Fossil apes
The hominoids--the group including humans and living and fossil apes--originated sometime during the Oligocene period, between 34 and 24 million years ago. But it was during the Early Miocene that ancient hominoids began the impressive differentiation that created many diverse ape lineages that came to inhabit most of the tropical and subtropical Old World. During most of the Miocene, climatic fluctuations appear to have been much less marked than during the subsequent Pliocene and Pleistocene. Tropical and subtropical forests covered large parts of the Old World. The East African Rift Valley and the mountains of South Asia, including the great Himalayas, had only begun to form, so that the climatic patterns of today, dominated by strong dry and monsoonal wet seasons, had not yet emerged. Early apes adapted to exploit the large forested environment, becoming established in Africa, across South and East Asia, and in large parts of Europe and West Asia.
Although fossils representing many Miocene ape lineages have been found, paleontologists do not have a clear idea of their relationship to the living species of hominoids. The common ancestors of orangutans, chimpanzees, gorillas, and humans all existed during the later parts of the Miocene, between 15 million and 6 million years ago. Thus, the earliest hominoid fossils, which date from earlier than 25 million years ago, lived long before the divergences of the living great apes. Some of these ancient apes may be our ancestors, but most of the great hominoid diversity of the Early Miocene ultimately became extinct.
Our own lineage, the hominids, arose during the latest part of the Miocene in Africa. In some senses, fossil apes are a sidebar to the story of our own evolution. Paleontologists do not know which, if any, of the fossil apes of the Miocene may have given rise to the hominids, but the impressive diversity of fossil apes has yielded insight into the evolutionary pathways taken by our ancestors. Most important, the Miocene apes show us the primitive conditions of many of the skeletal features that were later to undergo great changes during human evolution.
Fossils from the Oligocene that may be hominoids are rare. The most notable, Aegyptopithecus, may represent the ancestral catarrhines that later gave rise to both hominoids and Old World monkeys. But by the early Miocene, a great diversity of apes had arisen with a range of body sizes and dietary adaptations. Fossil genera such as Proconsul, for example had monkey-like locomotor adaptations and ape-like jaws and teeth. Others, like Morotopithecus, may show the development of the suspensory locomotor pattern of later great apes, while retaining dental anatomy somewhat distinct from the later apes.
Great ape fossils and relatives
By 13 million years ago, a series of fossil apes from Europe and Asia show clear signs that they belong to the group including living great apes and humans. Some of these apes had a full adaptation to suspensory locomotion of the form found in living chimpanzees and orangutans. Others--especially the larger apes--may have had a mixture of suspensory and quadrupedal adaptations. All these apes appear to have matured relatively slowly, like the living apes, and may have had brains essentially the same relative size as chimpanzees (Begun, 2003). Thus it is likely that these fossil apes represent the origin of the great ape adaptive pattern.
Shortly after the first of these apes arose, the early great apes divided into two lineages. One of these invaded South Asia, and ultimately its descendants colonized the tropics of China, Southeast Asia,and Indonesia. The other lineage spread across Europe and diversified quickly into several species of a single genus, Dryopithecus, and its larger descendant, Ouranopithecus. These European apes share many features with the living chimpanzees and gorillas, which may indicate that they are the closest fossil relatives of the living African apes and humans.
Asia has produced a great quantity of great ape fossils from the Miocene up through the Pleistocene. Ultimately, these apes were a distinct clade from those found in Europe and Africa, and they had no close relationship to the hominids. The most recent members of this clade are the living and fossil orangutans, of the genus Pongo. Today, orangutans survive as remnant populations only on the islands of Sumatra and Borneo, though fossil Pongo is found as far north as China. From China in the east to Turkey in the west, the fossil apes of Asia were a large and diverse group.
The common ancestors of humans, chimpanzees, and gorillas belong to a clade separate from the Asian fossil apes. The earliest representative of this clade is probably Dryopithecus, which itself is likely to have been very similar to the common ancestor of both clades. Dryopithecus and later European genera, called dryopithecines, belong to an adaptive radiation that resulted in a substantial diversity in body size and possibly in locomotor patterns. This radiation almost entirely known from European sites, since African fossil apes have not yet been found from the important time span from 10 million years ago to 7 million years ago, during which the African apes and hominids diverged. Nevertheless, the known dryopithecines present evidence of the anatomy of close relatives to later hominids, much closer in time to the beginnings of human evolution than are living species. It is likely that when African great ape fossils from this time period are discovered they will share many features with the European ape radiation. Thus, the anatomy of these ancient apes may partially represent the starting point from which human evolution began.
