10 mind-blowing facts about Earth's most amazing creatures

Time of India

24-05-2025

Animals are familiar to us all, not only because we encounter them daily, but also because humans themselves are animals with fascinating truths. We share the planet with an incredible diversity of animal species, many of which play essential roles in our survival and ecosystems.
Animals differ from other life forms like plants, fungi, and bacteria in key ways. They are multicellular, usually mobile at some stage, and rely on consuming organic material for energy. Unlike plants, animals lack cell walls and cannot photosynthesize. This unique combination of traits places animals in a distinct category, shaping their interactions with the environment and with each other. Discover 10 fascinating truths about the incredible animals on Earth.
Features of animals
living on Earth
Topic
Description
Animal life on Earth
Animal life began nearly 600 million years ago. Fossils of stromatolites, created by ancient microbes, date back to 3.8 billion years ago, but animals emerged 3.2 billion years later. Early animals like the Ediacara biota appeared during the late Precambrian.
Animals and energy
Animals are heterotrophs, meaning they must consume other organisms to obtain energy and carbon for survival. They cannot convert sunlight into energy like plants.
Movement in animals
Most animals can move during at least part of their life cycle. While animals like fish, birds, and mammals are highly mobile, some animals, such as sponges, are sessile or only move during early life stages.
Multicellular and eukaryotic
All animals are multicellular eukaryotes, meaning they consist of multiple cells and have complex cells with a nucleus and organelles. Most animal cells are organized into tissues such as connective, muscle, epithelial, and nervous tissues.
Animal diversity
Since their emergence 600 million years ago, animals have evolved into millions of distinct species. Currently, scientists estimate over 3 million living animal species.
The Cambrian Explosion
The Cambrian Explosion (570-530 million years ago) was a period of rapid diversification, where most of the basic animal body plans that exist today first appeared.
Sponges
Sponges are the simplest of all animals. They lack specialized tissues and have bodies made up of cells in a gelatinous matrix. They also filter-feed through pores and channels in their bodies.
Nerve and muscle cells in animals
All animals except sponges have specialized cells called neurons (nerve cells) that transmit electrical signals. Neurons form the basis of complex nervous systems in vertebrates and efficient systems in invertebrates.
Symmetry in animals
Most animals have symmetrical bodies. Types of symmetry include radial symmetry (as seen in sea urchins and sea stars) and pentaradial symmetry, which is found in some echinoderms like sea stars.
The largest living animal
The blue whale, a marine mammal weighing over 200 tons, is the largest living animal. Other large animals include the African elephant, Komodo dragon, and colossal squid.
Fascinating facts about animals
Animal life on Earth began nearly 600 million years ago
Life on Earth can be traced back about 3.8 billion years, based on the oldest known evidence. The first fossils discovered are of stromatolites—layered formations created by ancient microbial life. These organisms, however, were not animals. In fact, animals wouldn't make their debut for another 3.2 billion years. It was only during the late Precambrian period that animals began to show up in the fossil record. Among the earliest of these were the Ediacara biota—soft-bodied, frond-like, and tubular organisms that lived between 635 and 543 million years ago.
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This group appears to have disappeared by the close of the era of Precambrian.
Animals extract energy and nutrients by feeding on other organisms
Animals require energy to carry out every function essential to life—such as growing, developing, moving, metabolizing, and reproducing. Unlike plants, they lack the ability to convert sunlight into usable energy. Instead, animals are classified as heterotrophs, meaning they must consume plants or other organisms to obtain the carbon and energy necessary for survival.
Movement is a key trait of animals
While plants remain rooted in place, most animals have the ability to move during at least part of their life cycle. In many animals, this movement is clearly visible—fish glide through water, birds soar through the sky, and mammals walk, climb, or run. However, not all animals are constantly on the move. Some exhibit limited mobility or are mobile only briefly during early life stages. These animals are known as sessile.
For example, sponges spend most of their adult lives attached to surfaces, yet their larvae are free-swimming. Some sponge species have also been observed to move extremely slowly—just a few millimeters per day. Other largely immobile animals include barnacles and corals, which show only minimal movement.
Every animal is a multicellular eukaryotic organism
All animals are made up of multiple cells, meaning they are multicellular organisms. In addition to being multicellular, animals are classified as eukaryotes, as their cells contain complex structures.
These eukaryotic cells have internal components, such as the nucleus and various organelles, all enclosed by membranes. The DNA within a eukaryotic cell is organized into linear chromosomes. Except for sponges, which are the simplest animals, animal cells are organized into specialized tissues that carry out different functions.
These tissues include connective, muscle, epithelial, and nervous tissues.
Animals have evolved into millions of distinct species
Since animals first appeared 600 million years ago, their evolution has led to an astonishing variety of life forms.
Over time, animals have developed diverse body structures, along with various methods for movement, feeding, and sensing their surroundings. Throughout their evolutionary history, the number of animal groups and species has fluctuated, growing at times and shrinking at others. Currently, scientists estimate that over 3 million species of animals are living today.
The Cambrian Explosion stands as a crucial era in animal evolution
The Cambrian Explosion, which occurred between 570 and 530 million years ago, was a period of remarkable and rapid animal diversification.
During this time, early life forms evolved into a wide range of more complex organisms. Almost all of the fundamental animal body structures that exist today emerged during this era.
Sponges are the most basic of all animals
Sponges are the most basic of all animals. While they are multicellular like other animals, they differ significantly in other ways. Unlike other animals, sponges do not have specialized tissues. Their bodies are made up of cells embedded in a gelatinous matrix.
Within this matrix, tiny spiny structures called spicules provide structural support. Sponges also feature numerous small pores and channels that act as a filter-feeding system, allowing them to capture food from the water.
Sponges branched off from all other animal groups early in the evolutionary history of animals.
Animals generally have both nerve and muscle cells
With the exception of sponges, all animals have specialized cells known as neurons, or nerve cells.
Neurons transmit electrical signals to other cells and are responsible for conveying and processing various types of information, including an animal's health, movement, environment, and orientation. In vertebrates, neurons form the foundation of a complex nervous system that includes the sensory system, brain, spinal cord, and peripheral nerves.
While invertebrates have fewer neurons compared to vertebrates, their nervous systems are by no means simple.
In fact, invertebrate nervous systems are highly efficient and well-adapted to help these animals solve the survival challenges they encounter.
Symmetry is a common feature in most animals
With the exception of sponges, most animals have symmetrical bodies. Different animal groups display various types of symmetry. One example is radial symmetry, found in cnidarians like sea urchins and some species of sponges. In radial symmetry, an animal's body can be divided into identical halves by more than two planes that run through its length.
Animals with radial symmetry typically have a disk, tube, or bowl shape.
Echinoderms, such as sea stars, exhibit a specific form of radial symmetry called pentaradial symmetry, which is characterized by five points of symmetry.
Among all living animals, the blue whale is the largest animal
The blue whale, a marine mammal that can weigh over 200 tons, is the biggest living animal. Other notable large animals include the African elephant, Komodo dragon, and colossal squid.
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