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(Middle Devonian) Tetrapod Trackways from The Examensarbete vid Institutionen för geovetenskaper Degree Project at the Department of Earth Sciences ISSN 1650-6553 Nr 318 Palaeoenvironments of the Earliest (Middle Devonian) Tetrapod Trackways from the Holy Cross Mountains, Poland; Locomotion in a Terrestrial Setting? De tidigaste tetrapod-spåren från mellersta devon − liv i en död efemär sjö? Martin Qvarnström INSTITUTIONEN FÖR GEOVETENSKAPER DEPARTMENT OF EARTH SCIENCES Examensarbete vid Institutionen för geovetenskaper Degree Project at the Department of Earth Sciences ISSN 1650-6553 Nr 318 Palaeoenvironments of the Earliest (Middle Devonian) Tetrapod Trackways from the Holy Cross Mountains, Poland; Locomotion in a Terrestrial Setting? De tidigaste tetrapod-spåren från mellersta devon − liv i en död efemär sjö? Martin Qvarnström Title page: drawing of early tetrapod by Jakub Kowalski (reproduced with permission). ISSN 1650-6553 Copyright © Martin Qvarnström and the Department of Earth Sciences, Uppsala University Published at Department of Earth Sciences, Uppsala University (www.geo.uu.se), Uppsala, 2015 Abstract Palaeoenvironments of the Earliest (Middle Devonian) Tetrapod Trackways from the Holy Cross Mountains, Poland; Locomotion in a Terrestrial Setting? Martin Qvarnström The palaeoenvironment from which early tetrapods emerged is crucial to comprehend in order to understand the mechanisms that drove and allowed the terrestrialization of vertebrates; one of the most important evolutionary ‘events’ in the history of animals. Nevertheless, much of the terrestrialization is shrouded in obscurity, inter alia, due to scarcity of early tetrapods in the fossil record. Each new discovery of anything linked to vertebrate terrestrialization is therefore of great importance. Here, I present new detailed analyses of the palaeoenvironmental conditions at the time of formation of the earliest (early Middle Devonian) tetrapod trackways found in the Zachełmie Quarry in the Holy Cross Mountains of southern Poland. The trackways are found in three horizons in a clay-rich dolomitic succession represented by the Lower Complex of the Wojciechowice Formation. This Lower Complex is composed of short shallowing upward sequences that often terminate with desiccation cracks and/or paleosols. Vertically fluctuating δ18O values in the complex suggest multiple episodes of closed hydrological systems. A model of ephemeral to perennial lakes in a terrestrial setting is therefore proposed. Such environment is in concordance with evidence of scarce bioturbation and a flourish of microbial communities that, in contrast to a normal marine setting, most likely represent an ecologically stressed ecosystem. Furthermore: non-marine rare earth element (REE) signals, desiccation events, fossils of green algae (charophytes), paleosol development, low energy cyclic deposits and general lack of marine taxa in the body and trace fossil records in this complex firmly establishes the interpretation of palustrine carbonates formed in a lacustrine-like setting. However, in the lower part of the complex, some highly fractioned marine fossils occur. These are suggested to have been transported during wash-up events which temporally places the setting in marine proximity. Seasons of monsoonal rainfall resulted in erosion and influx of detrital grains which is evidenced by fine planar lamination (of seasonal cyclicity) in most of the sediments and occasional occurrence of blackened clasts (and rain-drop imprints). Thus, none of the pre-existing palaeoenvironmental hypotheses of tetrapod emergence are in full concordance with the data from the Zachełmie Quarry. Instead, a new palaeoenvironment is proposed for the earliest tetrapods: schizohaline ephermal to perennial lakes with periodic desiccation. This infers that already in the early Middle Devonian, tetrapods had conquered the terrestrial realm and were perhaps already capable of terrestrial locomotion over quite substantial distances. Keywords: Tetrapods, palaeoenvironment, trackways, paleosols, microfacies, trace fossils, fin-limb transition, Holy Cross Mountains Degree Project E in Earth Science, 1GV085, 45 credits Supervisor: Grzegorz Niedźwiedzki Department of Earth Sciences, Uppsala University, Villavägen 16, SE-752 36 Uppsala (www.geo.uu.se) ISSN 1650-6553, Examensarbete vid Institutionen för geovetenskaper, No. 318, 2015 The whole document is available at www.diva-portal.org Populärvetenskaplig sammanfattning De tidigaste tetrapod-spåren från mellersta devon − liv i en död efemär sjö? Martin Qvarnström Däggdjur, reptiler, fåglar och amfibier utgör tillsammans en besläktad djurgrupp som kallas för tetrapoder (fyrfotingar). Deras gemensamma förfader härstammade från de lobfenade fiskarna men skiljde sig från dem genom att inneha utvecklade ben med tår istället för de ”köttiga” fenor som de lobfeniga fiskarna karaktäriseras av. Denna evolutionära nyhet tillät, tillsammans med en rad andra egenskaper (lungor, skydd för uttorkning av dermis etc.), att vertebrater helt och hållet kunde koloni- sera land. I och med att vår egen existens är en direkt följd av denna evolutionära händelse är detta ett hett forskningsämne inom evolutionsbiologin. Ändå är mycket fortfarande höljt i dunkel beträffande hur koloniseringen av land gick till och vad det var som drev denna utveckling eftersom övergången skedde under en, i geologisk mått, snabb tidsrymd. Dock har de sista årtiondena resulterat i flertalet nya fossilfynd av primitiva tetrapoder. Ett fynd som är speciellt spektakulärt eftersom det är den hittills äldsta efterlämningen av tetrapoder, är fotspår som uppenbart är gjorda av ett djur som hade ben och tår istället för fenor. Detta förvånade hela det vetenskapliga samfundet eftersom det innebar att vi (tetrapoderna) utvecklades tidigare än vad som var dittills trott och att vertebrat-koloniseringen av land förmodligen skedde flertalet miljoner år tidigare. Vad som också skiljer ett spårfossil från andra fossil är att de är spår av djuren från när och där de levde till skillnad från bara deras skelettdelar som oftast transporterats från där de dog och bara preserveras i speciella miljöer. Detta har jag utnyttjat i detta arbete för att försöka avgöra i vilken miljö de är avsatta i. Jag har analyserat de sedimentära bergarterna i stenbrottet i södra Polen med skärningen som innehåller de lagren i vilka fotspåren finns. Analyser av sällsynta jordartsmetaller från de tre lager där fotspår är tydliga, antyder en speciell avsättningsmiljö som inte liknar en typisk havsmiljö. I den undre delen av lagerföljden där de spårbärande lagren påträffats finns återkristalliserade saltkristaller, torkningssprickor och fossila jordar som indikerar korta respektive långvariga perioder av uttorkning. Andra fossil som i en normal marin miljö borde bevaras i en dolomitisk kalksten lyser med sin frånvaro och istället påfinns massiv koloni- sering av cyanobakterier. Detta brukar ske i speciella miljöer som avviker från vanlig marin komposi- tion, så som äldre sötvattensmiljöer eller laguner med hög salthalt, som därmed är ”svårbebodd” för djur som annars livnär sig på de fotosyntiserande bakterierna. Implikationen av mitt arbete är att tetrapoderna redan i tidig mellan Devon (ca 390 miljoner år sedan) inte bara hade utvecklat ben utan också att de kunde använda dem över landsträckor för att ta sig till, och mellan, kontinentala vatten. Detta är ännu en viktig pusselbit i pusslet som ämnar rekonstruera tetrapodernas (och vår egen) uppkomst. Nyckelord: Tetrapoder, palaeomiljöer, spårfossil, microfacies, fin-limb transition, Holy Cross Mountains Examensarbete E i geovetenskap, 1GV085, 45 hp Handledare: Grzegorz Niedźwiedzki Institutionen för geovetenskaper, Uppsala universitet, Villavägen 16, 752 36 Uppsala (www.geo.uu.se) ISSN 1650-6553, Examensarbete vid Institutionen för geovetenskaper, Nr 318, 2015 Hela publikationen finns tillgänglig på www.diva-portal.org Table of Contents 1 Introduction .......................................................................................................................................... 1 1.1 Evolution of early tetrapods .......................................................................................................... 1 1.2 Palaeoenvironmental theories of tetrapod emergence................................................................... 2 2. Aim ..................................................................................................................................................... 4 3. Background ......................................................................................................................................... 4 3.1 Geological setting ......................................................................................................................... 4 3.3 Zachełmie Quarry ......................................................................................................................... 6 3.3.1 Fossil content ......................................................................................................................... 9 3.5 Geochemistry .............................................................................................................................. 11 3.5.1 Stable isotopes ..................................................................................................................... 11 3.5.2 Rare earth elements and trace elements ............................................................................... 13 4 Material and Methods .......................................................................................................................
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