Fossil ape genera
Aegyptopithecus (likely ancestral catarrhine)
Aegyptopithecus :: overview
The largest sample of early catarrhines come from the Fayum depression in present-day Egypt. Today this region is arid desert, but during the Oligocene around 34 million years ago, it was a swampy forest with a great density of ancient primates. Aegyptopithecus zeuxis was a small primate, around 6 kg, with essentially apelike teeth, including broad flat incisors, low molars with somewhat bulbous cusps, and sexually dimorphic canines. These dental features are more similar to living apes than to Old World monkeys, but because the distinctive shearing molars of cercopithecoids evolved later, Aegyptopithecus probably represents the ancestral condition for all catarrhines. Unlike living apes, the molar teeth had a broad extra ridge, called a cingulum, surrounding the main cusps, which increased the grinding area of the teeth.
The postcranial skeleton of Aegyptopithecus was basically monkey-like, with short, non-suspensory forelimbs and a tail. The skull had many features found in later hominoids, including strong temporalis muscle attachments, forming a low sagittal crest in most individuals. The two living catarrhine superfamilies, the hominoids and the cercopithecoides, may have diverged before Aegyptopithecus existed or after. Since Aegyptopithecus shows no derived similarities to either group, it may be very similar to the primitive catarrhine lineage that gave rise to both living groups, even if it represents an early hominoid or cercopithecoid.
Ankarapithecus :: overview
Ankarapithecus meteai remains include a handful of mandibles and partial faces from Central Turkey, and date to around 10 million years ago (Begun and Gulic, 1998). These remains show many similarities to Sivapithecus from South Asia, and have sometimes been included in that genus. However, Ankarapithecus lacks a number of features that link Sivapithecus with living and fossil orangutans, causing some paleontologists to suggest that it may represent the earliest radiation of Asian apes. Such a position would explain the retention of many primitive similarities with European apes like Dryopithecus, and would mean that the Anatolian population survived as a relict of the early Asian radiation even as the subsequent radiation of Sivapithecus into the later Asian apes occurred in South Asia.More on Chororapithecus
Ann Gibbons reports on the 10-million-year-old gorilla-like Chororapithecus, elaborating on the biogeographic interpretation I mentioned yesterday:
Gorilla or not, several experts agree that an ape of this antiquity in Africa strikes a blow at a hypothesis that the common ancestor of African apes arose in Eurasia and migrated to Africa. "These are very important fossils," says Alan Walker, a paleoanthropologist at Pennsylvania State University in State College. "They show that apes have always been in Africa--that they didn't come from Europe and Asia."
Paleoanthropologists have known for decades that apes (Hominoidea) arose in Africa, where researchers have found diverse apes from 22 million to 12 million years ago. But despite many searches, almost no ape fossils have been found in Africa between 12 million and 7 million years ago, with the notable exception of a 9.5-million-year-old upper jaw from Kenya. Some researchers inferred that apes went extinct in Africa while other apes flourishing in Eurasia gave rise to the ancestors of modern African apes.
This is an important issue. I was reading a book chapter the other day that concluded that the origin of nearly every higher-level primate group may have involved rafting; in that account catarrhines originated by rafting from Eurasia to Africa, dryopithecines from Africa to Eurasia, and possibly the African ape-hominid clade by rafting or walking back to Africa. These peregrinations been a feature of hominoid evolutionary hypotheses for the last 15 years or more. Possibly it is all an illusion -- only reflecting the rarity of Late Miocene fossil apes from Africa and their abundance in Europe.
Still, the dryopithecines really do look like plausible ancestors for later apes in many ways. More on that later.
References:
Gibbons A. 2007. Fossil teeth from Ethiopia support early, African origin for apes. Science 317:1016-1017. doi:10.1126/science.317.5841.1016a
Did Gen Suwa just save paleoanthropology?
That depends on whether these teeth are really from a gorilla, I suppose.
Chororapithecus abyssinicus teeth compared to gorilla mandible. Photo credit: Gen Suwa/University of Tokyo.
Oh yeah, sure, "saved paleoanthropology" is overdramatic. But what am I supposed to write? Over four years, we have had a series of genomic comparisons narrowing down the age of the human-chimp common ancestor to something like 2/3 the age of Sahelanthropus. I said it was a crisis, and it is: these data sources must agree. Either we have to cast out a bunch of hominids, or we have to wrench the genes by around a factor of two.
