Buzz
Evolution doesn’t follow a straight path. It’s a winding, unpredictable journey that occasionally gives rise to strange and unusual creatures. It doesn’t take into account the potential future of the species or streamline the process for efficiency. Instead, it veers off in all sorts of unexpected directions before eventually producing the more recognizable forms we see today. Human evolution, like all evolution, didn’t follow a smooth progression from fish to monkeys to apes. Instead, it involved numerous bizarre diversions. From the very moment we made our way onto land, here are some often-forgotten ancestors that together tell a curious and unconventional story of our evolutionary history.
10. Casineria
Around 340 million years ago, a significant event occurred. Some amphibians, which were similar in size to today’s giant river salamanders but lived in a comparable manner, began to lay amniotic eggs. These eggs had thin shells that allowed the embryo to breathe while still retaining enough water for the developing embryo. This adaptation proved incredibly successful, allowing vertebrates to conquer land. Before this, only insects had lived on land, so these early amniotes faced little competition as they spread and diversified into countless forms of life. One of the first creatures to emerge was Casineria, a four-legged animal the size of a modern salamander, measuring just 15cm. It fed on the abundant insects that had flourished on land for millions of years. In fact, Casineria likely spent more time avoiding insects than hunting them—thanks to different atmospheric conditions back then, insects grew much larger, with carnivorous dragonflies boasting wingspans over 70cm. Despite avoiding insects up to five times its size, Casineria thrived, ultimately becoming a key ancestor of some of the largest animals ever to walk the Earth.
9. Edaphosaurids
Edaphosauridae was a group of creatures that roamed the Earth approximately 300 million years ago. Though they might have looked like dinosaurs, they were actually synapsids—mammal-like reptiles that split from true reptiles about 320 million years ago. Edaphosaurids, along with their most famous relatives, the Dimetrodons, had a striking resemblance to large modern lizards, adorned with dramatic sails along their backs. The precise function of these sails remains unclear, but it's believed that they may have been used for mating displays or as a means of regulating heat—an important step in the evolution of temperature-regulated blood in mammals. Edaphosaurids grew to about 3 meters in length and were herbivores, feeding on leafy plants, as grass had not yet evolved by the time they went extinct. These creatures, along with other synapsids, were the dominant life forms on Earth for millions of years, until a mass extinction event allowed dinosaurs to take their place.
8. Caseids
After Edaphosauridae, Caseidae represented the second group of land-dwelling herbivores. These synapsids lived about 270 million years ago and were massive, with sizes ranging from 1 meter to 6 meters in length. They typically featured small heads and large, stocky bodies. Unusually for synapsids, the Caseids possessed teeth that were almost uniform in shape. A key distinction between mammals (synapsids) and other vertebrates is the variation in teeth: mammals have specialized teeth of different shapes within an individual’s mouth, whereas reptiles, fish, and amphibians typically have uniform teeth. The large Caseids, with their unique teeth, had thin, snake-like tails, incredibly short, sturdy limbs, and could weigh more than 2 tons. They resembled Komodo dragons, but with a bloated, barrel-shaped abdomen, standing as tall as an adult human. It's unclear whether their strong, stocky limbs with formidable claws were designed for digging up roots, fighting off predators, or simply supporting their massive size.
7. Dinocephalia
This group of synapsids lived around 260 million years ago, and their name, which translates to “terrible head,” reflects their most prominent feature: large, grotesque bony protrusions on their heads. These protrusions were likely used for displays during mating or in fights. Dinocephalians were less like reptiles and more akin to mammals, having a fine coat of hair and walking in a more upright posture. Some species were carnivorous, while others were herbivorous, and they grew to several meters in length. Despite their variety, they generally resembled muscular hippopotamuses with fine hair, large interlocking teeth, and strange, misshapen heads. Their skulls, with their bizarre horns and bumps, had larger brain cavities than their ancestors, marking the beginning of a trend in mammals: gradually increasing brain size. Rather than relying solely on physical adaptations, which can become useless in changing environments, mammals began to depend on larger brains, increasing their ability to learn and adapt during their lives. This ability to adjust to diverse environments rather than a single one would become the defining strength of mammals for the next hundreds of millions of years.
6. Pristerognathus
Around the time of the Caesars, a new subgroup of synapsids emerged: therapsids. These creatures were more advanced than their predecessors, with legs positioned directly beneath their bodies to support them vertically, unlike lizards whose legs protruded sideways for horizontal support. This anatomical shift allowed for more efficient walking rather than crawling. Therapsids also developed more specialized teeth, including incisors, canines, and molars for the first time. Additionally, they exhibited key mammalian traits, such as hair and lactation. One of the prominent therapsids around 250 million years ago was Pristerognathus. These sleek, carnivorous hunters, with large heads and prominent fangs, thrived in forested environments. Despite their modest size—roughly that of a housecat—they were highly successful predators, preying on smaller synapsids. Pristerognathus eventually went extinct at the end of the Triassic period due to a mass extinction, which allowed dinosaurs to rise to dominance. However, their descendants survived and, after the dinosaurs' extinction, reclaimed their position as Earth's dominant land animals.
