When did Placental Mammals originated
Placental mammals originated in the Mesozoic Era (around 251-66 mya), during this time they were mainly small, nocturnal animals, probably hiding from predators with camouflage and slow, quiet movement.
What let mammals take over
The extinction of the dinosaurs around 65.5 mya might have opened up the ecological niches that allowed the increased diversity and disparity of mammals in the tertiary period (65.5-2.5 mya)
What happened with mammals in the Paleocene
The Paleocene was the first epoch of the age of mammals. During this time new groups of placental mammals appeared in the fossil record. Many of these groups achieved a broad range of sizes as well as a great number of species before declining sometime in the Eocene.
These groups were ultimately replaced by modern orders of placental mammals, but it is unknown if this replacement occurred gradually or rapidly.
What emerged in the Paleocene
The Paleocene epoch saw the emergence of several families of mammals that have been implicated in the origins of primates. There as the Plesiadapiforms, which are archaic primates that posses some of the primate features, but lack others.
The word Plesiadapiforms means almost adapiforms (later appearing true primates)
How are Plesiadapiforms similar and different to primates
There are similarities in the molar teeth between Plesiadapiforms and adapiforms.
Differences include:
- unusual anterior teeth
- most have claws rather than nails
- None have been discovered with a postorbital bar (Seen in strepsirrhines) or septum (haplorhines)
- And weather or not the auditory bulb was formed by the petrosal bone remains unclear in many specimens.
Nevertheless, there are compelling reasons (partly from new skeletal material) for
including plesiadapiforms within the Order Primates.
What was the Earliest primate
The earliest primate is considered to be Purgatorius, which is known from teeth that are very plesiomorphic (ancestrol) for a primate. It has some characteristics that suggest it is a basal plesiadapiform, but little links it specifically to euprimates.
Its ankle bones suggest a high degree of mobility, potentially with an arboreal lifestyle.
It is Plesiomorphic enough to have given rise to all primates, including the plesiadapiforms.
However, new finds suggest the genus was more diverse and had more differing tooth morphologies than previously appreciated.
Were Plesiadapiforms dievrse
Plesiadapiform families were numerous and diverse during parts of the Paleocene in North America and Western Europe. Some genus were found on both continents, suggesting corridors for dispersal between them. A few Plesiadapiforms have been described from Asia
What were Plesiadapiforms like
Most were small, the largest was about 3 kg. They had small brains, and fairly large snouts, with eyes that faced more laterally than in euprimates. Many species show reduction and or loss of the canine and anterior premolars, with the resulting formation of a rodent-like diastema (a pronouced gap between the premolars and the incisors, with loss of at least the canine); this probably implies a herbivorous diet. Some families appear to have had very specialized diets, as suggested by unusual tooth and jaw shapes.
What were the Carpolestidae
Arguably the most interesting and unusual family of plesiadapiforms is the Carpolestidae. They are almost exclusively from North America (with a couple of possible members from Asia), and mainly from the Middle and Late Paleocene. Their molars are not very remarkable, being quite similar to other plesiadapiforms. However, their lower posterior premolars (p4) are laterally compressed and blade-like with vertical serrations topped by tiny cuspules.
This unusual dental morphology is termed plagianulacoid. The upper premolar occlusal surfaces are broad and are covered with many small cuspules; the blade-like lower premolars might have cut across these cuspules, between them, or both.
How did Plesiadapiforms move
Many plesiadapiforms have robust limb bones with hallmarks or arboreality. Most had sharp claws instead of nails on most or all digits. The extremities show grasping abilities compared to those of primates and some arboreal marsupials. They appear to have been able to cling to vertical substrates using their sharp claws, propelling themselves upward using powerful hindlimbs, bounding along horizontal supports, grasping smaller branches, and moving head-first down tree trunks.
In carpolestids in particular, the skeleton appears to have
been especially well adapted to moving slowly and carefully in small terminal branches.
What were considered primates in the mid 20th century
In the middle 20th century, treeshrews of the order Scandentia were often considered part of the Order Primates, based on anatomical similarities between some treeshrews and primates. For many people, plesiadapiforms represented intermediates between primates and treeshrews, so plesiadapiforms were included in true primates as well.
What happened with treeshrews
Studies of reproduction and brain anatomy in treeshrews and lemurs suggests that treeshrews are not primates. This led to the suggestion to expel plesiadapiforms from the Order Primates. Like treeshrews, plesiadapiforms lack a postorbital bar, nails, and details of the ear region that characterize true primates.
What did K. Christopher Beard and contemporary scientists find with Plesiadapiforns
Later, K. Chirstopher Beard found that in some ways, the digits of paromomyid plesiadapiforms are actually more similar to those of dermopterans (colugos), the closet living relatives of primates, than they are to those of primates themselves. At the same time other scientists found that the cranial circulation patterns and auditory bulla morphology in the paromomyid Ignacius, are more like those of dermopterans than of primates.
