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Chatar N, Boman R, Fischer V, Segura V, Julémont C, Tseng ZJ. Growing sabers: Mandibular shape and biomechanical performance trajectories during the ontogeny of Smilodon fatalis. Anat Rec (Hoboken) 2024. [PMID: 38801020 DOI: 10.1002/ar.25504] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2024] [Revised: 03/28/2024] [Accepted: 05/02/2024] [Indexed: 05/29/2024]
Abstract
The evolution of organisms can be studied through the lens of developmental systems, as the timing of development of morphological features is an important aspect to consider when studying a phenotype. Such data can be challenging to obtain in fossil amniotes owing to the scarcity of their fossil record. However, the numerous remains of Rancho La Brea allow a detailed study of the postnatal changes in an extinct sabertoothed felid: Smilodon fatalis. Despite numerous previous studies on the ontogeny of Smilodon, an important question remained open: how did the cubs of Smilodon acquire and process food? By applying 3D geometric morphometrics and finite element analyses to 49 mandibles at various developmental stages (22 of S. fatalis, 23 of Panthera leo, and 4 of early diverging felids), we assess the changes in mandibular shape and performance during growth. Both lions and sabertooths exhibit a shift in mandibular shape, aligning with eruption of the lower carnassial. This marks the end of weaning in lions and suggests a prolonged weaning period in S. fatalis owing to its delayed eruption sequence. We also highlight distinct ontogenetic trajectories, with S. fatalis undergoing more postnatal mandibular shape changes. Finally, although S. fatalis appears more efficient than P. leo at performing an anchor bite, this efficiency is acquired through ontogeny and at a quite late age. The delayed shape change compared with P. leo and the low biting efficiency during the growth in Smilodon could indicate an extended duration of the parental care compared with P. leo.
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Affiliation(s)
- Narimane Chatar
- Evolution and Diversity Dynamics Lab, UR Geology, Université de Liège, Liège, Belgium
- Functional Anatomy and Vertebrate Evolution Lab, Department of Integrative Biology, University of California, Berkeley, California, USA
| | - Romain Boman
- Department of Aerospace and Mechanical Engineering, Non-Linear Computational Mechanics (MN2L) Research Group, Université de Liège, Liège, Belgium
| | - Valentin Fischer
- Evolution and Diversity Dynamics Lab, UR Geology, Université de Liège, Liège, Belgium
| | - Valentina Segura
- Unidad Ejecutora Lillo, Consejo Nacional de Investigaciones Científicas y Técnicas (conicet)-Fundación Miguel Lillo, San Miguel de Tucumán, Argentina
| | - Cara Julémont
- Evolution and Diversity Dynamics Lab, UR Geology, Université de Liège, Liège, Belgium
| | - Z Jack Tseng
- Functional Anatomy and Vertebrate Evolution Lab, Department of Integrative Biology, University of California, Berkeley, California, USA
- University of California Museum of Paleontology, Department of Integrative Biology, University of California, Berkeley, California, USA
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2
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Marciszak A, Ivanoff DV, Semenov YA, Talamo S, Ridush B, Stupak A, Yanish Y, Kovalchuk O. The Quaternary lions of Ukraine and a trend of decreasing size in Panthera spelaea. J MAMM EVOL 2022. [DOI: 10.1007/s10914-022-09635-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
AbstractThe fossil record of the cave lion, Panthera spelaea, suggests a gradual decrease in body size, the process peaking just before the extinction of the species at the end of the Late Pleistocene. Such an evolutionary trend appears rather unusual for a large felid species and requires further investigation. This study reviews the cave lions of Ukraine, whose fossils are known from 46 localities dated from 800 kyr to 18–17 kyr ago, with a special emphasis on size changes through time. We describe several important finds including those of Panthera spelaea fossilis from Sambir, Panthera spelaea ssp. from Bilykh Stin Cave and Panthera spelaea spelaea from Kryshtaleva Cave. We make subspecific identifications of specimens from the region and focus on their size characteristics. Our analysis of Ukrainian cave lions agrees with the temporal trend of decreasing size, particularly accelerating during MIS 2, as exemplified by the extremely small female skull from Kryshtaleva Cave. We provide a direct AMS date for this specimen (22.0–21.5 cal kyr BP), which suggests that the Kryshtaleva lioness must have belonged to a Panthera spelaea spelaea population forced south by the spreading ice sheet. We discuss some palaeoecological aspects of the evolutionary history and eventual extinction of the cave lion. Finally, we review the subfossil records of the extant lion Panthera leo known from several Ukrainian sites archaeologically dated to 6.4–2.0 kyr BP. These finds most probably represent the Persian lion Panthera leo persica.
