While feathers have been known in
fossil Birds from the Mesozoic since the nineteenth century, they remain
extremely rare, with the vast majority of known specimens coming from a single
source, the Early Cretaceous Jehol Biota of northwest China, and the remainder
coming from a few other locations in Asia and Europe. To date no Bird with
preserved feathers has been described from the supercontinent of Gondwana,
which comprised the modern continents of South America, Africa, Antarctica,
Madagascar, India, Australia and New Zealand, forming an amalgamated landmass
covering much of the Southern Hemisphere during the late Mesozoic.
In a paper published in the
journal Nature Communications on 26 May 2015, Ismar de Souza Carvalho of the Departamento de Geologia at the Universidade Federal do Rio de Janeiro, Fernando Novas of
the Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’, Federico
Agnolín
and Marcelo Isasi of the Museo Argentino de Ciencias Naturales ‘Bernardino
Rivadavia’ and the Fundación de Historia Natural ‘Félix de Azara’ at the Universidad Maimónides, Francisco Freitas of Geopark Araripe and José Andrade of the Departamento Nacional da Produção Mineral describe a fossil Bird from the Early Cretaceous Crato Formation of
Brazil which possesses the first known feathers in any Mesozoic Bird from the
Southern Hemipshere.
The specimen is very small, about
6 cm in total length, and has large orbits and poor mineralization of the ends
of the long bones, for which reason it is thought to be a juvenile. It is not
assigned to a species or genus, but is recognized as an Enantiornithine, a
member of a group of Mesozoic Birds related to but not ancestral to the modern Neornithine
Birds, with a set of distinct features not found in any post-Mesozoic Birds,
including most notably the retention of a bony snout with teeth rather than an
keratinous beak.
Main slab and interpretative drawing of the Crato Bird specimen. (a)
Main slab. (b) Interpretative drawing of the skeleton and feathers. (c) Reconstructed
cross-section at the level of distal vanes of the feathers. (d) Reconstructed
cross-section at mid-length of the rachis. (e) Reconstructed cross-section of
the calamus. al, alula; cd, free caudal vertebrae; dv, dorsal vertebrae; fr,
frontals; lc, left coracoid; lcp, left carpometacarpus; lf, left foot; lh, left
humerus; lr, left radius; ls, left scapula; lu, left ulna; mx, maxilla; pub,
pubes; py, pygostyle; ra, rachis; rc, right coracoid; rh, right humerus; rr,
right radius; rt, right tibiotarsus; rtmt, right metatarsals; ru, right ulna;
sp, colour spots; v, vanes. Dark grey represents the vanes, light grey represents
the scapus. Scale bar is 10 mm. De Souza Carvalho et al. (2015).
One distinctive feature of the Jehol
Bird is the presence of a pair of enlarged ‘ribbon feathers’ on the tail. All
modern Birds, and some Enantiornithines, posses a tail comprising a fan of
feathers, but other Enantiornithines, as well as Confuciusornithids (another
group of Mesozoic Birds) posses tails comprising a single pair of elongate
‘ribbon feathers’. These are morphologically distinct from any feathers, with a
wide flattened middle part with a line down it, interpreted variously as a central
rachis (vein) surrounded by fused and undifferentiated vanes, or an flattened
and expanded rachis with a central groove. To date no fossil exhibiting this
has preserved the feathers in a way in which this could be resolved, but the
ribbon-feathers of the Crato Bird are preserved in relief, allowing examination
of their structure, which does indeed appear to comprise a flattened and
laterally expanded rachis for much of its length, a structure quite unlike
anything seen in modern Birds, and in some ways intermediate between a modern
Bird’s feather and a greatly extended Reptilain scale.
Details of tail feather of the Crato Bird specimen. (a) Proximal end.
(b) Distal end. cal, calamus; lg, longitudinal groove; ra, rachis; sp, colour
spot; v, vane. Scale bar is 2.5 mm. De Souza Carvalho et al. (2015).
See also…
The Crato Formation outcrops on the northern flanks of the Chapada do Araripe, a plateaux on the border between Ceará, Pernambuco andPiauí States in northern Brazil. In is noted for its exceptionally well preserved fossils, which include Dinosaurs, Crocodiles, Fish, Pterosaurs, Crustaceans, Arachnids, Plants...
The Early Cretaceous Jehol Group of China has produced a remarkable number of well-preserved fossils of Mesozoic Birds, adding greatly to our understanding of the early history of this group...
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