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The Pliocene-Pleistocene boundary presents a period of transformation in human evolution. This is a period after which it is clear that early humans are using subsistence strategies that can be characterized as hunting and gathering, assisted with the advent of stone tool technologies, and clearly dispersing from East African refugia at places like Oldovai, Koobi Fora, Daka and Bodo to destinations outside of Africa^[1][2][3].

And hominid physical morphology begins at this point to take on characters that can be more easily associated with anatomically modern humans: increases in brain sizes and stature as well as body proportions that more closely resemble that of modern humans than of our Australopithecus and Paranthropus predecessors^[4]. That modern humans evolved and dispersed, eventually around the planet, from hominid ancestors who very probably and ultimately originated from the Rift Valley of eastern Africa is a widely accepted supposition.

Physical remains of Homo erectus/ergaster showing up a places that are far and wide from their probable African origins: Java and the Indonesian archipelago^{[5][6][7][4][8]} the Yuanmou Basin of China, dating to about 1.7 Ma^[8]; Dmanisi, Georgia, also dating to about 1.7Â Ma^[9][10][4]; and in the Levant^[4].

At what geographic point or points did Homo erectus depart the African continent?

The answers to this question invariably include one or more of four possible locations: the Sinai Peninsula through the Levant; the strait of Bab el-Mandab near the Horn of Africa; the Strait of Gibraltar; or across the Mediterranean through Sicily^[3].

Several models of dispersal have been developed, examining the possible routes that early humans could have used to migrate out of the African continent. Whether those models work largely depends upon the period of time for a given migration event since factors to include are climate and resulting sea-levels as well as the capabilities of the population that is migrating. Crossing the Mediterranean at both a Morocco to Spain route or from Tunisia to Sicily would still require that Homo erectus navigate several kilometers of open water^[3]. The channel that passes through the Strait of Gibraltar, even accounting for lowered sea-levels of early Pleistocene glacial periods would have still been at least 5 km wide and hundreds of meters deep with a probable easterly current of 2 knots. The current at a Tunisia-Sicily crossing would likely have been less but the distance would have been far greater and still deep enough to have required a technological advantage not previously attributed to H. erectus. Nearly as challenging, though only slightly less so, would have been the strait at Bab el-Mandab at the southern end of the Red Sea where the Horn of Africa nearly joins with the Arabian Peninsula. Like the Strait of Gibraltar, Bab el-Mandab would have only been about 5 km wide though it’s been suggested that during the Early Pleistocene there may have been glacial periods in which sea-levels and the central channel may have been completely exposed^[10], though this hasn’t been substantiated. If it were the case, however, archaeological data would support a southern Red Sea crossing since there is significant evidence of both Oldowan and Acheulean industries at several undated strata on the Arabian Peninsula^[10] as well as off-shore at paleoshorelines as deep as 40 km^[11].

However, each of these three dispersal models are unnecessary to explain the dispersal of Homo erectus in the early Pleistocene. The most plausible and parsimonious and, therefore, the most probable dispersal point for H. erectus out of Africa into Eurasia and the Arabian Peninsula is via the Sinai Peninsula where the Nile river delta, the Red Sea and Asia meet. Even without the lowered sea-levels of glacial periods, migrations back and forth through the approximately 70 km wide strip of land that separates the Gulf of Suez from the Mediterranean Sea would have been possible. From there, H. erectus could have traveled to Dmanisi, the Arabian Peninsula, and further east into Asia as well as up through the Bosperus Strait region and into Europe then down into Italy and Spain. While it may have been more direct to leave Africa through one of the other routes, even the furthest European and Arabian destinations are less distance when traveled through the Sinai Peninsula than Java and China where it is clear Homo erectus was willing to travel. A dispersal through the Sinai Peninsula invokes the fewest new assumptions about the technology and culture of Homo erectus and eliminates any need for a water crossing.

