BA: Topic 9 Early Primate Evolution

Ancestral morphotype

"Ancestral morphotype" refers to the physical characteristics or traits that were present in the common ancestor of a group of organisms These traits may have been passed down to descendants through genetic inheritance, and may have persisted in some form over time The ancestral morphotype can be used as a reference point for studying the evolutionary history of a group of organisms and understanding how their physical traits have changed and diversified over time.

Missing link (note that there is no such thing)

"Missing link" refers to a hypothetical intermediate stage in the evolutionary history of a group of organisms, often used when there are gaps in the fossil record. It is considered an oversimplification of complex evolutionary patterns. "Ancestral morphotype" refers to a hypothetical reconstruction of the earliest members of a group of organisms based on shared characteristics. It helps researchers understand evolutionary relationships, but does not represent specific missing links in the fossil record.

What are the primates that occur in the Eocene, and where are they found? In the Oligocene? In the Miocene?

1.) Eocene Primates (54-34 mya) The first undisputed primates (Euprimates); i.e., having all the features found in modern primates Found on 4 continents: Africa, Europe, Asia, North America Very successful; widespread, 200 species Two major groups: Omomyoids -Small, Nocturnal, Similar to modern tarsiers Adapoids -Medium-sized, Diurnal, Arboreal quadrupeds, Similar to modern lemurs but no tooth comb *Anthropoids: -Anthropoid origins are probably in the early to middle Eocene -Until recently anthropoid origins were thought to be in Africa, but recent discoveries suggest that perhaps anthropoids originated in Asia (Archicebus & Eosimias) -Ex: Archicebus achilles (55 mya), Darwinius massilae "Ida." (47 mya), Eosimias (40-44 mya) ___________________________________________________________________________ - Small, primitive primates, lemur-like (Adapoids, 100g-7kg) and tarsierlike (Omomyoids, 30g-2kg) -Very successful and widespread. 2.) Oligocene Primates (34-23 mya) Many fossils are known from the Fayum, a 37-29 mya site in Egypt (It's now desert but was forest and swamp in the Oligocene) Many species, with three major groups of anthropoid primates One is a catarrhine (2-1-2-3) ___________________________________________________________________________ Fayum primates Saadanius from Arabia, a stem Catarrhine, 29 mya Early Anthropoids A split between Catarrhines & Platyrrhines, 34-40 mya A split between Hominoids and Cercopithecoids, 28 mya This is all occurring in Africa (remember that Africa and Eurasia are not connected as they are today). 3.) Miocene Primates (23-5.3 mya) The 3 Anthropoid groups (Platyrrhines, Cercopithecoids, & Hominoids) are established Africa is separated from Eurasia by the Tethys Sea until ~ 19 mya. When the two continents joined, cutting the Tethys Sea in two, the western part became what we call the Mediterranean Sea This allowed an exchange of fauna between the continents

What are the four hypotheses for the selective adaptations of primates?

1.) The Arboreal Hypothesis (Szalay & Dagosto, 1973) -the proposition that primates' unique suite of traits is an adaptation to living in trees 2.) The Visual Predation Hypothesis (Cartmill, 1974) -the proposition that unique primate traits arose as adaptations to preying on insects and on small animals 3.) The Angiosperm Hypothesis (Sussman, 1991) -The proposition that certain primate traits, such as visual acuity, occurred in response to the availability of fruit and flowers following the spread of angiosperms (flowering plants) 4.) The Fruit Hypothesis (Rasmussen, 1990) -we evolved color vision to be able to quickly identify fruit -need to remember location, ripening times and seasons *These hypotheses are not mutually exclusive; they are interrelated and elements of all may be involved *They are all possible explanations for the primate characteristics of forward-facing eyes, grasping hands and feet, relatively larger brains, color vision, fingernails, et al.

