Friday mystery object #67 answer

On Friday I gave you this object to identify:

As I suspected, you all worked out that it is the skull of a turtle, so well done all and particularly Jake, who got there first.

Turtle skulls are quite characteristic, in that they have a bill with no teeth and they have no openings apart from the obvious ones like the eye sockets and nose. Most other tetrapods have several openings in their skulls, something that is diagnostic for, and sometime provides the name for, major groups like the main ‘reptile’ group the Diapsida. This name that means two arches, which is a reference to two additional openings present in the skulls of this lineage (which includes the lizards, snakes, crocodiles and dinosaurs – including the birds). Turtles and tortoises are members of the Anapsida, which means without arches.

The characteristics of this skull are those of an Anapsid and the streamlined shape and quite large size (despite it being a youngish adult, as indicated by the unfused sutures) suggests that it is a sea-turtle. There are only 7 species of sea-turtle and the comments provide an example of features that can be used to distinguish this as a Green Turtle Chelonia mydas (Linnaeus, 1758). Before I expand, I should congratulate jonpaulkaiser for being the first one to get the species identification correct. Dave Godfrey and Jake gave their reasoning for how they narrowed it down to also get the correct identification:

Not a Loggerhead, the skull’s the wrong shape… the nasal opening looks too small for every[] species I’ve seen so far… I think it is a Olive Ridley Sea Turtle or a Green Sea Turtle but if I had to choose one I think it is most like a Green Sea Turtle because the other one has an extra bit of bone on the edge of the eye bit.

I also provided a bit of a clue as to what it wasn’t:

…it lacks the bony ‘fangs’ made up from the premaxilla and maxilla that give away a leatherback

It’s all of these little features that the eye takes in and the brain processes to make something identifiable. We do it with people’s faces all the time, but we seldom think about how we actually recognise someone – we don’t just see someone as being a narrow nose, wide mouth and crooked tooth – we see them as an assembly of these (and hopefully other!) features that fit together in a particular way. Identifying skulls is a similar challenge and it requires training and experience, but then we need to break down what features we are seeing in order to explain why we think something is what we have identified it as.

If you try explaining what somebody looks like and you will end up picking out their most unusual and distinguishing features. This is something biologists do for new species and they record all of this information in scientific papers and make sure a preserved specimen is kept in a museum where it can be accessed by other biologists who want to check the characters of other similar species that they have found. These original comparative specimens are called ‘type specimens’ and they underlie our understanding of the diversity of life – these are part of what make museums essential for biodiversity.

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