Carpus and tarsus of Temnospondyli

Dilkes, David W.

doi:10.18435/b5mw2q

Cited by 27 publications

(87 citation statements)

References 36 publications

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“…The description follows the terminology of Dilkes (), orienting the carpus and manus so that the palmar side of the hand faces ventrally, the side opposite to this is considered dorsal, the first digit is on the medial side of the hand, and the fifth digit is lateral to the other digits. These terms are used simply for ease of comparison with previous literature and are not intended to imply the actual anatomical position of the hand relative to the body during life.…”

Section: Methodsmentioning

confidence: 99%

The evolution of the manus of early theropod dinosaurs is characterized by high inter‐ and intraspecific variation

2017

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The origin of the avian hand, with its reduced and fused carpals and digits, from the five‐fingered hands and complex wrists of early dinosaurs represents one of the major transformations of manus morphology among tetrapods. Much attention has been directed to the later part of this transition, from four‐ to three‐fingered taxa. However, earlier anatomical changes may have influenced these later modifications, possibly paving the way for a later frameshift in digit identities. We investigate the five‐ to four‐fingered transition among early dinosaurs, along with changes in carpus morphology. New three‐dimensional reconstructions from computed tomography data of the manus of the Triassic and Early Jurassic theropod dinosaurs Coelophysis bauri and Megapnosaurus rhodesiensis are described and compared intra‐ and interspecifically. Several novel findings emerge from these reconstructions and comparisons, including the first evidence of an ossified centrale and a free intermedium in some C. bauri specimens, as well as confirmation of the presence of a vestigial fifth metacarpal in this taxon. Additionally, a specimen of C. bauri and an unnamed coelophysoid from the Upper Triassic Hayden Quarry, New Mexico, are to our knowledge the only theropods (other than alvarezsaurs and birds) in which all of the distal carpals are completely fused together into a single unit. Several differences between the manus of C. bauri and M. rhodesiensis are also identified. We review the evolution of the archosauromorph manus more broadly in light of these new data, and caution against incorporating carpal characters in phylogenetic analyses of fine‐scale relationships of Archosauromorpha, in light of the high degree of observed polymorphism in taxa for which large sample sizes are available, such as the theropod Coelophysis and the sauropodomorph Plateosaurus. We also find that the reduction of the carpus and ultimate loss of the fourth and fifth digits among early dinosaurs did not proceed in a neat, stepwise fashion, but was characterized by multiple losses and possible gains of carpals, metacarpals and phalanges. Taken together, the high degree of intra‐ and interspecific variability in the number and identities of carpals, and the state of reduction of the fourth and fifth digits suggest the presence of a ‘zone of developmental variability’ in early dinosaur manus evolution, from which novel avian‐like morphologies eventually emerged and became channelized among later theropod clades.

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Section: Methodsmentioning

confidence: 99%

The evolution of the manus of early theropod dinosaurs is characterized by high inter‐ and intraspecific variation

2017

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“…Balanerpeton has sometimes (Pawley, 2006;Clack et al, 2012b;Dilkes, 2015a), but not always (Milner & Sequeira, 1994;Ruta, 2009), been found as the sister-group of "Dendrerpeton"; we therefore follow Schoch & Milner (2014) in not including it in the Dendrerpetidae OTU. Rhynchonkos have shown that previous conceptions of Rhynchonkos (e.g.…”

Section: Manuscript To Be Reviewedmentioning

confidence: 98%

“…The eight phylogenetic analyses that have included it so far (Laurin & Soler-Gijón, 2001Pawley, 2006: fig. 44;Schoch & Witzmann, 2009a, b;Dilkes, 2015a;Pardo, Small & Huttenlocker, 2017: fig. 2, S7) have given seven different results, and two of them were based on very small matrices.…”

Section: Otus Added For a Separate Set Of Analysesmentioning

confidence: 99%

Peer Review #1 of "Phylogeny of Paleozoic limbed vertebrates reassessed through revision and expansion of the largest published relevant data matrix (v0.2)"

