Long in the tooth: evolution of sabertooth cat cranial shape

Sabertooths exhibit one of the most extreme feeding adaptations seen in mammals. The functional consequences of accommodating extremely elongate upper canine teeth are severe, resulting in a well-documented suite of cranial modifications. We used geometric morphometric methods to study the evolution of overall shape in the skulls of extant and extinct feline and machairodontine felids, as well as extinct nimravids. Trends in skull evolution were evaluated by using relative warps analysis and tested for association with body size and canine tooth length. Primitive sabertooths from all lineages exhibit cranial shapes more similar to conical-toothed cats, despite the presence of moderately developed saberteeth. More-derived forms in both nimravids and felids diverge in skull morphospace to form two distinct sabertooth types (dirk-toothed and scimitar-toothed) that differ in canine shape. Skull shape in conical-toothed cats is strongly associated with body size, but not canine length. However, within each sabertooth lineage, skull shape is significantly correlated with canine length, suggesting that gape-related demands drove the evolution of sabertooth skull morphology.

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Beyond the carapace: skull shape variation and morphological systematics of long-nosed armadillos (genus Dasypus)

10.7287/peerj.preprints.2924 ◽

2017 ◽

Author(s):

Lionel Hautier ◽

Guillaume Billet ◽

Benoit De Thoisy ◽

Frédéric Delsuc

Keyword(s):

Morphological Variation ◽

Distinct Species ◽

Morphological Characters ◽

Molecular Data ◽

Guiana Shield ◽

Shape Variation ◽

Skull Morphology ◽

Geometric Morphometric ◽

Skull Shape ◽

Shape And Size

Background. The systematics of long-nosed armadillos (genus Dasypus) has been mainly based on a handful of external morphological characters and classical measurements. Here, we studied the pattern of morphological variation in the skull of long-nosed armadillos species, with a focus on the systematics of the widely distributed nine-banded armadillo (D. novemcinctus). Methods. We present the first exhaustive 3D comparison of the skull morphology within the genus Dasypus, based on µCT-scans. We used geometric morphometric approaches to explore the patterns of the intra- and interspecific morphological variation of the skull with regard to several factors such as taxonomy, geography, allometry, and sexual dimorphism. Results. We show that the shape and size of the skull vary greatly between Dasypus species, with D. pilosus representing a clear outlier compared to other long-nosed armadillos. The study of the cranial intraspecific variation in D. novemcinctus evidences clear links to the geographic distribution and argue in favour of a revision of past taxonomic delimitations. Our detailed morphometric comparisons detected previously overlooked morphotypes of nine-banded armadillo, especially a very distinctive unit circumscribed to the Guiana Shield. Discussion. As our results are congruent with recent molecular data and analyses of the structure of paranasal sinuses, we propose that D. novemcinctus should be regarded either as a polytypic species (with three to four subspecies) or as a complex of several distinct species.

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Geographic variation in the skull morphology of the lesser grison (Galictis cuja: Carnivora, Mustelidae) from two Brazilian ecoregions

PeerJ ◽

10.7717/peerj.9388 ◽

2020 ◽

Vol 8 ◽

pp. e9388

Author(s):

Raissa Prior Migliorini ◽

Rodrigo Fornel ◽

Carlos Benhur Kasper

Keyword(s):

