Matrix Building Activity

Overview: How does one keep track of features describing a group of species?

The most satisfactory method of organizing data is by using a tabular summary called a data matrix. The data matrix presents taxa and characters (characters states) in a compact "spread-sheet" form, with the data arranged in continuous columns and rows as shown in the tetrapod example below.

NOTE: Statements of measurement must be definite and meaningful. A range such as "8 to 9 mm in length" vs. "20 to 21 mm in length," or "twice as long as broad" vs. "as long as broad" are adequate. However, statements such as "long" vs. "short," or "broad" vs. "narrow" are unacceptably ambiguous.

Creating a Sample Data Matrix

	Pencil	Mechanical Pencil	Short Pencil	Sharpie Marker	Click Pen
Character Description	Character Present or Absent (+ or -)
eraser	+	+	-	-	-
removable cap	-	-	-	+	-
made of wood	+	-	+	-	-
pocket clip	-	+	-	+	+
six-sided in cross section	+	-	+	-	-
writing color is black	+	+	+	+	+
writes w. graphite	+	+	+	-	-
felt-tipped	-	-	-	+	-
ethanol proof writing medium	+	+	+	+	-
made of plastic	-	+	-	+	+
contains metal parts	+	+	-	+	+
writes with ink	-	-	-	+	+
length longer than 10 cm	+	+	-	+	+

Arthropod Data Matrix

	class Insecta insects	class Chelicerata chelicerates	class Trilobita trilobites	class Pycnogonida pycnogonids	class Myriapoda centipedes and millipedes	class Onychophora velvet worms	class Tardigrada tardigrades
Character Description	Character Present or Absent (+ or -)
number of body regions

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