Differences In Skull Shape Research Articles

Skull Shape Differences among Myanmar and Adjacent Populations of the House Shrew, Suncus murinus (Mammalia: Eulipotyphla): Insights into Allometry and Phylogenetic Variances Using Geometric Morphometrics

Skull Shape Differences among Myanmar and Adjacent Populations of the House Shrew, Suncus murinus (Mammalia: Eulipotyphla): Insights into Allometry and Phylogenetic Variances Using Geometric Morphometrics

Determination of skull variation in Akkaraman and Kangal Akkaraman sheep by geometric morphometric method

Sheep breeding has an important place in the world and in Turkey, as sheep are farm animals that provide most of their nutritional needs from pasture, have good adaptability and are low in cost. Akkaraman sheep and the Kangal Akkaraman sheep, which was considered its sub-variety until 2012, constitute half of the sheep population in Turkey. In this study, morphometric diversity between the skulls of Akkaraman and Kangal Akkaraman breed sheep was examined by geometric morphometric method. 2D images obtained from 3D models of 24 male sheep skulls from two different provinces were analyzed using 10 landmarks from dorsal and lateral views. The results from the dorsal view, the first three principal components (PC1, PC2 and PC3) accounted for a total of 64.13% of the morphological variation and the largest changes in are associated with external occipital protuberance, midline nasofrontal suture and rostral edge of the incisive fissure. From the lateral view, three first principal components explained the morphological variation 27.56%, 22.32% and 10.65% respectively. In the comparison of the skull morphology of Akkaraman and Kangal Akkaraman sheep from dorsal and lateral views, no allometric components were identified, as most of the described shape variations were not size-dependent. As a result of these analyses, more detailed information was obtained about the shape differences of the skull. Geometric morphometric analysis is successful in detecting differences in skull shape of different sheep breeds and can be successfully used for classification.

Sample Size and Geometric Morphometrics Methodology Impact the Evaluation of Morphological Variation.

Geometric morphometrics has had a profound impact on our understanding of morphological evolution. However, factors such as sample size and the views and elements selected for two-dimensional geometric morphometric (2DGM) analyses, which are often dictated by specimen availability and time rather than study design, may affect the outcomes of those analyses. Leveraging large intraspecific sample sizes (n>70) for two bat species, Lasiurus borealis and Nycticeius humeralis, we evaluate the impact of sample size on calculations of mean shape, shape variance, and centroid size. Additionally, we assessed the concordance of multiple skull 2D views with one another and characterized morphological variation in skull shape in L. borealis and N. humeralis, as well as a closely related species, Lasiurus seminolus. Given that L. seminolus is a morphologically cryptic species with L. borealis, we assessed whether differences in skull shape and in 2DGM approach would allow species discrimination. We found that reducing sample size impacted mean shape and increased shape variance, that shape differences were not consistent across views or skull elements, and that trends shown by the views and elements were not all strongly associated with one another. Further, we found that L. borealis and L. seminolus were statistically different in shape using 2DGM in all views and elements. These results underscore the importance of selecting appropriate sample sizes, 2D views, and elements based on the hypothesis being tested. While there is likely not a generalizable sample size or 2D view that can be employed given the wide variety of research questions and systems evaluated using 2DGM, a generalizable solution to issues with 2DGM presented here is to run preliminary analyses using multiple views, elements, and sample sizes, thus ensuring robust conclusions.

Sexual dimorphism in skull size and shape of Laticauda colubrina (Serpentes: Elapidae).

Sexual dimorphism in size and shape is widespread among squamate reptiles. Sex differences in snake skull size and shape are often accompanied by intersexual feeding niche separation. However, allometric trajectories underlying these differences remain largely unstudied in several lineages. The sea krait Laticauda colubrina (Serpentes: Elapidae) exhibits very clear sexual dimorphism in body size, with previous studies having reported females to be larger and to have a relatively longer and wider head. The two sexes also differ in feeding habits: males tend to prey in shallow water on muraenid eels, whereas females prey in deeper water on congerid eels. I investigated sexual dimorphism in skull shape and size as well as the pattern of skull growth, to determine whether males and females follow the same ontogenetic trajectories. I studied skull characteristics and body length in 61 male and female sea kraits. The sexes differ in skull shape. Males and females follow distinct allometric trajectories. Structures associated with feeding performance are female-biased, whereas rostral and orbital regions are male-biased. The two sexes differ in allometric trajectories of feeding-related structures (female biased) that correspond to dietary divergence between the sexes. Sea kraits exhibit clear sexual dimorphism in the skull form that may be explained by intersexual differences in the feeding habits as well as reproductive roles. The overall skull growth pattern resembles the typical pattern observed in other tetrapods.

