|Kulindadromeus, the feathered ornithischian|
The first ever example of a plant-eating dinosaur with feathers and scales was reported from Russia in 2014. Previously only flesh-eating dinosaurs were known to have had feathers so this new find indicates that all dinosaurs could have been feathered. This has important implications for our understanding of the biology and success of dinosaurs and for the evolution of bird characters.
The new dinosaur, named Kulindadromeus zabaikalicus, meaning 'Kulinda runner from the Zabaikal region' as it comes from a site called Kulinda on the banks of the Olov River, in Zabaikal District, in Siberia, is described by Godefroit et al. (2014). Kulindadromeus shows epidermal scales on its tail and shins, and short bristles on its head and back. The most astonishing discovery, however, is that it also has complex, compound feathers associated with its arms and legs.
Kulindadromeus was a small plant-eater, only about 1m long. It had long hind legs and short arms, with five strong fingers. Its snout was short, and its teeth show clear adaptations to plant eating. In evolutionary terms, it sits low in the evolutionary tree of ornithischian dinosaurs. There are six skulls and several hundred partial skeletons of this new dinosaur at the Kulinda locality.
The Kulinda site was found in summer 2010 by Professor Sofia Sinitsa from the Institute of Natural Resources, Ecology and Cryology SB RAS in Chita, Russia. In 2013, the Russian-Belgian team excavated many dinosaur fossils, as well as plant and insect fossils.
The feathers were studied by Dr Maria McNamara and Professor Michael Benton of the University of Bristol, who has also worked on the feathers of Chinese dinosaurs, and Professor Danielle Dhouailly of the Université Joseph Fourier in Grenoble, France, who is a specialist on the development of feathers and scales in modern reptiles and birds.
Dinosaurs with feathersBirds arose from dinosaurs over 150 million years ago, so it was no surprise when theropod dinosaurs with feathers were found in China in 1996. But all those feathered dinosaurs were theropods, flesh-eating dinosaurs that include the direct ancestors of birds.
Two ornithischian dinosaurs have already been reported with feather-like structures, the early ceratopsian Psittacosaurus (Mayr et al. 2002) and the heterodontosaurid ornithopod Tianyulong (Zheng et al. 2009). In both cases, it is unclear whether these were true feathers, or some other epidermal appendage. Bristle-like epidermal appendages occur in pterosaurs, some early theropods, and extant mammals ('hairs'), and so the Psittacosaurus and Tianyulong filaments might have evolved independently of the feathers of theropods.
The specimens are notable for the excellent preservation of feathers and scales. There are three types of feathers, (1) monofilaments ('hairs') around the hed and trunk areas, measuring 1-3 cm long; (2) compound structures in which bunches of 6 to 7 filaments, each 10-15 mm long, attach to a basal plate, and located around the humerus and femur; and (3) ribbonlike structures, each up to 3 mm wide and 20 mm long and composed of about ten filaments.
There are also three types of scales: (1) tiny, nonoverlapping scales, 1 mm across, around the hand and foot; (2) larger, hexagonal scales, 3.5 mm across, on the shins; and (3) five longitudinal rows of slightly arched scales (~20 mm long and 10 mm wide) along the proximal part of the tail, overlapping each other.
The mix of feathers and scales shows that both epidermal structures could coexist, just as inmodern birds - chickens for example have scaly legs, and vultures and turkeys have scaly patches over their necks and heads. Developmental experiments in modern chickens suggest that bird scales are aborted feathers, an idea that explains why birds have scaly legs. Perhaps the molecular mechanisms needed for this switch might have existed already in Kulindadromeus.
This discovery suggests that feather-like structures were likely widespread in dinosaurs, possibly even in the earliest members of the group. Feathers probably arose during the Triassic, more than 220 million years ago, for purposes of insulation and signalling, and were only later co-opted for flight. Smaller dinosaurs were probably covered in feathers, mostly with colourful patterns, and feathers may have been lost as dinosaurs grew up and became larger. Feather loss is not surprising; it would have been analogous to the loss of hair in large mammals such as elephants, rhinos, and whales.
How do we know how old the dinosaurs are?The Kulinda locality is Middle to Late Jurassic in age, about 169-144 million years ago, and probably in the older part of this range, say from 169-150 million years ago. Its age is established from regional mapping in Siberia and from preliminary K/Ar dating. The Kulinda locality rocks belong to the lower part of the Ukureyksaya Formation, which covers large areas around Kulinda, and this geological formation (body of rocks with a certain thickness and geographic extent) is dated from associated plant and insect fossils which can be compared, and correlated, with fossils from other places to give the age. More exact study is needed, and perhaps some radiometric dates from the volcanic rocks at the Kulinda locality to narrow down the age range more closely.
