During the Late Pleistocene Australia and New Guinea formed a single continuous landmass, known as Sahul. This landmass was home to a wide range of large Marsupials, Reptiles, and Birds, the vast majority of which appear to have become extinct in a relatively short period of time towards the end of the Pleistocene. Although not well dated, these extinctions have widely been linked to the arrival of Modern Humans on Sahul, something which also happened towards the end of the Pleistocene, and which has been linked to other extinction events in different parts of the world.
However, some evidence appears to run contrary to this evidence, including fossil remains of Megafaunal Animals from Kangaroo Island, South Australia, and Willandra Lakes, New South Wales, which appear to considerably post-date the arrival of Humans in the area. This matter remains difficult to resolve, due to a paucity of Late Pleistocene Animal remains with accurate dating information, combined with a poor understanding of when Modern Humans colonised the different ecoregions of Sahul.
New Guinea today comprises about 10% of the remaining Sahul Landmass, and has a climate, geography, and ecology very different from most of Australia. The island is likely to be a key to understanding the Human settlement of Sahul, as it would have been reached first by any colonisers making their way from Eurasia across the islands of Indonesia, the only plausible model for the settlement of the region. Unfortunately, the Pleistocene fossil and archaeological record of New Guinea is even poorer than that of Australia (something common in tropical forested and upland environments, which cover most of the island).
There are currently five archaeological sites across Sahul which combine Human-made artefacts with Megafaunal remains. Four of these are in Australia: Clogg’s Cave in Victoria State, Cuddie Springs in New South Wales, Seton Rockshelter on Kangaroo Island, South Australia, and Warratyi Rockshelter, in the Flinders range of South Australia. The fifth is at Nombe Rockshelter in Chimbu Province, Papua New Guinea.
Nombe Rockshelter is particularly interesting, both because it is the only site on New Guinea which appears to combine Late Pleistocene Megafaunal remains with evidence of Human activity (a second possible such site, at Kelangurr Cave in West Papua, has yet to be confirmed), and because of the great distance that separates it from the Australian sites, all of which are on the southern part of that landmass.
The material at Nombe Rockshelter includes a variety of faunal remains, largely identified from cranial evidence (i.e. skull fragments and teeth), combined with archaeological remains (tools etc.) and charcoal fragments, from which dates ranging from 25 500 to 19 600 years before the present have been obtained, i.e. younger than the date generally given for the mass extinction event which impacted continental Australia and Tasmania, at about 40 000 years before the present.
However, our current understanding of the Nombe Rockshelter material suggests that it cannot be taken as unequivocal evidence of the co-existence of a Human population with indigenous Megafauna. This is because the site was disturbed during a Late Pleistocene occupation of the site; at some point a trench was dug at the back of the cave, and the much of the surface layer in the cave has been reworked by the action of both Humans and Pigs, making it possible that zoological material found in the same layers as tools and charcoal may have been excavated from an earlier layer by the makers of those items.
In a paper published in the journal Archaeology in Oceania on 16 September 2022, Gavin Prideaux, Isaac Kerr, and Jacob van Zoelen of the College of Science and Engineering at Flinders University, Rainer Grün of the Research School of Earth Sciences at the Australian National University, Sander van der Kaars of the School of Earth, Atmosphere and Environment at Monash University, Annette Oertle and Katerina Douka of the Department of Evolutionary Anthropology at the University of Vienna, Elle Grono, Aleese Barron, and Mary-Jane Mountain of the School of Archaeology and Anthropology at the Australian National University, Michael Westaway of the School of Social Science at the University of Queensland, and Tim Denham, also of the School of Archaeology and Anthropology at the Australian National University, review the faunal material from the Nombe Rockshelter, with an emphasis on the previously undescribed post-cranial material from the site, present uranium isotope dates obtained from these remains, examine other sources of dating information from the site, including pollen and protein, and discuss the implications of their findings for our understanding of the timing of Megafaunal extinctions on Sahul.
