Friday, August 5, 2016

Burmese Amber Reveals 99-Million-Year-Old Bird Wings

Scientists have known for some time that many species of dinosaur had feathers, most preserved in a two dimensional state as a result of fossilization

In normal fossilization activities, feathers are sometimes hard to interpret, as faint impressions in association with a complete skeleton, or in isolation.

The 1996 discovery of Sinosauropteryx, the first Chinese feathered dinosaur ever found, brought to light some of these difficulties. Some researchers at that time interpreted the filamentous impressions along Sinosauropteryx’s neck and back as remains of collagen fibers, rather than primitive feathers themselves (source: Wikipedia).  

Photo Credit:Wikipedia

Less than two years after the original description of Sinosauropteyx, two other spectacular feathered dinosaurs from Liaoning were reported. The 125-million-year-old turkey-sized Caudipteryx and slightly smaller Protarchaeopteryx were both found to unquestionably possess short, down like plumulaceous feathers as well as symmetrically vaned feathers. The strikingly modern appearance of these feathers, combined with the fact that the vanes have retained their integrity, suggests that the system of interlocking hooked and grooved barbules maintaining the planar geometry of modern vanes had amazingly already developed (**source: Glorified Dinosaurs, The Origin and Early Evolution of Birds. Luis M. Chiappe. 2007**).

Since then, a countless number of feathered dinosaurs have been discovered, many of which appear to be side branches in the bird family tree. Species such as Microraptor, Pedopenna and Anchiornis were all found covered in feathers. These include pennaceous feathers (with barbules) on the forearms and tail, as well as semiplumes and down-like feathers on the rest of the body. The purpose of feathers was originally thought to have provided insulation (thermoregulation) for these animals, co-opted later for sexual display, and for some, flight itself.   

In addition to the plumulaceous feathers covering its body, Microraptor had large, asymmetric pennaceous feathers (flight feathers) attached to its distal tail, forelimb, and most surprisingly, its hindlimb.

Photo Credit: Wikipedia

Equally surprising to paleo researchers is the latest discovery of two mummified bird wings found embedded in mid-Cretaceous Burmese amber. Published on 28 June 2016, the articles abstract introduces this incredible find to the world;

Our knowledge of Cretaceous plumage is limited by the fossil record itself: compression fossils surrounding skeletons lack the finest morphological details and seldom preserve visible traces of color, while discoveries in amber have been disassociated from their source animals. Here we report the osteology, plumage and pterylosis of two exceptionally preserved theropod wings from Burmese amber, with vestiges of soft tissues. The extremely small size and osteological development of the wings, combined with their digit proportions, strongly suggests that the remains represent precocial hatchlings of enantiornithine birds.

(**Enantiornithes is a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic Era. Almost all retained teeth and clawed fingers on each wing, but otherwise looked much like modern birds externally.

Enantiornithes Clawed Finger
Photo Credit: Paul Cianfaglione

Enantiornithes are thought to have left no living descendants. Source: Wikipedia.**)

These specimens demonstrate that the plumage types associated with modern birds were present within single individuals of Enantiornithes by the Cenomanian (99 million years ago), providing insights into plumage arrangement and microstructure alongside immature skeletal remains. This finding brings new detail to our understanding of infrequently preserved juveniles, including the first concrete examples of follicles, feather tracts and apteria in Cretaceous avialans (source; Nature Communications 7, article number: 12089).


See complete article below;

The introduction goes on to describe the rare preservation;

The mid-Cretaceous Burmese amber deposit of northeastern Myanmar is one of the most prolific and well-studied sources of exceptionally preserved Mesozoic arthropod and plant fossils, but work on feathers from this deposit has just begun. Previous studies of plumage in Cretaceous amber have been based on isolated feathers, leaving taxonomy of the feather-bearers open to debate and amber in vertebrate bone beds has seldom yielded fossils. Otherwise, Cretaceous feathers are commonly known from carbonaceous compression fossils, and three-dimensional preservation in amber is extremely rare. The combined fossil record of amber and compression fossils has provided many insights into how the feather types associated with modern bird’s developed but these glimpses are restricted by preservation in each fossil type. The discovery of two partial bird wings in Burmese amber unites taxonomic and ontogenetic information from osteology with microscopic preservation down to the level of individual feather barbules and their pigment distributions. This new source of information includes integumentary features incompletely known in the compression fossil record (source; Nature Communications 7, article number: 12089).   

The article goes on to show, with photomicrographs, that most of the feather types found in modern birds were already present in animals some 90 million-years-ago.

Of utmost importance to me were the photos depicting the actual interlocking of barbs, or more precisely, the barbules and hooklets. These findings, both the interlocking of barbules and feather asymmetry, are consistent with feathers that are being used in powered flight.   

My own personal Burmese feather inclusion clearly depicts those same type of interlocking barbs.

Burmese Feather Inclusion
Photo Credit: Paul Cianfaglione
Mourning Dove Contour Feather
Photo Credit: Paul Cianfaglione
Also amazing were the stark similarities between the 99 million-year-old feather and a modern feather under a microscope. Aside from the narrowness of the rachis on the amber feather, I found it impossible to decipher any real differences among the two feathers. 

Details of ancient bird feathers have mostly been restricted to compression fossils.

Compression Feather Fossil
Liaoning Province, China
Photo Credit: Paul Cianfaglione
The discovery of two 99 million-year-old wings encased in amber is like a dream come true for scientists, on par with the discovery of Sinosauropteryx.

Scientists at this point have confirmed that most feather types found in modern avialans were likely also present in Enantiornithes, with comparable feather arrangement and microstructure. These findings are consistent with recent work on preserved soft tissues and plumage within larger compression fossils of an enantiornithine wing from the Early Cretaceous of Spain (source; Nature Communications 7, article number: 12089).