Atlantic Forest ◽

Size Variation ◽

Neotropical Region ◽

Shape Variation ◽

Skull Morphology ◽

Geometric Morphometric ◽

Morphological Variations ◽

Skull Shape ◽

Temperature And Precipitation ◽

Forest Region

Background The lesser grison (Galictis cuja) is one of the least known carnivores in the Neotropical region. Its wide geographical occurrence and range of habitats could lead to morphological variations along its distribution. So, this study aimed to investigate the variation in skull shape and size of this species, by testing the existence of ecotypes adapted to their respective environments (Uruguayan savanna and Atlantic Forest), as well as its relationship with selected abiotic variables. Methods The skulls of 52 museum specimens were photographed in the ventral, dorsal, and lateral views, and were analyzed using geometric morphometric techniques. Results We found sexual size dimorphism, with males being larger than females. The shape variation between sexes, as well as between ecoregions, is mostly explained by the effect of allometry. The specimens from Uruguayan savanna are larger than the ones from the Atlantic Forest. Size variation was also significantly correlated to latitude, temperature and precipitation patterns. No correlation between skull shape with geographical distance was detected. Discussion Morphometric measurements and diet data of lesser grison in regions from higher latitudes than our sampling show a tendency to heavier individuals, and the consumption of bigger prey compared to Uruguayan savanna. The results indicated the smaller specimens associated to low variability in annual temperature, congruent to Atlantic Forest region. An explanation for observed variation may be related to the “resource rule” but, due the minimal natural history information regards this species, we can just speculate about this.

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Geometric morphometric analysis of skull morphology reveals loss of phylogenetic signal at the generic level in extant lagomorphs (Mammalia: Lagomorpha)

Contributions to Zoology ◽

10.1163/18759866-08404001 ◽

2015 ◽

Vol 84 (4) ◽

pp. 267-284 ◽

Cited By ~ 9

Author(s):

Deyan Ge ◽

Lu Yao ◽

Lin Xia ◽

Zhaoqun Zhang ◽

Qisen Yang

Keyword(s):

Dna Sequences ◽

Shape Change ◽

Morphological Evolution ◽

Phylogenetic Signal ◽

Lateral View ◽

Skull Morphology ◽

Generic Level ◽

Geometric Morphometric ◽

Skull Shape ◽

Long Time

The intergeneric phylogeny of Lagomorpha had been controversial for a long time before a robust phylogeny was reconstructed based on seven nuclear and mitochondrial DNA sequences. However, skull morphology of several endemic genera remained poorly understood. The morphology of supraorbital processes in Lagomorpha is normally used as a diagnostic characteristic in taxonomy, but whether shape change of this structure parallels its genetic divergence has not been investigated. In this study, we conducted a comparative analysis of the skull morphology of all 12 extant genera using geometric morphometrics. These results indicated that no significant phylogenetic signal is observed in the shape change of the dorsal and ventral views of the cranium as well as in the lateral view of the mandible. The supraorbital processes also show insignificant phylogenetic signal in shape change. Similarly, mapping the centroid size (averaged by genus) of these datasets onto the phylogeny also showed insignificant phylogenetic signal. Aside from homoplasy caused by convergent evolution of skull shape, the massive extinction of lagomorphs after the late Miocene is proposed as one of the main causes for diluting phylogenetic signals in their morphological evolution. Acknowledging the loss of phylogenetic signals in skull shape and supraorbital processes of extant genera sheds new light on the long-standing difficulties for understanding higher-level systematics in Lagomorpha.

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Evidence for Male Horn Dimorphism and Related Pronotal Shape Variation in Copris lunaris (Linnaeus, 1758) (Coleoptera: Scarabaeidae, Coprini)

Insects ◽

10.3390/insects9030108 ◽

2018 ◽

Vol 9 (3) ◽

pp. 108 ◽

Cited By ~ 5

Author(s):

Kaan Kerman ◽

Angela Roggero ◽

Antonio Rolando ◽

Claudia Palestrini

Keyword(s):

