‘The Evolution of Feathers’
(Foth and Rauhut editors 2020) is a new book the genesis of feathers and the animals that developed them. The following is a brief critique of abstracts from the 12 chapters.
From the introduction
“For years it was generally assumed that the origin of flight was the main driving force for the evolution of feathers.”
Was it really? If promoted by paleontologists that was inappropriate and short-sighted. No birds fly with proto-feathers. Birds don’t get flight feathers first.
“This book is devoted to the origin and evolution of feathers, and highlights the impact of palaeontology on this research field by reviewing a number of spectacular fossil discoveries that document the increasing morphological complexity along the evolutionary path to modern birds. Also featuring chapters on fossil feather colours, feather development and its genetic control, the book offers a timely and comprehensive overview of this popular research topic.”
Foth C 2020.
Introduction to the Morphology, Development, and Ecology of Feathers.
“The origin of feathers goes back deep into the Mesozoic, preceding the origin of flight, and early protofeathers were probably present in the ancestral Tetanurae, Dinosauria, or even Ornithodira.”
‘Ornithodira‘ is a junior synonym of Reptilia in the large reptile tree (LRT, 1656+ taxa), since it contains Dinosauria + Pterosauria. I mention ‘taxon exclusion’ here because the addition of pertinent taxa separates dinosaurs from pterosaurs.
Lin GW, Li A and Chuong C-M 2020.
Molecular and Cellular Mechanisms of Feather Development Provide a Basis for the Diverse Evolution of Feather Forms.
“The important questions include the regional specification of feather tracts, the formation of periodically arranged feather buds and their anterior-posterior orientation, the formation of feather follicles, and the establishment of cyclic regeneration with clustered stem cells and dermal papilla.”
Rauhut OWM and Foth C 2020.
The Origin of Birds: Current Consensus, Controversy, and the Occurrence of Feathers.
“Research in the late 1900s has established that birds are theropod dinosaurs, with the discovery of feather preservation in non-avian theropods being the last decisive evidence for the dinosaur origin of this group.”
Sadly this is so despite the discovery of several Solnhofen theropod birds in the 1800s.
“Birds are part of Paraves, together with such well-known theropod groups as dromaeosaurids and troodontids; Paraves are part of Maniraptora, which furthermore include Oviraptorosauria, Therizinosauria, and Alvarezsauroidea; Maniraptora belong to Maniraptoriformes, which also include Ornithomimosauria; Maniraptoriformes are a subclade of Coelurosauria, to which Tyrannosauroidea and some other basal taxa also belong; Coelurosauria are part of Tetanurae, together with Allosauroidea and Megalosauroidea; finally, Tetanurae are a subclade of Theropoda, which also include Ceratosauria and Coelophysoidea.”
The LRT finds a different tree topology for theropods transitioning to birds and basal birds transitioning to derived birds (Fig. 1). Note how two specimens attributed to Compsognathus are basal taxa in major theropod clades in the LRT. The theropod lineage that led to birds was never larger than Ornitholestes and likely smaller still as more small theropod taxa are added to the LRT.
Figure 4. Subset of the LRT focusing on the theropod-bird transition, distinctly different than in Hartman et al. 2019. Here in a fully resolved cladogram, birds and anchiornithids are monophyletic. Taxon inclusion resolves cladistic issues raised by Hartman et al.
Godefroit P et al. (5 co-authors) 2020.
Integumentary Structures in Kulindadromeus zabaikalicus, a Basal Neornithischian Dinosaur from the Jurassic of Siberia.
“Kulindadromeus zabaikalicus, a basal neornithischian dinosaur from the Jurassic of Siberia, preserves diverse integumentary structures, including monofilaments, more complex protofeather structures and scales on its tail and distal parts of its limbs. These exceptionally preserved specimens suggest that integumental features were diversified even in ornithischian dinosaurs and that “protofeather”-like structures were potentially widespread among the entire dinosaur clade.”
The LRT supports this hypothesis.
Xu X 2020.
Filamentous Integuments in Nonavialan Theropods and Their Kin: Advances and Future Perspectives for Understanding the Evolution of Feathers.
“The discovery of Sinosauropteryx in 1996 marks the beginning of a new era in the research on the origin and early evolution of feathers.”
True, but a century behind the discovery of feathered dinosaurs.
“Currently, there are still many issues that continue to be debated or remain unresolved, such as at what point in phylogeny the first feathers originated (e.g., at the base of Avemetatarsalia vs. within Theropoda), etc.”
‘Avemetatarsalia’, like ‘Ornithodira’ (see above) is a junior synonym for Reptilia in the LRT.
Foth et al. (4 co-authors) 2020.
Two of a Feather: A Comparison of the Preserved Integument in the Juvenile Theropod Dinosaurs Sciurumimus and Juravenator from the Kimmeridgian Torleite Formation of Southern Germany.
“Juravenator starki and Sciurumimus albersdoerferi … are preserved with phosphatized soft tissues, including skin and feathers. Both theropods possessed monofilamentous feathers and scaleless skin. In J. starki, short feathers could only be traced in the tail region. The tubercle-like structures, originally described as scales … were reinterpreted as remains of adipocere, maybe indicating the presence of a fat body. S. albersdoerferi was probably entirely plumaged, possessing a filamentous crest on the dorsal edge in the anterior tail section.”
In the LRT Juravenator nests between the large Compsognathus specimen (CN79) and feathered Therizinosauria + Oviraptoria, so it is should have had feathers. In similar fashion, feathered Sciurumimus nests between Ornitholestes and feathered Microraptor (Fig. 2) in the LRT.
