PI: Edward B. Daeschler, Associate Curator of Vertebrate Zoology, Academy of Natural Sciences of Philadelphia, 1900 Benjamin Franklin Parkway, Philadelphia, PA 19103
PI: Neil H. Shubin, Robert R. Bensley Distinguished Professor, Department of Organismal Biology and Anatomy, 1027 East 57th Street, University of Chicago, Chicago, IL 60637
Tiktaalik roseae is a fossil fish from the Late Devonian Period (385-362 million-years-ago) that was discovered in 2004 on Ellesmere Island, Nunavut, Canada. This species is the finned animal that is most closely related to tetrapods (limbed vertebrates). As an intermediate form, T. roseae helps us to recognize the sequence of morphological changes across the fish-to-tetrapod transition and can teach us about the forces that were driving these important evolutionary changes. T. roseae was first described in 2006 and has provoked a great deal of interest among evolutionary biologists. To date, however, the only published reports on this species have been short papers in Nature. With continued study and documentation of the abundant and well-preserved material of T. roseae, we will fill the need for a detailed investigation of this important fossil at the cusp of the fish-to-tetrapod transition.
A primary contribution of this research will be a detailed publication on a wide range of topics about T. roseae. The core of this publication will be a thorough morphological description including extensive figures of many of the 50+ specimens. We will also investigate the internal structure of bones in the fins for the first time, further document the ancient environment where T. roseae lived, and produce new studies of the evolutionary tree across the fish-to-tetrapod transition. The other major contribution of this project will take advantage of the quality of T. roseae fossils to assess the functional anatomy of the fins and skull. Evaluation of the hypothesis that the fins were capable of body support will involve detailed analysis of joint structure and the relative motions possible between bones, fin rays, and scales of the front fin and shoulder. The second set of analyses will explore the relationship between skull architecture and different stresses and strains in the skull related to movement, breathing and feeding. At the conclusion of this study, all T. roseae specimens are to be returned to the Government of Nunavut, and so the timely publication of these data via print and websites is of particular importance.
The discovery and description of T. roseae has received considerable attention from educational organizations and media internationally; as a textbook transitional fossil it has become a powerful tool in the communication of evolution to the general public. The PIs have a record of public lectures and development of web-based educational resources. We will make use of this research project to further communicate the results of the work, as well as the scientific process, to a broad audience and thereby help people get a better grasp of how evolution works.
This project led to the discovery and description of new fossils that tells us how animals evolved to walk on land. Tiktaalik roseae, a creature that lived about 375 million years ago, is one of the closest fish relatives to limbed creatures. Discovered in 2004 in the Canadian Arctic, it was only known from the front section: the hind appendages and girdle were unknown. The goals of this work were to discover and describe unknown portions of the anatomy and make all of the Tiktaalik material available to the community through scientific publications, websites, and casts for museums. Work on the type specimen of Tiktaalik gave the team a surprise: hidden within one of the original blocks was a pelvis and partial hindfin that was originall obscured as they were covered by rock. Preparation revealed a beautifully preserved pelvis, revealing the fish hip socket and parts of its pubis in three dimensions. The surprise lay in how much it is like a limbed animal in its size, yet like a fish in the configuration of the publis and ilium. This discovery revealed that fish were already using their hindfins extensively in locomotion prior to the actual transition to land. One of the major efforts of this work was in the digital reconstruction of the fossil in an effort to undertand the biomechanics of its skull and fins. CT technology can reveal structures hidden from view, such as tiny sutures in the skull or vascular canals in the bones. And, moreover, it can do do non destructively. Under the tenure of this award, we scanned all the skull, jaw and fin material that was articulated in three dimensions. This work revealed the internal structures of these features in great detail, showing parts of the skeleton that were hidden from us initially. One result is a new understanding of the skull itself. The skull is subdivided into two functional components: cheek teeth and bones, and internal fangs and supporting bones. The stuctures revealed by the scanning showed that the fangs are supported by a kind of bony I-Beam, meaning this portion of the cranium has adapted to resist bending moments. The scanning work is leading to us to view Tiktaalik as an active predator, capable of high performance biting (much like a crocodile). One of our goals from the outset has been to make these fossils available to the general public. Through publications, casts provided to museums and collections, and web resources the bones of Tiktaalik can be seen by students, teachers and interested members of the broader general public.