Body Size ◽

Common Phenomenon ◽

Shape Variation ◽

Allometric Relationship ◽

Geometric Morphometric ◽

Horn Length ◽

Functional Consequences ◽

Males And Females ◽

Morphological Differences ◽

Future Work

Male horn dimorphism is a rather common phenomenon in dung beetles, where some adult individuals have well-developed head horns (i.e., major males), while others exhibit diminished horn length (i.e., minor males). We focused on horn dimorphism and associated head and pronotum shape variations in Copris lunaris. We examined the allometric relationship between horn length (i.e., cephalic and pronotal horns) and maximum pronotum width (as index of body size) by fitting linear and sigmoidal models for both sexes. We then asked whether head and pronotum shape variations, quantified using the geometric morphometric approach, contributed to this allometric pattern. We found that female cephalic and pronotal horn growth showed a typical isometric scaling with body size. Horn length in males, however, exhibited sigmoidal allometry, where a certain threshold in body size separated males into two distinct morphs as majors and minors. Interestingly, we highlighted the same allometric patterns (i.e., isometric vs. sigmoidal models) by scaling horn lengths with pronotum shape, making evident that male horn dimorphism is not only a matter of body size. Furthermore, the analysis of shape showed that the three morphs had similar heads, but different pronota, major males showing a more expanded, rounded pronotum than minor males and females. These morphological differences in C. lunaris can ultimately have important functional consequences in the ecology of this species, which should be explored in future work.

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Ontogenetic shift in diet of a large elapid snake is facilitated by allometric change in skull morphology

10.21203/rs.3.rs-853742/v1 ◽

2021 ◽

Author(s):

Matthew Brenton Patterson ◽

Ashleigh K Wolfe ◽

Patricia A Fleming ◽

Philip W Bateman ◽

Meg Martin ◽

...

Keyword(s):

Body Size ◽

Morphological Changes ◽

Full Range ◽

Stomach Contents ◽

Prey Type ◽

Postnatal Ontogeny ◽

Shape Variation ◽

Ontogenetic Changes ◽

Skull Morphology ◽

Skull Shape

Abstract As snakes are limbless, gape-limited predators, their skull is the main feeding structure involved in prey handling, manipulation and feeding. Ontogenetic changes in prey type and size are likely to be associated with distinct morphological changes in the skull during growth. We investigated ontogenetic variation in diet from stomach contents of n = 161 dugite specimens (Pseudonaja affinis, Elapidae) representing the full range of body size for the species, and skull morphology of 46 specimens (range 0.25–1.64 m snout-vent-length; SVL). We hypothesised that changes in prey type throughout postnatal ontogeny would coincide with distinct changes in skull shape. Dugites demonstrate a distinct size-related shift in diet: the smallest individuals ate autotomised reptile tails, medium-sized individuals predominantly ate small reptiles (as snakes grew larger there was an increased likelihood of feeding on reptiles head-first), and the largest individuals (> 0.8 m SVL) ate mammals and large reptiles. Morphometric analysis revealed that ~ 40% of the variation in skull shape was associated with body size (SVL). Through ontogeny, skulls changed from a smooth, bulbous cranium with relatively small trophic bones (upper and lower jaws and their attachments), to more rugous bones (as an adaption for muscle attachment) and relatively longer trophic bones that would extend gape. Individual shape variation in trophic bone dimensions was greater in larger adults and this likely reflects natural plasticity of individuals feeding on different prey sizes/types. Rather than a distinct morphological shift with diet, the ontogenetic changes were consistent, but positive allometry of individual trophic bones resulted in disproportionate growth of the skull, reflected in increased gape size and mobility of jaw bones in adults to aid the ingestion of larger prey and improve manipulation and processing ability. These results indicate that allometric scaling is an important mechanism by which snakes can change their dietary niche.

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Beyond the carapace: skull shape variation and morphological systematics of long-nosed armadillos (genus Dasypus)

PeerJ ◽

10.7717/peerj.3650 ◽

2017 ◽

Vol 5 ◽

pp. e3650 ◽

Cited By ~ 8

Author(s):

Lionel Hautier ◽

Guillaume Billet ◽

Benoit de Thoisy ◽

Frédéric Delsuc

Keyword(s):

