seen from United States
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seen from United States
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seen from India
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Transitional Fossil Time!
Mammalodon
An ancient whale that has all the hallmark features of a baleen whale (loosely sutured bones in the snout, a broad and flat roof of the mouth, and an unjointed mandibular symphysis between the two halves of the jawbone)... Except it doesn’t have any baleen.
Blorbo from my Late Devonian Period
Random Fact #3,011
The oldest known example of a Turtle™ is Odontochelys.
Although it overall even looks fairly turtle-like, this critter was still very clearly in the early to mid stages of becoming turtles as we think of them. Despite having a plethora of turtle features (I mean, look at it), it was still missing a key trait its modern descendants all have: a shell.
Or rather, it had started to evolve a shell, but it only had part of its bottom section so far. It also lacked the ability to extend and retract its neck like modern turtles do.
Transitional Fossil Time!
Pezosiren portelli
Age: 50 million years old
Found in: Jamaica
Transitional form of: Sea cows becoming waterbound.
The earliest known ancestor of sea cows, it had 4 legs it used to walk on land, but it also had heavy ribs that could indicate it lived part time in water (not unlike a hippo).
We know it’s a sea cow despite it being leggy because apart from the legs, its body plan is basically that of a modern sea cow.
Transitional Fossil Time!
Tulerpeton
A large animal with paddle-like six-toed feet. Despite its many aquatic adaptations (nostrils at the top of the muzle, paddled feet, paddle-like tail, etc) it did not have gills in adulthood, and is thus the earliest labyrinthodont (amphibian) known to depend entirely on breathing with its lungs.
Modern Day Transitional Species
Mudskippers
Meet the mudskippers.
They’re 100% fish.
They’re weird fish, but they definitely be fish.
Some are tiny,
Some are big (the giant mudskipper, seen below, can reach up to 27 cm),
But they’re very solidly classified as fish.
They have gills and everything.
They also happen to have an ability that makes them rather fish-out-of-water among their fishy brethren:
They can breathe air.
Which means they’re able to flop awkwardly around on land much like how sea turtles can.
Now, this isn’t an entirely unique mudskipper feature.
There are a few other fish (lungfish, some kinds of gobies, etc) that are also able to breathe air (usually because they live in oxygen-poor environments).
The thing that sets mudskippers apart is what they do when the tide comes in.
Like any sensible fish would naturally do when faced with rising water levels...
They climb a tree.
...Obviously.
(No, really.)
They live 90% of their lives on land and lay their eggs in burrows without any water.
But they’re fish.
Transitional Fossil Equivalent: Tiktaalik
Note: Mudskippers and Tiktaalik aren’t necessarily related; animals that share the same niche or similar niches tend to have similar or even nearly identical body plans because what works best in that niche will inevitably be the most successful.
Transitional Fossil Time!
Prorastomus
Age: 40 million years.
Location Found: Jamaica
Year Discovered: 1855
Transitional form of: Manatees becoming aquatic.
Had distinctive rib shape found in manatees, but still had paws instead of flippers and the shape of its head indicates it lived a significant portion of its life on land.
Happy Darwin Day!
