Was Homo erectus the first human in the Americas 130,000BP?

I have covered the publication of a paper detailing the convincing evidence of man in the Americas, specifically in Southern California at 130,000BP here and here.

Holen et al. (2017) discuss the candidate species in some detail, and in their supplementary information come to the conclusion, that these species include:

1. Homo erectus

2. Homo neanderthalensis

3. Homo sp. “Denisovans”

4. “Archaic Homo sapiens”

Taking each species separately let us look at which may be the most likely candidate.

1. Homo erectus

First we should get the ‘Which Homo erectus?’ out of the way. By that I mean that some scientists, particularly Chinese scientists have suggested that “Homo erectus is a species confined to Asia. Specialized characters displayed by the Indonesian and Chinese skulls are said to be absent in material from eastern Africa, and individuals from Koobi Fora and Nariokotome are now referred by some workers to H. ergaster.” See Rightmire (1998).

Rightmire (1998), based on comparisons of facial morphology of African and Asian examples of Homo erectus, rejected this claim. From his abstract: “Much or all of the variation in facial form can be attributed to sex dimorphism and/or local differentiation of populations within the Asian and African geographic regions. Metric differences among the fossils are comparable to those documented in a subset of recent H. sapiens, and there is no evidence that the Pleistocene specimens show greater dispersion than expected within a single species. This finding is generally in keeping with observations made on other parts of the cranium, lower jaw, and teeth. All of the hominids can be placed in H. erectus. Although its phylogenetic origins remain obscure, this lineage must be rooted in Africa. The species flourished for a long time. At several sites in China, H. erectus is known from deposits of the later Middle Pleistocene, while at Ngandong in Indonesia, archaic people may have survived even into the Late Pleistocene (Swisher et al. [1996]). The Ngandong fossils may record the last appearance of the lineage.”

Having dealt with that, what specimens of Homo erectus have been discovered, in Asia, and what dates are they? Could Homo erectus possibly have been the hominid that made it to California 130,000 years ago?

The earliest Homo erectus fossils discovered are from Africa (KMN ER3733 East Lake Turkana) and the Caucasus (Georgia – Dmanisi) date to ca. 1.8-1.9 Mya. Given that all early hominid species so far discovered are from Africa, it seems logical to assume that Homo erectus evolved there and migrated East.

A few examples of Homo erectus from a timeframe which would fit with the peopling of the Americas by this hominid, from Asia and China are shown on the map below. A brief summary of each site is given further down.

However, a more detailed map, showing most known Homo erectus sites in east Asia,  is given below. Click on each location for a brief biography.

Here are the details for each Homo erectus site given on the first map above:

Specimen: Ngandong 7 (Solo 6)

Location: Solo River, Central Java, Indonesia

Age: Indriati et al., (2011), reported new 40Ar/39Ar, ESR and U-series dates for Ngandong. They argue that the different dating methods indicate an age in the range of 546-612 ka, placing these three sites in the Middle Pleistocene and significantly older than previous estimates. However, they caution that the ESR/U-series date that complies with all modelling criteria is ~143 ka.

Ngandong 7 from Weidenreich, (1951). Note the straight, square brow ridges.

Another view of the same specimen from Athena Review (2004).

Specimen: Zhoukoudian composite skull cast from the Smithsonian.

Location: Zhoukoudian Cave

Age: 770,000 ka, Shen et al. (2009), Smithsonian (2016) 780,000 – 400,000 ka.

Zhoukoudian Homo erectus from the Smithsonian (2016). Original caption reads: This composite skull combines several skulls from the same site, first named Sinanthropus pekingensis but later attributed to Homo erectus. The original fossils vanished while being shipped to the United States for safety during World War II, but scientists still have high-quality casts and descriptions to work with.

An interesting facial reconstruction can be seen in this photo by Pillard (2007).

I have been unable to identify the museum in which the picture was taken, however the caption card reads: Cast of skull fragments found at Choucoutien.

Specimen: Homo erectus molars

Location: Tham Khuyen Cave, Vietnam

Age: 745,000 ka (or perhaps as late as 140-80 kyr ago in the case of the nearby Hang Hum cave).

These teeth, and indeed, the occurrence of Homo erectus in Vietnam have were debated for a decade until Ciochon et al. (1996), definitively identified them as belonging to the above hominid and not for example, Gigantopithecus blacki.

The teeth in question, adapted from Ciochon et al. (1996). Original caption reads:

FIG. 2. ..Homo erectus molars (right) from Tham Khuyen.

TK 65/105 (top right) left upper M2 (MD = 12.0, BL = 12.7), TK 65/50 (bottom right) left upper M1 (MD = 11.7, BL = 12.9). Scale bar is in cm. Other hominid teeth identified from Tham Khuyen include TK 65/53, a right upper M1 (MD = 12.1, BL = 13.3), TK 65/167 left upper C (MD = 9.9, LL = 9.8), and TK 65/8, a left upper deciduous Ml (MD = 9.9, BL = 10.8).

Additionally, another Vietnamese site, within a couple of hundred kilometres of the Tham Khuyen, has yielded Homo erectus teeth, this time of a relatively recent date, according to Schwartz and colleagues (1995): “The cave of Hang Hum has also yielded three teeth.. These teeth were initially identified as Homo sapiens, but their large size places them outside the range of our own species. The two lower molars compare most closely in size and morphology with those of Homo erectus from Zhoukoudian. The third tooth is too worn to permit similar comparison. If the lower molars are indeed those of Homo erectus, this would suggest a remarkably late survival of this species in Vietnam.” Dated approximately 140,000BP.

Is there any evidence that Homo erectus was in America 130,000BP?

Many archaeologists and bloggers make assertions that it is impossible that man arrived in the Americas before ca. 20Kya. The main piece of evidence they cite is the lack of human skeletal remains. This is a fair point. However, it depends where and how deeply you dig.

A number of archaeologists have let their curiosity get the better of them and dug far deeper than the ‘20,000BP is the limit of human occupation in the Americas’ horizon. What did they find? Artifacts.. indisputably human-made artifacts!

A few examples of the evidence are:

Monde Verde, Chile excavated by Tom Dillehay dated to 39,000BP [see here and here]

Meadowcroft Rockshelter, Pennsylvania by Adovasio dated 33,000BP [see here]

Ground Sloth Kill site reported by Farima et al. [see here]

In addition, some other sites, which I haven’t covered yet, spring immediately to mind, for example:

Topper (Goodyear)

Pendejo Cave (MacNeish)

And the quite a few others such as those in the table in a previous post I wrote in February 2016 [see here]

The earlier sites from the above could be attributed to Homo erectus or their descendants in the Americas but where are the bones to prove it?

