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[dinosaur] Embryonic Muscular Activity from Basal Theropods to Modern Birds + tinamou phylogeny + Dodo bone histology and molting

Ben Creisler

Some recent avian papers:

Alexander O. Vargas,  Macarena Ruiz-Flores,  Sergio Soto-Acuña, Nadia Haidr,  Carolina Acosta-Hospitaleche,  Luis Ossa-Fuentes  & Vicente Muñoz-Walther (2017)
The Origin and Evolutionary Consequences of Skeletal Traits Shaped by Embryonic Muscular Activity, from Basal Theropods to Modern Birds.
Integrative and Comparative Biology icx074 (advance online publication)

Embryonic muscular activity (EMA) is involved in the development of several distinctive traits of birds. Modern avian diversity and the fossil record of the dinosaur-bird transition allow special insight into their evolution. Traits shaped by EMA result from mechanical forces acting at post-morphogenetic stages, such that genes often play a very indirect role. Their origin seldom suggests direct selection for the trait, but a side-effect of other changes such as musculo-skeletal rearrangements, heterochrony in skeletal maturation, or increased incubation temperature (which increases EMA). EMA-shaped traits like sesamoids may be inconstant, highly conserved, or even disappear and then reappear in evolution. Some sesamoids may become increasingly influenced in evolution by genetic-molecular mechanisms (genetic assimilation). There is also ample evidence of evolutionary transitions from sesamoids to bony eminences at tendon insertion sites, and vice-versa. This can be explained by newfound similarities in the earliest development of both kinds of structures, which suggest these transitions are likely triggered by EMA. Other traits that require EMA for their formation will not necessarily undergo genetic assimilation, but still be conserved over tens and hundreds of millions of years, allowing evolutionary reduction and loss of other skeletal elements. Upon their origin, EMA-shaped traits may not be directly genetic, nor immediately adaptive. Nevertheless, EMA can play a key role in evolutionary innovation, and have consequences for the subsequent direction of evolutionary change. Its role may be more important and ubiquitous than currently suspected.


Sara Bertelli (2017)
Advances on tinamou phylogeny: an assembled cladistic study of the volant palaeognathous birds.
Cladistics (advance online publication)
DOI: 10.1111/cla.12172

Tinamous are volant terrestrial birds, endemic to the Neotropics. Here, an inclusive phenotype-based phylogenetic study of the interrelationships among all extinct and living species of tinamous is conducted. In this cladistic analysis, results are compared between main character subsets and with previous molecular studies. Special attention is paid to character definition and scoring of integumentary and behavioural characters: transformation costs are applied to analyse egg coloration and plumage characters—on the basis of pigment composition and overlap of pigmentation patterns respectively—in the context of generalized (Sankoff) parsimony. Cladistic analysis recovers the traditional subdivision between those tinamous specialized for open areas (Nothurinae) and those inhabiting forested environments (Tinaminae) and support the monophyly of recognized genera. The present study demonstrates that morphological analysis yields highly congruent results when compared with previous molecular studies; thus, it provides morphological synapomorphies for clades that have been proposed by these molecular analyses. The placement of the fossil species within the open-area (Nothurinae) and the forest-dwelling (Tinaminae) tinamous is also consistent with the palaeoenvironmental conditions inferred from the associated flora and fauna.


Free pdf:

D. Angst, A. Chinsamy, L. Steel & J. P. Hume (2017)
Bone histology sheds new light on the ecology of the dodo (Raphus cucullatus, Aves, Columbiformes)
Scientific Reports 7, Article number: 7993 (2017)

The dodo, Raphus cucullatus, a flightless pigeon endemic to Mauritius, became extinct during the 17th century due to anthropogenic activities. Although it was contemporaneous with humans for almost a century, little was recorded about its ecology. Here we present new aspects of the life history of the dodo based on our analysis of its bone histology. We propose that the dodo bred around August and that the rapid growth of the chicks enabled them to reach a robust size before the austral summer or cyclone season. Histological evidence of molting suggests that after summer had passed, molt began in the adults that had just bred; the timing of molt derived from bone histology is also corroborated by historical descriptions of the dodo by mariners. This research represents the only bone histology analysis of the dodo and provides an unprecedented insight into the life history of this iconic bird.


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