Lefävre U, et al. (4 co-authors) 2020.
Feather Evolution in Pennaraptora.
“Here, we present a concise review of the plumage evolution within pennaraptora, the most inclusive clade containing Oviraptorosauria and Paraves.”
In the LRT this clade is a junior synonym for Compsognathidae.
“The feather-like structures in non-eumaniraptoran paravians were obviously not adapted for flight.”
In the LRT the bird mimics, Microraptor (Fig. 2) and Rahonavis are non-eumaniraptors.
“However, Microraptor and maybe some of its relatives preserve large pennaceous feathers along the limbs and tail, similar in morphology and organization to those in modern birds, so that they could have functioned in active flight or passive gliding.”
So the authors want it both ways? Microraptor (Fig. 2) and Sinornithosaurus both have elongate locked-down coracoids, so they were flapping, convergent with birds.
Figure 2. Microraptor gui (IVPP V 13352) reconstructed from tracings in figure 1. There are no surprises here, except a provisional closer relationship with Compsognathus than with Velociraptor. Microraptor has a large pedal claw two, but it is not quite the killing claw seen in droamaeosaurs.
Longrich NR, Tischlinger H and Foth 2020.
The Feathers of the Jurassic Urvogel Archaeopteryx.
“The Jurassic stem bird Archaeopteryx is an iconic transitional fossil, with an intermediate morphology combining features of non-avian dinosaurs and crown Aves.:”
Of the 13 Solnhofen specimens attributed to Archaeopteryx, no two are alike in the LRT. These authors put all 13 into a taxonomic wastebasket by not giving most of them a different genus.
“The hindlimbs bear large, vaned feathers as in Microraptor and Anchiornis. Feather morphology and arrangement in Archaeopteryx are consistent with lift-generating function, and the wing loading and aspect ratio are comparable to modern birds, consistent with gliding and perhaps flapping flight. The plumage of Archaeopteryx is intermediate between Anchiornis and more derived Pygostylia, suggesting a degree of flight ability intermediate between the two.”
In the LRT the pygostyle developed several times by convergence.
O’Connor J 2020. The Plumage of Basal Birds.
“Basal pygostylians show disparate tail plumages that are reflected by differences in pygostyle morphology.”
Pygostylia is not monophyletic in the LRT (see above).
Foth C 2020. A Morphological Review of the Enigmatic Elongated Tail Feathers of Stem Birds.
“Several stem birds, such as Confuciusornithidae and Enantiornithes, were characterized by the possession of one or two pairs of conspicuous, elongated tail feathers with a unique morphology, so-called rhachis-dominated racket plumes. As the rhachis-dominated racket plumes combine different morphologies that are apparent among modern feather types, this extinct morphotype does in fact not show any aberrant morphological novelties, but rather fall into the morphological and developmental spectrum of modern feathers.”
Smithwick F and Vinther J 2020. Palaeocolour: A History and State of the Art.
“From the overturning of the paradigm that lithified bacteria were responsible for vertebrate integumentary preservation to the development of analytical techniques used to probe pigment preservation, we review the origins and development of the field of palaeocolour.”
Campione NE, Barrett PM and Evans DC 2020. On the Ancestry of Feathers in Mesozoic Dinosaurs.
“Over the last two decades, the dinosaur fossil record has revealed much about the nature of their epidermal structures. These data challenged long-standing hypotheses of widespread reptile-like scalation in dinosaurs and provided additional evidence that supported the deeply nested position of birds within the clade. Ancestral state reconstructions demonstrate that irrespective of the preferred phylogenetic framework, the ancestral pterosaur condition or whether any one major dinosaur lineage had a Late Triassic-feathered representative, support values for a filamentous/feathered dinosaur ancestor are low.”
This contradicts Godefroit et al. from the same volume (see above). Phylogenetically pterosaurs have nothing to do with dinosaurs. Pterosaur ancestors (clade Fenestrasauria) developed morphologically different plumes and filaments by convergence.
If you want to see what the first feathers on the earliest naked dinosaurs looked like, the best clues come from embryo birds (Fig. 3). The outgroup for Dinosauria, the PVL 4597 specimen mistakenly attributed to Gracilisuchus, had parasagittal dorsal scutes lost thereafter in basal dinosaurs, like Herrerasaurus, but retained in basal bipedal crocodylomorphs, like Gracilisuchus and Scleromochlus.
Figure 3. Primordial feathers on the back of a 10-day-old chick embryo. Ontogeny recapitulates phylogeny in this pre-hatchling theropod.
The Solnhofen Archipelago was the Galapagos Islands of its day,
breeding at least 13 different Archaeopteryx-grade basal bird types, only one of which, Jurapteryx (the Eichstätt specimen, Fig. 4), gave rise to the one clade of birds that survives and flourishes today. If not for that single evolutionary variation, we would be surprised to see feathered theropods in the fossil record.
Figure 4. The Eichstätt specimen, Jurapteryx recurva, nests with the living ostrich, Struthio, presently in the LRT. It is the only lineage of Solnhofen birds still flying.
The following earlier posts may prove helpful
for those interested in the genesis and loss of feathers.
Foth C and Rauhut OWM (editors) 2020. The Evolution of Feathers: From Their Origin to the Present. Series: Fascinating Life Sciences, Year: 2020. Springer, Cham
Print ISBN: 978-3-030-27222-7 Online ISBN: 978-3-030-27223-4