Canis Dirus Research Articles

The Dire Consequences of Specializing on Large Herbivores

Niche differentiation is a way in which similar species avoid competition. Some species do this by specializing in certain prey items. This review aims to determine why the dire wolf (Canis dirus) went extinct while its similar and less abundant relative, the grey wolf (Canis lupus) did not. Both species were present in North America during the Pleistocene, though only one went extinct during the Quaternary extinction event. Physiological differences existed between the two species, mostly due to a greater focus in hypercarnivory for dire wolves. Dire wolves had more robust frame and skull, greater bite strength, and larger carnasials and canines. These differences in dire wolf morphology all help it to handle and kill larger prey species, while the more lithe grey wolf is better adapted to switching to smaller alternative prey. Dire wolves at have been shown to consume mostly large herbivores while grey wolves can survive with lagomorphs as a primary food source. Larger carnivore body size means reduction in locomotor performance, which means that when many mega-herbivores went extinct at the end of the Pleistocene, dire wolves were not as well adapted to switch to smaller prey as grey wolves are. Their naturally larger body mass also means that they needed higher caloric input to maintain their body condition and fecundity. Overall, Canis dirus specialized in larger prey than Canis lupus, so when this prey became extinct, the dire wolf went extinct along with other hypercarnivores such as the North American lion, Smilodon, and short-faced bear.

Dental caries in the fossil record: a window to the evolution of dietary plasticity in an extinct bear

During the late Pleistocene of North America (≈36,000 to 10,000 years ago), saber-toothed cats, American lions, dire wolves, and coyotes competed for prey resources at Rancho La Brea (RLB). Despite the fact that the giant short-faced bear (Arctodus simus) was the largest land carnivoran present in the fauna, there is no evidence that it competed with these other carnivores for prey at the site. Here, for the first time, we report carious lesions preserved in specimens of A. simus, recovered from RLB. Our results suggest that the population of A. simus from RLB was more omnivorous than the highly carnivorous populations from the Northwest. This dietary variation may be a consequence of different competitive pressures.

The Tule Springs local fauna: Rancholabrean vertebrates from the Las Vegas Formation, Nevada

A middle to late Pleistocene sedimentary sequence in the upper Las Vegas Wash, north of Las Vegas, Nevada, has yielded the largest open-site Rancholabrean vertebrate fossil assemblage in the southern Great Basin and Mojave Deserts. Recent paleontologic field studies have led to the discovery of hundreds of fossil localities and specimens, greatly extending the geographic and temporal footprint of original investigations in the early 1960s. The significance of the deposits and their entombed fossils led to the preservation of 22,650 acres of the upper Las Vegas Wash as Tule Springs Fossil Beds National Monument. These discoveries also warrant designation of the assemblage as a local fauna, named for the site of the original paleontologic studies at Tule Springs.The large mammal component of the Tule Springs local fauna is dominated by remains of Mammuthus columbi as well as Camelops hesternus, along with less common remains of Equus (including E. scotti) and Bison. Large carnivorans including Canis dirus, Smilodon fatalis, and Panthera atrox are also recorded. Micromammals, amphibians, lizards, snakes, birds, invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. The fauna occurs within the Las Vegas Formation, an extensive and stratigraphically complex sequence of groundwater discharge deposits that represent a mosaic of desert wetland environments. Radiometric and luminescence dating indicates the sequence spans the last ∼570 ka, and records hydrologic changes in a dynamic and temporally congruent response to northern hemispheric abrupt climatic oscillations. The vertebrate fauna occurs in multiple stratigraphic horizons in this sequence, with ages of the fossils spanning from ∼100 to ∼12.5 ka.

