Polydactyly in the earliest known tetrapod limbs

Coates, Michael I.; Clack, Jennifer A.

doi:10.1038/347066a0

Cited by 281 publications

(181 citation statements)

References 18 publications

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“…To see if the developmental integration in the formation of the digital skeleton and the consequent predictability of relative phalanx sizes is a basal feature of tetrapods, we measured the phalanges present in the earliest autopods known from the fossil record, including several extinct amphibian species (22,23), and from lungfish embryos, because they are a living representative of a basal sarcopterygian, the group from which tetrapod vertebrates evolved (24). The ratios of phalanx sizes in these early autopods are similar to those seen in modern tetrapods, suggesting that the digit skeletal elements have been formed as a developmental module with biased variations since the origination of the autopod, with metapodials later evolving into a separate module.…”

Section: Resultsmentioning

confidence: 99%

Developmental bias in the evolution of phalanges

Kavanagh

Shoval

Winslow

et al. 2013

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

119

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Evolutionary theory has long argued that the entrenched rules of development constrain the range of variations in a given form, but few empirical examples are known. Here we provide evidence for a very deeply conserved skeletal module constraining the morphology of the phalanges within a digit. We measured the sizes of phalanges within populations of two bird species and found that successive phalanges within a digit exhibit predictable relative proportions, whether those phalanges are nearly equal in size or exhibit a more striking gradient in size from large to small. Experimental perturbations during early stages of digit formation demonstrate that the sizes of the phalanges within a digit are regulated as a system rather than individually. However, the sizes of the phalanges are independent of the metatarsals. Temporal studies indicate that the relative sizes of the phalanges are established at the time of initial cell condensation. Measurements of phalanges across species from six major taxonomic lineages showed that the same predictable range of variants is conserved across vast taxonomic diversity and evolutionary time, starting with the very origins of tetrapods. Although in general phalangeal variations fall within a range of nearly equal-sized phalanges to those following a steep large-to-small gradient, a novel derived condition of excessive elongation of the distal-most phalanges has evolved convergently in multiple lineages, for example under selection for grasping rather than walking or swimming. Even in the context of this exception, phalangeal variations observed in nature are a small subset of potential morphospace.developmental module | developmental constraint | phalanx

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Section: Resultsmentioning

confidence: 99%

Developmental bias in the evolution of phalanges

Kavanagh

Shoval

Winslow

et al. 2013

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

119

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“…This makes it hard to determine ancestral character states without help from the fossil record 1,41 . For example, in the absence of a fossil record we would not know that the first tetrapods were not fully terrestrial 42 , or that they had more than five digits per limb 43 , that the first lungfish were marine 41,44 , that fivefold symmetry is not ancestral for echinoderms 45 , that many of the synapomorphies of living birds evolved before flight 46 , nor could we have inferred the unexpected morphology of Ardipithecus, which lies close to the last common ancestor of humans and chimpanzees 47 .…”

Section: The Fifth Law Of Palaeobiologymentioning

confidence: 99%

Five palaeobiological laws needed to understand the evolution of the living biota

Marshall

2017

Nat Ecol Evol

179

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TitleFive palaeobiological laws needed to understand the evolution of the living biota O ne of the cornerstones of evolutionary theory is the idea of differential survival. The fact of death, the termination of the lives of individuals, is central to evolutionary change. For biologists working on the timescales of generations, the importance of differential survival has been well understood and well studied since Darwin. On longer timescales, however, although it is well recognized that there has been extensive termination of unique morphologies and lineages, study of the living biota alone offers relatively little when trying to determine the importance of these extinctions, given that among the living we only have direct data on the survivors. This presents significant challenges when trying to elucidate the evolutionary process that produced the living biota.Fortunately, the fossil record provides unique and invaluable data on the nature of extinction, including its selectivity, recurrence times, magnitudes and causes. While there has been a dramatic increase in the number of integrated palaeontological and neontological studies [1][2][3][4] , from a palaeobiological perspective, the field of biology has not yet fully assimilated the fundamental findings from the fossil record. Here I summarize these findings in the context of their relevance to our understanding of the living biota. I express this knowledge in the form of simple laws (Box 1), in the hope of facilitating the incorporation of the longstanding and fundamental discoveries of palaeontology into the foundations of thinking in evolutionary biology and ecology, something that has yet to be fully realized. The first law of palaeobiologyLineages become extinct. While the notion of immortality at the level of individuals has been rejected for millennia, it was not until around 1800 that the idea that species could become extinct was established through the discovery of fossils that could not be ascribed to any living species 5 . More formally, the first law can be expressed in terms of the probability that clade will ultimately go extinct, P e :Five palaeobiological laws needed to understand the evolution of the living biota Charles R. MarshallThe foundations of several disciplines can be expressed as simple quantitative laws, for example, Newton's laws or the laws of thermodynamics. Here I present five laws derived from fossil data that describe the relationships among species extinc tion and longevity, species richness, origination rates, extinction rates and diversification. These statements of our palaeo biological knowledge constitute a dimension largely hidden from view when studying the living biota, which are nonetheless crucial to the study of evolution and ecology even for groups with poor or non existent fossil records. These laws encapsulate: the critical fact of extinction; that species are typically geologically short lived, and thus that the number of extinct species typically dwarfs the number of living species; that extinction and orig...

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“…Although most extant tetrapods have a pentadactyl digit formula, an analysis of the fossil record indicated that ancestral stem tetrapods had polydactylous extremities with seven to eight digits (14). It therefore is assumed that the evolutionary transition between limbs without digits (adactylous), such as in Panderychtis, and limbs with five digits (pentadactylous) involved an intermediate stage of polydactyly, a state that perhaps was linked to the aquatic status of these primitive ancestral tetrapods (15).…”

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confidence: 99%

Regulation of number and size of digits by posterior Hox genes: A dose-dependent mechanism with potential evolutionary implications

Zákány

Fromental-Ramain

Warot

et al. 1997

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

209

102

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The proper development of digits, in tetrapods, requires the activity of several genes of the HoxA and HoxD homeobox gene complexes. By using a variety of lossof-function alleles involving the five Hox genes that have been described to affect digit patterning, we report here that the group 11, 12, and 13 genes control both the size and number of murine digits in a dose-dependent fashion, rather than through a Hox code involving differential qualitative functions. A similar dose-response is observed in the morphogenesis of the penian bone, the baculum, which further suggests that digits and external genitalia share this genetic control mechanism. A progressive reduction in the dose of Hox gene products led first to ectrodactyly, then to olygodactyly and adactyly. Interestingly, this transition between the pentadactyl to the adactyl formula went through a step of polydactyly. We propose that in the distal appendage of polydactylous short-digited ancestral tetrapods, such as Acanthostega, the HoxA complex was predominantly active. Subsequent recruitment of the HoxD complex contributed to both reductions in digit number and increase in digit length. Thus, transition through a polydactylous limb before reaching and stabilizing the pentadactyl pattern may have relied, at least in part, on asynchronous and independent changes in the regulation of HoxA and HoxD gene complexes.Posterior (AbdB-related) Hox genes belonging to both the HoxD and the HoxA complexes are necessary for the proper organization and development of tetrapod digits (for review, see ref.

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Polydactyly in the earliest known tetrapod limbs

Cited by 281 publications

References 18 publications

Developmental bias in the evolution of phalanges

Developmental bias in the evolution of phalanges

Five palaeobiological laws needed to understand the evolution of the living biota

Regulation of number and size of digits by posterior Hox genes: A dose-dependent mechanism with potential evolutionary implications

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