Dodo weblog Dodo-expeditie 2007

Based on the experiences and analyses of the 2006 excavation, new aims have been identified for the 2007 excavation:

• To collect bulk samples from in situ to map and assess the anatomy of fossil layer to map and assess the taphonomy of fossil layer to sub-sample from in situ position for various disciplines.
• By means of sheet piles, pumps and mechanical digger a dry excavation pit will be realised. All material that will be removed in order to generate the excavation pit will be stored in sample bags and sieved. All rock material that cover the fossil layer will be dumped back. All excess unused sieve residue will be dumped back in the ditches and excavation pits.
• We observed that fossils finer than 5 mm are preserved at Mare aux Songes (MAS). They include for example fine bird bones, bat bones and teeth and mollusca. These smaller organisms must have formed a major part of the ecosystem and it is therefore crucial to obtain a representative sample of these.
• In order to understand the biostrationomic processes (transport, disarticulation, scatter, modification) that led to the formation of the bone layer it is crucial to map the bone layer in detail. Measuring the 3d orientations of the fossils will provide insight in the organisation of the bone layer and will help to resolve the question what processes led to the bone concentration at MAS and ultimately what was the death cause of the animals.
• Transportation of bones
• We will pay special attention into assessing the effects of post syn mortem transportation.
• Transportation may be minimal where vertebrates are in marine or lacustrine sedimentary basins. Organisms may also be transported considerable distances by predators, scavengers, fluvial systems, or marine currents. Other taphonomic aspects of the fossils will be assessed especially macroscopic aspects of bone modification will be described. Bone modification includes any form if alteration to individual bones, including cracking, surface marks, abrasion, polishing and breakage.
• Damage to bone may occur at various stages throughout the taphonomic history of a vertebrate bone. They can be divided into: pathological and traumatic damage sustained during life, including diseased bone and natural fractures, post-mortem damage due to predation, scavenging, trampling, or transport and post-burial damage sustained due to compaction, cracking or dissolution
• Damage sustained during life may show evidence of healing, including new bone growth. Post-mortem damage will not show new bone growth and it may be difficult to distinguish from damage sustained during compaction.
• Conditions of preservation
• In order to understand the conditions of preservation of the fossils including collagen and aDNA we will take soil samples to study in situ geochemical and microbiological conditions. Further subsamples will be taken to study molluscs, insects and microfossils.
• When relevant, the orientation of fossils, tree stems, rootlets will be measured with a 3d compass and data will be registered in a database and plotted in polar plots (fig 1c). Orientation of fossil long axes will help to reconstruct taphonomic processes. Post mortem transportation of bones may result in specific orientation of skeletons, in most cases post mortem stable positions of fossil are when ab axes (a is long axis of symmetry, b is second longest axis of symmetry, c is smallest axis of symmetry) are horizontal, with specific sides up or down. Trampling, bioturbation, plant growth and soil movement can disturb this pattern into near vertical positions. Fossil skeletons in life position indicate rapid burial.
• The focus will be on bone elements of which orientations can be related to the organism death position. Long axes will be measured, axes of symmetry, dip orientation of proximal bone and wood ends. The positions of stems and rootlets will be measured, also here distal and proximal ends will recorded and for rootlets way upward criteria will be mapped. The orientations will be mapped in polar plots.
• Location of excavation
• Based on the 2006 excavation and geohydrological requirements for the 2007 excavation the position of the excavation pit is determined. The pit will be position on a location with a rich fossil concentration and where a thick (>0.5 m) and continuous impermeable layer underlying the fossil layer is present. Borehole data indicate that central in the basin these conditions are fullfilled.
• Re-calibration of preservation and valuation of the site
• Our findings so far indicate that Mare aux Songes is a globally exceptionally fossil depository and may be indicated as a fossil Lagerstatten. The fossil site is therefore extremely valuable scientifically. As the fossil layer contains remains of the world famous dodo (Raphus cucullatus) the site is also culturally very important. The excavation activities and continue press releases around the dodo will provide free advertisement to Mauritius as a tropical paradisiacal island where once the dodo lived.
• The state of Mauritius declared a special status to Mare aux Songes and is now listed as a national heritage site, that is only accessible for research when permissions are onbtained by the Nation Heritage Fund and Mauritian government.
• Our research focuses to reconstruct the world of the dodo and determining the factors of its demise. It will provide a scientifically based substantiation of the claim of its uniqueness and completeness. We strife to minimise the damage done on the fossil layer and record all data in detail in maps, films, photographs and databases. All data collected and analysed will be shared with the community through museum displays and publications.
• We will follow ethical guidelines of Archeological and Paleontological disciplines that encompass not to collect fossils without scientific justification and inflict unnecessary damage to the fossil site.