Histological description and bone compactness analysis of fossil (Aldabrachelys sp.) and extant Aldabra giant tortoise (Aldabrachelys gigantea) shell bone fragments
In brief
Fossil and living Aldabra tortoise shells show wide variation in bone compactness
Shell bone compactness ranged from 45.1% to 84.9% in fossil fragments and from 45.8% to 86.1% in living Aldabra giant tortoises. Fossil bones usually had distinct outer and inner layers around spongy bone, while living samples were generally more uniform, but variation within and between fragments was substantial. The findings set a baseline for future comparisons and caution against assuming one shell pattern.
- Journal
- Anatomical record (Hoboken, N.J. : 2007) (Q2)
- Published
- 23 October 2026
- Study design
- Unclassified
- Evidence level
- Level 5, Expert Opinion (CEBM 5)
- Authors
- Stefanie Herter, Nicole Klein, Massimo Delfino, Erik de Boer, Julian P Hume, Jordan Bestwick, et al.
- PMID
- 42920209
- DOI
- 10.1002/ar.70374
Why clinicians should know about it
- Picked for Histology (top studies of the week, 25 October 2026): Direct comparative bone microanatomy and compactness histomorphometry
Abstract
Aldabra Atoll, north of Madagascar and part of the Seychelles Outer Islands, is home to the Aldabra giant tortoise, Aldabrachelys gigantea, the only survivor of several species of giant tortoises that were once widespread on islands across the Western Indian Ocean. Aldabra Atoll preserves an extensive fossil record of giant tortoises, providing a unique opportunity to compare the shell bone microanatomy of extinct and extant forms. This study presents the first detailed histological investigation of fossil Aldabrachelys sp. shell fragments and a preliminary comparison with extant A. gigantea. Additionally, bone compactness is determined. Most fossil specimens exhibit the typical diploe structure of tortoise shell bones, comprising external and internal cortices surrounding cancellous bone, although considerable variation in cortical thickness, vascularization, remodeling, the presence and abundance of Sharpey's fibers, and preservation was observed. In contrast, extant specimens generally display a more homogeneous microanatomy with less distinct regions. This variation is also reflected in the bone compactness. Fossil Aldabrachelys sp. fragments range between 45.1% and 84.9%, and those of extant A. gigantea fragments between 45.8% and 86.1%. The substantial intra- and interfragment variability observed in both histology and compactness complicates the identification of general microanatomical patterns and highlights the importance of considering regional shell variation. Our study establishes a baseline for future investigations of giant tortoise evolution, ecology, and insular adaptation via histological characterization of shell bones.
Abstract as published, via PubMed.
For healthcare professionals. The summary is generated by AI from the published abstract, and the evidence level is assigned automatically from the study design on the Oxford CEBM hierarchy. Neither is medical advice. Read the full paper before changing practice.