Friday mystery object #320

I hope everyone had a lovely Christmas break!

This week I have another specimen from the Dead Zoo to identify – this one has an identification already, but the taxonomy is rather archaic and I think that once you’ve investigated the modern version of the name, you’ll realise that it’s wrong.

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Skull length = 121mm

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So, any idea what this name should actually be and, more importantly, what the identification actually is?

As always, you can put your thoughts, questions and suggestions in the comments box below – have fun!

Friday mystery object #319 answer

Last week I gave you this unidentified skull from the Dead Zoo to have a go at identifying:

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It seems that everyone recognised this as the skull of a gull straightaway – the scars from the salt-glands on the top of the head and the shape of the bill combined to make it a bit of a give-away.

However, working out which species of gull is a bit more tricky, since many are remarkably similar in morphology, making size an important factor for consideration (I’ve talked about this before).

Now size is always a somewhat tricky thing to use for identification, for a variety of reasons. One is that there may be an overlap in size between species, another is that there will often be sexual dimorphism within a species that means you can’t just compare the length against another specimen of a species without considering sex. Then of course there’s age – if it’s not fully grown, it’s going to be smaller. Of course you also have to consider whether the bill sheath is present or absent, as this will add a few millimetres.

On top of all these issues, there’s the problem of how you actually measure the length in the first place. This is something I’ve researched in the past (link to pdf) and it’s a more significant problem than you might think. For example, when looking at the image I originally provided for the mystery object, it looks like the skull measures around 125mm, but if I chop the scale bar from the image, reduce the transparency to 50% and lay it directly over the centreline of the image of the specimen, it turns out to be around 128mm.

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Length is apparently 128mm

Add to this the fact that in the original image you can see a shadow under the scale bar, it becomes clear that the scale is somewhat elevated. This is because I raise the scale to be near the vertical midline of the specimen, to help keep everything in focus and limit the effect of parallax error. Normally this is good, because it allows a more accurate estimation of the length of a 3D specimen with a longest axis near the vertical midline, but in this case the longest part of the specimen is actually at the lowest part of the skull, so the elevated scale will make it look slightly shorter than it really is (due to the parallax error I was hoping to avoid…). This means that the specimen is probably closer to 129mm or 130mm in length.

With this in mind, the discussion about the lengths of various gull skulls between Wouter van Gestle (of Skullsite fame), Ric, Tim Dixon, Richard Lawrence, Gerard van den Brink and jennifermacaire needs to be reconsidered.

Richard Lawrence reported skull lengths for a variety of gulls as follows:

6x GBBG: 129 to 141 mm
2x LBBG: 117 mm
6x HG: 111 to 117mm
9x YLG: 111 to 126 mm ( larger with beak sheath though so would be smaller without).

So factoring in a length of 129-130mm for the mystery object it seems to fit well into the range for the Great Black-backed Gull Larus marinus Linnaeus, 1758. So well done to everyone who went for GBBG – this does seem most likely to be a skull from the largest gull species.

Great Black-backed Gull by Andreas Trepte, 2010

Great Black-backed Gull by Andreas Trepte, 2010

Friday mystery object #318 answer

Last week I gave you this bird skull from the Dead Zoo in Dublin to have a go at identifying:

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It’s a fairly distinctive looking specimen with that massive bill, immediately narrowing down the possible families to two likely contenders – the Toucans (Ramphastidae) or the Hornbills (Bucerotidae).

On closer examination it lacks the serrated bill margins and remarkably long medial (in this case that means ‘towards the midline of the skull’) process of the quadrate bone (a part of the jaw in birds that I’ve blogged about before) that you see in Toucans. So, it’s a Hornbill – as everyone correctly spotted in the comments – but then we have the question of the species.