The Nombe Rockshelter was discovered in 1964 by Peter White of the Australian National Museum, on a limestone outcrop in the Porol Range, part of the Papua New Guinea Highlands, and was the subject of a series of investigations led by Mary-Jane Mountain between 1971 and 1980.
The stratigraphy of the Nombe Rockshelter is complex, with the site apparently having been the subject of repeated episodes of disturbance, but the deposits there can be grouped into four main strata. Radiocarbon dating has enabled broad time-frames to be applied to each of these strata, and suggests that three of the four deposits has suffered considerable internal mixing, but that there is little or no mixing between the layers.
The layer at Nombe Rockshelter that does show reliable internal stratigraphy, is termed Stratum B, which forms a clearly layered and well dated Holocene sequence, dated to between 10 400 and 6300 years before the present, which has produced numerous archaeological artefacts.
However, the layer of of interest in Prideaux et al.'s study is Stratum D, which is rather more complicated to interpret. Stratum D can be divided into five sub-strata, with the uppermost of these being D1 and D5. Sub-stratum D1 being a red-brown clay, and D5 being similar, but with limestone flecks. These overlay sub-stratum D2, a gingerish red-brown clay, which in turn overlies D3, a dense red-brown clay, which in turn overlays D4, a dense brown clay. Substrata D2-D4 are all more than 25 500 years old, and comprised of reworked material which was originally laid down in the beds and banks of a drainage channel. D1 and D5, on the other hand, were laid down on top of these deposits after the channel had ceased activity.
Previous analysis of the site has reported remains attributed to a Thylacine, Thylacinus sp., in both Pleistocene and and Holocene strata at Nombe, as well as four extinct species of large, herbivorous Marsupials, Dendrolagus noibano, Protemnodon tumbuna, Nombe nombe (originally identified as Protemnodon nombe), and a Pig-sized Diprotodontid from the Pleistocene layers (but principally substrata D1 and D5), as well as later, Holocene, deposits.
Little archaeological material has been recovered from the Pleistocene layers at Nombe, but sufficient to establish the presence of Humans. These include a waisted blade and other materials found directly in context with Megafaunal remains, as well as other archaeological remains older than this. Noteworthy items include an axe blade with a ground edge, recovered from Substratum D1, and the waisted blade, which was found within a crack which had penetrated down into Substratum D3, but was filled with material from Substratum D1, with Megafaunal remains found directly above it, still within Substratum D1. Similar waisted blades are known from some of the oldest known Human settlements on New Guinea, at Bobongara and Ivane Valley, although their use appears to have continued for a long time, and there are much younger examples.
The bones buried in Pleistocene strata at Nombe Rockshelter show some loss of nitrogen (and therefore collagen) and carbon, but on the whole are well preserved, having been quickly incorporated into a clay-rich, anoxic matrix. These Pleistocene layers include faunal remains which have apparently derived from a number of different sources, with a higher proportion of smaller elements than is the case in later Holocene deposits at the site. This may be because bones in the Holocene layers remained at the surface for longer, exposing them to trampling and the deleterious effects of the tropical climate, although it may also indicate that small predators, such as Owls or Dasyurids, were bringing prey items to the site for consumption. Whatever the case, the site is also contains medium and large bones, possible brought to the site by Thylacines, as well as sparse archaeological material, which probably implies the site being visited by Humans only infrequently. The tools and the larger bones appear to date from about the same time as the stone tools, but none of them show direct evidence of Human activity (such as cut-marks)m and no robust stratigraphy has been developed for the site.
Previous studies of the Nombe site and the materials recovered from it have concentrated on attempting to date the material and determine whether New Guinea saw a long period of Human-Megafauna coexistence, with more recent studies turning to isotope dating methods to try to understand the stratigraphy of the site.