Miocene

23-5.3 mya From a high in the Mid-Miocene (about 9 degrees Farenheit higher than today's average), temperatures fell significantly The 3 Anthropoid groups (Platyrrhines, Cercopithecoids, & Hominoids) are established Early Cercopithecoids existed from the early to middle Miocene era There is a gap in the fossil record between the early catarrhines (~28 mya) and the Miocene hominoids The early Miocene hominoids occur from 23-14 mya. They are successful and widespread; several genera, many species European Miocene Hominoids 17-9 mya Asian Miocene Hominoids 15-6 mya Late Miocene: -There are gaps in the fossil record in Africa and Eurasia: very few hominoid fossils are found from 9-6 mya -Modern African hominoids cannot be firmly linked to any known Miocene species -Fossils of Asian hominoids have been suggested to be ancestral to the Asian orangutan -Toward the end of the Miocene hominins "appear" (i.e., the hominin lineage splits from the other African apes) -At the close of the Miocene hominin fossils become more common, all in Africa -Many hominin fossils have been found, but essentially no fossils of the modern African "apes" are known

Index fossil

A fossil known to have lived in a particular geologic age that can be used to date the rock layer (strata) in which it is found

Deep time

A framework for considering the span of human history within the much larger age of the universe and planet earth

Fused dentary

A fused dentary is a type of jaw bone found in some primates, including hominoids, that is formed by the fusion of two separate bones, the dentary and the angular. In primates with fused dentaries, the dentary bone, which forms the lower jaw, extends to the ear region of the skull, and the angular bone, which forms part of the jaw joint, fuses with the dentary to form a single, continuous bone. The evolution of the fused dentary is considered to be a significant landmark in primate evolution, as it represents a key adaptation for efficient mastication and the ability to chew tough, fibrous foods. The presence of a fused dentary is one of the defining characteristics of the hominoid lineage, which includes the great apes and humans. How can we define a mammal in the fossil record? -We need a skeletal trait, and paleontologists have selected the trait of a fused dentary for differentiating reptiles from mammals

Sivapithecus

A genus of Miocene sivapithecids, proposed as ancestral to orangutans Synapomorphies link Sivapithecus with the Asian orangutans, but not the African chimpanzees

What is the difference between hominoids and cercopithecoids, and when do these differences appear in the fossil record?

A split between Hominoids and Cercopithecoids, 28 mya (Oligocene Period) --> This is all occurring in Africa (remember that Africa and Eurasia are not connected as they are today) Hominoids: -Dorsal scapula -Broad, shallow rib cage -Shorter lumbar region -Relatively larger brain -Y-5 lower molars -No tail -Hominoid ("ape") postcrania are adapted for hanging and climbing in trees Cercopithecoids: -Lateral scapula -Narrow, deep rib cage -Longer lumbar region -Relatively smaller brain -Bilophodont lower molars -Tail -Cercopithecoid ("monkey") postcrania have adaptations for quadrupedal locomotion

Adaptive radiation

Adaptive radiation is a process of evolutionary diversification in which a single ancestral species gives rise to many new species that are adapted to a wide range of ecological niches This occurs when a group of organisms is exposed to new or varied environmental conditions, which creates opportunities for different adaptations to evolve Over time, these adaptations can result in the formation of new species that are specialized for specific ecological niches Ex: Placental mammals undergo diversification around 105 mya (Late Mesozoic, Cretaceous Period) Mammalian Adaptive Radiation: -At the Mesozoic/Cenozoic (K/Pg, formerly K/T) boundary, approximately 66 mya, non-avian dinosaurs go extinct; "birds" and mammals proliferate -Late Mesozoic-Early Cenozoic: a rapid spread and diversification of mammals and avian dinosaurs (birds) into many environmental niches -This is called an Adaptive Radiation and it includes the appearance of all major living lineages of mammals -Mammals and "birds" replace "dinosaurs" & "reptiles" as the dominant vertebrates on land

Why do we not find fossil hominoids in Eurasia until about 19 mya?