There are around 60 Hornbill species, with most of them sporting quite distinctive casques which make them quite identifiable (I’ve blogged about several before):

Ceratogymna atrata skull

Black Hornbill Ceratogymna atrata

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Great Hornbill Buceros bicornis

Bucorvus abyssinicus (Boddaert, 1783) sectioned skull

Northern Ground-hornbill Bucorvus abyssinicus

However, this specimen seems to be lacking a casque. This could be due to a few reasons. There are some casqueless species, such as the Sri Lanka Grey Hornbill, it could be a young female adult from a small casqued species with sexual dimorphism in casque development, or it could be a young juvenile from a species that has a small casque that grows as the animal matures.

Assuming it’s one of these, it’s easy to check the few casqueless species by looking at the overall bill shape, the position of the nares (nostrils) relative to the orbits (eye sockets) and checking the structure of the jugal and quadratojugal (the thin bones on the side of the skull under the orbit) – this last only if you can find a reliable skull image for comparison.

Using Skullsite and images on the internet it’s time-consuming, but straightforward to rule out a lot of possibilities, since most Hornbills have a fairly robust jugal/quadratojugal and nares located much further away from the orbit than you see in the mystery specimen. In fact the only Hornbills with a similar nares/orbit position and gracile (skinny) jugal/quadratojugal and in the right size range (that I was able to find) were in the genus Rhyticeros L. Reichenbach, 1849.

Unfortunately I’ve not found good skull images of juveniles for all of the species to make a final comparison and you can’t just compare the skull of a juvenile with an adult and expect to see the same configuration and development of features, as there’s still growth to happen (something else I’ve talked about before).

So based on the information it looks like jennifermacaire was the closest with her suggestion of Wreathed Hornbill, although I’m leaning slightly more towards the Papuan Hornbill Rhyticeros plicatus (J.R.Forster, 1781).

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Hope you enjoyed the challenge!

Friday mystery object #317 answer

Last week I gave you this unidentified bird skull from the Dead Zoo to try your hand at identifying:

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It seems that everyone recognised it as being from a charadriiform, and one of the waders at that. The first response was from Chris, who made reference to Lewis Carroll’s poem the Walrus and the Carpenter in which the eponymous characters eat an enormous quantity of oysters – hinting that this is an Oystercatcher.

There were some other suggestions that it could be from one of the birds in the genus Tringa, which includes the ‘shanks’ (Redshank, Greenshank, etc.), but the morphology fits one of the Oystercatchers better – in particular that weird constriction about halfway down the mandible when you look at the skull in profile.

This mandibular ‘waist’ is quite unusual and it doesn’t even seem to occur strongly in all of the Oystercatchers, which helps narrow down the likely species within the genus Haematopus, especially when you factor in things like the relative bill proportions, although you have to be careful doing this as there is some sexual dimorphism in the shape of the bill, with the females’ being longer.

The three closest species are the American Oystercatcher, the Sooty Oystercatcher and the Blackish Oystercatcher, but unfortunately I’ve not been able to find good reference skulls all of these species to be able to look for any distinguishing cranial characters. Based on bill morphology I’m leaning towards this being the skull of the American Oystercatcher, Haematopus palliatus Temminck, 1820.

American Oystercatcher by DonaldRMiller, 2010

American Oystercatcher by DonaldRMiller, 2010

My next step will be to check through our collections to see if we have comparative material to check the identification (once I get some time – a sadly rare commodity). If I can’t confirm I’ll just stick with Haematopus sp. on the label.

If you’re not familiar with Oystercatchers, they walk along the tideline either prying or breaking open bivalves. In my experience they seem more fond of mussels than oysters, but what do I know?

Another mystery next week!

Friday mystery object #317

For this week’s mystery object I’ve decided to stick with my favourite subject of skulls. This time it’s a bird from the Dead Zoo’s collection, that was in a drawer labelled “Unidentified” – let’s fix that!

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Any idea what species this skull belonged to? I have my suspicions, but I’d love to hear what you think.

As always, you can leave your clues, questions and suggestions in the comments section below. Have fun!