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Balisi MA, Sharma AK, Howard CM, Shaw CA, Klapper R, Lindsey EL. Computed tomography reveals hip dysplasia in the extinct Pleistocene saber-tooth cat Smilodon. Sci Rep 2021; 11:21271. [PMID: 34711910 PMCID: PMC8553773 DOI: 10.1038/s41598-021-99853-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2021] [Accepted: 09/24/2021] [Indexed: 11/30/2022] Open
Abstract
Reconstructing the behavior of extinct species is challenging, particularly for those with no living analogues. However, damage preserved as paleopathologies on bone can record how an animal moved in life, potentially reflecting behavioral patterns. Here, we assess hypothesized etiologies of pathology in a pelvis and associated right femur of a Smilodon fatalis saber-toothed cat, one of the best-studied species from the Pleistocene-age Rancho La Brea asphalt seeps, California, USA, using visualization by computed tomography (CT). The pelvis exhibits massive destruction of the right hip socket that was interpreted, for nearly a century, to have developed from trauma and infection. CT imaging reveals instead that the pathological distortions characterize chronic remodeling that began at birth and led to degeneration of the joint over the animal's life. These results suggest that this individual suffered from hip dysplasia, a congenital condition common in domestic dogs and cats. This individual reached adulthood but could not have hunted properly nor defended territory on its own, likely relying on a social group for feeding and protection. While extant social felids are rare, these fossils and others with similar pathologies are consistent with a spectrum of social strategies in Smilodon supported by a predominance of previous studies.
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Affiliation(s)
- Mairin A Balisi
- La Brea Tar Pits and Museum, Natural History Museum of Los Angeles County, Los Angeles, CA, USA.
- Department of Life and Environmental Sciences, University of California, Merced, CA, USA.
| | - Abhinav K Sharma
- David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Carrie M Howard
- La Brea Tar Pits and Museum, Natural History Museum of Los Angeles County, Los Angeles, CA, USA
| | - Christopher A Shaw
- La Brea Tar Pits and Museum, Natural History Museum of Los Angeles County, Los Angeles, CA, USA
- Idaho Museum of Natural History, Idaho State University, Pocatello, ID, USA
| | - Robert Klapper
- Orthopaedics, Cedars Sinai Medical Group, Los Angeles, CA, USA
| | - Emily L Lindsey
- La Brea Tar Pits and Museum, Natural History Museum of Los Angeles County, Los Angeles, CA, USA
- Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA
- Institute of the Environment and Sustainability, University of California - Los Angeles, Los Angeles, CA, USA
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4
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Reynolds AR, Seymour KL, Evans DC. Smilodon fatalis siblings reveal life history in a saber-toothed cat. iScience 2021; 24:101916. [PMID: 33532710 PMCID: PMC7835254 DOI: 10.1016/j.isci.2020.101916] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 11/18/2020] [Accepted: 12/07/2020] [Indexed: 11/23/2022] Open
Abstract
The saber-toothed cat Smilodon fatalis is known predominantly from “predator trap” deposits, which has made many aspects of its life history difficult to infer. Here, we describe an association of at least two subadult and one adult S. fatalis from Pleistocene coastal deposits in Ecuador. The assemblage likely derived from a catastrophic mass mortality event, and thereby provides insights into the behavior of the species. The presence of a P3 in the subadult dentaries suggests inheritance, a rare instance of familial relatedness in the fossil record. The siblings were at least two years old and were associated with an adult that was likely their mother, indicating prolonged parental care in S. fatalis. Comparison with the growth of pantherine cats suggests that S. fatalis had a unique growth strategy among big cats that combines a growth rate that is similar to a tiger and the extended growth period of a lion. Association of two subadult and one adult Smilodon fatalis from Ecuador Rare, likely genetic condition suggests subadults are siblings S. fatalis appears to have exhibited fast growth over a prolonged period Comparison with growth in lions and tigers suggests a unique growth strategy
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Affiliation(s)
- Ashley R. Reynolds
- Department of Natural History, Royal Ontario Museum, 100 Queen's Park, Toronto, ON M5S 1C6, Canada
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON M5S 3B2, Canada
