Phytogeny, Variation, and Morphological Integration

Shubin, Neil; Wake, David B.

doi:10.1093/icb/36.1.51

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“…Urodela | phylogeny | fossil record | molecular clock S alamanders are a diverse group of modern amphibians, with high ecological diversity and extreme morphological conservatism (1)(2)(3)(4). Among the 10 extant families, the Hynobiidae and Cryptobranchidae are classified in the suborder Cryptobranchoidea, and the remaining families (except for the Sirenidae) in another suborder, Salamandroidea.…”

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Late Jurassic salamandroid from western Liaoning, China

Gao

Shubin

2012

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

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A Jurassic salamander, Beiyanerpeton jianpingensis (gen. et sp. nov.), from a recently found site in western Liaoning Province, China is the earliest known record of Salamandroidea. As a Late Jurassic record of the group, it extends the range of the clade by ~40 Ma. The Late Jurassic taxon is neotenic and represented by exceptionally preserved specimens, including fully articulated cranial and postcranial skeletons and bony gill structures close to the cheek region. The fossil beds, consisting of dark-brown volcanic ash shales of the Upper Jurassic Tiaojishan (Lanqi) Formation (Oxfordian), underlie trachyandesite rocks that have yielded a SHRIMP zircon U-Pb date of 157 ± 3 Ma. The fossiliferous beds are substantially older than the Jehol Group, including the Yixian Formation ( 40 Ar/ 39 Ar dates of 122–129 Ma), but slightly younger than the Middle Jurassic Daohugou horizon ( 40 Ar/ 39 Ar date of 164 ± 4 Ma). The early fossil taxon shares with extant salamandroids derived character states, including: separated nasals lacking a midline contact, angular fused to the prearticular in the lower jaw, and double-headed ribs on the presacral vertebrae. In contrast to extant salamandroids, however, the salamander shows a discrete and tooth-bearing palatine, and unequivocally nonpedicellate and monocuspid marginal teeth in large and presumably mature individuals. The finding provides insights into the evolution of key characters of salamanders, and also provides direct evidence supporting the hypothesis that the split between Cryptobranchoidea and Salamandroidea had taken placed before the Late Jurassic Oxfordian time. In this aspect, both paleontological and molecular data now come to agree.

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confidence: 99%

Late Jurassic salamandroid from western Liaoning, China

Gao

Shubin

2012

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

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“…Yet, based on the robust and congruent morphological and molecular evidence that supports the Batrachia hypothesis, the interpretation of these developmental patterns would need to be quite different. Digit formation in frogs is considered to be the ancestral condition for all tetrapods, whereas the salamander pattern represents a derived condition (46,55,57,58). Recent molecular developmental studies demonstrate that expression patterns of Hoxa-11 in the limb buds of frogs are similar to those found in amniota (59), whereas salamanders show a derived pattern.…”