5. Cynognathus
Following the smaller Pristerognathus came the larger Cynognathus, a creature about one meter long that resembled a peculiar mix between a crocodile and a wolf. It had a long, reptilian snout, comprising 30% of its body length, and featured large protruding canines among its diverse teeth. Its body also had a tapering crocodilian tail and sprawling, sideways reptilian forelegs, yet it possessed a mammalian trait with fur-covered, upright hind legs. Fossils reveal that Cynognathus had whiskers, an important sensory feature found in mammals. Living around 240 million years ago, its fossils have been discovered worldwide, indicating how successful and widespread these creatures were. Interestingly, due to the abundance of fossils, discoverers from different countries were unaware of its widespread existence, leading to an impressive fifteen different names being given to the same remarkable creature.
4. Multituberculata
Mass extinctions play a key role in accelerating evolution. Species that survive these catastrophic events find themselves in a world with fewer competitors, enabling them to expand into new ecological niches that were previously out of reach. The dinosaurs, for example, exploited this opportunity, leaving behind the synapsids and therapsids, which were quickly outcompeted. The smaller therapsids survived by emphasizing their advantages over reptiles, evolving into rodent-like creatures. Multituberculata were mammals that not only coexisted with dinosaurs but also benefited from their mammalian traits, which played a crucial role in their survival after the dinosaurs' great extinction. Despite their small size and relatively tiny brains, the multituberculata had efficient brain structures, which helped them become increasingly intelligent over time. These creatures lived for an astonishing 120 million years, making them the longest-surviving mammals in history, until their extinction 35 million years ago. Similar to modern rodents, multituberculata were small, burrowing animals covered in thick fur, with some species living in trees like squirrels and others believed to have been swimmers. Unlike their egg-laying ancestors, multituberculata gave birth to tiny, underdeveloped young, similar to modern marsupials, and nursed them with milk from specialized sweat glands. Eventually, multituberculata were outcompeted and went extinct, supplanted by their rodent descendants.
3. Hominids
Apes are known for relying more on their large, adaptable brains than on any specific physical traits. This has led to offspring that take many years to mature, as they learn essential skills from their mothers. The learning process is slow but rewarding, allowing the young to gain a deep understanding of their environment. A strong bond between mother and infant forms naturally during this time. Some ancient apes show early signs of walking upright. In most animals, the spinal column enters the skull at the back, but in bipedal creatures like humans, it enters at the bottom to support upright walking. Around 7 million years ago, a chimpanzee-like species called Sahelanthropus exhibited this feature while retaining adaptations for climbing. Its descendants, the hominids, began abandoning their arboreal traits and ventured into open plains, which accelerated the evolution toward walking on two legs. As a result, their pelvises, feet, and spines started to resemble ours. Some hominids, like Paranthropus, developed bony crests on their skulls for powerful jaw muscles, while others, like Homo ergaster, became taller and more slender than we are today. These hominids became smarter and started using tools and fire to catch and cook food, making hunting more efficient and providing the energy needed for their brains to grow even larger. Homo sapiens, our species, evolved from these early hominids. Although we don’t have the largest brains, we are the only hominid species still alive today and are the most widespread ape on the planet.
2. Proconsul
Early primates evolved into many different forms, some of which are still around today. Around 35 million years ago, a new group emerged: the Old World monkeys. These primates had flat nails instead of the long, curved claws of their ancestors, and they developed elongated toes that aided in climbing, making them more adaptable. Since Old World monkeys do not have a specialized diet, they are generally able to find food easily and often live in large groups. Their survival depends on the strength of the group, so their brain size tends to be in proportion to the size of the social group. The tails of their ancestors, once long and fluffy, were no longer able to move much, and instead, Old World monkeys now use them as counterweights for balance. Around 30 million years ago, a genus called Proconsul evolved, eventually losing their tails altogether. Proconsul only retained a vestigial tailbone and relied on a larger brain to maintain balance. This shift in brain size created a need for extended periods of infant dependence, as the brain required more time to develop outside the womb. Proconsul eventually gave rise to the first apes.
1. Plesiadapis
Approximately 55 million years ago, Plesiadapis, a descendant of Multituberculata, evolved into a distinct genus. It had the appearance of a small lemur, similar to a squirrel, with a bushy tail, curved claws for gripping, a long muzzle, and a flat head. Its eyes, unlike ours, were positioned sideways, granting it only two-dimensional vision. As an expert climber, Plesiadapis is considered the ancestor of all primates. While its ancestors were carnivorous and tree-dwelling, Plesiadapis had evolved towards an omnivorous diet, with sharp teeth for tearing meat and flat molars suited for chewing plants. Due to its diverse diet, it likely possessed color vision, much like modern primates. These tree-dwelling creatures gave birth to fully-formed but helpless young, just like many mammals today.
