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Reappraisal of the extinction of Canariomys bravoi, the giant rat from Tenerife (Canary Islands)
Quaternary Science Reviews 94 (2014) 22e27
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Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev
Reappraisal of the extinction of Canariomys bravoi, the giant rat from Tenerife (Canary Islands) Juan Carlos Rando a, *, Josep Antoni Alcover b, Bertila Galván c, Juan Francisco Navarro c a
Departamento de Biología Animal (UDI Zoología), Universidad de La Laguna (ULL), E-38206 La Laguna, Tenerife, Canary Islands, Spain Departament de Biodiversitat i Conservació, IMEDEA (CSIC-UIB), Cr Miquel Marquès 21, 07190 Esporles, Mallorca, Balearic Islands, Spain c Departamento de Prehistoria, Antropología e Historia Antigua, Universidad de La Laguna (ULL), E-38071 Canary Islands, Spain b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 February 2014 Received in revised form 10 April 2014 Accepted 13 April 2014 Available online 5 May 2014
All the Quaternary endemic rodents of the Canary Islands are currently extinct. The Lava Mouse Malpaisomys insularis inhabited the easternmost islands, whereas the giant rats Canariomys bravoi and Canariomys tamarani lived in the central islands of Tenerife and Gran Canaria, respectively. Bones of C. bravoi have appeared in archaeological sites together with shellfish and butchery remains. Traditionally, they have been considered as an evidence of the sporadic consumption of C. bravoi by the aboriginal people, in some instances as recently as the time of the first European contact (14th century AD). Accordingly, the extinction of C. bravoi has been linked to the European colonization of Tenerife. The plausibility of this extinction date has been explored through new radiocarbon dates obtained on selected C. bravoi bones and through a reappraisal of the published dates. Our analysis allowed us to establish an earlier last documented occurrence age for C. bravoi, prior to the third century cal BC, much earlier than previously assumed. The analysis of formerly published 14C dates of archaeological remains from Tenerife shows that samples with confidence intervals (95.54%) that are older or overlap with the last documented record of C. bravoi were performed on materials with large sources of error (such as wood, charcoal or bulk ash-sediments). Conversely, the new radiocarbon dates and analyses presented herein are in agreement with the occurrence of an earlier rapid extinction linked to the first human presence on the island. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Aboriginal settlement Canariomys bravoi Insular rodent Quaternary extinctions Radiocarbon dating
1. Introduction The three species of rodents known to have inhabited the Canary Islands during the Quaternary are currently extinct. The Lava Mouse Malpaisomys insularis inhabited the Eastern islands (Fuerteventura and Lanzarote) and islets, while the giant rats Canariomys bravoi and Canariomys tamarani occupied the central islands of Tenerife and Gran Canaria, respectively (Fig. 1). M. insularis survived to the introduction of the House Mouse Mus musculus and the aboriginal settlement of the islands, that took place sometime between 756 cal BC and 313 cal AD (Alcover et al., 2009), a time range established from AMS 14C dating on bones of introduced M. musculus and on bones of endemic fauna on sites lacking it. The extinction of M. insularis was probably an asynchronous process that correlates with the introduction of the Black Rat Rattus rattus by European sailors that took place before 650 cal AD in Lanzarote
* Corresponding author. Tel.: þ34 922318380. E-mail addresses: [email protected], [email protected] (J.C. Rando). http://dx.doi.org/10.1016/j.quascirev.2014.04.013 0277-3791/Ó 2014 Elsevier Ltd. All rights reserved.
and after the 13th century in Fuerteventura (Rando et al., 2008, 2012). Available information on C. tamarani and on its extinction is very scarce (López-Martínez and López-Jurado, 1987; LópezJurado and López-Martínez, 1988). Published radiocarbon dates of C. bravoi bones collected from palaeontological sites (lava tubes) cover a time span from 12,230 140 BP (12,880e11,810 cal BP) to 2305 40 BP (471e 208 cal BC) (Michaux et al., 1996; Bocherens et al., 2006). Since the weight of this rodent could exceed 1 kg, hunting by aboriginal people, competition and predation by alien species have been proposed as factors that ultimately led to its extinction (Michaux et al., 1996; Bocherens et al., 2006). The discovery of C. bravoi bones in association with shellfish and livestock remains in an archaeological dwelling site in the north of the island (Las Arenas3) was initially interpreted as an evidence of its sporadic exploitation by the aboriginals until dates very close to the European contact (Galván et al., 1999) in the 14th century (Aznar et al., 2006). The archaeological site of Las Arenas-3 is a lava cave with three stratigraphic layers (ranging from III to I) (Galván et al., 1992).
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Fig. 1. (a) Location of Canary Islands and (b) the distribution of extinct endemic rodents on the archipelago.
