At least a half dozen threads at Cryptomundo have been devoted to the analysis of an early 20th century postcard depicting a number of US Marines standing next to the carcass of an unknown aquatic animal next to the sea.
According to Cryptomundo editor Loren Coleman (in the thread linked above), "over 1,000,000 views of the Cryptomundo “Mystery Fish” photo have occurred."
Speculation has run rife over the past six or so months regarding this animal. Along with the absurd (if humourous) ("some type of snake that has been genetically altered with a eel" and "a cross between a fish and a crocodile") there have been scores of constructive insights.
This author, too, has frenetically contributed to the commentary debate.
The analysis extends well beyond the unknown critter, encompassing the men featured in the postcard and even the postcard itself.
Summarises Coleman: "Due to research on the type of postcard it is, there was a determination, thanks to Cryptomundo readers, that this specific item would have been produced between 1904-18".
In addressing the question of the postcard's date, this author found a most interesting forum titled "Nicaragua Living" showing a very similar beach scene from 1912. Says one contributer to the discussion there:
"This is one in a series of about 40 or so from 1912 ... There are 2 others from this series taken in San Juan Del Sur that I’ve seen. One shows the street (San Juan) and another was taken from another vantage point. Writing is part of the photo and was etched on the negative and contact sheet.
These cards were sold to US Marines who then sent them back to the States. Many of the cards in the series have Marines shown in the Postcards.
This series of cards comes with good story…
Civil strife took over Nicaragua in 1911 and the US Marines were sent in. They took over customs, reorginized finances, and kept a legion until 1925 only to have to return a year later. Eventually US Marines defeated these insurrectos in a time before CNN and video cameras.
There were insurrections and massacres in Leon and other towns. Insurrectos would come into towns or villages and murder anyone who supported the US business interests like fruit and such. Politicians were also targeted along with their families. This time was one of the lowest points in Nicarguan history.
Eventually Sandino consolidated this lot and became the defacto leader, however US Marines could never catch him."
So perhaps we now have a date very close to 1912, and a location near to San Juan Del Sur in Nicaragua.
At the same time, the type of critter remains unknown.
In attempting to address this question in one small way (as time is a limiting factor!), I have produced the following image analysis of the tail of the animal.
Closeup of the tail (click to enlarge)
Firstly, we have a closeup of the tail, enlarged 4x. Brightness, contrast and gamma levels have been adjusted to emphasise the delineation between various elements.
Note the distinction between the dorsal (top) edge of the animal and the background, which is a wall.
The dark portion of the wall is caused by the shadow of a person standing off-frame.
Note the dark colouration along the top half of the side of the animal's body. Note that it comes to an abrupt end (at right) whilst the dorsal surface continues further to the right.
We can conclude that the tail of the animal extends beyond the length of the dark colouration along the animal's side.
Closeup of the tail with overlay (click to enlarge)
In this version of the previous closeup, I have overlaid a number of lines to illustrate various points.
The red line shows the dorsal (top) surface of the animal. Note how far to the right I have extended this line.
The blue line shows the ventral (bottom) surface of the animal.
The yellow line runs approximately down the centre of the body markings. Note that it stops well before the dorsal (red) line.
The magenta (purple) line defines the caudal peduncle, which is the join between the tail fin and the body of the animal.
Finally, the three black lines depict what may be fin rays in the caudal (tail) fin.
I am assuming that the shape of the man's shadow is delineated by the fish's tail in the foreground. That is, I am assuming the man's shadow does not have some odd shape of its own to make it look like there is a tail in the foreground.
Secondly, I am assuming that the termination of the body markings occurs because of a caudal peduncle (join between the body and a tail).
Some would not be satisfied if I didn't point out that I am assuming the dark mark on the body is in fact due to colouration of the animal itself, and not some material on the animal such as smeared blood.
The options, as I see them are that this could be a shark, bony fish or mammal. In the case of shark and mammal, however, I believe it would not be common for body colouration to terminate in a way mimicing a bony fish's tail.
Based on the analysis of the tail region alone, I therefore conclude that this postcard depicts the carcass of a bony fish.
(As an aside, if I were to analyse the head in isolation, I would probably conclude this were a shark. That speculation will have to wait for another day!)