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Title: Living Fossils: Critters That Outlived the Dinosaurs

In the grand tapestry of life on Earth, not a single individual creature that lived contemporaneously with dinosaurs, which roamed the planet between 246 and 66 million years ago, is still alive today. However, some species that exist now have ancestors with striking similarities to those ancient beasts. These so-called "living fossils" are not unchanged relics from the past. Their DNA has evolved and morphed over countless generations. Yet, they offer fascinating glimpses into life during the dinosaur era. Let’s explore seven such species that have stood the test of time.

1. Crocodilians (Crocodiles, Alligators, Caimans, Gharials)

With over two dozen species alive today, crocodilians trace their lineage back to a common ancestor that coexisted with dinosaurs in the late Cretaceous period around 80 million years ago. Their ancient forebears resembled modern crocodilians, spending most of their time lounging in or near water, basking in the sun, and waiting for prey. However, today’s crocodilians are vastly different from their earliest predecessors, which appeared in the Triassic period about 235 million years ago. The extinct relatives were much more diverse than their modern descendants.

2. Horseshoe Crabs (Limulidae)

Despite their name, horseshoe crabs are more closely related to spiders, mites, and scorpions than true crabs. Their lineage began in the Ordovician period around 445 million years ago, with the modern Limulidae family emerging in the early Triassic period about 250 million years ago. Since then, horseshoe crabs have experienced little anatomical change, a state known as morphologic stasis. They continue to dwell on ocean bottoms, feeding on worms and small mollusks, just like their ancient ancestors.

Horseshoe crabs have avoided several mass extinctions, including the asteroid impact that doomed the dinosaurs. Their tolerance for harsh conditions, such as low oxygen levels, likely contributes to their resilience.

3. Cedar Tree Pitcher Plant Mites (Syntexis libocedrii)

This tiny, 1 cm-long (0.3 in) mite is the sole survivor of a family that boasted nearly 50 species during the mid-Jurassic period around 165 million years ago. Endemic to the central mountains of California (USA) and British Columbia (Canada), its ancestors once roamed Eurasia. Cedar tree pitcher plant mites lay their eggs in recently burned cedar wood. After hatching, the larvae burrow into the wood, feeding and maturing over several years before emerging as adults and living out their brief remaining days.

4. Tuatara (Sphenodon punctatus)

As dinosaurs diversified during the early Jurassic period around 200 million years ago, so did a group of lizard-like reptiles called Sphenodontidae. Today, only one tuatara species remains, found on several small, uninhabited islands surrounding New Zealand’s North Island. Tuataras share a common ancestor with other reptiles that lived around 250 million years ago, following the devastating "Great Dying" extinction event.

Like some lizards, tuataras possess a third, parietal eye on top of their heads, used to regulate circadian rhythms and potentially help modulate body temperature.

5. Platypus (Ornithorhynchus anatinus)

Charles Darwin himself coined the term "living fossil" when describing the platypus in his groundbreaking work, On the Origin of Species. Unlike other mammals, platypuses lay eggs, have beak-like mouths, and possess venomous spurs on their hind legs. They use their electroreceptors-packed bills to detect prey movements in murky waters, then sieve riverbed sediment to consume small animals like crayfish and insects.

Platypuses are the last surviving members of the egg-laying mammal order Monotremata, which diverged from other mammals around 170 million years ago during the Jurassic period.

6. Lungfish (Dipnoi)

With origins tracing back to the early Devonian period over 410 million years ago, lungfish are one of Earth’s oldest and most iconic living fossils. Six extant species inhabit freshwater habitats across Africa, South America, and Australia. Despite their ancient lineage, lungfish are not primitive; their unique multi-chambered lungs allow them to extract oxygen more efficiently than most other fish. Their ancestors coexisted with the early tetrapods that eventually conquered land.

7. Coelacanths (Latimeria chalumnae and L. menadoensis)

Once believed extinct alongside dinosaurs 66 million years ago, the coelacanth was rediscovered in 1938 off South Africa’s eastern coast. Over 100 extinct coelacanth species have been identified in fossil records, dating back to the early Devonian period around 409 million years ago. Today, only two species survive, inhabiting deepwater locations in the western Indian Ocean.

Coelacanths avoided multiple mass extinctions by adapting to stable, deep-sea environments. They Hunt small fish at night, emerging from their aquatic hiding places like their ancient forebears.

These remarkable creatures have withstood the test of time, outliving dinosaurs and surviving numerous extinction events. Their enduring presence serves as a testament to life’s incredible adaptability and resilience.