The Braincase of Eocaecilia micropodia (Lissamphibia, Gymnophiona) and the Origin of Caecilians

Maddin, Hillary C.; Jenkins, F. A.; Anderson, J. G. C.

doi:10.1371/journal.pone.0050743

Cited by 70 publications

(139 citation statements)

References 41 publications

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“…The topology for visualisation purposes is based upon Zhang & Wake (), supplemented with Wilkinson & Nussbaum () and Maddin et al. (). Endocasts are not shown to scale.…”

Section: Resultsmentioning

confidence: 99%

“…This is a hypothesis that could be tested if adequately preserved fossils existed. These data are also not available at this time (Jenkins et al 2007;Maddin et al 2012).…”

Section: Evolution Of Inner Ear Traits Within Caeciliansmentioning

confidence: 99%

“…Left otic capsule endocasts of the caecilian species used in this study, arranged in phylogenetic order. The topology for visualisation purposes is based uponZhang & Wake (2009), supplemented withWilkinson & Nussbaum (1999) andMaddin et al (2012). Endocasts are not shown to scale.…”

mentioning

confidence: 99%

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Influence of fossoriality on inner ear morphology: insights from caecilian amphibians

Maddin

Sherratt

2014

Journal of Anatomy

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It is widely accepted that a relationship exists between inner ear morphology and functional aspects of an animal's biology, such as locomotor behaviour. Animals that engage in agile and spatially complex behaviours possess semicircular canals that morphologically maximise sensitivity to correspondingly complex physical stimuli. Stemming from the prediction that fossorial tetrapods require a well-developed sense of spatial awareness, we investigate the hypothesis that fossoriality leads to inner ear morphology that is convergent with other spatially adept tetrapods. We apply morphometrics to otic capsule endocasts of 26 caecilian species to quantify aspects of inner ear shape, and compare these with a sample of frog and salamander species. Our results reveal caecilians (and also frogs) possess strongly curved canals, a feature in common with spatially adept species. However, significantly shorter canals in caecilians suggest reduced sensitivity, possibly associated with reduced reliance on vestibulo-ocular reflexes in this group of visually degenerate tetrapods. An elaboration of the sacculus of caecilians is interpreted as a unique adaptation among amphibians to increase sensitivity to substrate-borne vibrations transmitted through the head. This study represents the first quantitative analyses of inner ear morphology of limbless fossorial tetrapods, and identifies features within a new behavioural context that will contribute to our understanding of the biological consequences of physical stimuli on sensory function and associated morphological evolution.

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“…The topology for visualisation purposes is based upon Zhang & Wake (), supplemented with Wilkinson & Nussbaum () and Maddin et al. (). Endocasts are not shown to scale.…”

Section: Resultsmentioning

confidence: 99%

“…This is a hypothesis that could be tested if adequately preserved fossils existed. These data are also not available at this time (Jenkins et al 2007;Maddin et al 2012).…”

Section: Evolution Of Inner Ear Traits Within Caeciliansmentioning

confidence: 99%

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Influence of fossoriality on inner ear morphology: insights from caecilian amphibians

Maddin

Sherratt

2014

Journal of Anatomy

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“…The evolutionary and functional implications of zygokrotaphic and stegokrotaphic crania have long been debated. Zygokrotaphy is reasoned to be the ancestral condition for caecilians because this occurs in rhinatrematids (sister group to all other living caecilians) and because frogs and salamanders have fully open-roofed crania (gymnokrotaphy) (reviewed in Kleinteich et al 2012;Maddin et al 2012a). While our findings cannot further resolve the ancestral condition in caecilians, the position of zygo-and stegokrotaphic crania in morphospace (Fig.…”