- Corresponding author
| | - Kevin L. Seymour
- Department of Natural History, Royal Ontario Museum, 100 Queen's Park, Toronto, ON M5S 1C6, Canada
| | - David C. Evans
- Department of Natural History, Royal Ontario Museum, 100 Queen's Park, Toronto, ON M5S 1C6, Canada
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON M5S 3B2, Canada
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Saitta ET, Stockdale MT, Longrich NR, Bonhomme V, Benton MJ, Cuthill IC, Makovicky PJ. An effect size statistical framework for investigating sexual dimorphism in non-avian dinosaurs and other extinct taxa. Biol J Linn Soc Lond 2020. [DOI: 10.1093/biolinnean/blaa105] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Abstract
Despite reports of sexual dimorphism in extinct taxa, such claims in non-avian dinosaurs have been rare over the last decade and have often been criticized. Since dimorphism is widespread in sexually reproducing organisms today, under-reporting in the literature might suggest either methodological shortcomings or that this diverse group exhibited highly unusual reproductive biology. Univariate significance testing, especially for bimodality, is ineffective and prone to false negatives. Species recognition and mutual sexual selection hypotheses, therefore, may not be required to explain supposed absence of sexual dimorphism across the grade (a type II error). Instead, multiple lines of evidence support sexual selection and variation of structures consistent with secondary sexual characteristics, strongly suggesting sexual dimorphism in non-avian dinosaurs. We propose a framework for studying sexual dimorphism in fossils, focusing on likely secondary sexual traits and testing against all alternate hypotheses for variation in them using multiple lines of evidence. We use effect size statistics appropriate for low sample sizes, rather than significance testing, to analyse potential divergence of growth curves in traits and constrain estimates for dimorphism magnitude. In many cases, estimates of sexual variation can be reasonably accurate, and further developments in methods to improve sex assignments and account for intrasexual variation (e.g. mixture modelling) will improve accuracy. It is better to compare estimates for the magnitude of and support for dimorphism between datasets than to dichotomously reject or fail to reject monomorphism in a single species, enabling the study of sexual selection across phylogenies and time. We defend our approach with simulated and empirical data, including dinosaur data, showing that even simple approaches can yield fairly accurate estimates of sexual variation in many cases, allowing for comparison of species with high and low support for sexual variation.
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Affiliation(s)
- Evan T Saitta
- Life Sciences Section, Integrative Research Center, Field Museum of Natural History, Chicago, IL, USA
| | | | - Nicholas R Longrich
- Department of Biology and Biochemistry and Milner Centre for Evolution, University of Bath, Bath, UK
| | - Vincent Bonhomme
- Institut des sciences de l’évolution, Université de Montpellier, Montpellier, France
| | | | - Innes C Cuthill
- School of Biological Sciences, University of Bristol, Bristol, UK
| | - Peter J Makovicky
- Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN, USA
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6
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Solitary meat-eaters: solitary, carnivorous carnivorans exhibit the highest degree of sexual size dimorphism. Sci Rep 2019; 9:15344. [PMID: 31653949 PMCID: PMC6814822 DOI: 10.1038/s41598-019-51943-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 10/09/2019] [Indexed: 12/15/2022] Open
Abstract
Although sexual size dimorphism (SSD) is widespread across the animal tree of life, the underlying evolutionary processes that influence this phenomenon remains elusive and difficult to tease apart. In this study, I examined how social system (as a proxy for sexual selection) and diet (as a proxy for natural selection) influenced the evolution of SSD in terrestrial carnivorans (Carnivora; Mammalia). Using phylogenetic comparative methods, I found that are territorial solitary and carnivorous carnivorans exhibited selection towards increased degree of male-biased SSD compared to other carnivorans with alternative social systems and diets. I also found the absence of Rensch’s rule across most carnivoran clades, suggestion a relaxation of the influences of sexual selection on SSD. These results together suggest that sexual selection and niche divergence together are important processes influencing the evolution of male-biased SSD in extant terrestrial carnivorans.
