From the primordial soup and dinosaur extinction to modern genetic discovery, tracing the deep evolutionary history of the world's last surviving Ailuridae.
Cover caption: Parailurus and the red panda.
KATHMANDU: The origin of Earth occurred approximately 4.6 billion years ago. At that time, Earth lacked a biological environment. Initially, due to lightning strikes, volcanic heat, and ultraviolet radiation, inorganic elements such as hydrogen, methane, ammonia, and water vapor synthesized into amino acids and organic molecules. Proof of this was demonstrated in 1953 by Stanley Miller and Harold Urey through an experiment conducted inside a simple glass jar, widely known as the Miller-Urey experiment. This proved that organic molecules are formed from the combination of inorganic elements.
From this process, it is believed that unicellular life evolved approximately 3.8 billion years ago. That initial life form was single-celled. Following that, life on Earth remained confined to unicellular organisms for roughly 1.7 billion years. Initially, such single-celled organisms lacked a nucleus. In the course of time, unicellular organisms with a nucleus evolved approximately 1.6–2.1 billion years ago. Such organisms are referred to as eukaryotic organisms. From them, more complex cellular organizations gradually developed. Subsequently, around 1.5–1.6 billion years ago, unicellular animals and plants diverged.
About 540 million years ago, an explosion in the evolutionary development of organisms occurred, known as the Cambrian Explosion. This took place entirely within the oceans.
Following this, multicellular organisms evolved from unicellular ones approximately 1 billion years ago. The development of multicellularity paved the way for different cells to perform distinct functions within a single organism, allowing body structures to grow more complex. In the history of life on Earth, this very transformation laid the foundation for the later expansion of numerous branches of plants and animals. Subsequently, plant and animal lineages continued to evolve. Life on Earth then essentially spread and diversified across the aquatic world.
The Cambrian Explosion
Photosynthetic microorganisms and algae (aquatic plants—algae and fungi) played a vital role in Earth’s ecosystems. Around 540 million years ago, an explosion in the evolution of organisms took place, known as the Cambrian Explosion. It occurred entirely in the ocean. This phenomenon is extensively explained on pages 34–49 of the book Extinctions: How Life Survives, Adapts and Evolves authored by Michael J. Benton, published in 2023.
Although primitive amphibians could walk on land, they were entirely dependent on water for reproduction, which prevented them from venturing into dry habitats.
Following the evolution of aquatic animals, vertebrates such as fish evolved around 500 million years ago. Various branches of fish developed, and one lineage of these vertebrates adapted from water toward land, evolving into four-legged creatures on land approximately 410 million years ago. At that time, plants and small insects were also developing on land.
Board placed along the path to Mukkumlung (Pathibhara) in Taplejung. Photo: Kamal Maden.
From that lineage, the branch of amphibians evolved approximately 365 million years ago. They began enclosing their eggs or offspring in special membranes or sacs. This protected the eggs or young of aquatic organisms from drying out outside of water. Consequently, this shift eliminated the obligation to rely on water for reproduction. Following this, new evolutionary possibilities opened up for terrestrial life, leading to the evolutionary radiation of amphibian life.
From reptiles to mammals
Although primitive amphibians could walk on land, they were entirely dependent on water for reproduction, which prevented them from venturing into dry habitats. Solving this problem, certain amphibians developed amniotic eggs featuring a hard shell and internal fluid that allowed them to lay eggs on land, leading to the evolution of the first reptiles approximately 340 million years ago. This revolutionary shift helped organisms disperse away from the water’s edge into deep and dry land, where their skin became scaly and rough to prevent water loss through evaporation.
Two-legged carnivorous dinosaurs initially developed feathers to keep their bodies warm, which later transformed into wings for flight.
Subsequently, reptiles split into two main branches. From one group, dinosaurs emerged around 240 million years ago. From ecological and evolutionary perspectives, the primary reasons for dinosaurs becoming colossal were the abundant food resources available during that era, vast open ecological niches, and natural pressure for self-defense. The widespread availability of nutritious vegetation supplied herbivorous dinosaurs with sufficient energy to sustain massive body sizes, while generational adaptation against predators led to larger physical dimensions, which progressively drove predators to become massive as well.
This biological development was fully supported by their efficient respiratory system—similar to that of modern birds—and a unique bone structure that was hollow and lightweight inside, making it biologically possible for them to maintain balance and move around effortlessly despite extreme weight.
During the Jurassic period, when dinosaurs ruled the Earth, another branch of reptiles moved toward the evolution of birds. Two-legged carnivorous dinosaurs initially developed feathers to keep their bodies warm, which later transformed into wings for flight.
More than 30 avian traits in theropod dinosaurs—such as growing feathers, developing wings, and acquiring flight capability—did not appear all at once; rather, they had been developing gradually long before.
To facilitate flight, their bones became hollow and lightweight. The strongest evidence of this is the Archaeopteryx fossil, which exhibited both reptile-like teeth and bird-like wings. As noted by Michael Benton on pages 183–185 of his book Extinctions: How Life Survives, Adapts and Evolves, the process of dinosaurs evolving into modern birds was not a sudden event, but the result of gradual and accelerated evolution that continued uninterrupted for over 50 million years.
According to the book, more than 30 avian traits in theropod dinosaurs—such as growing feathers, developing wings, and acquiring flight capability—did not appear all at once; rather, they had been developing gradually long before. In this journey toward becoming birds, physical shrinkage played the most critical role, causing the bodies of these organisms to become small and light 150 times faster compared to other dinosaurs.
As a result, their skull structure altered, brains expanded, teeth vanished to give way to lightweight beaks, and tails shortened. Feathers, initially used only for thermoregulation and attracting mates, eventually enabled gliding through the air and ultimately flapping wings to fly, marking the origin of true birds.
Due to this precise and rapid physical transformation, when an asteroid impact annihilated the giant dinosaurs 66 million years ago, the avian ancestors survived. Explaining that day of dinosaur destruction in his book, Michael J. Benton notes that an asteroid roughly 10 kilometers wide struck the Yucatán Peninsula in Mexico approximately 66 million years ago.
In the absence of sunlight, plants died and the food chain completely collapsed, wiping out giant non-avian dinosaurs and roughly 75 percent of all living species on Earth.
The energy generated by this massive impact triggered global tsunamis and wildfires, while dispersing billions of tons of dust and sulfur particles into the atmosphere, blocking sunlight for years and causing a “nuclear winter” and acid rain across the globe.
In the absence of sunlight, plants died and the food chain completely collapsed, wiping out giant non-avian dinosaurs and roughly 75 percent of all living species on Earth. According to Benton, this catastrophe proved to be an “ecological reset” in Earth’s history. Although it ended the age of dinosaurs, it provided a historic opportunity for small burrowing mammals and avian ancestors that had already undergone rapid physical transformation to adapt and flourish in a new world.
Subsequently, small burrowing mammals survived. The surviving birds, meanwhile, successfully evolved into the more than 10,000 species seen today.
Let us trace back further. Another branch of reptiles transformed into the synapsids group around 310 million years ago. Synapsids then converted into therapsids, and subsequently into cynodonts. From a branch of the cynodont lineage, early mammals began evolving around 210 million years ago. Early mammals were small in size, resembling shrews or mice. It was these very creatures that managed to survive during the cataclysm 66 million years ago.
A red panda spotted in Ilam district. Photo courtesy: Chungba Sherpa.
Mammals and the family Ailuridae
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