Monday, November 11, 2013

Was the Swamp Ape Bipedal?

by Marcel F. Williams 

Tuscany is renowned for its beautiful cities of Florence and Siena, and is  historically famous as the birthplace of the Italian Renaissance. But amongst the paleontological community, Tuscany is also known as the birthplace of an  extinct Late  Miocene ape-- that some paleontologist controversially believe may have been the earliest primate to walk predominantly on just two legs-- and possibly the earliest bipedal ancestor of humankind.

Oreopithecus bambolii first emerged on an ancient island bioprovince known as Tuscany-Sardinia (Tusco-Sardinia) sometime after 9 million years ago where it existed as the sole primate on the island until approximately  7 million years ago. Tuscany-Sardinia was  isolated from the rest of the Italian peninsula  and from  the rest of  continental Europe by the marine waters of the Late Miocene Mediterranean.
Skull of Oreopithecus bambolii
Between 11 to 9 million years ago, sea levels fell during a glacial period caused by the  deposition of  ice and snow on polar land masses. The lower sea levels allowed various mammals from  North Africa and Southern Europe  to enter the Tuscany region.   Small mammals from Europe apparently entered the isolated island region through rafting or swimming. But fauna from North Africa appears to have entered the region via ephemeral land bridges.

The mostly likely ancestor of Oreopithecus was a small African ape know as Mabokopithecus which  appears in the fossil record in Africa about 15 million years ago.  Oreopithecus and Mabokopithecus were both folivores (planet eaters) that shared a unique dental attribute in their upper molars: a well-defined hypocone-metaconule crest on the upper molars--  a unique characteristic that has never been found in any other monkey or ape  living or extinct.

Because  its fossil remains are strongly associated with the wetland freshwater environments that existed on Tuscany-Sardinia at that time, Oreopithecus  is frequently referred to as the 'swamp ape'. Dryer areas did exist on the island, but Oreopithecus was rare in those deposits while being abundantly represented in the swampy wetland coastal environments on the island.

It is interesting that the African oreopithecine ancestor, Mabokopithecus, existed in an ecological niche largely restricted to riparian woodland areas. This is a niche similar to that of the extant folivorous primate Colobus guereza (the Colobus monkey).  Although the Colobus monkey is  highly arboreal, it is known to come down from the trees in order to feed on aquatic plants in nearby swamps.

Oreopithecus bambolii has long  been at the center of controversy principally because of its remarkable cranio-dental and post cranial  similarity to African hominins (human ancestors) which was first fully noted by Johannes Hurzeler as far back as the 1950s.   Further adding to the controversy is  the argument that Oreopithecus may have also been the earliest obligatory bipedal primate and the first ape to walk exclusively on just two legs. 

Oreopithecine remains display a significant  number of post cranial characteristics that could be associated with either arboreal or  bipedal locomotion. However, there is one post cranial characteristic that is clearly related to bipedality and that's lumbar lordosis, a curvature of the spine that is unique to the hominins (humans and their bipedal ancestors).   However, a recent paper by Russo and Shapiro has question the existence of lumbar lordosis in Oreopithecus, arguing that  the supposed features  may be simply  be an artifact of the skeleton's distortion caused by  its compression during fossilization. Russo and Shapiro  also argue that the arboreal three toed sloth (Bradypus) would be a better convergent model for the skeletal anatomy and  locomotive behavior of the extinct oreopithecines rather than the bipedal hominins.

Three-toed sloth (Bradypus)

While slow climbing suspensory behavior has long been argued as an explanation for some of the anatomical attributes of Oreopithecus, such locomotive behavior appears to be contradicted by the exceptionally robust metatarsals of the oreopithecine foot along with the proportions of the foot's entocuneiform which was proximally-distally short and dorso-ventrally high. The length-height index of the oreopithecine  entocuneiform related to the mass placed on the hind limbs and is most similar to that of the gorilla. The gorilla's low entocuneiform length-height index is related to the large amount of mass placed on the hind limbs due to its large body size. Oreopithecus, however, was a very small ape, with males typically weighing about 32 kilograms and females approximately half that size. The average Gorilla male weighs 175 kg with average female gorillas weighing about 85 kilograms.    So in order to explain, the gorilla-like entocuneiform index, in Oreopithecus, the swamp ape must have been carrying its entire body weight on just its hind limbs.   Kohler and Moya- Sola also noted that the  power armload arm ratio strongly suggest that Oreopithecus carried its entire body weight on its hind limbs.