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Voyta LL, Zazhigin VS, Petrova EA, Krjutchkova LY. Shrew dentition (Lipotyphla: Soricidae)—endodontic morphology and its phylogenetic resolving power. MAMMAL RES 2019. [DOI: 10.1007/s13364-019-00455-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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8
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Harano T, Kutsukake N. Directional selection in the evolution of elongated upper canines in clouded leopards and sabre-toothed cats. J Evol Biol 2018; 31:1268-1283. [PMID: 29904973 DOI: 10.1111/jeb.13309] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2017] [Accepted: 06/11/2018] [Indexed: 11/30/2022]
Abstract
Extremely developed or specialized traits such as the elongated upper canines of extinct sabre-toothed cats are often not analogous to those of any extant species, which limits our understanding of their evolutionary cause. However, an extant species may have undergone directional selection for a similar extreme phenotype. Among living felids, the clouded leopard, Neofelis nebulosa, has exceptionally long upper canines for its body size. We hypothesized that directional selection generated the elongated upper canines of clouded leopards in a manner similar to the process in extinct sabre-toothed cats. To test this, we developed an approach that compared the effect of directional selection among lineages in a phylogeny using a simulation of trait evolution and approximate Bayesian computation. This approach was applied to analyse the evolution of upper canine length in the Felidae phylogeny. Our analyses consistently showed directional selection favouring longer upper canines in the clouded leopard lineage and a lineage leading to the sabre-toothed cat with the longest upper canines, Smilodon. Most of our analyses detected an effect of directional selection for longer upper canines in the lineage leading to another sabre-toothed cat, Homotherium, although this selection may have occurred exclusively in the primitive species. In all the analyses, the clouded leopard and Smilodon lineages showed comparable directional selection. This implies that clouded leopards share a selection advantage with sabre-toothed cats in having elongated upper canines.
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Affiliation(s)
- Tomohiro Harano
- Department of Evolutionary Studies of Biosystems, School of Advanced Sciences, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Japan
| | - Nobuyuki Kutsukake
- Department of Evolutionary Studies of Biosystems, School of Advanced Sciences, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Japan
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9
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Wysocki MA, Feranec RS, Tseng ZJ, Bjornsson CS. Using a Novel Absolute Ontogenetic Age Determination Technique to Calculate the Timing of Tooth Eruption in the Saber-Toothed Cat, Smilodon fatalis. PLoS One 2015; 10:e0129847. [PMID: 26132165 PMCID: PMC4489498 DOI: 10.1371/journal.pone.0129847] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Accepted: 05/12/2015] [Indexed: 11/19/2022] Open
Abstract
Despite the superb fossil record of the saber-toothed cat, Smilodon fatalis, ontogenetic age determination for this and other ancient species remains a challenge. The present study utilizes a new technique, a combination of data from stable oxygen isotope analyses and micro-computed tomography, to establish the eruption rate for the permanent upper canines in Smilodon fatalis. The results imply an eruption rate of 6.0 millimeters per month, which is similar to a previously published average enamel growth rate of the S. fatalis upper canines (5.8 millimeters per month). Utilizing the upper canine growth rate, the upper canine eruption rate, and a previously published tooth replacement sequence, this study calculates absolute ontogenetic age ranges of tooth development and eruption in S. fatalis. The timing of tooth eruption is compared between S. fatalis and several extant conical-toothed felids, such as the African lion (Panthera leo). Results suggest that the permanent dentition of S. fatalis, except for the upper canines, was fully erupted by 14 to 22 months, and that the upper canines finished erupting at about 34 to 41 months. Based on these developmental age calculations, S. fatalis individuals less than 4 to 7 months of age were not typically preserved at Rancho La Brea. On the whole, S. fatalis appears to have had delayed dental development compared to dental development in similar-sized extant felids. This technique for absolute ontogenetic age determination can be replicated in other ancient species, including non-saber-toothed taxa, as long as the timing of growth initiation and growth rate can be determined for a specific feature, such as a tooth, and that growth period overlaps with the development of the other features under investigation.