Morphological Variation ◽

Distinct Species ◽

Morphological Characters ◽

Molecular Data ◽

Shape Variation ◽

Micro Computed Tomography ◽

Dasypus Novemcinctus ◽

Skull Morphology ◽

Geometric Morphometric ◽

Skull Shape

Background The systematics of long-nosed armadillos (genus Dasypus) has been mainly based on a handful of external morphological characters and classical measurements. Here, we studied the pattern of morphological variation in the skull of long-nosed armadillos species, with a focus on the systematics of the widely distributed nine-banded armadillo (Dasypus novemcinctus). Methods We present the first exhaustive 3D comparison of the skull morphology within the genus Dasypus, based on micro-computed tomography. We used geometric morphometric approaches to explore the patterns of the intra- and interspecific morphological variation of the skull with regard to several factors such as taxonomy, geography, allometry, and sexual dimorphism. Results We show that the shape and size of the skull vary greatly among Dasypus species, with Dasypus pilosus representing a clear outlier compared to other long-nosed armadillos. The study of the cranial intraspecific variation in Dasypus novemcinctus evidences clear links to the geographic distribution and argues in favor of a revision of past taxonomic delimitations. Our detailed morphometric comparisons detected previously overlooked morphotypes of nine-banded armadillos, especially a very distinctive unit restricted to the Guiana Shield. Discussion As our results are congruent with recent molecular data and analyses of the structure of paranasal sinuses, we propose that Dasypus novemcinctus should be regarded either as a polytypic species (with three to four subspecies) or as a complex of several distinct species.

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Beyond the carapace: skull shape variation and morphological systematics of long-nosed armadillos (genus Dasypus)

10.7287/peerj.preprints.2924v1 ◽

2017 ◽

Author(s):

Lionel Hautier ◽

Guillaume Billet ◽

Benoit De Thoisy ◽

Frédéric Delsuc

Keyword(s):

Morphological Variation ◽

Distinct Species ◽

Morphological Characters ◽

Molecular Data ◽

Guiana Shield ◽

Shape Variation ◽

Skull Morphology ◽

Geometric Morphometric ◽

Skull Shape ◽

Shape And Size

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Allometry and Paleoecology of Medial Miocene Dwarf Rhinoceroses from the Texas Gulf Coastal Plain

Paleobiology ◽

10.1017/s0094837300004322 ◽

1982 ◽

Vol 8 (1) ◽

pp. 16-30 ◽

Cited By ~ 53

Author(s):

Donald R. Prothero ◽

Paul C. Sereno

Keyword(s):

Body Size ◽

Coastal Plain ◽

Sympatric Species ◽

High Plains ◽

Gulf Coastal Plain ◽

Canine Tooth ◽

Positive Allometry ◽

Mammalian Faunas ◽

The Common ◽

Limb Proportions

Barstovian (medial Miocene) mammalian faunas from the Texas Gulf Coastal Plain contained four apparently sympatric species of rhinoceroses: the common forms Aphelops megalodus and Teleoceras medicornutus, a dwarf Teleoceras, and a dwarf Peraceras. Previous work has suggested positive allometry in tooth area with respect to body size in several groups of mammals, i.e., larger mammals have relatively more tooth area. However, dwarfing lineages were shown to have relatively more tooth area for their body size. Our data show no significant allometry in post-canine tooth area of either artiodactyls or ceratomorphs. Similarly, dwarf rhinoceroses and hippopotami show no more tooth area than would be predicted for their size. Limbs are proportionately longer and more robust in larger living ceratomorphs (rhinos and tapirs) than predicted by previous authors. Limb proportions of both dwarf rhinoceroses and dwarf hippopotami are even more robust than in their living relatives.The high rhinoceros diversity reflects the overall high diversity of Barstovian faunas from the Texas Gulf Coastal Plain. The first appearance of several High Plains mammals in these faunas indicates “ecotone”-like conditions as faunal composition changed. Study of living continental dwarfs shows that there is commonly an ecological separation between browsing forest dwarfs and their larger forebears, which are frequently savannah grazers. This suggests that the dwarf rhinoceroses might have been forest browsers which were sympatric with the larger grazing rhinos of the High Plains during the Barstovian invasion. The continental dwarf model also suggests that insular dwarfism may be explained by the browsing food resources that predominate on islands.