Section: Congruent Molecular and Morphological Evidence Provides A Romentioning

confidence: 99%

On the origin of and phylogenetic relationships among living amphibians

Zardoya

Meyer

2001

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

104

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The phylogenetic relationships among the three orders of modern amphibians (Caudata, Gymnophiona, and Anura) have been estimated based on both morphological and molecular evidence. Most morphological and paleontological studies of living and fossil amphibians support the hypothesis that salamanders and frogs are sister lineages (the Batrachia hypothesis) and that caecilians are more distantly related. Previous interpretations of molecular data based on nuclear and mitochondrial rRNA sequences suggested that salamanders and caecilians are sister groups to the exclusion of frogs. In an attempt to resolve this apparent conflict, the complete mitochondrial genomes of a salamander (Mertensiella luschani) and a caecilian (Typhlonectes natans) were determined (16,656 and 17,005 bp, respectively) and compared with previously published sequences from a frog (Xenopus laevis) and several other groups of vertebrates. Phylogenetic analyses of the mitochondrial data supported with high bootstrap values the monophyly of living amphibians with respect to other living groups of tetrapods, and a sister group relationship of salamanders and frogs. The lack of phylogenetically informative sites in the previous rRNA data sets (because of its shorter size and higher among-site rate variation) likely explains the discrepancy between our results and those based on previous molecular data. Strong support of the Batrachia hypothesis from both molecule-and morphology-based studies provides a robust phylogenetic framework that will be helpful to comparative studies among the three living orders of amphibians and will permit better understanding of the considerably divergent vertebral, brain, and digit developmental patterns found in frogs and salamanders.iving amphibians (Lissamphibia) are highly successful tetrapods that evolved diverse body plans that differ in modes of locomotion, reproductive specializations, and life histories (1, 2). For instance, the slender body of living salamanders (Caudata) has a well developed tail and proportionally paired limbs, whereas modern caecilians (Gymnophiona) are completely limbless, and are adapted to a fossorial lifestyle, with elongated bodies, protrusible tentacles, and reduced eyes. Extant frogs (Anura) lack tails, and evolved powerful hind limbs and a shortened, stiffened vertebral column (the urostyle)-a unique adaptation for jumping. The earliest fossils currently known of salamanders (Marmorerpeton; ref. , and demonstrate that all three lineages of extant amphibians acquired their peculiar body plan early on in their evolutionary history. The diversity among amphibians coupled with the lack of shared derived characters plus a poor fossil record complicate assessment of the phylogenetic relationships among the three living orders.Early workers on amphibian systematics repeatedly rejected the monophyly of Lissamphibia by proposing independent origins of the living orders of modern amphibians (see ref. 7 for a review). However, these studies failed to distinguish between ancestral and derived c...

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“…Virtually all novelties of salamander limb structure arise through reduction: apomorphic states consist of a smaller number of mesopodials and digits than do plesiomorphic conditions. This well-defined trend exhibits a great degree of homoplasy (Wake, 1991;Shubin et al, 1995;Shubin and Wake, 1996) as similar patterns of reduction arise independently in diverse clades. One of the most extreme examples of this phenomenon relates to the amalgamation of the two most postaxial distal tarsals, distal tarsal four and five (Alberch, 1983).…”

Section: Bridging the Gap Between Microevolution And Macroevolutionmentioning

confidence: 77%

“…Fusions of proximal and distal carpals and tarsals typically occur in the central portion of the appendage (e.g., the fusion of c and dt4 in Thorius and Oedipina). The centrale (c), dt4, and dt5 exhibit high levels of homoplasy in salamander phylogeny (Wake, 1991;Shubin et al, 1995;Shubin and Wake, 1996). Some bolitoglossines possess the highly derived trait of amalgamation of distal tarsals 3, 4, and 5.…”

Section: Phylogenetic Patterns Of Reductionmentioning

confidence: 99%

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Origin of evolutionary novelty: Examples from limbs

Shubin¹

2002

Journal of Morphology

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Classic hypotheses of vertebrate morphology are being informed by new data and new methods. Long nascent issues, such as the origin of tetrapod limbs, are being explored by paleontologists, molecular biologists, and functional anatomists. Progress in this arena will ultimately come down to knowing how macroevolutionary differences between taxa emerge from the genetic and phenotypic variation that arises within populations. The assembly of limbs over developmental and evolutionary time offers examples of the major processes at work in the origin of novelties. Recent comparative developmental analyses demonstrate that many of the mechanisms used to pattern limbs are ancient. One of the major consequences of this phenomenon is parallelism in the evolution of anatomical structures. Studies of both the fossil record and intrapopulational variation of extant populations reveal regularities in the origin of variation. These examples reveal processes acting at the level of populations that directly affect the patterns of diversity observed at higher taxonomic levels.

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Phytogeny, Variation, and Morphological Integration

Cited by 50 publications

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Late Jurassic salamandroid from western Liaoning, China

Late Jurassic salamandroid from western Liaoning, China

On the origin of and phylogenetic relationships among living amphibians

Origin of evolutionary novelty: Examples from limbs

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