Lecture 16 Early Primate Evolution


Hi, everybody. The title of today's lecture is Early Primate Evolution. This is Anthropology 225, online. The Cenozoic Era, is divided into a series of epochs. And they're indicated in the following slide. We are currently in the Holocene. And the Holocene's from the present to about 0.01. Which is about 10,000 years ago. That's followed by the Pleistocene, the Pliocene,the Miocene, the Oligocene, the Eocene, and the Paleocene. The Pleistocene's from 10,000 years ago to 1,8 million years ago. The Pliocene's from 1.8 million years ago to 5 million years ago. The Miocene is from 5 million years ago to 22 million years ago. The Oligocene is from 22 million years ago to 35 million years ago. The Eocene is from 35 million years ago to 54 million years ago. And the Paleocene is from 54 to 65 million years ago. What I plan on doing, is for each of these epochs, excluding the Holocene. I plan of reviewing the major forms of primates that evolved during each of these time periods.

So, the primates that evolved during each of these various epochs. And we'll start out at 65 million years ago, the very beginning of the Cenozoic. The first epoch of the Cenozoic that I want to mention is the Paleocene. The Paleocene is from 65 to 54 million years ago. It is probably one of the most poorly known epochs. This is not because we don't have a lot of geogra-, geological samples from this time period. But rather, we don't have a lot of non-human primate samples from these geological epoch, from this geological epoch. Despite the fact that it's one of the most poorly known epochs, it does represent the first radiation of placental mammals. During this time period of the Paleocene from 65 to 54 million years ago. Climates were a lot cooler than they were during the preceding epoch of the Cretaceous during the Mesozoic. We know that climates were cooler based on the flora. We're seeing primarily coniferous trees. You know, the trees with pine cones, and many, many fewer tropical plants.

Geologically. [COUGH]. Excuse me. Geologically, the Paleocene was a very, very active epoch in Earth history. And it's marked by the rise of several different mountain groups. It was during this epoch that the Rocky mountains actually were formed. During this time period, geologically, North America, Europe and Asia were all connected. So they formed one continental mass. Australia, South America and Antarctica we also connected. Forming a sec- a second continental mass. And India and Africa were each separate entities. And India had not yet collided with mainland Asia, so we didn't yet have the Himalayas. So this is just an example of continental position 65, 66 million years ago. Relatively similar to today. But there are some very important differences.

Okay. So what about primates? Because that's really what we're interested in. We're talking about our own evolution and understanding our own evolution, we need to understand primate evolution per se. The earliest primates are known to have evolved from an insectivore-like mammal during this, this time period, during the Paleocene. That this is known it, it's impossible to determine exactly how primates are related to other orders of mammals. But it's, there are suggestions indications from both paleontology, anatomy, and biomolecular studies. That primates, tree shrews and flying lemurs are all more closely related to one another than to other mammals. And thus, they are placed together in what we call the Superorder Euarchonta. So it's probably the earliest primate probably looked something like a mix of primates, tree shrews and flying lemurs. And flying lemurs are nothing, are not related to lemur, the lemurs of Madagascar.

In addition to these extant mammals, fossil plesiadapiforms also lie near the origin of primates. Either within the order Primates or as another order of closely related archontans. The suborder Plesiadapiform, as I've noted, constitute a group of primate-like mammals. And the, these species really flourished during the Paleocene and Eocene in both North America, Europe and Asia. So notice these are the earliest primates that we know of or primate-like mammals that we know of. And they are all from North America, Europe and Asia. Not normally where we consider the evolution of primates to have occurred. The known diversity of these plesiadapiform primates is greater than living strepsirhines or New World Monkeys. There are over 50 genera, over 135 species. The primate status of these plesiadapiforms though, has been questioned for decades. And it's very unclear whether plesiadapiforms are in fact, primitive primates. Or just closely related to the primates.

So these are some examples of what some of these earliest plesiadapiforms are believed to have looked like. So, what happened to the, these plesiadapiforms? Why did they go extinct? Well, there's several explanations for the demise of these primates, or primate-like mammals. The first is there was extensive competition with other mammals, such as rodents and early pro- prosimians. So they were basically out competed for resources. And also a, a second hypothesis is climate change. That there was a dramatic drop in sea level during this time. And perhaps the drop in sea level caused some environmental changes that the plesiadapiforms forms were not able to adapt to. As I noted, their primate status has been challenged for decades. Every decade people, the text books change as to whether or not plesiadapiforms are or are not primates. So, but for the purposes of this class, we're not gonna consider them primates. We're gonna consider them primate-like mammals, closely related.

