Early Hominins (2)

Time Frame: 65 million years ago (MYA) – present.
Significance: Marks major adaptive radiations of mammals after the Cretaceous extinction event, with mammals evolving to fill newly available ecological niches.

Characteristics: Beginning of adaptive radiation of early primate-like mammals, known as plesiadapiforms.
Example: Carpolestes, a representative of early primate-like mammals.

Features: Development of the first true primates known as adapids and omomyids.
Basal Anthropoids: Emergence of early anthropoids like Eosimias and Biretia.

Key Events: More pronounced adaptive radiation of anthropoids.
Notable Species: Aegyptopithecus and Branisella, along with the divergence of New World monkeys.

Duration: 23 – 5 MYA.
Adaptive Radiation: Significant diversification and evolution of the first hominoids and the emergence of hominins.
Key Changes: Migration and isolation of continents affected species distributions. Tropical climates evolved to cooler, drier conditions over the epoch.

Branches: Divergence between Old World monkeys and hominoids (apes and humans).
Continental Movements: South America and Australia became isolated while Eurasia and Africa merged around 16-17 MYA.

Defining Traits:
- Absence of tail.
- Bodies larger than monkeys.
- Larger brain size with a higher encephalization quotient (EQ).
- More complex brains leading to complex behaviors.
- Y-5 molar pattern indicative of less specialized dentition.
- Enhanced mobility due to flexible clavicles and shoulder joints suited for brachiation.
- Longer front limbs (varying with hominin evolution).
- Long fingers adapted for grasping.
- Long infant dependency period necessitating high parental investment.

Key Features:
- Displays a mixture of ape and monkey characteristics.
- Lacks a tail, indicating ape lineage.
- Exhibited equal limb proportions typical of monkeys.
- Possessed shoulder structures and cranial features consistent with apes.
- Considered an early ancestor to later hominoids.
Habitat: East Africa; adapted to both terrestrial and arboreal environments.

Habitat: Asia, particularly the regions of modern-day India and Pakistan.
Evolutionary Significance: Ancestral lineage to modern orangutans.
Distinct Features:
- Close-set eye orbits.
- Similarities in cranial and dental anatomy to current orangutans.

Key Points:
- Known primarily from teeth and jawremains found in Asia.
- Characterized by large canines relative to rest of teeth, thick molar enamel suggesting adaptation to a tough diet.
- Possible ancestor to modern orangutans.

Final Diaspora: Eurasian apes likely migrated back into Africa due to climate changes, leading to evolutionary divergence into African ape and human lineages.

Climate Change: Continued cooling from the late Miocene.
Geological Connections: North and South America connected; Africa merged with Europe, allowing for further adaptive radiation of hominins.

Physical Traits:
- Adapted dentition with smaller canines.
- Obligate bipedal locomotion, with significant anatomical changes from other great apes.
- Reproductive strategies involving shorter intervals between births.
- Female sexual characteristics evolved to display hidden estrus cycles.
- Significant increase in cranial capacity indicating larger brain sizes leading to advanced language and culture.

Definition Review:
- Hominid: Includes all great apes and humans; primarily quadrupedal locomotion; flat feet with an opposable toe.
- Hominin: Sub-group of hominids that includes humans and ancestral humans; obligate bipeds, characterized by foot arch without an opposable big toe.

Key Species:
- Sahelanthropus tchadensis (7 – 6 MYA): Discovered in Chad, significant for its ape-sized brain, non-protruding face, and foramina magnum located centrally indicative of upright posture.
- Orrorin tugenensis (6.2-5.8 MYA): Found in Kenya, showcasing anatomical features reflecting both arboreal and terrestrial adaptation.
- Ardipithecus ramidus (5.8 – 4.4 MYA): A species exhibiting a mix of terrestrial and arboreal traits with key anatomical features supporting bipedalism.
Notable Trait: Ardipithecus (referred to as "Ardi") had a body structure suggesting a blend of both lifestyles, exemplifying early stages of hominin evolution.

The Miocene epoch marks a pivotal era for the evolution of hominoids, setting the stage for the eventual emergence of true hominins, characterized by key anatomical adaptations supporting bipedalism and advanced cognitive capabilities.