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1. Stringer, C.  (1995). “The evolution and distribution of later Pleistocene human populations,” in E. S. Vrba, G. H. Denton, T. C. Partridge, and L. H. Bickele, (Eds.), Paleoclimate and Evolution with an Emphasis on Human Origins, 524-532. New Haven: Yale University Press, 524-532
2. Dennell, R. (2003). Dispersal and colonisation, long and short chronologies: how continuous is the Early Pleistocene record for hominids outside East Africa? Journal of Human Evolution, 45, 421-440
3. Derricourt, R. (2005). Getting “out of Africa”: sea crossings, land crossings and culture in the hominin migrations. Journal of World Prehistory, 19, 119-132
4. Antón, S.C. and Swisher, C.C. (2004). Early dispersals of Homo from Africa. Annual Review of Anthropology, 33, 271-296
5. Wolpoff, M., A. G. Thorne, J. Jelinek, and Z. Yinyun (1994). The case for sinking Homo erectus. 100 years of Pithecanthropus is enough!, in J.L. Franzen  (Ed.), 100 Years of Pithecanthropus: The Homo Erectus Problem. Frankfort am Main: Courier Forschungs-Institut Senckenberg
6. Stinger, C. (2002). Modern human origins: progress and prospects. Philosophical Transactions of the Royal Society of London Biological Science, 357 (1420), 563-579
7. Antón, S.C. (2003). Natural history of Homo erectus. Yearbook of Physical Anthropology, 46, 126-170
8. Zhu, R.X., et al (2008). Early evidence of the genus Homo in East Asia. Journal of Human Evolution, 55(6), 1075-1085
9. Stringer, C. (2000). “Human evolution: how an African primate became global,” in  S. J. Culver and P.F. Rawson. (Eds.), Biotic Response to Global Change: The Last 145 Million Years, 379-390. London: Cambridge University Press
10. Petraglia, M.D. (2003). The Lower Paleolithic of the Arabian Peninsula: Occupations, Adaptations and Dispersals. Journal of World Prehistory, 17 (2), 141-179
11. Flemming, N.C. (2004). Submarine prehistoric archaeology of the Indian continental shelf: a potential resource. Current Science 86, 1225–1230

There were a stream of posts on the anthropology blogs about Ardipithecus ramidus, the 4.4 million year old fossil hominid originally discovered by a team led by Tim White in Ethiopia between 1992-1993. I really wanted to get in on it but barely had time to read some of the reports and none to offer up a post until now. So what can I say that others in the blogosphere haven’t already pointed out? Probably not much, but I thought I’d highlight some of the reactions by creationists
(Agnopithecus creationus» ).

Chris Esparza, a writer for the Dallas Christian Living Examiner, made some comments that may or may not be from the creationist point of view, but certainly call into question what the find means to “Christians^[1].

Esparza gets a little heat in the comments section for his mis-quoting the age of Ardi to “3.2 million years ago” rather than the 4.4 mya date arrived at by the research team. This is interesting since it reveals the dedication the author had in the science, perhaps symbolic for the dedication that creationist and the 40 percenters» have for science: they read the headlines, skim for key words, and pick out the bits they feel support their conclusions -even if that latter bit means twisting the words or even re-inventing them. Esparza goes on to say about the “theory of evolution:”

[it's] idea of the missing link is that somewhere way back when, there was a primate who almost seemed to be half monkey and half human, proving that there was at some point an evolutionary split. A recent discovery in Ethiopia disproves that theory.

Not only did Esparza get wrong the concept that the Nat. Geo. quote was trying to convey, he conveniently reshapes the quote into his own pre-conceived notion that evolution is questionable to begin with and probably that “only” belongs in front of theory whenever talking about evolution. It doesn’t. What the National Geographic article^[2] was pointing out is that there *is* a common ancestor to chimpanzees and modern humans, but it might probably isn’t something that would be “half-chimp / half-human,” rather it is an ape that exhibits a mix of derived and primitive characters, appearing very different from any modern primate (i.e. chimps, gorillas, humans), but still ancestral.

In another online Christian publication, Michael Foust of the Baptist Press^[3] quotes Answers in Genesis, headed by cult leader Ken Ham, as saying Ardi has “relatively little in common with humans.” What’s interesting with the AiG stance is that they at once criticize the methods by which the analyses were done:

“And we can’t forget that all of these conclusions are inferred from digital reconstructions and fallible reconstructions of bones that were in very bad shape.”

Then align with a quote mined from the National Geographic article quoted above in their dismissal of Ardi as a human ancestor:

“Instead, the new evidence suggests that the study of chimpanzee anatomy and behavior — long used to infer the nature of the earliest human ancestors — is largely irrelevant to understanding our beginnings,” National Geographic science writer Jamie Shreeve wrote. “Ardi instead shows an unexpected mix of advanced characteristics and of primitive traits seen in much older apes that were unlike chimps or gorillas.”

