Sinosauropteryx prima

Sinosauropteryx prima is the only known species of the extinct genus Sinosauropteryx (Chinese lizard with wings") of a feathered compsognathid theropod dinosaur, which lived in the middle of the Cretaceous period, approximately 120 million years ago, in the Aptian, in what is now Asia. It inhabited China during the Early Cretaceous and was probably a close relative of Compsognathus. It was the first genus of dinosaur found in the Jehol Biota in Liaoning Province. Described in 1996, it was the first dinosaur taxon outside of Avialae, birds and their immediate relatives, to be found with evidence of feathers. The extremely well-preserved fossil shows that Sinosauropteryx was covered with a layer of very simple feathers, although some controversy presented an alternative interpretation of the filamentous imprint as collagen fibers, but this has not been widely understood. accepted. These filaments consisted of a simple two-branched structure, very similar to the primitive secondary feathers of the modern kiwi. Structures indicating coloration have also been preserved in some of their feathers, making Sinosauropteryx the first non-avian dinosaurs where coloration has been determined. The coloration includes a reddish tail with light bands. certain has emerged

Sinosauropteryx was a small theropod with an unusually long tail and short arms. The longest known specimen reaches up to 1.07 meters long, with an estimated weight of 0.55 kilograms. It was a close relative of the similar but older genus Compsognathus, both genera belonging to the family Compsognathidae. Only one species of Sinosauropteryx has been named, S. prima, which means "first" in reference to its status as the first non-avian feathered dinosaur species discovered. Three specimens have been described. The third specimen previously assigned to this genus represents a second, as-yet-unnamed species, or a distinct related genus.

Sinosauropteryx lived in what is now northeastern China during the early Cretaceous period. It was one of the first dinosaurs discovered in the Yixian Formation in Liaoning Province and was a member of the Jehol Biota. Well-preserved fossils of this species illustrate many aspects of its biology, such as its diet and reproduction.

Description

Sinosauropteryx was a small bipedal theropod, known for its short arms, large index finger that functions as a thumb, and long tail. The taxon includes some of the smallest known adult non-avian theropod specimens with the holotype specimen measuring only 68 centimeters long including the tail. However, this individual was relatively young. The longest known specimen reaches up to 1, 07 meters long, with an estimated weight of 0.55 kilograms.

Sinosauropteryx was anatomically similar to Compsognathus, differing from its European relatives in its proportions. The skull of Sinosauropteryx was 15% longer than the thigh bones, unlike Compsognathus, where the skull and thigh bones are approximately equivalent in length. The arms of Sinosauropteryx, humerus and radius, were only 30% the length of its legs, femur and tibia, compared to 40% in Compsognathus. In addition, Sinosauropteryx had several unique characteristics among all other theropods. It had 64 vertebrae in its tail. This high number made its tail the longest relative to body length of any theropod. Its hands were long compared to its arms, about 84% to 91% of the length of the rest of the arm, humerus and radius, and half the length of the foot. The first and second digits were approximately the same length, with a large claw on the first digit. The first fingers were large, longer and thicker than any of the forearm bones. The teeth differed slightly, being heterodont, according to the position: those near the tips of the upper jaws, on the premaxillaries, were thin and lacked serrations, while those behind them, on the maxillae, were serrated and laterally compressed. The teeth of the lower jaws were equally differentiated.

A pigmented area on the abdomen of the holotype has been suggested as possible traces of organs, and John Ruben and his colleagues interpreted this as the liver, which they described as part of a respiratory system of " hepatic piston " similar to a crocodile. A later study, although agreeing that the pigmented area represented something originally within the body, found no defined structure and noted that any organ would have been distorted by processes that flattened the skeleton into an essentially two-dimensional. Dark pigment is also present in the eye region of the holotype and in another specimen.

Feathers

All specimens of Sinosauropteryx preserve integumentary structures, filaments emerging from the skin, which paleontologists have described as primitive feathers. These short, down-like filaments are preserved along the back half of the skull, the arms, the neck, the back, and the tail below and above. Additional patches of feathers have been identified on the sides of the body, and paleontologists Chen, Dong and Zheng proposed that the density of feathers on the back and the randomness of patches to other parts of the body indicate that the animals would have been completely feathered in life, the ventral feathers not being preserved in the specimens fossilized by decomposition.

The filaments are preserved with a space between the bones, which several authors have noted corresponds closely to the expected amount of skin and muscle tissue that would have been present in life. According to several authors, the attachment of the filaments is closer to the bones in regions where there is little or no muscle, such as the skull and the end of the tail, while it is more separated from the bones in areas with greater musculature, as occurs in the posterior vertebrae, which seems to clearly indicate that they were arranged on the skin and were not subcutaneous structures.

