The taxonomic implications of cranial shape variation in Homo erectus

Abstract Morphological variation among the viviparous sea snakes (Hydrophiinae), a clade of fully aquatic elapid snakes, includes an extreme “microcephalic” ecomorph that has a very small head atop a narrow forebody, while the hind body is much thicker (up to three times the forebody girth). Previous research has demonstrated that this morphology has evolved at least nine times as a consequence of dietary specialization on burrowing eels, and has also examined morphological changes to the vertebral column underlying this body shape. The question addressed in this study is what happens to the skull during this extreme evolutionary change? Here we use X-ray micro-computed tomography and geometric morphometric methods to characterize cranial shape variation in 30 species of sea snakes. We investigate ontogenetic and evolutionary patterns of cranial shape diversity to understand whether cranial shape is predicted by dietary specialization, and examine whether cranial shape of microcephalic species may be a result of heterochronic processes. We show that the diminutive cranial size of microcephalic species has a convergent shape that is correlated with trophic specialization to burrowing prey. Furthermore, their cranial shape is predictable for their size and very similar to that of juvenile individuals of closely related but non-microcephalic sea snakes. Our findings suggest that heterochronic changes (resulting in pedomorphosis) have driven cranial shape convergence in response to dietary specializations in sea snakes.

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A three-dimensional geometric morphometrics view of the cranial shape variation and population history in the New World

American Journal of Human Biology ◽

10.1002/ajhb.22845 ◽

2016 ◽

Vol 28 (5) ◽

pp. 646-661 ◽

Cited By ~ 16

Author(s):

Manon Galland ◽

Martin Friess

Keyword(s):

Geometric Morphometrics ◽

New World ◽

Three Dimensional ◽

Population History ◽

Shape Variation ◽

Cranial Shape

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Morphometric variation of extant platyrrhine molars: taxonomic implications for fossil platyrrhines

10.7287/peerj.preprints.1796v2 ◽

2016 ◽

Author(s):

Mónica Nova Delgado ◽

Jordi Galbany ◽

Alejandro Pérez-Pérez

Keyword(s):

Middle Miocene ◽

Phylogenetic Position ◽

Ancestral State ◽

Shape Variation ◽

Geometric Morphometric ◽

Morphometric Variation ◽

Morphological Stasis ◽

Taxonomic Implications ◽

Geometric Morphometric Analysis ◽

Evolutionary Continuity

The phylogenetic position of many fossil platyrrhines with respect to extant ones is not yet clear. Two main hypotheses have been proposed: the layered or successive radiations hypothesis suggests that Patagonian fossils are Middle Miocene stem platyrrhines lacking modern descendants, whereas the long lineage hypothesis argues for an evolutionary continuity of all fossil platyrrhines with the extant ones. Our geometric morphometric analysis of a 15 landmark-based configuration of platyrrhines' first and second lower molars suggest that morphological stasis, may explain the reduced molar shape variation observed. Platyrrhine lower molar shape might be a primitive retention of the ancestral state affected by strong ecological constraints thoughout the radiation the main platyrrhine families. The Patagonian fossil specimens showed two distinct morphological patterns of lower molars, Callicebus -like and Saguinus -like, which might be the precursors of the extant forms, whereas the Middle Miocene specimens, though showing morphological resemblances with the Patagonian fossils, also displayed new, derived molar patternss, Alouatta- like and Pitheciinae -like, thereby suggesting that despite the overall morphological stasis of molars, phenotypic diversification of molar shape was already settled during the Middle Miocene.

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Morphometric variation of extant platyrrhine molars: taxonomic implications for fossil platyrrhines

10.7287/peerj.preprints.1796 ◽

2016 ◽

Author(s):

Mónica Nova Delgado ◽

Jordi Galbany ◽

Alejandro Pérez-Pérez

Keyword(s):

