Doing the Haplomastodon Breakdown

African elephants are sturdy beasts. They don’t break down easily. After death, elephant bodies become temporary islands of intense activity – providing nourishment to scavengers from hyenas to beetles – and the same was true of prehistoric elephants.

At Águas de Araxá, Brazil, a resort hotel sits on top of an ancient elephant graveyard. Construction workers found the large cache of Pleistocene fossils there while excavating the site in 1944, and later studies determined that many family groups of prehistoric elephants had all died during some catastrophic event, perhaps a drought. There were no complete skeletons – the bones were scattered throughout the site – and an in-press study at the Journal of South American Earth Sciences reports that some of the bones bear the traces of scavengers that helped disarticulate the carcasses.

There are no natural populations of elephants in South America today, but, until relatively recently, many species of proboscidean called the continent home. Migrants from the north, elephants may have arrived in the southern continent as early as nine million years ago, but by about 6,000 years ago they had entirely disappeared. These were not elephants as we would recognize them today. They were gomphotheres, members of a long-lived and widespread subgroup of low-skulled, long-tusked elephants that proliferated into several different forms when they reached South America.

As reported in the new paper by Victor Hugo Dominato and co-authors, the elephant bones from Águas de Araxá are definitely those of gomphotheres. What species of gomphothere, however, is difficult to say.

Dominato and colleagues assign the femur, humerus, and three ulnae that form the basis of their study to the species Haplomastodon waringi. This sounds simple enough, but the pedigree of Haplomastodon is a contested topic among fossil elephant experts. A short-skulled gomphothere with short, upturned tusks, Haplomastodon is best known from fossils found in Ecuador and given the species name H. chimborazi, but some paleontologists claim that these animals are indistinguishable from the closely-related Stegomastodon.

Even if the Haplomastodon specimens from Ecuador turn out to be distinct from closely-related forms, though, paleontologists have generally agreed that the specimens from Brazil do not represent a second Haplomastodon species. Just last year Marco Ferretti determined that the poorly-preserved fragments from which H. waringi was initially described were too scrappy to justify identifying them as a Haplomastodon species. The Águas de Araxá certainly belong to some kind of gomphothere, but probably not Haplomastodon.

All that taxonomic wrangling aside, a rotting “Haplomastodon” carcass by any other name would smell just as sweet to opportunistic carnivores. By studying the damage left on the Águas de Araxá long bones, Dominato’s team have been able to reconstruct what happened to the elephants after death.

There were a total of 69 toothmarks on the five bones, ranging from 32 on the humerus to five on an ulna. Most of the damage was located on the proximal parts of the bones – the ends closest to the body near the points of articulation. This pattern was consistent with scavengers attempting to disarticulate limbs in order to carry off large chunks of flesh to consume away from all the action around the carcass. Think of it as carrion take-out.

Precisely what species of carnivore left the pits and scratches on the elephant bones cannot be definitely determined. Cats, bears, and dogs are all possible culprits, but Dominato and co-authors favor dogs as the probable scavengers. Feeding dogs typically leave more toothmarks than cats, fewer than hyenas, and do not remove as much bone tissue with their gnawing as bears, and this appears to be consistent with the gomphothere bones. The fossil dog Protocyon – found throughout Brazil – lived during the time the Águas de Araxá bonebed was formed, and so the scientists propose that this canid was most likely responsible for the bone damage. Such a large collection of rotting carcasses probably attracted other scavengers – it has been estimated that there were 40 elephants or more, and such a rich resource would have certainly attracted opportunistic carnivores from far away – but the canids were the ones to most prominently leave their mark on the remains.

The scavenging canids broke up and scattered the carcasses before burial, but they were not the only organisms to contribute to the gomphothere breakdown. Several gomphothere vertebrae from the site have trace fossils on them – a characteristic pattern of damage called Cubiculum ornatus. This is the name given to pupal chambers bored into fossil bones by dermestid beetles. These flesh-eating beetles typically eat and inhabit carcasses once much of the fat and soft tissue has already been removed, meaning that the gomphothere bones probably sat out on the surface for weeks. The bodies did not lay exposed so long that the bone itself began to crack and weather under the influence of the elements, but the carcasses were almost completely disarticulated by the time they were buried. Killed by drought, the battered records of these prehistoric elephants were preserved when the heavy rains finally returned and washed their bones together.

Top Image: The skull of a Stegomastodon on display in Argentina’s Museo de Ciencias Naturales de La Plata. From Flickr user tom )º(

References:

ARROYO CABRALES, J., POLACO, O., LAURITO, C., JOHNSON, E., TERESAALBERDI, M., & VALERIOZAMORA, A. (2007). The proboscideans (Mammalia) from Mesoamerica Quaternary International, 169-170, 17-23 DOI: 10.1016/j.quaint.2006.12.017

Cozzuol, M., Mothé, D., & Avilla, L. (2011). A critical appraisal of the phylogenetic proposals for the South American Gomphotheriidae (Proboscidea: Mammalia) Quaternary International DOI: 10.1016/j.quaint.2011.01.038

Dominato, V., Mothé, D., da Silva, R., & Avilla, L. (2011). Evidence of scavenging on remains of the gomphothere Haplomastodon waringi (Proboscidea: Mammalia) from the Pleistocene of Brazil: Taphonomic and paleoecological remarks Journal of South American Earth Sciences DOI: 10.1016/j.jsames.2011.01.002

FERRETTI, M.P. (2010). Anatomy of Haplomastodon chimborazi (Mammalia, Proboscidea) from the late Pleistocene of Ecuador and its bearing on the phylogeny and systematics of South American gomphotheres Geodiversitas, 32 (4), 663-721

FICCARELLI, G., BORSELLI, V., HERRERA, G., MORENOESPINOSA, M., & TORRE, D. (1995). Taxonomic remarks on the South American Mastodons referred to Haplomastodon and Cuvieronius Geobios, 28 (6), 745-756 DOI: 10.1016/S0016-6995(95)80071-9

Mothé, D., Avilla, L., & Winck, G. (2010). Population structure of the gomphothere Stegomastodon waringi (Mammalia: Proboscidea: Gomphotheriidae) from the Pleistocene of Brazil Anais da Academia Brasileira de Ciências, 82 (4), 983-996 DOI: 10.1590/S0001-37652010005000001