Vertebrate paleontology, stratigraphy, and paleohydrology of Tule Springs Fossil Beds National Monument, Nevada (USA)

Tule Springs Fossil Beds National Monument (TUSK) preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley (Nevada, USA). TUSK is home to extensive and stratigraphically complex groundwater discharge (GWD) deposits, called the Las Vegas Formation, which represent springs and desert wetlands that covered much of the valley during the late Quaternary. The GWD deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). The deposits also entomb the Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene (Rancholabrean) vertebrate assemblages in the American Southwest. The TSLF is both prolific and diverse, and includes a large mammal assemblage dominated by Mammuthus columbi and Camelops hesternus. Two (and possibly three) distinct species of Equus, two species of Bison, Panthera atrox, Smilodon fatalis, Canis dirus, Megalonyx jeffersonii, and Nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. Invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. This field compendium highlights the faunal assemblage in the classic stratigraphic sequences of the Las Vegas Formation within TUSK, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem.

Skeletal trauma reflects hunting behaviour in extinct sabre-tooth cats and dire wolves.

Skeletal-injury frequency and distribution are likely to reflect hunting behaviour in predatory vertebrates and might therefore differ between species with distinct hunting modes. Two Pleistocene predators from the Rancho La Brea asphalt seeps, the sabre-tooth cat, Smilodon fatalis, and dire wolf, Canis dirus, represent ambush and pursuit predators, respectively. On the basis of a collection of over 1,900 pathological elements, the frequency of traumatic injury across skeletal elements in these two species was calculated. Here we show that the frequency of trauma in the sabre-tooth cat exceeds that of the dire wolf (4.3% compared to 2.8%), implying that the killing behaviour of S. fatalis entailed greater risk of injury. The distribution of traumatic injuries also differed between the two species. S. fatalis, an ambush predator, was injured more often than expected across the lumbar vertebrae and shoulders whereas C. dirus, a pursuit predator, had higher than expected levels of injury in the limbs and cervical vertebrae. Spatial analysis was used to quantify differences in the distribution of putative hunting injuries. Analysis of injury locations discriminated true hotspots from injury-dense areas and facilitated interpretation of predatory behaviour, demonstrating the use of spatial analyses in the study of vertebrate behaviour and evolution. These results suggest that differences in trauma distribution reflect distinct hazards of each species' hunting mode.

Comparative digitization techniques of a dire wolf (Canis dirus) ulna fossil

Recent technological advances, like three-dimensional (3D) digitization have assisted in expanding paleontological research collections. Digitization equipment varies in accuracy and cost, offering a range of abilities while efficiency and accuracy of the replications have not yet been explored. Assessing the potential of these methodologies, we compared processing time, accuracy, and costs of a medical computer tomography (CT) scanner, an Artec Eva portable handheld 3D light scanner, and a NextEngine 3D laser scanner. We digitized one dire wolf (Canis dirus) ulna fossil. The digitized replicas underwent 3D printing on a ZPrinter 250 3D rapid prototyping machine. We hypothesized that the cost and ease of the user interface will affect the digital replicas’ accuracy of reaching less than 5% error. Percent error was tested by various landmark measurements and visual assessments of both digital models and 3D printed models compared to the original fossil material. Results show that the dire wolf ulna digitized by the Artec Eva scanner captures the fossil but does not result in less than 5% error due to small features the scanner is unable to capture. The NextEngine has similar limitations as the Artec Eva and the CT image is closer to an ideal replica of less than 5% error with less post processing time but still lacks the ability to capture certain features of the fossil. The ZPrinter 250 3D printer creates ideal replicas only limited by print layer thickness. Each digitization method was able to successfully replicate the fossil with the CT replica being the most accurate followed by the NextEngine then the Artec Eva.

Vertebrate paleontology, stratigraphy, and paleohydrology of Tule Springs Fossil Beds National Monument, Nevada (USA)

Tule Springs Fossil Beds National Monument (TUSK) preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley (Nevada, USA). TUSK is home to extensive and stratigraphically complex groundwater discharge (GWD) deposits, called the Las Vegas Formation, which represent springs and desert wetlands that covered much of the valley during the late Quaternary. The GWD deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). The deposits also entomb the Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene (Rancholabrean) vertebrate assemblages in the American Southwest. The TSLF is both prolific and diverse, and includes a large mammal assemblage dominated by Mammuthus columbi and Camelops hesternus. Two (and possibly three) distinct species of Equus, two species of Bison, Panthera atrox, Smilodon fatalis, Canis dirus, Megalonyx jeffersonii, and Nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. Invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. This field compendium highlights the faunal assemblage in the classic stratigraphic sequences of the Las Vegas Formation within TUSK, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem.