Reed bamboos drive skull shape evolution in bush frogs of the Western Ghats, Peninsular India.

Reed bamboo is a major ecological and economic resource for many animals, including humans. Nonetheless, the influence of this plant's evolutionary role on the morphology of animal species remains unexplored. Here, we investigated the significance of bamboo habitats as ecological opportunities in shaping the skull morphology of bush frogs (Raorchestes) from the Western Ghats, Peninsular India. We applied a three-dimensional (3D) geometric morphometric approach to capture the skull shape of 55 species of bush frogs. We visualized the skull shape variables in phylomorphospace with principal component analysis and performed phylogenetic generalized least-squares analysis to assess the impact of cranial size (evolutionary allometry) and habitat (bamboo or non-bamboo) on cranial shape. We quantified the morphological disparity between bamboo and non-bamboo bush frogs' skull shape, and employed RRphylo, a phylogenetic ridge regression method, to access the evolutionary rate and rate shifts of skull shape change. The phylomorphospace delineated bamboo and non-bamboo bush frogs. While cranial shape exhibited a significant but smaller association with size, its association with habitat type was non-significant. We detected, however, significant differences in skull shape between the two frog groups, with bamboo frogs showing higher morphological disparity and a remarkable shift in the evolutionary rate of skull shape diversification. These findings underscore the role of reed bamboo in the evolution of skull shape in the radiation of frogs, endemic to the Western Ghats. We demonstrate that the association between the members of two distinct endemic clades (bamboo reeds and bamboo frogs) is the outcome of a deep-time ecological opportunity that dates back to the Miocene.

Cranial variation between coastal and offshore bottlenose dolphins, Tursiops truncatus (Cetacea: Delphinidae) in Ecuador and the Mediterranean: a three-dimensional geometric morphometric study

Abstract Skull shape analysis provides useful information on wildlife ecology and potential local adaptations. Common bottlenose dolphins (Tursiops truncatus) often differentiate between coastal and offshore populations worldwide, and skull shape analyses can be particularly useful in this context. Here we quantify skull shape variation between coastal populations from the Gulf of Guayaquil (Ecuador) and the Mediterranean Sea, compared to offshore specimens from multiple oceans. We analysed skull shape differences using 3D models from museum specimens through geometric morphometrics (3DGM). Two complementary landmark approaches included single-point semi-landmarks in homologous features, as well as pseudo-landmarks placed automatically. Results show skull shape distinction between both coastal populations and offshore specimens. Offshore specimens showed little differentiation between distinct locations. Skull shape patterns mostly diverged in the shape and length of rostrum, as well as the shape of the ascending processes of the maxilla, pterygoids, and occipital bones. However, both coastal populations differed in the patterns and direction of change of those features and were also morphologically distinct. Our results are consistent with local data on site fidelity and social structure in the coastal populations. Skull shape changes suggest divergent feeding and sound production patterns are potential drivers, probably specific to the local environment of each community.

Examination of Shape Variation of the Skull in British Shorthair, Scottish Fold, and Van Cats.

A variety of skull shapes are frequently used for discrimination between animal species, breeds, and sexes. In this study, skulls of three different breeds of cats were examined by the geometric morphometric method, with the aim of revealing skull shape differences. For this purpose, 27 cats (6 British Shorthair, 7 Scottish Fold, and 14 Van cats) were used. The skulls of cats were modeled by computed tomography. Geometric morphometrics was applied using dorsal (8 landmarks, 63 semilandmarks) and lateral (8 landmarks, 63 semilandmarks) skull projections on these models. Centroid size differences between the breeds were statistically insignificant. However, the differences in shape were statistically significant for both the dorsal view and lateral view. Shape variation was less in the British Shorthair than in other breeds. Shape differences generally occurred around the orbit. In the skull of Scottish Folds, the orbit was situated more caudally than in other breeds. The British Shorthair had the largest orbital ring. In dorsal view, the Scottish Fold had the largest orbital diameter. The orbital ring of Van cats was smallest in both dorsal and lateral views. In the canonical variate analysis, it was seen that the breeds were separated from each other. The shape difference in the skull between different cat breeds could be revealed by geometric morphometrics. The results of this study provide useful information for taxonomy.