Well there is actually, a number of specimens, one of which, I covered here.

Since that post I have come across some additional evidence from a paper published by Irish et al. (2000). The brief paper states:

“The likelihood of a late-Pleistocene human presence in Jalisco, Mexico, is supported by culturally modified faunal bones, diagnostic lithics, and mineralized human bones; this report concerns the latter, which were analyzed by Irish, using standard osteological procedures (Bass 1981; Brothwell 1981; Ortner and Putschar 1985; Shipman et al. 1986; Ubelaker 1989; White 1991). All materials were recovered 50 km southeast of Guadalajara, in the Lake Chapala and Zacoalco Playa basins.

            The human remains are thought to be of late-Pleistocene age based on faunal correlation. Many have been in Solórzano’s possession for some time; others were recently collected. Like associated fauna, all are mineralized, dark in color, and fragmentary. We have a focus on their origins and will work to establish exact field proveniences in May 2000.

            The Chapala bones (n = 10) have a MNI of three, based on two left superciliary arches (brow ridges) and a deciduous incisor. The super border of each brow is blunt, implying the sex was male in both cases. However, size variations of other fragments suggest males and females are represented. The deciduous incisor is from a three-year-old; the rest represent young adults.

            One Chapala superciliary arch deserves specific mention due to its large size. Studies by Solórzano show the bone resembles that in archaic Homo sapiens at Arago, France. In an unpublished 1990 report, Texas A&M osteologists suggest the brow’s thickness and robustness are comparable to those of  KNM-ER 3733 (African Homo erectus). Our measurements show the central torus thickness is 13.3, compared with 8.5 mm for KNM-ER 3733; the lateral torus thickness is 11.5 versus 9.0 mm (Rightmire 1998). Thus for the sake of comparison, the brow is more like that of Zhoukoudian Skull XI (Asian Homo erectus), with a central torus thickness of 13.2 +/- mm; lateral torus thickness was not measured (Rightmire 1998). Modern brows are too diminutive to allow these measurements. The brow also shows pneumatization (air pockets) along its length.

            However, to reiterate the findings of the Texas A&M workers, these comparisons do not imply that pre-Homo sapiens were in the Americas.    No phylogenetic or age implications are intended. Instead, the comparisons demonstrate the size relative to most New World specimens, although brows on the Lagoa Santa skull (Bryan 1978) and on recent Tierra del Fuego and Patagonia crania (Lahr 1995; C.L. Brace pers. comm. 1998) appear comparable.

            Twenty-one fragments from Zacoalco also have a MNI of three, based on duplicate mandible and parietal fragments. Sex determination is difficult, but size variation suggest both males and females. Concerning age, an unerupted third molar crypt indicates a 12- to 16-year-old. The remainder were adults or older adults, based on cranial suture closure, a fully formed third molar socket, and Pacchionian depressions on an inner parietal surface (see Ortner and Putschar 1985).

            A Zacoalco maxilla fragment, with sockets for the canine and premolars, also deserves mention due to its size. It is much thicker and more robust than comparative specimens from other prehistoric Native American males. Like the Chapala brow, the fragment could be lost in a collection of archaic Homo sapiens maxillae. However, again, no phylogentic inferences are intended. Instead, the robust Chapala and Zacoalco remains may be suggestive of region-specific variation in late-Pleistocene central Mexico, as noted elsewhere (Pompa 1987).

            Lastly, despite the fact that the remains are mineralized and recovered with Pleistocene-age fauna, we are continuing an attempt to obtain a chronometric date. Radiocarbon dating of the remains is difficult due to mineralization. However, a Zacoalco molar was thought to contain remnant organics for AMS dating. With permission from the Museo Regional de Guadalajara, the tooth was sent to a U.S. lab that previously dated a Chapala swamp deer (Blastoceros spp.) incisor at 18,200 yr B.P. Unfortunately, the human protein was more heavily mineralized; the amount of carbon after combustion was too small to provide a reliable date. Thus, we must locate additional remains. Still, a 13C value of -24 was obtained, implying that the tooth came from a non-agriculturalist; this value exceeds that from known Paleoindian fossils (e.g., Kennewick).

            In sum, these cursory descriptions are presented for the purpose of initiating comparisons with other New World Pleistocene-age remains. A future objective is to delineate the Jalisco finds in a broader spatial and temporal context. However, in-depth regional and extra-regional comparisons must await additional data collection. Although our research team received a major setback by the death of Jack Lobdell, continuing work in the project area appears promising.”

Although I cannot identify the source I additionally I came across the following picture from Charlie Hatchett (2010):

Conclusion

Much lithic and modified bone evidence has been uncovered in the Americas, apart from that, from the CM site.

Human bones of uncertain taxonomic affinity, have also been found in the Americas, which could, plausibly be those of Homo erectus.

Much of this evidence has been contested on spurious grounds (I will write an entire post on that later) or completely ignored.

As shown by the specimens illustrated and the additional one detailed on the Google map at the link further up this post, Homo erectus was in Asia for at least a million and could easily have crossed the Beringian Land Bridge. That these land bridges existed on numerous occasions in that timeframe is shown in my post here.

Therefore from the volume of evidence listed above, it is more than possible that Homo erectus was indeed the species of human responsible for modifying the Mastodon bones found in southern California 30 years ago and reported by Holen et al. (2017) and thus had peopled the Americas by 130,000BP.

References

Athena Review, Anon. 2004. Athena Review, Vol. 4, No.1: Homo erectus Introduction: The long journey of an ancient human ancestor. [ONLINE] Available at: http://www.athenapub.com/13intro-he.htm. [Accessed 20 June 2017].

Ciochon, R, et al., 1996. Dated co-occurrence of Homo erectus and Gigantopithecus from Tham Khuyen Cave, Vietnam. Proceedings of the National Academy of Science. USA, Vol. 93, April 1996, 3016-3020.

PDF download available from: http://www.pnas.org/content/93/7/3016.long

Hatchett, C. 2010. Paleo Planet, Archaeology/Anthropology Forum, The Tail Wagging the Dog. [ONLINE] Available at: http://paleoplanet69529.yuku.com/topic/33439/The-Tail-Wagging-the-Dog#.WZJTZVV97IV. [Accessed 15 August 2017].

Holen, S. R., et. al. (2017) A 130,000-year-old archaeological site in southern California, USA Nature 544, 479–483 doi:10.1038/nature22065

Can be accessed here: http://www.nature.com/nature/journal/v544/n7651/full/nature22065.html

Indriati, E, et al. 2011. The Age of the 20 Meter Solo River Terrace, Java, Indonesia and the Survival of Homo erectus in Asia. PLoS ONE, [Online]. 6(6): e21562. doi:10.1371/journal.pone.0021562, 1-10. Available at: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0021562 

[Accessed 19 June 2017].