Now, Suwa and colleagues show up with a 10-million-year-old gorilla. A 10-million-year-old gorilla works just fine with 7-million-year-old hominids. It doesn't work at all with a 7-million-year-old human-gorilla common ancestor. So there's no doubt about the centrality of this particular ancient gorilla -- if it is one.
So far, all the articles I've seen have someone on the record expressing some reluctance to accept the teeth belonged to the gorilla lineage. Reuters has Peter Andrews; Nature has Jay Kelley; National Geographic has Richard Potts.
Should we be skeptical? Well, there are lots of convergences among Miocene apes. Many of the dental convergences are detailed in our paper about Sahelanthropus, available open-access from PaleoAnthropology. These convergences make it difficult to identify hominids based on the teeth alone. They also make it hard to say that any particular big-toothed, leaf-eating ape is definitely a gorilla. After all, if it eats like a gorilla, why shouldn't it have teeth like a gorilla?
Suwa and colleagues go to some pains to demonstrate that the dental similarities with gorillas are more than enamel-deep. Their strongest argument is that the tooth morphology exhibits a derived gorilla-like condition well below the surface, at the enamel-dentine junction. That is, while the tooth was forming, the initial growth surface took on a distinctive shape which was then reflected by the form that the growing enamel took.
The most distinctive features of the Chororapithecus dentition are the derived shearing structures seen in portions of its molars (Fig. 2), despite a generally low cuspal topography (the latter is apparently a primitive retention).
Examination of internal morphology by micro-computed tomography (micro-CT) demonstrates that these occlusal features were underlain by distinct enamel-dentine junction (EDJ) structure (Fig. 2). In particular, the straight to weakly concave mesial protocone crest seen in the EDJ of CHO-BT 4, -BT 5 and -BT 6 is gorilla-like, and is formed by a mesiobucally located junction of the mesial protocone crest and mesial marginal ridge. Such spatial placements are best considered to be regulated by enamel-knot-related signalling patterns during early morphogenesis [23, 24], and may be one of the underlying causes of the mesiodistally elongate upper molar shape generally characteristic of folivorous primate species. In the lower molars, the most distinctive EDJ topography occurs at the trigonid crest, the structural counterpart that occludes with the upper molar mesial protocone crest. The high trigonid EDJ crest is continuous between the metaconid and protoconid cusp tips (Fig. 2). Because recent experimental and quantitative genetic studies suggest significant degrees of morphogenetic independence between corresponding upper and lower molar structures [25, 26], the presence of a functionally integral inter-jaw pattern of morphological expression, as seen in the Chororapithecus molars, suggests adaptation by natural selection, as opposed to chance emergence of neutral morphological minutia.
Still, "minutia" is a loaded term. Why shouldn't an ape that evolves the same shear characteristics as a gorilla molar use the same developmental process to achieve them? The more that development of the teeth are constrained by these genes, the more likely it is that different lineages will evolve in parallel.
Nor is it entirely obvious that Chororapithecus is actually gorilla-like in these characters. The paper compares two ratios involving cusp dimensions measured internally beneath the enamel cap. That's high-tech, but the ratios do not sort out gorillas from chimpanzees, don't sort Chororapithecus from either of those apes or early hominids, and -- even worse -- it's not even clear how these ratios may vary with size. Does Chororapithecus look sort-of like a gorilla on these ratios because it's a sort-of gorilla? Or because it's big? The enamel is relatively thicker than gorillas, like other Miocene apes and orangutans. Clearly the specimen is much less derived than gorillas, but could that be because it isn't a gorilla?
Well, there's the problem: there's not too much to go on with these teeth. I think Suwa et al. laid out as good a case as there is. A 10-million-year-old gorilla can't be expected to look just like gorillas today. It's not like the teeth look more like something else besides a gorilla. Gorillas really are far more derived in these dental characters than the Chororapithecus dentition, which makes the comparison more difficult. And so, the conclusion of the paper is equivocal:
The similarities seen between the two genera raise the possibility that Chororapithecus is a Miocene member of the Gorilla clade. Alternatively, with its combination of thick enamel and distinct molar cresting pattern, Chororapithecus may represent a unique adaptation that is convergent with gorillas in molar structure and function. Although the evidence for phylogenetic affinity between Chororapithecus and Gorilla is inconclusive, it may be that the basal members of the gorilla clade shared large tooth size and incipiently enhanced molar shear as a part of an herbivorous diet that accompanied (presumed) larger body size. Chororapithecus may then represent one example of adaptational (and perhaps phyletic) differentiation within that clade.
