The Work

Specialist Report 2004 - Amphibian Bone

Posted by steven on 11/04/2005 at 02:25 PM

AMPHIBIAN REMAINS FROM THE 2004 EXCAVATIONS AT HIGH PASTURE CAVE, ISLE OF SKYE

C. P. Gleed-Owen - The Herpetological Conservation Trust

Abstract

This is an assessment of small amphibian remains from contexts 1 to 7 of the 2004 excavations at High Pasture Cave, Skye. Only common toad (Bufo bufo) and common frog (Rana temporaria) were present, and although a few bones are burnt, it appears that the remains were accumulated by avian or mammalian predators.

Introduction

West Coast Archaeological Services carried out excavations at High Pasture Cave on the Isle of Skye during spring 2004. In August 2004, I received a box of vertebrate remains and unsorted residues, as follows:
· Seven bags of small vertebrate remains, picked from bulk samples representing contexts 1 to 7, each with a finds number.
· Eight unsorted residues from bulk sieving of contexts 1 to 7, and 9, each weighing c.1kg.
Samples had been sieved to a minimum mesh size of 1.5mm (S. Birch, pers. comm.). The sorted bones had been recognised as containing amphibian remains (as well as rodents and birds). I was asked to examine them, identify herpetofaunal remains, and comment on any environmental and archaeological significance. The sorted remains were examined, but owing to the paucity of material, it would have been fruitless to examine the unsorted residues. The results are presented here.

Methodology

The small bags of picked bones were examined under x7-x40 binocular microscope, and all herpetofaunal remains were removed, identified to the highest taxonomic level possible (and/or worthwhile), separately bagged and labelled. Total number of identifiable specimens (NISP), and minimum number of individuals (MNI) were counted by size and siding of elements, generally using the ones that are most commonly recovered from archaeological contexts, such as scapulae and humeri. (The limitations of NISP and MNI ought to be emphasised however, particularly when dealing with depositional systems of difficult or unknown taphonomy).


Amphibian and rodent bones from High Pasture Cave

Results

The remains from each of the seven samples are described below, with notes on condition and taphonomic observations. The bones in all of the samples are in a peaty/dirty condition.

HPC04, C001, HP0023
Common toad (Bufo bufo): 1 L ilium, 3 tibiofibulae, 3 L and 2 R radioulnae, 1 R coracoid, 2L and 2R scapulae, 2 partial trunk vertebrae (1 in 2 pieces), 3 femora, 2 partial R humeri, 2 tibiale (1 in 2 pieces).
Common frog (Rana temporaria): 1 male R humerus.
Frog cf. common frog (Rana cf. temporaria): 1 juvenile distal phalanx, 1 sphenethmoid, 1 urostyle, 1 partial femur, 1 metacarpal, 1 R ilium, 1 R coracoid, 1 juvenile L humerus (<1yr).
Frog/toad (Anura indet.): 5 metapodials/phalanges, 1 urostyle.
Non-herps: 192 various elements/fragments (rodent, fish, bird; some strong digestion in one or two rodent long bones, producing holes where thinning is severe).
Comments: most of the bones are quite worn and in poor condition, and some are definitely digested; frog MNI = 2; the frog distal phalanx is 1.3mm long; 2 of the toad femora are very worn and flaking, 1 is pure white and calcined; the partial toad humeri are crunched (predated); 1 toad tibiale is worn; toad MNI = 4 from the radioulnae; indeterminate anuran urostyle is very worn.

HPC 04, T1, C002, HP0079
Toad (Bufo sp.): 1 partial tibiofibula, 1 partial fibulare, 1 metacarpal.
Common frog (Rana temporaria): 1 male L humerus.
Frog cf. common frog (Rana cf. temporaria): 1 female R humerus, 2 R angulosplenials, 1 femur, 1 L and 1 R radioulnae, 1 tibiale, 1 fragmentary ilial ala, 1 partial tibiofibula.
Frog/toad (Anura indet.): 1 phalanx, 1 partial tibiofibula or radioulna.
Non-herp: 77 various elements/fragments (mostly rodent, 1 fish).
Comments: the frog humerus appears possibly calcined and is covered in tiny charcoal fragments; the frog femur has one end apparently crunched cf. predation; both the frog radioulnae are in poor condition, especially the L which is possibly digested; the frog tibiale has worn ends cf. digestion; the frog tibiale and the partial tibiofibula exhibit unusual grease-like red stain spots due to crystallisation within the bone; the male and female humeri are the same size; frog MNI = 3 as the angulosplenials do not match the size of the humeri; toad MNI = 1.