Irish, J.D., Lobdell, J.E., Davis, S.D. and Solórzano Barreto, F.A., 2000. Prehistoric human skeletal remains from Jalisco, Mexico. Current Research in the Pleistocene, 17, pp.95-97.

Pillard, S. 2007. Homo erectus. [ONLINE] Available at: http://zipcodezoo.com/index.php/File:Homo_erectus_17.jpg. [Accessed 21 June 2017

Rightmire, G.P. (1998) Evidence from facial morphology for similarity of Asian and African representatives of Homo erectus. Am J Phys Anthropol.106(1):61-85.

Schwartz, J. et al. 1995. A review of the Pleistocene hominoid Fauna of the socialist Republic of Vietnam (excluding hylobatidae) Anthropological papers of The American museum of natural history, Number 76 New York: 1995.

Download available from: https://digitallibrary.amnh.org/bitstream/handle/2246/259/v2/dspace/ingest/pdfSource/ant/A076a00.pdf?sequence=1&isAllowed=y

Schwartz J. H. and I. Tattersall. 2003. The Human Fossil Record: Craniodental Morphology of Genus Homo (Africa and Asia) v. 2 Wiley-Blackwell; 2003 p284-293

Shen, G., et al, 2009. Age of Zhoukoudian Homo erectus determined with 26Al/10Be burial dating. Nature, 458 (12 March 2009), 198-200.

Abstract available at: https://www.nature.com/nature/journal/v458/n7235/full/nature07741.html

Smithsonian National Museum of Natural History. 2016. 

What does it mean to be human? Zhoukoudian. [ONLINE]

Available at: http://humanorigins.si.edu/evidence/human-fossils/fossils/zhoukoudian. [Accessed 20 June 2017].

Swisher III, C.C., Rink, W.J., Anton, S.C. and Schwarcz, H.P., 1996. Latest homo erectus of Java: Potential contemporaneity with homo sapiens in Southeast Asia. Science, 274(5294), p.1870.

Weidenreich, F. (1951) Morphology of Solo Man. Anthropological Papers of the American Museum of Natural History, Vol. 43: Part 3. New York.

Which species of humans were in southern California 130,000 years ago?

Ever since the Holen (2017) paper, that I covered here I have wondered which species of humans could possibly have migrated to America during this era. Yes, who were the humans that left the modified bones, teeth and cobbles at the Cerutti Mastodon (CM) site? In their Supplementary information, section 9. “Asian origins of early humans on the west coast of North America” Holen et al. engage in some discussion on the matter (from their Supplementary Information, Section 9. Asian origins of early humans on the west coast of North America):

“Hominins in Eurasia during MIS 5 include Homo sapiens, Homo neanderthalensis, Homo sp. (Denisova), Homo floresiensis and Homo erectus^{80, 81}. These taxa, except Homo floresiensis, could have dispersed into northeastern Asia as temperatures increased at the end of MIS 6 and during the Last Interglacial MIS 5⁸². Plausible dispersal routes for hominins to arrive on the west coast of North America at the end of MIS 6 include a land route across Beringia prior to 135 ka⁸³ and a coastal water route along the coasts of Asia, Beringia and North America…

The continuous presence of hominins beginning ~300 ka in southern Siberia at the end of the Lower Paleolithic, although many of the sites are not well-dated⁸⁴, provides a potential source of populations that could disperse eastward. By adapting to conditions in southern Siberia, hominins could have extended their range further northeast to cross Beringia during interglacial intervals. The southern edge of the Beringian land bridge at its maximum extent is estimated to have been close to 63° N, about 200 km further north than the Diring Yuriakh site situated at 60° N in Siberia. The best age estimate for the lower level of the site containing stone tools is based upon TL dates of 267-366 ka⁸⁵. However, the geoarchaeological position and age (especially of the oldest stone artefacts) have been questioned⁸⁶. It is noteworthy that fossil remains of a cold-adapted female hominin, possibly an archaic Homo sapiens, have been discovered in Manchuria, China (40° 34ʹ N). Animal teeth at the site were dated to ~ 260 ka by electron-spin resonance and uranium series dating⁸⁷. It is not yet known how far north these cold-adapted hominins dispersed, but they may be responsible for archaeological sites like Diring Yuriakh and other Early Paleolithic sites in southern Siberia.

At Denisova Cave (51.4° N) in southcentral Siberia, Homo neanderthalensis is first evidenced by the appearance of Middle Paleolithic stone tools in Stratum 22 with bracketing radio thermoluminescence (RTL) ages of 282 ± 56 and 171 ± 43 ka⁸⁸. Biostratigraphic and paleomagnetic data (Blake polarity episode) correlate more recent Denisova Cave Middle Paleolithic stone tool industries with MIS 586. Thus, there are several possible hominin candidates (late Homo erectus, Neanderthals or archaic Homo sapiens) resident in eastern Asia that could have entered North America via Beringia and dispersed to the west coast of North America at 130 ka. Another possibility is that the little-known Denisovans, related most closely to Neanderthals⁸⁹, and known only from DNA studies at Denisova Cave, were the first hominins to reach North America.

The authors then examine the evidence for sea-faring in ancient hominids and the possibility that the Skoglund (2015) “population Y” were the humans that were in California 130,000 years ago and conclude:

“The CM site currently is the only locality in North America that supports such an early hominin dispersal. This speculative discussion poses the challenge to initiate archaeological research in MIS 5e and MIS 6-age geological deposits in North America.”

From the whole section, some of which I have not quoted, the, authors have therefore established:

1. The climate in California 130,000 years ago was wetter and milder in comparison to other eras of the Pleistocene, by reference to the relevant literature.  For example, the wider distribution of mammals, including mastodon and sloth above the arctic circle and at higher altitudes in the Rocky Mountains and as witnessed by fossils found at the CM site such as a capybara (Hydrochoerus) tooth, far north of its usual range.

2. Food was therefore, plentiful for any incoming human migrants from Beringia to the Panamanian isthmus and beyond during the timeframe in question (MIS5e).

3. The humans could be candidates: “Hominins in Eurasia during MIS 5 include Homo sapiens, Homo neanderthalensis, Homo sp. (Denisova), Homo floresiensis and Homo erectus80, 81. These taxa, except Homo floresiensis, could have dispersed into northeastern Asia as temperatures increased at the end of MIS 6 and during the Last Interglacial MIS 5.”