The description. What, what are these, what are these mammals like? They have a low flat skull, a long snout, small brain, large zygomatic arches. And the primary reasons that I do not consider them as primates at present, is that they do not posses a post-orbital bar. Remember this bony ring surrounding the eye? No plesiadapiform, possesses a post-orbital bar. In addition, the auditory bulla is not part of the petrosal portion of the temporal bone. Another really good synapomorphe for these non-human primates. What are a couple of these ancestral primate features that plesiadapiforms do have, that suggest maybe they are in fact primates? Well, they have a Nail bearing hallus in one species called, Carpolestes. That is, they have a grooming claw.

I'm sorry, they don't have a grooming claw, they have have a flat nail on their on their toe in Carpolestes. And, you know, that flat nail is a really good primate characteristic. They also have a bulla that in some species, that is in fact part formed from the petrosal. Or suggested that they might be. But there are really no direct relationships of relations of Eocene prosimians or later primates to these plesiodapiforms. The most important thing we can get from these plesiadapiforms, is a better understanding of the earliest evolution of features that are characteristic of these primates. So, as you can see, there wasn't much that I could tell you for the Paleocene. Because we really don't have very much about primate evolution during the Paleocene. The second epoch that I wanna mention is that of the Eocene.

The Eocene is from 54 to 35 million years ago. And it is marked by a major change in fauna. Basically, what we see is that all modern mammals start replacing all the archaic ones. So, all the archaic forms of mammals are, go extinct and the modern ones prevail. In primate evolution, this epoch is marked by the disappearance of Plesiadapiforms. So the Plesiadapiforms go extinct during the Eocene. We also see the appearance of the first primates that actually represent strepsirrhine primates. In fact, the Eocene is often referred to as the epoch of primates of modern aspect. Because the primates from the Eocene look remarkably like those of modern day primates. The faunal changes that occured during the Eocene are tremendous. And it results in changing geography.

North America and Europe are an increasingly separate and distinct. There are intermittent connections between them. But they're still predominantly separate. There's more regularly connections between North America and Asia. India also begins to collide into Asia. And Africa is still separate from Europe. So just keep these continental positions in mind, as we're talking about the evolution and distribution of these primates. Okay? As I noted earlier, we see that the Eocene is marked by the disappearance of plesiadapiforms. As well as the first appearance of primates resembling living strepsirhine primates, living prosimians. So, we have lemurs, lorises and tarsiers all starting to appear during this Eocene epoch. We see a large number of fossils, all generally strepsirhines from this time period. These fossils are very, very different from the plesiadapiforms of the Paleocene. Because they specifically have anatomical features characteristic of living primates.

They've small infraorbital foramen. They have flat nails. They have grasping halluxes. They have postorbital bars. Char- good synapomorphic characteristics are found in all these living primates. And this suggests a very different way of life from these plesiadapiforms. Many of the cranial features of these Eocene primates, indicate increased reliance on vision rather than olfaction. The postcranial changes suggest an increased importance in manipulative abilities. You need flat nails instead of claws when you're trying to manipulate things with your hands. We also see that they're much more acrobatic and that they have leaping abilities. Okay? So, these are, these primates of the Eocene, are often referred to as primates of modern aspect. But they're also referred to as crown primates. So here, we see no postorbital bar. We see no postorbital closure, back here. And we see postorbital closure here. So these primates had a very, very different distribution than the previous set previous epoch. They, they had a tremendous adaptive radiation. There were four times as many strepsirhine genera during the Eocene as there are known today.

And there's quite a number of lemurs and Madagascar and primate. And for them to, for us to say that there are four times as many different species in the fossil record as we see today, is tremendous. Now, all these fossil specimens are not equally kno-, well known on all these different continents. They're very common in North America and in Europe. There are a couple in Asia, a couple in Africa. But pretty mu-, not very many. And they are completely unknown in South America, Antarctica and Australia. So what are some of the similarities between extant strepsihines, those are the living persimeans today, and Eocene Strepsirhines. Well basically, their mandibular synthesis. Remember the two halves of the jaw? Are unfused in, in, extant strepsirhines. That's also true in the Eocene strepsirhines. They also have an unfused mytopic suture. The Eocene strepsirhines have no post-orbital closure.

