#transitional fossils

Anchiornis

Age: 160 million years

Location: Liaoning, China

Transitional form of: Dinosaurs to birds.

Anchiornis is at the point in the transition where it’s hard to decide whether it falls in the bird or dinosaur side of the fence:

It has wings, but they’re symmetrical and rounded, probably not used for flight but instead are used to keep warm, for mating displays, and gliding.

Its legs are more like that of other-bird-like dinos, but like birds and unlike bird-like dinos, Anchiornis had arms nearly the same length as the hind legs.

Its spine connects at the back of the skull instead of at the base like in birds, but it had flexible wrists, which is more a bird thing.

It had a mostly bony tail, but also had primary and secondary contour feathers on both arms, legs, toes, and wrists.

Don’t underestimate wilful ignorance, the Dunning-Kruger Effect, the need to believe things based on emotion and comfort - remembering they already hold a belief in supernatural magic that is, by definition, irrational - and a smug satisfaction that science cannot produce “transitional fossils” that correspond with their demand.

And being correct, but without any comprehension of why.

Puijila

Lived: About 21 to 24 million years ago

Transitional form of: Earliest known form of seals

Discovered: 2009

You might note that this weirdo looks more like the lovechild of an otter and a weasel.

Being a very early form of seal, it has notably very few adaptations for aquatic life.

So how do we know it’s an early seal?

Rodhocetus 

Lived circa 45 million years ago.

Discovered: 1994

Location: Pakistan

Transitional form of: Whales becoming waterbound.

We have two partial skeletons which together give us a full picture of this early whale.

As you can see in the above representation by Pavel Riha, its limbs were shortening but its toes were very long, indicating they were probably webbed and paddle-like. The overall look of their limbs is already remarkably similar to that of modern whales’ fins:

But the real key feature of their transitional state I wanna bring to your attention though, is... their nostrils. 

Most animals with a muzzle have their nostrils at the front of their muzzle. 

The ones that don’t tend to be water-dwellers like crocs, who tend to have their nostrils slightly further up the muzzle so they don’t have to stick their whole head out of the water to breathe to avoid giving away their location.

Dimetrodon

Year discovered: 1877

Transitional form of: Reptile to mammal

Dimetrodon is probably the most famous of the synapsids (commonly referred to as “mammal-like reptiles”).

It looks an awful lot like a reptile, perhaps even like an early dinosaur, but it was anything but.

Like reptiles, it was cold-blooded, and dependent on an outer heat source, which is where the sail came into play -- when they were cold they could turn their sails to the sun and soak up the heat (they may have also have had secondary uses of helping to scare away predators and/or to attract a mate). They also had no secondary palate, a trait found in modern mammals. 

Another primitive trait it had was an awkward-looking sprawling gait (not unlike a croc’s gait on land).

But you know what game-changing trait it did have that’s like a bright neon sign that it was our ancestor?

Multiple kinds of teeth.

That’s a very mammalian trait. 

Panderichthys

^ Had very flexible and powerful fins. Based on the shape and size of its spiracles, it’s very likely it used its lungs quite a bit for breathing. It also notably had lost the third set of fins common in a lot of fish.

Tiktaalik

^ Had strong fleshy fins that included bony bits that would become elbows in later animals and could be used to flop/drag awkwardly on land not unlike how mudskippers do today.

^ Modern giant mudskipper

Elginerpeton

^ Had shoulderblades and webbed limbs closer to feet than fins.

Acanthostega

First known animal with toes rather than fins.

Ichthyostega

^ Had toes and likely spent much time on land but still had gills and a tail with fin rays (a feature found in fishtails).

Hynerpeton

^ Had toes and shoulders that suggest it was a powerful walker.

Tulerpeton

^ Had paddle-like toes and, most crucially, did not have gills in adulthood, making it the first known true amphibian.

Pederpes