THE MANY BENEFITS OF 3D XRAY IMAGING IN PALEONTOLOGY: PREPARATION OF A DELICATE FOSSIL CONTAINED INSIDE A PLASTER JACKET

CARDENAS, MAGALI; MORENO KAREN

Calgary

Congreso; SVP anual meeting; 2017

Traditionally the preparation of a fossil contained in a plaster jacket requires a great dealof guess, because often its detailed content is unknown. Therefore, the preparation can begreatly improved by the use of Xray imaging, such as Computed Tomography (CT),since it makes possible a preliminary observation.Here we present our results on the preparation of three plaster jackets which containedbones of Caraguatypotherium munozi, a Mesotheriinae (Nothoungulate mammal, lateMiocene) found in Northern Chile. The bedrock consisted on a semi consolidated finegrained sandstone with abundant diaclases. Also plant roots are usually squeezed into thefractures. All of these factors makes difficult the extraction. Thus, a plaster jacket wasapplied with minimal superficial preparation. At this stage, sediment removal wasperformed only to know the fossil boundaries. Hence, its precise content was leftunexplored.Once at the Laboratory of Paleontology, Universidad Austral de Chile (UACh), a CTscan was performed in a medical equipment (UACh), and images analyzed with Osirix®free software. Image treatment included the search for the appropriated density range(Houndfield units) to distinguish the fossil and then perform a 3D reconstruction.The 3D reconstruction permitted to: 1) identify bones, their position, size andpreservation status. 2) to prioritize the sediment removal on areas of interest, such as thearea comprising the occipital, an unknown skull bone in previously collected materials ofthe species including the holotype. 3) to choose and adjust extraction and consolidationtechniques, such as the use of dentistry wax for filling cracks, and Paraloid (B-72) atvarious concentrations.The use of CT scan allowed the successful extraction of two complete skulls with theircorresponding mandibles, a series of 5 cervical vertebrae, a semi articulated arm and afew other isolated bones in just 20 days.It is important to note that fossils were extremely fragmented within the sediment matrix,being often cut through by numerous one-centimenter wide cracks disposed in differentdirections. Hence, if the fossils were collected by in-situ picking, there would haveliterally resulted in a bunch of little unidentifiable pieces. Similarly, if the laboratorypreparation would have not used CT scan, it would have been a difficult task to identifythe puzzle, multiplying its preparation time. In conclusion, as 3D reconstructiontechnology becomes more accessible, it is possible to use it to facilitate, speed up andimprove the preparation results.Grant Information:The present work is funded by the FONDECYT Project 1150879 ?Skeletal morphofunction of Caragua´s Miocene Fauna? awarded to KM.