Higher Vertebrates (Mammals and Birds) Exhibit Lateralized Behaviors, Commonly Referred

Essay

Higher vertebrates (mammals and birds) exhibit lateralized behaviors, commonly referred
to as "handedness." Recently an investigator studied the coiling behavior of the
Agkistrodon piscivorus leucostoma - more commonly known as the cottonmouth snake.
The cottonmouth is a venomous snake that spends much of its time in a coil, sometimes
coiled in a counter-clockwise direction, other times in a clockwise direction. The
investigator made many observations of coiling behavior, and calculated a "laterality
index" for 30 cottonmouths. He defined the laterality index for each snake as the
percentage of observations of the snake that were categorized as coils in the counter-
clockwise direction. In the table below the data on laterality has been separated into two
groups: females and males. $\begin{array}{l}\text { Laterality: Females }\\\begin{array}{|l|l|l|l|l|l|l|l|l|l|}\hline 58 & 55 & 61 & 54 & 64 & 60 & 42 & 49 & 56 & 42 \\\hline 59 & 55 & 55 & 60 & 66 & 70 & 49 & 51 & 57 & 43 \\\hline\end{array}\end{array}$


$\begin{array}{l}\text { Laterality: Males }\\\begin{array}{|c|c|c|c|c|c|c|c|c|c|}\hline 56 & 56 & 52 & 54 & 40 & 49 & 49 & 48 & 46 & 49 \\\hline\end{array}\end{array}$
-Grey Kangaroos are large social marsupials, indigenous to Australia. As part of a study of these creatures, biologists measured various aspects of their skeletal structure. A sample of 148 palate widths is presented in the stem-and-leaf plot below. The display uses five lines for each stem. Thus, "2t|" is the stem for palate widths of 22 and 23 , "2f|" for 24 and 25, "2s|" for 26 and 27, and so on. (The "t" then stands for leaves that are twos and threes, the " $f$ " for leaves of fours and fives, etc. " $2 . "$
Indicates leaves that are zeros and ones; " $2 *$ " indicates leaves that are eights and nines.) The mean palate width of this sample is $2.6 \mathrm {~cm}$ , and the standard deviation is $0.3 \mathrm {~cm}$ .
Palate Width - Grey Kangaroos
$$1 \mid 0=1 \mathrm{~cm} \quad N=124$$
$$\begin{array}{l}\begin{array} {lll } 1.&|\\1t&|\\1f&|\\1s&|&77\\1*&|&89\\2.&|&01111111111\\2 t& |& 222222222223333333333333\\2 \mathrm{f}&|&444444444444444455555555555555\\2 s &|& 6666666666667777777\\2*&|&88888888888889999999999999\\ 3.&|& 10000011\\3 t &|& 223\\3f&|\\3s&|\\3*&|\\\end{array}\end{array}$$

(a) Approximately what percent of palate widths in this sample are less than $2.9 \mathrm {~cm}$ ?
(b) What is the approximate percentile of a palate width that is $2.0 \mathrm {~cm}$ ?