Africa is separated from Eurasia by the Tethys Sea until ~ 19 mya When the two continents joined, cutting the Tethys Sea in two, the western part became what we call the Mediterranean Sea This allowed an exchange of fauna between the continents

What are the South American primates, where did they originate, and when and how did they get to South America?

At that time, Africa and South America were closer together, but still hundreds of miles apart 40 mya Africa and South America were closer together than today; about 900 miles apart Caviomorph rodents, also of African origin, appear in South America at the same time The most widely accepted explanation is the Rafting Hypothesis Masses of vegetation from riverbanks, torn loose by storms, have been seen over 100 miles at sea, with animals carried along Around the beginning of the Oligocene sea levels were much lower, making rafting more plausible In 2016 fossil teeth of a different species were discovered at another Peruvian site, dated to the early Oligocene, and resembling Parapithecids from the Fayum This has been suggested to imply a third rafting event

Concerning catarrhine evolution, what are Eosimias, Archicebus, Darwinius massilae, and Aegyptopithecus?

Eosimias: -anthropoid -Discovered in in China in 1992 -Three species known -40-44 mya, China -Unfused mandible -Post orbital closure -2.1.3.3 dental formula -An ancestral anthropoid? Archicebus: -anthropoid -55 mya -From Hubei Province, China -Diurnal, arboreal, insectivorous -Tiny, weighing about one ounce -Combines features of anthropoids and tarsiers -Anthropoid origins are probably in the early to middle Eocene -Until recently anthropoid origins were thought to be in Africa, but recent discoveries suggest that perhaps anthropoids originated in Asia Darwinius massilae "Ida": 47 mya Weight under 4 ounces From the Messel site in Germany Fine-grained slate gives fine detail Beautiful specimen, although squashed flat Argued to be ancestral to all anthropoids Aegyptopithecus Fayum Primates (37-32 mya) The largest Fayum anthropoid Medium sized (13-18 lbs.) An arboreal frugivore Equal length limbs, so probably slow-moving; not a leaper Dental formula 2-1-2-3 Closed orbits Sexually dimorphic Smaller brain than same-sized modern monkeys

Biostratigraphy/Faunal correlation

Fossils from a site with known dates are used to date fossils from another site For example, radiometrically dated East African fossils can used to date South African fossils In this graphic, the column on the left shows layers that can be radiometrically dated, and the fossil species associated with those layers We have excavated the first area and have identified fossil species A, B, & C for which we have radiometric dates. We then find a hominin fossil at the second site in association with species A & B; this lets us determine an approximate date for a hominin fossil that we could not otherwise date The branch of geology concerned with the order and relative position of strata and their relationship to the geological time scale -the analysis of the order and position of layers of archaeological remains. -the structure of a particular set of strataLateral continuity is a key ideaArea with fossils of a known age to date the fossils -To date these layers we need a reference Providing an absolute date Dating a layer and not the fossils directly Using fossils with a known date

What are the differences in locomotor behavior between hominoids and cercopithecoids, and how do the differences in their skeletons reflect this? How are these differences related to their ecology?

Hominoids: Hominoids generally exhibit more suspensory and brachiating behaviors than cercopithecoids This is reflected in differences in their skeletons, as hominoids have longer and more robust arms, a shorter and broader torso, and a more stable wrist joint These differences allow hominoids to move more efficiently through the trees and to engage in behaviors such as suspensory feeding and tool use 1.) Dorsal scapula 2.) Broad, shallow rib cage 3.) Shorter lumbar region 4.) Relatively larger brain 5.) Y-5 lower molars 6.) No tail Cercopithecoids: Cercopithecoids have longer and more slender arms, a longer and narrower torso, and a more mobile wrist joint, which allows them to engage in quadrupedal locomotion and to manipulate objects with greater precision 1.) Lateral scapula 2.) Narrow, deep rib cage 3.) Longer lumbar region 4.) Relatively smaller brain 5.) Bilophodont lower molars 6.) Tail Environments: Hominoids generally inhabit forested environments where suspensory and brachiating behaviors are advantageous Cercopithecoids inhabit a wider range of habitats and rely on quadrupedal locomotion for terrestrial travel and foraging

How would you explain what I have called the "holding hands problem"?