Radiocarbon dates performed on charcoal from the two more recent levels (II and I) yield less than a millennium: 730 90 BP (1049e1412 cal AD) and 730 60 BP (1169e1393 cal AD), respectively (Galván et al., 1999). Bones are abundant in these layers, and mainly pertain to livestock, but include a small proportion of C. bravoi and the giant lizard Gallotia goliath as well (Alberto, 1998). Bones of both extinct species have also been found in the contiguous burial site of Las Arenas-1 (Galván et al., 1999). A natural deposition has been proposed to explain the presence of G. goliath and C. bravoi at this burial site (Galván et al., 1992; Alberto, 1998). The interpretation of extinction events is almost always submitted to considerable debate due to the interplay of several causes of potential error, not always taken into account by researchers. One of them consists of the false co-occurrence of man and the autochthonous species due to, among diverse factors, the reworking of sites (e.g., Olsen, 1999; Burney et al., 2001; Macphee et al., 2007). To analyse the reliability of the associations, we dated bones from the more recent levels of these two archaeological sites (Las Arenas-3 and Las Arenas-1). It was expected that all samples of C. bravoi from these two sites would have a more recent age than the samples obtained from palaeontological localities around the island (Fig. 2). In order to obtain an accurate chronology informative to understand the causes and processes involved in the extinction of C. bravoi, we also dated bones of two commensal rodents: M. musculus from a palaeontological site and R. rattus from an archaeological site (both from Tenerife Island).
formed by 7.37e4.5 Ma basaltic rocks (Ancochea et al., 1990). No distinctive stratigraphic units were identified. Bones of C. bravoi, G. goliath and M. musculus were present in this site. 2.3. Las Arenas-1 (archaeological site) This is a small lava tube in Quaternary basaltic rocks (Ancochea et al., 1990). It is located in the Northwest of Tenerife. This secondary burial site contains seven archaeological levels that were excavated by Prof. B. Galván team (Galván et al., 1992). In addition to human remains, bones of sheep, goat, pig, dog, C. bravoi and G. goliath were found concurrently. It was established that these remains were incorporated as part of a ritual-ceremony, although the accumulation of C. bravoi and G. goliath bones might be the result of a natural deposition prior to the human activities (Alberto, 1998; Galván et al., 1999). 2.4. Las Arenas-3 (archaeological site) This is a lava cave in Quaternary basaltic rocks (Ancochea et al., 1990), located about 50 m from Las Arenas-1. It was used as a
2. Sites The samples that were submitted for radiocarbon dating were recovered from two palaeontological and two archaeological sites (Fig. 2). 2.1. Cave at Barranco de Las Moraditas (palaeontological site) This is a small lava tube located at the East of Tenerife, in Quaternary basaltic rocks (Ancochea et al., 1990). Bones of C. bravoi and G. goliath were collected on the soil surface inside the cave and still preserved soft tissues. 2.2. Fissure at old roost in La Fortaleza (palaeontological site) It is an infilled fissure (“old roost”) containing sediment and a few bones. It is located in the Teno massif, Northeast Tenerife,
Fig. 2. Tenerife Island showing the sites where the samples of this paper were collected. AArchaeological and Ppalaeontological site.
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dwelling space by the aboriginal people (Galván et al., 1999). In two of the three stratigraphic levels, seashells and bones from butchery were abundant (n ¼ 2256). They mainly included goat, sheep and pig, but also a smaller proportion of C. bravoi (n ¼ 40) and G. goliath (n ¼ 75) (Alberto, 1998). Cut marks were observed on a bone of Canariomys (Alberto, 1998). Nevertheless, during our revision of the available material from the archaeological sites to select samples for 14C dating, no C. bravoi bones with cut marks were found. 3. Material and methods Five samples of C. bravoi were dated by Accelerator Mass Spectrometer (AMS) 14C: a burned humerus (KIA-47428; recovered from the surface of level I of Las Arenas-3); a fragmented burned ulna and a maxilla (KIA-40849; collected from the level I of Las Arenas-3); a mandible (KIA-40846; recovered from the surface of the level I of Las Arenas-1) (Fig. 3); two fragments of radius with remains of mummified soft tissue from the surface of a palaeontological site at Barranco de Las Moraditas (KIA-36264); and a femur collected from a palaeontological site (“old roost”) in La Fortaleza (WK-28571), found in association with bones of M. musculus. Additionally, we dated a right maxilla of the giant lizard G. goliath collected from the level I of Las Arenas-3 (KIA47429). Finally, potentially old samples of introduced commensal rodents were also dated to establish comparisons. We dated bones of M. musculus (KIA-40847) found associated with Canariomys remains at La Fortaleza, and bones of R. rattus (KIA-40844) from the level III of Las Arenas-1. Samples KIA-36264, 40846, 40849 and 47428 of C. bravoi; KIA47429 of G. goliath; KIA-40847 of M. musculus; and KIA-40844 of R. rattus were AMS dated using an improved collagen extraction procedure (Van Strydonck et al., 2005) modified (Longin method; Brown et al., 1998) at the Radiocarbon and Stable Isotope Laboratory of the Royal Institute for Cultural Heritage (Brussels). The sample WK-28571 of C. bravoi was processed at the Radiocarbon Laboratory of The University of Waikato (Hamilton, New Zealand) and AMS determinations were made on extracts of ultrafiltered bone collagen gelatine (Bronk Ramsey et al., 2004). The AMS radiocarbon dates given in years “BP” are conventional radiocarbon ages with standard error, where “BP” is before present, and present is the year 1950, following standard reporting procedures. Radiocarbon calibration was calculated by using the