Prideaux et al. used uranium-thorium dating to obtain direct dates from Megafaunal remains at Nombe Rockshelter, as well as identifying the post-cranial remains used in the study. Uranium-thorium dating works because uranium decays to thorium at a known rate, so that the ratio of the two elements in minerals that naturally incorporate uranium but not thorium can be used to establish a date for the minerals. Neither uranium nor thorium are typically found in organic tissues, but uranium can be absorbed into mineral skeletal elements, such as tooth and bone, after an animal is dead, creating the possibility for using uranium-thorium dating to at least establish a minimum age for such tissues; the uranium can potentially be absorbed at any point after death, not necessarily immediately post-mortem, so the method cannot be used to establish a maximum age. They used palynology (pollen analysis) as a way of assessing the environment in which the deposits were laid down, and to better refine the boundaries between strata C and D.
The first piece of fossil evidence examined, NCA A3 11, is comprised of four fragments of thin cortical bone, with a thin spine which starts 15 mm from the articular facet. The bone lacks a distal articulation, indicative of being either the end of a limb or part of the pelvic or shoulder girdle, and its general morphology is consistent with that of a Mammalian scapula. The size of the bone, combined with its age and location, would indicate that it came from either a very large Monotreme or a medium-to-large Marsupial, and since Monotremes have a quite differently structured scapula to other Mammals, the bone can be assumed to be the scapula of a Marsupial.
Five groups of Marsupials which would have been present in the Late Pleistocene of New Guinea produce members large enough to have a scapula the size of the specimen; the Macropodidae (Kangaroos and Wallabies), Thylacinidae (Thylacines), Thylacoleonidae (Marsupial Lions), Diprotodontidae (an extict group of large Marsupial browsers) and Vombatidae (Wombats). Macropods have a distinctive scapular spine, which is deflected towards the cranium, whereas that of NCA A3 11 is deflected at 10° from the perpendicular. The scalpulas of Thylacoleonids are compressed craniocaudally, giving them a very straight cranial border with a small scapular notch, quite unlike the shape of NCA A3 11. The only Pleistocene Wombat large enough to have produced the specimen, Phascolonus gigas, has a scapula inwardly deflected with outward-bowed borders, rulling out the specimen coming from a Vombatid. The scapulas of Diprotodontids are significantly larger and more robust than NCA A3 11.
This leaves a Thylacine as the only plausible origin of the bone, with specimens assigned to the species Thylacinus cynocephalus (which became extinct on the island of Tasmania in the 20th century) previously described from the Late Pleistocene of Chimbu Province. Since specimen NCA A3 11 is morphologically a good match for Thylacinus cynocephalus, Prideaux et al. feel confident in assigning the specimen to that species.
The second specimen examined, NCA X2.12 255, is identified as a Mammalian ascending ramus (the rear part of the upper jaw, and the part which connects to the skull), based upon the presence of distinct coronoid and condylar processes, the shallow temporo-masseteric concavity and the flattened nature of the specimen.
Again, the size and shape of the specimen indicates that it is derived from a large Marsupial, although in this instance the specimen is clearly not a Macropodid, Diprotodontid or Vombatid, as these groups have a coronid process which narrows rapidly when seen in lateral view, while the coronid process of NCA X2.12 255 is broad in lateral view, something seen in only in the carnivorous Thylacoleonidae and Thylacinidae. The only Thylacoleonid likely to have been present in the area in the Late Pleistocene is Thylacoleo carnifex, which has a distinct hook upon its coronid process, something absent from NCA X2.12 255. The morphology is again consistent with the Thylacinid Thylacinus cynocephalus, a species already identified as being present at Nombe Rockshelter, and Prideaux et al. also assign this specimen to the species.
Surface scans of a partial right dentary of Thylacinus cynocephalus (NCA X2.12 255). (a) Lateral view; (b) medial view; (c) dorsal view. Prideaux et al. (2022).A piece of bone from close to the area where the fourth molar would have been present in life was removed from NCA X2.12 255 was removed for uranium-thorium dating.
