Rancho La Brea

The species Equus occidentalis Leidy, 1865, was initially described from three teeth, one recovered from an unknown locality in Tuolumne County, California, and the others from asphalt deposits inset into sediments of the Tulare Formation, Kern County, California. The single tooth from Tuolumne County is the lectotype. None of these teeth is sufficiently diagnostic to warrant specific distinction, and so E. occidentalis is generally interpreted to be a nomen dubium.
Another less common interpretation suggests that E. occidentalis may be a valid plesippine equid dating to the Blancan North American Land Mammal Age. This view is based upon plesippine characters exhibited by teeth of large Equus from the Asphalto fossil locality. At this site, lower cheek teeth of large Equus from outcrops of the Tulare Formation exhibit deep ectoflexids, a diagnostic character of plesippine equids.
Our investigation relocated the Asphalto site and its  fossiliferous asphalt beds, examined equid fossils from the Tulare Formation to confirm their plesippine character, and directly examined the original types of E. occidentalis in order to assess their similarity to nonasphaltic fossils from the Tulare Formation. Efforts to relocate Asphalto were successful, but encountered only oil-saturated sands of the Tulare Formation—not asphalt beds. Nonasphaltic localities in the Tulare Formation contain abundant remains of plesippine equids, but these fossils—and other vertebrate remains
from the formation—lack the deep asphalt staining characteristic of Leidy’s types from this region. In contrast, fossils in Leidy’s original type series are heavily impregnated
with asphalt, resembling abundant fossil remains from the nearby McKittrick asphalt deposits. Leidy’s type series also includes previously unpublished topotypes representing
a derived, nonplesippine equid similar to the Late Pleistocene large horse species represented at McKittrick.
We propose that Leidy’s original fossils of E. occidentalis from northwest of Buena Vista Lake are most likely from the McKittrick asphalt deposits, rather than from the Asphalto paleontological locality. Based upon actual topotypes comprising Leidy’s original type series, E. occidentalis is a derived horse closely resembling the large Pleistocene horses from localities such as McKittrick, Maricopa, and Rancho La Brea. The species cannot be considered a plesippine horse and is unlikely to date to the Blancan NALMA.

The Rancho La Brea (RLB) fossil collection at the La Brea Tar Pits and Museum represents one of the largest assemblages of carnivoran fossils in the world. This is certainly true of the bacula; the collection houses several hundred bacula of Canis dirus, more than a dozen of Canis latrans, two Mustela sp., one Taxidea taxus, and a one baculum previously described as belonging to Urocyon cinereoargenteus. Unfortunately, no bacula from any of the RLB felids or ursids have yet been recovered. In the current study, we compare the RLB fossil bacula to those of all of the modern analogues curated at the American Museum of Natural History and the Smithsonian. Nine measurements were taken on each complete specimen, and three of these were combined to create an overall volumetric size proxy. The Mustela and Taxidea specimens are both similar to their modern congeners, but the Urocyon specimen is smaller than the three modern specimens available for comparison. The sample of 18 C. latrans fossils is nearly statistically indistinguishable from the 21 modern conspecific
samples from across their current geographic range, though the mean of the fossil sample is slightly larger than the modern sample for eight of the 10 metrics. Of the large La Brea Tar Pits and Museum collection of C. dirus bacula, 159 are complete. They have been recovered from nearly all of the fossiliferous RLB deposits and span the entire Late Pleistocene accumulations represented at the site. The C. dirus bacula are almost five times as large as those of C. lupus (N 5 10) in terms of a volumetric proxy, and the C. dirus mean total bacular length exceeds that in C. lupus by 44%. The C. dirus bacular width and height variables are even more dramatic in comparison, ranging up to 236% the size of those of C. lupus. No statistically discernable size or shape pattern emerges when considering the chronological sequence of the specimens, though the chronology of the deposits is complicated by the substantial mixing that is becoming evident, for instance, with Project 23 (John R. Southon and Benjamin T. Fuller, personal communication). However, the sample is large enough to see ontogenetic differences within it. In this respect, though, there are a few clearly juvenile bacula; the sample heavily skews to older, more robust, apparent age classes. Furthermore, several C. dirus bacula in the RLB sample are clearly broken and healed. Perhaps the extreme robusticity in this bone is an evolutionary response to aggressive mating competition—a hypothesis supported by the presence of several broken and healed bacula in the RLB sample.