software OxCal v4.2 (Bronk Ramsey, 2009) and the IntCal13 curve (Reimer et al., 2013). All dates derived from calibrations are expressed as 2s interval (95.4% confidence) and given as “cal AD” or “cal BC”, where “AD” is Annus Domini and “BC” is Before Christ. Isotope ratios for C are presented as d values, where d ¼ 1000 [(Rsample/Rstandard) 1], and R ¼ 13C/12C. The isotopic reference standard is ViennaePeeDee Belemnite. Additionally, we have compiled the available terrestrial radiocarbon-dated samples from archaeological sites in Tenerife (Supplementary Table 1) to explore the earliest reliable date of human presence on the island through the implementation of chronological hygiene protocols (Anderson, 1991; Spriggs and Anderson, 1993; Hunt and Lipo, 2006; Wilmshurst et al., 2011). We used the Bayesian radiocarbon calibration software BCal (Buck et al., 1999; Buck and Bard, 2007) to calculate the probability that the extinction of C. bravoi occurred: (i) close to European contact and; (ii) after aboriginal arrival, assuming that radiocarbondated materials were deposited at a uniform rate. We used the ten more recent radiocarbon dates of C. bravoi (Table 1) and the ten oldest radiocarbon ages obtained from human remains, domestic or commensal species (Supplementary Table 1) to perform the analysis with this program. 4. Results The last documented occurrence of C. bravoi on Tenerife Island is dated prior to 204 cal BC and posterior to 400 cal BC (Table 1). The age of the M. musculus sample analysed was 641e679 cal AD, whereas the age of the bone of C. bravoi found in association with it was 410e232 cal BC. The youngest sample analysed in this study corresponds to R. rattus from Las Arenas-1 (1479e1644 cal AD). All the radiocarbon-dated terrestrial samples from archaeological sites on Tenerife whose 2s intervals overlap or are older than the last occurrence of C. bravoi were performed on wood, charcoal or bulk ash-sediment (Fig. 4, and Supplementary Table 1). In sharp contrast, all dates obtained from human, domestic or alien species bones are more recent than those of C. bravoi (Fig. 4). The BCal software indicates that the probability that the extinction of C. bravoi had occurred close to the European contact (i.e. after the year 1350 cal AD) is 0.09, whereas the probability that the extinction of this rodent had occurred after aboriginal arrival was 0.61.
Fig. 3. Radiocarbon dated samples of C. bravoi: bones from level I of Arenas-3 (A: humerus [KIA-47428], B: fragments of ulna and maxilla [KIA-40849]); and from level I of Arenas-1 burial site (C: mandible [KIA-40846]).
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Table 1 14 C AMS dates. Cb: Canariomys bravoi; Gg: Gallotia goliath; Mm: Mus musculus; Rr: Rattus rattus; (p) palaeontological site; (a) archaeological site. Species
Lab code
Site
Radiocarbon age (BP)
Cb Cb Cb Cb Cb Cb Cb Cb Cb Cb Cb Gg Mm Rr
OxA-54502 GrA-22656 GrA-22657 GrA-22658 GrA-22680 GrA-22661 KIA-36264 WK-28571 KIA-40846 KIA-47428 KIA-40849 KIA-47429 KIA-40847 KIA-40844
(p) Cueva del Viento (p) Icod (p) El Sobrado (p) Cueva del Viento (p) Cueva del Viento (p) Cueva del Viento (p) Bco. Moraditas (p) La Fortaleza (a) Arenas 1 (burial) (a) Arenas 3 (a) Arenas 3 (a) Arenas 3 (p) La Fortaleza (a) Arenas 1 (burial)
12,230 3010 3720 4515 2305 5840 2275 2304 3605 2315 5400 4895 1365 325
140 45 45 45 40 50 25 32 25 55 30 40 20 30
2s interval (cal BC/AD)
C/N
d13C (&)
Reference
Observations
12,880e11,810 BC 1397e1118 BC 2281e1977 BC 3364e3036 BC 471e208 BC 4826e4552 BC 400e231 BC 410e232 BC 2027e1898 BC 726e204 BC 4338e4172 BC 3769e3636 BC 641e679 AD 1479e1644 AD
e 3.2 3.2 3.2 3.2 3.2 3.2 3.3 3.2 3.3 3.2 3.2 3.11 3.1
e 19.5 19.5 20.0 19.6 20.2 16.48 17.9 16.83 15.7 16.93 18.5 22.20 17.79
Michaux et al., 1996 Bocherens et al., 2006 Bocherens et al., 2006 Bocherens et al., 2006 Bocherens et al., 2006 Bocherens et al., 2006 This paper This paper This paper This paper This paper This paper This paper This paper
In surface Without stratigraphy Level I Burned (in surface) Burned (level I) Level I Without stratigraphy Level III
5. Discussion The range of radiocarbon dates obtained on bones from Las Arenas-3 documents a mixing of materials of different ages (Table 1), and do not support the contention that the aboriginal people exploited this rodent because all dates of C. bravoi could be prior to the human presence on the island (Fig. 4). These new data point out to a new hypothesis to explain the extinction process of C. bravoi. According to chronometric hygiene criteria, the dated samples with an inbuilt age potential (i.e., unspecified charcoals and wood) or with a mixture of various isotopic fractions (i.e., ash-sediments) have large sources of error, making them unsuitable for dating early human presence on the island (Anderson, 1991; Spriggs and Anderson, 1993; Hunt and Lipo, 2006; Wilmshurst et al., 2011). A problem to obtain reliable chronologies from charcoals or wood are the old trees, which can reach hundreds of years (“old wood” effect) but an additional inbuilt age arises from the durability of some timbers after the death of the trees (Anderson, 1991). In