The next specimen examined, NCA Z6 13/14 316, an end portion of a long bone, identified by the presence of what are clearly recognisable as a deltoid tuberosity, pectoral crest, greater tubercle and lesser tubercles as the proximal extremity of a right humerus. The specimen has a fused epiphysis, indicating it came from an adult Animal. The proportions and size of this specimen are incompatible with it having come from anything other than a large Diprotodontid Marsupial. Furthermore, it is very similar to the right humerus of the holotype specimen of Hulitherium tomasettii, making it very unlikely that it came from any other species.
A sample of bone was taken from this specimen for uranium-thorium dating.
Specimen NCA X2.12 250 is another fragment of a long bone, on this occasion heavily abraded and showing signs of having been gnawed at by a rodent. One end of this specimen has what appear to be the remains of a large, inverted process, which makes it likely that it is a fragment of ulna. The specimen has what appears to be a large styloid process, something characteristic of Plio-Pleistocene Diprotodontids. The specimen is to badly preserved to be classified any more precisely, although Prideaux et al. note that its size is compatible with it being derived from Hulitherium tomasettii, the only confirmed Diprotodontid species at the site.
Specimen NCA A1:6 18 measures 122 mm x 51 mm, and is broken at either end, indicating that it is a fragment of a much larger bone. The fragment is roughly triangular in cross-section at one end, with slightly convex edges, but changes about half-way along its length into a thickened-planar shape. One face of the triangular section has an articular facet, while the planar section has an attachment for a large muscle or ligament. This general morphology is consistent with the middle portion of a right ilium, with the thickened planar section being the caudodorsal iliac spine and the scarred area the sacral surface.
The size of this specimen implies a large Marsupial. An origin from a member of the Vombatidae can be ruled out, as the ilium of large Wombats is rounded with a dorsally twisted iliac spine. Similarly, the Palorchestidae (large Diprotodontids) can be excluded, as these Marsupials have a broad, triangular iliac spine and a distinctive projected rectus tubercule. The presence of an iliac spine rules out other Diprotodontid groups, as well as the Thylacoleonidae.
The general morphology of the bone is consistent, however, with it having come from a Macropodid, although most large members of this group have a lateral projection on the iliac spine, which NCA A1:6 18 lacks. This absence is found in members of the genus Protemnodon, an extinct genus closely related to Grey Kangaroos, but thought to have resembled large, robust Wallabies.
Two members of the genus Protemnodon have previously been described from Nombe, Protemnodon tumbuna, and 'Protemnodon' nombe; although 'Protemnodon' nombe has recently been shown not to be closely related to other species assigned to the genus, and renamed Nombe nombe. This being the case, Prideaux et al. assign specimen NCA A1:6 18 to Protemnodon tumbuna.
Specimen NCA M71 9 is another section of long bone, in this case curved and with three articular facets set into one side, roughly a fifth of the way along the shaft. This specimen is roughly 130 mm long and 32 mm thick, and is split into two fragments. The proportions and morphikigyof this bone are consistent with is being a Mammalian limb-bone, and its possession of a shaft which extends beyond the articular facets marks it out as the ulna of a Marsupial, with the position of those facets indicating it is a right ulna. The bone probably came from a juvenile, as the olecranon process lacks a fused proximalepiphysis.
The specimen lacks the outward deflected ventral margin of a Thylacine ulna, and the robust nature and large olecranon process of a Wombat, nor the robust nature and enlarged oronoid process, of the Diprotodontid Thylacoleo carnifex. The bone does, however, fit well with the expected proportions of a large Macropodid, and in particular with members of the genus Protemnodon. Two species of Protemnodon are known from the Late Pleistocene of New Guinea, Protemnodon otibandus and Protemnodon tumbuna. Prideaux et al. believe the specimen is most similar to Protemnodon tumbuna, a species already known from the Nombe assemblage, and that NCA M71 9 is therefore highly likely to be another example of that species.