Imagine that you're holding hands with your mother, and she's holding hands with her mother, and so on back through the ages You and your mother are the same species, and your mother is the same species as her mother, and so on However, at some point in the distant past, perhaps 500,000 years ago, that woman, although she is your direct ancestor, is not recognizably a modern human; i.e., she is a different species, and this continues farther into the past But because every mother gives birth to a daughter of her own species, there is no point at which a new species "appears." By the time we are 6,000,000 years back, our ancestor is an "ape." By 70,000,000 years ago, our ancestor is a small tree-dwelling insectivore (no more hands, but let's keep going) And 400,000,000 years ago, she's a fish The only way we can differentiate species in a lineage is if our fossil record is incomplete; if we had a perfect fossil record we could not determine a point where one species "becomes" another

When do mammals appear in the fossil record? Placental mammals?

Mammals: Mammals and dinosaurs "appear" in the fossil record at about the same time, in the Late Triassic Placental Mammals: The first placental mammals appear around 180-160 mya (Middle Mesozoic, Jurassic Period)

The Fayum

Many fossils of the Oligocene Primates (34-23 mya) are known from the Fayum, a 37-29 mya site in Egypt The Fayum is a region in Egypt that is known for its rich fossil record of early primates and other animals that lived during the Eocene epoch, approximately 56 to 33.9 million years ago. The Fayum deposits are particularly important for the study of early primate evolution, as they include some of the earliest known anthropoids, including the parapithecids and the propliopithecids. These fossils provide important insights into the morphology, ecology, and biogeography of early primates, and have helped to shed light on the origins and diversification of the primate order.

Y-5 molars

Molar that has five cusps with grooves running between them, forming a Y shape This is characteristic of hominoids

Platyrrhines

New World Monkeys Platyrrhine Evolution: -The earliest New World primate fossils are from the Oligocene -Peru 36-30 mya -Bolivia about 26-28 mya -Small anthropoid "monkeys." -2-1-3-3 dental formula -African ancestry Rafting A split between Catarrhines & Platyrrhines, 34-40 mya The 3 Anthropoid groups (Platyrrhines, Cercopithecoids, & Hominoids) are established

Catarrhine

Old World monkeys, apes (Ape: any hominoid that is not bipedal), and humans 2-1-2-3 tooth formula A split between Catarrhines & Platyrrhines, 34-40 mya There is a gap in the fossil record between the early catarrhines (~28 mya) and the Miocene hominoids ❕A catarrhine is a type of primate that belongs to a group of Old World monkeys and apes They have narrow, downward-facing nostrils This includes the hominoids (great apes and humans) and the cercopithecines (Old World monkeys) The term "catarrhine" comes from the Greek word for "downward flow," referring to the position of their nostrils Catarrhines are found in Africa and Asia and are characterized by their complex social behaviors, adaptations for arboreal or terrestrial locomotion, and a diet that includes fruits, leaves, insects, and occasionally small animals

Paleoanthropology

Paleoanthropology is the study of human evolution from the evidence in the fossil record Both paleontology and paleoanthropology have been supplemented, enhanced, and sometimes modified by studies of ancient DNA (aDNA), based on recent technological advances that enable scientists to extract DNA from organisms as old as several hundred thousand years, including extinct species.

Paleontology

Paleontology is the study of the forms of life existing in prehistoric or geologic times, as represented by the fossils of plants, animals, and other organisms Both paleontology and paleoanthropology have been supplemented, enhanced, and sometimes modified by studies of ancient DNA (aDNA), based on recent technological advances that enable scientists to extract DNA from organisms as old as several hundred thousand years, including extinct species.