AiG is relying scientific analysis to dismiss a scientific conclusion because a result of the analysis appears to fit their preconceived conclusions. Yet they don’t think the analysis is accurate! And, they get the implications of the result wrong to begin with! Agnopithecus creationus! In its natural habitat.

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1. http://www.examiner.com/x-10272-Dallas-Christian-Living-Examiner~y2009m10d1-Oldest-human-skelton-disproves-missing-link-theory
2. http://news.nationalgeographic.com/news/2009/10/091001-oldest-human-skeleton-ardi-missing-link-chimps-ardipithecus-ramidus.html
3. http://www.sbcbaptistpress.org/BPnews.asp?ID=31389

The front of my new T-Shirt

Australopithecus Afarensis skeleton was discovered in 1974 near Hadar in Ethiopia, and she was nicknamed “Lucy” by the paleoanthropologists who found her. As the story goes, “Lucy in the Sky with Diamonds” by the Beatles was playing during their celebration of finding the 3.2 million year old hominid.

Because of their find, pages upon pages of data have been written on early hominid evolution and many questions have been answered with, perhaps, many more now able to be asked just because of Lucy.

Which is why I’m happy to have my new t-shirt to wear on the first day of class for my graduate class “The Emergence of Humankind!”

If you’d like to get this or other thought-provoking t-shirts, visit Mental Floss, which specializes in things that make you think. Afarensis, you’ve got to get one of these!

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The most recent online issue of Current Biology has an article describing the research which reveals evidence that the first Americans immigrated via two distinct populations at around the same time. One population is comprised of haplogroup D4h3, which took the Pacific coastal route; the second is made up of haplogroup X2a and they migrated through the land corridor between the Laurentide and Cordilleran Ice Sheets.

Both haplogroups migrated Siberia between 15,000 and 17,000 years ago just after the Last Glacial Maximum with D4h3 migrating the Pacific coast all the way to Tierra del Fuego at the tip of South America. X2a stayed in North America.

The data comes from the studies in molecular genetics by Antonio Torroni, Ugo Perego, and Alessandro Achilli at the Università di Pavia in Italy. They examined the mitochondrial DNA the two rare haplogroups above. mtDNA is passed through the generations from mother to child and is very useful in studying the phylogeny of organisms including humans.

Neanderthals probably weren't stupid

It has long been thought that one of the reason Homo sapiens eventually dominated the hominid line, colonizing Africa and Europe beginning at around 40,000 years ago and eradicating or out-competing the Neanderthals, was that they were technologically advantaged. The idea was that because H. sapiens had better stone tool technologies, they had the edge, so to speak, on their Neanderthal cousins who already occupied the lands H. sapiens were migrating into.

This sort of explanation, perhaps, is easily believed whether one wants to accept it or not since H. sapiens are us and we do, after all, have a not-so-proud history of simply taking the lands we need from those less advanced or capable.

The Dim-Witted Cave Man?

I ♥ My ♣

It’s also been a common preconception that Neanderthals = “cave men,” which carries the cultural connotation of being stupid or of diminished wit, bringing to mind the humorous television commercials produced by Geico and the thousands of magazine and newspaper cartoons over the years that depicted cave men in various antics, the most prevalent theme being, perhaps, clubbing a cave woman over the head and taking her home.

However, new information has come to light with a study published today in the Journal of Human Evolution in which researchers in experimental archaeology spent three years producing flakes, stone tools created through the process of flintknapping in which cores of stone are shaped through percussion and pressure to manufacture tools like blades, axes, scrapers, and points.

The production of three years worth of flakes and blades, the former used by Neanderthals and the latter by Homo sapiens, allowed the researchers to gather statistical data on the quantities of tools, amounts of produced cutting-edges, durability of cutting-edges, and efficiency of the tools. The empirical data allowed the researchers to conclude that the difference in stone tool technology used by the H. sapiens vs. the Neanderthals offered no technological advantage.

The lead author of the paper in the J. of Human Evolution, Metin Eren of the University of Exeter, remarked:

Our research disputes a major pillar holding up the long-held assumption that Homo sapiens were more advanced than Neanderthals. It is time for archaeologists to start searching for other reasons why Neanderthals became extinct while our ancestors survived. Technologically speaking, there is no clear advantage of one tool over the other. When we think of Neanderthals, we need to stop thinking in terms of ‘stupid’ or ‘less advanced’ and more in terms of ‘different.’

The University of Exeter in the U.K. offers the only degree in Experimental Archaeology in the world. The other researchers on the project were from Southern Methodist University and Texas State University as well as the Think Computer Corporation.