Dan Flores's American Serengeti: The Last Big Animals of the Great Plains

Dan Flores's American Serengeti:The Last Big Animals of the Great Plains George E. Wolf Editor's Note: The 2017 Stubbendieck Distinguished Book Prize was awarded to Dan Flores, A. B. Hammond Professor Emeritus of Western History, University of Montana, Missoula, for American Serengeti: The Last Big Animals of the Great Plains, University Press of Kansas (2016). Given annually since 2005, the award comes with a cash prize of $10,000 and the Stubbendieck Distinguished Book Prize medallion. The prize was created to emphasize the interdisciplinary importance of the Great Plains in today's publishing and educational market. Only first-edition, full-length nonfiction books published in 2016 were evaluated for the award. We asked George Wolf, chair of the book prize committee, to talk about the characteristics of Flores's book that led to its selection as the winner of this year's award. About eleven million years ago, give or take a million, a gigantic volcanic eruption in what is now southwestern Idaho swept a thick mantle of ash over huge areas of the evolving grasslands in what we now know as the Great Plains. In a corner of northeast Nebraska, at Ashfall Fossil Beds State Historical Park, twenty-first-century visitors can view the startling articulated remains of some of the area's abundant ancient wildlife—various species of rhinos, camels, horses, dogs, and deer—that gathered to drink and bathe at a subtropical watering hole where they succumbed to the deadly ash and were buried in it. Ashfall tells us mammalian megafauna were at home here a very long time, well before their extinction. Dealing with vast stretches of time is what environmental historian Dan Flores calls Big History. The Big History he recounts early on in American Serengeti: The Last Big Animals of the Great Plains is far more recent, starting about 13,200 years ago, when mammoths, giant ground sloths, antelopes, ancient bison, dire wolves, Late Pleistocene camels and horses—a bestiary, all told, more diverse than the present Serengeti's—and the Clovis people who hunted them inhabited the Great Plains. By laying out with clarity and concision the dramatic changes in Plains climate, plant and animal life, and human cultures between that time and roughly two centuries ago—changes that drove most of these species to extinction—Flores establishes what gave rise to the flourishing environment in which the great grassland mammals we're familiar with thrived at the start of the nineteenth century. It is the catastrophic story of the loss of "the last big animals of the Great Plains" during the nineteenth century—far briefer than [End Page 251] Click for larger view View full resolution [End Page 252] a heartbeat in terms of Big History—that is the subject of his remarkable book. To grasp the momentousness of that loss requires a sense of its magnitude. Among the few places left on Earth that provide a limited impression of that sense, Flores proposes, is the Serengeti Plain of East Africa, where bountiful mammalian wildlife still abides, though under grave threat, as all natural places now are. There may be glimpsed over a million wildebeest, a quarter of a million zebras, along with numerous lions, leopards, cheetahs, hyenas, elephants, jackals, gazelles, antelopes, eland, giraffes, rhinos, hippos, African buffaloes, and impalas. The American Great Plains wildlife that explorers Lewis and Clark and painters George Catlin, John James Audubon, and Karl Bodmer encountered early in the nineteenth century—and Native Plains people had long lived among—was less diverse than the Serengeti's, but far more copious. Millions of bison, perhaps as many as 20 to 30 million, grazed the Plains grasslands. Grizzly bears may have numbered close to 9,000. Horses, reintroduced by Spanish colonists to the New World bestiary, had been let loose or escaped, bred, gone wild, and by 1800 roamed the Plains in numbers estimated at a million or so. Pronghorns, the only large Plains species to have survived their predators from 13,200 years ago as well as the profound extinction event that wiped out most Pleistocene megafauna, likely numbered 15 million. The howls of 200,000 to perhaps 1 million wolves are thought to have...