What do we know about Proconsul? Is it a monkey, or an ape, or neither?

Proconsul (23-14 mya) Several species known Relatively large brain Short snout Y-5 molars with low cusps and thin enamel, indicating frugivory Heavy, more monkey-like body Does not have the hanging and climbing adaptations of modern hominoids Elbow articulation like modern apes Arboreal, but a climber, not a leaper The presence of a tail is disputed ? The primary feature linking Proconsul with living apes is its lack of a tail; other "ape-like" features include its enhanced grasping capabilities, stabilized elbow joint and facial structure ❕While the exact placement of Proconsul in the primate family tree is debated among researchers, it is generally considered to be neither a monkey nor an ape, but rather an early member of the hominoid (or ape) lineage.

Rafting

Rafting, in an evolutionary context, refers to the dispersal of organisms across large bodies of water by means of floating on vegetation or other debris This process can occur naturally, such as when a landmass becomes isolated from a larger continent, or it can be facilitated by human activities, such as transportation of species on boats or other vehicles Rafting can lead to the colonization of new habitats and the establishment of new populations, which can ultimately lead to the evolution of new species or the diversification of existing lineages _____________________________________________________________ How did primates get to South America? -At that time, Africa and South America were closer together, but still hundreds of miles apart 40 mya Africa and South America were closer together than today; about 900 miles apart Caviomorph rodents, also of African origin, appear in South America at the same time The most widely accepted explanation is the Rafting Hypothesis Masses of vegetation from riverbanks, torn loose by storms, have been seen over 100 miles at sea, with animals carried along Around the beginning of the Oligocene sea levels were much lower, making rafting more plausible In 2016 fossil teeth of a different species were discovered at another Peruvian site, dated to the early Oligocene, and resembling Parapithecids from the Fayum This has been suggested to imply a third rafting event

Bilophodont

Referring to molars that have four cusps oriented in two parallel rows, resembling ridges, or 'lophs'. This trait is characteristic of Old World monkeys Cercopithecoids have them

Saadanius

Saadanius from Arabia, a stem Catarrhine, 29 mya Saadanius is a genus of extinct primates that lived during the Oligocene epoch, approximately 30 million years ago, in what is now Tanzania. Saadanius is notable for its unusual combination of features that suggest it may have been an early ancestor of both Old World monkeys and apes, and may represent a transitional form between the two groups. The most distinctive feature of Saadanius is its skull, which has a mixture of monkey-like and ape-like characteristics, including a small braincase and a muzzle-like snout. The discovery of Saadanius has helped to illuminate the early evolution of the catarrhine primates, which includes Old World monkeys and apes, and has provided important insights into the origins of the hominoid lineage.

Ecology

Scientific study of interactions among organisms and between organisms and their environment The difference between a clade (based on evolutionary relationships) and a grade (based on morphology and ecology)

Paleospecies

Species identified from the fossil record based on similarities and differences to other species Classifying extinct species (Paleospecies) is more difficult What tests can we use for fossils?: 1.) Synapomorphies, 2.) comparison with known fossil species This is subject to different interpretations

East African Rift

The East African Rift is nearly 2,000 miles in length, and the valley it forms is 18-30 miles wide It was formed by the African Plate pulling apart, a process that started in the Miocene and then stopped Erosion exposes the layers and the fossils in themVolcanic action in and around the rift allows the layers to be dated accurately

Biological species concept

The biological species concept defines a species as members of populations that actually or potentially interbreed in nature, not according to similarity of appearance. Organisms may look different and yet be the same species. Although appearance is helpful in identifying species, it does not define species John Ray, 1691 This is only testable with living species

Mosaic evolution

The concept that evolutionary change takes place in some body parts or systems without simultaneous changes in other parts Ex: Mammals are descended from one lineage of reptiles (another lineage led to dinosaurs; some lineages led to extinction) The appearance of a new group is not a sudden event; it is a process, with the ancestral reptiles accumulating mammalian characteristics bit by bit, in different lineages, over a period of perhaps 20 million years

Faunal exchange

The exchange of animals between two regions Africa is separated from Eurasia by the Tethys Sea until ~ 19 mya When the two continents joined, cutting the Tethys Sea in two, the western part became what we call the Mediterranean Sea This allowed an exchange of fauna between the continents

When and where did primates originate?