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Affiliation(s)
- M. Aleksander Wysocki
- Department of Biological Sciences, Clemson University, Clemson, South Carolina, United States of America
| | - Robert S. Feranec
- Research and Collections Division, New York State Museum, Albany, New York, United States of America
- * E-mail:
| | - Zhijie Jack Tseng
- Division of Paleontology, American Museum of Natural History, New York, New York, United States of America
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Meachen JA, O'Keefe FR, Sadleir RW. Evolution in the sabre-tooth cat, Smilodon fatalis, in response to Pleistocene climate change. J Evol Biol 2014; 27:714-23. [PMID: 24779050 DOI: 10.1111/jeb.12340] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The late Pleistocene was a time of environmental change, culminating in an extinction event. Few fossil localities record a temporal series of carnivore fossil populations from this interesting interval as well as Rancho La Brea (RLB). We analysed mandibles of Smilodon fatalis from RLB using 2-D geometric morphometrics to examine whether, and how, mandibular shape changes through time. Smilodon fatalis shows mandibular evolution with oscillations between a small, ancestral-type morph in pits 77 (≈37 Kybp) and 2051 (≈26 Kybp), a larger, more derived morph in pits 91 (≈28 Kybp) and 61-67 (≈13.6 Kybp), and an intermediate morph from pit 13 (≈17.7 Kybp). These oscillations end in pit 61-67, with greatest body size, and are estimated to have its widest gape and lowest bite force. Additionally, variation is lowest in pit 61-67, which was deposited concurrent with the Bølling–Allerød warming event, which may have important implications for the timing or conditions during the extinction event. Contra to a temporal Bergmann's rule, such rapid warming events appear to be correlated with larger, derived, morphologies whereas static, cooler, climates correlate with gracile, ancestral morphologies.
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11
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O'Keefe FR, Meachen J, Fet EV, Brannick A. Ecological determinants of clinal morphological variation in the cranium of the North American gray wolf. J Mammal 2013. [DOI: 10.1644/13-mamm-a-069] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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12
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Desantis LRG, Schubert BW, Scott JR, Ungar PS. Implications of diet for the extinction of saber-toothed cats and American lions. PLoS One 2012; 7:e52453. [PMID: 23300674 PMCID: PMC3530457 DOI: 10.1371/journal.pone.0052453] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2012] [Accepted: 11/19/2012] [Indexed: 11/30/2022] Open
Abstract
The saber-toothed cat, Smilodon fatalis, and American lion, Panthera atrox, were among the largest terrestrial carnivores that lived during the Pleistocene, going extinct along with other megafauna ∼12,000 years ago. Previous work suggests that times were difficult at La Brea (California) during the late Pleistocene, as nearly all carnivores have greater incidences of tooth breakage (used to infer greater carcass utilization) compared to today. As Dental Microwear Texture Analysis (DMTA) can differentiate between levels of bone consumption in extant carnivores, we use DMTA to clarify the dietary niches of extinct carnivorans from La Brea. Specifically, we test the hypothesis that times were tough at La Brea with carnivorous taxa utilizing more of the carcasses. Our results show no evidence of bone crushing by P. atrox, with DMTA attributes most similar to the extant cheetah, Acinonyx jubatus, which actively avoids bone. In contrast, S. fatalis has DMTA attributes most similar to the African lion Panthera leo, implying that S. fatalis did not avoid bone to the extent previously suggested by SEM microwear data. DMTA characters most indicative of bone consumption (i.e., complexity and textural fill volume) suggest that carcass utilization by the extinct carnivorans was not necessarily more complete during the Pleistocene at La Brea; thus, times may not have been "tougher" than the present. Additionally, minor to no significant differences in DMTA attributes from older (∼30-35 Ka) to younger (∼11.5 Ka) deposits offer little evidence that declining prey resources were a primary cause of extinction for these large cats.
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Affiliation(s)
- Larisa R G Desantis
- Department of Earth and Environmental Science, Vanderbilt University, Nashville, Tennessee, United States of America.
