During the era of dinosaurs, which occurred 246 million to 66 million years ago, none of the species existing today were present. However, there are several groups of species currently inhabiting the earth whose lineage can be traced back to ancient ancestors with striking similarities.
These creatures, known as “living fossils,” seem to have remained almost unchanged over time. Nevertheless, it doesn’t imply that there have been no changes at all. Their DNA is distinct and has undergone numerous refinements throughout the process of evolution.
These living fossils provide a glimpse into life millions of years ago. They also demonstrate the resilience of certain groups to catastrophic prehistoric events that led to the extinction of others, such as the dinosaurs.
1. Crocodile
Presently, there are over 20 species of crocodiles, including true crocodiles, alligators, caimans, and gharials. These extant crocodiles share a common ancestor that coexisted with dinosaurs during the Late Cretaceous period, approximately 80 million years ago (Mya).
This common ancestor bore a strong resemblance to today’s crocodiles, spending the majority of its time near water, basking in the sun, and hunting prey. Despite nearly 80 million years passing, modern crocodiles differ significantly from their ancient ancestors that first appeared around 235 million years ago in the late Triassic period.
Some extinct crocodile relatives, like Ritargosuchus, had a slim and agile build, hunting prey on land similar to wolves, while others, like the massive Sarcosuchus, reached lengths of up to 12 meters (about 40 feet) and preyed on animals by the riverbanks.
The diversity among early crocodile ancestors has led some scientists to argue against labeling them as “living fossils.” Although resembling prehistoric creatures, today’s crocodiles have evolved substantially from their ancestors and are likely to continue diversifying in response to climate change.
2. Horseshoe crab
Despite its crab-like name, the horseshoe crab is more closely related to spiders, ticks, and scorpions than to crabs. Its ancestors emerged during the Late Ordovician Period around 445 million years ago, while the modern group, Limuridae, appeared approximately 250 million years ago during the Early Triassic Period.
For the majority of the last 250 million years, horseshoe crabs have remained largely unchanged, displaying minimal anatomical alterations. A comparison between fossilized and living specimens would lead one to believe they are the same creature.
Their lifestyle has also endured; just like their ancestors, modern horseshoe crabs feed on small insects and mollusks at the murky bottom of the ocean.
These creatures have survived multiple mass extinctions, including the cataclysmic event caused by an asteroid that resulted in the extinction of dinosaurs. Their ability to endure extreme conditions, such as low oxygen levels, is believed to contribute to their resilience against extinction.
3. Wasp
Measuring at 1 cm (0.3 inches) in length, this small hornet is the sole surviving member of the Waspidae family, which boasted nearly 50 species around 165 million years ago during the mid-Jurassic period.
The modern-day wasp, Syntesis libocedrii, is native to the mountains of central California (USA) and British Columbia (Canada), whereas its ancestors resided across Eurasia. At that time, the Eurasian continent was closely connected to North America through a series of islands.
Wasps are known to lay eggs in freshly burned cedar wood. Upon hatching, the larvae emerge cylindrically, burrowing into the forest to feed and grow. They spend up to three years in this larval stage before maturing into adults. Their lifecycle is intricately tied to wildfires and can contribute to significant economic damage to cedar wood stocks.
4. Tuatara
As the diversity of dinosaurs flourished around 200 million years ago during the Early Jurassic Period, another group of scaly, lizard-like creatures began thriving. This group, the Sphenodontidae family, was once very diverse but is now represented by the single species, Sphenodon punctatus or tuatara.
Although tuataras bear resemblance to skinks with scaly skin, splayed limbs, and clawed digits, they do not share a direct relationship. Instead, they share a common ancestor that lived around 250 million years ago, shortly after the Great Extinction event.
Presently, tuataras inhabit several small uninhabited islands surrounding New Zealand’s North Island, coexisting with burrowing seabirds and utilizing their burrows for shelter.
The guano produced by these seabirds supports vast populations of centipedes, crickets, and snails, forming an essential ecosystem on these islands.
5. Platypus
Charles Darwin coined the term “living fossil” when discussing the semi-aquatic egg-laying mammal, the platypus, in his renowned book “On the Origin of Species.”
Unlike other mammals, platypuses lay eggs and possess a duck-like beak, along with venomous spines on the hind legs of males. They use their beaks filled with electroreceptors to navigate their habitat and hunt for prey.
Adult platypuses lack teeth, while babies are born with tiny teeth that are later absorbed into their beaks. These vestigial teeth have helped researchers trace the evolutionary lineage of platypuses.
Alongside their closest living relative, the echidna, platypuses represent the last survivors of monotremes, a group of early mammals that diverged from marsupials and placentals during the Middle Jurassic Period around 170 million years ago.
6. Lungfish
Slender and reminiscent of insects, lungfish belong to an ancient group that emerged over 410 million years ago during the early Devonian period. This era marked the rise of ray-finned and lobe-finned fish, to which lungfish belong.
Similar to other lobe-finned fish, lungfish have limb-like fins and lungs enabling them to breathe air, aiding in their survival during drought periods.
While lungfish have changed little over hundreds of millions of years, they are anything but “primitive.” Their lungs are intricate structures optimized for gas exchange, with most modern lungfish possessing two lungs, with the exception of the Australian lungfish having one.
Currently, six lungfish species exist, distributed across Africa, South America, and Australia, preferring freshwater habitats unlike their ancestors. During the Devonian period, lungfish thrived worldwide and coexisted with tetrapods, the ancestors of modern amphibians, reptiles, birds, and mammals.
7. Horsetail
Horsetail, an ancient plant resembling bamboo with tall hollow stems and horizontal bands, emerged around 185 million years ago, preceding the rise of flowering plants by 55 million years.
During the early Jurassic period, horsetails formed the undergrowth of dense forests, providing shelter and sustenance to various dinosaur species. Their hardy nature allows them to thrive globally, even being considered invasive in many regions including the UK.
coelacanth
The coelacanth, a prehistoric fish once believed to be extinct alongside dinosaurs 66 million years ago, was rediscovered in 1938 off the coast of South Africa.
Presently, only two coelacanth species are known, showcasing significant diversity during their prime that has led to the development of over 100 fossil species from the Early Devonian period to date.
The coelacanth’s evolutionary zenith occurred during the Mesozoic Era, between 252 million and 66 million years ago, where it exhibited a wide range of adaptations. These elusive fish reside in the deep waters of the western Indian Ocean, surfacing only at night to hunt small fish.
The coelacanth’s survival through multiple mass extinctions, including the asteroid event that wiped out dinosaurs, speaks to its remarkable resilience and adaptation to the deep-sea environment.
These living fossils have withstood catastrophic events and continue to thrive in their unique habitats, offering invaluable insights into the evolutionary history of Earth’s diverse ecosystems.
Source: www.sciencefocus.com
