North American Tadpoles
Labial Tooth Row Formula (LTRF)
||The LTRF is written as a fraction designating the location and number of
labial tooth rows. The most common LTRF is 2/3. The numerator indicates the number of rows
on A, the anterior labium, while the denominator indicates the number of rows on P, the
posterior labium. A LTRF only tells how many tooth rows there are on each labium and which
ones have medial gaps-the lengths or positions of the rows are not designated. In the
drawing on the left, the anterior labium has 2 rows, A-1 and A-2; the posterior labium has
3 rows, P-1, P-2 and P-3. Rows are numbered from anterior to posterior on each labium.
|Ontogenetic or geographic variation in the number of tooth rows is
indicated with a hyphen. Tooth rows are added during development in the following
sequence: A-1, P-2, A-2, P-1, P-3, and, if more rows are present, continue in an
approximately alternate upper/lower sequence on each labium. A hyphen can be used to
indicate ontogenetic variation or variation among species within a genus, as shown in the
LTRF 2/2-3 in the drawing on the right.
||A number in parentheses designates a labial tooth row with a median gap.
In the drawing to the left, the median gap is shown in the second row of the anterior
|As illustrated in the drawing to the right, a number in brackets indicates
variation in the presence of a median gap. The first row in the posterior labium may or
may not have a median gap...2(2)/3.
The proportional relationship of the length of one tooth row to another (e. g., length
of P-2 divided by length of P-3) or of half of a tooth row to its gap (e.g., length of
left half of A-2 divided by length of A-2 gap) is useful sometimes to distinguish among
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