I don't know about anybody else, but I don't think this helps us with our little problem very much. Here's what I think: the problem is not so much the 10-million-year-old gorilla, as it is the 17-million-year-old orangutan that it necessitates. Here's the very next paragraph of the paper:
Acceptance of Chororapithecus as a basal member of the gorilla clade would push back the gorilla species split to >10.5 Myr ago. Because this is a minimum date established from a meagre fossil record, the actual divergence would have predated this by an unknown time gap. From the currently available evidence, we consider that a species split of 20 Myr ago for Pongo, 12 Myr ago for Gorilla, and 9 Myr ago for Pan are all probable estimates (see Supplementary Information). We consider that the early divergence hypothesis is congruent with both fossil and molecular data, and should be further evaluated using both sides of the evidence.
I think those dates don't really need to be so old. A 10.5-million-year gorilla divergence could easily correspond to a 17-million-year orangutan divergence. Still, for those of us who have gotten used to the idea that Dryopithecus might have something to do with the origin of African apes, this idea might seem a little troubling. So, let's look at the part of the Supporting Information that, well, supports their assertion that all these dates are "congruent":
The above summarized molecular predictions are in concert with the notion that the Pongo lineage existed in Africa prior hominoid migration to the Eurasian continent, the earliest such opportunity for dispersal (barring significant rafting) being at circa 17 Ma (44). If in fact the Gorilla split was 12 Ma, then the OWM split estimate (33.6-43 Ma) largely predates the earliest known definitive occurrence of catarrhines (Propliopithecus and Aegyptopithecus) (45), and many would consider this to be somewhat outside an acceptable boundary condition. However, it may be indicative of variable molecular rates of evolution across lineages (46, 47), with higher mutation rates in the OWMs (48) (and early hominoids) because of their shorter generation lengths (48, 49) and/or higher metabolic rate in relation to smaller body mass (50).
Well, that's a tricky bit of argument. We might believe that African apes never left Africa and that all the dryopithecines are therefore on the orangutan line. At least, that makes some biogeographic sense. But it's hard to argue that any of these dates are "congruent" with genetic evidence as we currently understand it. Many of the recent methods don't make any prior assumptions about "calibrated" divergence times like the orangutan-human divergence. Worse, Hobolth et al. (2007) found a human-chimp speciation time of 4 million years even considering an orangutan-human divergence of 18 million years.
The "shorter generation lengths" explanation doesn't help much -- after all, if we infer that the current great ape lineages existed as early as 20 million years ago, then almost all of the divergence time is occupied by long-generation-length species. Much faster evolution in Old World monkeys should show a strong signal of acceleration in that lineage (with a higher number of derived substitutions), and we don't see it.
If we believe these interpretations of the genes, a 10-million-year-old gorilla did not exist. Chororapithecus was something else.
If we believe that Chororapithecus was a gorilla, then these genetic interpretations are simply wrong. And Dryopithecus was on the orangutan lineage. And hominoids diverged from Old World monkeys in the Eocene.
And Sahelanthropus could have been a hominid.
References:
Suwa G, Kono RT, Katoh S, Asfaw B, Beyene Y. 2007. A new species of great ape from the late Miocene epoch in Ethiopia. Nature 448:921-924. doi:10.1038/nature06113
Hobolth A, Christensen OF, Mailund T, Schierup MH. 2007. Genomic Relationships and Speciation Times of Human, Chimpanzee, and Gorilla Inferred from a Coalescent Hidden Markov Model. PLoS Genet 3(2): e7. doi:10.1371/journal.pgen.0030007
Dryopithecus::overview
Today, the only non-human primate native to Europe is the Barbary macaque, which has extended its North African range to a small area including Gibraltar, on the southern coast of Iberia. The geographic ranges of living apes do not extend north of the tropics. Thus, it may be surprising that once Europe was the home to a considerable diversity of apes. With the warmer and wetter climate of the Miocene, Europe was an ideal habitat for early hominoids, and they extended across the continent from Spain to Turkey, as far north as Paris. What may be even more surprising than the great productivity of Europe for paleontologists seeking Miocene apes is that Europe possibly was the principal center of their evolution and home of the common ancestors of humans, chimpanzees, and gorillas.
For the background to human evolution, the most important European fossil ape is Dryopithecus. The original European ape, Dryopithecus fontani was discovered in France in the 1850Õs. Among the first evidence for ancient primate evolution, these fossil remains have been joined in recent years by newer fossils excavated from Spain, Hungary, and as far east as the Caucasus. These newer sites have extended the sample of Dryopithecus to include relatively complete crania and a diversity of postcranial elements. All remains date to between 13 million and 10 million years ago, likely after the common ancestor of the Asian and African ape clades. The features of the cranial material of Dryopithecus are generally more similar to living African apes than to orangutans (Kordos and Begun, 2001), although fossil Sivapithecus and Dryopithecus are very similar to each other.
