AUTOPSY ON SCIPIONYX REVEALS IT IS THE WORLD S BEST PRESERVED DINOSAUR

Transcription

1 AUTOPSY ON SCIPIONYX REVEALS IT IS THE WORLD S BEST PRESERVED DINOSAUR WHO S SCIPIONYX? Scipionyx samniticus, popularly dubbed Ciro (Cyrus), is a tiny fossil dinosaur that was unearthed at Pietraroja (southern Italy) in 1980 and acknowledged by the world s scientists in 1998 (cover of Nature) as one of the most relevant finds in the history of palaeontology. In facts, this specimen showed a unique state of preservation, which included soft tissue remains. But research on it was only started. WHAT'S NEW? Recently, the Italian palaeontologists Cristiano Dal Sasso and Simone Maganuco performed a real palaeo autopsy on the soft tissues of the specimen, that revealed anatomical details never seen before in a dinosaur. Through ultraviolet induced fluorescence photography, computed tomography and scanning electron microscopy coupled with element microanalysis, Dal Sasso & Maganuco demonstrated that the soft tissues of Scipionyx are exceptionally preserved even at cellular and subcellular levels to a point that, after 110 million years, an unrivalled variety of biological structures can be seen in a single fossil (e.g., ligaments, articular cartilage, tracheal rings, intestinal cells, muscular fibres, blood vessels, and even bacteria). Moreover, Scipionyx also contains numerous remains of food, which in the first examination of the fossil had not been noticed. The diet of this carnivorous dinosaur actually consisted not only of meat (small reptiles), but also fish. A long list of neonate like characters indicates that Scipionyx was less than three weeks old at the time of death. THE MONOGRAPH The number of new finds, which the scientific community has been eagerly waiting for, is large, to the point that Dal Sasso & Maganuco wrote a volume of 300 pages. It is a richly illustrated monograph, co edited by the Società Italiana di Scienze Naturali and the Museo di Storia Naturale di Milano. The full title of the monograph is: SCIPIONYX SAMNITICUS (THEROPODA: COMPSOGNATHIDAE) FROM THE LOWER CRETACEOUS OF ITALY Osteology, ontogenetic assessment, phylogeny, soft tissue anatomy, taphonomy and palaeobiology

2 BONE BY BONE, TOOTH BY TOOTH Part I of the monograph describes the whole osteology of Scipionyx. The major cranial novelties include the identification of formerly unrecognised braincase bones, reinterpretation of palatal and mandibular elements, and identification of differently shaped teeth. Preservation in in life position of very delicate abdominal bones, called gastralia, which are rarely preserved in fossil specimens, allowed to estimate with precision the volume of the dinosaur's body. A NEONATE, NOT SIMPLY AN IMMATURE SPECIMEN In the only specimen of Scipionyx so far unearthed, the small size and strange body proportions, such as large eyes and short snout, was already a clear indication of immaturity. Now we also know that Cyrus had the frontoparietal fontanelle still open, just like our babies. The comparison with the chicks of some species of birds showed, in addition to this similarity, the likely presence of a similar space for the yolksac in the abdomen. This indicates that Scipionyx died a few days after birth. The dinosaur weighed only 200 grams and was 50 cm long including the tail. Difficult to understand what would grow, however, a comparison with its closest relatives, shows that they were no longer than eight feet. SCIPIONYX AND ITS KIN A phylogenetic analysis of coelurosaurian dinosaurs (90 taxa, 360 characters), evaluating also the ontogeny related characters, allows to identify Scipionyx as a basal member of a monophyletic Compsognathidae, which results to be more derived than Tyrannosauroidea. Compsognathid theropods are agile bipedal predatory dinosaurs related to the ancestors of birds. A UNIQUE VARIETY OF SOFT TISSUES Part II of the monograph by Dal Sasso & Maganuco illustrates in detail the superbly preserved internal organs and soft tissues of Scipionyx samniticus: axial ligaments, axial and appendicular articular cartilage, neck muscles and connective tissue, part of the trachea, oesophageal remains, traces of the liver and other blood rich organs, the entire intestine, mesenteric blood vessels, and pelvic and hindlimb muscles. External soft tissues are beautifully represented by the horny manual claws. Most of the soft tissues can be easily identified by their ochre colour, whereas other organic remains are preserved as thin films that are visible under ultraviolet induced fluorescence (UV). Scanning electron microscopy (SEM) analyses have revealed an exceptional three dimensional preservation of the soft tissues and astonishing information at a cellular and even subcellular level, such as the sarcomere related banded pattern observable within every single muscular myofibre. The SEM element microanalysis showed that the red spot contained in the

