Thursday, 17 February 2011

Elephants, maggots and cadaver decay islands.

Last night saw the broadcast on Channel 4 here in the UK of an excellent documentary called The Elephant: Life after Death. The documentary is available online, but I think might be blocked to non-uk residents: The Elephant: Life after Death

The basic premise of the programme runs thus: A sub-adult bull elephant that had been mortally injured by poachers has to be put down, and an experiment is set up whereby the carcass is placed by a stream bed (such areas are busy spots on the savannah for a variety of reasons), the cameras are set up and a team of experts sit and watch what happens. The next six days and nights see the elephant, all 6 million calories (enough to feed 300 people for a week) of it reduced to skin and bones. A veritable parade of secondary consumers (hyaena, leopard, flies, jackal, soldier death beetles, civet) then appear to partake of the proboscidian feast. Some of these become food for other predators such as birds, civets and ants which come to dine on the maggots and flies, a secondary food chain created by the carcass for the duration it can provide food.

The programme had a good smattering of interesting information, such as the dining habits of Pine Nut Vultures and the fact female hyaenas have penises and give birth through them (wince). Some animals, such as the aforementioned Soldier Death Beetles rely on elephant carcasses to complete their life cycles and feed, mate, lay eggs and provide food for their young. More worrying was the absence of vultures at the site; it seems something is wrong in the ecosystem and numbers are declining and there have been changes observed in the behaviour of the birds, who have become more skittish in recent years.

The programme was an excellent illustration of the flow of energy within an ecosystem, the unlocking of that converted solar energy that is contained in the elephant carcass as a result of it's enormous intake of sunlight-processing plants (elephants can eat up to 300kg of forage a day) and it's dispersal across a wide area by a variety of animals, microbes and also fungi in the longer term.

I bet this smells quite awful . . .

Did something similar occur with dinosaurs in Mesozoic ecosystems? Well, there is an obvious analogue between the death of a megafaunal primary consumer such as an elephant and the death of a hadrosaur or a sauropod (to name but two examples from many), and this makes it tempting to speculate on Mesozoic equivalents, but to find out we need to look at the smallest but vitally important players in the ecosystem. Slightly disappointingly not the not all decomposers at all trophic levels were mentioned (wot no microbes?) in the documentary which also payed fleeting attention the effect of the juices flowing from the carcass on the local environment (although the image of the civet licking maggots up out of the juices surrounding the dead animal was a slightly stomach-churning and fascinating image). This creates a (wonderfully named) cadaver decay island, and during the excavation of Dakota (the hadrosaur mummy found by Tyler Lyson in the badlands of the Hell Creek Formation, Montana) Phil Manning and the crew from the Marmarth Research Foundation and Manchester Univerisity noticed the presence of staining around the body, possibly produced by the seepage of fluids from the decaying dinosaur (Manning, 2008). All this is detailed in Phil's excellent book Grave Secrets of Dinosaurs, which goes into more detail is well worth a read. It would have been really fascinating to have sectioned the ground within the cadaver decay island after six days to see how fluid seepage had affected the soil below the carcass; there was speculation about the appearance of ants which prey on maggots feeding on the carcass, as they live underground and seemed to sense the presence of the carcass from the fluids percolating down through the soil.

On the art front, the cover of  Grave Secrets of Dinosaurs was illustrated by the brilliant paleo-artist Julius T. Csotonyi. I don't have permission to illustrate his work here but it's worth swinging by his site to have a look at his work, which is outstanding. Favourites of mine include his illustration of Cretaceous wildlife of Midland Provincial Park and a Dsungaripterus weii about to dine on a nautliod.

Manning, P. (2008). Grave Secrets of Dinosaurs: Soft Tissues and Hard Science. Washington: National Geographic Society. pp181

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