The random placement of the filaments and preservation often in 'wavy' lines, indicate that they were soft and flexible in life. Microscopic examination demonstrates that each individual filament appears dark along the edges and light internally, suggesting that they were hollow, like modern feathers. Compared to modern mammals the filaments were excessively thick, with each individual filament much larger and denser than the corresponding hairs of mammals of the same size.

The length of the filaments varies depending on their position in the body. They were shorter near the eyes, with a length of 13 millimeters. Along the body, the filaments rapidly increase in length until they reach 35 millimeters long at the withers. The length is uniform over the back until beyond the hips, where the filaments lengthen again and halfway down they reach the maximum length at the end of the tail with 40 millimeters. The filaments on the underside of the tail are shorter and the decrease in length occurs more rapidly than on the dorsal surface. On the lower surface at the height of the twenty-fifth tail vertebra, the filaments reach a length of only 35 millimeters. The longest feathers present on the forearm measured 14 millimeters.

Although the feathers are too dense to isolate a single structure for examination, several studies have suggested the presence of two distinct types of filament, thick and fine, intermingled. The tendency is for the thick filaments to appear stiffer than the thin filaments, and the tendency for the thin filaments to be parallel to each other but at an angle to the nearby thick filaments suggests that the individual feathers consisted of a central rachis with the thinner like baleen, branching from it, similar to but more primitive than the structure of the feathers of modern birds. Superficially, the filaments resemble "downs" or inner feathers of some modern birds, with a thick central quill and long, thin barbs. The same structures are seen in other fossils from the Yixian Formation, including Confuciusornis.

However, a 2018 study considered that thick filaments could simply be bundles of thin filaments overlapping each other. This possibility is supported by the observation that thin filaments tend to run parallel to each other and to thick filaments, rather than branching as identified by previous authors. Some of the thick filaments are quite long but end in small strands of thin filaments. The plumaceous, down-like plumage typically has an opposite appearance, with a short central feather and long tufts. Furthermore, the thick filaments preserve no evidence of calcium phosphate, the mineral from which modern feathers are made. The large amount of curvature present in the filaments also makes a strong central calamus unlikely. Therefore, the idea that thick filaments are simply bundles of thin filaments is less unusual than the idea that they were a variant of plumaceous feathers that evolved a morphology opposite to that of birds and other feathered theropods. Overall, the study preferred the hypothesis that Sinosauropteryx feathers were simple single-branched filaments, although it is conceivable that they were occasionally joined together at the base into tufts as predecessors to the down-like plumaceous feathers..

While Sinosauropteryx had feather-like structures, it was not closely related to the earlier "first bird" Archaeopteryx. There are many clades of dinosaurs that were more closely related to Archaeopteryx than to Sinosauropteryx, including deinonycosaurians, oviraptorosaurians, and therizinosauroids. This indicates that feathers may have been a feature of many theropod dinosaurs, not just those that obviously look like birds, making it very likely that similarly distant animals like Compsognathus also had feathers.

Some researchers have interpreted the filamentous impressions around the Sinosauropteryx fossils as remains of collagen fibers, rather than primitive feathers. Since they are clearly external to the body, these researchers have proposed that the fibers formed a sail on the animal's back and on the undersurface of its tail, similar to that of some modern aquatic lizards.

This would refute the proposal that Sinosauropteryx is the most basal known genus of feathered theropod, and also challenges current theory about the origins of feathers itself. It challenges the proposal that the first feathers evolved not for flight but for insulation, and that they made their first appearance in the relatively basic dinosaur lineages that later evolved into modern birds.

Coloration

Fossils of Sinosauropteryx have alternating light and dark bands on the tail, which may be indicative of what the animal looked like in life. Chen and colleagues initially interpreted this banding pattern as a result of the breakdown of the stone matrix containing the fossil. However, at the 2002 Society of Vertebrate Paleontology conference, paleontologist Nick Longrich suggested that these bands of coloration are remnants of the original color of the specimens that the animal would have actually exhibited in life. He maintained that the dark bands on the tail were spaced too evenly to have originated from the separation of fossil slabs, and that they represented fossilized pigments present in the feathers. Furthermore, the presence of dark feathers along only the upper part of the body may also reflect the color pattern in life, indicating that Sinosauropteryx prima had a contrasting coloration, dark on its upper part and lighter on its back. its lower surface, with bands or stripes on the tail for camouflage.