There's also strong evidence in the oreopithecine feet of a significantly reduced arboreal ability. The Oreopithecus foot had robust metatarsals plus a non helical ankle joint, characteristics typically associated with terrestrial catarrhines. Kohler and Moya-Sola have also noted that the mobility and grasping ability of the oreopithecine foot had been appreciably reduced relative to arboreal primates and even more so than in terrestrial baboons.

It would also be difficult to understand why Oreopithecus would expend the energy and the risk of  being a highly arboreal tree living primate on an island where there were no terrestrial predators. But even on the ground, why would  Oreopithecus abandon terrestrial quadrupedalism for bipedalism? The answer may come from its food source.

Chimpanzee wading bipedally with a stick

Orangutan wading bipedally

Gorilla wading bipedally

The coastal wetlands that Oreopithecus preferred were rich in aquatic plants. Harrison and Rook   have suggested that Oreopithecus may have specialized in feeding  on aquatic plants which were abundant in the wetland coastal areas of the island such as: sedges, water lilies, reeds, cattail, pond- weeds, horestails, and stoneworts which were abundantly represented in the fossil pollen spectrum.

Extant primates that feed on aquatic plants, usually wade bipedally in the shallow waters to access the food resource. Bipedal wading in primates has been observed in: baboons, macaques, the gorilla, orangutan, and in the chimpanzee. Such aquatic bipedalism in order to access aquatic plants  comprises as much as 27% of the feeding behavior of the Western Gorilla.

Additionally,  freshwater mollusk and turtles were also abundant in the wetland areas of Tuscany-Sardinia island-- along with predatory crocodiles. Turtle and crocodile eggs may have served as a good source of protein for Oreopithecus.

Marine biologist, Alister Hardy, hypothesized that the power precision grip in humans originally evolved as an adaptation for picking up benthic invertebrates. Wading bipedally in shallow water for food resources such as shellfish and aquatic plants is, of course, common behavior in many hunter-gatherer human populations. But such behavior has also been observed in non-human primates such as baboons, macaques,  guenons, and capuchin monkeys.

Curiously, Oreopithecus also had a hominin-like power precision grip. Such manual dexterity could have evolved in Oreopithecus as a feeding adaptation for picking up   the shelled invertebrates that existed in the wetland areas of Tuscany-Sardinia while it was also feeding on aquatic plants.

As the sole primate on the ancient island of Tuscany-Sardinia for nearly two million years, it seems unlikely that Oreopithecus would have avoided the exploitation of freshwater aquatic food resources   that were so rich in carbohydrates and proteins

Sea levels in the Mediterranean began to fall sometime after 7.4 million years ago and the island's isolation from Europe and Africa appears to have ended sometime between 6.9 to 7.2 million years ago. By 6.1 million years ago, global sea levels fell to such an extent that the Mediterranean Sea became completely isolated from in the inflow of marine waters from the Atlantic Ocean. During this period of lowering sea levels, land bridges were created between Europe and North Africa.

 The  earliest African hominin,  Sahelanthropus, appeared in the fossil record in North Africa sometime between 6.8 and 7.2 million years ago. While not much is known about the postcranial remains of Sahelanthropus, its craniodental morphology is remarkably similar to that of Oreopithecus bambolii.

Marcel F. Williams


Cranio-dental evidence of a hominin-like hyper-masticatory apparatus in Oreopithecus bambolii . Was the swamp ape a human ancestor?
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Francesca Mansfield said...

Fascinating! So our aquatic ancestor may have evolved in Europe after all? And then returned to Africa? Would this also explain the missing baboon marker?

Marcel F. Williams said...

Thanks for your comments!

The earliest hominins appear to have radiated into Africa from Southern Europe at the beginning of the Messinian (just before 7 million years ago).

The baboon C retrovirus that heavily infected all African primates, except for Homo, didn't occur until after the baboon and gelada diverged from each other which was sometime after 5 million years ago. The retrovirus also had to occur before the emergence of Homo (2.6 million years ago).

But the australopithecines should have been fully exposed to the baboon retrovirus sometime between that time range.

I argue that the ancestors of Homo were geographically isolated from the rest of Africa during the Pliocene, probably on an island in the Northern Afar region which was flooded by marine waters during the early Pliocene.

But this period of geographic isolation would have ended when sea levels began to lower dramatically at the beginning of the Pleistocene (~2.6 million years ago).


Marcel F. Williams said...

Did human ape ancestors go through a semiaquatic phase or phases in their evolution sometime during the last 10 million years?

Cast your vote at:

DDeden said...

