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Iridescence is responsible for some of the most striking visual displays in the animal kingdom. Now, thanks to a new study of feathers from almost 100 modern bird species, scientists have gained new insights into how this colour diversity evolved.

Two of the fossils sampled for the study with the fossil melanosomes found in each fossil (scanning electron microscope images). Scaniacypselus to the left and Primotrogon to the right. Melanosome shape varies in the different samples, and is indicative of colour. The sample furthest to the left was predicted as iridescent [Credit: Jakob Vinther & Fiann Smithwick]

Iridescence refers to the phenomena where colour changes when an object is viewed from different angles. Birds produce this varying coloration in their feathers by using nanoscale arrays of melanin-filled organelles (melanosomes) layered with keratin. In this form of structural colouration, the shapes of melanosomes together with the thickness of keratin layers determine what colour is produced.

While melanosome morphology has previously been used to predict colour in fossil animals, melanosome variation in iridescent feathers has not been analysed on as large a scale until this study.

As reported in the journal Evolution, a team of University of Bristol researchers used scanning electron microscopy to quantify melanosome extracts from the feathers of 97 species of modern birds with iridescent plumage, taken from the collections of the Zoological Museum of Copenhagen.

The study showed that iridescent feathers contain the most varied melanosome morphologies of all types of bird coloration sampled to date. Unlike black, grey and brown feathers that always contain solid melanosomes, iridescent feathers can contain melanosomes that are hollow and/or flattened.

Scaniacypselus fossil (above) compared with its modern day equivalent, the Plume-toed Swiftlet [Credit: Fossil: Jakob Vinther & Fiann Smithwick/Daniel Field]

"We found that melanosomes in modern iridescent feathers are more diverse in shape than those found in grey, black or brown feathers combined (that also contain melanosomes)," said lead author Klara Nordén, who conducted the study during her undergraduate years at Bristol's School of Earth Sciences. "It is already known that structural colouration is responsible for 70 per cent of the colour variability in birds. These two facts might be coupled -- birds evolved varied forms of melanosomes to achieve ever greater diversity in colour.

"I wanted to find out if we could improve current predictive models for fossil colour based on melanosome morphology by including all types of melanosomes found in iridescent feathers."

Dr Jakob Vinther, co-author of the study and a leading researcher in the field of paleocolour at Bristol's School of Biological Sciences, had already collected the perfect fossil samples to test the new model on.

"We had sampled Scaniacypselus, related to modern tree swifts, and Primotrogon, ancestor to modern trogons. These groups are iridescent today and have flat and hollow melanosomes. Did their 48-million-year-old ancestors from Germany also have iridescent plumage?"

Primotrogon fossil (above) compared with its modern day equivalent, the Narina Trogon [Credit: Fossil: Jakob Vinther & Fiann Smithwick/Daniel Field]

Interestingly, the model predicted that Primotrogon probably was iridescent, but it used solid rather than hollow melanosomes, unlike its modern descendants.

"This demonstrates how we now have the tools to map out the evolution of iridescence in fossil lineages," said Klara, who is now a PhD student at Princeton University. "It opens the door to many new discoveries of dazzling displays in fossil birds and other dinosaurs."

The current study focused on mapping out how melanosomes vary in iridescent feathers. Further avenues of research might examine why birds utilise such diversity of melanosome types in iridescent feathers. These insights could ultimately enhance our understanding of why fossil birds or dinosaurs might have used such morphologies, revealing something about their behaviour.

Source: University of Bristol [December 10, 2018]

Paleontologists from Russia have described a new dinosaur, the Volgatitan. Seven of its vertebrae, which had remained in the ground for about 130 million years, were found on the banks of the Volga, not far from the village of Slantsevy Rudnik, five kilometers from Ulyanovsk. The study has been published in the latest issue of Biological Communications.

Volgatitan simbirskiensis anterior caudal vertebra (holotype), in right lateral (A), anterior (B), left lateral (C), posterior (D), dorsal (E), and ventral (F) views [Credit: Alexander Averianov and Vladimir Efimov]

The Volgatitan belongs to the group of sauropods - giant herbivorous dinosaurs with a long neck and tail, who lived on Earth about 200 to 65 million years ago. Weighing around 17 tons, the ancient reptile from the banks of the Volga was not the largest among its relatives. The scientists described it from seven caudal vertebrae. The bones belonged to an adult dinosaur which is manifested by neural arches (parts of the vertebrae protecting the nerves and blood vessels), which completely merged with the bodies of the vertebrae.