Diet and habitat of mesomammals and megamammals from Cedral, San Luis Potosí, México

AbstractUsing carbon and oxygen isotopic relationships from dental enamel, diet and habitat were inferred for both mesomammals and megamammals that lived in Cedral (San Luis Potosi, north-central México) during Late Pleistocene time. δ13C and δ18O values show that bison, some horses and mammoth were eating C4 plants and lived in open areas, while tapir, camel and some llamas ate C3 plants and inhabited closed areas. All other studied herbivores (pronghorn, glyptodont, mylodont ground sloth, javelina, mastodon, and other llamas, horses and mammoth) had a C3/C4 mixed diet, living in areas with some percentage of tree coverage. On the other hand, American lion and dire wolf ate either C4 or mixed-diet herbivores, and short-faced bear ate C3 herbivores. At Cedral, more humid conditions existed than presently, allowing the presence of a forested area near the grassland.

First occurrence of <i>Panthera atrox</i> (Felidae, Pantherinae) in the Mexican state of Hidalgo and a review of the record of felids from the Pleistocene of Mexico

Abstract. Panthera atrox was a common large-sized cat in North America during the late Pleistocene. An isolated lower canine and a fifth metacarpal bone referable to this species were recovered from fluvial Quaternary deposits that outcrop in southeastern Hidalgo, central Mexico. Associated fossil material belonging to Bison indicates a Rancholabrean North American Land Mammal Age; the age assignment is corroborated by the presence of P. atrox. A comparative study with selected specimens of Panthera and Smilodon indicates that the Hidalgoan sample shares the following diagnostic features with P. atrox: a large, robust, and non-strongly curved lower canine; a large and relatively slender fifth metacarpal with a well-developed projection on the palmar side at the proximal end, narrow articulating surface for the unciform; a narrow notch on the articulating surface for the fourth metacarpal; and a diaphysis that at the middle is oval in cross section. The record supplements the evidence of P. atrox in central Mexico and represents the first reported occurrence of this cat species in the state of Hidalgo. By the same token, the known geographic distribution of P. atrox in the Mexican territory suggests that it was relatively common in temperate areas of central Mexico between 19 and 24° N at an altitudinal range from 1500 to 2250 m a.s.l. The large size (mean body mass of 300 kg) and hypercarnivorous adaptations of the American lion suggest it was the top predator of the mammalian community recorded at southeastern Hidalgo, displacing other members of the carnivore guild at the mesopredator level, such as the dire wolf (Canis dirus ), which has been also reported in the area. The high diversity of large herbivores recorded at southeastern Hidalgo, which in turn could represent potential prey of P. atrox, suggests that some areas that now are part of central Mexico were suitable hunting sites for this large-sized cat. A review of the Pleistocene record of Felidae from Mexico revealed that it encompasses 87.5 and 73.3 % of generic and specific diversity known for North America, respectively, including seven genera (Felis, Miracinonyx, Panthera, Puma, Lynx, Leopardus, and Smilodon) and 11 species (Felis rexroadensis, Miracinonyx inexpectatus, Panthera atrox, Panthera onca, Puma concolor, Puma yagouaroundi, Lynx rufus, Leopardus pardalis, Leopardus wiedii, Smilodon fatalis, and Smilodon gracilis). The majority of these taxa have been reported from numerous late Pleistocene localities; in particular, Panthera atrox was relatively common and widely distributed across the Mexican territory.

First records of Canis dirus and Smilodon fatalis from the late Pleistocene Tule Springs local fauna, upper Las Vegas Wash, Nevada.