addition, dates that were based on mixed materials like bulk ash-sediments (including soil or both old and young organic components) are problematic resulting in dates that are too old (Butler et al., 2004; Wilmshurst et al., 2011). Except for radiocarbon-dated materials with large sources of error (ash-sediments, unspecified charcoals and wood; see Anderson, 1991; Butler et al., 2004; Wilmshurst et al., 2011), all the available 2s age intervals of archaeological materials from Tenerife never overlap with those of C. bravoi (Fig. 4). Consequently, the current available radiocarbon dates do not support the coexistence of C. bravoi and humans. Considering the new radiocarbon dates, how could we explain the presence of bones of these extinct animals in archaeological horizons? G. goliath and C. bravoi bones are abundant at palaeontological sites (lava tubes) around the island (e.g., Michaux et al., 1996). A natural pre-human deposition has been proposed to explain the presence of G. goliath and C. bravoi bones at Las Arenas1 burial site (Galván et al., 1992; Alberto, 1998), that is located around 50 m apart to Arenas-3 archaeological dwelling site. Las Arenas-3 site could have been initially a no human-mediated fossil site, with pre-human and archaeological bones mixed altogether only after the human occupation had taken place. The process to create suitable space for humans in the cave could have contributed to the disturbance of the deposit (Galván et al., 1992, 1999). Moreover, the bones of C. bravoi do not need to be in direct contact with the fire to be burned. In fact, bones situated below of a hearth can be affected by a subsequent fire (e.g., Bennett, 1999; Olsen, 1999).
Applying chronological hygiene criteria, the earliest reliable known presence of humans on Tenerife is currently 641e679 cal AD (based on the first occurrence of commensal rodents), whereas it is widely assumed that the aboriginal peoples reached the island in the middle of the 1st millennium BC (see Galván et al., 1999). This early human radiocarbon-documented presence (prior to 679 AD) and the last radiocarbon-documented presence of C. bravoi (later than 400 cal BC) (Table 1) are around one millennium apart. The lack of evidence for the coexistence of C. bravoi and the aboriginal people should not be interpreted as a true absence of contact. Upon current radiocarbon dates, the probability of this coexistence is 0.61, although the evidence to prove it is elusive. There is little doubt that the ultimate cause for the C. bravoi extinction was almost certainly related to the arrival of the first humans to the island. The available radiocarbon evidence fits well with a very swift process leaving to the extinction in a time span too short as to leave archaeological traces. Swift changes in the native fauna as a consequence of human arrival and the introduction of alien species on islands are evident elsewhere (Burney and Flannery, 2005; Steadman, 2006; Wyatt et al., 2008). The direct cause for the extinction of C. bravoi remains unsolved empirically. C. bravoi fed on a diverse diet including plants, fruits and insects (Firmat et al., 2010). The introduction of goats, sheep and pigs by the aboriginal people could have affected negatively C. bravoi populations. Nevertheless, the strongest impact was probably caused by the introduction of M. musculus. The data presented herein indicate that M. musculus reached Tenerife prior to 679 cal AD (Table 1). It is currently present over all habitats, from sea level to the high mountains (Rodríguez and Rando, 2009). Once settled, the M. musculus population could have reached very high densities, particularly in the absence of rats (Rattus spp.). In this case, a wide range of native biota should have been impacted, and the impacts should have been severe (Wanless et al., 2007, 2012; Angel et al., 2009). Under this situation, a combination of multiple negative effects upon C. bravoi populations could have taken place. Although hunting by the aboriginal people cannot be completely ruled out, factors like predation or hyper-predation, competition for resources with alien mammals, and the introduction of new parasites and diseases could have been involved in the extinction process, acting either separately or synergistically, as reported on other islands (Burney and Flannery, 2005; Steadman, 2006; Wanless et al., 2007, 2012; Rando et al., 2012). Due to the scarcity of native predators and as reported for other insular rodents, C. bravoi had very probably a low reproductive rate (Adler and Levins, 1994). A low reproduction combined with a limited geographic range (2034 km2) add up to a high extinction risk
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Fig. 4. 2s intervals of 14C dates of land samples from archaeological sites of Tenerife (Supplementary Table 1) plus samples of Table 1 (except the date of G. goliath (KIA-47429) and the oldest sample of C. bravoi (OxA-54502)).
(Davidson et al., 2009), making C. bravoi highly vulnerable to the environmental and ecological changes that took place shortly after the first human arrival to the island.
Research Project CGL2012-38089. We thank for comments provided by anonymous referees on a previous versions of the manuscript.
Acknowledgements Appendix A. Supplementary data We thank F. Siverio for the finding of the fossil site on Teno, V. Alberto, D. Jaume, Y. Yanes, C. Hernández, M. Arnay-de-la-Rosa and E. González-Reimers. This paper was partially supported by DGICYT
Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.quascirev.2014.04.013.