Island Tiger Snakes (Notechis scutatus) Gain a ‘Head Start’ in Life: How Both Phenotypic Plasticity and Evolution Underlie Skull Shape Differences

Island Tiger Snakes (Notechis scutatus) Gain a ‘Head Start’ in Life: How Both Phenotypic Plasticity and Evolution Underlie Skull Shape Differences

Molecular phylogenetic and taxonomic status of the large-eared desert shrew Notiosorex evotis (Eulipotyphla: Soricidae)

Abstract Notiosorex is the only genus of shrews in North America with particular adaptations for arid habitats such as deserts. Five species currently are recognized in the genus, one of which, Notiosorex evotis, lives in deciduous rain forest from northern Sinaloa to the state of Jalisco in México. Notiosorex evotis originally was described as a subspecies of N. crawfordi; however, it was recently proposed as a valid species based on a discriminant function analysis of craniodental characters. Morphological differentiation between N. evotis populations and sympatric occurrences with N. crawfordi in northern Sinaloa have been recognized. Here, we used a phylogenetic analysis of a mitochondrial gene (Cytb; 1,140 bp) and the nuclear beta fibrinogen intron 7 (β-fib I7; 385 bp), as well as cranial geometric morphometrics, to assess the taxonomic status of N. evotis. We found sequences of N. evotis forming two main subclades: one that includes the populations of the state of Sinaloa, the other including populations of Nayarit and Jalisco. The boundaries between the two groups seem to be related to the ecotonal cline between the Pacific Lowlands province and the Trans-Mexican Volcanic Belt province, which acts as a geographical barrier. The discriminant function analysis revealed clear differences in skull shape between the three species of Notiosorex to the northwest of its distribution. Considering these multiple lines of evidence from our data set, we confirm that N. evotis is a monotypic species. Our results suggest that geometric morphometrics can be used successfully to identify sibling species by shape, especially in groups where determination by craniodental measurements is not possible.

Burrowing constrains patterns of skull shape evolution in wrasses.

The evolution of behavioral and ecological specialization can have marked effects on the tempo and mode of phenotypic evolution. Head-first burrowing has been shown to exert powerful selective pressures on the head and body shapes of many vertebrate and invertebrate taxa. In wrasses, burrowing behaviors have evolved multiple times independently, and are commonly used in foraging and predator avoidance behaviors. While recent studies have examined the kinematics and body shape morphology associated with this behavior, no study to-date has examined the macroevolutionary implications of burrowing on patterns of phenotypic diversification in this clade. Here, we use three-dimensional geometric morphometrics and phylogenetic comparative methods to study the evolution of skull shape in fossorial wrasses and their relatives. We test for skull shape differences between burrowing and non burrowing wrasses and evaluate hypotheses of shape convergence among the burrowing wrasses. We also quantify rates of skull shape evolution between burrowing and non burrowing wrasses to test for whether burrowing constrains or accelerates rates of skull shape evolution in this clade. We find that while burrowing and non burrowing wrasses exhibit similar degrees of morphological disparity, for burrowing wrasses, it took nearly twice as long to amass this disparity. Furthermore, while the disparities between groups are evenly matched, we find that most burrowing species are confined to a particular region of shape space with most species exhibiting narrower heads than many non-burrowing species. These results suggest head-first burrowing constrains patterns of skull shape diversification in wrasses by potentially restricting the range of phenotypes that can perform this behavior.

Ontogenetic allometry underlies trophic diversity in sea turtles (Chelonioidea)