The initial dental discoveries of Dryopithecus identified it as a fossil ape on the basis of the pattern of cusps and grooves on its molar teeth, which is similar to the great apes and humans. With grooves between the cusps arranged in the form of a Y, this pattern is often called the Y-5 dental pattern. In addition to the phylogenetic significance of the molars, their form probably indicates that the basic dietary niche of more recent apes arose at their origin and initial radiation.
Other features link Dryopithecus to the living apes. The elbow joint was capable of a full range of extension, which is not possible in quadrupeds like monkeys. The face was downward-directed like living chimpanzees and gorillas, called klinorhynch, unlike orangutans and Sivapithecus (Begun, 2003). The tear ducts opened substantially anteriorly, with a relatively wide interorbital pillar, again like African apes and unlike orangutans. These features were probably the ancestral condition for the great apes, with the Asian apes being derived, so they do not necessarily show that Dryopithecus was ancestral to African apes and humans. Nevertheless, they illustrate the presence of almost every component of the ape anatomy in these Late Miocene fossils, which set the stage for the later rise of the hominids.
The life and times of Gigantopithecus
Russ Ciochon has a very nice article about Gigantopithecus up on his department webpage. The article appeared in Natural History magazine in 1991. It features the history of Gigantopithecus discoveries, our current understanding of their anatomy, diet, and history, and Ciochon's own attempts to find fossil Gigantopithecus in Vietnam. It's a very nice review.
When I went looking for it, I was thinking about diet in Miocene apes. Gigantopithecus is generally described as a panda-like bamboo eater. Giant pandas have several specialized feeding adaptations to support their bamboo diet. The most famous of these is the expanded radial sesamoid bone, or "thumb," celebrated by Stephen Jay Gould as a unique evolutionary solution. The thumb is used to grip the bamboo stems so that the teeth can work through the indigestible fiber and woody portions of the bamboo stems into the softer shoots.
Some information on the dietary proportions of giant pandas is available from BBC News. The following is quoted from that site:
Ninety nine per cent of a panda's diet is made up of 30 species of bamboo. The remaining one per cent is made up of other plants and meat. Their digestion of bamboo is very inefficient; pandas only digest about 20 per cent of the dry matter of bamboo, whereas most herbivores assimilate about 80 per cent. This means that they must eat large amounts to obtain their energy requirements. They can eat between 12 and 38kg of bamboo shoots, leaves and stems per 24 hour period.
Giant pandas can maintain this dietary solution only by sustaining a high feeding rate. The digestibility of bamboo varies markedly across the year (Wei et al. 1999), and in the winter when new growth is rare or absent, there are very few nutrients available. Pandas do not have any significant digestion of the structural elements of cell walls or other fibers. They therefore must extract the proteins and simple carbohydrates from bamboo and pass the bulk as quickly as practicable. To this end, they have wide and flat molars and premolars compared to other bears. These are not teeth with high crowns and shearing surfaces. This makes them different from primates, like gorillas and colobus monkeys, that eat a high proportion of leaves and other vegetation. It seems that pandas are not really in the business of cutting fibrous bamboo into a pulp; but instead they crush the bamboo to extract as much of the cell contents as possible.
Gigantopithecus also had broad, flat molars and premolars. These teeth had relatively thick enamel. Enamel thickness is a tricky indicator of diet, because there are actually advantages to having enamel that wears through completely during life. If the goal is to maintain an effective shearing surface on the tooth for cutting fibrous plant material, then thin enamel exposes the softer dentin, which wears faster. The wear gradient between the two maintains a topography to the tooth surface that is a better shearing implement than a flat, thick-enameled tooth. So the thick molar enamel in Gigantopithecus would not be very useful for shearing bamboo leaves into an undifferentiated mush. But those teeth might have been used to crush bamboo to extract the cell contents while leaving the mass mostly intact.There are indications that Gigantopithecus differed from giant pandas in having a more varied diet. Ciochon describes looking for phytoliths on the teeth as evidence of diet. When the fossil teeth of Gigantopithecus were examined with scanning electron microscopy, dozens of phytoliths were found:
More than half of the phytoliths we observed were long and needlelike and could be attributed to the vegetative part of grasses, possibly bamboo. The rest were conical or hat shaped, attributable to the fruits and seeds of dicotyledons. Piperno tentatively identified them as fruits from a tree of the family Moraceae, quite possibly durian or jackfruit, both of which are common throughout tropical Southeast Asia. This proved that Gigantopithecus had a varied diet, although we still suspect that bamboo was its staple food.