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Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev
Reappraisal of the extinction of Canariomys bravoi, the giant rat from Tenerife (Canary Islands) Juan Carlos Rando a, *, Josep Antoni Alcover b, Bertila Galván c, Juan Francisco Navarro c a
Departamento de Biología Animal (UDI Zoología), Universidad de La Laguna (ULL), E-38206 La Laguna, Tenerife, Canary Islands, Spain Departament de Biodiversitat i Conservació, IMEDEA (CSIC-UIB), Cr Miquel Marquès 21, 07190 Esporles, Mallorca, Balearic Islands, Spain c Departamento de Prehistoria, Antropología e Historia Antigua, Universidad de La Laguna (ULL), E-38071 Canary Islands, Spain b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 February 2014 Received in revised form 10 April 2014 Accepted 13 April 2014 Available online 5 May 2014
All the Quaternary endemic rodents of the Canary Islands are currently extinct. The Lava Mouse Malpaisomys insularis inhabited the easternmost islands, whereas the giant rats Canariomys bravoi and Canariomys tamarani lived in the central islands of Tenerife and Gran Canaria, respectively. Bones of C. bravoi have appeared in archaeological sites together with shellfish and butchery remains. Traditionally, they have been considered as an evidence of the sporadic consumption of C. bravoi by the aboriginal people, in some instances as recently as the time of the first European contact (14th century AD). Accordingly, the extinction of C. bravoi has been linked to the European colonization of Tenerife. The plausibility of this extinction date has been explored through new radiocarbon dates obtained on selected C. bravoi bones and through a reappraisal of the published dates. Our analysis allowed us to establish an earlier last documented occurrence age for C. bravoi, prior to the third century cal BC, much earlier than previously assumed. The analysis of formerly published 14C dates of archaeological remains from Tenerife shows that samples with confidence intervals (95.54%) that are older or overlap with the last documented record of C. bravoi were performed on materials with large sources of error (such as wood, charcoal or bulk ash-sediments). Conversely, the new radiocarbon dates and analyses presented herein are in agreement with the occurrence of an earlier rapid extinction linked to the first human presence on the island. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Aboriginal settlement Canariomys bravoi Insular rodent Quaternary extinctions Radiocarbon dating
1. Introduction The three species of rodents known to have inhabited the Canary Islands during the Quaternary are currently extinct. The Lava Mouse Malpaisomys insularis inhabited the Eastern islands (Fuerteventura and Lanzarote) and islets, while the giant rats Canariomys bravoi and Canariomys tamarani occupied the central islands of Tenerife and Gran Canaria, respectively (Fig. 1). M. insularis survived to the introduction of the House Mouse Mus musculus and the aboriginal settlement of the islands, that took place sometime between 756 cal BC and 313 cal AD (Alcover et al., 2009), a time range established from AMS 14C dating on bones of introduced M. musculus and on bones of endemic fauna on sites lacking it. The extinction of M. insularis was probably an asynchronous process that correlates with the introduction of the Black Rat Rattus rattus by European sailors that took place before 650 cal AD in Lanzarote
* Corresponding author. Tel.: þ34 922318380. E-mail addresses: [email protected], [email protected] (J.C. Rando). http://dx.doi.org/10.1016/j.quascirev.2014.04.013 0277-3791/Ó 2014 Elsevier Ltd. All rights reserved.
and after the 13th century in Fuerteventura (Rando et al., 2008, 2012). Available information on C. tamarani and on its extinction is very scarce (López-Martínez and López-Jurado, 1987; LópezJurado and López-Martínez, 1988). Published radiocarbon dates of C. bravoi bones collected from palaeontological sites (lava tubes) cover a time span from 12,230 140 BP (12,880e11,810 cal BP) to 2305 40 BP (471e 208 cal BC) (Michaux et al., 1996; Bocherens et al., 2006). Since the weight of this rodent could exceed 1 kg, hunting by aboriginal people, competition and predation by alien species have been proposed as factors that ultimately led to its extinction (Michaux et al., 1996; Bocherens et al., 2006). The discovery of C. bravoi bones in association with shellfish and livestock remains in an archaeological dwelling site in the north of the island (Las Arenas3) was initially interpreted as an evidence of its sporadic exploitation by the aboriginals until dates very close to the European contact (Galván et al., 1999) in the 14th century (Aznar et al., 2006). The archaeological site of Las Arenas-3 is a lava cave with three stratigraphic layers (ranging from III to I) (Galván et al., 1992).
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Fig. 1. (a) Location of Canary Islands and (b) the distribution of extinct endemic rodents on the archipelago.