Despite only comprising seven species, extant sea turtles (Cheloniidae and Dermochelyidae) display great ecological diversity, with most species inhabiting a unique dietary niche as adults. This adult diversity is remarkable given that all species share the same dietary niche as juveniles. These ontogenetic shifts in diet, as well as a dramatic increase in body size, make sea turtles an excellent group to examine how morphological diversity arises by allometric processes and life habit specialisation. Using three-dimensional geometric morphometrics, we characterise ontogenetic allometry in the skulls of all seven species and evaluate variation in the context of phylogenetic history and diet. Among the sample, the olive ridley (Lepidochelys olivacea) has a seemingly average sea turtle skull shape and generalised diet, whereas the green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) show different extremes of snout shape associated with their modes of food gathering (grazing vs. grasping, respectively). Our ontogenetic findings corroborate previous suggestions that the skull of the leatherback (Dermochelys coriacea) is paedomorphic, having similar skull proportions to hatchlings of other sea turtle species and retaining a hatchling-like diet of relatively soft bodied organisms. The flatback sea turtle (Natator depressus) shows a similar but less extreme pattern. By contrast, the loggerhead sea turtle (Caretta caretta) shows a peramorphic signal associated with increased jaw muscle volumes that allow predation on hard shelled prey. The Kemp’s ridley (Lepidochelys kempii) has a peramorphic skull shape compared to its sister species the olive ridley, and a diet that includes harder prey items such as crabs. We suggest that diet may be a significant factor in driving skull shape differences among species. Although the small number of species limits statistical power, differences among skull shape, size, and diet are consistent with the hypothesis that shifts in allometric trajectory facilitated diversification in skull shape as observed in an increasing number of vertebrate groups.

Connexin 43 contributes to phenotypic robustness of the mouse skull.

We compared skull shape and variation among genetically modified mice that exhibit different levels of connexin43 (Cx43) channel function, to determine whether Cx43 contributes to craniofacial phenotypic robustness. Specifically, we used two heterozygous mutant mouse models (G60S/+ and I130T/+) that, when compared to their wildtype counterparts, have an ~80% and ~50% reduction in Cx43 function, respectively. Both mutant strains showed significant differences in skull shape compared to wildtype littermates and while these differences were more severe in the G60S/+ mouse, shape differences were localized to similar regions of the skull in both mutants. However, increased skull shape variation was observed in G60S/+ mutants only. Additionally, covariation of skull structures was disrupted in the G60S/+ mutants only, indicating that while a 50% reduction in Cx43 function is sufficient to cause a shift in mean skull shape, the threshold for Cx43 function for disrupting craniofacial phenotypic robustness is lower. Collectively, our results indicate Cx43 can contribute to phenotypic robustness of the skull through a nonlinear relationship between Cx43 gap junctional function and phenotypic outcomes.

Sexual dimorphism and skull size and shape in the highly specialized snake species, Aipysurus eydouxii (Elapidae: Hydrophiinae).

BackgroundSnakes exhibit sexual dimorphism in both head size and shape. Such differences are often attributed to different reproductive roles and feeding habits. We aim to investigate how sexual dimorphism is displayed in the highly specialised fish-egg-eating snake, Aipysurus eydouxii, by analysing two complementary features: body size and skull morphology.MethodsWe used data on body length, weight, and skull shape from 27 measurements of 116 males and females of A. eydouxii. We investigated both sexual dimorphism and allometric (multivariate and bi-variate) properties of skull growth in the analysed data set.ResultsWe found that although there was female-biased sexual size dimorphism in body length, females were not heavier than males, contrary to what is commonly observed pattern among snakes. Moreover, females tend to possess relatively smaller heads than males. However, we only found very subtle differences in skull shape reflected in nasal width, mandibular fossa, quadrate crest and quadrate length.DiscussionWe suggest that the feeding specialisation in A. eydouxii does not allow for an increase in body thickness and the size of the head above a certain threshold. Our results may be interpreted as support for prey-size divergence as a factor driving skull dimorphism since such species in which the sexes do not differ in prey size also shows very subtle or no differences in skull morphology.

Retraction to: Molecular phylogenetic and taxonomic status of the large-eared desert shrewNotiosorex evotis(Eulipotyphla: Soricidae), with the designation of a neotype