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13
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Christiansen P. Phylogeny of the sabertoothed felids (Carnivora: Felidae: Machairodontinae). Cladistics 2012; 29:543-559. [DOI: 10.1111/cla.12008] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/30/2012] [Indexed: 11/27/2022] Open
Affiliation(s)
- Per Christiansen
- Department of Biotechnology, Chemistry, and Environmental Engineering; University of Aalborg; Sohngaardsholmsvej 57; Aalborg; DK-9000; Denmark
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14
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Christiansen P, Harris JM. Variation in craniomandibular morphology and sexual dimorphism in pantherines and the sabercat Smilodon fatalis. PLoS One 2012; 7:e48352. [PMID: 23110232 PMCID: PMC3482211 DOI: 10.1371/journal.pone.0048352] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2012] [Accepted: 09/24/2012] [Indexed: 11/19/2022] Open
Abstract
Sexual dimorphism is widespread among carnivorans, and has been an important evolutionary factor in social ecology. However, its presence in sabertoothed felids remains contentious. Here we present a comprehensive analysis of extant Panthera and the sabertoothed felid Smilodon fatalis. S. fatalis has been reported to show little or no sexual dimorphism but to have been intraspecifically variable in skull morphology. We found that large and small specimens of S. fatalis could be assigned to male and female sexes with similar degrees of confidence as Panthera based on craniomandibular shape. P. uncia is much less craniomandibularly variable and has low levels of sexual size-dimorphism. Shape variation in S. fatalis probably reflects sexual differences. Craniomandibular size-dimorphism is lower in S. fatalis than in Panthera except P. uncia. Sexual dimorphism in felids is related to more than overall size, and S. fatalis and the four large Panthera species show marked and similar craniomandibular and dental morphometric sexual dimorphism, whereas morphometric dimorphism in P. uncia is less. Many morphometric-sexually dimorphic characters in Panthera and Smilodon are related to bite strength and presumably to killing ecology. This suggests that morphometric sexual dimorphism is an evolutionary adaptation to intraspecific resource partitioning, since large males with thicker upper canines and stronger bite forces would be able to hunt larger prey than females, which is corroborated by feeding ecology in P. leo. Sexual dimorphism indicates that S. fatalis could have been social, but it is unlikely that it lived in fusion-fission units dominated by one or a few males, as in sub-Saharan populations of P. leo. Instead, S. fatalis could have been solitary and polygynous, as most extant felids, or it may have lived in unisexual groups, as is common in P. leo persica.
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Affiliation(s)
- Per Christiansen
- Department of Biotechnology, Chemistry, and Environmental Engineering, University of Aalborg, Aalborg, Denmark.
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15
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Christiansen P. The making of a monster: postnatal ontogenetic changes in craniomandibular shape in the great sabercat Smilodon. PLoS One 2012; 7:e29699. [PMID: 22235326 PMCID: PMC3250457 DOI: 10.1371/journal.pone.0029699] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2011] [Accepted: 12/01/2011] [Indexed: 12/23/2022] Open
Abstract
Derived sabercats had craniomandibular morphologies that in many respects were highly different from those of extant felids, and this has often been interpreted functionally as adaptations for predation at extreme gape angles with hypertrophied upper canines. It is unknown how much of this was a result of intraspecific postnatal ontogeny, since juveniles of sabercats are rare and no quantitative study has been made of craniomandibular ontogeny. Postnatal ontogenetic craniomandibular shape changes in two morphologically derived sabercats, Smilodon fatalis and S. populator, were analysed using geometric morphometrics and compared to three species of extant pantherines, the jaguar, tiger, and Sunda clouded leopard. Ontogenetic shape changes in Smilodon usually involved the same areas of the cranium and mandible as in extant pantherines, and large-scale modularization was similar, suggesting that such may have been the case for all felids, since it followed the same trends previously observed in other mammals. However, in other respects Smilodon differed from extant pantherines. Their crania underwent much greater and more localised ontogenetic shape changes than did the mandibles, whereas crania and mandibles of extant pantherines underwent smaller, fewer and less localised shape changes. Ontogenetic shape changes in the two species of Smilodon are largely similar, but differences are also present, notably those which may be tied to the presence of larger upper canines in S. populator. Several of the specialized cranial characters differentiating adult Smilodon from extant felids in a functional context, which are usually regarded as evolutionary adaptations for achieving high gape angles, are ontogenetic, and in several instances ontogeny appears to recapitulate phylogeny to some extent. No such ontogenetic evolutionary adaptive changes were found in the extant pantherines. Evolution in morphologically derived sabercats involved greater cranial ontogenetic changes than among extant felids, resulting in greatly modified adult craniomandibular morphologies.
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Affiliation(s)
- Per Christiansen
- Department of Biotechnology, Chemistry, and Environmental Engineering, University of Aalborg, Aalborg, Denmark.
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