No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Response to: Phylogenetic placement, developmental trajectories and evolutionary implications of a feathered dinosaur tail in Mid-Cretaceous amber
Abstract
In his correspondence, Markus Lambertz [1] raises some concerns about the phylogenetic placement and feather development of DIP-V-15103, the amber-entombed tail section that we recently reported [2] as fragmentary remains of a non-pygostylian coelurosaur (likely within the basal part of Coelurosauria). We here would like to respond to these concerns.
... However, it also has been hypothesized that bird scutate scales appeared later in evolution and are secondary structures derived from feathers (Dhouailly 2009). It is interesting that an ancient hatchling bird preserved in amber has both feathers and scales on its feet (Xing et al. 2017). ...
... However, it also has been hypothesized that bird scutate scales appeared later in evolution and are secondary structures derived from feathers (Dhouailly 2009). It is interesting that an ancient hatchling bird preserved in amber has both feathers and scales on its feet (Xing et al. 2017). ...
A list of all known taxa described or recorded from Burmese amber from the published literature up to the end of 2018 is given, along with a comprehensive bibliography. The history of the study of inclusions is summarised, and demonstrates that the number of species has risen exponentially over the past two decades. The first three species were named in 1916 and by the end of 1920 a total of 42 species had been named by T.D.A. Cockerell. Only three more species were named by 1999 though by the end of 2018 the total had risen to an incredible 1,192 species, of which over half were named in the past three years. Some 320 species were named in 2018, the highest number described from one type of amber in any one year in the entire history of amber studies.
This taxonomic list is based on Ross et al (2010) plus non-arthropod taxa and published papers up to the end of August 2018. It does not contain unpublished records or records from papers in press (including on-line proofs) or unsubstantiated on-line records. Often the final versions of papers were published on-line the year before they appeared in print, so the on-line published year is accepted and referred to accordingly. Note, the authorship of species does not necessarily correspond to the full authorship of papers where they were described. The latest high level classification is used where possible though in some cases conflicts were encountered, usually due to cladistic studies, so in these cases an older classification was adopted for convenience. The classification for Hexapoda follows Nicholson et al. (2015), plus subsequent papers. † denotes extinct orders and families. New additions or changes to the previous list (v.2018.1) are marked in blue, corrections are marked in red. The list comprises 38 classes (or similar rank), 102 orders (or similar rank), 525 families, 777 genera and 1013 species (excluding Tilin amber and copal records). This includes 8 classes, 65 orders, 480 families, 714 genera and 941 species of arthropods.
This taxonomic list is based on Ross et al (2010) plus non-arthropod taxa and published papers up to the end of April 2018. It does not contain unpublished records or records from papers in press (including on-line proofs) or unsubstantiated on-line records. Often the final versions of papers were published on-line the year before they appeared in print, so the on-line published year is accepted and referred to accordingly. Note, the authorship of species does not necessarily correspond to the full authorship of papers where they were described. The latest high level classification is used where possible though in some cases conflicts were encountered, usually due to cladistic studies, so in these cases an older classification was adopted for convenience. The classification for Hexapoda follows Nicholson et al. (2015), plus subsequent papers. † denotes extinct orders and families. New additions or taxonomic changes to the previous list (v.2017.4) are marked in blue, corrections are marked in red. The list comprises 37 classes (or similar rank), 99 orders (or similar rank), 510 families, 713 genera and 916 species. This includes 8 classes, 64 orders, 467 families, 656 genera and 849 species of arthropods.
This taxonomic list is based on Ross et al (2010) plus non-arthropod taxa and published papers up to the end of December 2017. It does not contain unpublished records or records from papers in press (including on-line proofs) or unsubstantiated on-line records. Often the final versions of papers were published on-line the year before they appeared in print, so the on-line published year is accepted and referred to accordingly. Note, the authorship of species does not necessarily correspond to the full authorship of papers where they were described. The latest high level classification is used where possible though in some cases conflicts were encountered, usually due to cladistic studies, so in these cases an older classification was adopted for convenience. The classification for Hexapoda follows Nicholson et al. (2015), plus subsequent papers. † denotes extinct orders and families. New additions or taxonomic changes to the previous list (v.2017.3) are marked in blue, corrections are marked in red. The list comprises 35 classes (or similar rank), 91 orders (or similar rank), 429 families, 668 genera and 870 species. This includes 7 classes, 57 orders, 389 families, 612 genera and 805 species of arthropods. In this version, for the non-parasitiform mites I have reverted from the 2 order (Sarcoptiformes and Trombidiformes) to 1 order (Acariformes) classification following the recent review of Burmese amber arachnids by Selden & Ren (2017).
