Larger mammals have longer faces because of size-related constraints on skull form

Cardini, Andrea; Polly, P. David

doi:10.1038/ncomms3458

Cited by 186 publications

(293 citation statements)

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“…The trend for the face to elongate with allometry has also been noted in mammals (17) and is postulated to be related to heterochrony, an important factor in the evolution of birds from dinosaurs (46) and a demonstrated mode of generating diversity of beak forms in Darwin's finches (6,9). In mammals, it has been shown that integration constrains evolution along paths of least evolutionary resistance, meaning that heterochronic or allometric changes offer a simple mechanism by which evolution can act to produce high disparity (47,48).…”

Section: Discussionmentioning

confidence: 97%

“…Larger animals generally have access to larger prey due to their increased gape and greater absolute muscular power, and size is further related to morphology via allometry, the tendency of traits to vary with size throughout a morphological structure. Allometry has been demonstrated to be a key contributing factor to craniofacial form across a range of mammalian (17,18) and avian (15,19) clades, and evolvability of body size is proposed to be a major evolutionary pathway in the avian stem (20).…”

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confidence: 99%

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The shapes of bird beaks are highly controlled by nondietary factors

Bright

Marugán‐Lobón

Cobb

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

209

274

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Bird beaks are textbook examples of ecological adaptation to diet, but their shapes are also controlled by genetic and developmental histories. To test the effects of these factors on the avian craniofacial skeleton, we conducted morphometric analyses on raptors, a polyphyletic group at the base of the landbird radiation. Despite common perception, we find that the beak is not an independently targeted module for selection. Instead, the beak and skull are highly integrated structures strongly regulated by size, with axes of shape change linked to the actions of recently identified regulatory genes. Together, size and integration account for almost 80% of the shape variation seen between different species to the exclusion of morphological dietary adaptation. Instead, birds of prey use size as a mechanism to modify their feeding ecology. The extent to which shape variation is confined to a few major axes may provide an advantage in that it facilitates rapid morphological evolution via changes in body size, but may also make raptors especially vulnerable when selection pressures act against these axes. The phylogenetic position of raptors suggests that this constraint is prevalent in all landbirds and that breaking the developmental correspondence between beak and braincase may be the key novelty in classic passerine adaptive radiations.geometric morphometrics | integration | allometry | birds | modularity T he avian beak offers a classic example of adaptation to feeding ecology, with beak morphology frequently considered to represent evolutionary adaptation to specialized trophic niches [e.g., Galápagos finches (1), Hawaiian honeycreepers (2), and Madagascan vangas (3)]. Despite this axiom, we lack quantitative data on the degree to which skull and beak morphology is influenced not only by feeding ecology, but also by other sources of variation or constraint (4). Although the beak is often seen as the target of selection mechanisms closely allied to feeding ecology, such as prey type, feeding style, or beak use, evidence also suggests that beak morphology and variation may be constrained by a number of other factors, including evolutionary history (phylogeny) and development on the component parts of the entire skull. Breakthrough experiments in molecular genetics have shown that the mechanisms driving beak shape variation encompass modifications to the timing of expression of conserved developmental pathways (5-9), resulting in beak diversity described by a few relatively simple geometric transformations (10). However, pleiotropic associations between different skull structures can also contribute to the shape of the avian beak (11), and Sonic hedgehog signaling from the forebrain also relates to the spatial organization of, and changes to, face and beak shape (12)(13)(14). Furthermore, assessments of bird skull phenotypic variation suggest that beak morphology may evolve cohesively with cranial morphology (15,16). Size is also an important consideration when assessing morphological variation. Larger animals gene...

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Section: Discussionmentioning

confidence: 97%

mentioning

confidence: 99%

The shapes of bird beaks are highly controlled by nondietary factors

Bright

Marugán‐Lobón

Cobb

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

209

274

View full text Add to dashboard Cite

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“…A focus on craniofacial variation showed that closely related species of mammals often present a common trend, so that smallest species tend to be short-faced and largest ones have proportionally longer faces (Cardini & Polly 2013;Cardini et al 2015a). So far, this has been shown in four lineages of placentals (African antelopes, squirrels and fruit bats, and also mongooses -Cardini & Polly 2013), belonging to different orders, as well as in kangaroos (Cardini et al 2015a).…”

Section: Valkenburgh 2009)mentioning

confidence: 99%

Anyone with a Long-Face? Craniofacial Evolutionary Allometry (CREA) in a Family of Short-Faced Mammals, the Felidae

2017

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Anyone with a Long-Face? Craniofacial Evolutionary Allometry (CREA) in a Family of Short-Faced Mammals, the Felidae http://researchonline.ljmu.ac.uk/6790/ Article LJMU has developed LJMU Research Online for users to access the research output of the University more effectively. Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Users may download and/or print one copy of any article(s) in LJMU Research Online to facilitate their private study or for non-commercial research. You may not engage in further distribution of the material or use it for any profit-making activities or any commercial gain.The version presented here may differ from the published version or from the version of the record. Please see the repository URL above for details on accessing the published version and note that access may require a subscription. Abstract: Among adults of closely related species, a trend in craniofacial evolutionary allometry (CREA) for larger taxa to be long-faced and smaller ones to have paedomorphic aspects, such as proportionally smaller snouts and larger braincases, has been demonstrated in some mammals and two bird lineages. Nevertheless, whether this may represent a 'rule' with few exceptions is still an open question. In this context, Felidae is a particularly interesting family to study because, although its members are short-faced, previous research did suggest relative facial elongation in larger living representatives. Using geometric morphometrics, based on two sets of anatomical landmarks, and traditional morphometrics, for comparing relative lengths of the palate and basicranium, we performed a series of standard and comparative allometric regressions in the Felidae and its two subfamilies. All analyses consistently supported the CREA pattern, with only one minor exception in the geometric morphometric analysis of Pantherinae: the genus Neofelis. With its unusually long canines, Neofelis species seem to have a relatively narrow cranium and long face, despite being smaller than other big cats. In spite of this, overall, our findings strengthen the possibility that the CREA pattern might indeed be a 'rule' among mammals, raising questions on the processes behind it and suggesting future directions for its study. smaller than other big cats. In spite of this, overall, our findings strengthen the possibility that the CREA pattern might indeed be a 'rule' among mammals, raising questions on the processes behind it and suggesting future directions for its study. Powered by Edit orial Manager® and ProduXion Manager® from Aries Syst em s Corporat ion Running Head: Cranial allometry 'RULE' in Felidae

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“…Indeed, allometric directions of molar shape changes were not congruent between intra--and inter--population levels, were not parallel to Pmax, and did not contribute significantly to any of the evolutionary shape changes documented here. This undermines the role of allometry as a significant evolutionary force in traits such as murine molars, although allometric constraints may be of prime importance for other traits such as skull (e.g., Cardini and Polly 2013).…”

Section: Limited Role Of Allometry In Molar Shape Evolutionmentioning

confidence: 99%