4. Although they discount archaic modern humans (AMH), given the recent findings of much older, ca. 300,000BP archaic modern humans from Jebel Irhoud (Richter, et al. 2017) and the 120,000BP Chinese teeth from Fuyan Cave in Daoxian, province (Lui et al. 2015) there seems at least a possibility that Homo sapiens were the species that came to America 130,000 years ago.

The candidate species therefore are:

• Homo erectus

• Homo neanderthalensis

• Homo sp. “Denisovans”

•  Archaic Homo sapiens

Here are a few mug shots:

Clockwise from top left:

Homo erectus from Wikipedia (2017). Original caption reads: Dmanisi skull 3, Fossils skull D2700 and D2735 jaw, two of several found in Dmanisi in the Georgian Caucasus.

Homo neanderthalensis from North Carolina School of Science and Mathematics (2017). Original caption reads: Hominid Skull - Homo neanderthalensis La Chapelle-aux-Saints 1 "The Old Man". Estimated Age: 60,000 years. Location: La Chapelle-aux-Saints, France

Homo sp. “Denisovans” from Discover magazine (2016). Original caption reads: A molar that belonged to an ancient Denisovan. Max Planck Institute for Evolutionary Anthropology

Archaic Homo sapiens from Peter Brown Palaeoanthropology (2017). Original caption reads: Dali is reasonably complete and well preserved, with damage restricted to postdepositional crushing and displacement of the palate and left maxilla. A large section of the right parietal is missing, as are the maxillary teeth and left zygomatic arch. Wu (1981, 1989) found that most of the cranial dimensions and morphological features of Dali were intermediate between Homo erectus and H. sapiens, with Dali assigned to archaic H. sapiens.

In future posts, I will consider each of the above species of human and what the possibility/evidence of them reaching the Americas 130,000 years ago is.

References

Discover magazine (2016), retrieved from:

http://discovermagazine.com/2016/dec/meet-the-denisovans

Holen, S. R., et. al. (2017) A 130,000-year-old archaeological site in southern California, USA Nature 544, 479–483 doi:10.1038/nature22065

Can be accessed here: http://www.nature.com/nature/journal/v544/n7651/full/nature22065.html

And the Supplementary information can be downloaded from here:

https://www.nature.com/article-assets/npg/nature/journal/v544/n7651/extref/nature22065-s1.pdf

Liu, Wu, et al. "The earliest unequivocally modern humans in southern China." Nature 526.7575 (2015): 696-699.

North Carolina School of Science and Mathematics (2017), retrieved from:

http://www.dlt.ncssm.edu/tiger/360views/Hominid_Skull-H_neanderthalensis_LaChapelleA_1200x900/index.html

Peter Brown Palaeoanthropology (2017). Retrieved from:

http://www.peterbrown-palaeoanthropology.net/dali.html

Richter, Daniel, et al. "The age of the hominin fossils from Jebel Irhoud, Morocco, and the origins of the Middle Stone Age." Nature 546.7657 (2017): 293-296.

Skoglund, P. et al. Genetic evidence for two founding populations of the Americas. Nature 525, 104-108 (2015).

A 130,000-year-old archaeological site in southern California, USA – Pre-Clovis archaeological sites of the Americas VIII: The CALTRANS/Cerutti Mastodon site

The paper all Clovis-first and Beringian Standstill rejectionists have been waiting for. Finally, finally someone stuck their head above the parapet! Holen et. al. (2017) have published a rock-solid piece of evidence to support human presence in the Americas at a shockingly, early date of 130,000 BP right smack in the middle of the of the Pleistocene.

The route of the peopling of the Americas at that date, must have been via Beringia.  I have already and repeatedly talked about, when and for how long the Americas were connected to Asia [see Here, Here and Here].

The humans involved could have been, modern humans, Neanderthals, Denisovans, Homo erectus or Homo heidelbergensis depending on which narrative of human dispersals you subscribe to.

What exactly does the paper present? Well it’s all about the fractured and splintered bones and teeth of a Mastodon, Mammut americanum, the skeleton of which, from Crawford (2017) is shown below:

Anyway here’s the abstract:

The earliest dispersal of humans into North America is a contentious subject, and proposed early sites are required to meet the following criteria for acceptance: (1) archaeological evidence is found in a clearly defined and undisturbed geologic context; (2) age is determined by reliable radiometric dating; (3) multiple lines of evidence from interdisciplinary studies provide consistent results; and (4) unquestionable artefacts are found in primary context (1, 2). Here we describe the Cerutti Mastodon (CM) site, an archaeological site from the early late Pleistocene epoch, where in situ hammerstones and stone anvils occur in spatio-temporal association with fragmentary remains of a single mastodon (Mammut americanum). The CM site contains spiral-fractured bone and molar fragments, indicating that breakage occurred while fresh. Several of these fragments also preserve evidence of percussion. The occurrence and distribution of bone, molar and stone refits suggest that breakage occurred at the site of burial. Five large cobbles (hammerstones and anvils) in the CM bone bed display use-wear and impact marks, and are hydraulically anomalous relative to the low-energy context of the enclosing sandy silt stratum. ²³⁰Th/U radiometric analysis of multiple bone specimens using diffusion–adsorption–decay dating models indicates a burial date of 130.7 ± 9.4 thousand years ago. These findings confirm the presence of an unidentified species of Homo at the CM site during the last interglacial period (MIS 5e; early late Pleistocene), indicating that humans with manual dexterity and the experiential knowledge to use hammerstones and anvils processed mastodon limb bones for marrow extraction and/or raw material for tool production. Systematic proboscidean bone reduction, evident at the CM site, fits within a broader pattern of Palaeolithic bone percussion technology in Africa (3, 4, 5, 6), Eurasia (7, 8, 9) and North America (10, 11, 12). The CM site is, to our knowledge, the oldest in situ, well-documented archaeological site in North America and, as such, substantially revises the timing of arrival of Homo into the Americas.

Setting

A photomontage showing the dig at various stages gives an idea of how the excavation was carried out:

Top: The Cerutti Mastodon site borders state highway 54. From the San Diego Natural History Museum (2017) video on their website.  As far as can work out, the site is behind the banking on the left near the house with three windows.

Middle left: Initial stages of the rescue, excavation at the Cerutti Mastodon site from USA today (2017).

Original caption reads: Caltrans archaeologists Karen Crafts, Chris White, and Don Laylander excavating fossils found at the Cerutti Mastodon site off State Route 54 in San Diego.  San Diego Natural History Museum.

Middle Right: The rescue excavation funded by the National Geographic, was carried out in just a few short weeks between late November 1992 and the end of April 1993. Time pressure was a factor but the palaeontologists found so much material to excavate that an extension was granted for extensive recording of the site. Looking back, this was a very important and farsighted decision by The State of California, Department of Transportation (Caltrans), picture from Ritter (2017).

