Sometimes we look at animals on this planet and can feel their ancestry in their eyes. From reptiles to birds, they carry the unspeakable weight of a millennia of ancestors, and we only know a fraction of their story.
While birds are technically the only living descendants of dinosaurs around today, there are plenty of animals on earth whose family trees actually extend beyond the Mesozoic Era when dinosaurs reigned supreme.
This guide traces those lineages back to when dinosaurs walked the earth to get a glimpse at where our modern monsters truly came from.
1. All Birds
Ostrich struts out on the plains – Image Credit: Thomas Fuhrmann, CC BY-SA 4.0 via Wikimedia Commons
You may have heard that chickens are the closest relative to the T. Rex., and those claims aren’t wrong. When comparing DNA to other animals, dinosaurs match most with birds like chickens and ostriches.
This is likely because birds are the only living descendants of dinosaurs around today, while other species on this list relate to creatures that predate dinosaurs. While the definition is constantly changing, the National Parks Service defines dinosaurs as “extinct animals with upright limbs that lived on land during the Mesozoic Era (252 to 66 million years ago”.
Within this definition, our modern birds relate back to a clade known as theropods, including the T. Rex. and smaller velociraptors. By definition, birds like ostriches actually meet the criteria for maniraptors, a group of theropods that have modifications that make flight strokes possible.
2. Crocodiles
While scientists are rapidly turning away from the reptilian image of dinosaurs, it’s the one that many grew up with. It’s still plausible, but creatures like crocodiles and alligators actually share ancestors with dinosaurs (rather than simply existing as descendants of them).
This means that the crocodiles we know today actually predate the dinosaurs that went extinct roughly 66 million years ago. During the Jurassic Period the world saw the evolution of smaller, terrestrial crocodiles that ran on two legs and ate mostly plants.
The end of the dinosaurs saw the first iteration of the modern crocodile, much smaller than the 50-to-70-foot long Aegisuchus and the bipedal Carnufex.
3. Sea Turtles
All seven sea turtle species can follow their family line back to ancient times, with the modern Leatherback Sea Turtle the only survivor of the Dermochelyidae family. While ancient relatives are much larger, those of the dinosaur era actually come pretty close.
Take Desmatochelys padillai, for example. Known as the oldest marine turtle, the complete skeleton of the shelled creature measures about 6.5 feet long (compared to about 6 feet for Leatherback Sea Turtles).
Despite their similar appearance, evidence shows Desmatochelys padillai laid hard-shelled eggs, although scientists are not sure why. This is how modern hard-shell turtles lay their eggs, but sea turtles lay soft-shelled eggs that can survive the drop into the egg chamber when they lay their eggs on the beach.
4. Sharks
Sharks predate dinosaurs with over 450 million known years of experience patrolling Earth’s seas. Before they had more competition, ancient sharks like Megalodon were much bigger (e.g. the size of a blue whale). It wasn’t until later that evolution began to favor smaller, more efficient packaging.
They also weren’t very active during the Mesozoic era. Sharks had to share the seas with marine reptiles like plesiosaurs and ichthyosaurs, so being apex predators wasn’t on their list of priorities.
The Hybodus, a now extinct creatures, was gradually replaced by modern sharks as the dinosaurs went extinct, but they had unique features like two rows of teeth (one sharp for fish and the other flat for mollusks) and a sharply bladed dorsal fin.
5. Horseshoe Crabs
Crustaceans like lobsters predate dinosaurs, but the horseshoe crab isn’t really a crustacean. Instead, it’s related to arachnids like spiders and scorpions, and therefore – trilobites.
While the first trilobites also predate dinosaurs by about 290 years, they are also some of the most popular fossils people come across in modern times. These marine arthropods went extinct at the end of the Permian era about 251 million years ago.
The vulnerable horseshoe crabs we know today actually evolved before dinosaurs did and managed to survive that major extinction event. Fossils we have of horseshoe crabs from the Jurassic era show they’ve barely changed, settling on what they considered the perfect form many millennia ago.
6. Bees
We aren’t considering most prehistoric insects for this list, but the idea that bees survived the great extinction event over 60 million years ago only to be done in by habitat loss now is bleak. Hopefully, we will never have to see a world without bees.
This isn’t the first time they’ve been at risk, but ancient apiformes have always managed to pull through. Scientists theorize the bees we see today come from a sphecid ancestor that existed during the early Cretaceous period.
How do we know this? A few unlucky bees got trapped while collecting resin from the trees, and the fossilized amber has carried them through the year to modern research.
This just goes to show that these creatures existed well before our conception of history, and they’ve persevered through some major extinction events.
