Procedure and Workflow for Sorting and Assembling Fossil Bones Exposed to Surface Conditions

Fossil bones that have been exposed to surface conditions can present a variety of challenges, including fragmentation, erosion, and mixing of different bones from multiple animals or species. Effective sorting and assembly require a systematic approach to ensure that each bone is accurately identified and that fragments are appropriately pieced together.

This workflow outlines the necessary steps to sort, identify, and assemble fossil bones exposed to surface conditions. It emphasizes careful observation, documentation, and collaboration to ensure the correct identification of each element.

Step 1: Initial Sorting and Collection

The first step is to collect and group all exposed bones or fragments from the site. This should be done in a way that minimizes further damage and ensures no additional mixing of bones occurs.

1.1 Field Collection and Documentation

• Document Site Conditions: Record the location where each bone or fragment is found. Use a grid system or GPS to accurately log the position of bones relative to each other. Photograph each fragment or grid before removing it from the surface.

• Label and Bag Bones: Place each bone or fragment in a labeled bag or container. Each bag should include a unique identifier, the GPS coordinates, a description of the fossil, and any relevant notes about its condition.

• Preliminary Sorting by Type : If Practical, While still in the field, sort bones by general categories (e.g., long bones, vertebrae, ribs, skull fragments). This initial sorting will help avoid confusion when transported to the lab.

Step 2: Stabilization and Cleaning of Bones

Once the bones are brought to the lab, they should be stabilized and cleaned to allow for more detailed sorting and identification.

2.1 Stabilizing Fragile Bones

• Apply Consolidants: Fragile bones or fragments that show signs of cracking, flaking, or erosion should be consolidated using a reversible consolidant such as Paraloid B-72. Apply the consolidant carefully to avoid covering important surface details.

• Handle Gently: Transport and store fragile bones on padded trays to prevent further damage.

2.2 Cleaning Bones

• Dry Cleaning: Begin by cleaning bones using soft brushes, air bulbs, or low-pressure air scribes to remove loose dirt and debris. Avoid using water or chemicals at this stage unless necessary, as water may further weaken weathered bones.

• Detailed Cleaning: If needed, use a small dental pick or micro-sandblaster to remove harder matrix adhering to the bone. Proceed with caution, especially on surfaces that have been exposed to weathering.

Step 3: Detailed Sorting by Size, Shape, and Type

After stabilization and cleaning, begin sorting the bones in more detail, grouping them by species, element type, and size. This process requires careful observation and a systematic approach.

3.1 Initial Grouping

• Sort by General Bone Type: Start by grouping bones into broad categories (e.g., vertebrae, limb bones, skull fragments). Use anatomical guides and reference materials to assist with identification.

• Group by Size and Shape: Once grouped by type, further sort bones by size and general shape. Bones from the same species tend to have consistent proportions, even when fragmented. This step will help narrow down the bones that might belong to the same animal.

3.2 Identifying and Cataloging Bones

• Identify Specific Bones: Use anatomical keys, comparative skeletons, or digital resources to identify specific bones (e.g., femur, humerus, rib). Note any distinguishing features (e.g., muscle attachment points, articulation surfaces) to confirm identification.

Step 4: Matching Fragments

Once bones are sorted, fragments of the same bone should be matched and assembled where possible. This requires careful attention to detail and testing of different fragment combinations.

4.1 Test Fitting Fragments

• Examine Fracture Patterns: Closely examine the edges of each fragment for matching break patterns. Look for jagged edges, grain patterns, or specific shapes that suggest the fragments fit together.

• Test Fit Fragments Without Adhesive: Before applying any adhesive, perform a dry test fit by gently aligning fragments. Adjust the fit to ensure there are no gaps or misalignments. If necessary, use magnification to help match small or intricate pieces.

4.2 Bonding Fragments

• Use Appropriate Adhesive: Once the test fit is successful, use a suitable adhesive, such as Paraloid B-72 dissolved in acetone or ethanol, to bond the fragments. Apply the adhesive sparingly with a fine brush or syringe.

• Clamp or Support as Needed: Hold the fragments in place using clamps, supports, or padding to maintain the correct alignment while the adhesive dries.

Step 5: Species Identification and Assemblage

Once individual bones are identified, the next step is determining which bones belong to the same species or animal. This can be particularly challenging when dealing with mixed deposits from different species or individuals.

5.1 Comparing to Reference Specimens

• Use Comparative Anatomy: Compare the sorted bones with reference specimens, whether physical or digital. Pay close attention to size, proportions, and morphology to distinguish between species.

• Group by Species: Based on your comparisons, begin grouping bones by likely species. Record your reasoning for each grouping in the catalog, noting any uncertainties.

5.2 Differentiating Individuals

• Examine Wear and Pathology: Bones from different individuals often show different patterns of wear, pathology, or trauma. Examine the bones for signs of healing fractures, tooth wear, or other features that suggest differences between individuals.

• Assess Age Differences: Juvenile and adult bones can often be distinguished by their size, bone fusion, and surface texture. Group bones by age to further refine your assemblage.

Step 6: Reassembly of Skeletons

Once bones are identified and sorted by species, the final step is to begin reassembling skeletons. This process is iterative and may require adjustments as more information becomes available.

6.1 Establishing Anatomical Position

• Lay Out Bones: Lay out the bones anatomically, following known skeletal structures for the species. This helps visualize the entire skeleton and identify missing elements.

• Fit Together Adjacent Elements: Begin reassembling adjacent bones, such as vertebrae or limb bones, ensuring that the articulation points match and the fit is anatomically correct.

6.2 Reconstructing Missing Parts

• Reconstruction: For heavily fragmented or missing bones, consider using archival materials to reconstruct sections for display or research. Clearly document all reconstructive work.

• Mark Reconstructions: Make sure any reconstructed elements are visibly distinguishable from the original fossil to prevent confusion during future study or display.

Step 7: Final Documentation and Storage

Once sorting and reassembly are complete, it is important to thoroughly document your work and prepare the fossils for storage or display.

7.1 Final Documentation

• Record Assemblage Process: Create detailed records of how bones were sorted, identified, and assembled. Include photographs, notes on matching processes, and species identification.

• Update Catalog: Ensure that the catalog is up to date with any new identifications, reconstructions, or bonding of fragments.

7.2 Storage Preparation

• Store Fragile Assemblies Carefully: Once assembled, store fragile bones and assemblies in padded trays or custom-built supports to prevent damage.

• Label and Organize: Clearly label all bones and groupings with their unique identifiers and species information. Organize bones in storage cabinets or boxes that minimize handling.

Summary

Sorting and assembling fossil bones exposed to surface conditions is a complex process that requires careful handling, observation, and documentation. By following this workflow, preparators can systematically identify, sort, and assemble bones from multiple animals or species, preserving the scientific value of each specimen and ensuring accurate reconstructions. Regular communication with other experts and thorough record-keeping are essential to maintaining the integrity of the fossil collection throughout the process.