Original caption reads:

In this February 1993 photo provided by the San Diego Natural History Museum, San Diego Natural History Museum palaeontologists C. Paul Majors and Matt Colbert work at the Cerutti Mastodon site in San Diego, Calif. In a report released on Wednesday, April 26, 2017, researchers say the southern California site shows evidence of human-like behaviour from about 130,000 years ago, when bones and teeth of an elephant-like mastodon were evidently smashed with rocks. (San Diego Natural History Museum).

Bottom: After the emergency, excavation the site was backfilled on the 28^th of April 1993, from Zimmer (2017). Original caption: A bulldozer refilling the Cerutti Mastodon site after excavation and salvage of fossils was completed in 1993. Credit San Diego Natural History Museum.

Evidence Presented

First of the all the stratigraphy was found to be intact, with the evidence for man’s presence found in situ, within a discrete layer. The authors state “Mastodon fossils and cobbles were found in a 20-30 cm thick sandy silt bed (Bed E) that was contained within a 12m thick sequence of Pleistocene sediments. The stratigraphic section consists of multiple upward-fining sequences of silt and fine-grained sand deposited in a low energy fluvial environment.”

This is a key statement, basically it means that, in the opinion of the authors the fossil bone and cobbles were not washed there.

This is more than evident from the position of some of the bones:

The Femoral Heads: Two severed femur heads, one positioned vertically downwards and one upwards. Recall: this is a “low energy fluvial environment”, therefore these bones and their breakage are highly unusual. Low energy streams do not break femur heads off in this manner, and therefore human modification is the most likely explanation. Furthermore, they should settle according, to, the laws of gravity on their sides. Consequently, these positions are once again highly suggestive of placement by human hands.

The two femur heads in situ at the Caltrans site.

Photo: Greshko (2017) Original caption reads: Two mastodon femur balls, one face up and one face down, are among the remains found at the Cerutti site in San Diego.

PHOTOGRAPH BY SAN DIEGO NATURAL HISTORY MUSEUM

The concentration of bones and cobbles found during excavation at the Caltrans site, adapted from Holen (2017) extended data figure 3. Original caption reads: a, Oblique view of concentration 1 in grid unit E3. Note the position of anvil CM-281, spirally-fractured femoral fragments CM-288 and CM-292 and molar fragment CM-286.

The tusk: The position of this find is inexplicable. It was found penetrating several layers of sediment. It had an intrusive wedge of sediment from the upper layers, running down its length from above. This must have been done post-deposition of the layers, otherwise there would have been no infilling of the sediment down the side of tusk. It therefore cannot have just been buried by normal sedimentary processes. The only sensible conclusion, being that the mastodon tusk was shoved vertically through several layers of sediments by human hands.

This tusk diagram also appeared in Deméré (1995). Original 2017 caption reads: Extended Data Figure 7: Pleistocene land mammal excavation grid maps and stratigraphic profile of in situ tusk. c, Profile of vertically oriented mastodon tusk CM-56 recovered from grid unit B2. Note that the tusk extends from the level of Bed E into underlying Beds D and C through a caliche layer. Note the infilling of sediment from Bed D along the leading margin of the embedded tusk.

Spirally Fractured Femur: This specimen is a vital piece of evidence leading to the conclusion that humans were in California and indeed the Americas 130,000 years ago. The spiral bone breakage pattern only occurs when the bones are fresh. To break bones in this manner, the bones need to be de-fleshed while the carcass is fresh either by animal or human predators. As no carnivore tooth marks were found on the bones, hence, human hunters recovering meat seems the most likely explanation for the de-fleshing. Additionally, humans in African hunter-gatherer societies historically broke the long bones of elephant to obtain the fatty marrow. Patterns of breakage observed from these activities, and from experiments carried out by the authors match those found on the bones at the Caltrans archaeological site. Once again, the only logical explanation is that humans broke these bones.

Suspected human fractured femur shaft from the Caltrans site, from Holen (2017). The spirally fractured nature of the bones means they were broken when ‘green’ or fresh.

Original caption reads:

Extended Data Figure 4: Diagnostic anvil wear on CM bone.

a–e, Spiral-fractured femur segment CM-288. a, V-shaped projection with anvil polish (rectangle). b, Side view with V-shaped projection. c, Outer, cortical surface. d, Side view with impact surface and bulb of percussion (highlighted with a black dashed line) on opposite side from anvil wear. e, Enlarged area from a showing impact fracture marks (arrows) where the bone rested on the anvil. f, Spiral-fractured V-shaped cortical bone CM-329 with anvil polish (oval). g. Spiral-fractured bone CM-255 that refits with CM-329 (white rectangle showing the location of the close-up shown in h). h, Enlarged area from g showing anvil striations. Scale bars, 2 cm (a), 5 cm (b–d), 5 mm (e), 10 mm (f–h).

Close-up of panel a above, from Greshko (2017). Original caption reads:  A close-up view of a spirally fractured mastodon femur bone from the site. Photograph by Tom Deméré, San Diego Natural History Museum.

Shattered and flaked second femur

Found in Concentration 1, this shattered and flaked second femur was refitted and visualised using 3D surface models, much of the work carried out at the University of Michigan.

The authors go into great, detail about the taphonomic processes that could have formed this bone assemblage. In their opinion the bone was shattered by blows from the exact type of rounded river cobbles, or ‘hammerstones’ found in the same concentrations of artifacts. Although I am no expert in this area, being a physics graduate, their chain of reasoning seems undeniable. Consequently, these bones, based on decades of taphonomic work by dozens of scientists are human altered.

The assemblage is show in a kaleidoscope of views in Holen  Figure 2. Original caption reads: Percussion-modified bone specimens (illustrated by 3D surface models). a, b, Cone flakes CM-238a (a) and CM-230 (b). From left to right the images show the ventral, dorsal and lateral views (as defined in lithic technology). c, Impact flake CM-222. From left to right the images show the ventral, dorsal and impact surface views. d, Femur fragment CM-340. Images show the cortical surface (left) and longitudinal section showing cortical bone thickness (right). bp bulb of percussion; c, caliche remnant on bone surface; dfs, dorsal flake surface; hf, hinge termination; in, impact notch; is, impact surface; lm, lateral margin (ventral surface); nbp, negative bulb of percussion; udf, undetached flake; vfs, ventral flake surface. Impact surfaces that are external cortical surfaces are shown in a, b, d, whereas a fracture surface is shown in c. Scale bars, 1cm (a-c) and 5 cm (d).