Radiocarbon dates performed on charcoal from the two more recent levels (II and I) yield less than a millennium: 730 90 BP (1049e1412 cal AD) and 730 60 BP (1169e1393 cal AD), respectively (Galván et al., 1999). Bones are abundant in these layers, and mainly pertain to livestock, but include a small proportion of C. bravoi and the giant lizard Gallotia goliath as well (Alberto, 1998). Bones of both extinct species have also been found in the contiguous burial site of Las Arenas-1 (Galván et al., 1999). A natural deposition has been proposed to explain the presence of G. goliath and C. bravoi at this burial site (Galván et al., 1992; Alberto, 1998). The interpretation of extinction events is almost always submitted to considerable debate due to the interplay of several causes of potential error, not always taken into account by researchers. One of them consists of the false co-occurrence of man and the autochthonous species due to, among diverse factors, the reworking of sites (e.g., Olsen, 1999; Burney et al., 2001; Macphee et al., 2007). To analyse the reliability of the associations, we dated bones from the more recent levels of these two archaeological sites (Las Arenas-3 and Las Arenas-1). It was expected that all samples of C. bravoi from these two sites would have a more recent age than the samples obtained from palaeontological localities around the island (Fig. 2). In order to obtain an accurate chronology informative to understand the causes and processes involved in the extinction of C. bravoi, we also dated bones of two commensal rodents: M. musculus from a palaeontological site and R. rattus from an archaeological site (both from Tenerife Island).
formed by 7.37e4.5 Ma basaltic rocks (Ancochea et al., 1990). No distinctive stratigraphic units were identified. Bones of C. bravoi, G. goliath and M. musculus were present in this site. 2.3. Las Arenas-1 (archaeological site) This is a small lava tube in Quaternary basaltic rocks (Ancochea et al., 1990). It is located in the Northwest of Tenerife. This secondary burial site contains seven archaeological levels that were excavated by Prof. B. Galván team (Galván et al., 1992). In addition to human remains, bones of sheep, goat, pig, dog, C. bravoi and G. goliath were found concurrently. It was established that these remains were incorporated as part of a ritual-ceremony, although the accumulation of C. bravoi and G. goliath bones might be the result of a natural deposition prior to the human activities (Alberto, 1998; Galván et al., 1999). 2.4. Las Arenas-3 (archaeological site) This is a lava cave in Quaternary basaltic rocks (Ancochea et al., 1990), located about 50 m from Las Arenas-1. It was used as a
2. Sites The samples that were submitted for radiocarbon dating were recovered from two palaeontological and two archaeological sites (Fig. 2). 2.1. Cave at Barranco de Las Moraditas (palaeontological site) This is a small lava tube located at the East of Tenerife, in Quaternary basaltic rocks (Ancochea et al., 1990). Bones of C. bravoi and G. goliath were collected on the soil surface inside the cave and still preserved soft tissues. 2.2. Fissure at old roost in La Fortaleza (palaeontological site) It is an infilled fissure (“old roost”) containing sediment and a few bones. It is located in the Teno massif, Northeast Tenerife,
Fig. 2. Tenerife Island showing the sites where the samples of this paper were collected. AArchaeological and Ppalaeontological site.
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dwelling space by the aboriginal people (Galván et al., 1999). In two of the three stratigraphic levels, seashells and bones from butchery were abundant (n ¼ 2256). They mainly included goat, sheep and pig, but also a smaller proportion of C. bravoi (n ¼ 40) and G. goliath (n ¼ 75) (Alberto, 1998). Cut marks were observed on a bone of Canariomys (Alberto, 1998). Nevertheless, during our revision of the available material from the archaeological sites to select samples for 14C dating, no C. bravoi bones with cut marks were found. 3. Material and methods Five samples of C. bravoi were dated by Accelerator Mass Spectrometer (AMS) 14C: a burned humerus (KIA-47428; recovered from the surface of level I of Las Arenas-3); a fragmented burned ulna and a maxilla (KIA-40849; collected from the level I of Las Arenas-3); a mandible (KIA-40846; recovered from the surface of the level I of Las Arenas-1) (Fig. 3); two fragments of radius with remains of mummified soft tissue from the surface of a palaeontological site at Barranco de Las Moraditas (KIA-36264); and a femur collected from a palaeontological site (“old roost”) in La Fortaleza (WK-28571), found in association with bones of M. musculus. Additionally, we dated a right maxilla of the giant lizard G. goliath collected from the level I of Las Arenas-3 (KIA47429). Finally, potentially old samples of introduced commensal rodents were also dated to establish comparisons. We dated bones of M. musculus (KIA-40847) found associated with Canariomys remains at La Fortaleza, and bones of R. rattus (KIA-40844) from the level III of Las Arenas-1. Samples KIA-36264, 40846, 40849 and 47428 of C. bravoi; KIA47429 of G. goliath; KIA-40847 of M. musculus; and KIA-40844 of R. rattus were AMS dated using an improved collagen extraction procedure (Van Strydonck et al., 2005) modified (Longin method; Brown et al., 1998) at the Radiocarbon and Stable Isotope Laboratory of the Royal Institute for Cultural Heritage (Brussels). The sample WK-28571 of C. bravoi was processed at the Radiocarbon Laboratory of The University of Waikato (Hamilton, New Zealand) and AMS determinations were made on extracts of ultrafiltered bone collagen gelatine (Bronk Ramsey et al., 2004). The AMS radiocarbon dates given in years “BP” are conventional radiocarbon ages with standard error, where “BP” is before present, and present is the year 1950, following standard reporting procedures. Radiocarbon calibration was calculated by using the
