Taxidermy of a black rhinoceros (Diceros bicornis) from the Dublin Natural History Museum. There was a notice next to the specimen apologising for the appearance of the rhinoceros due to the lack of horns; there is a growing market for them to be used for traditional medicines despite the benefits being scientifically disproved time and time again. The horns are often poached from the critically endangered wild rhinoceros but recently there has been an increase in zoo populations as well as museum specimens having their horns stolen from them. This taxidermy was a reminder that their horns, made from the same proteins found in our own hair and fingernails, are highly sought after at any cost.
For millions of years life thrived in the abyssal plains and shallow seas, yet during this time the continental surface was barren and bleak, except for the few pioneering plants slowly creeping their way onto the land. As plant life got a foothold on the deserted surface rocks they began to transform the landscape waiting for animal life to follow.
The transition from fish to tetrapod is one of the most important events in life’s history and we are lucky enough to have most of the puzzle on how it happened complete…
Eusthenopteron… Eusthenopteron was a late member of a now extinct group of lobe-finned fishes and it existed during the Late Devonian, around 385 million years ago. The fishes pectoral and pelvic fins had a fleshy anterior part and very robust bones, the fore-fins exhibit a distinct radius, humerus and ulna and the pectoral fins have a femur, tibia and fibula showing that this 6 foot long fish was well on the way to developing primitive legs.
Pandericthys… This was another lobe-finned fish from the late Devonian (378 million years ago). Panderichtys begins to show a more developed, longer humerus as well as primitive digits. Its tail is also more like the early tetrapod tails than the caudal fins of other lobe-finned fishes. They have also lost their intracranial joint to their skull (but it is still present), rather than it being external to the skull like in other lobe-finned fishes.
Tiktaalik… Tiktaalik existed 375 million years ago and is still considered to be a lobe-finned fish although it shows even more tetrapod-like features than Panderichthys. The fleshy fins have primitive wrist bones and digits. They also have spiracles on top of their skull which may be possible indicators of primitive lungs. The humeral bones have large muscle scars suggesting that these appendages were highly mobile and the joints were capable of rotation, enabling Tiktaalik to have some sort of propulsion through the water. The eyes of Tiktaalik has moved further on top of a flatter skull and so it likely lived in a swampy, shallow water environment but was not yet completely terrestrial.
Acanthostega… Acanthostega existed 365 million years ago and is the first to have distinct limbs, each of which has digits. However, the front legs were unable to bend forwards at the elbow and so it is unlikely that the animal was terrestrial as it was unable to move itself into weight-bearing positions.
Icthyostega was likely the first true tetrapod and existed between 365 and 360 million years ago. It has 4 robust limbs (with an unknown number of digits) and lungs which were still used in conjunction with gills. Icthyostega had wide overlapping ribs which likely helped to protect the lungs under its own weight without the buoyancy of water. Icthyostega has powerful limbs enabling it to haul itself onto the land but would still have spent much of its time in shallow, swampy water.
When I was in high school, I learned that the definition of a species is two animals that can interbreed and give birth to fertile offspring. Like, dogs are all one species because they technically can interbreed (although, functionally, watching a Great Dane and a Chihuahua work it out might be… difficult), but donkeys and horses are different because – although they can mate and give birth – their offspring (mules) are sterile.
At the time, I thought – well, that’s pretty straight forward. Thanks, scientists, for solving yet another mystery of life.
Fast forward to a few months ago when I asked one of my taxonomist colleagues to define a ‘species’ for me. The result of that (many hour-long) conversation inspired this video. Turns out, the answer isn’t, at all, straight-forward.
Pictures I took in the London Natural History Museum. Love that place, man. So many skeletons and great taxidermy specimens (though some of them could really use some airbrushing). I especially loved their thylacine, since thylacines are my favourite animals. And they had tons of deer, which I can always appreciate.