They all possess a post-orbital bar. They all had nails, no claws. They have forward facing eyes, an opposable thumb and toe. A grooming claw, a smaller snout, small infraorbital foramen. A small little hole right here. And the cranial blood supply from the internal carotid artery. So we see tremendous similarities between living persimean primates and Eocene persimean primates. These primates first appear at the same time in Europe and North America. The fauna in fact, of these two continents are very, very similar. And once again, this was enabled by the geographic connection between these continents, at high altitude. As well as high global temperatures enabling primate dispersion at those high latitudes. There is no clear phyletic ancestor of early primates among closely related mammals. There are two poorly known species from Africa and Asia, that may in fact lie close to the origins of all later primates.

These are the following. Altanius orlovi and Altiatlasius kouchii. I apologize for my pronunciation. Altanius is from the Eocene in Mongolia, so this is a, like north of Russia. And it's originally described as an early omomyid, but probably a plesiadapiform. It has elevated trigonids and tall premolars. And it's considered a basal primate near the common ancestry of the adapids and the omomyids, very, very early. We also have Altiatlasius, koulchii, we'll say. And it's a Paleocene primate from Morocco, which is Northern Africa. And it's known only from ten isolated teeth. It's 50 to 100 grams. So it's relatively larger than some of the other stuff that we're, we've looked at. And it's considered part early omomyoid, part basal primate, part early anthropoid. It is literally the oldest fossil primate. And it has affinities within the order prim- affinities within the order Primates are uncertain. But it's most likely a primate. But how it's related to the other primates is not clear. So those are the absolute earliest primates that we know of. After that the earliest primates from the east, from the late Paleocene and Eocene.

We now have these strepsirhine primates from the Eocene and they can be divided into two distinct superfamilies. So the Eocene strepsirhines are divided into two distinct superfamilies. The Adapoids and the Omomyids. The earliest members of both superfamilies, both the Adapoids and the Omomyids. Are very, very similar suggesting a divergence just prior to the Eocene. So in the very, very late Paleocene, members of both superfamilies of Donrusello, Cantius and Teilhardina. So let's talk about both the date, Adapoids and Omomyids. These are su, superfamily Adapoids. And these guys are lemur like. They have very large, they're relatively large, comparable to living lemurs in body size. They have a dental formula of 2143. So you have four premolars, three molars, one canine, two incisors in each quadrant of the mouth. The limbs are similar to modern strepsirhines, but are more robust.

So this is what some of these aday, adapoid prosimians probably look like. Relatively similar to this ring-tailed lemur here. So how do they resemble living strepsirrhines. Well, they resemble living Strepsirrhines in their anterior dentition, to begin with. their lower incisors are small and positioned vertically. Their upper incisors are broad, short and separated by a median gap. The, so there's a, effectively there's a space between your two front teeth.The upper and lower canines are larger than the incisors. And the anterior premolars are caniniform, meaning they are like sharp and pointy, instead of square and flat. So, what else can I tell you about these, these adapoids? Generally they, we see that they have a relatively long snout.

But they have a small infraorbital foramen, suggesting a reduced reliance on olfaction. They all possess postorbital bars. Their brain case, the size of their brain, is larger than those of the Paleocene forms. But it's smaller than extant lemurs. The blood supply is from stapedial and promontory branches, of the internal carotid artery. And they all have nails, no claws. They also have an opposable big thumb, an opposable big toe. So there are six families within the Adapids. And I'm going to go through each of them. So we have the family Notharctidae. And it's from the Early middle Eocene of North America. And the best known genus is Cantius. They're in numerous species of Notharctidae in North America. And there are two of them in Europe. So it's a predominately North American family. They are all very small to medium sized prosimians, one to three kilos. They have a dental, a very primitive dental formula of 2143, that fourth premolar again. Their mandibular symphysis is unfused. Their orbit sizes are relatively small, suggesting that their diurnal.

