They're just as old: in fact, they pre-date dinosaurs, mammals and insects!
- Life is believed to have begun around 3.8 billion years ago
- Bacteria life evolved to cells around 580 million years ago
- Fish popped up around 510 million years ago
- And then came sharks, somewhere between 460-425 million years ago (disagreements with the exact time still exists between paleontologists)
So, yeah. I'd like to think that this is a pretty long time, especially when you realize dinosaurs didn't claim the terrestrial environment as their home until around 230 million years ago (around the same time mammals scurried about; they were much smaller back then). With modern humans dating back around 60,000 years and civilizations being recorded only 5,000 years back, sharks are old. Very, very, very old.
Shark teeth are our primary source of knowledge about ancient sharks. Fossilized shark dermal denticles and other body parts have also been found, and these help paint the whole picture (such as species and size). Nothing beyond that is known, though.
"So how far back is the oldest fossil?"
The oldest fossil of a "shark" comes from fossilized skin, dating back to 455 million years ago during the Ordovician Period. The cool thing about this fossil was that they were found in Colorado! The reason shark is in quotes is because paleontologists disagree on whether this is actually sharky enough to be considered as such. Scales that are 100% agreed upon to be shark have been found, dating back to 420 million years ago (Silurian Period); scales from this period have been discovered in Siberia and Mongolia. In 2003, paleontologists found a 409 million year old fossil of a small, primitive species, Doliodus problematicus, in New Brunswick, Canada. The oldest shark teeth, from the Devonian Period, are about 400 million years old, found in Europe. A fossil that includes a brain case, dating back to 380 million years old (maybe a xenacanth) was found in Australia. Other similar remains were discovered in Antarctica and Saudi Arabia.
Sharks have survived all five mass extinctions, all occurring within the past 439 million years (where some wiped 95% of living animals). For those who survived, it allowed them to flourish in new habitats or new roles. That an animal survived all five of these catastrophes is a testament to their hardiness as well as flexibility (both literally and not).
To read and see more about ancient sharks, visit here and here.
An early shark may be such a lineage is Mcmurdodus, which appeared about 390 million years ago. Most of the early sharks of this period were coastal predators. It wasn't until about 100 million years ago, around the middle of the Cretaceous period, that sharks began to forage off-shore. At the end of this period, around 65 million years ago, another mass extinction occurred, killing our dinosaurs. The sharks who survived this include the modern sharks of today (if you don't think that's cool, you're wrong).
Which are some of the oldest modern sharks? The cow sharks (both the sixgill and sevengill), and frilled sharks. The cow sharks are about 190 million-years old, being spotted during the early Jurassic. The frilled shark first popped up at around 95 million years ago. Both of these animals are deep-sea dwellers (though sevengills are known to roam kelp beds in South Africa).
During the Tertiary Period (65-35 million years ago), several orders went from being predators... to filter feeding plankton.
"I'm sorry, what?"
Yup. The carpet shark lineage (order Orectolobiformes) is what helped pave the way for the modern Whale Shark (Rhincodon typus), while two lineages of Mackerel shark (Lamniformes) paved the way for the Basking (Cetorhinus maximus) and Megamouth (Megachasma pelagios) sharks.
First lets talk about Lamnoids. Lamnoids (order Lamniformes) include some of the best known sharks, like great white sharks, threshers and goblin sharks. Megalodon (Carcharocles megalodon) is an extinct shark- no matter what Discovery Channel/Shark Week says- whose total size has been heavily debated. Some say this shark was, at a maximum, 15 m (around 50 ft) long, while others say even larger. Their teeth can measure up to 17.78 cm (7 in)-- that's a big shark!
Megalodon probably evolved from Cretolamna appendiculata, which was around 100-60 million years ago. The fossils of Megalodon are only around about 16 million years ago to around 1.6 million years ago, when they croaked.
Keep that in mind.
Some say if it was from Megalodon, then the common ancestor would be Cretolamna appendiculata. Opposing theories state great white teeth are the likes of the mako, and are then traced to Isurus hastalis, whose teeth were found in Oligocene from around 30 million years ago. Whatever the theory, the modern white shark we see splayed across most movies, Carcharodon carcharias, made its debut about 11 million years ago.
"So what are the newest sharks?"
Hammerheads (family Sphyrnidae, order Carcharhiniformes) are amongst the newest of modern sharks. Their teeth appear in the mid-to-late Eocene deposits, from about 50- 35 million years ago.
"What does the future look like, for sharks, then?"
With slow reproduction rates, small quantities of pups living to adulthood and high rates of mortality, these ancient beasts may be facing their greatest challenge thus far. Sadly, unless we do something to help these animals out, we'll be the cause for the fall of these mighty predators.