ON THE EDGE OF EXTINCTION - A - THE TIGER (Panthera tigris)

[peter]

(06-11-2015, 09:28 AM)'tigerluver' Wrote: Much, much thanks for the in depth description. I will have to read it another dozen times at least in the coming days. Though, in order to better help me visualize, I have a few questions. By upper skull, you are referring to the cranium, lacking the mandible, correct? By scale, are you referring to sliding scale that has similar mechanics to the caliper?

Moreover, when measuring GTL, you stated you have the skull upright, with the skull on the lap. If I am understanding this correctly, the scale was positioned between the two points of interest. You then brought the skull up to the table for the measurement. Now, relative to the table, how does the skull positioning look exactly? I'm having trouble seeing it, as I have the Christiansen method currently engraved in my head. When I think compensate for the angle, I think "method b's" positioning. 

I'll have more questions about the method specifically, but I first need to grasp these points. 

Now beyond your method specifically, how compatible do you think skull measurements from different literature are? I feel some authors have taken the idea of "greatest length" to be that when the canines are angling the skull relative to the plane below, as this position does produce in essence the "greatest" length if taken literally. I'm very certain vK has done this. Then, there's Christiansen. If he truly did measure the skull as he has shown, CN5698 would have an angled, vK style CBL of around 375 mm, which seems too large. My direct interest in this issue at the moment is how it affects my equations and all current weight estimates. Depending on the "measurer," a skull length may be inflated.

I understand the benefits/convenience of digital measuring. It might also provide a way for a level playing field between literature. At the same time, I agree that you can't beat an in person measurement if the option is available.
 

1 - " ... By upper skull, you are referring to the cranium, lacking the mandibula ... "? Yes.

2 - " ... Sliding scale with similar mechanics to the caliper ... "? Yes. The scale can measure skulls of up to 500,00 mm. in GTL.

3 - " ... You then brought the skull up to the table for measurement. How does the skull positioning look exactly ... ? Not important. What is important, is that GTL is measured with the scale (and not the skull per se) positioned on a virtual horizontal line. To do that, I used the table and the one assisting. When the measurement was taken, the skull wasn't on the table, but just above it, I mean. I held it in my hands and positioned the skull in such a way that the scale, compared to the table, was completely horizontal. This means I used the table (and the one assisting) to position it in a virtual horizontal line. Important? Yes. If it wasn't positioned in that way (but the skull, for instance), the measurement would be increased. Sure? Yes. It was tested.

4 - " ... How compatible are skull measurements from different literature ... "? I don't know, but I do know there are many ways to measure a skull. Everyone probably thinks his method is the best. Same for me. Also remember modern (digital) scales are more accurate than the old ones. 

Some of the skulls I measured were also measured by others. When comparing the results, I noted there wasn't much difference regarding Pm4 and zygomatic width. The Pm4 is small. You just measure the distance between both ends in a straight line and that's it. Zygomatic width also is easy to measure. I can't say anything about upper canine length, as most didn't measure the upper canines in big cat skulls. 

The results of measurements of maxillary width, greatest total length and, in particular, condylobasal length often were somewhat different. Too much to understand, I concluded in some cases. The most likely reason is the method used. In maxillary width, it's understandable, as it heavily depends on the place you measure the width.

Condylobasal length, however, should be easy to measure. You insert the first tooth of the scale at the tip of the palate (directly behind the insertion of the incisors) and the second directly behind outer back edge of the condylae. Than you measure the distance between both points with the scale positioned on a (virtual) horizontal line. Apparently not that easy. One reason is not all insert the first tooth of the scale in the same position. In nearly every skull, you can see many insertions. They all use a different place, and the obvious result is different measurements. 

GTL should be easy as well. You insert the first tooth of the scale just before the insertion of the incisors in the maxillary bone and the second directly after the outer back edge of the occipital ridge. The problem is removing the angle(s). If the measurement isn't taken on a virtual horizontal line, the measurement will be increased. This takes a bit of work, as I explained above.    

As for the results. I noticed my measurements (and GTL and CBL in particular) were a bit shorter in most cases. Reasons explained above. In order to learn a bit more, I asked others to measure skulls. Competent people who should know about skulls and measurements. I watched them and saw they didn't need a lot of time, whereas I did. The reason is I measured hundreds of skulls and, for this reason, know inaccuracy is close when you don't pay attention. Measuring skulls really needs concentration and time. I also concluded (hidden) preference can be a factor. You can measure a distance in a straight line with a reliable scale and, apart from including angles, still deduct or add a few mm. if you want to.

5 - Although I read a lot about measuring skulls before I started (a), Dr. P. van Bree taught me how it should be done (b). Later, when I had gained some experience, I noted measuring a skull takes more time than I anticipated ©. Modern, digital, scales are more reliable than the old ones (d). And then there's angles and (hidden) preference (e). All in all, measuring skulls is a bit of an undertaking. 

If you want to know about the reliability of skull measurements, accept you won't find the answer. Not without indulging in generalisations and (some degree of) preference. You will insult some and my advice is to refrain from it. As for my measurements. I did my best to get as informed, experienced and accurate as possible. I also took my time and I learned about (hidden) preference. We're all humans, degree or no degree. 

As to preference. Let's take tigers and bears. Russia. Many biologists think tigers preying on brown bears take a risk, especially when adults are involved. Miquelle (2010) thought it would be a dangerous undertaking and he wasn't the only one. But there's mounting evidence they, to an extent, could be wrong.

Today, I read an interesting article about Amur tigers and food. Kerley was involved and so was Miquelle. The conclusion is tigers prey more often on bears than many think, especially in summer. The percentages they found were quite impressive. Although details were still lacking (age? - weight? - health? - circumstances?), the word 'adults' (referring to bears) was included in the document. This should tell you something.

Biologists are better educated and trained than most posters. They also are much better informed. That, however, doesn't always mean they are very different from posters with firm opinions. The difference between them is posters will never change their opinion, whereas biologists do. When they're true biologists interested in reality. And they very often are. If what I saw in captivity and heard from experienced trainers would hold for wild animals, things could be different than many think. But that's another topic. Reply