A good close-up of part of the refitted assembly can be found in Bower (2017). This clearly shows the impact notch at the top centre border. Original caption reads: An unidentified Homo species pounded apart mastodon bones with large stones in southern California around 130,700 years ago, a new study concludes. Finds at what’s proposed as the oldest archaeological site in the Americas include this mastodon leg bone. T. Deméré/San Diego Natural History Museum.

The 3D visualisation used in the paper can also be viewed on University of Michigan (2017a) website. The image can be rotated or examined in extreme close-up using the zoom facility as shown below. 

Use wear on cobbles

To break Mastodon long bones (the femur) takes a huge effort. To do so requires a ‘tool’, something that can apply an extreme amount of force e.g. something heavy yet heftable. Large rocks or cobbles were historically used by African hunter-gathers to break elephant bones.

Such cobbles were found amongst the broken bones at the Caltrans archaeological site. Again I repeat: this was a ‘low energy fluvial environment’.

As Greshko (2017) says: “There’s also the matter of the stones’ placement. The site was entombed in siltstone, a type of sedimentary rock that forms from fine-grained sediments—the sort that would settle out only in very slow-moving, low-energy water. But the large stones that appear to be rudimentary tools are far heavier than the surrounding particles. One is roughly 30 pounds. If water didn’t move the rocks there, then perhaps people carried them to the site.”

So, what wear/usage patterns were found on the cobbles that indicate that they were used by humans to break the bones?

Well the authors found quite a lot of evidence:

Hammerstones. These the authors contend were used to break the Mastodon bones and teeth. For each stone tool found multiple signs of use/wear were identified, including for this specimen. Here is a complete, andesite one (CM-383) included in the paper, here illustrated from Joyce (2017). Original caption reads: A boulder discovered at the Cerutti Mastodon site in San Diego County thought to have been used by early humans as a hammerstone. Tom Démeré/San Diego Natural History Museum

Hammerstone with refitted flakes from Callaway (2017).

The authors conclude, that the modification of the Mastodon bones was accomplished using a ‘hammer and anvil’ technique’. This is where the bone being worked is placed between the two rocks and smashed. Original caption reads:

A 'hammer' stone — possibly shaped by ancient humans — found in California and dated to 130,000 years ago.  Image from A. Rountrey, C. Abraczinskas and D. Fisher/Univ. Michigan

As can be noted from the picture above the hammer stone was found in several pieces. It was refitted by scientists from the University of Michigan. They have a very nice animation of the refitting process on their website [here] 

This picture from The University of Michigan (2017b) shows a still from that animation. 

Original caption:  Rock assembly associated with the Cerutti mastodon. Includes CM 109, 254, 262, 283, 284, 304, and 423 (largest). CM 423 was found meters away from the refitting fragments.

Note: The caption read in conjunction with the ‘low fluvial energy’ environment that the authors establish in their paper basically means that the University of Michigan believe this rock was moved by humans and is indeed a hammer stone.

The in-situ Anvil

The purpose of an anvil in a Palaeolithic context, is much the same as its use in a blacksmith’s shop: You place objects on it when you want to hit them. In this case the authors believe the anvils found at the Cerutti Mastodon (CM) site were used to break bones/teeth for the extraction of marrow or to obtain raw materials for tool making.

Anvil CM-281 made of andesite, was found right, plumb in the middle of concentration 1 amongst many of the, bones which the authors contend were broken by humans. Here it is, centre picture, in situ from Holen (2017) Extended data figure 3:

Original caption reads:

Extended Data Figure 3: Bones and cobbles exposed during excavation. a, Oblique view of concentration 1 in grid unit E3. Note the position of anvil CM-281, spirally-fractured femoral fragments CM-288 and CM-292 and molar fragment CM-286.

Here is another view of it from the media release pictures showing it after its recovery, but still on site, from Adams State University (2017).

The import of the find was the tiny molar fragments found around and under the anvil. In a fluvial environment with enough energy to cause collisions between rock and these huge molars, and break them, one would expect small fragments to be washed away and lay scattered across the site. This was not the case. They were found only in concentrations near the anvil and hammerstones. Original caption reads: A researcher holds a mastodon molar fragment found under a rock anvil discovered at the California site.

I won’t go into the detail here, but the authors show in great, detail how each of the above rock specimens has use/wear consistent with their employment as tools to break the bones found at the site yet inconsistent with natural processes. Furthermore, they carried out experimental archaeological tests on elephant bones with cobbles of similar mass and rock types. The results showed that identical damage resulted when they were wielded by human hands.

The CM site dating

This is THE crucial piece of evidence. If the rocks and bones had dated to 14,500 BP for instance, they would be interesting to the archaeological community but unlikely to provoke the criticism and outrage shown by some academics.

It is the very ancient, paradigm challenging date of ca. 130,000BP that has caused the strong negative reaction. Let us look at how the artifacts and site were dated.

In the words of Holen, et al. (2017):

“Initial attempts to date the CM site using radiocarbon analysis at two independent laboratories failed, because the samples lacked sufficient collagen. Several attempts to date the site with optically stimulated luminescence indicated that samples were near or beyond the upper limits of dose saturation, and that the depositional age of the sediment is greater than 60-70 thousand years (kyr) (Supplementary Information7). Subsequently, multiple bone fragments (Extended Data Fig 9e-g) were analysed by uranium-series disequilibrium methods (Methods and Supplementary Information 8)…

Results calculated using diffusion-absorption-decay modelling for profiles of multiple specimens (Extended Data Fig 10c) indicate a burial age estimate of 130 +/- 9.4 Kyr (weighted mean of three maximum likelihood ages determined for bone profiles; Extended Data Fig. 10d). Isotope data are consistent with diffusion of U into interior portions of cortical bone and show no evidence for post-burial U leaching that would yield erroneously old ages (Supplementary Information 8).”

Here is their Extended data Fig 10d:

Original caption reads: Extended Data Figure 10: Results of U-series isotope analyses.

See also Supplementary Table 12.  d, Best estimate of burial age of 130.7 ka (solid horizontal line) and 2σ uncertainties (±9.4 ka; dashed lines) determined as the mean of DAD dates for profiles shown in c weighted by their respective uncertainties.

To me that’s a pretty watertight dating of the site and its artifacts. That being the case, the authors move closer to providing sufficient evidence to thoroughly support their claims of the antiquity of man in the Americas.

Now as this dating was carried out so assiduously by scientists independent of the excavators it seems that the scientific naysayers are reluctant to challenge this dating. However, as they fundamentally disagree with the possibility of humans in the Americas 130,000 BP many of the other aspects of the evidence are attacked. See further down this post for some naysayer reactions.