The presence of (high protein) Hydrocharis today in Tuscan marshes plausibly indicates the main aquatic food of Oreo., as it is for the Congo lowland gorilla, who rake it with their fingers while partly submerged (~97% Hydrocharis, ~3% sedges).
History and traditions
As weIl as the richness of its landscape and nature, the Marshes have maintained the fascination of the historical events related to the great Medici and Lorena families. Here still remain important testimonies of the work of man, which over the centuries have shaped and changed the very structure of the wetland: the canals and port systems, signs of ancient and important waterways; the Medicean Bridge at Cappiano, the centre for controlling the water regime and fishing activities, as well as an important stop along the Via Francigena; the Capannone Farm complex, which was one of the main berthings of the Valdinievole; the buildings of industrial archaeology like the tobacco dryhouses.
The commemorative plaques so often found on the cabins or along the banks tell a more recent story: the tragedy of the barbaric massacre committed by the Germans on 23rd August, 1944.
A few skilful craftsmen still carry on residual activities related to the marsh grasses in the marshes: gathering and weaving "sarello" (tufted sedge) and "sala" reed-mace (False bulrush) (to wicker seats and cover wine flasks), "Gaggia" (False Indigo) and other typical wetland plants.

Situated on the boundary between the Mediterranean and Continental climates of the Peninsular, the Marshes simultaneously shelter plants adapted to different climates; for example in the Ramone Marshlet, on the edges of the Chiusi Woods, still survive the Frogbit (Hydrocharis morsus-ranae) and the Royal Fern (Osmunda regalis), both plants from a warm wet climate, alongside certain mosses (Sphagnum sp.), more adapted to cold climates of the north and which descended as far as the Marshes during the last Ice Age. Only in the Marshlet, and in a few other areas of the Marsh basin, can still be found fair extensions of the Tufted Sedge (Carex elata), locally called "sarello"; this plant of northern origin develops in bushy formations of more than one individual.
Where the immense reed thickets leave space to the free waters, are the "laminas" formed of plants with floating leaves (e.g. the large White and Yellow Water-lilies) which offer one of the last refuges for several highly specialised species: the Southern Bladderwort (Utricularia australis), a floating carnivorous plant, the Fringed Water-lily (Nymphoides peltata), with its beautiful yellow flowers, and the strange, tiny floating fern Salvinia natans, now extremely rare in Tuscany.

Marcel F. Williams said...

Very interesting comments DDeden. And thanks for the link!


Anonymous said...

Most Mio-Pliocene hominoids were typically orthograde (ie, with vertical spine), wading/climbing/floating in swamp & litoral forests (google "aquarboreal", word coined by Marcel), surface-feeding on AHV & HSI: aquatic herbaceous vegetation (eg, Hydrocharis, Cyperus) & hard-shelled invertebrates, as well as waterside & presumably arboreal foods. Oreopithecus is just one of these, with insular adaptations, no direct ancestor of chimps or humans: AAT (better terms are "littoral theory" or "coastal dispersal model", google "econiche Homo") is about Plio-Pleistocene erectus-like archaic Homo populations trekking along coasts as far as Flores island, the Cape & Pakefield in England (where they dived for shellfish etc.), and from the coasts inland along rivers, probably at first seasonally (eg, follwing salmon etc.), later also permanently.
Fossil data on human relatives ("emergence of Homo") should not be confused with biochemical data on human ancestors ("baboon retrovirus"): Pan & Homo split c 5 Ma, possibly in coastal forests (Zambesi mouth?), presumably our Pliocene ancestors first followed the Indian Ocean to Sunda (explaining the retroviral data).
Human Evolution publishes in 2 special editions the proceedings of the symposium with David Attenborough on human waterside evolution "Human Evolution: Past, Present & Future" in London 8-10 May 2013:
- Peter Rhys-Evans: Introduction
- Stephen Oppenheimer: Human's Association with Water Bodies: the 'Exaggerated Diving Reflex' and its Relationship with the Evolutionary Allometry of Human Pelvic and Brain Sizes
- JH Langdon: Human Ecological Breadth: Why Neither Savanna nor Aquatic Hypotheses can Hold Water
- Stephen Munro: Endurance Running versus Underwater Foraging: an Anatomical and Palaeoecological Perspective
- Algis Kuliukas: Wading Hypotheses of the Origin of Human Bipedalism
- Marc Verhaegen: The Aquatic Ape Evolves: Common Misconceptions and Unproven Assumptions about the So-Called Aquatic Ape Hypothesis
- CL Broadhurst & Michael Crawford: The Epigenetic Emergence of Culture at the Coastline: Interaction of Genes, Nutrition, Environment and Demography
SPECIAL EDITION PART 2 (begin 2014) with 12 contributions.
--marc verhaegen, google "Greg Laden blog Verhaegen"

Ceren Peker said...

Bravo a tutti! :D
Thanks for very important informations..
Tuscany is always a place of main source of artistic and humanistic nutrition.

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