We radiocarbon dated the domestic dog found associated with La Brea Woman at the Rancho La Brea tar pits (Los Angeles, CA) to determine the validity of this human–dog connection. The domestic dog yielded a radiocarbon age of 3125 ± 25 14C yr BP (3250–3400 cal yr BP) and La Brea Woman had a re-dated age
of 9080 ± 15 14C yr BP (10,220–10,250 cal yr BP). This ∼7000-year offset dispels the hypothesis this was an intentional and ceremonial human–dog burial.

A fragmentary timber wolf (Canis lupus) femur from the late Pleistocene Rancho La Brea asphalt deposits of Los Angeles, California, shows evidence of healed traumatic injury incurred well before the death of the individual. The specimen, from San Bernardino County Museum (SBCM A3356-1), consists of proximal and metaphyseal portions of the right femur, including the complete femoral head, neck, and greater trochanter. The fragment terminates abruptly in a well-remodeled surface oriented caudally and oblique to the shaft axis. This surface consists primarily of smooth cortical bone that has almost completely covered the underlying trabecular bone. Two possibilities arise from the observation: (1) this
fragment represents only the proximal portion of a pseudarthrosis (false joint) resulting from osseous nonunion of a femoral fracture, or (2) a complete amputation event occurred with subsequent healing of the remaining bony shaft. Either case indicates that the animal survived for a significant amount of time after the traumatic injury was inflicted. A premortem lesion on the caudomedial femoral head suggests
that forced hyperextension of the hind limb occurred simultaneously with the femoral shaft breakage. A violent bite injury with subsequent shearing, torsion, and hip hyperextension provide the best fit for all the osseous evidence. The fact that the proximal femoral segment had adequate time to heal means the violent event could
not have been itself the cause of death. Furthermore, that the individual lived for a significant amount of time postinjury means it must have retained adequate hunting and/or scavenging ability to survive. Alternatively, pack or other social provisioning and protection may have facilitated or, minimally, permitted the healing of the injured individual. Because no functional bony connection to the more distal limb elements appears to have been present, the individual must have had either an entirely missing or useless lower right leg, and may have adopted a completely tripodal lifestyle.

Accurate radiocarbon dating and stable isotope ratio analysis of bone from Rancho La Brea and other tar seep sites is complicated by the necessity for the efficient and complete removal of asphalt from collagen. In this paper we review a new sample preparation method specifically designed for this purpose, that utilizes sonication in solvents, gelatinization, and selection of a specific molecular weight fraction by successive ultrafiltrations at 30 and 3 kDa. The middle fraction (3–30 kDa) produces white spongy collagen with excellent atomic C:N ratios between 3.2 and 3.5 and %C (42.0 6 2%) and %N (15.0 6 1%) values indicative of uncontaminated collagen. We also list past bone radiocarbon dates from Rancho La Brea and assess them in terms of quality and discuss the dangers of using “pit average” dates for individual specimens. Given the overall lack of stratigraphy at Rancho La Brea, more direct radiocarbon dates on bone specimens will be required to take full advantage of the amazing wealth of paleontological material available

The Rancho La Brea collections at the George C. Page Museum in Los Angeles, California, contain the largest single inventory of Smilodon fatalis remains representing virtually every bone in the skeleton. Eighteen clavicles of two distinctive shapes have been recovered from historical and recent excavations at Rancho La Brea. In this study, we identify these specimens to species through comparison of their morphology and morphological variability with clavicles found in modern felids. This study includes a reevaluation of clavicles that have been previously assigned to S. fatalis, which are more likely to be those of Panthera atrox, and the description of pantherine cat clavicles. A previously undescribed sample of clavicles not only includes some of the same pantherine morph but also 10 specimens, herein assigned to S. fatalis, which are morphologically distinctive and significantly smaller than the previously described specimens. In addition, we report unexpected variations between clavicles of Panthera leo and P. tigris: the clavicles of P. leo closely resemble those of the large Rancho La Brea clavicle morph—which presumably belongs to P. atrox—thus supporting a P. leo/P. atrox clade. We report distinctive morphology of the clavicles of Acinonyx jubatus. Possible functional and phylogenic significance of felid clavicles is suggested.
Published online 17 May 2012 in
Wiley Online Library (wileyonlinelibrary.com)
DOI: 10.1002/jmor.20036

