Happy New Year!
On Friday I gave you these two bones to compare, asking whether you thought they were from the same species.
There were some excellent responses with useful observations reflecting some of the difficulties faced when trying to identify postcrania. Unlike skulls which are composed of several bones forming a composite structure, including highly diagnostic elements (teeth for example), postcrania tend to be a bit more limited in the number of diagnostic characters visible. That said, the shape of the articulation points, the grooves and crests from tendons and ligaments, the scars from muscle attachments and the holes from nerves and blood vessels can all provide clues as to what a bone belonged to.
Size can also provide a clue, but as pointed out by Debi Linton:
…there’s a size differential, that could nevertheless be intraspecific variation…
This is a valid point – size can vary within a species for all sorts of reasons, the most obvious being the age or sex of the animal. However, in this instance the size difference is accompanied by quite a substantial set of differences in shape that go beyond what you would expect to find within a species. So well done to Dave Godfrey, Jamie Revell and Jake for making that deductive leap! That said, Debi also deserves congratulations for identifying the differences and then exercising caution in the light of insufficient information – it may be unsatisfying to say I’m not sure, but it’s often the only truly correct answer available.
That said, I’m a little surprised that nobody worked out what these femurs were from. The bottom one (B) has a small area of damage on the proximal end (the end nearest the body), which shows a honey-comb structure in the bone beneath. Jake also spotted that the angle at which these femurs would articulate with the hip would be unlike a deer – or other mammal in fact. These are the femurs of two species of bird – very big birds for that.
Any idea which species?
Zygoma 
Is the biggest one a Moa ?
Yep – well done!
A moa is the biggest bird I know, and I saw one when I had a tour of Perth Museum. Their skeleton is made out of lots of different moa bones.
http://jakes-bones.blogspot.com/2010/08/behind-scenes-at-perth-museum.html
(4th picture)
Given that they’re on the order of 30cm long, they’re large birds indeed, and that rather limits the options. They a look a little too sturdy to be from an emu or cassowary, judging from the (admittedly not close up) images I’ve been able to find, where the femurs seem to be relatively narrow. An ostrich does look possible, especially for ‘A’. But if ‘A’ is an ostrich, then I guess – as Jake says – there’s not much else ‘B’ can be but a moa.
Spot-on!
Sorry, I meant to go on record last night after our conversation in the car, but I forgot. As I said, it’s difficult to discuss things when you don’t know the names of the bits, but it’s pretty obvious this is a hip joint or mayyybe the shoulder joint of a four-legged creature, but I thought immediately of a flightless bird. Bird because when you were little we looked quite hard at the difference between bird- and reptile-hipped dinosaurs and the joint looks very like that of a bird. Flightless because the bones are so robust – and this would be a big thing up in the sky! Or things, because two species. Noted what you said about individual differences, also sexual dimorphism, but this here engineer sees a difference in the angles. I think the legs come off the hips at different pitches, thus different species. I said ostrich straightaway, but resorted to “that b*****y great big New Zealand bird, think it’s extinct” for moa
They could both be Moas. There’s what, 16-odd species of them? In all sorts of sizes.
Depends whether you are talking to a lumper or a splitter on that one. Everything from about 4 to 30 at various times!
Are they not both Moa? Two separate species?
Although, yes, Ostrich looks about right too.