Middle Miocene ◽

Phylogenetic Position ◽

Ancestral State ◽

Shape Variation ◽

Geometric Morphometric ◽

Morphometric Variation ◽

Morphological Stasis ◽

Taxonomic Implications ◽

Geometric Morphometric Analysis ◽

Evolutionary Continuity

The phylogenetic position of many fossil platyrrhines with respect to extant ones is not yet clear. Two main hypotheses have been proposed: the layered or successive radiations hypothesis suggests that Patagonian fossils are Middle Miocene stem platyrrhines lacking modern descendants, whereas the long lineage hypothesis argues for an evolutionary continuity of all fossil platyrrhines with the extant ones. Our geometric morphometric analysis of a 15 landmark-based configuration of platyrrhines' first and second lower molars suggest that morphological stasis, may explain the reduced molar shape variation observed. Platyrrhine lower molar shape might be a primitive retention of the ancestral state affected by strong ecological constraints thoughout the radiation the main platyrrhine families. The Patagonian fossil specimens showed two distinct morphological patterns of lower molars, Callicebus -like and Saguinus -like, which might be the precursors of the extant forms, whereas the Middle Miocene specimens, though showing morphological resemblances with the Patagonian fossils, also displayed new, derived molar patternss, Alouatta- like and Pitheciinae -like, thereby suggesting that despite the overall morphological stasis of molars, phenotypic diversification of molar shape was already settled during the Middle Miocene.

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Morphometric variation of extant platyrrhine molars: taxonomic implications for fossil platyrrhines

PeerJ ◽

10.7717/peerj.1967 ◽

2016 ◽

Vol 4 ◽

pp. e1967 ◽

Cited By ~ 3

Author(s):

Mónica Nova Delgado ◽

Jordi Galbany ◽

Alejandro Pérez-Pérez

Keyword(s):

Middle Miocene ◽

Phylogenetic Position ◽

Ancestral State ◽

Shape Variation ◽

Geometric Morphometric ◽

Morphometric Variation ◽

Morphological Stasis ◽

Taxonomic Implications ◽

Geometric Morphometric Analysis ◽

Evolutionary Continuity

The phylogenetic position of many fossil platyrrhines with respect to extant ones is not yet clear. Two main hypotheses have been proposed: thelayeredorsuccessive radiationshypothesis suggests that Patagonian fossils are Middle Miocene stem platyrrhines lacking modern descendants, whereas thelong lineagehypothesis argues for an evolutionary continuity of all fossil platyrrhines with the extant ones. Our geometric morphometric analysis of a 15 landmark-based configuration of platyrrhines’ first and second lower molars suggest that morphological stasis may explain the reduced molar shape variation observed. Platyrrhine lower molar shape might be a primitive retention of the ancestral state affected by strong ecological constraints throughout the radiation of the main platyrrhine families. The Patagonian fossil specimens showed two distinct morphological patterns of lower molars,Callicebus—like andSaguinus—like, which might be the precursors of the extant forms, whereas the Middle Miocene specimens, though showing morphological resemblances with the Patagonian fossils, also displayed new, derived molar patterns,Alouatta—like andPitheciinae—like, thereby suggesting that despite the overall morphological stasis of molars, phenotypic diversification of molar shape was already settled during the Middle Miocene.

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Evolutionary morphology of the rabbit skull

PeerJ ◽

10.7717/peerj.2453 ◽

2016 ◽

Vol 4 ◽

pp. e2453 ◽

Cited By ~ 5

Author(s):

Brian Kraatz ◽

Emma Sherratt

Keyword(s):

Small Proportion ◽

Phylogenetic Signal ◽

Morphological Data ◽

Shape Variation ◽

Evolutionary Morphology ◽

Crown Group ◽

Size Change ◽

Generalist Species ◽

Facial Region ◽

Cranial Shape

The skull of leporids (rabbits and hares) is highly transformed, typified by pronounced arching of the dorsal skull and ventral flexion of the facial region (i.e., facial tilt). Previous studies show that locomotor behavior influences aspects of cranial shape in leporids, and here we use an extensive 3D geometric morphometrics dataset to further explore what influences leporid cranial diversity. Facial tilt angle, a trait that strongly correlates with locomotor mode, significantly predicts the cranial shape variation captured by the primary axis of cranial shape space, and describes a small proportion (13.2%) of overall cranial shape variation in the clade. However, locomotor mode does not correlate with overall cranial shape variation in the clade, because there are two district morphologies of generalist species, and saltators and cursorial species have similar morphologies. Cranial shape changes due to phyletic size change (evolutionary allometry) also describes a small proportion (12.5%) of cranial shape variation in the clade, but this is largely driven by the smallest living leporid, the pygmy rabbit (Brachylagus idahoensis). By integrating phylogenetic history with our geometric morphometric data, we show that the leporid cranium exhibits weak phylogenetic signal and substantial homoplasy. Though these results make it difficult to reconstruct what the ‘ancestral’ leporid skull looked like, the fossil records suggest that dorsal arching and facial tilt could have occurred before the origin of the crown group. Lastly, our study highlights the diversity of cranial variation in crown leporids, and highlights a need for additional phylogenetic work that includes stem (fossil) leporids and includes morphological data that captures the transformed morphology of rabbits and hares.

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