Pyron¹

2019

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The largest published phylogenetic analysis of early limbed vertebrates (Ruta M, Coates MI. 2007. Journal of Systematic Palaeontology 5:69-122) recovered e.g. Seymouriamorpha, Diadectomorpha and (in some trees) Caudata as paraphyletic and found the "temnospondyl hypothesis" on the origin of Lissamphibia (TH) to be more parsimonious than the "lepospondyl hypothesis" (LH)-though only, as we show, by one step. We report 4200 misscored cells, over half of them due to typographic and similar accidental errors. Further, some characters were duplicated; some had only one described state; for one, most taxa were scored after presumed relatives. Even potentially continuous characters were unordered, the effects of ontogeny were not sufficiently taken into account, and data published after 2001 were mostly excluded. After these issues are improved-we document and justify all changes to the matrix-, but no characters are added, we find (Analysis R1) much longer trees with e.g. monophyletic Caudata, Diadectomorpha and (in some trees) Seymouriamorpha; Ichthyostega either crownward or rootward of Acanthostega; and Anthracosauria either crownward or rootward of Temnospondyli. The LH is 9 steps shorter than the TH (R2; constrained) and 12 steps shorter than the "polyphyly hypothesis" (PH-R3; constrained). Brachydectes (Lysorophia) is not found next to Lissamphibia; instead, a large clade that includes the adelogyrinids, urocordylid "nectrideans" and aïstopods occupies that position. As expected from the taxon/character ratio, most bootstrap values are low. Adding 56 OTUs to the original 102 increases the resolution (and decreases most bootstrap values). The added taxa range in completeness from complete articulated skeletons to an incomplete lower jaw. Even though the lissamphibian-like temnospondyls Gerobatrachus, Micropholis and Tungussogyrinus and the extremely peramorphic salamander Chelotriton are added, the difference between LH (R4; unconstrained) and TH (R5) rises to 10 steps, that between LH and PH (R6) to 15; the TH also requires several more regains of lost bones than the LH. Casineria, in which we tentatively identify a postbranchial lamina, emerges rather far from amniote origins in a gephyrostegid-chroniosuchian grade. Bayesian inference (Analysis EB, settings as in R4) mostly agrees with R4. High posterior probabilities are found for Lissamphibia (1.00) and the LH (0.92); however, many branches remain weakly supported, and most are short, as expected from the small character sample.

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“…Abbreviations: as, astragalus; i, intermedium; te, tibiale; 1,2,3,4, centralia; i,ii,iii,iv,v, distal tarsals. Taxa were redrawn from the following sources: Acheloma (Dilkes, 2015); Greererpeton (Godfrey, 1989); Proterogyrinus (Holmes, 1984); Gephyrostegus (Carroll, 1970); Seymouria (Berman et al, 2000); Westlothiana (Smithson 1989, Smithson et al,1994;…”

Section: Manuscript To Be Reviewedmentioning

confidence: 99%

Peer Review #2 of "The ontogenetic transformation of the mesosaurid tarsus: a contribution to the origin of the primitive amniotic astragalus (v0.1)"

Gaetano¹

2016

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The hypotheses about the origin of the primitive amniotic tarsus are very speculative. Early studies argued that the origin of the astragalus, one of the largest proximal bones in the tarsus of basal amniotes, was produced by either the fusion of two, three, or even four of the original tarsal bones, the intermedium, the tibiale and the proximal centralia (c4 and c3), or that the intermedium alone transforms into the primitive astragalus. More recent studies have shown that the structure of the tarsus in Captorhinus supports the former hypothesis about a fusion of the intermedium, the tibiale, the proximal centrale (c4) and eventually c3, producing a purportedly multipartite structure of the amniotic astragalus, but the issue remained contentious. Very well preserved tarsi of the Early Permian aquatic amniote Mesosaurus tenuidens Gervais,1864-1865, which represent the most complete ontogenetic succession known for a basal amniote (the other exceptional one is provided by the Late Permian diapsid Hovasaurus boulei Piveteau,1926), suggest that there is more than one ossification center for the astragalus and that these fuse during late embryonic stages or maybe early after birth. A non-hatched Mesosaurus in an advanced stage of development shows that the tarsus is represented by a single bone, most probably the astragalus, which seems to be formed by the suturing of three bones, which we interpret as being the intermedium, the tibiale, which could have already integrated the c4 in an earlier stage of the development, and the c3. An amniote-like tarsal structure is observed in very basal Carboniferous and Permian tetrapods such as Proterogyrinus, Gephyrostegus, the diadectids Diadectes and Orobates, some microsaurs like Tuditanus and Pantylus, and possibly Westlothiana, taxa that were all considered as true amniotes in their original descriptions. Therefore, the structure of the amniotic tarsus, including the configuration of the proximal series formed by the astragalus and the calcaneum, typically a pair of enlarged bones, could have been established well before the first recognized amniote walked on Earth. Accordingly, the tarsus of these taxa does not constitute specialized convergences that appeared in unrelated groups, they might be instead, part of a transformation series that involves taxa closely related to the early amniotes as some hypotheses have suggested.

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Carpus and tarsus of Temnospondyli

Cited by 27 publications

References 36 publications

The evolution of the manus of early theropod dinosaurs is characterized by high inter‐ and intraspecific variation

The evolution of the manus of early theropod dinosaurs is characterized by high inter‐ and intraspecific variation

Peer Review #1 of "Phylogeny of Paleozoic limbed vertebrates reassessed through revision and expansion of the largest published relevant data matrix (v0.2)"

Peer Review #2 of "The ontogenetic transformation of the mesosaurid tarsus: a contribution to the origin of the primitive amniotic astragalus (v0.1)"

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