software OxCal v4.2 (Bronk Ramsey, 2009) and the IntCal13 curve (Reimer et al., 2013). All dates derived from calibrations are expressed as 2s interval (95.4% confidence) and given as “cal AD” or “cal BC”, where “AD” is Annus Domini and “BC” is Before Christ. Isotope ratios for C are presented as d values, where d ¼ 1000 [(Rsample/Rstandard) 1], and R ¼ 13C/12C. The isotopic reference standard is ViennaePeeDee Belemnite. Additionally, we have compiled the available terrestrial radiocarbon-dated samples from archaeological sites in Tenerife (Supplementary Table 1) to explore the earliest reliable date of human presence on the island through the implementation of chronological hygiene protocols (Anderson, 1991; Spriggs and Anderson, 1993; Hunt and Lipo, 2006; Wilmshurst et al., 2011). We used the Bayesian radiocarbon calibration software BCal (Buck et al., 1999; Buck and Bard, 2007) to calculate the probability that the extinction of C. bravoi occurred: (i) close to European contact and; (ii) after aboriginal arrival, assuming that radiocarbondated materials were deposited at a uniform rate. We used the ten more recent radiocarbon dates of C. bravoi (Table 1) and the ten oldest radiocarbon ages obtained from human remains, domestic or commensal species (Supplementary Table 1) to perform the analysis with this program. 4. Results The last documented occurrence of C. bravoi on Tenerife Island is dated prior to 204 cal BC and posterior to 400 cal BC (Table 1). The age of the M. musculus sample analysed was 641e679 cal AD, whereas the age of the bone of C. bravoi found in association with it was 410e232 cal BC. The youngest sample analysed in this study corresponds to R. rattus from Las Arenas-1 (1479e1644 cal AD). All the radiocarbon-dated terrestrial samples from archaeological sites on Tenerife whose 2s intervals overlap or are older than the last occurrence of C. bravoi were performed on wood, charcoal or bulk ash-sediment (Fig. 4, and Supplementary Table 1). In sharp contrast, all dates obtained from human, domestic or alien species bones are more recent than those of C. bravoi (Fig. 4). The BCal software indicates that the probability that the extinction of C. bravoi had occurred close to the European contact (i.e. after the year 1350 cal AD) is 0.09, whereas the probability that the extinction of this rodent had occurred after aboriginal arrival was 0.61.
Fig. 3. Radiocarbon dated samples of C. bravoi: bones from level I of Arenas-3 (A: humerus [KIA-47428], B: fragments of ulna and maxilla [KIA-40849]); and from level I of Arenas-1 burial site (C: mandible [KIA-40846]).
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Table 1 14 C AMS dates. Cb: Canariomys bravoi; Gg: Gallotia goliath; Mm: Mus musculus; Rr: Rattus rattus; (p) palaeontological site; (a) archaeological site. Species
Lab code
Site
Radiocarbon age (BP)
Cb Cb Cb Cb Cb Cb Cb Cb Cb Cb Cb Gg Mm Rr
OxA-54502 GrA-22656 GrA-22657 GrA-22658 GrA-22680 GrA-22661 KIA-36264 WK-28571 KIA-40846 KIA-47428 KIA-40849 KIA-47429 KIA-40847 KIA-40844
(p) Cueva del Viento (p) Icod (p) El Sobrado (p) Cueva del Viento (p) Cueva del Viento (p) Cueva del Viento (p) Bco. Moraditas (p) La Fortaleza (a) Arenas 1 (burial) (a) Arenas 3 (a) Arenas 3 (a) Arenas 3 (p) La Fortaleza (a) Arenas 1 (burial)
12,230 3010 3720 4515 2305 5840 2275 2304 3605 2315 5400 4895 1365 325
140 45 45 45 40 50 25 32 25 55 30 40 20 30
2s interval (cal BC/AD)
C/N
d13C (&)
Reference
Observations
12,880e11,810 BC 1397e1118 BC 2281e1977 BC 3364e3036 BC 471e208 BC 4826e4552 BC 400e231 BC 410e232 BC 2027e1898 BC 726e204 BC 4338e4172 BC 3769e3636 BC 641e679 AD 1479e1644 AD
e 3.2 3.2 3.2 3.2 3.2 3.2 3.3 3.2 3.3 3.2 3.2 3.11 3.1
e 19.5 19.5 20.0 19.6 20.2 16.48 17.9 16.83 15.7 16.93 18.5 22.20 17.79
Michaux et al., 1996 Bocherens et al., 2006 Bocherens et al., 2006 Bocherens et al., 2006 Bocherens et al., 2006 Bocherens et al., 2006 This paper This paper This paper This paper This paper This paper This paper This paper
In surface Without stratigraphy Level I Burned (in surface) Burned (level I) Level I Without stratigraphy Level III
5. Discussion The range of radiocarbon dates obtained on bones from Las Arenas-3 documents a mixing of materials of different ages (Table 1), and do not support the contention that the aboriginal people exploited this rodent because all dates of C. bravoi could be prior to the human presence on the island (Fig. 4). These new data point out to a new hypothesis to explain the extinction process of C. bravoi. According to chronometric hygiene criteria, the dated samples with an inbuilt age potential (i.e., unspecified charcoals and wood) or with a mixture of various isotopic fractions (i.e., ash-sediments) have large sources of error, making them unsuitable for dating early human presence on the island (Anderson, 1991; Spriggs and Anderson, 1993; Hunt and Lipo, 2006; Wilmshurst et al., 2011). A problem to obtain reliable chronologies from charcoals or wood are the old trees, which can reach hundreds of years (“old wood” effect) but an additional inbuilt age arises from the durability of some timbers after the death of the trees (Anderson, 1991). In addition, dates that were based on mixed materials like bulk ash-sediments (including soil