Initial stages and divergence of protozoa
The first stage of the evolutionary process originates from archaea. According to the phylogenetic model under consideration, it is they that gave rise to life forms such as viruses, as well as blue-green and red algae. Further complexification is associated with the appearance of green flagellates, which underwent extensive divergence (divergence of traits).
The evolutionary vector of green flagellates split into two main directions:
- Green algae, which transformed into higher plants during historical development.
- Colorless rhizoflagellates, which evolved into diatoms, sponges, molds, and protozoa. It is worth noting that a certain proportion of protozoa subsequently adapted to a parasitic lifestyle.
Transition to multicellularity and animal evolution
The second major stage marks the transition of organisms to a multicellular structure. This colossal leap was accomplished thanks to ciliated protozoa (ciliates). It is from them that multinucleated (syncytial) flatworms descended.
The emergence of flatworms served as the starting point for the extensive phylogeny of the entire animal kingdom. These organisms gave rise to five ancestral forms. Their evolutionary fates diverged:
- One of the ancestral forms became the progenitor of Echinoderms and Chordates.
- The remaining four forms served as the basis for the formation of most other known types of the animal kingdom.
Phylogeny of vertebrates
The vertebrate evolutionary lineage is characterized by a diversity of forms and a sequential complexification of structure.
The first vertebrate representatives were ostracoderms, which traced their origins back to invertebrate ancestors. Later, ostracoderms gave rise to lampreys and armored sharks. Armored sharks, in turn, split into cartilaginous fish (which include modern sharks and rays) and bony fish.
The colonization of land and the emergence of new classes proceeded as follows:
- Crossopterygii (lobe-finned fish) evolved into diplovertebrons—early amphibians, also known as stegocephalians.
- Diplovertebrons gave rise to modern amphibians and reptiles.
- The first reptiles were cotylosaurs. This group subsequently gave rise to a vast spectrum of animals: extinct dinosaurs and marine reptiles, as well as currently living turtles, crocodiles, lizards, snakes, birds, and mammals.
Human evolutionary lineage
The formation of modern human ancestors is a prolonged process that began about 70 million years ago. The starting point in this chain is considered to be tupaiids—small forest mammals from which early primates evolved.
Subsequently, the order Primates branched into several major groups:
- New World monkeys.
- Old World monkeys.
- Pongids (great apes), which today include orangutans, gorillas, and chimpanzees.
- Hominids—the branch that includes the direct predecessors of modern humans.
Briefly: answers to topical questions
Due to whataromorphosis did lobe-finned fish (Crossopterygii) manage to evolve into amphibians?
The evolution of lobe-finned fish into amphibians was made possible by the transformation of their swim bladder into lungs.
- Swim bladder—in the course of evolution, it transformed into an organ for breathing atmospheric air.
This process is an example of the evolutionary shift in functions, in which the primary function of an organ loses its biological significance and the secondary one becomes the main one. Simultaneously, the structure changes as well. As a result, Crossopterygii were able to give rise to early amphibians.
The ancestors of amphibians and reptiles can be remembered through the chain: Crossopterygii → Diplovertebrons → Cotylosaurs (C-D-C).
Class and exam questions
From whom did the first multicellular animals in this diagram descend?
Multicellularity arose thanks to ciliated protozoa (ciliates), from which multinucleated flatworms descended.
Which organisms became the ancestors of chordates?
The ancestors of chordates (as well as echinoderms) became one of the five ancestral forms that originated from flatworms.
Which reptile group is considered the very first?
The first reptiles are considered to be cotylosaurs, which gave rise to birds, mammals, and modern reptiles.
What else to study on this topic
- Divergence of colorless rhizoflagellates
- Origin of viruses from archaea
- Evolution and extinction of armored sharks
- Differences between hominids and pongids
- Transitional forms: from ostracoderms to fish
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