This taxonomic list is based on Ross et al (2010) plus non-arthropod taxa and published papers up to the end of September 2017. It does not contain unpublished records or records from papers in press (including on-line proofs) or unsubstantiated on-line records. Often the final versions of papers were published on-line the year before they appeared in print, so the on-line published year is accepted and referred to accordingly. Note, the authorship of species does not necessarily correspond to the full authorship of papers where they were described. The latest high level classification is used where possible though in some cases conflicts were encountered, usually due to cladistic studies, so in these cases an older classification was adopted for convenience. The classification for Hexapoda follows Nicholson et al. (2015), plus subsequent papers. † denotes extinct orders and families. New additions or taxonomic changes to the previous list (v.2017.2) are marked in blue, corrections are marked in red. The list now comprises 34 classes (or similar rank), 91 orders (or similar rank), 412 families, 639 genera and 819 species. This includes 6 classes, 57 orders, 373 families, 584 genera and 757 species of arthropods.
In the two decades since the discovery of feathered dinosaurs [1-3], the range of plumage known from non-avialan theropods has expanded significantly, confirming several features predicted by developmentally informed models of feather evolution [4-10]. However, three-dimensional feather morphology and evolutionary patterns remain difficult to interpret, due to compression in sedimentary rocks [9, 11]. Recent discoveries in Cretaceous amber from Canada, France, Japan, Lebanon, Myanmar, and the United States [12-18] reveal much finer levels of structural detail, but taxonomic placement is uncertain because plumage is rarely associated with identifiable skeletal material [14]. Here we describe the feathered tail of a non-avialan theropod preserved in mid-Cretaceous (∼99 Ma) amber from Kachin State, Myanmar [17], with plumage structure that directly informs the evolutionary developmental pathway of feathers. This specimen provides an opportunity to document pristine feathers in direct association with a putative juvenile coelurosaur, preserving fine morphological details, including the spatial arrangement of follicles and feathers on the body, and micrometer-scale features of the plumage. Many feathers exhibit a short, slender rachis with alternating barbs and a uniform series of contiguous barbules, supporting the developmental hypothesis that barbs already possessed barbules when they fused to form the rachis [19]. Beneath the feathers, carbonized soft tissues offer a glimpse of preservational potential and history for the inclusion; abundant Fe(2+) suggests that vestiges of primary hemoglobin and ferritin remain trapped within the tail. The new finding highlights the unique preservation potential of amber for understanding the morphology and evolution of coelurosaurian integumentary structures.
Mayr questions the plausibility of our hypothesis that structural color signaling was the initial selective advantage in the evolution of pennaceous feathers. Our hypothesis is grounded in the accepted phylogenetic framework for theropods, which shows that pennaceous feathers evolved before flight
Recent discoveries of feathered dinosaur specimens have greatly improved our understanding of the origin and early evolution of feathers, but little information is available on the ontogenetic development of early feathers. Here we describe an early-juvenile specimen and a late-juvenile specimen, both referable to the oviraptorosaur Similicaudipteryx, recovered from the Lower Cretaceous Yixian Formation of western Liaoning, China. The two specimens have strikingly different remiges and rectrices, suggesting that a radical morphological change occurred during feather development, as is the case for modern feathers. However, both the remiges and the rectrices are proximally ribbon-like in the younger specimen but fully pennaceous in the older specimen, a pattern not known in any modern bird. In combination with the wide distribution of proximally ribbon-like pennaceous feathers and elongate broad filamentous feathers among extinct theropods, this find suggests that early feathers were developmentally more diverse than modern ones and that some developmental features, and the resultant morphotypes, have been lost in feather evolution.
Summary In a recent report in Current Biology , Xing and colleagues [1] present a small fragment of a vertebrate tail preserved in amber that bears integumentary appendages (DIP-V-15103, Dexu Institute of Paleontology, Chaozhou, China; Figure 1). Following several analyses using cutting-edge technology the authors conclude that: the tail belongs to a non-avian theropod dinosaur (non-avialan according to the authors, but non-avian used synonymously here); the dinosaur most likely was a member of the Coelurosauria, possibly even Maniraptora; and, the integumentary appendages are feathers that support a barbule-first evolutionary pattern for feathers. DIP-V-15103 is indeed an intriguing specimen with potential implications for contributing to understanding the evolution of feathers among dinosaurs, which remains a current and undoubtedly controversial topic [2,3]. However, I would like to raise several concerns about the available evidence for the phylogenetic hypothesis concerning the placement of DIP-V-15103 as concluded by Xing and colleagues [1], and furthermore discuss the developmental trajectories predicted by them in light of their far-reaching evolutionary implications.