Section: Implications For Caecilian Biology and Understanding Fossorimentioning

confidence: 99%

Evolution of Cranial Shape in Caecilians (Amphibia: Gymnophiona)

et al. 2014

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Insights into morphological diversification can be obtained from the ways the species of a clade occupy morphospace. Projecting a phylogeny into morphospace provides estimates of evolutionary trajectories as lineages diversified information that can be used to infer the dynamics of evolutionary processes that produced patterns of morphospace occupation. We present here a large-scale investigation into evolution of morphological variation in the skull of caecilian amphibians, a major clade of vertebrates. Because caecilians are limbless, predominantly fossorial animals, diversification of their skull has occurred within a framework imposed by the functional demands of head-first burrowing. We examined cranial shape in 141 species, over half of known species, using X-ray computed tomography and geometric morphometrics. Mapping an existing phylogeny into the cranial morphospace to estimate the history of morphological change (phylomorphospace), we find a striking pattern: most species occupy distinct clusters in cranial morphospace that closely correspond to the main caecilian clades, and each cluster is separated by unoccupied morphospace. The empty spaces in shape space are unlikely to be caused entirely by extinction or incomplete sampling. The main caecilian clades have different amounts of morphological disparity, but neither clade age nor number of species account for this variation. Cranial shape variation is clearly linked to phyletic divergence, but there is also homoplasy, which is attributed to extrinsic factors associated with head-first digging: features of caecilian crania that have been previously argued to correlate with differential microhabitat use and burrowing ability, such as subterminal and terminal mouths, degree of temporal fenestration (stegokrotaphy/ zygokrotaphy), and eyes covered by bone, have evolved and many combinations occur in modern species. We find evidence of morphological convergence in cranial shape, among species that have eyes covered by bone, resulting in a narrow bullet-shaped head. These results reveal a complex history, including early expansion of morphospace and both divergent and convergent evolution resulting in the diversity we observe today.

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“…This is problematic for two reasons. First, phylogenetically microsaurs are more closely related to the amniote crown group than any early tetrapod [5,11,24,25]. They are derived in both lacking a spiracular embayment and in possessing a short, robust stapes, unlike all taxa that span the water-toland transition up to, and including, frogs (figure 1).…”

Section: Microsaurs Are Not Representative Of Early Tetrapodsmentioning

confidence: 99%

Is there an exemplar taxon for modelling the evolution of early tetrapod hearing?

et al. 2016

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Christensen et al. recently published a study of hearing in neotenic and experimentally metamorphosed axolotls (Ambystoma mexicanum) and a larval and adult tiger salamander (A. tigrinum), which contributes greatly to our understanding of salamander sound perception in water and air [1]. They demonstrate that premetamorphic, atympanic aquatic salamanders are capable of perceiving high frequency airborne sounds similar to terrestrial adults, demonstrating an interesting capacity for an atympanic ear to function for sound perception in a variety of media. This important research, in combination with other recent studies on the sound perception capabilities of lungfish [2], is helping to better clarify issues related to the water-to-land transition. However, the implication of their experimental design demands a consideration of the evolutionary history of their selected exemplar taxa so these valuable data can be interpreted in a broader context. Our criticisms focus on two major points: the use of salamanders as a proxy for hearing ability intermediate between aquatic and terrestrial vertebrates, and the use of microsaurs as exemplars of the early tetrapod condition.The currently accepted hypothesis for the origin of a tympanic ear is as a derivation from the spiracle of sarcopterygian fish [3]. In 'fish' the spiracle is associated with gill breathing: water passes through the spiracular notch in the rear of the skull, past the braincase and the bracing hyomandibula, to the oropharynx and gill arches [4]. With the loss of gills, the persisting spiracular lumen is co-opted into a middle ear chamber, and the cranial support role of the hyomandibula (now termed stapes) is eliminated, leaving this bone to extend freely into the middle ear chamber (figure 1). In derived tetrapods, the spiracular opening is expanded and covered by a membrane (the tympanum) that collects sound. Vibrations are transmitted to the inner ear via the stapes, which becomes more delicate and better able to propagate fine vibrations [7][8][9][10].

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The Braincase of Eocaecilia micropodia (Lissamphibia, Gymnophiona) and the Origin of Caecilians

Cited by 70 publications

References 41 publications

Influence of fossoriality on inner ear morphology: insights from caecilian amphibians

Influence of fossoriality on inner ear morphology: insights from caecilian amphibians

Evolution of Cranial Shape in Caecilians (Amphibia: Gymnophiona)

Is there an exemplar taxon for modelling the evolution of early tetrapod hearing?

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