Other Evidence

A few brief, other points to consider:

1. The distribution of the bones, hammerstones and anvils.

If the bones and rock fragments/cobbles which caused the damage to them were moved through the agency of water, the bones should, by the laws of physics be more, or less evenly distributed across the site. They were not. They were found in concentrations as shown by Holen et al. (2017) Fig 1:

Original caption reads: Figure 1. Plan of CM excavation site. a, Distribution of complete and fragmentary bones, teeth and cobbles. Note the circular cross- section of the tusk (CM-56) in grid unit 2B. Red arrows indicate bones sampled for U-Th dating. b, Distribution of spiral- fractured bone, molar fragments and andesite anvils (CM-281, CM-114) in concentrations 1 and 2. c, Distribution of impact-fractured bone, cone flakes, impact flakes, bone refits and anvils in concentrations 1 and 2. Molar refits (yellow lines were distributed between grid units D3 and E3. Cone flakes (CM-438a, CM-438b) that were found when screening grid unit E3 cannot be precisely plotted. Impact flake CM-236 was found above anvil CM-281.

2. Large, thick bones with a lot of tensile strength, such as the femora were found fractured, flaked and splintered. Smaller lighter bones, such as ribs were found whole within a few inches of each other. If the bone breakage were due to fluvial transport, one would expect the pattern to be reversed, i.e. small bones would be broken, while large ones remained intact.

Overall the authors assert that these two pieces of evidence support their theory that the bones were modified by humans who had reached California by 130,000 BP.

Let us now turn to the conclusion of the paper:

Holen paper conclusions:

"We conclude that the reliably dated Cerutti Mastodon site constitutes an in situ archaeological association based on: comparative taphonomy; bone modification like those produced by Palaeolithic percussion technology and replicated by experimental archaeology; presence of hammerstones and anvils that exhibit use-wear and impact marks; and the presence of rock fragments that can be refitted to breakage scars. Bone breakage for marrow extraction and/or bone and molar tool manufacture is the preferred archaeological interpretation of the CM site, as there is no evidence of butchery. Concordant interdisciplinary lines of evidence from this study suggest the presence of Homo in North America during the last interglacial (MIS5e) and as early as 130 thousand years ago (ka) (Supplementary Information 9). This discovery calls for further archaeological investigation focused on North American strata of early late Pleistocene age."

Naysayer reactions

In the interests of ‘balanced reporting’ many websites elicited quotes/opinions about the paper from palaeontologists. I include some below:

From Zimmer (2017) in the New York Times:

“Some experts were intrigued by the research, but many archaeologists strongly criticized it, saying the evidence didn’t come close to supporting such a profound conclusion.

“I was astonished, not because it is so good but because it is so bad,” said Donald K. Grayson, an archaeologist at the University of Washington, who faulted the new study for failing to rule out more mundane explanations for markings on the bones.

“They present evidence that the broken stones and bones could have been broken by humans,” said Vance T. Holliday, an archaeologist at the University of Arizona. “But they don’t demonstrate that they could only be broken by humans.”

Gary Haynes, an archaeologist at the University of Nevada, Reno, said the researchers should have ruled out more alternatives. Some of the bone fractures could have been caused by pressure from overlying sediment, he suggested.

“Extraordinary claims require unequivocal evidence,” Dr. Waters of Texas A&M said. Unlike the stone knife he and his colleagues found in Florida, the stones at the San Diego site are not indisputably human tools.”

From Bower (2017)

“The ancient southern California landscape also may have included streams. These could have washed broken mastodon bones and large stones from separate areas. They might simply have collected at the spot where they were eventually unearthed, says Vance Holliday. Also an archaeologist, he works at the University of Arizona in Tucson.

Perhaps hominids used stones found at the site to break bones, he says. Still, the new study doesn’t rule out other explanations. For instance, the bones might have suffered a trampling by animals at locations where the bones originated. “Making a case for [hominids] on this side of the Pacific Ocean at 130,000 years ago is a very heavy lift,” Holliday argues. “And this site doesn’t make it.”

Michael Waters is an archaeologist at Texas A&M University in College Station. Nothing at the mastodon site clearly qualifies as a stone tool, he argues. Indeed, he adds, mounting genetic evidence indicates that the first people to reach the Americas — the ancestors of present-day Native Americans — arrived no earlier than about 25,000 years ago.”

From Letters and Kleske (2017), archaeologist Matt Tennyson had this to say:

“I read your article on the Cerutti site (“Study revises time line on arrival of humans,” April 27). As an archaeologist, I wanted to write because while the mastodon is certainly a noteworthy find, I’m skeptical that this is an archaeological site. The hammers and anvils found at the site are dubious artifacts, at best. Not to mention that modern humans hadn’t even left Africa 130,000 years ago and other hominid species were nowhere near North America. This isn’t just pushing back the dates when people came to North America, this is re-writing human history.

Much of the reporting I’ve encountered on this story is all too ready to accept the findings. The recent March for Science stressed the importance of facts in today’s world. Right now, the facts don’t add up and the data shared to date are incomplete at best. To his credit, Dr. Deméré has indicated he welcomes debate about the site, so hopefully time will tell.”

From Callaway (2017):

“Before invoking humans, however, the researchers need to better rule out the possibility that natural forces broke the rocks and bones, says David Meltzer, an archaeologist at Southern Methodist University in Dallas, Texas. “If you are going to push human antiquity in the New World back more than 100,000 years in one fell swoop, you’ll have to do so with a far better archaeological case than this one.””

From Wong (2017);

“We need to leave our minds open. I admire these colleagues for sticking their necks out. They should be commended for doing that,” says archaeologist Tom Dillehay of Vanderbilt University, who fought for years to convince the archaeological community that remains from the controversial site of Monte Verde in Chile predate the Clovis culture. Today most scholars accept that Monte Verde dates, back to, around 15,000 years old, if not 18,000 to 20,000 years ago, as Dillehay would have it. “But more evidence is going to be needed” for something this early, he says of the claims for human activity at the Cerutti Mastodon site.”

It is really, telling to note that NO criticism of the dating of the site has so far emerged. Instead the main, focus of the attack is whether the surface modification of the bones and cobbles (the anvils and hammerstones) is caused by natural processes or by their use by humans.

All I can say is that the likes of Dillehay, Meltzer and Waters should have known better than to voice negative comment shot from the hip in the immediate aftermath of the paper’s publication. Each has, had, involvement with controversial sites and so knows how distorting uninformed commentary can be. I say uninformed because I do not believe that any of them will have had enough time to study the use/wear evidence provided in the paper sufficiently well to make fact-based judgements.  In point of fact, none of these eminent scientists actually, gave evidence based reasons for their criticisms. They merely offered opinions. This is a great shame as it could, colour the argument going forward.