Late Pleistocene groundwater discharge deposits (paleowetlands) in the upper Las Vegas Wash north of Las Vegas, Nevada, have yielded an abundant and diverse vertebrate fossil assemblage, the Tule Springs local fauna (TSLF). The TSLF is the largest open-site vertebrate fossil assemblage dating to the Rancholabrean North American Land Mammal Age in the southern Great Basin and Mojave Desert. Over 600 discrete body fossil localities have been recorded from the wash, including an area that now encompasses Tule Springs Fossil Beds National Monument (TUSK). Paleowetland sediments exposed in TUSK named the Las Vegas Formation span the last 250 ka, with fossiliferous sediments spanning ∼100–13 ka. The recovered fauna is dominated by remains of Camelopsand Mammuthus, and also includes relatively common remains of extinct Equusand Bisonas well as abundant vertebrate microfaunal fossils. Large carnivorans are rare, with only Puma concolor and Panthera atrox documented previously. Postcranial remains assigned to the species Canis dirus (dire wolf) and Smilodon fatalis (sabre-toothed cat) represent the first confirmed records of these species from the TSLF, as well as the first documentation of Canis dirus in Nevada and the only known occurrence of Smilodonin southern Nevada. The size of the recovered canid fossil precludes assignment to other Pleistocene species of Canis. The morphology of the felid elements differentiates them from other large predators such as Panthera, Homotherium, and Xenosmilus, and the size of the fossils prevents assignment to other species of Smilodon. The confirmed presence of S. fatalis in the TSLF is of particular interest, indicating that this species inhabited open habitats. In turn, this suggests that the presumed preference of S. fatalis for closed-habitat environments hunting requires further elucidation.

Tar Pits

Tar Pits George Bilgere (bio) The last time I saw my fatherwas at the La Brea Tar Pitsa year after the divorce. He was still living in St. Louis,running the businessto the bottomof a fifth of Jim Beam. In my mind’s eyehe is a specimen, a fetusof a father, floating in a jarin some roadside museum. I was nine. We had nothingto say, so he took meto the La Brea Tar Pits, asdivorced fathers do. He was a membraneat that point.An effigy tremblingin another man’s suit. We staredat the three-toed sloth,the dire wolf with itsmarble eyes. My father, I wishyou could rise from thatblack pit and emerge into light, like the tigerwe saw that day,sheathed again in muscle,its great teeth like sabers. [End Page 485] George Bilgere GEORGE BILGERE’s most recent collection of poetry is Imperial (University of Pittsburgh Press, 2014). His work is familiar to National Public Radio audiences through his frequent appearances on Garrison Keillor’s The Writer’s Almanac. He has received grants and fellowships from the NEA, the Pushcart Foundation, the Witter Bynner Foundation, and the Ohio Arts Council. He lives and teaches in Cleveland, Ohio, which has made him hardy and resolute. Copyright © 2016 George Bilgere

Dealing with the Issues of the Urban Coyote: One County’s Experience

Behind dire wolves and saber-toothed cats, coyotes rank as the third most commonly found mammal in the La Brea Tar Pits proving they have been residents of Los Angeles County for thousands of years. There has probably always been some degree of human-coyote conflict, but to many current residents, the situation seems to be getting worse. The Los Angeles County Department of Agricultural Commissioner/Weights and Measures is one of the last public agencies in the County attempting to manage coyotes in certain situations, which is proving to be challenging, given the changing nature of public opinion on coyote control issues and the public’s general knowledge of wildlife. I discuss how the Los Angeles County, Department of Agricultural Commissioner/Weights and Measures attempts to meet the expectations of the public in the light of these changing attitudes.

Accuracy of mandibular force profiles for bite force estimation and feeding behavior reconstruction in extant and extinct carnivorans.

Mandibular force profiles apply the principles of beam theory to identify mandibular biomechanical properties that reflect the bite force and feeding strategies of extant and extinct predators. While this method uses the external dimensions of the mandibular corpus to determine its biomechanical properties, more accurate results could potentially be obtained by quantifying its internal cortical bone distribution. To test this possibility, mandibular force profiles were calculated using both external mandibular dimensions ('solid mandible model') and quantification of internal bone distribution of the mandibular corpus obtained from computed tomography scans ('hollow mandible model') for five carnivorans (Canis lupus, Crocuta crocuta, Panthera leo, Neofelis nebulosa and the extinct Canis dirus). Comparison reveals that the solid model slightly overestimates mandibular biomechanical properties, but the pattern of change in biomechanical properties along the mandible remains the same. As such, feeding behavior reconstructions are consistent between the two models and are not improved by computed tomography. Bite force estimates produced by the two models are similar, except in C. crocuta, where the solid model underestimates bite force by 10-14%. This discrepancy is due to the more solid nature of the C. crocuta mandible relative to other carnivorans. Therefore, computed tomography improves bite force estimation accuracy for taxa with thicker mandibular corpora, but not significantly so otherwise. Bite force estimates derived from mandibular force profiles are far closer to empirically measured bite force than those inferred from jaw musculature dimension. Consequently, bite force estimates derived from this method can be used to calibrate finite-element analysis models.