This work is described in Ciochon et al. (1990) in PNAS, which includes scanning electron micrographs of the phytoliths.
Of course the relative quantities of phytoliths do not directly address dietary composition, since different plants have different phytolith abundances. Likewise, one might speculate that the phytoliths on fossil teeth represent foods eaten near the time of death -- a "last meal" effect. This might explain the apparent evidence for one kind of fruit in the Gigantopithecus data: the individual died at the time that fruit was in season. In any event, Ciochon and colleagues (1990) conclude it likely that Gigantopithecus had a very broad diet, that nonetheless included bamboo as a staple. In support of this, they cite an examination of tooth wear by Daegling and Grine (1989 in abstract; later published in 1994 in SAJS) that found Gigantopithecus microwear to be similar to chimpanzees. Chimpanzees themselves eat a majority of fruit, with smaller proportions of leaves, insects, and meat.
References:
Wei F, Feng Z, Wang Z, Zhou A and Hu J. 1999. Use of the nutrients in bamboo by the red panda (Ailurus fulgens). J Zool Lond 248:535-541.
Ciochon RL, Piperno DR and Thompson RG. 1990. Opal phytoliths found on the teeth of the extinct ape Gigantopithecus blacki: implications for paleodietary studies. Proc Natl Acad Sci U S A 87:8120-8124. JSTOR
Dean MC and Schrenk F. 2003. Enamel thickness and development in a third permanent molar of Gigantopithecus blacki. J Hum Evol 45:381-387.
Daegling DJ and Grine FE. 1994. Bamboo feeding, dental microwear, and diet of the Pleistocene ape Gigantopithecus blacki. S Afr J Sci 90:527-532.
Ungar P. 1998. Dental allometry, morphology and wear as evidence for diet in fossil primates. Evol Anthropol 6:205-217.
Gigantopithecus :: overview
Gigantopithecus blacki was, as its name implies, a gigantic ape from the Pleistocene of China. Its remains consist only of teeth and jaws, but these are of a tremendous size, with the largest specimens nearly twice the dimensions of male gorilla teeth and jaws. A similar, slightly smaller jaw is known from the Miocene of northern India, and has been called Gigantopithecus bilaspurensis (Simons and Ettel, 1970). Assuming that Gigantopithecus had the same proportion of tooth size and body mass as living apes, these Chinese remains suggest a body mass of over 400 kg for the largest individuals. The molars are relatively thicker than most living apes, and the overall body size may not quite have matched that of the jaws, but even so Gigantopithecus was the largest primate ever to exist.
With such a large body mass for a primate, Gigantopithecus must have spent most of its waking hours eating. It is likely that the giant ape depended on a steady diet of vegetative matter, and scientists speculate that bamboo made up the largest part of this diet. If so, Gigantopithecus may have a close analog in the living giant panda, which is not a primate but lives largely on bamboo today. The factors leading to the extinction of Gigantopithecus may be similar to those that threaten the panda, especially the fragmentation and loss of bamboo forest. Although Gigantopithecus and early humans may have coexisted for a period of time in China and Southeast Asia, there is no evidence that they interacted, or that humans led to the ape's extinction.
Lufengpithecus :: overview
Lufengpithecus lufengensis is a fossil ape from China, dating to the latest Miocene and Pliocene. A single mandible from the site of Longgupo argues that Lufengpithecus may have survived until as recently as a million years ago, possibly overlapping with both Gigantopithecus and ancient Pongo in the region (Crummett et al. 2000). Like Sivapithecus, Lufengpithecus has thick molar enamel and it also has relatively low canine teeth, especially in females. The lower third premolars sometimes have a slight second cusp, denoting a shift from their principal role as cutting teeth in other ape species.A related species from Thailand, Lufengpithecus chiangmuanensis, has recently been uncovered. This species is known only from teeth, but these appear to be intermediate in morphology between Sivapithecus and recent orangutans. At 10 million years old, the fossils may be ancestral to later Pongo (Chaimanee et al. 2003).