In January 2010, the journal Nature published an article by a team of paleontologists led by Michael Benton from the University of Bristol, England, and Zhonghe Zhou from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China. This is a milestone for paleontology because they are the first demonstrable evidence of color in fossil saurians. This article presents the discovery of color-producing organelles in the feathery structures of this fossil. The only fossils known up to this time with the presence of these pigment-producing organelles, called melanosomes, had been birds. The team discovered two types of melanosomes in the structure of the feathers, if these primitive structures can be called that, from the fossil from the Jehol site, Laioning province, in northeastern China, on the one hand sausage-shaped organelles called eumelanosomes that today They are seen in the stripes of zebras and the black masks of American birds known as cardinals, and spherical organelles called phaeomelanosomes, which produce and store the reddish-rust pigment in some falcons and in human red hair.

Fossils of this theropod dinosaur reveal that stripes of light and dark feathers alternated along its tail. The team found that the feathers that developed in the darker-appearing regions on the tails of the fossils had numerous phaomelanosomes, indicating that they were reddish-orange in color. Possibly the feathers that grew in the stripes that have been fossilized in light color were white, although this has not been proven. The same article reveals that Sinosauropteryx was not the only species with colored feathers. Another small theropod, Sinornithosaurus, also had filamentous pseudofeathers with the presence of eumelanosomes or pheomelanosomes, which allows us to deduce that the color of those structures similar to feathers could be black in some cases and reddish-orange in others..

Fucheng Zhang and his colleagues examined the fossilized feathers of several dinosaurs and early birds and found evidence that they preserved melanosomes, the cellular components that give bird feathers their color. Among the specimens studied was a previously undescribed specimen of SinosauropteryxIVPP V14202. By examining the structure and distribution of melanosomes, Zhang and his colleagues were able to confirm the presence of light and dark color bands in the tail feathers of Sinosauropteryx. Additionally, the team was able to compare melanosome types with those of modern birds to determine a general range of colors. From the presence of pheomelanosomes, spherical melanosomes that produce and store red pigment, they concluded that the darkest feathers of Sinosauropteryx were chestnut or reddish brown. More research on the coloration of Sinosauropteryxreveal that it had a raccoon-like bandit mask and shading patterns likely associated with open habitat, indicating that Jehol likely had a variety of habitat types.

Discovery and research

The first fossil that would later be called Sinosauropteryx prima was unearthed in August 1996 by Li Yumin. Yumin is a farmer and part-time fossil hunter who often explored Liaoning Province looking for fossils to sell to people and museums. Yumin recognized the unique quality of the specimen, which was separated into two slabs, and sold the slabs to two different museums in China: the National Geological Museum in Beijing, and the Nanjing Institute of Geology and Paleontology. Beijing museum director Ji Qiang recognized the importance of the find, as did visiting Canadian paleontologist Phil Currie and artist Michael Skrepnick, who discovered the fossil by chance while exploring the Beijing Museum's collections. After conducting an expedition to the area during the first week of October 1996, Currie recognized the fossil's importance immediately. He declared to the New York Times: & # 34; When I saw this slab of silt stone mixed with volcanic ash that the creature fit into, I was stunned. When it was originally described, the authors called Sinosauropteryx which means 'Chinese Reptile Wing.';.

Three specimens have been assigned to Sinosauropteryx prima: The holotype GMV 2123 and its counterplate, the other half of the slab, NIGP 127586, NIGP 127587 and D 2141. Another specimen, IVPP V14202, was assigned to the genus but not the sole species by Zhang and colleagues. It was later discovered that the assignment of an additional larger specimen toS. cousinwas a mistake. [13] [14] The assignment of a fourth, larger specimen, GMV 2124, to S. primawas the product of an error. All fossils come from the Jianshangou and Dawangzhangzi beds of the Yixian Formation in Liaoning, China. These beds are dated between 124.6 to 122 million years ago, during the late Barremian to early Aptian during the Early Cretaceous.

The Chinese authorities initially prevented the publication of photographs of the specimen. However, Currie brought a photograph to the 1996 meeting of the Society of Vertebrate Paleontology at the American Museum of Natural History in New York, allowing all paleontologists to discuss the new discovery. The media reported how John Ostrom, who in the '70s had pioneered the theory that birds evolved from dinosaurs, was left "in a state of shock." Ostrom later participated in the commission that traveled to China to study the fossils. The other members were feather expert Alan Brush, bird fossil expert Larry Martin, and Peter Wellnhofer, (an expert on the early bird Archaeopteryx).