The remains of the dinosaur were discovered near the village of Slantsevy Rudnik. This is where, in 1982, Vladimir Efimov discovered three large vertebrae that had fallen out of a high cliff. Later, in 1984-1987, three nodules of limestone fell off, which contained the remaining vertebrae. In his works, the head of the Undorovsky Paleontology Museum called the unusual finds "giant vertebrae of unknown taxonomic affiliation".

"In the early 1990s, Vladimir Efimov showed photographs of the bones to Lev Nesov, a well-known Leningrad paleontologist," recollected Alexander Averianov. Lev Nesov thought that the vertebrae belonged to sauropods, giant herbivorous dinosaurs. In 1997, Vladimir Efimov published a preliminary note about this find in the Paleontological Journal. He referred to the vertebrae as a sauropod of the Brachiosauridae family. Last July, I finally managed to visit him in Undory and study the bones, and also managed to determine that they belonged to the new taxon of titanosaurs."

The dinosaur received a scientific name - Volgatitan simbirskiensis. It comes from the Volga River and the city of Simbirsk (currently, Ulyanovsk). Titans are ancient Greek gods known for their large size. Therefore, according to a paleontological tradition, this word is used in many scientific names of sauropods from the group of titanosaurs. It is also part of the name of the group.

Today, along with the Volgatitan from Russia, 12 valid dinosaur taxa have already been described. There are only three sauropods among them: Tengrisaurus starkovi, Sibirotitan astrosacralis and Volgatitan simbirskiensis. The first two are the first sauropods in Russia, which were also studied by St Petersburg University scientists in 2017. According to Aleksandr Averianov, the description of dinosaur taxa in recent years has become possible due to the progress in understanding the anatomy and phylogeny of dinosaurs. In addition, the Russian sauropod allowed scientists to learn more about how these species of ancient reptiles had lived and developed.

"Previously, it was believed that the evolution of titanosaurs took place mainly in South America with some taxa moving into North America, Europe and Asia only in the Late Cretaceous," explained the St Petersburg University professor. In Asia, representatives of a broader group of titanosauriform, such as the recently described Siberian titanium, dominated in the early Cretaceous. However, the recent description of the Tengrisaurus from the Early Cretaceous of Transbaikal Region and the finding of the Volgatitan indicate that titanosaurs in the Early Cretaceous were distributed much more widely; and, perhaps, important stages of their evolution took place in Eastern Europe and Asia."

Source: Akson Russian Science Communication Association [December 06, 2018]

An ancient, dolphin-like marine reptile resembles its distant relative in more than appearance, according to an international team of researchers that includes scientists from North Carolina State University and Sweden's Lund University. Molecular and microstructural analysis of a Stenopterygius ichthyosaur from the Jurassic (180 million years ago) reveals that these animals were most likely warm-blooded, had insulating blubber and used their coloration as camouflage from predators.

Spectacular soft-tissue fossil (MH 432; Urweltmuseum Hauff, Holzmaden, Germany). Cells, cellular organelles and original  biomolecules have been discovered in preserved soft parts of an approximately 180-million-year-old ichthyosaur (literally 'fish-lizard'). Photographic (top) and diagrammatic (bottom) representation of the 85-cm-long fossil (which corresponds to roughly half of the original length of the animal) [Credit: Johan Lindgren]

"Ichthyosaurs are interesting because they have many traits in common with dolphins, but are not at all closely related to those sea-dwelling mammals," says research co-author Mary Schweitzer, professor of biological sciences at NC State with a joint appointment at the North Carolina Museum of Natural Sciences and visiting professor at Lund University. "We aren't exactly sure of their biology either. They have many features in common with living marine reptiles like sea turtles, but we know from the fossil record that they gave live birth, which is associated with warm-bloodedness. This study reveals some of those biological mysteries."

Johan Lindgren, associate professor at Sweden's Lund University and lead author of a paper describing the work, published in Nature, put together an international team to analyze an approximately 180 million-year-old Stenopterygius fossil from the Holzmaden quarry in Germany.

"Both the body outline and remnants of internal organs are clearly visible," says Lindgren. "Remarkably, the fossil is so well-preserved that it is possible to observe individual cellular layers within its skin."

Researchers identified cell-like microstructures that held pigment organelles within the fossil's skin, as well as traces of an internal organ thought to be the liver. They also observed material chemically consistent with vertebrate blubber, which is only found in animals capable of maintaining body temperatures independent of ambient conditions.

