Observations from the fossil record suggest a preservational bias against fish in flood basin lakes and ponds and fluvial settings, presumably due to the susceptibility of their skeletal hard parts to destructive taphonomic processes. This study was designed to compare the durability of fish and mammalian skeletons to elucidate taxon-based biases. Two trout (
Oncorhynchus mykiss) and two rat (
Rattus norvegicus) carcasses were interred in ten pits representing two distinct burial environments during the spring of 2011. Burial site A is a well-drained soil and burial site B a poorly drained soil. A surface site (S) with one carcass each of trout and rat was established in a wire cage for comparison. Pits were exhumed 30, 71, 128 and 361 days after interment. The fifth set of pits will be exhumed at the two-year mark. Immediately following exhumation 3-6 bones per carcass were studied under scanning electron and light microscopes and scored for dissolution and cracking. Dissolution (D) was scored as follows: 0 (no dissolution), 1 (isolated pits), 2 (abundant pits), 3 (>50% surface etched/pitted). Cracking (C) was scored as follows: 0 (no cracks), 1 (minor), 2 (prevalent), 3 (extensive), 4 (pervasive deep cracks/brecciation). The percentage of bones at the highest taphonomic grade for each sample is indicated below:
Exhumation 1 (30 days):
Trout: A 27% C1, 27% D1; B 10% C1, 30% D1; S 100% C0, 60% D1
Rat: A 50% C1, 75% D1; B 20% C1, 80% D1; S 40% C1, 60% D1
Exhumation 2 (71 days):
Trout: A 25% C2, 38% D1; B 11% C2, 11% D2; S 25% C1, 25% D3
Rat: A 63% C1, 63% D2; B 13% C2, 38% D2; S 25% C1, 75 % D2
Exhumation 3 (128 days):
Trout: A 57% C2, 43% D1; B 50% C2, 63% D2; S 50% C1, 50% D3
Rat: A 25% C3, 25% D3; B 50% C1, 38% D3; S 25% C1, 75% D3
Exhumation 4 (361 days):
Trout: A 44% C4, 33% D3; B 50% C1, 25% D3; S 100% C0, 60% D3
Rat: A 100% C3, 75% D3; B 25% C2, 100% D3; S 50% C1, 100% D3
Overall, bones at site B (poorly drained soil) were less altered than at site A (well drained soil), suggesting that drainage plays an important role in floodplain preservation. Surface bones of both taxa were initially more prone to dissolution than buried bones and more resistant to cracking. Mammalian bone appears to be more susceptible to dissolution and fish bone more susceptible to cracking. After one year differences are minimal but they may be substantial after a second year.
