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Specimen of the Week: Week Eighty-Six

By Emma-Louise Nicholls, on 3 June 2013

Scary MonkeyThe decision for this week’s specimen of the week was an exciting adventure through the paths of taxonomic mishaps and similar looking un(closely)related animals. I chose (actually the curator suggested) a particular species and so off I went to find what specimens we had of said creature. Confusingly, the two specimens I found looked not a great deal alike (upon close inspection with the eye and thought process of a super duper scientist such as myself. Uh hum.) A wee while of interwebbing later I came to an interesting conclusion. So excited was I, by the chance to do real live comparative anatomy, that I wanted to share the experience with you. Therefore, this week you get TWO specimens. Oh yes. This week’s Specimens of the Week are…

 

**Some kinds of large-snouted fish** (Nooooo, I’m not giving it away that easily. Read on my intrepid literary explorer…)

 

1) A long time ago in an ocean far far away…
There were two fish. They will eventually turn out in our story to be different species so actually the correct vernacular here would be ‘There were two fishes’. Some things happened, including their deaths, and somehow the bill of one and the skull and mandible of the other, came to dock at the Grant Museum of Zoology. They were labelled ‘swordfish’ by a human of long ago, and there they sat, undisturbed and undiscovered, in the cupboard under a display case until…

 

The tips of the two billfish rostrums (Istiophoridae family) at the Grant Museum of Zoology. LDUCZ-V328

The tips of the two billfish rostrums (Istiophoridae
family) at the Grant Museum of Zoology.
LDUCZ-V328

2) Along came a Museum Assistant who wanted to write a blog about swordfish and so got these two specimens out for a better look. After some up-close-and-personal-time with them, the MA deducted that they could not be of the same birth mother. Primary clues were 1) one was wide and flat whilst the other was thin and rounded, and 2) one was very rough underneath whilst the other was smooth all over.

 

3) Taxonomicon was consulted and some subsequent fish sites were perused. Turns out, swordfish belong to the Suborder (a high-end level in animal classification) Scombroidei, which is divided into five families including the Xiphiidae and the Istiophoridae. Both of which will become important very shortly. These two families are collectively (and unhelpfully) known in the common tongue as billfishes, due not to their unrivaled ability to pay their expenses each month, but to their most prominent morphological feature- the enlarged rostrum (nose, snout, or indeed ‘bill’). I say ‘unhelpfully’ as members of the family Istiophoridae are also known as billfishes at the exclusion of other familes. Anyway, clear it was, that our specimens were within this Suborder of fishes due to their elongated bills, but to which species do they belong?

 

4) The Xiphidae (swordfish) have a single morphology of rostrum and apparently, a single species; Xiphias gladius. Aka the swordfish. The most useful point (HAH) used to establish that you have a swordfish’s rostrum on your hands is that it will be flat. It is also edentulous (a superb and posh word for ‘toothless’, or ‘smooth-skinned’ in this particular situation) and blunt tipped. This describes the first specimen in our pool of unidentified fish bills perfectly. Identification job one- DONE.

 

The Billfish rostrum at the Grant Museum of Zoology LDUCZ-V328

The Billfish rostrum at the Grant Museum of Zoology.
LDUCZ-V328

5) Having none of the above features, the second specimen was clearly not a swordfish and thus should be within the Istiophoridae. Identifying members of the Istiophoridae (billfish) down to species level is a way more intense exercise as they are ‘XXX’ more diverse (insert positive or negative adverb depending on whether you enjoy complicated comparative anatomy. Which- who doesn’t.) To establish your rostrum belongs to a billfish, check that it is rounded in cross-section, that it is denticulated (covered in tiny tooth-like structures; like shark’s skin) (ergo; cool) and with a pointed tip. With your nose up to the screen looking for these features on the tiny compressed image of it here, you will undoubtedly agree that our second specimen is clearly a billfish, yes? Getting it down to which of the eleven species it is however, would unfortunately take longer than the designated hour that I am allocated in which to write Specimen of the Week. However, all suggestions are welcome.

 

6) Bonus point. Unfortunately it seems that anything with a long and pointy snout is classified by fish-noobs as a swordfish. So knowing now as you do, how to tell your swordfish from your billfish, what do we think of this poor creature?

 


Emma-Louise Nicholls is the Museum Assistant at the Grant Museum of Zoology

One Response to “Specimen of the Week: Week Eighty-Six”

  • 1
    Nath wrote on 3 February 2019:

    I also have one of these billfsh type skulls.. Want is it?

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