HPC04, T1, C003, HP0087
Common toad (Bufo bufo): 1 femur, 1 R ilium, 2 tibiofibulae, 1 partial tibiofibula.
Toad (Bufo sp.): 1 L and 1 R radioulnae, 1 L angulosplenial, 1 partial trunk vertebra, 1 urostyle.
Common frog (Rana temporaria): 1 L and 1 R ilia.
Frog (Rana sp.): 4 metatarsals, 3 tibiale, 2 fibulare, 1 R squamosal, 1 trunk vertebra, 1 L and 1 R male 2nd metacarpal, 1 L and 1 R scapulae, 1 femur, 1 partial urostyle, 1 partial ilial ala (2 pieces), 1 R radioulna, 1 omosternum, 1 L and 1 R tibiofibulae (1 in 2 pieces), 1 tibiofibula, 1 partial tibiofibula.
Frog/toad (Anura indet.): 1 partial humerus (shaft fragment), 1 partial L angulosplenial, 4 metatarsals, 5 metapodials/phalanges, 1 partial metapodial/phalanx.
Non-herp: 325 various elements/fragments (some mammals are strongly digested).
Comments: toad MNI = 3 from tibiofibulae; frog MNI = 2 (most elements form pairs); the frog radioulna has splayed ends, apparently crunched by predation; 1 frog tibiofibula is bowed, blue and calcined; the indeterminate anuran humeral shaft is burnt black.

HPC 04, T1, C004, HP0179
Common toad (Bufo bufo): 1 femur.
Frog cf. common frog (Rana cf. temporaria) – 1 L and 1 R scapula, 1 femur, 1 partial femur, 1 metatarsal.
Frog/toad (Anura indet.): 1 pterygoid, 1 metapodial.
Non-herp:  13 various elements/fragments (mammal, bird, plant, possibly fish).
Comments: the toad femur is subadult and very worn; the frog partial femur is very crunched, digested, and possibly has toothmarks; toad MNI = 1, frog MNI = 1.

HPC 04, T1, C005, HP0212
Common toad (Bufo bufo): 1 trunk vertebra, 1 phalanx, 1 fibulare.
Frog cf. common frog (Rana cf. temporaria):  1 partial tibiofibula.
Frog/toad (Anura indet.): 1 partial trunk vertebra.
Non-herp: 27 various elements/fragments (mostly rodent).
Comments: the toad fibulare has a hole in the side, possibly due to digestion; the frog tibiofibula has a well-worn medial tip with the appearance of digestive corrosion, and cracking almost resembling calcination; toad MNI = 1, frog MNI = 1.

HPC 04, T1, C006, HP0199
Common toad (Bufo bufo):  1 sacrum (in four pieces), 1 juvenile sacrum (<1yr), 1 parasphenoid.
Toad (Bufo sp.): 1 metatarsal, 1 phalanx.
Non-herp: 12 various elements/fragments (mostly rodent).
Comments: all the toad remains are adult/subadult except for the juvenile sacrum; the parasphenoid’s anterior end is broken, crunched in a way characteristic of predation; toad MNI = 2.

HPC 04, T1, C007, HP0208
Common toad (Bufo bufo): 1 L and 1 R femur, 1 tibiofibula, 1 partial tibiofibula, 1 L scapula, 2 trunk vertebrae, 1 L and 1 R humerus, 1 tibiale.
cf. Frog (cf. Rana sp.): possible femoral fragment.
Frog/toad (Anura indet.): 1 metapodial.
Non-herp: 15 various elements/fragments (mostly rodent).
Comments: the toad trunk vertebrae are pathologically fused; the toad tibiofibulae give MNI 2 and the humeri are of different condition (one being weaker and missing proximal end) also suggesting MNI 2; all the toad remains are adult; the possible frog fragment is whitish, i.e. of different condition (MNI = 1).