Abstract Notiosorex is the only genus of shrews in North America with particular adaptations for arid habitats such as deserts. Five species currently are recognized in the genus, one of which, Notiosorex evotis, lives in deciduous rain forest from northern Sinaloa to the state of Jalisco in Mexico. Notiosorex evotis originally was described as a subspecies of N. crawfordi; however, it was recently proposed as a valid species based on a discriminant function analysis of craniodental characters. Morphological differentiation between N. evotis populations and sympatric occurrences with N. crawfordi in northern Sinaloa have been recognized. Here, we used a phylogenetic analysis of a mitochondrial gene (Cytb; 1,140 bp) and the nuclear beta-fibrinogen intron 7 (β-fib I7; 385 bp), as well as cranial geometric morphometrics, to assess the taxonomic status of N. evotis. We found sequences of N. evotis forming two main subclades: one that includes the populations of the state of Sinaloa, the other including populations of Nayarit and Jalisco. The boundaries between the two groups seem to be related to the ecotonal cline between the Pacific Lowlands province and the Trans-Mexican Volcanic Belt province, which acts as a geographical barrier. The discriminant function analysis revealed clear differences in skull shape between the three species of Notiosorex to the northwest of its distribution. Considering these multiple lines of evidence from our data set, we confirm that N. evotis is a monotypic species. Our results suggest that geometric morphometrics can be used successfully to identify sibling species by shape, especially in groups where determination by craniodental measurements is not possible.

Cranial evolution of the Late Triassic phytosaurs (Diapsida, Archosauria): preliminary observations from landmark-based morphometric analysis

ABSTRACT Landmark-based Principal Component Analysis was performed on multiple phytosaur and crocodilian skulls. Multiple landmark points were selected defining suture points of bone tissues and regions of maximum or minimum curvature along the skull. Scatter plots of the principal component scores show that phytosaurs cluster according to their higher order taxonomic groups, and the convex hull polygons of the different clades occupy distinct morphospaces albeit with variable degrees of overlap. Disparity between the morphospaces of non-Mystriosuchinae parasuchids and Mystriosuchinae phytosaurs suggests marked differences in skull shape among basal and derived taxa. The vector deformation plots of phytosaur skulls showcase the evolution of skull shape from basal to advanced forms. The morphological changes imply evolution of the phytosaur skulls towards a wider and deeper snout, cage-like grip, tendency for increasing jaw strength, and faster-snapping action. In addition, heightening of the nostrils suggested that phytosaurs evolved into ambush predators, and increased their ability to remain submerged underwater with their nostrils high above the water surface, thereby enhancing their ability to ambush prey. The study supports prior assumptions of dietary preferences among the phytosaurs and maps the evolution and prevalence of cranial morphotypes, associated with such dietary preferences, across the different phytosaur clades.

Evolutionary trends of the conserved neurocranium shape in angel sharks (Squatiniformes, Elasmobranchii)

Elasmobranchii (i.e., sharks, skates, and rays) forms one of the most diverse groups of marine predators. With a fossil record extending back into the Devonian, several modifications in their body plan illustrate their body shape diversity through time. The angel sharks, whose fossil record dates back to the Late Jurassic, some 160 Ma, have a dorsoventrally flattened body, similar to skates and rays. Fossil skeletons of this group show that the overall morphology was well established earlier in its history. By examining the skull shape of well-preserved fossil material compared to extant angel sharks using geometric morphometric methods, within a phylogenetic framework, we were able to determine the conservative skull shape among angel sharks with a high degree of integration. The morphospace occupation of extant angel sharks is rather restricted, with extensive overlap. Most of the differences in skull shape are related to their geographic distribution patterns. We found higher levels of disparity in extinct forms, but lower ones in extant species. Since angel sharks display a highly specialized prey capture behaviour, we suggest that the morphological integration and biogeographic processes are the main drivers of their diversity, which might limit their capacity to display higher disparities since their origin.

Skull-shape variation and modularity in two Japanese field mice, Apodemus speciosus and Apodemus argenteus (Rodentia: Muridae)

Two congeneric species of Japanese field mice, Apodemus speciosus and Apodemus argenteus, differ considerably in their feeding strategies and habitat utilizations. Although both species are omnivorous, previous studies demonstrated that A. argenteus typically eats a wide variety of food items than A. speciosus. Moreover, A. speciosus is a ground dweller, while A. argenteus commonly shows arboreal movements. These dietary and lifestyle differences suggest potential disparity in morphological structure. In this study, we used geometric morphometrics to examine the skull shape differences are related to their feeding strategies and habitat preferences. We found that A. argenteus showed wider zygomatic arches and a broader mandibular ramus. These traits are linked to enlargement of the attachment sites for the masticatory muscles. We also found a relatively short mandibular diastema in A. argenteus, which may increase the mechanical advantage of the lower jaw by reducing the out-lever arm. These results suggest that A. argenteus has a greater relative bite force that is suitable for diversified diets as a more generalist feeder. Interspecific differences in the upper incisor, inter-orbital width, and auditory bullae might be associated with the lifestyles of these two species. Additionally, the presence of two distinct modules in the cranium (rostrum and braincase) and mandible (ascending ramus and alveolar region) may reflect similar patterns of intraspecific variation within both species. In conclusion, skull shape enables distinction between these two species and may favor adaptation to their ecology and lifestyle, despite the similarities in craniomandibular modules associated with common developmental factors.