Morotopithecus :: overview
The site of Moroto, in Uganda, has produced a few ape fossils dating to around 20 million years ago, including a large palate and partial face. The palate is approximately the size of a female gorilla, and postcranial bones including vertebral and femoral portions estimate a mass of around 50 kg, about the size of the largest Proconsul species. The preserved lumbar vertebra indicates that the lower spine was short and relatively inflexible, as in living apes, and may indicate a much greater degree of vertical climbing ability than in Proconsul (Gebo et al. 1997). This vertebral evidence may represent the earliest locomotor adaptation that was fundamentally like living apes, and unlike the quadrupedal ancestral hominoids such as Proconsul.
Oreopithecus :: overview
Oreopithecus bambolii is known from a series of well-preserved fossils, including some relatively complete skeletons, from the north of Italy dated to between 7 and 9 million years ago. This date makes the fossils much later than Proconsul, Afropithecus, and other early hominoids, but its relationships may be closer to these ancient lineages than to other apes dating to the past ten million years. Oreopithecus fossils come from a region that was an island during the Late Miocene, so the population may have been isolated for some period of time during its evolution. The teeth of Oreopithecus make it morphologically unlike most other hominoids. The upper incisors are relatively large and rounded, but the lateral upper incisors are small, peg-like teeth. Both upper and lower molars are high-cusped teeth for shearing plant matter, with an extra cusp on the lower molars. The unique characteristics and primitive dentition make it difficult to determine the exact relationships of Oreopithecus with other fossil hominoids around its age, which are known almost exclusively from their teeth.What is most interesting about Oreopithecus is the extensive preservation of its postcrania. At around 30 kg, Oreopithecus shows evidence for below-branch suspensory locomotion, including a relatively short trunk and hindlimbs and long forelimbs. Joint mobility was high, and the elbow joint was like that of living apes (Fleagle, 1988). Together, these details tend to indicate an adaptation much like living apes, in a form slightly smaller than chimpanzees.
On the other hand, some details have prompted some scientists to suggest hominid-like resemblances for Oreopithecus. The pelvic bones may indicate a more vertical habitual posture for Oreopithecus than in other apes (Rook et al., 1999), perhaps indicating a greater use of bipedal posture for above-branch walking. Evidence from the hand and wrist may indicate greater manual dexterity than in living apes, another possible hominid resemblance (Moya-Sola, 1999). These resemblances may not indicate a close relationship, but they certainly point to the diversity of adaptations of the Miocene apes among the great number of different lineages that existed.
Ouranopithecus
Ouranopithecus macedoniensis (called by some Graecopithecus) is from the Late Miocene of Greece, around 8 million years old. Based on its facial and dental anatomy, Ouranopithecus is clearly a dryopithecine, but it is not clear if it may be particularly related to either humans or some living ape lineage. The morphology of the male skull appears similar to living gorillas, with a large and broad face, prominent supraorbital torus, and square-shaped orbits. These similarities may reflect nothing more than a relatively large body size, though a close relationship with gorillas is a possibility.
Some of the features of Ouranopithecus are similar to hominids. Most notably, like some other Late Miocene remains, the canines are relatively smaller in size than in many apes, especially in females. With fairly thick molar enamel and low cusps, the molar teeth are not gorilla-like, but instead are more similar to later hominids. Sexual dimorphism is substantial between the teeth, however, and males have large canines and shearing lower premolars.
Proconsul :: overview
Perhaps the largest sample of Miocene ape fossils, dated over the longest time period, is Proconsul. Extending from over 22 million years ago to around 10 million years ago across East Africa, the fossil record of this genus consists of over a thousand skeletal elements, representing much of its anatomy.
Unlike living apes, Proconsul was a quadruped, with several features reflecting this adaptation, including:
- forelimbs and hindlimbs of the same approximate length
- the lower part of the spine is long and flexible for quadrupedal movement
- the hands were used for palm-down walking as in living monkeys
Some scientists believe that Proconsul may have had a tail, based on the evidence for tendon attachments on the sacrum, although other scientists disagree and no tail bones have been found. There appear to have been at least three species of Proconsul, though the level of sexual dimorphism was high in each, making it difficult to separate within-species and between-species variation. The species varied in body size, ranging from a small form at 15 to 20 kg to a large form that approached 50 kg. The molar teeth of all species had thin enamel and low cusps, which may reflect a diet concentrating on fruits. As in Aegyptopithecus and other early catarrhines, the molars had an extensive cingulum.
It is possible that all later apes share a Proconsul-like ancestor, with the development of vertical body posture and suspensory locomotion that distinguish later hominoids. But it is not out of the question that the Proconsul lineage is a much more distant relative to living apes, perhaps even representing an extinct catarrhine superfamily separate from hominoids and cercopithecoids. The position of Proconsul in the hominoid phylogeny is potentially important because of its implications for the evolutionary relationships of later apes. If later apes evolved from a Proconsul-like form rather than a gibbon-like brachiator, for example, then their locomotor evolution may have followed a substantially different path.