Biotic responses of canids to the terminal Pleistocene megafauna extinction

Trophic downgrading is a major concern for conservation scientists. The largest consumers in many ecosystems have become either rare or extirpated, leading to worry over the loss of their ecosystem function. However, trophic downgrading is not a uniquely modern phenomenon. The extinction of 34 genera of megafauna from North America ∼13 000 yr ago must have led to widespread changes in terrestrial ecosystem function. Studies that have examined the event address impacts on vegetative structure, small mammal communities, nutrient cycling, and fire regimes. Relatively little attention has been paid to community changes at the top of the food chain. Here, we examine the response of carnivores in North America to the Pleistocene extinction. We employ fossil data to model the climatic niche of endemic canids, including the extinct dire wolf Canis dirus, over the last 20 000 yr. Quantifying the abiotic niche allows us to account for expected changes due to climate fluctuations over the Late Quaternary; deviations from expected responses likely reveal influences of competition and/or resource availability. We quantify the degree of niche conservatism and interspecific overlap to assess species and community responses among canids. We also include in our analyses a novel introduced predator, the domestic dog Canis lupus familiaris, which accompanied humans into the New World. We find that endemic canid species display low fidelity to their climatic niche through time, We find that survivors increasingly partition their climatic niche throughout the Holocene and, surprisingly, do not expand into niche space presumably vacated by the extinction of very large carnivores. These results suggest that loss of megaherbivores and competition with humans likely outweighed advantages conferred from the loss of very large predators. We also find that wolves and dogs decrease their niche overlap throughout the Holocene, suggesting a distinctive relationship between dogs and man.

Inland California during the Pleistocene—Megafaunal stable isotope records reveal new paleoecological and paleoenvironmental insights

Abstract We measured oxygen and carbon isotope compositions from teeth from three fossil localities in California, The McKittrick Tar seeps (Rancholabrean), Fairmead Landfill, and Irvington (both Irvingtonian). These sites have produced a variety of megafauna fossils, and to date are relatively understudied. Previous ecological studies of Pleistocene California megafauna have focused on the coastal Rancho La Brea tar seeps (RLB), neglecting inland faunas. Both Fairmead Landfill and McKittrick are located in California's San Joaquin Valley, and provide the first isotopic data from the region. We sampled a wide range of taxa; Equus, Camelops, Mammuthus, Mammut, Hemiauchenia, Odocoileus, Tetrameryx, Capromeryx, Platygonus, Canis dirus, Canis latrans, Arctodus simus, Smilodon, Homotherium, Miracinonyx, Panthera onca and Panthera atrox. Stable carbon values from both middle Pleistocene localities are consistent with a C3 dominated environment. Mean annual precipitation (MAP) estimates for the middle Pleistocene localities are ~ 340 mm/year for Fairmead Landfill and ~ 900 mm/year for Irvington. While the inland MAP estimate is similar to modern levels, Irvington MAP estimates are significantly higher than the modern average. In contrast, the McKittrick tar seeps show clear evidence of C4 consumption among Equus, Bison and Camelops, suggesting a mixture C4 grasses and halophytes. Similarly, comparing between McKittrick and published data for RLB indicate a higher level of C4 resources inland. Serially sampled teeth from both inland localities reveal diet and resource partitioning between browsers and grazers.