How does the age of these specimens compare with that of other feathered dinosaurs?The Russian feathered dinosaurs are similar in age to some of the feathered Chinese dinosaurs, such as Anchiornis from the Tiaojishan Formation in NE China. In fact, neither the Russian nor the Chinese rock formations are really well dated, and it will take further work by geologists in both China and Russia to determine the ages of the rocks better, and then to discover whether the Kulinda or Tiaojishan fossils are older.
What environments did they live in?The Kulinda dinosaur bones are associated with abundant, well preserved fossils of plants, insect larvae, and freshwater crustaceans that suggest deposition in a low-energy, likely lacustrine, fresh-water environment. Probably Kulindadromeus fed on the plants that are found with it, including conifers, seed ferns, and horsetails. The dinosaur bones are not in the form of complete skeletons, which indicates that the bones have been transported by rivers, but not far, because some elements are associated, such as bones of an arm or leg, and the skin, bearing scales and feathers, is close to the relevant bones.
How are the feathers preserved?The feathers and scales are preserved as carbon-rich films on the rock. These show three types of scales on the lower legs and along the tail, and three types of feather-like structures. The carbon within the feathers and scales appears to have survived (but not necessarily the original biomolecules such as proteins), and so the fine detail of the scales and feathers is preserved with high fidelity.
Why are the feathers preserved?Normally hair, scales, and feathers disappear during fossilization. This usually happens very early in the long road from the dead animal to the fossil. After the dinosaur died, its carcass would have been picked over by scavengers, including flesh-eating dinosaurs, and perhaps some early mammals, as well as insects. These might well remove all flesh from the bones over a week or so. In the case of the Kulinda dinosaurs, their carcasses did not undergo this scavenging phase, but they were probably washed away by a river and dumped on a slow-moving stretch, perhaps at a bend in the river. They were rapidly covered with muddy sand, and, together with plant and other debris, quickly buried. The mud seems to be still rich in organic matter, so this suggests that there was not a great deal of oxygen in these river-bottom sediments, and the whole site might have been black and sulphurous, so inhibiting further decay.
How important is this new locality?The Kulinda locality opens a new window on ecosystem evolution. Middle Jurassic terrestrial sites are very rare worldwide, being known mainly from England and China so far. To find a nearly complete ecosystem, from plants to dinosaurs, is very exciting, and each group of fossils requires detailed study. The fossils are also immensely abundant – there are dozens of dinosaur individuals represented - so a detailed ecosystem reconstruction can be made. Of course, to find diverse feather types in an ornithischian dinosaur is of key importance.
How common are ornithischians?Ornithischians represent about half of all dinosaurs, and all of them were plant-eaters. They include unarmoured, two-legged forms that ranged in length from 1-10 m, such as Iguanodon and Lambeosaurus. The most abundant were the hadrosaurs of the Late Cretaceous. Other ornithischians sported armour of various kinds, such as the stegosaurs, with bony plates and spikes down their backs and tails, the ankylosaurs, enclosed in a chain mail of armour plates, the thick-headed pachycephalosaurs, and the ceratopsians, with bony frills over their necks and horns over their eyes and snouts. There are 300 or more species of ornithischians so far known, and they have been found worldwide. Dinosaurs are, however, rare in Russia, with only isolated finds reported from Siberia before.
What is the key significance of the new find?The new find proves that all dinosaurs had feathers.
Up to now, feathers have been reported from numerous species of theropod dinosaurs, the flesh-eating groups, and this has confirmed a remarkable evolution in feather type and complexity through 50 million years of the Late Jurassic and Cretaceous. Feathers in theropods had begun as simple bristles that provided two functions: insulation and signalling (through bright colours and patterns). They were associated with miniaturization of the advanced theropods, called Paraves, and their wide experimentation with flight.
'Feathers' have been reported before in two ornithischians, Tianyulong and Psittacosaurus, but palaeontologists had been cautious about the significance of these because they appeared to be rather simple quills, and perhaps limited in extent over the body. Our new find shows that feathers occurred all over the body in a primitive ornithischian, and that there were three types of feathers, including branching, down-type feathers.
Reconstruction imagesReconstructions of this amazing dinosaur are here.
The official Science videoView here.
Summaries by Pascal Godefroit1. The The discovery in Kulinda, Siberia. View here.
2. The function of Kulindadromeus feathers. View here.
3. Inhibition mechanisms in the development of feather like structures of Kulindadromeus. View here.
4. Fossilisation in Kulinda. View here.
Overview by Maria McNamaraView here.
Copyright movie showing the dig site: https://www.dropbox.com/s/fn0hhslgvg0khjw/selection%20Kunlinda2.mov