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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Article
  • Peer Reviewed
UCLA Previously Published Works (2020)
Ecological specialization has costs and benefits at various scales: traits benefitting an individual may disadvantage its population, species or clade. In particular, large body size and hypercarnivory (diet over 70% meat) have evolved repeatedly in mammals; yet large hypercarnivores are thought to be trapped in a macroevolutionary "ratchet", marching unilaterally toward decline. Here, we weigh the impact of this specialization on extinction risk using the rich fossil record of North American canids (dogs). In two of three canid subfamilies over the past 40 million years, diversification of large-bodied hypercarnivores appears constrained at the clade level, biasing specialized lineages to extinction. However, despite shorter species durations, extinction rates of large hypercarnivores have been mostly similar to those of all other canids. Extinction was size- and carnivory-selective only at the end of the Pleistocene epoch 11,000 years ago, suggesting that large hypercarnivores were not disadvantaged at the species level before anthropogenic influence.
    Cover page: Iterative evolution of large-bodied hypercarnivory in canids benefits species but not cladesCreative Commons 'BY' version 4.0 license
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2018)
    How traits influence species persistence is a fundamental question in ecology, evolution and palaeontology. We test the relationship between dietary traits and both species duration and locality coverage over 40 million years in North American canids, a clade with considerable ecomorphological disparity and a dense fossil record. Because ecomorphological generalization-broad resource use-may enable species to withstand disturbance, we predicted that canids of average size and mesocarnivory would exhibit longer durations and wider distributions than specialized larger or smaller species. Second, because locality coverage might reflect dispersal ability and/or survivability in a range of habitats, we predicted that high coverage would correspond with longer durations. We find a nonlinear relationship between species duration and degree of carnivory: species at either end of the carnivory spectrum tend to have shorter durations than mesocarnivores. Locality coverage shows no relationship with size, diet or duration. To test whether generalization (medium size, mesocarnivory) corresponds to an adaptive optimum, we fit trait evolution models to previously generated canid phylogenies. Our analyses identify no single optimum in size or diet. Instead, the primary model of size evolution is a classic Cope's Rule increase over time, while dietary evolution does not conform to a single model.
      Cover page: Dietary specialization is linked to reduced species durations in North American fossil canids
      • Thesis
      • Peer Reviewed
      UCLA Electronic Theses and Dissertations (2018)

      Competition likely shaped the evolution of the mammalian family Canidae (dogs and their ancestors; order Carnivora). From their origin 40 million years ago (Ma), early canids lived alongside potential competitors that may have monopolized the large-carnivore niche—such as bears, bear-dogs, and nimravid saber-toothed cats—before becoming large and hypercarnivorous (diet of >70% meat) later in their history. This ecomorphological context, along with high phylogenetic resolution and an outstanding fossil record, makes North American fossil canids an ideal system for investigating how biotic interactions (e.g. competition) and ecological specialization (e.g. hypercarnivory) might influence clade evolution.

      Chapter 1 investigates whether ecological generalization enables species to have longer durations and broader geographic range. I developed and applied a carnivory index to 100+ species, processing 3708 occurrences through a new duration-estimation method accounting for varying fossil preservation. A non-linear relationship between duration and carnivory emerged: both hyper- and hypocarnivores have shorter durations than mesocarnivores.

      Chapter 2 tests the cost of hypercarnivory, quantified as elevated extinction risk. Large hypercarnivorous canids experienced extinction rates on par with other canids. However, in each canid subfamily, extinction rates rose after the first occurrence of large hypercarnivores, supporting the idea of hypercarnivory as a “macroevolutionary ratchet” for individual clades. Large hypercarnivores originated just over 10 Ma after the origin of Canidae, exhibiting constant diversification rates and peaking in richness around 12 Ma. Relationships emerge between diversification rates of canid subfamilies and temperature, suggesting future hypotheses to be investigated.

      Chapter 3 quantifies functional morphology in 114 fossil canids and non-canid competitors from 40 to 15 Ma, testing for ecological congruence between continental and regional scales and whether ecomorphological disparity reflects taxonomic diversity. Disparity appears inversely related to diversity. All four geographic regions examined preserved a narrower range of ecomorphology than at the continental scale. These results suggest that partitioning dietary as well as geographic resources, despite constraints to size, permitted canids to minimize competition and diversify.

      These macroecological and macroevolutionary studies of early canids and their potential competitors improve understanding of the resilience of the carnivore niche over long timescales, including periods of accelerated global change.