Cranial shape predicts arboreal activity of Sigmodontinae rodents

AbstractBrain enlargement is an adaptation in animals that use the space in three dimensions and need to integrate information of complex environments. As consequence, this adaptation can result in differences in skull shape among species with different types of locomotion and level of arboreality. We directly tested for the relation between the cranial shape and arboreality (based on field data) of 11 Sigmodontinae rodent species from a Neotropical savanna (Cerrado). For that, we used geometric morphometrics considering both dorsal and lateral views of the cranium. We also accounted for any possible allometric effects (i.e. the relationship between size and shape) and evolutionary constraints (i.e. phylogenetic signal) on the cranial shape. The dorsal view presented strong allometric effects but no phylogenetic signal. On the other hand, the lateral view showed a weak allometric effect and a significant phylogenetic signal. After controlling for size and evolutionary constraints, we found significant relationships between rodent arboreality and cranial shape for both lateral (r2 = 0.74) and dorsal cranium views (r2 = 0.40). Patterns for both views showed that arboreal rodents present more expanded crania, suggesting larger brains. The dorsal view showed a general cranial expansion in arboreal rodents, whereas the lateral view showed a more rounded and posteriorly expanded cranium. This later suggests a larger cerebellum, an important brain portion responsible for orientation and sense of balance. Our study provides evidence that the cranial shape can be used as a proxy to infer arboreal activity of sigmodontine rodents. Moreover, the observed differences in cranial shape between arboreal and terrestrial species are probably related to brain enlargement in the former driven by the need to cope with a three‐dimensional environment.

Cranial size and shape variation in isolated populations of the Olkhon mountain vole (Alticola olchonensis Litvinov, 1960)

The Olkhon mountain vole (Alticola olchonensis) is an endemic species of the Lake Baikal area with an extremely restricted range. We investigated the pattern of differentiation of cranial shape and size in five isolated insular populations of A. olchonensis from the Baikal islands (Olkhon, Hubyn, Borokchin, Ogoy, and Zamogoy). The ventral aspect of the cranium was analysed using landmark-based geometric morphometric methods While the sexes of A. olchonensis did not differ regarding cranium size and shape, multivariate statistical analyses showed that there were inter-island differences in skull morphology. Voles from the four small islands were similar in cranium size; the large skull size of voles inhabiting the Olkhon Island may be due to the more favourable habitat conditions on Olkhon. Shape differences among island populations were not associated with the geographic distances between islands. The voles from Borokchin Island differ the most in skull shape compared to other island populations. The combination of reduced gene flow among island populations (due to isolation and drift during population fluctuations) may be a suitable explanation for the significant differences in skull shape among island populations of A. olchonensis.

Habitat shapes skull profile of small cetaceans: evidence from geographical variation in Black Sea harbour porpoises (Phocoena phocoena relicta)

Morphological differentiation in skull shape in small toothed whales is sometimes explained as driven by differences in ontogeny or adaptation to a benthic or pelagic habitat. To test these hypotheses, the comparison was made, using two-dimensional geometric morphometry, between neighbouring populations of harbour porpoises from the north-eastern Black Sea and the adjoining Sea of Azov, from the same genetically isolated subspecies, both known for their extreme paedomorphosis in body and skull development but differing in seasonal habitats (very shallow waters vs open sea). There were major differences between populations in the following traits: in Azov animals, rostrum was slightly shorter and more deflected downwards; premaxillary eminences shifted backward and facial region proportionally longer; more concave facial fossa and higher vertex; lower, downward-facing foramen magnum. Meanwhile, each of the populations followed its own ontogenetic trajectory. Therefore, differences in skull shape between populations were primarily directed by habitat. Shape differences were less discriminating than size; they might involve both echolocation and feeding mechanisms and could be associated with suction feeding. These adaptations were characterized by mixed allometric patterns including both paedomorphosis and peramorphosis in their ontogeny. Shallow habitat was found to be critical in forming specific adaptations even for animals migrating between different habitat types.