A comparison of metrics for quantifying cranial suture complexity

White, Heather E; Clavel, Julien; Tucker, Abigail S.; Goswami, Anjali

doi:10.1098/rsif.2020.0476

Cited by 10 publications

(10 citation statements)

References 83 publications

(142 reference statements)

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“…Increases in complexity ( i.e. , interdigitation vs simple contacts) through growth reflects an increase in surface area of the sutural contacts, which suggests that the snout and braincase would be more resistant to stresses (such as masticatory), in older individuals ( White et al, 2020 ). This is further supported by the lack of deformation ( e.g.…”

Section: Discussionmentioning

confidence: 99%

Ontogenetic growth in the crania ofExaeretodon argentinus(Synapsida: Cynodontia) captures a dietary shift

Wynd

Abdala

Nesbitt

2022

PeerJ

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Background An ontogenetic niche shift in vertebrates is a common occurrence where ecology shifts with morphological changes throughout growth. How ecology shifts over a vertebrate’s lifetime is often reconstructed in extant species—by combining observational and skeletal data from growth series of the same species—because interactions between organisms and their environment can be observed directly. However, reconstructing shifts using extinct vertebrates is difficult and requires well-sampled growth series, specimens with relatively complete preservation, and easily observable skeletal traits associated with ecologies suspected to change throughout growth, such as diet. Methods To reconstruct ecological changes throughout the growth of a stem-mammal, we describe changes associated with dietary ecology in a growth series of crania of the large-bodied (∼2 m in length) and herbivorous form, Exaeretodon argentinus (Cynodontia: Traversodontidae) from the Late Triassic Ischigualasto Formation, San Juan, Argentina. Nearly all specimens were deformed by taphonomic processes, so we reconstructed allometric slope using a generalized linear mixed effects model with distortion as a random effect. Results Under a mixed effects model, we find that throughout growth, E. argentinus reduced the relative length of the palate, postcanine series, orbits, and basicranium, and expanded the relative length of the temporal region and the height of the zygomatic arch. The allometric relationship between the zygomatic arch and temporal region with the total length of the skull approximate the rate of growth for feeding musculature. Based on a higher allometric slope, the zygoma height is growing relatively faster than the length of the temporal region. The higher rate of change in the zygoma may suggest that smaller individuals had a crushing-dominated feeding style that transitioned into a chewing-dominated feeding style in larger individuals, suggesting a dietary shift from possible faunivory to a more plant-dominated diet. Dietary differentiation throughout development is further supported by an increase in sutural complexity and a shift in the orientation of microwear anisotropy between small and large individuals of E. argentinus. A developmental transition in the feeding ecology of E. argentinus is reflective of the reconstructed dietary transition across Gomphodontia, wherein the earliest-diverging species are inferred as omnivorous and the well-nested traversodontids are inferred as herbivorous, potentially suggesting that faunivory in immature individuals of the herbivorous Traversodontidae may be plesiomorphic for the clade.

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Section: Discussionmentioning

confidence: 99%

Ontogenetic growth in the crania ofExaeretodon argentinus(Synapsida: Cynodontia) captures a dietary shift

Wynd

Abdala

Nesbitt

2022

PeerJ

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“…We chose the right side of the crania to measure the maxillofrontal and premaxillofrontal sutures unless these were damaged, in which case, we measured the sutures on the left side. The complexity of each suture was quantified as a length ratio (LR), whereby the total length of the suture path is divided by the linear distance between the start and end [ 35 , 92 , 93 ]. Suture complexity data were analyzed with an ANCOVA, with sex as a covariate.…”

Section: Methodsmentioning

confidence: 99%

Craniodental divergence associated with bite force between hybridizing pine squirrels (Tamiasciurus)

2023

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Bite force can be a limiting factor in foraging and can significantly affect the competitive ability and lifetime fitness of mammals. Tamiasciurus squirrels feed primarily on conifer seeds and have a strong bite force to mechanically extract seeds from conifer cones with their mouths. In the North Cascades region, Douglas squirrels (Tamiasciurus douglasii) and red squirrels (T. hudsonicus) occupy ecologically different forests with different hardnesses in conifer cones. The ranges of these species overlap in a narrow hybrid zone where these forests meet near the crest of the North Cascades. We examined interspecific divergence in dietary ecomorphology in allopatry, in sympatry within the hybrid zone, and between hybrids and each parental species. We focused on three craniodental traits, including the incisor-strength index as a proxy measure for maximal bite force, cranial-suture complexity, and mandible shape. We find that these sister squirrel species differ in bite force and suture complexity in allopatry and sympatry and that mandible shape changes with the expected hardness of accessed food items, but is not significantly different between species. Furthermore, we find that hybrids display morphologies that overlap with hybrid zone red squirrels but not with hybrid zone Douglas squirrels. This work shows how important ecological processes at shallow evolutionary timescales can impact the divergence of morphological traits in taxa with extreme conservation of craniomandibular shape.