or both old and young organic components) are problematic resulting in dates that are too old (Butler et al., 2004; Wilmshurst et al., 2011). Except for radiocarbon-dated materials with large sources of error (ash-sediments, unspecified charcoals and wood; see Anderson, 1991; Butler et al., 2004; Wilmshurst et al., 2011), all the available 2s age intervals of archaeological materials from Tenerife never overlap with those of C. bravoi (Fig. 4). Consequently, the current available radiocarbon dates do not support the coexistence of C. bravoi and humans. Considering the new radiocarbon dates, how could we explain the presence of bones of these extinct animals in archaeological horizons? G. goliath and C. bravoi bones are abundant at palaeontological sites (lava tubes) around the island (e.g., Michaux et al., 1996). A natural pre-human deposition has been proposed to explain the presence of G. goliath and C. bravoi bones at Las Arenas1 burial site (Galván et al., 1992; Alberto, 1998), that is located around 50 m apart to Arenas-3 archaeological dwelling site. Las Arenas-3 site could have been initially a no human-mediated fossil site, with pre-human and archaeological bones mixed altogether only after the human occupation had taken place. The process to create suitable space for humans in the cave could have contributed to the disturbance of the deposit (Galván et al., 1992, 1999). Moreover, the bones of C. bravoi do not need to be in direct contact with the fire to be burned. In fact, bones situated below of a hearth can be affected by a subsequent fire (e.g., Bennett, 1999; Olsen, 1999).
Applying chronological hygiene criteria, the earliest reliable known presence of humans on Tenerife is currently 641e679 cal AD (based on the first occurrence of commensal rodents), whereas it is widely assumed that the aboriginal peoples reached the island in the middle of the 1st millennium BC (see Galván et al., 1999). This early human radiocarbon-documented presence (prior to 679 AD) and the last radiocarbon-documented presence of C. bravoi (later than 400 cal BC) (Table 1) are around one millennium apart. The lack of evidence for the coexistence of C. bravoi and the aboriginal people should not be interpreted as a true absence of contact. Upon current radiocarbon dates, the probability of this coexistence is 0.61, although the evidence to prove it is elusive. There is little doubt that the ultimate cause for the C. bravoi extinction was almost certainly related to the arrival of the first humans to the island. The available radiocarbon evidence fits well with a very swift process leaving to the extinction in a time span too short as to leave archaeological traces. Swift changes in the native fauna as a consequence of human arrival and the introduction of alien species on islands are evident elsewhere (Burney and Flannery, 2005; Steadman, 2006; Wyatt et al., 2008). The direct cause for the extinction of C. bravoi remains unsolved empirically. C. bravoi fed on a diverse diet including plants, fruits and insects (Firmat et al., 2010). The introduction of goats, sheep and pigs by the aboriginal people could have affected negatively C. bravoi populations. Nevertheless, the strongest impact was probably caused by the introduction of M. musculus. The data presented herein indicate that M. musculus reached Tenerife prior to 679 cal AD (Table 1). It is currently present over all habitats, from sea level to the high mountains (Rodríguez and Rando, 2009). Once settled, the M. musculus population could have reached very high densities, particularly in the absence of rats (Rattus spp.). In this case, a wide range of native biota should have been impacted, and the impacts should have been severe (Wanless et al., 2007, 2012; Angel et al., 2009). Under this situation, a combination of multiple negative effects upon C. bravoi populations could have taken place. Although hunting by the aboriginal people cannot be completely ruled out, factors like predation or hyper-predation, competition for resources with alien mammals, and the introduction of new parasites and diseases could have been involved in the extinction process, acting either separately or synergistically, as reported on other islands (Burney and Flannery, 2005; Steadman, 2006; Wanless et al., 2007, 2012; Rando et al., 2012). Due to the scarcity of native predators and as reported for other insular rodents, C. bravoi had very probably a low reproductive rate (Adler and Levins, 1994). A low reproduction combined with a limited geographic range (2034 km2) add up to a high extinction risk
26
J.C. Rando et al. / Quaternary Science Reviews 94 (2014) 22e27
Fig. 4. 2s intervals of 14C dates of land samples from archaeological sites of Tenerife (Supplementary Table 1) plus samples of Table 1 (except the date of G. goliath (KIA-47429) and the oldest sample of C. bravoi (OxA-54502)).
(Davidson et al., 2009), making C. bravoi highly vulnerable to the environmental and ecological changes that took place shortly after the first human arrival to the island.
Research Project CGL2012-38089. We thank for comments provided by anonymous referees on a previous versions of the manuscript.
Acknowledgements Appendix A. Supplementary data We thank F. Siverio for the finding of the fossil site on Teno, V. Alberto, D. Jaume, Y. Yanes, C. Hernández, M. Arnay-de-la-Rosa and E. González-Reimers. This paper was partially supported by DGICYT
Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.quascirev.2014.04.013.
J.C. Rando et al. / Quaternary Science Reviews 94 (2014) 22e27
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