And their post crania suggest that they are arboreal quadrupeds. The second family that I want to mention are the family Cercomoniidoe also known as protoadapines. These are from the early to middle Eocene. They are predominately Eur- European in their distribution. But there are a couple in North America, Africa, and Asia. Not many. They're much more diverse than the Northarctidae. The best known genus of this family is Donrusellia. It's the earliest and most primitive gen-, genus. So, 213, 2143 dental formula. Simple tritubercular molars. So tritubercular molars are molars that are almost triangular in shape. They also have a hypocone from the lingual cingulum, rather than from the protocone as the Northarctines. They hypocone is one of these little bumps or grooves on your molars.

And it's showing where it's coming out of when we, we make these assessments. So this is a Notharctus and this is a Cercomonius. This third family is the Family Asiadapidae. It's primarily from West India and the early Eocene. Basically, from the Vastan coal mines,. And it's a very, probable that it's at the base of the adapoid radiation. They're very closely related to Sivaladapids and they're two genera. In terms of its description, they're about the size of a Bushbaby, 200 to 600 grams. They have very simple premolars with no nannopithex folds on their upper molars. Which is analogous to what we see in bush babies. The hypocones and lingual cingula are weak or absent. And they are very agile quadrupeds. The next family is family Caenopithecidae.

These are found in Europe, North America, Africa and Asia. And for, and slightly later in the Eocene, we're looking in mid to late Eocene. It's traditionally they were grouped under the Cercamonidae. But now they've been separated out. There are nine genera and 11 species. The most important one is Mahgarita stevensi. It's from late Eocene of Texas. And the most intriguing feature of Mahgarita stevensi are, is the following. It has a fused mandibular symphysis. Which is sugge-, a clear haplorhine characteristic. And it has an enlarged promontory artery canal also, for larger brains. A good anthropoid, haplorhine characteristic. But it has no postorbital closure. So we're seeing a mosaic of characteristics in this species. And then we have another one. Same family as Dar, Darwinius masillae, which is from Messel, Germany. And we have a young female with almost the entire skeleton preserved.

As well as impressions of fur and the remains of even the stomach contents. And she weighed about 660 grams. The teeth and the stomach contents, which contained leaves and fruit, indicate a herbivorous diet. Large orbit size indicates that she was nocturnal. And long hindlimbs with a low intermembral index, suggest in fact she was a leaper. This is her, isn't that cool, can you imagine finding that? I can't. Very cool. And then we have the family Adapidae. And this is from the middle of the Eocene up through early Ooligocene, predominantly found in Europe. In fact, the member of the family Adapidae, was the first non-human primate named. It was so unusual that Kuvea didn't recognize it as a primate. They all possess molarized last pre-molar. So, the pre-molar instead of you, being a tiny little square is an elongated square.

They have well developed shearing crests, and a lot of post-cranial peculiarities. One of the best known species is Adapis pari-, parisensis, from the late Eocene of France. It has a 2143 dental formula. It has small upper central incisors with a gap between their bases. This is probably for the organ of Ja, organ of Jacobson. Which is very important for the sense of smell, for olfaction. Their upper lateral incisors are very, very small. They have lower incisors and canines form a single cutting edge. And some people have suggested this is indicative of the development of a tooth comb. There is a lot of controversy about that, because there's no wear or hair striations evident on these teeth. We see it has a very long, low skull. Fl-, flaring zygomatics. A pronounced sagittal and nuchal crests on larger individuals, especially the males. These big orbit, I'm sorry [LAUGH] these little orbits suggest diurnality. And the blood supply is from the internal carotid of the promontory as well as the stapedial.

So here's the organ of Jacobson. Okay, right here. And just very important for your, for your sense of smell. Okay? The last family I wanna mention within the Adapids is the family Sivaladapidae. And it's in the Eocene to late Miocene in Asia. Sivaladipis nagrii. It's three kilos, 2133 dental formula. And it's folivorous. We see that based on sharp crests on its molars and its premolars. So this is the first family where we're really seeing a reduction in the number of premolars. So what can we tell based on all of this variation in the morphology of these Adapoids? What, what do we really know about their behavior, and their origin, and their taxonomy? Well,some people have suggested that there's evidence of an ancient African origin for the strepsirhines.