A second specimen, NCA X2.13 241, also appears to be a Macropodid right ulna. This is loosely similar to NCA M71 9, but smaller, and has a fused proximal epiphysis, indicating that it is from an adult. Since this adult specimen is smaller than the juvenile NCA M71 9, it is unlikely to be another specimen of Protemnodon tumbuna, nor does it bear any obvious similarity to any other Macropodid known from the Late Pleistocene of Papua New Guinea for which the ulna is known. The only other Macropodid from the Nombe assemblage is Nombe nombe, which was described from cranial material only, with no known post-cranial elements. It is quite possible that NCA X2.13 241 represents the ulna of this species, but until more complete specimens are found, there is no way to be certain of this.
A third specimen, NCA H71 9, appears to be another Macropodid ulna, this time the left. This specimen is broken into two segments. The specimen is very similar to specimens of Protemnodon, although not similar enough to specimens of Protemnodon tumbuna to be assigned to that species. It is also close enough to NCA X2.13 241 that is is likely to be an adult member of the same species, for which reason Prideaux et al. have decided not to make any taxonomic assessment of this specimen at this time.
The final specimen examined, NCA X2.13 249, is a collection of small bones, interpreted as a left capitatum magnum, a left trapezoid, a left scaphoid, a probable pisiform fragment, and a distal phalanx. These appear to be from a moderately large Marsupial, and probably a ground-dwelling Macropodid.
Uranium-thorium dating can only provide a minimum age for a specimen, as, uranium can seep into a specimen shortly after death, it can also enter the same specimen at later stages, effectively overwriting the original signal, and making the specimen appear younger than it actually is. Prideaux et al. took samples from five specimens from the Nombe assemblage for uranium-thorium dating, chosen for their preservation state, and taxonomic identifiability.
These were part of a tooth from a mandible assigned to the Thylacine, Thylacinus cynocephalus, a section of bone taken from the humerus assigned to the Diprotodontid Marsupial, Hulitherium tomasetti, a piece of bone taken from the ilium assigned to the Macropodid, Protemnodon tumbuna, and three fragments of ulna, one from the specimen of Protemnodon tumbuna, and the two from unknown Macropodids.
Three separate dates were obtained from different sections of the Thylacine tooth, these being 126 700, 134 100, and 136 800 years before the present, i.e. all comfortably before the arrival of Humans on New Guinea.
The specimen from the Diprotodontid Marsupial, Hulitherium tomasetti, was dated to 54 600 years before the present, around the time Humans are thought likely to have arrived in the area.
The ilium assigned to the Macropodid, Protemnodon tumbuna, could not be assertained.
The three Macropodid ulnas, however, produced much younger dates, with the specimen assigned to Protemnodon tumbuna producing a date of 25 100 years before the present, and the two unidentified specimens producing dates of 22 300, and 27 200 years before the present, after the arrival of Humans in the area.
Collagen fingerprinting (a technique which seeks to identify specimens from their collagen content, the exact molecular structure of collagen being species specific) was carried out on 163 unidentified bone samples from Nombe. Of these, 26 were identified, three as Diprontodontids and 23 as Macropodids. Notably, the three Diprontodontids came from the same strata as Macropodid ulnas, indicating that these Animals were also present after the arrival of Humans.
A pollen analysis of the deposits suggests that these Animals lived in a forested environment dominated by Southern Beach, Nothofagus sp., trees, with abundant Mosses, Tree Ferns, Ferns, and other Pteridophytes, but very few Grasses. This type of environment is still found in New Guinea today, at altitudes of between 600 and 3100 metres above sealevel. The site seems to have been in an area of relatively undisturbed, which is consistent with the low level of archaeological material present, suggesting the area was only infrequently visited by Humans.
The oldest signs of Human activity at Nombe, including stone tools and charcoal, significantly predate the youngest specimens of at least two Megafaunal species, Protemnodon tumbuna and another, unknown, Macropodid, with another Megafaunal Marsupial, Hulitherium tomasettii, present at around the time Humans are thought to have appeared in the area.