I’ve been watching for the article, but it doesn’t seem to have made it to online publication just yet even though it’s slated for today. It’ll be interesting to see just what, specifically, the differences are between cutting edges of flakes versus blades.

Regardless, this sort of research is always great since it eliminates assumptions, which, when wrong, are bad since they lead archaologists down the wrong path. If blade technology wasn’t the clear advantage H. sapiens had over Neanderthals, then the question becomes, “what, then, caused the Neanderthals to go extinct and why were H. sapiens more adapted to deal it? Or could H. sapiens simply not have faced the same pressures at all?”

Acouple of online editions of U.K. newspapers reported the recent finds of 30 carvings recovered at an archaeological site in Poland, dating to about 15,000 years ago. Most anthropologists and archaeologists would probably be immediately familiar with the Venus Figurine motif, but the recent media report was been picked up by a few blogs, each appealing to the title gag.

(Note: This post originally appeared on Anthropology.net in March 2007 and I was considering a follow up post linking to it, but couldn’t find it in the archives. I think a few posts were lost Kambiz’s server move. I’m reposting it here and using it for my Four Stone Hearth entry this fortnight with more (hopefully) on the Venus Figure motif in the future.)

Venus Figurines of the Paleolithic and Their Caricatured Features

Admittedly, the gag is funny, but looking deeper at the Venus Figurines reveals an interesting and fascinating motif and one that, amazingly enough, spans large geographic and chronological ranges. The distinctive motif has been found from Spain and France to Russia and back down to Anatolia and Mesopotamia (Turkey and Iran/Iraq). They date to as far back as 24,000 years and as recent as the Bronze Age, perhaps about 5,000 years ago.

Venus of Willendorf
The motif itself includes several prominent and relatively consistent features. In almost all cases the figure is obese, often very obese. Voluptuous breasts and thighs, and an overall curvaceous appearance are features present almost without fail. Other frequently occurring characteristics include the presence of unusually small arms and legs, prominent buttocks, the lack of feet, and obvious vaginal features like a pronounced vulva. Regional features are also notable: the Venus of Willendorf, perhaps the most recognizable Venus Figurine, appears to be wearing a hat or headdress. The goddess figurines of Çatalhöyük are depicted seated in a throne flanked by felines with her hands resting on their heads. She’s also presented as giving birth and James Mellart, who excavated Çatalhöyük in the 1950s, interpreted the shrine where such a figurine was discovered to be a birthing place. A goddess seated between two felines was also found in a Çatalhöyük granary, suggesting that fertility may, indeed, be a theme there.

But did cavemen prefer big butts? The recent media reports about the Polish Venus carvings note that historians attribute this reverence for curves and voluptuousness as attributes that were considered to be ideal for prehistoric societies since they implied wealth and healthy diet.

They also suggested she would be a successful mother, able to produce lots of children and sent out a message to other men that her partner was a strong and successful hunter – making him more attractive to other women.

But this is the Venus Figurine simplified. The fact is, any speculation on what the figurines really meant is, well, speculation. It’s a fact that they span many societies and still have a relatively common appearance. It’s a fact that they greatly out-number male figurines. It’s a fact that the earliest figurines accurately represented what a fat woman looks like, so there must have been fat women from whom the craftsman / artist derived inspiration. It’s a fact that the earliest figurines included details like vulva. And it’s a fact that some features were prominent (breasts, stomachs, buttocks, vulva) and detailed while others were not (feet, arms, face). It’s a fact that red ochre has been found in association with some of the figurines.

When these facts are considered, it becomes clear that the artist spent some time on the details that he wanted to be noticed and diminished the details that were insignificant. The Venus of Willendorf, for instance had a hat: a very detailed and complex representation of a woven textile that must have involved much of the artist’s time. Seven concentric rows that circle a rosette comprise the headgear and dimples, folds and rolls of adipose were carefully crafted. Yet, the artist omitted a face and feet. Could this mean she’s an anonymous representation of the “perfect” woman for the sophisticated hunter-gatherer? Or could it have been a way of representing a generic mother goddess? The pronounced vulva and red ochre that the Willendorf figure was painted in may have, together, been reminiscent of menstruation and thus fertility. Certainly a prehistoric woman with large stores of fat would be better equipped to nourish children and a caricatured, obese representation might have been used to refer to the mother goddess who nourishes all life. Her lack of feet (they weren’t broken off –they were never added) may have been intentional, affording the goddess figurine no way to depart from her assigned station (a birthing shrine or granary); or, maybe, the artist simply wasn’t good at feet and didn’t find them important. Without feet, the figurine couldn’t have been stood up nor would it sit or lie in any manner that appeared natural or intended. But it could be held and the person holding it would feel the curves and the shape of the figure.

