Dr. Tiiu Märss
Fish studies by Tiiu Märss in Estonia started due to two needs. One was to give to a undergraduate student topics for two term papers to be presented in 1967 and 1969, and later on for the diploma work, which she defended in 1970. Her first steps in paleoichthyology were taken at Tartu University, supervised by prof. Arvo Rõõmusoks, to make acquaintance with Estonian osteostracans, with their morphology and publications about them. The second need arose because the correlation difficulties between the Estonian Silurian sections with the international British standard as in Britain the upper part of the sequence did not contain shelly fauna such as ostracodes or brachiopods neither graptolites or conodonts but did contain fish scales.
Logania ludlowiensis Gross (now called as Paralogania ludlowiensis) was the taxon which was needed to be found in Estonian Silurian. Dr Dimitri Kaljo, director of the Institute of Geology at that time, and the leading Silurian biostratigrapher, was behind that idea. T. Märss agreed with the task and in 1970 became a permanent member of the Institute of Geology working in palaeontology, with an emphasis on morphology-based taxonomy and biostratigraphy of Silurian vertebrates. To say beforehand, during her career she did find one scale of P. ludlowiensis in the Ohesaare core, Saaremaa, basal beds of Kuressaare Regional Stage, Ludlow.
During her scientific career a high number (about 3800) of rock samples from up to 70 drill cores of East Baltic and many outcrops from Estonia, Russia, Bohemia, British Isles, Canadian Arctic and elsewhere have been treated by T. Märss to obtain fish microremains. Scales and fragments that have been used for taxonomic as well as for biostratigraphic and palaeoecological studies, supporting posterior phylogenetic constructions. A big part of these material (but far from all) has been already published in numerous contributions authored or co-authorer by her.
Tiiu’s work has been deeply developed under the umbrella of international projects. In this sense, since 1970’s fish studies have been tightly tied with the studies of the other Silurian fauna carried out in the Institute of Geology. These works in turn were linked with the International Geological Correlation Programme (IGCP) projects, highlighting the importance of the Estonian fish fossil record in the Project Ecostratigraphy’ and ’Global Events and Event Stratigraphy in the Phanerozoic’, led by A. Boucot and O. Walliser, respectively. Highly valuable for Palaeozoic fish researches were two specific international projects, the IGCP project 328 ’Mirovertebrates’ (leaders S. Turner and A. Blieck), and the IGCP project 406 ’Circum-Arctic Palaeozoic Vertebrates’ (led by M. Wilson, T. Märss and P. Männik), the second one continued the vertebrate microremain studies but included also invertebrates and focused on the sections of modern Arctic regions. In addition, very important was the project on the remote Russian and Canadian Arctic, revealing new and diverse fossils as well as new data about the biostratigraphy of these regions, where T. Märss participated in both. T. Märss was the first among the international geologists’ team investigating the Canadian Arctic islands (Baillie-Hamilton and Cornwallis) to simultaneously use the distribution data of several faunal groups (fishes, conodonts, ostracodes) to solve stratigraphical problems.
Among her main scientific results, T. Märss proved that most of the known Silurian agnathans and fishes dwelled in marine environments, some, maybe were migratory fishes refuting the widespread opinion of their freshwater habitats.She has devoted great attention to the use of agnathans and fish scales in the subdivision and correlation of sedimentary rocks of the Silurian Sea basins. She proved that new vertebrate taxa appeared during the transgressive phases of the development of the Palaeobaltic Sea and identified the levels of bioevents in the distribution of Silurian vertebrates. As the author of the Regional Vertebrate Biozonal Scheme, she initiated the creation of the Global Silurian Vertebrate Biozonal Scheme. She mapped the squamation of thelodont Phlebolepis elegans Pander and reconstructed its sensory-line canal system from Estonia, and lateron continued similar work on thelodonts from Scotland, and Cornwallis and Baillie-Hamilton islands, Arctic Canada. She discovered a second pair of ventral fins in the thelodont Shielia taiti Stetson from Scotland, which can be used in elucidating the formation and phylogeny of fins of early vertebrates. Osteostracans were treated in the monographic paper, and also this 16th ISELV conference talk is about a taxon of that group, Tremataspis, about their tiniest external endolymphatic structures. As a result of her individual or co-authored studies, T. Märss has established 167 new vertebrate and 4 invertebrate taxa with the focus on the Silurian agnathan thelodonts, anaspids, osteostracans, heterostracans,and less on the gnathostome acanthodians, chondrichthyans and osteichthyans. All that resulted over 190 publications including three monographs and four monographic papers.