Here's just a ha'penny more, regarding the perplexing ankles of birds. In our ankle, the long bone of the lower leg (tibia) articulates with several small bones, the tarsals, in the rear part of our plantigrade foot. The basic anatomy is similar in other mammals, except that in more cursorial forms, like cats and dogs, the rear part of their digitigrade feet (composed of tarsals and metatarsals) is generally raised above the ground, so that the ankle appears as an elevated, backward-pointing hinge, as in birds.
In Theropod dinosaurs, such as birds, the ankle joint forms among the tarsal bones, with some tarsal components fusing with the tibia (forming the tibiotarsus, above the ankle), and others, on the far side of the joint, fusing with each other and with metatarsal bones (forming the tarsometatarsus, below the ankle). Clearly, the apparent length of a bird's leg is influenced not only by the actual lengths of these two bones, but also by their angle relative to each other, and the degrees to which the top of the tibiotarsus is concealed within the body plumage and the bottom of the tarsometatarsus (i.e., foot) is concealed by grass, water, or mud. The surest bet is to patiently assess the length of the whole tarsometatarsus when both the ankle and the toes are visible. That said, the overall setup tends to look rather different in Dunlin and Curlew Sandpiper: https://picasaweb.google.com/109808209543611018404/CalidrisII#5747741452480409570 Shai Mitra Bay Shore, NY ________________________________ From: [email protected] [[email protected]] on behalf of Paul R Sweet [[email protected]] Sent: Saturday, July 18, 2015 6:31 PM To: robert adamo; NY BIRDS Subject: Re: [nysbirds-l] A hummer of a breakfast + my "2 cents" ! Hi Robert Just a quick note on bird anatomy. The lower (distal) long bone of the hindlimb to which the toes attach is the tarsometatarsus which is homologous with our foot. Thus the joint above this is the ankle not the knee. (look at the direction of hinging). The second long bone is the tibiotarsus which in shorebirds is partially exposed and scaly. The knee is where this joins the femur and is not visible as it is surrounded by muscle. Happy shorebirding. Paul From: robert adamo <[email protected]<mailto:[email protected]>> Reply-To: robert adamo <[email protected]<mailto:[email protected]>> Date: Saturday, July 18, 2015 at 1:17 AM To: "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>> Subject: [nysbirds-l] A hummer of a breakfast + my "2 cents" ! Over breakfast, my doctor (Michael Dempsey) called with good news, and I in turn, was able to share my good news re: the Ruby-throated Hummingbird, who was having her breakfast around the patio, while we were talking ! And now for my "2 cents" concerning the ID question posed by the Arie Gilbert/Phil Urubaru posting on 7/16. After reading Angus Wilson's response to them, in particular re: the longer legs of the Curlew Sandpiper, I would like to advance the idea that in some cases of limited viewing, just the length of the tibia is a fairly good mark in helping to separate the Curlew from the Dunlin. Admittedly, I can't find this referenced in the text of any of the many general bird guides, or the 2 excellent shorebird guides I own (the size is probably too variable), but a number of them show it in their illustrations. Thus, I know it stands to reason, one shouldn't rely on this, but if, and when, the next opportunity arises to consider it..."check it out" ! Although I certainly could not tell by looking at the Gilbert/Urubaru photos which of the two species the bird was, I can attest to identifying both species in the past, using the tibia, along with some of both species other field marks, ie, on 10/3/78 at the East Pond, J.B.W.R.(my first C.S. sighting). "Winter plumage - saw white rump both while standing & in flight - noticed slight curve throughout length of bill - also noticed longer legs than Dunlin, with more showing above knee"...didn't know it was called tibia back then ! I have also been able to make this direct comparison on at least one other occasion. Cheers, Bob -- ________________________________ CSI Tops MONEY magazine’s Best Colleges list for 2015-2016><http://csitoday.com/2015/07/csi-tops-money-magazines-best-colleges-list-for-2015-2016/> -- NYSbirds-L List Info: http://www.NortheastBirding.com/NYSbirdsWELCOME http://www.NortheastBirding.com/NYSbirdsRULES http://www.NortheastBirding.com/NYSbirdsSubscribeConfigurationLeave.htm ARCHIVES: 1) http://www.mail-archive.com/[email protected]/maillist.html 2) http://www.surfbirds.com/birdingmail/Group/NYSBirds-L 3) http://birdingonthe.net/mailinglists/NYSB.html Please submit your observations to eBird: http://ebird.org/content/ebird/ --