Originally, the Venus Figurine was named “Venus” as a joke. A pejorative meant to demean the “uncivilized” and “primitive” opinion of beauty that the “caveman” obviously had. The irony isn’t lost, however, if the figurine motif is, indeed, a goddess. Venus was, of course, the Roman goddess of beauty and love, an analog of the Greek goddess Aphrodite, and consistently depicted in the nude. The Roman/Greek version, however, is more in line with the modern (or, at least, Western) idea of beautiful, sensual, and sexually attractive with her thin form and ample, but not pendulous, breasts. Nor was her pubic region depicted as more than a mere space, absent of vulva, vaginal lips, and the details present in her more ancient predecessor.

There is much more that can be written on the Venus Figurine, so perhaps I’ll revisit this subject again in the future. But I’ll close with the following thought: the most convincing evidence to me that the Venus of Willendorf (and, therefore, probably most of the Venus figurines) was a goddess and not a representation of an actual person is the hat and lack of face. Traditionally, representations of elites (kings, queens, nobility, and gods) include headgear. That the face was omitted might signify that there was more anonymity involved than a female ruler, shaman, oracle, or other elite. Certainly the reverence for feminine attributes might indicate matriarchal societies existed, or at least a much less patriarchal one than more recent human cultures are guilty of.

Further Reading:

Evans, Martin (2007). Why cavemen liked curvy cavewomen … like Kylie. Daily Express, Tuesday, March 13, 2007. http://www.express.co.uk/news_detail.html?sku=1356

Soffer, Olga; Adovasio, J.M.; Hyland, D.C. (2000). The “Venus” Figurines: Textiles, Basketry, Gender, and Status in the Upper Paleolithic, Current Anthropology 41, pp. 511-537.

Not alive. I just wanted to clarify that first.

But the fossil remains of what is being dubbed Chororapithecus abyssinicus by the Ethiopian-Japanese team that discovered the ancient ape “represents the earliest recognised primate directly related to modern-day gorillas, chimpanzees and bonobos.”

Found were a single canine and eight molars which show that Chororapithecus was either an early ancestor to the gorilla or an independent branch of ape with the same adaptations. While he admits this is an exciting discovery, Peter Andrews, a paleontologist at the British Natural History Museum, was skeptical enough about characteristics of the teeth to indicate it may be hasty to name a new species ancestral to gorillas. Andrews noted that if it is, indeed, a new species, the ape-human split must be pushed back on the evolutionary timeline.

The point at which a humans and chimpanzees had a common ancestor is generally held to be at around 7-8 million years ago.

“Chororapithecus indicates that a reconsideration of this assumption is needed,” the researchers [who discovered Chororapithecus] said. “In fact, if the orang line was present in Africa prior (to the) first migration of Miocene (some 23-25 million years ago) apes from Africa to Eurasia, then the human-orang split could have easily have been as old as 20 million years ago.”

More on this story can be found at this Reuters article: Researchers find prehistoric ape fossils.

At least that’s the title I should have used on March 20, 2007 when I scooped the BBC, the LA Times, National Geographic and other major and minor media outlets.

My original post on the topic was at Anthropology.net, titled New Research on Ötzi, the Iceman, Cometh. From that post I discussed the study conducted on Ötzi’s remains:

a projectile point that lacerated the left subclavian artery, and that the attempted removal of the arrow at the time of death may have caused Ötzi to bleed to death.

I also discussed a related study that used forensic analysis to determine where Ötzi had been in the last days of his life. Using the data from these two studies, I also reconstructed a speculative bit of fiction on the events that might have transpired in Ötzi’s last days.

Go there. Read it. And when you’re looking at the other sites around the net, or in print or video media and they bring up “the Iceman,” tell everyone who broke the story first!

P.S. I’m kidding, by the way… I’m not so shallow that I need that sort of validation. I was actually shocked to find that I wrote on something before the rest of the media.

