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> I sent this yesterday to Naturens but for so ------=_Part_5963_7036104.1222474427507 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline David, I have no information on skull length for beavers. However, I did find the following on zygomatic breadth: Kits: 2.50 - 3.00 inches Yearlings: 3.20 - 3.40 inches Two-year olds: 3.50 - 3.60 inches Adults: 3.65-up (After Patric and Webb 1960 as reported on page 378 in Wildlife Management Techniques 1971) My apologies for not offering metric conversions (calculator not handy). I have no information whether or not Nova Scotia beavers are likely to differ in size from the size range indicated above. In addition, there is also no indication of the geographical origin of the beavers used to determine the above measurements. As I recall, one can also use the suture lines as an indication of age on mammalian skulls. Easily visible suture lines suggest a young animal. These sutures gradually disappear, with the bones fusing as the animal ages. Dave, are the cranial sutures readily apparent? Ron 2008/9/26 David & Alison Webster <dwebster@glinx.com> > Hi All, Sept 26, 2008 > The skull, measured from the bulge that is dorsad of the upper incisors > to the posterior extremity of the part that articulates with the neck, is > 129 mm long. I suspect , sheer guess by picturing beaver, this is about 3/4 > adult size. > > The right lower jawbone was missing but, in the left jawbone (in looking > at this more carefully, I see that the lower jawbone was from a different > and smaller beaver; both bones were within feet of each other near the small > dumbell-shaped pond on Little River), the curved incisor pulls out readily > and is essentially the same width (6.2 mm) from one end to the other. This I > think follows from, if I understand correctly, the teeth growing from the > base as use wears the cutting edge away. Thus incisor tooth width would not > increase with age (unless nursing beaver have baby teeth ?). Perhaps Randy > or Andrew can comment on this. This left lower incisor, measured along the > curved anterior face is 98 mm in length (~80 mm from end to end). > > My estimate of 2/3 width, if it applies at all, would apply especially to > initial cuts where there is no opportunity for sideways motion of the chips. > Once there is a gap, into which chips can by pried, they likely do cut to > full width and rather than make shavings make fairly thick chips (again by > sublimital memory) chip size being dependent somewhat on the wood being cut. > > Yt, DW > > > > Ronald Arsenault wrote: > > Hello Steve, Dave and others, >> >> >> As everybody seems to be in a confession mode.... >> >> >> I made an assumption that may be erroneous should Dave's suggestion be >> correct. It is actually the gnaw marks of an adult beaver which measure >> approximately 6 mm in width. I assumed a this represented the width of the >> teeth of an adult beaver. If Dave's suggestion that the width of the gnaw >> marks represent 2/3 of the width of the incisor teeth is correct, then an >> adult beaver would have incisors 9 mm wide. Dave, is the skull you have >> that of an adult beaver? >> >> >> However, the above does not change my initial conclusions that the >> evidence still strongly points to a beaver (the presence of muskrats does >> not exclude beaver) and that the beaver responsible for the cutting was >> likely a sub adult. >> >> >> Ron >> >> 2008/9/24 Steve Shaw < srshaw@dal.ca <mailto:srshaw@dal.ca> > >> >> >> Hi Dave and others, >> No Dave, your note didn't come through on NNS, only the recent one >> direct to me. One of my earlier 2 posts came through in the wrong >> order, though, and NNS has seemed erratic or slow sometimes, >> recently, as others have noted. >> >> Yes, you caught me with an inexcusable error when I converted 3.75 >> mm to 5/64 inch (thinking that some out there may not like >> millimeters) when it should have read approximately 5/32 inch. >> Actually I missed this error because I didn't convert it >> arithmetically but stuck a ruler next to two lines I'd drawn, and >> mis-read 32ths as 64ths on the ruler. ( No, I'm not the guy who >> designed the lens in Imperial for the Hubble telescope which was >> then made in metric units, or was it the other way round?). >> However and in consequence, I'm VERY glad to find that you made >> complimentary (admittedly smaller) error: 3.75 mm is actually IS >> a little bit larger than 1/8 inch, not smaller -- I make it 1.181 >> eighths-of-an-inch if you want to get fancy. >> >> To be serious, your reply is useful because it helps to clarify my >> original short post on this beaver size thing, which may have been >> well-intended but was a really ill-conceived as written, I've >> realized since. The round alder branches were gnawed at a >> shallow angle, so the en face view of the cut was roughly >> elliptical, with the long axis of the ellipse in line with the >> branch. The branch and the long axis of the cut would actually >> have been parallel to the axis of the beaver's body as it stood up >> in the lake to gnaw away. But the 8 or so gnaw marks that I >> measured as 3.75 mm each, ran ACROSS the ellipse (i.e. parallel to >> the short minor axis of it). This would have been orthogonal to >> (at right angles to) the beaver's incisors, not parallel with >> them! It then makes no sense to ask (as I did) how wide the >> teeth are in a beaver of a certain age in relation to these cuts: >> the marks will not be related to tooth width, but to the depth of >> each of the 8 chisel-cuts it made in lopping off the branch, as >> you correctly point out. So the question should be reformulated >> to ask how long or deep is each of the series of chisel-cuts made >> by a beaver of a certain age or size, probably harder to assess >> accurately. From Ron Arsenault's reply that the teeth on an >> adult are about 6 mm wide which agrees with your specimen, it >> sounds like you may have an adult beaver skull in your possession. >> If your estimate of a cut-depth of 3.4 mm for such a beast is >> realistic, "ours" then could have been a pretty large beaver. >> >> I also put the local observations round an e-mail list for people >&