On silk purses and pig's ears
This new paper by Jay Kelley (University of Illinois, Chicago) is about as close to a detective story that paleontologists get (via Palanthsci message board). Here's an excerpt from the introduction:
This paper concerns the regular misidentification for nearly 100 years of a number of non-primate upper canine teeth as belonging to the Miocene, Siwalik hominoid Sivapithecus. The same misidentification was repeatedly made by numerous paleontologists who collected in the Siwaliks, beginning with Guy Pilgrim. It went unrecognized by every hominoid expert who has either collected in the Siwaliks or analyzed the Siwalik hominoid collections, including me until recently (Kelley 2005:2).
The basic story is that the sample of Sivapithecus upper canine teeth has included many that actually belong to an extinct pig. The morphology of these canines is atypical for hominoid canines, but their identity as hominoid teeth has apparently not been questioned previously. Instead, analysts have suggested that the teeth represent evidence for taxonomic distinctions within the genus, such as a division into three species based on relative male canine size (Greenfield 1979), or a division into two temporal species based on a segregation of canine anatomy into earlier and later samples (Kelley 1986).
The article is a great description of comparative anatomy at work, and its taxonomic consequences. Here is part of the conclusion:
The most significant implication of removing the atypical canines from Sivapithecus is that there is no longer any clear morphological justification for recognizing S. indicus and S. sivalensis as time-successive species. Accepting the stated provenance of the two Chinji canines with a typical Sivapithecus morphology, GSI D. 238 and BMNH M34438, there are no discernable differences in hominoid upper-canine size or morphology between older and younger levels in the Siwaliks. While there are suggestions of other differences in the Sivapithecus samples from the Chinji and Dhok Pathan Formations, for example in tooth proportions (Kelley 1988), that might indicate the presence of different species, these have not been systematically assessed (Kelley 2005:8).
The other conclusion is that sexual dimorphism in Sivapithecus should be reassessed without the pig canines. According to Kelley, this is problematic because the upper canines of only a single female individual have been recovered, along with those of several males. Taking this single female as average, the level of canine dimorphism is consistent with orangutans or gorillas, again according to Kelley.
To me, this is the best kind of story -- it seems so obvious in retrospect, but somehow everyone missed it until the right person came along asking the right question.
References:
Greenfield LO. 1979. On the adaptive pattern of "Ramapithecus." Am J Phys Anthropol 50:527-548.
Kelley J. 1986. Paleobiology of Miocene hominoids. Ph.D. Dissertation, Yale University.
Kelley J. 1988. A new large species of Sivapithecus from the Siwaliks of Pakistan. J Hum Evol 17:305-324.
Kelley J. 2005. Misconceptions arising from the misassignment of non-hominoid teeth to the Miocene hominoid Sivapithecus Paleontologica Electronica 8:16A. Paleontologica Electronica online
Sivapithecus
Sivapithecus includes a great diversity of Miocene ape species from South Asia. Fossils are known from between 10 and 7 million years ago, with many fossils recovered from the Siwalik region of Pakistan, but fossils assigned to Sivapithecus are found as far as China and Turkey. Sivapithecus represents the large radiation of the fossil Asian apes, and one or more forms are ancestral both to living orangutans as well as many fossil apes, including Lufengpithecus and Gigantopithecus.The cranial morphology of at least one specimen of Sivapithecus clearly shows its relation to living orangutans. Like orangutans, Sivapithecus had a concave face, with projecting incisors and large canines. The face curves markedly upward in profile, a condition called airorhynchy. Also, the orbits are shaped like elongated ovals, tall from top to bottom, and with a similar orientation of the tear ducts in the inner corners of the orbits.
There are dental differences between Sivapithecus and living orangutans. Both apes have thick molar enamel, but in orangutans, the enamel of orangutans is wrinkled into complicated tooth surfaces. In contrast, the surfaces of Sivapithecus teeth are basically uncomplicated and similar in form to Dryopithecus. This primitive molar form is also similar to early hominids, and some of the earliest-known specimens of Sivapithecus were once believed by many paleoanthropologists to be hominid ancestors (see Ramapithecus). From later discoveries, it has become clear that Sivapithecus was already removed from the line of descent of the living African apes and humans.
John Hawks Department of Anthropology
University of Wisconsin—Madison
Copyright © 2007 John Hawks