The first identifiable primates are probably from about 74 mya (toward the end of the Mesozoic in the Late Cretaceous Period) Primates are not defined by a single synapomorphy, but by a suite of characteristics In the same way as for mammals, the characteristics that define modern primates develop over time, in various lineages, some of which are extinct North America, Europe, Asia, and Africa

Postcranium

The skeleton excluding the skull Cercopithecoid ("monkey") postcrania have adaptations for quadrupedal locomotion Hominoid ("ape") postcrania are adapted for hanging and climbing in trees.

Which one is possibly ancestral to a living hominoid and how do we know?

There are gaps in the fossil record in Africa and Eurasia: very few hominoid fossils are found from 9-6 mya Modern African hominoids cannot be firmly linked to any known Miocene species Fossils of Asian hominoids have been suggested to be ancestral to the Asian orangutan Toward the end of the Miocene hominins "appear" (i.e., the hominin lineage splits from the other African apes) At the close of the Miocene hominin fossils become more common, all in Africa Many hominin fossils have been found, but essentially no fossils of the modern African "apes" are known

Plesiadapiforms

They lack most primate features, but are closely related, perhaps ancestral Fossils date from ~70 mya in North America and they became extinct in the Early Eocene Many species are known from North America, but they are also found in Eurasia Small (mouse to squirrel-sized), arboreal Ex: Purgatorius, Plesiadapis, Carpolestes

Why are plesiadapiforms thought to be related to primates, but are not actually primates (think of synapomorphies)?

They lack most primate features, but are closely related, perhaps ancestral Plesiadapiforms share some traits with living primates, including long fingers well designed for grasping, and other features of the skeleton that are related to arboreality Fossils date from ~70 mya in North America and they became extinct in the Early Eocene Many species are known from North America, but they are also found in Eurasia Small (mouse to squirrel-sized), arboreal

Euprimate

True primate Eocene Primates (54-34 mya) -The first undisputed primates (Euprimates); i.e., having all the features found in modern primates

Quadruped

a four-footed animal

Anthropoid

humanlike primates that include New World monkeys, Old World monkeys, and hominoids Anthropoid origins are probably in the early to middle Eocene Until recently anthropoid origins were thought to be in Africa, but recent discoveries suggest that perhaps anthropoids originated in Asia (Archicebus & Eosimias) Anthropoid origins: Archicebus achilles, Darwinius massilae "Ida", Eosimias The 3 Anthropoid groups (Platyrrhines, Cercopithecoids, & Hominoids) are established in the Miocene

Where do we find hominoid fossils?

❕Hominoid fossils have been found in various locations around the world, including East Africa, South Africa, Europe, and Asia.

Where and when did hominoids evolve, and when do we find them on other continents?

❕Hominoids evolved in Africa approximately 25 million years ago. The earliest hominoid fossils have been found in East Africa and date back to around 17-20 million years ago. Hominoid fossils have also been found on other continents, with the oldest fossils found in Europe and dating back to around 11 million years ago. Hominoids have been found in Asia dating back to around 8-9 million years ago, and in South America dating back to around 13-16 million years ago.

What are the living hominoids and where do they live now?

❕The living hominoids include the four species of great apes: orangutans, gorillas, chimpanzees, and bonobos, as well as humans Orangutans are found in the rainforests of Borneo and Sumatra in Southeast Asia Gorillas are found in central and eastern Africa Chimpanzees and bonobos are found in central and western Africa Humans are found all over the world