Remember we, the earliest ones were found in North America, Europe and Asia. So an ancient African origin is quite surprising to read about. And we see that there are large adapoids from North Africa, such as Caenopithecids. And we're also, in recent years, finding an increasing number of tiny primates from North Africa and the Arabian peninsula. And they have a number of dental similarities to Eocene adapoinds and to extant strepsirhines. As an, just as an example we have Azibius, trerki from the Eocene of Algeria on northern Africa. And it's really unusual premolars the ave, alveolus suggests the species and another related species Algeripithicus possessed a procumbent canine, suggestive of a tooth comb. They all have premolars and molar crowns that overlap as do extant strepsirhines. So, there, there's some indication for an African origin for strepsirhine primates.

But the majority of, of it says North America, Europe and Asia. A big question that re, results from a lot of this, our knowledge of Adapid morphology and behavior. Is, some people have wondered, are these Adapidae actually strepsirhines? Virtually all authors have noted their similarities to living strepsirhines. In particular, to the lemurs. Similarities to the lemurs include their cheek teeth, their configuration of the skull. Their postorbital bar, the long snout. Nasal region morphology, and inflated auditory bulla. Free ectotympanic ring, as well as the carotid circulation. Most individuals within the Adapidae have a stapedial artery of moderate size. So, what I want to point out is all these features are primitive features. They retain the primitive condition found in mammals. Instead of sharing a unique specialization. The Adapids lack the unique specializations of these Eocene primates. They lack the tooth comb. And the tooth comb is probably one of the most clearly def, distinguishing features of the strepsirhine primates. So, but these strepsirhine primates that are living today, do have some links with these Adapids. Which justifies why some people have argued that the Adapids are, in fact, fossil strepsirhines.

For example, Adapids also have a grooming claw on the second toe of the foot. This has been known from Circumoniines and other living strepsirhines. They have a flaring fibular surface of the talus. The similar, a similar arrangement of the cuneiform facets of the vernacular, these are features of the feet. And, and a unique articulation between the ulna and the carpus. So, we have all, except in North Arctis. So we have a lot of, not a lot, but we have some anatomical similarities between living and Adapids, living strepsirhines. And living strepsirhines and fossil Adapids, was what I'm trying to say. Although living strepsirhines and fossil Adapids are similar in over all, overall morphology and probably represent sister taxa. There's very little evidence demonstrating a unique phyletic relationship between strepsirhine and Eocene Adapoids. So they probably, the answer's probably not. Okay. The second superfamily that I want to mention in today's lecture are the Omomyoids.

Okay? We had the adapoids now we're going to have the omomyoids. The omomyoids are what you might call Tarsier-like. They first appear in the early Eocene. They're found both in North America, Europe and Asia, much like the Adapids. They have a very different evolutionary history though, in North America and Europe. And this is because in North America the Omomyoids are very, very diverse. In Europe, there's only one genus from the early Eocene, Teilhardina. And four genera from mid to late Eocene. There are dozens in North America. The most primitive of the Omomyoids is Teilhardina, Steinus and Altanius. And they're all very, very similar to the early adapids that I mentioned earlier such as Donrussellia and Cantius. They're similar in terms of their dental morphology and in the dental formula. They all have a 2143 dental formula.

Later, Omomyoids start to have dental reductions. Okay? So, these are some examples of the fossil Omomyoids and current possible Omomyoids. So, the family, Omamidae. They basically are characterized by. Let's see, did I skip? No. Okay. The family Omomidae, they have very large procumbent lower central incisors. They have a small, lateral incisor. And the canines are relatively small. The premolars in most species are reduced to three or fewer. And most have a post or porto cingulum. What's called a nanospithex fold, joining the protocone distally. Mandibular symphysis is always unfused in the Omomidae. And their skull morphology is also very, very, specific. They have a very short, narrow snout. Their palate get broader as it goes towards the posterior. They have really large eyes.