Historically, the identification of Marsupial remains at archaeological sites has relied almost exclusively on cranial and dental material. The study of a wider range of material at sites such as Nombe clearly has the potential to identify a greater range of taxa, enabling a better understanding of the fauna associated with these sites.
Of the species identified at Nombe from their postcranial remains, Thylacinus cynocephalus and Protemnodon tumbuna had previously been identified from cranial material, but Hulitherium tomasettii had only been recorded as a 'Pig-sized Diprotodontid'. The Macropodid Nombe nombe may also be represented by postcranial remains at the site, as it is the most likely source of the unidentified Macropodid ulnas, but this is impossible to confirm at this time. Collagen fingerprinting also appears to have considerable potential for the identification of fragmentary bones in archaeological material.
Uranium-thorium dates obtained from Megafaunal Macropodid remains at Nombe suggest that these Animals were still present here 30 000 years after the arrival of Humans on Sahul, although it is worth remembering that this method can produce dates substantially younger than the true age of a fossil. However, these bones are stratigraphically above the oldest tools, which does support the proposition that they are younger. Prideaux et al. suggest that a definite resolution of this matter would require a careful re-excavation of the site, with the deployment of multiple dating methods to all excavated material of biological material, as well as flowstones separating the layers, as well as detailed studies of all bones, artefacts, charcoal, pollen, and sediments.
The Clogg's Cave site in eastern Victoria State, Australia, produced Megafaunal Macropodid remains which were, until recently, thought to be of a relatively young age, but which have now, by careful re-examination of the site, been shown to be about 45 000 years old. Prideaux et al. believe such an approach should also be applied to the Nombe Rockshelter, as well as to other places showing late Megafaunal survival, such as Seton Rockshelter on Kangaroo Island, and the sites of the Willandra Lakes region.
Records of early Human (and Hominin) settlement of the interior highlands of Papua New Guinea are rare, although a series of archaeological sites in the Ivane Valley suggest that areas between 1900 and 2000 m above sealevel were being visited by 45 000 years ago. There is evidence for the consumption of starch-rich tuberous Plants and the leaves and nuts of Pandanus Palms, as well as burning in the Kosipe Swamp. Other intra-montane valleys along the highland spine of New Guinea, although these are generally not well dated, and only two sites, in the Upper Wahgi Valley and Upper Baliem Valley, show signs of Human activity which can be confidently dated to more than 30 000 years ago.
The Nombe Rockshelter is in an area which appears to have been dominated by Montane (Nothofagus) Beech forests, showing little sign of large-scale disturbance, human or otherwise, before the Early Holocene, something which fits with the very low number of pre-Holocene tools found. A very low Human population density with a low frequency of visits to the area would explain the ability of Magafauna to survive in the area till around 25 000 years ago.
This raises the possibility that pockets such Megafauna may also have survived in other remote and rugged environments in Sahul, if such environments were not favoured by early Human settlers, and were visited only seldomly. Other research has shown that in the nearby Sunda Islands the local Megafauna also survived for an extended period after the arrival of Modern Humans. This has been explained by the presence of earlier Hominids on the islands, something which would have given the local fauna an opportunity to adapt to Human-like behaviour before the arrival of Modern Humans. No direct evidence of earlier Hominins has ever been found on Sahul, but inferences from genetic data have been used to suggest that New Guinea may have been settled by Denisovans, an archaic Human group, before the arrival of fully Modern Humans, and Prideaux et al. suggest that this might have given the wildlife there a degree of resilience to Human behaviour.
Current evidence from the Nombe Rockshelter suggests that some elements of the Sahul Megafuana may have survived on New Guinea for tens of thousands of years after the arrival of Modern Humans, at least in areas where the environment was considered less than favourable by those Humans, and which were subsequently visited infrequently. However, the dating of this site is still less than perfect, and further, and more complete, investigations of the site are needed before the late dates for the Megafauna can be confirmed.
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