Lindgren sent samples from the fossil to international colleagues, including Schweitzer. The team conducted a variety of high-resolution analytical techniques, including time-of-flight secondary ion mass spectrometry (ToF SIMS), nanoscale secondary ion mass spectrometry (NanoSIMS), pyrolysis-gas chromatography/mass spectrometry, as well as immunohistological analysis and various microscopic techniques.

Schweitzer and NC State research assistant Wenxia Zheng extracted soft tissues from the samples and performed multiple, high-resolution immunohistochemical analyses. "We developed a panel of antibodies that we applied to all of the samples, and saw differential binding, meaning the antibodies for a particular protein -- like keratin or hemoglobin -- only bound to particular areas," Schweitzer says. "This demonstrates the specificity of these antibodies and is strong evidence that different proteins persist in different tissues. You wouldn't expect to find keratin in the liver, for example, but you would expect hemoglobin. And that's what we saw in the responses of these samples to different antibodies and other chemical tools."

Lindgren's lab also found chemical evidence for subcutaneous blubber. "This is the first direct, chemical evidence for warm-bloodedness in an ichthyosaur, because blubber is a feature of warm-blooded animals," Schweitzer says.

Taken together, the researchers' findings indicate that the Stenopterygius had skin similar to that of a whale, and coloration similar to many living marine animals -- dark on top and lighter on the bottom -- which would provide camouflage from predators, like pterosaurs from above, or pliosaurs from below.

"Both morphologically and chemically, we found that although Stenopterygius would be loosely considered 'reptiles,' they lost the scaly skin associated with these animals -- just as the modern leatherback sea turtle has," Schweitzer says. "Losing the scales reduces drag and increases maneuverability underwater.

"This animal's preservation is unusual, especially for a marine environment -- but then, the Holzmaden formation is known for its exceptional preservation. This specimen has given us more evidence that these tissues and molecules can preserve for extremely long periods, and that soft tissue analysis can shed light on evolutionary patterns, relationships, and how ancient animals functioned in their environment.

"Our results were repeatable and consistent across labs. This work really shows what we're capable of discovering when we perform a multidisciplinary, multi-institutional study of an exceptional specimen."

Source: North Carolina State University [December 05, 2018]

A team of scientists led by Jingmai O'Connor from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), Chinese Academy of Sciences, reported the first occurrence of medullary bone in Enantiornithes, the dominant clade of birds during the Cretaceous.

Main slab of Pengornithid Enantiornithine, preserved in three-dimensions unlike most compression fossils  from the Jehol Biota. Scale bar is one centimetre [Credit: Jingmai O'Connor]

Medullary bone is a bone tissue unique to birds today. It is present only in females about to lay eggs and forms in the empty spaces within the skeleton. This bone tissue serves as a reservoir for calcium needed to form the eggshell. Medullary bone has been reported in a variety of non-avian dinosaurs including Tyrannosaurus rex, ornithopod dinosaurs like Tenontosaurus, and several sauropods (huge long-necked dinosaurs) including Mussasaurus. It has also been identified in pterosaurs, which are flying reptiles closely related to dinosaurs.

Since the first report of medullary bone in a Mesozoic fossil in 2005, this tissue has attracted great interest because it links birds and dinosaurs. However, the presence of this bone tissue in pterosaurs and non-avian dinosaurs is perplexing. Non-avian dinosaurs were so large and their eggs so small that they shouldn't have required medullary bone. Since pterosaurs laid soft-shelled eggs, they also shouldn't have required medullary bone.

Cross section of the femur bone viewed under polarized light showing the thick layer of medullary bone within the medullary cavity [Credit: Jingmai O'Connor]

Some reported instances of medullary bone are probably actually bone pathologies causing abnormal growth. However, in this report, IVPP scientists, working together with Mark Norell from the American Museum of Natural History and Greg Erickson from Florida State University, argued that no previous description of medullary bone in a Mesozoic reptile was well supported.

The new report is the best support for medullary bone in the Mesozoic so far since it was found throughout the entire preserved skeleton, suggesting it was part of a system-wide process rather than a local pathology. However, the authors concede that scientists still know too little about medullary bone to confirm, without additional evidence (e.g., association with a nest or eggs), that the fossilized individual with this tissue was reproductively active.

In light of the currently available evidence, medullary bone might have been an entirely avian feature even in the Mesozoic. It evolved as a result of the thinned, hollow bones in birds, which lightened the skeleton for flight, as well as their increased egg size.

The findings were published in Nature Communications.

Source: Chinese Academy of Sciences [December 05, 2018]