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The isotopic niche of Atlantic, biting marine mammals and its relationship to skull morphology and body size

Scientific Reports ◽

10.1038/s41598-021-94610-w ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Massimiliano Drago ◽

Marco Signaroli ◽

Meica Valdivia ◽

Enrique M. González ◽

Asunción Borrell ◽

...

Keyword(s):

Body Size ◽

Atlantic Ocean ◽

Fisheries Management ◽

Marine Mammals ◽

Trophic Position ◽

Sympatric Species ◽

Isotopic Niche ◽

Apex Predators ◽

Skull Morphology ◽

Ecosystem Based Fisheries Management

AbstractUnderstanding the trophic niches of marine apex predators is necessary to understand interactions between species and to achieve sustainable, ecosystem-based fisheries management. Here, we review the stable carbon and nitrogen isotope ratios for biting marine mammals inhabiting the Atlantic Ocean to test the hypothesis that the relative position of each species within the isospace is rather invariant and that common and predictable patterns of resource partitioning exists because of constrains imposed by body size and skull morphology. Furthermore, we analyze in detail two species-rich communities to test the hypotheses that marine mammals are gape limited and that trophic position increases with gape size. The isotopic niches of species were highly consistent across regions and the topology of the community within the isospace was well conserved across the Atlantic Ocean. Furthermore, pinnipeds exhibited a much lower diversity of isotopic niches than odontocetes. Results also revealed body size as a poor predictor of the isotopic niche, a modest role of skull morphology in determining it, no evidence of gape limitation and little overlap in the isotopic niche of sympatric species. The overall evidence suggests limited trophic flexibility for most species and low ecological redundancy, which should be considered for ecosystem-based fisheries management.

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Pattern and pace of morphological change due to variable human impact: the case of Japanese macaques

Primates ◽

10.1007/s10329-021-00933-7 ◽

2021 ◽

Author(s):

Madeleine Geiger

Keyword(s):

Body Size ◽

Human Impact ◽

Morphological Variation ◽

Japanese Macaques ◽

Linear Measurements ◽

Skull Shape ◽

Rates Of Change ◽

Animal Populations ◽

Captive Populations ◽

In Captivity

AbstractHuman impact influences morphological variation in animals, as documented in many captive and domestic animal populations. However, there are different levels of human impact, and their influence on the pattern and rate of morphological variation remains unclear. This study contributes to the ongoing debate via the examination of cranial and mandibular shape and size variation and pace of change in Japanese macaques (Macaca fuscata). This species is ideal for tackling such questions because different wild, wild-provisioned, and captive populations have been monitored and collected over seven decades. Linear measurements were taken on 70 skulls from five populations, grouped into three ‘human impact groups’ (wild, wild-provisioned, and captive). This made it possible to investigate the pattern and pace of skull form changes among the human impact groups as well as over time within the populations. It was found that the overall skull shape tends to differ among the human impact groups, with captive macaques having relatively longer rostra than wild ones. Whether these differences are a result of geographic variation or variable human impact, related to nutritional supply and mechanical properties of the diet, is unclear. However, this pattern of directed changes did not seem to hold when the single captive populations were examined in detail. Although environmental conditions have probably been similar for the two examined captive populations (same captive locality), skull shape changes over the first generations in captivity were mostly different. This varying pattern, together with a consistent decrease in body size in the captive populations over generations, points to genetic drift playing a role in shaping skull shape and body size in captivity. In the captive groups investigated here, the rates of change were found to be high compared to literature records from settings featuring different degrees of human impact in different species, although they still lie in the range of field studies in a natural context. This adds to the view that human impact might not necessarily lead to particularly fast rates of change.

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