Feather controversy

Controversy regarding the identity of the filaments preserved in the Sinosauropteryx specimen began almost immediately. The team of scientists spent three days in Beijing examining the specimen under a microscope. The results of their studies, released during a press conference at the Philadelphia Academy of Natural Sciences on Thursday, April 24, 1997, were inconclusive; The team agreed that the structures preserved with Sinosauropteryx were not modern feathers. Further investigation was required to know its exact nature. Paleontologist Alan Feduccia, who had not yet examined the specimen, stated in Audubon Magazine that the structures in Sinosauropteryx, which He considered it as a synonym for Compsognathus, under the name Compsognathus prima, it was part of a rigid sail that ran along its back, and that the paleontologists who studied this dinosaur were very optimistic when comparing the structures with feathers. Subsequent publications commented that some of the same team members disagreed about the identity of the structures, although most scientists have been in favor of their relationship with feathers compared to internal or structural fibers of the skin.

The Feduccia frill argument was followed in several other publications, in which researchers interpreted the filamentous impressions around the Sinosauropteryx fossils as remains of collagen fibers rather than primitive feathers. Since the structures are clearly external to the body, these researchers have proposed that the fibers formed a frill on the back of the animal and the underside of the tail, similar to some modern aquatic lizards. The absence of feathers would refute the proposal that Sinosauropteryx is the most basal genus of feathered theropods known, and also raises questions about the current theory of the origins of feathers themselves. It calls into question the idea that the first feathers evolved not for flight but for insulation, and that they first appeared in relatively basal dinosaur lineages that later evolved into modern birds.

Most researchers do not agree with the identification of the structures as collagen or other structural fibers. In particular, the team of scientists who reported the presence of pigmentation cells in the structures argued that their presence demonstrated that the structures were feathers, not collagen, because collagen does not contain pigment. Gregory S. Paul re-identified what Proponents of the collagen hypothesis consider a body outline outside the fibers as an artifact of the preparation: breaks and brushed sealant have been misidentified as the body outline.

The hypothesis that the structures were collagen fibers was closely analyzed and refuted by a 2017 paper published by Smithwick et al. The integument of Sinosauropteryx was compared closely with less controversial evidence of preserved collagen fibers in the ichthyosaur Stenopterygius. Although the collagen hypothesis claimed that the central shafts, rachis, of supposed theropod feathers were actually misidentified examples of shaft-like collagen fibers, higher quality images showed that these similarities were artificial. The supposed axes in the ichthyosaur collagen were actually scratch marks, cracks and indentations created during the preparation of one of the ichthyosaur specimens. On the other hand, the axes in the Sinosauropteryx specimens were legitimate examples of fossilized structures. The collagen hypothesis also states that the integument of Sinosauropteryx includes beaded structures similar to structures occasionally found in the decaying collagen of modern marine mammals. However, this claim was also not supported, with Smithwick et al. finding no evidence of the bead structures that proponents of the collagen hypothesis identified in the specimens. The study proposes that some areas of the fossil preserved in three dimensions cast shadows that would have resembled bead structures in low-quality photographs.

Other examples of suspected collagen fibers in the tail area were revealed to be scratches, similar to those on the rest of the specimen. An area of bone with an irregular surface was considered evidence that some collagen fibers were less damaged than others. However, the study by Smithwick et al. noted that, after additional preparation, this irregular surface was simply a layer of sediment with a different color than the rest of the slab. It was also determined that the "steering wheel" or "halo" of collagen identified by Feduccia was a misidentified sediment surrounding one of the specimens. The study by Smithwick et al. concluded by stating that the integument preserved in Sinosauropteryx closely resembled that of birds preserved in the same formation. The supposed features of collagen fibers were, in fact, misidentified shadows formed by scratches or irregular sediments, a misidentification perpetuated by the poor quality of early photographs of Sinosauropteryx.

Classification

With a single named species of Sinosauropteryx, S. cousin. A second possible species would be represented by the specimen GMV 2124, also known as NGMC 2124, which has been described as another large specimen ofS. primaby Ji and Ji in 1997. However, this specimen differs in several anatomical aspects from the others, including its relatively longer tibia and a shorter tail. In later work, Ji, Ji and colleagues changed their opinion and indicated that GMV 2124 is probably a new taxon. In 2007, Gishlick and Gauthier supported this position and tentatively classified it Sinosauropteryx? sp., although it may belong to a new genus.

