Abstract
Today, the UNESCO World Heritage Site of Aldabra Atoll is home to about 100 000 giant tortoises, Aldabrachelys gigantea, whose fossil record goes back to the Late Pleistocene. New Late Pleistocene fossils (age ca. 90–125 000 years) from the atoll revealed some appendicular bones and numerous shell fragments of giant tortoises and cranial and postcranial elements of crocodylians. Several tortoise bones show circular holes, pits and scratch marks that are interpreted as bite marks of crocodylians. The presence of a Late Pleistocene crocodylian species, Aldabrachampsus dilophus, has been known for some time, but the recently found crocodylian remains presented herein are distinctly larger than those previously described. This indicates the presence of at least some larger crocodylians, either of the same or of a different species, on the atoll. These larger crocodylians, likely the apex predators in the Aldabra ecosystem at the time, were well capable of inflicting damage on even very large giant tortoises. We thus propose an extinct predator–prey interaction between crocodylians and giant tortoises during the Late Pleistocene, when both groups were living sympatrically on Aldabra, and we discuss scenarios for the crocodylians directly attacking the tortoises or scavenging on recently deceased animals.
Highlights
The identification of species interactions in the form of predation is fundamental to understand ecosystem complexity and community structure [1], but evidence of predator–prey interactions is rarely preserved in the fossil record [2]
Besides tortoise remains with cut marks and tooth marks, or those found associated with tools left by humans, Late Cretaceous protostegid turtles were reported to have been bitten by sharks [16], an undetermined Late Cretaceous marine turtle has been ingested by a large lamniform shark [17], and mosasaurs are thought to be the cause of circular depression bite marks in the shell bones of Cretaceous sea turtles such as Protostega gigas [18,19,20]
The giant tortoise remains studied include one large nuchal with first left peripheral attached (SNHM 1448/17), one small nuchal (SNHM 1449/17), a larger costal fragment (SNHM 1450/17), a smaller costal fragment with sulcus (SNHM 1451/17), a smaller (SNHM 1452/17) and a larger (SNHM 1453/17) hyo- or hypoplastron fragment, one small shell fragment (SNHM 1454/17), which might pertain to a costal and a pelvic girdle consisting of the distal part of a right ilium (SNHM 1455/17) and associated fused pubes (SNHM 1456/17) and fused ischia (SNHM 1457/17)
Summary
The identification of species interactions in the form of predation is fundamental to understand ecosystem complexity and community structure [1], but evidence of predator–prey interactions is rarely preserved in the fossil record [2]. Besides tortoise remains with cut marks and tooth marks, or those found associated with tools left by humans (among others, [12,13,14,15]), Late Cretaceous protostegid turtles were reported to have been bitten by sharks [16], an undetermined Late Cretaceous marine turtle has been ingested by a large lamniform shark [17], and mosasaurs are thought to be the cause of circular depression bite marks in the shell bones of Cretaceous sea turtles such as Protostega gigas [18,19,20]. Compression punctures and tapering scratches have been identified as bite marks in a number of fossil turtles from the Eocene of North America, caused by either mammals (carnivorans, ‘creodonts’ and ‘condylarth’ mammals) or crocodylians such as Borealosuchus and Allognathosuchus, among others [22]
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