We see both the stapedial and the promontory present. And they tremendously resemble tarsiers and galagos. There's some evidence that the tibia and the fibula are partly fused in some specimens of Omomyidae. We know that the Calcaneus is also elongated. And the morphology of the Omomyoid semicircular canals indicate agile or jo- jerky motion, as in extant lemurs. You know, the constant leaping. And so you need your semicircular canals to handle that constant, rapid motion. The earliest, it's probable that the earliest and most primitive Omomyoid, Teilhardina probably gave rise to all three subfamilies. The second sub family is the Anaptomorphinae. These are from North America. They are most, mostly primitive. They're ancestral to both Omamyines and Microchorerids.

The earliest genus is Telhardinia. And found in the early Eocene of Europe and North America. And it weighs 50 to 500 grams. They are characterized by having tall, pointed lower 4th premolars and reduced lower 3rd molars. They are probably frugivorous, with a few specie showing adaptations for processing invertebrates that have hard shells. There are two complete crania remains from the family Anaptomorphinae. And that known from Tetanius homunculus, from Wyoming,. And Wyoming probably has one of the most detailed records of population and species changes in the entire fossil record. We see remarkable documentation of transitions between paleospecies. And a tremendous amount of evidence of considerable parallelism, the simultaneous development features in different species. This is a Tetonius.

The second subfamily is the Omomyinae. This is from North America and one specimen from China, so Asian. It's found in the middle Eocene. We have 100 grams to two kilos. They replace the anaptomorphines in the middle Eocene. Reasons why, probably have to do with the global climate change. And they could be derived from anaptomorphone ancestors such as Steinius. The last molar is elongated. One specimen of, from the family Omomyinae is Rooneyia viejaen-, viejaensis. It's also from the late Eocene of Texas. It's a nearly complete cranium. It has a body mass of 400 grams. It is probably diurnal based on the small orbits. And it was frugivorous with rounded molar cusps. The third family of the Omomyoids is the family microchoerinae.

This is the European group and they're find early to late Eocene. There are seven genera. They vary in size. Pseudoloris is 50 to 100 grams. Grams, Microchoerus 500 to 1800 grams. So, its very small, so small. The upper dentition is 2133. This characteristic of new world monkeys. And the lower dentition has one less tooth. A classic example of a microchoerinae is necrolemur,. And we have many complete, but albeit crushed crania. We know that they have a very short, narrow snout. They have a bell-shaped palate, a gap between the upper incisors for the organ of Jacobson. Large eyes indicative of nocturnality. A large infraorbital foramen, the ectotympanic forms a ring within the bulla, nebula. But extends laterally to form a bony tube. And so it resembles prosimians in the position of the ring, but Tarsius in the tube. And it also has a partly fused tibia and fibula.

So very, very interesting [UNKNOWN]. And so this Necrolemur,. And Pseudoloris. So, the Tarsiids. Numerous fossil primates have been described that are attributable to the same family as the living Tarsiers. Three of them are, Tarsius eocaenus is from the Middle Eocene of China. We have teeth and cranial fragments that are identical to extant Tarsius in orbital and nasal morphology. We have Afrotarsius cahthrathi from the Oligocene of Egypt. And we have Tarsius thailandica from the Miocene in Thailand. These remains, these Tarsiid remains, appear to document the presence of Tarsiids in Asia for over 50 million years. So, some people refer to the Tarsiers as a result, as living fossils. Because these Tarsiers look just like these fossils from 50 million years ago. And interestingly, this is very consistent with morphological and biomolecular distinctiveness. So, are these Omomyoids, tarsiers or are they haplorhines? Well the Omomyoids are in fact, have a number of features that are in fact similar to Tarsiers.

They're very small in their size. They have large eyes. They have an elongated calcaneis. And they have a fused tibula-fibula, tibia-fibula. So they have a number of anatomical characteristic. Several authorities actually placed the European Microchoerines within the actual family Tarsiidae. Obviously, this is debated extensively. And we're not gonna take that, take that path today. But I just want you to know that there are features that link them and some people take it even further. But I wanna make it clear that many of the similarities that actually link Omomyoids with Tarsiers, are very superficial. They're either shared with other European strepsirhines. Or they're actually primitive traits. Using Tarsiidae fossils suggest that true Tarsiids are older than most Omamyoids. And therefore Omomyoids are not actually Tarsiids. Omomyids, Tarsiids, and anthropoids all do share a number of features, that leads all researchers to group them together in the semiorder Haplorhini. But it doesn't mean that Omomyids are in fact tarsiers. [SOUND].