Sinosauropteryx is important because it had feather-like structures, without being very closely linked to the previous "first bird" Archaeopteryx. There are many families of dinosaurs that were more closely linked to Archaeopteryx than Sinosauropteryx, including Deinonychosauria, Oviraptorosauria, and Therizinosauria. This indicates that feathers may have been a feature of many theropod dinosaurs, not necessarily related to birds, making it possible for equally distant animals such as Ornitholestes, Coelurus and Compsognathus also had feathers, although its close proximity to the origin of feathers and the presence of scales in Juravenator and Tyrannosaurus makes it very difficult to estimate the distribution of the genera. feathered among theropods.

Most paleontologists do not consider Sinosauropteryx a bird, because phylogenetically it is very far from the Aves clade, usually defined as Archaeopteryx + modern birds. The scientists who described Sinosauropteryx, however, used a basal character, apomorphy in the definition of the Class Aves, so any animal with feathers would be birds. They argued that the Sinosauropteryx plumose filaments represent true feathers with rachises and barbs, so Sinosauropteryx should be considered a bird. In this way they classified it in a new order, Sinosauropterygiformes, family Sinosauropterygidae, within the subclass Sauriurae. These proposals have not been accepted, and Sinosauropteryx is generally classified in the family Compsognathidae, a group of long-tailed, small-bodied coelurosaur theropods known from the Late Jurassic and Early Cretaceous of Asia, Europe, and South America.

Ji and Ji in 1996 identified many characteristics that make Sinosauropteryx different from other birds and dinosaurs. They found that it was a small, primitive dinosaur with a relatively tall skull, a blunt face, and a slightly high premaxilla. That the antorbital fenestra was elliptical but not enlarged, the dentary was robust, the surangular was narrow and elongated, and the dentition was extremely well developed and sharp. That there are more than 50 extremely elongated caudals, which constitute 60% of the body length, and the forelimb is extremely short with a short and thick humerus. The pubis was elongated and extremely inflated at its distal end and the ischium is wide; the hind limb was long and robust, the tibia is only slightly longer than the femur, the tarsals are separated and the metatarsals are relatively robust with unfused proximal ends and the feathers are short, small and uniform; many adorn the top of the skull.

Phylogeny

Below is a cladogram showing the placement of Sinosauropteryx within Coelurosauria by Senter et al. in 2012.

Paleobiology

Diet

The specimen NIGP 127587 has been preserved with remains of a lizard, complete with skull, in its stomach, indicating that Sinosauropteryx prima included small animals in its diet and fast. Numerous such lizards had previously been found in the same rocks as Sinosauropteryx. These lizards have been interpreted as probably belonging to the genus Dalinghosaurus, which was probably a racing lizard. quickly adapted to living in open habitats, like Sinosauropteryx itself.

In the other possible specimen of Sinosauropteryx, GMV 2124, Sinosauropteryx? sp., three mammalian jaws were found in the stomach region. Hurum, Luo & Kielan-Jaworowska identified two of these jawbones as belonging to the genus Zhangheotherium and the other to Sinobaatar, demonstrating that these mammals were also part of their diet. Of great interest is the fact that Zhangheotherium had a venom-secreting quill, as in the modern platypus, shown that they could feed on poisonous mammals.

Playback

In the copy of S. primapreserving complete stomach material includes a lizard, NIGP 127587 several small eggs were also discovered in its abdominal region. Two of them were located just in the antero-superior region of the pubic peduncle, and several more lined up below them on the slab. It is unlikely that these were eaten by the animal, since they were in a part of the body cavity where the shells could not have remained intact. Therefore, it is more likely that they were eggs gestated by the animal itself. On average, each egg measures 36 millimeters on its major axis and 24 on its minor axis. The total length of this specimen is 107 centimeters. The presence of two developed eggs suggests that Sinosauropteryx had dual oviducts and laid eggs in pairs, like other theropods.

Paleoecology

Sinosauropteryx, as a dinosaur from the Yixian Formation, is a member of the Jehol Biota, the set of organisms found in the Yixian Formation and the overlying Jiufotang Formation. The Yixian Formation is composed of much of volcanic rocks such as andesite and basalt. Between the volcanic layers are several beds of sedimentary rocks that represent deposition in a lake. The freshwater lake strata of the Yixian Formation have preserved a wide variety of plants, invertebrates, and vertebrates. The gymnosperm forests were extensive, with some of the first flowering plants as well. Ostracods and insects were diverse, and bivalves and gastropods were abundant. Mammals and birds are also well known from the formation. The environment was subject to periodic mortality events, including volcanic eruptions, forest fires, and noxious gases gushing from lakes. The climate has been interpreted as temperate, with distinct wet and dry seasons. The annual temperature during this time period It averaged around 10 °C, indicating a temperate climate with unusually cold winters for the generally warm Mesozoic era, possibly due to the high latitude of northern China during this time.