The ancient world was full of massive and fearsome creatures, but none achieved such fame as dinosaurs. In fact, many of these lesser-known animals are mistakenly classified as T. rex, stegosaurus, And Brontosauruswith whom they have only a distant relationship.
When English anatomist Sir Richard Owen coined the word “dinosaur” in 1842, its provocative literal translation—“terrible lizard”—captured the public imagination. Soon enough, says Daniel Barta, a dinosaur anatomist at Oklahoma State University, “it became a catch-all for anything that was large and reptilian and lived in prehistoric times.”
However, despite the external similarity, many scaly animals with sharp teeth were evolutionarily and anatomically different from each other. These are some of the groups that are most often confused with dinosaurs.
Pterosaurs: flying reptiles, not dinosaurs
Quetzalcoatlus
(Image credit: Kamomin/Shutterstock)
This is perhaps the most understandable mistake. Pterodactyls and other flying reptiles were the closest relatives of dinosaurs, and their time on Earth coincided almost exactly. Their common ancestors were bipedal and used two legs to move. pterosaurs and dinosaurs are separate from other reptiles.
However, several defining features allow paleontologists to easily tell them apart. First, there were no flying dinosaurs, although some (eg. Archeopteryx And Microraptor) could glide; their wing structure was fundamentally different from that of pterosaurs.
Dinosaurs also had an open hip joint and a long crest on the humerus, or upper arm bone, that no other reptile has.
Pseudosuchians: ancient crocodiles, not dinosaurs
(Image credit: AlexanderLS/Shutterstock)
(Image credit: AlexanderLS/Shutterstock)
Dinosaurs and pterosaurs (along with modern birds) make up half of the taxonomic group of archosaurs. The other half are the pseudosuchians, a diverse lineage of crocodile-like reptiles that first appeared around the same time as their dinosaur cousins and now outlive them by 65 million years.
It is not surprising that, given their common archosaur ancestry, some pseudosuchians are very dinosaur-like. It takes a trained eye to discern a key difference: the placement of the ankle joint. Dinosaurs have a simple hinged ankle joint, while crocodiles and their ancient ancestors have a more complex joint that allows the ankle to rotate.
Of course, this would be easy for the average museum visitor to miss. Even experts can be misled if skeletons are not examined carefully. “We have to be very careful as anatomists,” Bartha says, “in terms of taking the whole skeleton into account and not being distracted by convergent similarities.”
Plesiosaurs, Ichthyosaurs, Mosasaurs: sea monsters
PINES?
(Image credit: Bilardo/Shutterstock)
Dinosaurs may have ruled the prehistoric continents, but their territory more or less ended at the coastline. The depths of the ocean belonged to marine reptiles, which, although equally majestic and formidable, were creatures of an entirely different kind.
Long-necked PINTLEAS, The dolphin-like ichthyosaurs and mosasaurs, which are most closely related to lizards and snakes, evolved from land reptiles. But their body plan changed significantly: streamlined shapes and fins appeared instead of limbs. They were well adapted to dominate the underwater world; on the contrary, not a single dinosaur (with possible exception to Spinosaurus) was built for an aquatic lifestyle.
Birds: dinosaurs of the last days
sandhill crane
(Image credit: Kami Neumann/Shutterstock)
We've become so accustomed to birds that it's easy to forget that they are the dinosaurs' closest living relatives—in fact, their only living descendants.
There are three main groups of dinosaurs: ornithischians, such as Stegosaurus; sauropods such as Brontosaurus; and theropods such as T. rex. Early paleontologists insisted that birds could not be related to either of these groups because of one important anatomical detail: birds have a wishbone (a bifurcated bone between the neck and thorax), which was clearly not present in known dinosaur fossils.
Besides this was present in some theropods, as later researchers discovered. This was a decisive moment that showed where birds truly belonged on the tree of life. It turns out, as Bartha puts it, “there's not much that distinguishes what we call a bird from a theropod. It's just one branch—a very large branch—of the theropod lineage.”
Read more: Dimetrodon, a giant sail-finned predator, was more related to mammals than dinosaurs
Article sources
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- This article references information from Daniel Bartha, a dinosaur anatomist at Oklahoma State University.