Currently what is though of Plesiadapiforms
However, in the last two decades, the tide of opinion has turned again, with many researches reinstating plesiadapiforms as members of the Order primates. This is due to new and more complete specimens demonstrated that the postcranial skeletons of plesialapiforms, including the hands and feet, were primate-like, not dermorpteran-like.
Fine grained CT scans of complete plesiadapiform skulls revealed several key traits with primates to the exclusion of other placental mammals. Most significant was the suggestion that Carpolestes simposoni possessed an auditory bulla formed by the petrosal bone, like in all living primates.
What were the first universally accepted primates
The first universally accepted fossil primates are the adapoids and the omomyoids. These groups became quite distinct over time, filling mutually exclusive niches for the most part. However, the earliest adapoids are very similar ot the earliest omomyoids.
what were the adapouids and Omomyoids like
The adapoids were mainly diurnal herbivores, with larger sizes.
The Omomyoids were mainly nocturnal, insectivorous or frugivorous, smaller primates.
Describe the history of the Omomyoids and Adapoids
Both appear at the start of the Eocene, and were present in Western NA, Western Europe, and India.
Both groups achieved considerable diversity in the middle Eocene, then mostly died out at the end of that epoch. In some areas, they are the most dominant mammals in the fossil record.
Both groups barely survived the Eocene-Oligocene extinctions, when colder temperatures, increased seasonality, and the retreat of rainforests to lower latitudes led to changes in mammalian biogeography.
What Adapoides survived into the Miocene
In North America, one genus (an Adapoidea) persisted until the Miocene: Ekgmowechashala. This taxa has highly unusual teeth and might have been a late immigrant to North America from Asia.
In Asia, one familiy of Adapoids, the Sivaladapidae, retained considerable diversity as late as the Late Miocene.
What were the Adapoids like
Adapoids were very diverse, particularly in Eocene North America and Europe. They can be divided into six families, with a few species of uncertain familial relationship. As a group, they share some features. Important features include a postorbital bar, flattened nails, grasping extremeties, and a petrosal bulla. In addition, some adapoids retain the ancestral dental formula of 2.1.4.3. In general, the incisors are small compared to the molars, but the canines are relatively large, with sexual dimorphism in some species. Cutting crests on the molars are well developed in some species, and the two halves of the mandible were fused at the midline in some species.
Some adapoids were smaller than 100g and some were larger than 10Kg. Futhermore, the spaces and attachment features for the chewing muscles were truly enormous in some species, suggesting that these muscles were very large and powerful. This suggests an overall adaptive profile of diurnal herbivory. The canine sexual dimorphism suggests a possible mating pattern of polygyny in some species.
What were the Omomyoids like
Appeared at the start of the Eocene and then became very diverse with most species dying out before the Oligocene. Omomyoids are known from thousands of jaws with teeth, relatively complete skulls from about a half-dozen species and very little postcranial material.
They were relatively small primates, with the largest being less than 3 kg. All known crania posses a post orbital bar, which in some has ben described as “incipient closure”.
Some crania have an elongated bony ear tube extending lateral to the location of the eardrum, a feature seen in living tarsiers and catarrhines. The anterior teeth tend to be large, with canines that are usually not much larger than the incisors. The premolars tend to be distinct from one species to another.
The postcranial skeletons of most omomyoids show hallmarks of leaping behaviour reminiscent of that of tarsiers.
This group became very diverse and abundant in North America.
What was Teilhardina
Teilhardina, is one of the earliest and arguably the most plesiomorphic of omomyoids. It had several species, most of which are from North America, with one from Europe and one from Asia.
What are Crown Strepsirrhines
Crown Strepsirrhines = Living Strepsirrhines.
What is up with lemur fossils
The Quaternary record of Madagascar contains many amazing forms of lemurs, including giant sloth-like lemurs with perhaps monkey-like habits, lemurs with koala-like habits, and eve a giant aye-aye. However, early Tertiary continental sediments are lacking, and there is no record of lemur fossils before the pleistocene.
what is up with galagos fossils
The fossil record of galagos is slightly more informative. There are Miocene African fossils that are very likely progenitors of lorisids. These are much like modern galagos and do not reveal anything about the relationship between crown strepsirrhines and Eocene fossil primates.
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1b - Evolution of Evolutionary Theory31
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2a - Intro to genetics15
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2b - Ancient DNA13
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3a - Biology of Variation25
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3b - Mechanisms of Evolution18
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4a - Primates30
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4b - Primate Behaviour and Ecology28
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5a - Primate Evolution29
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Ch859
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Ch726
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Ch 60
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Ch 547
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Hominin Origins15
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Earliest Hominins19
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Mid-Late Pleistocene Hominins I: Eurasia16
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Mid-Late Pleistocene Hominins II: Asia and Africa13
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Modern Humans: Origins, Dispersals, and adaptation20
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Modern Humans 2: Origins, dispersals, and adaptations23
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Modern Human Variation14
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Understanding Human variability: Dismantling the concept of race22
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Climate and Human evolution20
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The influences of health and disease on contemporary humans22