3 chest of the dinosaur is an accumulation of iron ore. Because iron is completely absent in the rest of the fossil as well as the surrounding sediments, this element derives from the decay of hemoglobin in the blood of the dinosaur, concentrated in the liver, heart and spleen, which is right in the chest cavity. HOW DID IT GET PRESERVED THIS WAY? Scipionyx was buried in a single, rapid event by a turbidite (a submarine landslide of fine muddy sediments). The exceptional preservation of labile soft tissue indicates that, after death, the carcass of this hatchling dinosaur was subjected to very little decay and rapid authigenic mineralisation, in the presence of a high concentration of phosphates and of anaerobic bacteria. As for the possibility of finding DNA traces of Cyrus, this is highly unlikely. The replacement of organic matter with inorganic crystals was complete and took place molecule by molecule. This made it possible to replicate the shapes of the cells and retain many elements accumulated by the cells themselves, such as phosphorus and iron, but not to keep long chains of complex molecules, such as DNA. THE PREY OF SCIPIONYX Part III of the monograph focuses on the functional morphology and the palaeobiology of Scipionyx samniticus. Outstandingly, the degree of preservation of the soft tissues has permitted an analysis of the relative position of the food remains in the digestive apparatus and, thus, reconstruction of a feeding chronology for this specimen, an insight that is usually impossible to obtain for fossil vertebrates. In fact, Scipionyx s gut has been found to contain allogenous bones from a lepidosaurian reptile in the stomach region, lizard like polygonal squamae in the duodenum, fish scales in the rectum, and a variety of tiny remains in several points of the intestine. This is compelling evidence that Scipionyx fed on both lizards and fish. The relatively large size of a leg of lizard found in the stomach region suggests that the little dinosaur has been fed by their parents with pieces of prey captured and dismembered specifically to feed the nestlings. SCIPIONYX VS THE CHINESE FEATHERED DINOSAURS: WHAT IS THE DIFFERENCE? Scipionyx is strictly related to the Chinese Sinosauropteryx, as both are compsognathid theropods. Therefore, it is likely that also the Italian species was covered with proto feathers, but they did not fossilise. However, the amount and detail of information gained from this single specimen make the Pietraroja Plattenkalk a unique fossil locality. In contrast to the Chinese Jehol Group, which is a lacustrine/volcanic freshwater deposit that has preserved dinosaurs with delicate integumentary structures, such as filaments, feathers and bristles, the Italian shallow marine Lagerstätte has preserved internal organs. This is unprecedented

4 not only for a dinosaur, but also for any other Mesozoic terrestrial vertebrate. Contemporary examination of the ingested prey, the internal organs of Scipionyx, and their osteological correlates, allows to investigate the digestive physiology and respiratory physiology of Scipionyx. With regards to the latter, Dal Sasso & Maganuco demonstrate that the remains or imprints purported by some authors to be of the diaphragmatic muscles are, in fact, a calcite nodule of amorphous microstructure, inconsistent with the preservation of other muscle tissue in this specimen. This evidence deny the hypothesis that dinosaurs had a crocodile like (hepatic piston assisted) breathing mechanism. WHY THIS RESEARCH IS IMPORTANT? WHO CARES ABOUT IT? To describe and illustrate with such detail the anatomy of a dinosaur is not an academic exercise. Comparing the soft tissue morphology from a relevant extinct taxon with the analogous biological structures of extant vertebrates, may interest a broad community of scientists, including palaeontologists, evolutionary biologists, functional morphologists, comparative anatomists, biologists, veterinaries, herpetologists and ornithologists. In addition, given the popular appeal of dinosaurs, also a non scientific audience will be interested in such unusual palaeo autopsy, and the media will be fascinated by the amount of information provided by such a tiny, single fossil specimen on the life and death of a hatchling predatory dinosaur. C.D.S. & S.M.

5 Comments by M. Carrano, F. Huchzermeyer e K. Peyer, referees of this monograph It is rare to have any dinosaur s anatomy published in such detail, even when only the skeleton is present. The unrivaled soft tissue preservation makes some of the descriptions here unique, and they will be important when any future discoveries produce soft tissue preservation. It will be an extremely valuable contribution for comparative anatomy. Matthew Carrano (vertebrate palaeontologist), Washington DC, USA The amount of detail that has been extracted from the specimen in years of intensive studies with the help of up to date technology and the well documented conclusions drawn from the find altogether constitute a major contribution to our widening knowledge and merit to be read by as wide as possible a public I have to admit, that I enjoyed reading the exact anatomical descriptions. Except for the scientific contents they are somehow akin to poetry. Fritz Huchzermeyer (veterinary pathologist), Onderstepoort, South Africa This description aids in a better understanding in how dinosaur functioned, behaved, what they ate at what rate. In return this information further provides a lot of new insights on the paleoenvironment. This little dinosaur not only brings new behavioral aspects to dinosaur research but also provides a large array of in detail described anatomical characters which help understand the relations of compsognathids and how they relate to other theropods Scipionyx also puts a newly renounced focus on the Pietraroja Plattenkalk and Italian dinosaur research in general. Great job. Karin Peyer (vertebrate palaeontologist, Muséum National d'histoire Naturelle), Paris, France Milan, Italy, 22 June 2011