Discussion

The assemblage is notably species-poor, with only common toad and common frog present. The non-specific remains almost certainly belong to these species too. There is no sign of newts or reptiles. This may be due to the sieve mesh size being too large; it should be no more than 0.5mm to be sure of retaining newt and lizard remains. Snake vertebrae are normally larger than 1.5mm. However, it is possible that this cave assemblage contained only common frog and common toad anyway. There are modern or historical records, albeit sparse, for smooth newt, palmate newt, common lizard, slow-worm and adder on Skye (Arnold, 1995). Common frog and common toad are widespread across the Scottish Highlands and some of the inner islands, but the toad is much more patchy in its distribution. There are modern records of both species on Skye, and the distribution of all species is almost certainly under-recorded anyway. The common frog is an open country species, often spawning in the shallowest of temporary water bodies. The common toad is often associated with open woodlands, and is more reliant on deeper ponds and lochans for spawning.

All of the samples show signs of digestion in the amphibian remains, and often in the small mammal remains too. Some work has been carried out on amphibian taphonomy and possible predator species (Pinto Llona & Andrews, 1999), but it is still difficult to identify predator species. The most likely candidates are mustelids and raptors, but possibly also canids. Predation as an accumulative agent would mean that the prey species could have originated several kilometres away; this should be borne in mind in making any local environmental reconstructions. The presence of a few burnt/calcined bones in this assemblage raises the intriguing possibility that amphibians were deliberately prepared as food by humans; or they could have been burnt accidentally. There is no obvious overall difference in bone condition (and taphonomic clues) between layers. Both species are more-or-less present throughout the 7 contexts examined here, and there is no apparent relationship between the assemblage and the sedimentology/ stratigraphy. Toads have slightly higher MNI values, but as the greatest MNI for either species is four, it is impossible to discuss relative abundance meaningfully. There is some variation in NISP values between samples and species, but aggregated NISP values are almost identical for the two species. There is an apparent vertical increase in NISP values but this too is probably not significant.

Conclusions

This assemblage contains a very sparse herpetofauna of only two amphibian species: common frog and common toad. Both may be present in Skye today, but the west of Scotland is very under-recorded. It is not unusual to find amphibian bones in very large numbers in cave sequences, particularly those of Holocene origin (Gleed-Owen, 1999), and the assemblage here is relatively sparse and uninformative. It has probably entered the cave via predators as accumulating agents. There is a possibility that humans ate amphibians here as a few of the bones are burnt, but very little anecdotal evidence exists for human consumption of amphibians anywhere in Europe, let alone in Britain. The dirty/peaty appearance of all the sampled bone gives it a relatively recent appearance. A fine sieve mesh (0.5mm) should be used in future, to retain all amphibian and reptile remains.

Acknowledgements

Thank you to Steven Birch for the opportunity to study these remains.

References

Arnold, H.R. 1995. Atlas of amphibians and reptiles in Britain. HMSO, London.
Gleed-Owen, C.P. 1999. Age of the Creag nan Uamh Caves ‘frog-earth’ (Assynt, northwest Scotland) and its relationship to climate and deposits elsewhere. Quaternary Newsletter, 87, 1-14.

Pinto Llona, A.C. & Andrews, P.J. 1999. Amphibian taphonomy and its application to the fossil record of Dolina (middle Pleistocene, Atapuerca, Spain). Palaeogeography, Palaeoclimatology, Palaeoecology, 149, 411-429.

Tables
Context Toad MNI Frog MNI
1 4 2
2 1 3
3 3 2
4 1 1
5 1 1
6 2 0
7 2 1?
Total 14 10
Table 1 - Minimum Number of Individuals
Context Toad NISP Frog NISP Frog/Toad NISP
1 23 29 6
2 3 10 2
3 10 26 12
4 1 5 2
5 3 1 1
6 5 0 0
7 10 1? 1
Total 55 51 24
Table 2 - Total Number of Identifiable Specimens


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