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“…At this gross scale, suture morphology is once again highly variable, with the same suture having a very different morphology even in relatively closely related species of mammal ( Figure 3 ). Patterns span a range of morphologies, including straight, highly curved, looping, and interdigitated outlines ( White et al, 2020 ). Interestingly, there is a strong association between the microscopic fibre organisation and the gross suture morphology ( Khonsari et al, 2013 ).…”

Section: Suture Morphologymentioning

confidence: 99%

“…Interspecific suture morphological variation likely implies the presence of heightened developmental variation. Several metrics have previously been proposed to quantify this gross morphological complexity of sutures, which have recently been compared on mammal sutures ( White et al, 2020 ). Quantification of gross suture morphological complexity will enable the untangling of mechanisms driving the alterations in complexity.…”

Section: Suture Morphologymentioning

confidence: 99%

“…The influence mechanical pressures have on shaping sutures, where external forces alter sutures from a butt joint morphology to a bevelled or finger joint or create a gross interdigitated morphology, means it may be possible, in the future, to interpret the diet, behaviour, ecology and mechanical stresses of an individual from the suture morphology ( Moss, 1957 ; Oudhof, 1982 ; Kathe, 1999 ; Monteiro and Lessa, 2000 ; Clack, 2002 ; Nicolay and Vaders, 2006 ). As the complexity of mammal suture morphology is also thought to respond to biological pressures ( Herring, 1972 ; Nicolay and Vaders, 2006 ), advances in morphometric techniques make it is possible to quantify and compare suture morphological complexity across a range of mammalian species ( White et al, 2020 ). As such, we may be able to use suture morphology to better infer organismal biology and morphology alone.…”

Section: What Can We Learn From a Suture?mentioning

confidence: 99%

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The Intertwined Evolution and Development of Sutures and Cranial Morphology

White

Goswami

Tucker

2021

Front. Cell Dev. Biol.

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Phenotypic variation across mammals is extensive and reflects their ecological diversification into a remarkable range of habitats on every continent and in every ocean. The skull performs many functions to enable each species to thrive within its unique ecological niche, from prey acquisition, feeding, sensory capture (supporting vision and hearing) to brain protection. Diversity of skull function is reflected by its complex and highly variable morphology. Cranial morphology can be quantified using geometric morphometric techniques to offer invaluable insights into evolutionary patterns, ecomorphology, development, taxonomy, and phylogenetics. Therefore, the skull is one of the best suited skeletal elements for developmental and evolutionary analyses. In contrast, less attention is dedicated to the fibrous sutural joints separating the cranial bones. Throughout postnatal craniofacial development, sutures function as sites of bone growth, accommodating expansion of a growing brain. As growth frontiers, cranial sutures are actively responsible for the size and shape of the cranial bones, with overall skull shape being altered by changes to both the level and time period of activity of a given cranial suture. In keeping with this, pathological premature closure of sutures postnatally causes profound misshaping of the skull (craniosynostosis). Beyond this crucial role, sutures also function postnatally to provide locomotive shock absorption, allow joint mobility during feeding, and, in later postnatal stages, suture fusion acts to protect the developed brain. All these sutural functions have a clear impact on overall cranial function, development and morphology, and highlight the importance that patterns of suture development have in shaping the diversity of cranial morphology across taxa. Here we focus on the mammalian cranial system and review the intrinsic relationship between suture development and morphology and cranial shape from an evolutionary developmental biology perspective, with a view to understanding the influence of sutures on evolutionary diversity. Future work integrating suture development into a comparative evolutionary framework will be instrumental to understanding how developmental mechanisms shaping sutures ultimately influence evolutionary diversity.

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A comparison of metrics for quantifying cranial suture complexity

Cited by 10 publications

References 83 publications

Ontogenetic growth in the crania ofExaeretodon argentinus(Synapsida: Cynodontia) captures a dietary shift

Ontogenetic growth in the crania ofExaeretodon argentinus(Synapsida: Cynodontia) captures a dietary shift

Craniodental divergence associated with bite force between hybridizing pine squirrels (Tamiasciurus)

The Intertwined Evolution and Development of Sutures and Cranial Morphology

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