Conclusion

This is a fantastic, extremely thorough presentation of the evidence found at the site. The key points are:

1. The dating seems to be extremely thoroughly done. The Cerutti Mastodon site is therefore established as 130,000 years old.

2. Extensive analysis of the bones found at the site, including their surface taphonomy, secure stratigraphic position and proved modification while still fresh point towards humans being responsible.

3. The use/wear on cobbles from the site is consistent with their being the tools used to carry out the modification of the bones and teeth.

4. The authors carried out experiments on fresh (green) elephant femoral bones using similar cobbles to those found at the CM site. The analysis of which showed minutely similar damage to the bones and to the cobbles employed.

5. The in situ distribution of the bones and anomalous positions cobbles within a undisturbed well stratified geological context characterised as a low energy fluvial environment leave little room for argument that these specimens were left there by humans.

6. The low energy fluvial environment rules out water motion as a reasonable, alternate explanation for the damage to and placement of the bones, hammerstones and anvils. Therefore, humans almost certainly placed these materials there.

Taken together the evidence is pretty, strongly in favour of the fact, yes the fact, that humans were in the Americas by and probably for some time before 130,000 BP.

Overall the evidence is very strong for humans being in the Americas by or before 130,000 BP. As far as it goes.

However there are some unanswered questions and a lot of back-story to this site. Three questions that spring to mind, immediately are:

1. Why are there no cut marks from butchery on the bones? If processing of a mastodon carcass was taking place, why no scraping or notch marks at the usual places?

2. Why is no mention made of the conflicting dating found in the previous report by Deméré, T. A., Cerutti, R. A. & Majors (1995), which puts an even older date on site?

3. Who were the humans that were in the Americas 130,000BP? What species were they?

The main weakness of this post are that I have not had time to include details on the materials and methods used by the authors to prove the use/wear to stone artifacts and damage to the Mastodon bones is caused by human agency.

I will most likely update this post, when further information regarding these questions, and others surrounding the swirl of conspiracy theories, innuendo and rumour which have made the Cerutti Mastodon site such a controversial one over the years, come to light.

References

Adams State University, Colorado. 2017. Adams State professor contributes to ground breaking research. [ONLINE] Available at: https://www.adams.edu/news/apr1725.php. [Accessed 10 June 2017]

Bower, B. Science News for Students. 2017. America’s first settlers may have arrived 130,000 years ago Mastodon bones, stone tools place unknown Homo species in California surprisingly early. [ONLINE] Available at: https://www.sciencenewsforstudents.org/article/americas-first-settlers-may-have-arrived-130000-years-ago. [Accessed 13 June 2017].

Callaway, E. Nature.com.. 2017. Controversial study claims humans reached Americas 100,000 years earlier than thought - Broken mastodon bones hint that Homo sapiens wasn’t the first hominin to get to the New World.. [ONLINE] Available at: http://www.nature.com/news/controversial-study-claims-humans-reached-americas-100-000-years-earlier-than-thought-1.21886. [Accessed 12 June 2017].

Crawford, G. The Blog formerly known as... 2017. Peale’s “Barber Farm” Mastodon. [ONLINE] Available at: https://theclovissite.wordpress.com/2015/01/22/peales-barber-farm-mastodon/. [Accessed 13 June 2017].

Deméré, T. A., Cerutti, R. A. & Majors, C. P. (1995). State Route 54 Paleontological Mitigation Program: Final Report (San Diego Natural History Museum, 1995)

Greshko, M. National Geographic News. 2017. Humans in California 130,000 Years Ago?. [ONLINE] Available at: http://news.nationalgeographic.com/2017/04/mastodons-americas-peopling-migrations-archaeology-science/. [Accessed 4 June 2017].

Holen, S. R., et. al. (2017) A 130,000-year-old archaeological site in southern California, USA Nature 544, 479–483 doi:10.1038/nature22065

Can be accessed here: http://www.nature.com/nature/journal/v544/n7651/full/nature22065.html

Joyce, C. The Two Way, Breaking News from NPR. 2017. New Evidence Suggests Humans Arrived In The Americas Far Earlier Than Thought. [ONLINE] Available at: http://www.npr.org/sections/thetwo-way/2017/04/26/525628056/new-evidence-suggests-humans-arrived-in-the-americas-far-earlier-than-thought.

[Accessed 4 June 2017].

Letters U. T and Kleske, A. The San Diego Union Tribune. 2017. Don’t draw conclusions from mastodon bones. [ONLINE] Available at: http://www.sandiegouniontribune.com/opinion/letters-to-the-editor/sd-mastodon-bones-conclusions-20170502-story.html. [Accessed 15 June 2017].

Ritter, M. WBZW online. 2017. Neanderthals in California? Maybe so, provocative study says. [ONLINE] Available at: http://1520wbzw.com/news/national/neanderthals-in-california-maybe-so-provocative-study-says . [Accessed 13 June 2017].

San Diego Natural History Museum. 2017. The Cerutti Mastodon Discovery. [ONLINE] Available at: http://www.sdnhm.org/exhibitions/the-cerutti-mastodon-discovery/. [Accessed 12 June 2017].

University of Michigan, Museum of Palaeontology, Repository of online Fossils. 2017a. Specimen: SDSNH 49926 Taxon: Mammut americanum Element: CM 340; bone fragment. [ONLINE] Available at: https://umorf.ummp.lsa.umich.edu/wp/specimen-data/?Model_ID=1245. [Accessed 14 June 2017].

University of Michigan, Museum of Palaeontology, Repository of online Fossils. 2017b. Specimen: SDSNH 49926. Element: Rock assembly. [ONLINE] Available at: https://umorf.ummp.lsa.umich.edu/wp/specimen-data/?Model_ID=1255. [Accessed 12 June 2017].

USA Today. 2017. Scientists claim humans reached North America 130,000 years ago. [ONLINE] Available at: https://www.usatoday.com/picture-gallery/news/2017/04/26/scientists-claim-humans-reached-north-america-130000-years-ago/100890426/. [Accessed 12 June 2017].

Wong, K. Scientific American online. 2017. Ancient Bones Spark Fresh Debate over First Humans in the Americas. [ONLINE] Available at: https://www.scientificamerican.com/article/ancient-bones-spark-fresh-debate-over-first-humans-in-the-americas/. [Accessed 16 June 2017].

Zimmer, C The New York Times.. 2017. Humans Lived in North America 130,000 Years Ago, Study Claims. [ONLINE] Available at: https://www.nytimes.com/2017/04/26/science/prehistoric-humans-north-america-california-nature-study.html?_r=0. [Accessed 15 June 2017].