Croc Files: ‘Petrified’ diet of a ‘floating log’
Often found in African water bodies, camouflaged as drift wood to unsuspecting prey, the Nile crocodile (Crocodylus niloticus) is the second largest surviving reptile today.
Hidden within its carnivorous diet is surprisingly a variety of stones of different shapes and sizes. This puzzling discovery was made in the 1800s, when scientists first uncovered stones within the stomach (also known as gastroliths) of a fossilized crocodile. (Taylor, 1993)
These stones as one may expect, are not ingested for nutrition. Why then would a crocodile ‘eat’ stones? Scientists have come up with several explanations for this phenomenon, though not all have been widely accepted in the field of science. The most notable arguments are as follows.
a) Gastroliths aid digestion, by pounding the huge chunks of flesh in the Nile crocodile’s stomach. (Cott, 1960; Taylor, 1993)
b) Gastroliths help to increase their body weight and shift their centre of mass in order to adjust their buoyancy and balance. This allows them to suspend with their eyes just above the surface for prey ambush or to dive deeper to drown larger prey without expending much energy using their limbs or tail. (Cott, 1960; Taylor, 1993)
However, the former among the above two reasons is still disputed, simply because even without gastroliths, flesh (being without exoskeletons or cell walls) is still easily digestible by gastric juices in the Nile crocodile’s stomach. (Cott, 1960; Taylor, 1993) Congruent with the second reason, studies have further shown that the larger the crocodile, the larger the mass of gastroliths found in its stomach. (Cott, 1960) Interestingly, crocodiles usually only start displaying this behavior from the age of one, and as a result juveniles tend to avoid open water due to its poor balance relative to their elder stone-bearing counterparts. (Cott, 1960).
Swallowing stones is just one among many other fascinating behaviors of the Nile crocodile. Unfortunately, they might soon be pushed to the brink of extinction if demand for crocodile leather products continues driving illegal hunting. With that I end off with a quote by Rue Mclanahan (American actress, animal welfare advocate), Cruelty is one fashion statement we can all do without.
Taylor, M. A., 1993, Stomach Stones for Feeding or Buoyancy? The Occurrence and Function of Gastroliths in Marine Tetrapods. Philosophical Transactions of the royal society B, vol. 341 no. 1296 pp 163-175.
URL: http://rstb.royalsocietypublishing.org.libproxy1.nus.edu.sg/content/341/1296/163.full.pdf+html (accessed on 6 Apr 2013)
Cott, H. B., 1960, Scientific Results of an inquiry into the ecology and economic status of the Nile Crocodile (Crocodilus niloticus) in Uganda and Northern Rhodesia, The Transactions of the Zoological Society of London, vol. 29 issue 4 pp 236-242
URL: http://onlinelibrary.wiley.com.libproxy1.nus.edu.sg/doi/10.1111/j.1096-3642.1961.tb00220.x/pdf (accessed on 6 Apr 2013)
“Nile Crocodile (Crocodylus niloticus) – attacking a Wildebeest crossing the Mara River. Maasai Mara Reserve, Kenya, Africa”, By Suzi Eszterhas
URL: http://www.arkive.org (accessed on 6 Apr 2013)
Crocodile Stomach stones, National Geographic September 1960
URL: http://anasaziofferings.com (accessed on 6 Apr 2013)