        Cover page: Carnivory in the Oligo-Miocene: Resource Specialization, Competition, and Coexistence Among North American Fossil Canids
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2018)
        The Hemphillian-age Mehrten Formation has yielded several fossil dogs (family Canidae). Initial study had identified all larger canids as Borophagus secundus (= Osteoborus cyonoides), a bone-crushing borophagine (a diverse subfamily of extinct canids), and all smaller canids as Canis cf. C. davisi, a canine (a subfamily including all living canids). Later analysis split B. secundus into two taxa and reassigned Canis cf. C. davisi to Eucyon davisi, yet omitted fragmentary remains of possible vulpines. Despite this wealth of Mehrten canid materials, a detailed systematic treatment is lacking. More recently, additional specimens have become available, further necessitating a systematic examination of the canids at this site. The present study finds four canid species: two borophagines (Borophagus parvus and B. secundus) and two canines (E. davisi and Vulpes stenognathus, newly identified). We support the division of ‘B. secundus’ into the smaller B. parvus and the larger, more hypercarnivorous B. secundus and find two morphotypes within B. parvus. A specimen from the Coyote Hill fauna, earliest in the Mehrten sequence, is reassigned to B. secundus, extending the temporal range of the species in California into the early Hemphillian. Borophagus parvus co-occurs with B. secundus only in the lower Modesto Reservoir Member; higher in the sequence, B. parvus co-occurs only with canines. Despite the apparent turnover in its co-inhabitants, B. parvus exhibits no size change. Given that the characteristics of B. parvus and B. secundus are intermediate among other Borophagus, the Mehrten canids may represent a rapid transition early in the evolution of the Borophagus lineage. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Balisi, M., X. Wang, J. Sankey, J. Biewer, and D. Garber. 2018. Fossil canids from the Mehrten Formation, Late Cenozoic of Northern California. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1405009.
          Cover page: Fossil canids from the Mehrten Formation, Late Cenozoic of Northern California
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2020)
          Collaborative hunting by complex social groups is a hallmark of large dogs (Mammalia: Carnivora: Canidae), whose teeth also tend to be hypercarnivorous, specialized toward increased cutting edges for meat consumption and robust p4-m1 complex for cracking bone. The deep history of canid pack hunting is, however, obscure because behavioral evidence is rarely preserved in fossils. Dated to the Early Pleistocene (>1.2 Ma), Canis chihliensis from the Nihewan Basin of northern China is one of the earliest canines to feature a large body size and hypercarnivorous dentition. We present the first known record of dental infection in C. chihliensis, likely inflicted by processing hard food, such as bone. Another individual also suffered a displaced fracture of its tibia and, despite such an incapacitating injury, survived the trauma to heal. The long period required for healing the compound fracture is consistent with social hunting and family care (food-sharing) although alternative explanations exist. Comparison with abundant paleopathological records of the putatively pack-hunting Late Pleistocene dire wolf, Canis dirus, at the Rancho La Brea asphalt seeps in southern California, U.S.A., suggests similarity in feeding behavior and sociality between Chinese and American Canis across space and time. Pack hunting in Canis may be traced back to the Early Pleistocene, well before the appearance of modern wolves, but additional evidence is needed for confirmation.
            Cover page: Hypercarnivorous teeth and healed injuries to Canis chihliensis from Early Pleistocene Nihewan beds, China, support social hunting for ancestral wolves
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2018)
            Borophagine canids have long been hypothesized to be North American ecological 'avatars' of living hyenas in Africa and Asia, but direct fossil evidence of hyena-like bone consumption is hitherto unknown. We report rare coprolites (fossilized feces) of Borophagus parvus from the late Miocene of California and, for the first time, describe unambiguous evidence that these predatory canids ingested large amounts of bone. Surface morphology, micro-CT analyses, and contextual information reveal (1) droppings in concentrations signifying scent-marking behavior, similar to latrines used by living social carnivorans; (2) routine consumption of skeletons; (3) undissolved bones inside coprolites indicating gastrointestinal similarity to modern striped and brown hyenas; (4) B. parvus body weight of ~24 kg, reaching sizes of obligatory large-prey hunters; and (5) prey size ranging ~35-100 kg. This combination of traits suggests that bone-crushing Borophagus potentially hunted in collaborative social groups and occupied a niche no longer present in North American ecosystems.
              Cover page: First bone-cracking dog coprolites provide new insight into bone consumption in Borophagus and their unique ecological niche.
              • Article
              • Peer Reviewed
              UCLA Previously Published Works (2024)
              Abstract: The trend of global cooling across the Cenozoic transformed the North American landscape from closed forest to more open grasslands, resulting in dietary adaptations in herbivores in response to shifting resources. In contrast, the material properties of the predator food source (muscle, skin, and bone) have remained constant over this transition, suggesting a corresponding lack of change in predator dietary adaptations. We investigated the North American mammalian predator fossil record using a tooth-shape metric and body mass, predicting that the former would exhibit stability. Instead, we found that mean molar morphology became more blade-like, with our tooth-shape metric sharply increasing in the late Eocene and remaining high from the Oligocene onward. Subsequent tests in extant carnivorans reveal taxa with more bladelike teeth are prevalent in more open environments. Our results reveal an unexpected functional shift among North American predators in response to large-scale environmental changes across the Cenozoic.
                Cover page: Cenozoic climate change and the evolution of North American mammalian predator ecomorphology
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