleoenviromnents of Early Theropods, Chinle Formation (Late Triassic), Petrified Forest National Park, Arizona

Paleoenviromnents of Early Theropods, Chinle Formation (Late Triassic), Petrified Forest National Park, Arizona

Reducing Theft of Petrified Wood at Petrified Forest National Park

The theft of petrified wood from Petrified Forest National Park is the park's primary resource-protection problem. Several interventions to control theft currently exist in the park, yet an estimated 12 tons of wood disappear from the park each year. This study evaluated three interventions to reduce the theft of wood from the park. Tested interventions included a sign, a signed pledge, and a uniformed volunteer. A field experiment revealed that all three interventions significantly reduced theft of wood over control conditions. In addition, the interventions were not significantly different from each other in their effectiveness.

The Late Triassic Araucarioxylon Arizonicum trees of the Petrified Forest National Park, Arizona, USA

Examination and measurement of many of the trunks attributed to Araucarioxylon arizonicum Knowlton eroded from the Late Triassic Chinle Formation in the Petrified Forest National Park, Arizona demonstrate that the living tree did not closely resemble any of the present‐day Araucaria trees of the southern hemisphere as postulated in past reconstructions. The research indicates that it was a tall monopodial tree with branches occurring in a disordered manner on the trunk from the base to the crown. Calculations using the allometric method of Niklas indicate that the trees were of considerable size. The largest recorded trunk has a basal diameter of nearly 3 m and may represent a tree 59 m high, when living. The root system of the A. arizonicum tree consisted of a ring of four to six steeply inclined lateral roots and a massive, vertically directed tap root. Many of the trunks still have their root systems attached, a circumstance that indicates their felling by the cut‐bank operations of the local river system. The massive roots of these trunks, particularly the large tap root, are consistent with growth in soft, deep, alluvial soil, and the thin scale bark is to be expected in a tropical climate free from frost.