EVOLUTION OF VERTEBRATES THROUGH GEOLOGIC TIME

Evolution of Vertebrates Through Geologic Time

• The history of vertebrates is interesting, spanning hundreds of millions of years.
• Fish, amphibians, reptiles, birds, and mammals are all vertebrates, or backboned creatures.
• Understanding the development of vertebrates across geological time can help us comprehend how complicated life is on Earth. 

1. Early Vertebrates: The Cambrian Period (about 541–485 million years ago)

• Vertebrates first appeared during the Cambrian Period.
• Agnathans were primitive fish-like organisms with no jaws.
• Fossil evidence, such as Myllokunmingia, sheds light on the early evolution of vertebrate morphology.
• The Cambrian Explosion was crucial for increasing biological diversity throughout this time period.
• Early vertebrates adapted to various ecological niches.

2. The Silurian and Devonian Periods, or around 443–359 million years ago, are when jawed vertebrates first appeared.

• During the Silurian epoch, vertebrates gained jaws, resulting in jawed fish or gnathostomes. This was crucial since jaws allowed for more effective feeding methods.
• Famous Groups: armoured fish known as placoderms thrived throughout the Devonian period.
• In addition, cartilaginous fish, such as sharks, began to emerge.
• Challenges and Adaptations: Fish evolved via competition and predation, leading to variety.

3. Transition to Land: The Devonian Period

• Tetrapods, or land-based vertebrates, emerged in the late Devonian period. This change was essential to vertebrate evolution.
• Key Species: Tiktaalik, a fish-like organism, possessed limbs that could support their body weight on land, bridging the gap between fish and vertebrates.
• Climate change, including the formation of shallow seas and marshes, has led certain fish to adapt to terrestrial life.

4. Amphibian Age: Carboniferous Period (about 359–299 million years ago)

• Amphibian dominance: As tetrapods emerged, amphibians became more ubiquitous.
• Early forms, such as Acanthostega and Ichthyostega, were adaptable to both land and water.
• Amphibians evolved to breed on land but still needed water to lay eggs.

5. The Rise of Reptiles: The Permian Period (Approximately 299–252 Million Years Ago)

• Reptiles evolved from amphibians during the Permian period.
• The creation of amniotic eggs enabled reptiles to breed apart from water, which was an important adaptation for life on land.
• Reptiles evolved into many forms, including early synapsids and diapsids. This epoch laid the groundwork for major evolutionary branching that led to birds and mammals.
  
  

6. The Mesozoic Era, which spanned around 252–66 million years, had mass extinctions

• The Permian-Triassic Extinction, which wiped out 90% of life, led to the development of reptiles and dinosaurs throughout the Mesozoic era.
• Dinosaurs dominated land ecosystems, developing from tiny to large predators and herbivores.
• Archaeopteryx, the first real bird, emerged from theropod dinosaurs in the late Jurassic era, marking the start of avian evolution.

7. The Rise of Mammals: The Mesozoic-Cenozoic Transition (Approximately 66 Million Years Ago to Present)

• The K-T Extinction Event, which occurred at the end of the Cretaceous epoch, caused dinosaurs to become extinct. This freed up ecological niches for mammals to thrive in.
• Mammals have developed into diverse forms, such as placental mammals, marsupials, and monotremes. This diversification happened quickly in the following Paleogene era.
• Human Evolution: Primates evolved into hominids and then modern humans.

IMAGE SOURCE (THUMBNAIL)