The imagery on this page is the basis for a paper entitled Osteological description of an embryonic skeleton of the extinct elephant bird, Aepyornis (Palaeognathae: Ratitae), by A.M. Balanoff and T. Rowe (2007, Journal of Vertebrate Paleontology Memoir 9, 27(4 Supplement), 53 pp.). The abstract is as follows:
The embryonic skeleton of the most massive bird ever discovered, the extinct elephant bird Aepyornis, has remained until this time essentially unknown. This state is due, in large part, to the reluctance to open complete, unbroken eggs. However, the advent of high-resolution X-ray computed tomography (HRCT) provides a non-destructive means of looking inside such eggs to observe the contents that they conceal. This study uses HRCT technology to digitally extract an embryonic skeleton from a complete Aepyornis egg and subsequently to aid in the systematic description of this specimen. Skeletal elements digitally retrieved from the egg include portions of the braincase, palate, rostrum, vertebral column, and both the fore- and hindlimbs. Because this specimen is at a relatively early stage of ontogenetic development, the bones that were recovered reveal morphology that typically is obliterated in the adult due to the highly fused state of the skeleton, especially seen in the skull. The usefulness of this information, however, is limited unless a level of ontogenetic maturity can be assigned to the specimen. Therefore, we use an extant phylogenetic bracket in a novel analysis comparing the morphological developmental of living ratites and chickens with this specimen of Aepyornis to assess its level of ontogenetic maturity.
About the Species
This specimen, which now resides in Explorer’s Hall at the National Geographic Society in Washington D.C., is a completely intact egg containing a disarticulated embryonic skeleton of Aepyornis. The egg was collected in Madagascar in 1967 by Luis Marden, a photographer for National Geographic Magazine.
Sitting at the bottom of the egg is a loose accumulation of bones along with an unknown matrix (possibly travertine derived from the inside of the eggshell). A number of bones are easily identifiable from a three-dimensional rendering of the egg’s contents: the tarsometatarsus, tibiotarsus, premaxilla, both frontals, and at least one vertebra. In order to facilitate a more thorough osteological study, each individual bone was digitally isolated from the two-dimensional CT scan images. All of the isolated bones may be seen in the 'Additional Imagery' section of this page. Although well over half the bones from the embryonic skeleton are preserved inside the egg, many elements from the left side of the specimen are missing (including the entire left hindlimb). It is possible that the embryo was laying on its left side at the time of death or subsequently was knocked over allowing bacterial action to break down much of that side. | |
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The isolated bones were printed on a three-dimensional rapid prototyper in the CT lab at The University of Texas at Austin to create physical models of the bones at 300% their actual size. Casts of the printouts were then affixed together to create a reconstruction of the skull belonging to the embryo. Accordingly, this study takes what was an inaccessible specimen and, through the use of CT, allows its reconstruction and study. |
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Funding for the scanning was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of The University of Texas at Austin.
About this Specimen
The National Geographic egg was scanned at the High-Resolution X-Ray Computed Tomography Facility at The University of Texas at Austin. Two scans were made of this specimen on 4 October 1999. The higher resolution dataset (1024 x 1024 pixel images) proceeds from the base of the eggshell up to just above the level in which bone is found for a total of 382 slices (see coronal slice-by-slice movie). The slices are 0.25 mm thick and have an interslice spacing of 0.22 mm. The reconstructed field of view is 218 mm yielding an interpixel value of 0.21 mm/pixel.
The second dataset consists of the entire egg scanned along its long axis from the base to the apex of the eggshell for a total of 177 slices (see 'Additional Imagery' page for this animation). These slices were gathered with less resolution and were reconstructed as 512 x 512 pixel images. The slice thickness is 2.0 mm, and the interslice spacing is 1.8 mm. The reconstructed field of view is 248 mm, for an interpixel value of 0.484 mm/pixel.
About the
Scan
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Literature
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