Anyway, here are some other mentions around in online media:

Washington Post
Los Angeles Times
People’s Daily (China)
Times of India
National Geographic
BBC

The multiregional evolution hypothesis asserts that modern humans are the present manifestation of older species of hominids including Homo neanderthalensis and H. erectus. The replacement hypothesis, however, states that modern humans are a new species and that the older species mentioned above were replaced.

In the latter hypothesis, transition of archaic H. sapiens to modern doesn’t occur anywhere in the world except Africa at around 200,000 years ago. Anatomically modern humans then dispersed outward to other regions, replacing other hominid species by out-competing them for resources or by displacing them from environments optimal for their continued survival.
There is, however, a very persistent group of paleoanthropologists who adhere to the multiregional evolution argument, which doesn’t, by the way, imply that there was parallel evolution or multiple origins of modern humans. This theory suggest that genetic exchange explains how differentiation, geographic variation, and evolutionary change within humans occurred.

The arguments have gone back and forth between the two camps for many years, but new research is supporting the multiregional evolution hypothesis. In a recent article by National Geographic , “Neandertals, Modern Humans Interbred, Bone Study Suggests”, Erik Trinkaus, an anthropologist at Washington University in St. Louis, Missouri. comments on a fossil remains found at Petera Muierii (“Cave of the Old Woman”) in Romania, which date to about 30,000 years ago.

While the remains are largely typical of modern humans, they also show some distinctly Neandertal traits, says Trinkaus. [...] These telltale skeletal features include the shape of the lower jaw and the back of the skull.

Unfortunately, the National Geographic article doesn’t go into a great amount of detail regarding the cranial and post-cranial morphology of the remains found in Romania, but classic Neanderthal features include a distinct brow ridge, lack of a chin, and occipital bun and their cranial capacities were significantly larger than that of modern humans. Trinkaus does say in the article:

“The only way I can explain the anatomy of these fossils and the fossils from a number of other sites across Europe is that there was a fair amount of interbreeding.”

According to National Geographic, the research is reported in the Proceedings of the National Academy of Sciences , though, I’ve not been able to locate a citation yet to the research article itself. I’m sure this won’t settle the Multiregional vs. Replacement debate, but it certainly is thought provoking.

Hat tips go to Abnormal Interests who set me to looking for the PNAS article and clicking on the National Geographic article with a post of his own on the subject and another to a friend that emailed the PNAS article to me this morning: thanks!

I hope if you read this far in this four part series, that you enjoyed reading about one of the most enigmatic New World monkeys. Below is the list of works cited in the previous three parts, but I’m also going to include a few sources that are Internet accessible for those without quick access to the books and journal articles.

Internet Sources

Google Image Results for “howler monkey”

Wikipedia Entry for howler monkey. This link includes some images including the one used to show schizodactyly.

Honolulu Zoo Fact Sheet

The Loudest Animal In the World, an article by Terry Dunn hosted by the Smithsonian National Zoological Park website.

Cited References

Carpenter, C. R. (1934). A Field Study of the Behavior and Social Relations of Howling Monkeys. New York: AMS Press.

Fleagle, J. G. (1999). Primate Adaptation and Evolution, 2nd Ed.. San Diego, CA: Academic Press.

Gilbert, K. A., & Stouffer, P. C. (1989). Use of a ground water source by mantled howler monkeys (Alouatta palliata). Biotropica, 21(4), 380.

Kinzey, W. G. (1997). New World Primates: Ecology, Evolution, and Behavior. New York: Aldine De Gruyter.

Kitchen, D. M. (2004, 19/03). Alpha male black howler monkey responses to loud calls: Effect of numeric odds, male companion behavior and reproductive investment. Animal Behavior, 67, 125-139.

Milton, K. (1980). The Foraging Strategy of Howler Monkeys: A Study in Primate Economics. New York: Columbia University Press.

Pinto. Liliam P., & Setz, E. Z. (2004, December). Diet of Alouatta belzebul discolor in an Amazonian rain forest of Northern Mato Grosso State, Brazil. International Journal of Primatology, 25(6), 1197-1211.

Regan, B. C., Julliot, C., Simmen, B., Viénot, F., Charles-Dominique, P., & Mollon, J. (1998, November). Frugivory and colour vision in Alouatta seniculus, a trichromatic platyrrhine monkey. Vision Research, 38(21), 3321-3327.

Richard-Hansen, C., Vié, J.-C., & de Thoisy, B. (2000). Trnaslocation of red howler monkeys (Alouatta seniculus) in French Guiana. Biological Conservation, 93, 247-253.