The fossil record of phenotypic integration and modularity: A deep-time perspective on developmental and evolutionary dynamics

Variation is the raw material for natural selection, but the factors shaping variation are still poorly understood. Genetic and developmental interactions can direct variation, but there has been little synthesis of these effects with the extrinsic factors that can shape biodiversity over large scales. The study of phenotypic integration and modularity has the capacity to unify these aspects of evolutionary study by estimating genetic and developmental interactions through the quantitative analysis of morphology, allowing for combined assessment of intrinsic and extrinsic effects. Data from the fossil record in particular are central to our understanding of phenotypic integration and modularity because they provide the only information on deep-time developmental and evolutionary dynamics, including trends in trait relationships and their role in shaping organismal diversity. Here, we demonstrate the important perspective on phenotypic integration provided by the fossil record with a study of Smilodon fatalis (saber-toothed cats) and Canis dirus (dire wolves). We quantified temporal trends in size, variance, phenotypic integration, and direct developmental integration (fluctuating asymmetry) through 27,000 y of Late Pleistocene climate change. Both S. fatalis and C. dirus showed a gradual decrease in magnitude of phenotypic integration and an increase in variance and the correlation between fluctuating asymmetry and overall integration through time, suggesting that developmental integration mediated morphological response to environmental change in the later populations of these species. These results are consistent with experimental studies and represent, to our knowledge, the first deep-time validation of the importance of developmental integration in stabilizing morphological evolution through periods of environmental change.

The devil is in the details: identification of postcranial elements of Canis dirus and Canis lupus from Rancho La Brea using discriminant function and morphometric analyses (919.7)

The preservation of fossils in the tar pits at Rancho La Brea makes identification of postcranial material difficult, especially separating Canis lupus form Canis dirus. Generally, distinguishing C. dirus from C. lupus is achieved by study of the dentition and cranial features; otherwise most postcranial bones are identified by size. Because the tar pits at Rancho La Brea disarticulate the remains during the fossilization process, one bony element can rarely be associated with any other. Therefore, another means of identification is needed for postcranial canid materials. I compiled a series of measurements of scapulae, humeri, and ulnae of C. dirus to compare with similar measurements of modern C. lupus. The wolf specimens in this study represent wild populations of North American subspecies that often included sex and age information. By comparing linear measurements of both taxa, I was able to determine statistically relevant differences in the forelimb bone using discriminant function analysis and morphometrics. Being able to provide composite size ranges for individual bony elements, these disarticulated canid specimens of C. dirus and C. lupus can be more accurately identified only from postcranial material. These comparisons can serve as a reference tool for accurately comparing other fossil canid specimens as well as modern species when cranial material is unavailable.

Cranial morphometrics of the dire wolf, Canis dirus, at Rancho La Brea: temporal variability and its links to nutrient stress and climate

Cranial morphometrics of the dire wolf, Canis dirus, at Rancho La Brea: temporal variability and its links to nutrient stress and climate

A Cat among the Wolves: An attempt to reveal the identity of a felid‐like humerus misidentified as Canis dirus from Rancho La Brea

There have been many kinds of animals found at Rancho La Brea located in Los Angeles, California; both carnivore and herbivore alike. The most common species found in the tar pits are the predators of the area such as Canis dirus (Dire wolf), Smilodon fatalis (saber‐tooth cat), and Canis latrans (American coyote). Other large carnivores that are not as common but still prevalent include Panthera atrox (American lion), Puma concolor (mountain lion), Panthera onca (jaguar), and Arctodus simus (short‐faced bear). Multitudes of these fossil specimens have been excavated from Hancock Park since the 1870s, and the University of California, Berkeley, was the first institution to house these fossils. Since these early dig operations in the 1900s, University of California, Berekely has traded fossil specimens with other large institutions, including the Field Museum of Natural History located in Chicago, Illinois. It was during a recent visit to the Field Museum to study the La Brea specimens in the Geology collection, that I found a misidentified limb bone. The bone is a humerus which was labeled Aenocyon dirus (Canis dirus). This humerus shows some characteristics that hint toward it belonging to a felid of some kind rather than a large canid. The most likely taxa include Panthera onca and Puma concolor.Grant Funding Source: Nothern Illinois University