Over the course of the last two decades, the understanding of the early evolution of feathers in non-avian dinosaurs has been revolutionized. It is now recognized that early feathers had a simple form comparable in general structure to the hairs of mammals. Insight into the prevalence of simple feathers throughout the dinosaur family tree has gradually arisen in tandem with the growing evidence for endothermic dinosaur metabolisms. This has led to the generally accepted opinion that the early feather coats of dinosaurs functioned as thermo insulation. However, thermo insulation is often erroneously stated to be a likely functional explanation for the origin of feathers. The problem with this explanation is that, like mammalian hair, simple feathers could serve as insulation only when present in sufficiently high concentrations. The theory therefore necessitates the origination of feathers en masse. We advocate for a novel origin theory of feathers as bristles. Bristles are facial feathers common among modern birds that function like mammalian tactile whiskers, and are frequently simple and hair-like in form. Bristles serve their role in low concentrations, and therefore offer a feasible first stage in feather evolution. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Avian neoptile feathers are defined as the first feather generation, which covers the chick after hatching, and usually described as simple structures consisting of numerous downy barbs which are radially symmetrically arranged and come together in a short calamus. In contrast, in some birds (e.g., Anas platyrhynchos, Dromaius novaehollandiae) the neoptile feathers have a prominent rhachis, and therefore display clear bilateral symmetry. Because the symmetrical variety found in neoptile feathers is poorly understood, their morphology was studied in a more comprehensive and phylogenetic approach. Neoptile body feathers from over 22 bird species were investigated using light microscopy, SEM, and MicroCT. Characters such as an anterior-posterior axis, a central rhachis, medullary cells, and structure of the calamus wall were defined and mapped onto recent phylogenetic hypotheses for extant birds. It can be shown that bilaterally symmetric neoptile feathers (with a solid calamus wall) were already present in the stem lineage of crown-group birds (Neornithes). In contrast, simple radially symmetric neoptile feathers (with a fragile calamus wall) are an apomorphic character complex for the clade Neoaves. The simple morphology of this feather type may be the result of a reduced period of development during embryogenesis. To date, embryogenesis of neoptile feathers from only a few bird species was used as a model to reconstruct feather evolution. Because this study shows that the morphology of neoptile feathers is more diverse and even shows a clear phylogenetic signal, it is necessary to expand the spectrum of "model organisms" to species with bilaterally symmetric neoptile feathers and compare differences in the frequency of feather development from a phylogenetic point of view.
Xu et al. describe the extraordinarily preserved feathers from two subadults of the oviraptorisaur Similicaudipteryx from the Yixian Formation of Liaoning, China. The preserved tail feathers of the juvenile specimen (STM4.1) show a morphology not previously observed in any fossil feathers. The tail feathers of an older, immature specimen (STM22-6) show a typical closed pennaceous structure with a prominent, planar vane. I propose that the feathers of the tail of the juvenile specimen are not a specialized feather generation, but fossilized 'pin feathers' or developing feather germs.
Avian feathers are a complex evolutionary novelty characterized by structural diversity and hierarchical development. Here, I propose a functionally neutral model of the origin and evolutionary diversification of bird feathers based on the hierarchical details of feather development. I propose that feathers originated with the evolution of the first feather follicle-a cylindrical epidermal invagination around the base of a dermal papilla. A transition series of follicle and feather morphologies is hypothesized to have evolved through a series of stages of increasing complexity in follicle structure and follicular developmental mechanisms. Follicular evolution proceeded with the origin of the undifferentiated collar (stage I), barb ridges (stage II), helical displacement of barb ridges, barbule plates, and the new barb locus (stage III), differentiation of pennulae of distal and proximal barbules (stage IV), and diversification of barbule structure and the new barb locus position (stage V). The model predicts that the first feather was an undifferentiated cylinder (stage I), which was followed by a tuft of unbranched barbs (stage II). Subsequently, with the origin of the rachis and barbules, the bipinnate feather evolved (stage III), followed then by the pennaceous feather with a closed vane (stage IV) and other structural diversity (stages Va-f). The model is used to evaluate the developmental plausibility of proposed functional theories of the origin of feathers. Early feathers (stages I, II) could have functioned in communication, defense, thermal insulation, or water repellency. Feathers could not have had an aerodynamic function until after bipinnate, closed pennaceous feathers (stage IV) had evolved. The morphology of the integumental structures of the coelurisaurian theropod dinosaurs Sinosauropteryx and Beipiaosaurus are congruent with the model's predictions of the form of early feathers (stage I or II). Additional research is required to examine whether these fossil integumental structures developed from follicles and are homologous with avian feathers. J. Exp. Zool. (Mol. Dev. Evol.) 285:291-306, 1999.
Die Nestdunen der Vögel und ihre Bedeutung für die Phylogenie der Feder
- S Schaub
Schaub, S. (1912). Die Nestdunen der Vögel
und ihre Bedeutung für die Phylogenie der
Feder. Verhandl. Naturforsch. Ges. Basel 23,
131-182.