Excavations near the Los Angeles County Museum of Art in 2006 uncovered Pleistocene-age fluvial deposits containing the disarticulated skeleton of an adult Columbian mammoth (Mammuthus columbi). The skeleton is about 80% complete, with osteological and dental features suggesting a male with a Laws’ Age Class of XXVI, representing an adult of prime reproductive age. A sample was excised from near the proximal end of the left tusk to evaluate the last years of life and assess season of death. This sample was scanned by microCT then thin-sectioned. Viewing microCT data in transverse section, the dentin is organized in concentric zones paralleling the pulp cavity surface. Between the dentin–cementum interface and the pulp surface, there are somewhat regularly spaced, abrupt transitions (inward, in the direction of dentin apposition) from higher to lower x-ray attenuation, suggesting shifts from higher to lower density. Similar transitions have been interpreted previously as reflecting winter–spring boundaries. These same loci are associated consistently with periradicular topographic features on the external surface of the alveolar portion of the tusk. Analysis of approximately weekly incremental features in a transverse thin section shows little systematic seasonal variation in rates of dentin apposition—not surprising for southern California—but shorter term patterns of rate variation do help confirm some of our identifications of year boundaries. Daily dentin increments are visible in parts of the sequence, but not consistently. Judging from rates of tusk growth in the last years of life, death appears to have come in early summer, the season identified in prior work as normal for musth, the period of heightened aggression and sexual activity in which mating and male–male conflict would be expected to occur. We suspect that this male died as a result of soft-tissue injuries sustained in a musth conflict.

Fossil-bearing asphalt deposits are an understudied and potentially significant source of ancient DNA. Previous attempts to extract DNA from skeletons preserved at the Rancho La Brea tar pits in Los Angeles, California, have proven unsuccessful, but it is unclear whether this is due to a lack of endogenous DNA, or if the problem is caused by asphalt-mediated inhibition. In an attempt to test these hypotheses, a recently recovered Columbian mammoth (Mammuthus columbi) skeleton with an unusual pattern of asphalt impregnation was studied. Ultimately, none of the bone samples tested successfully amplified M. columbi DNA. Our work suggests that reagents typically used to remove asphalt from ancient samples also inhibit DNA extraction. Ultimately, we conclude that the probability of recovering ancient DNA from fossils in asphalt deposits is strongly (perhaps fatally) hindered by the organic compounds that permeate the bones and that at the Rancho La Brea tar pits, environmental conditions might not have been ideal for the general preservation of genetic material.

A novel protocol to purify bone collagen for radiocarbon dating and stable isotope ratio analysis from asphalt-impregnated skeletal remains stored in the George C. Page Museum of La Brea Discoveries (Los Angeles, California) is presented. This simple technique requires that bones be crushed (1e2 mm), sonicated in a 2:1 toluene/methanol solution, and gelatinized at 75
C overnight to break down collagen strands for ultrafiltration. However, here the traditional protocol of ultrafiltration is reversed, and the high molecular weight fraction (>30 kDa) contains mainly the asphalt (too big to pass through the filter), while the lower molecular weight fraction (<30 kDa) contains the collagen. A second ultrafiltration (>3 kDa) is then performed on the <30 kDa fraction to remove lower molecular weight contaminants such as hydrocarbons and humic acids. The middle fraction (3e30 kDa) is freeze dried and produces
collagen with excellent atomic C:N ratios between 3.2 and 3.5. The steps involved in the design of the protocol will be discussed in detail, and the first isotopic results and radiocarbon dates from the Project 23 site will be presented. In addition, the largest compilation of carbon and nitrogen isotopic results directly paired with radiocarbon ages on bone collagen from 38 land mammals found at the Rancho La Brea site are presented. Finally, while this protocol was specifically designed to extract collagen from samples at the Rancho La Brea site, it is likely that it can be applied to other localities (e.g. Cuba, Ecuador, Peru, Venezuela, etc.) where bones have been impregnated with petroleum.