Walter Joyce and Jacques Gauthier,at Yale University,obtained three measurements in these particular bones of 71 species of turtles and tortoises.They used a kind of triangular graph paper to plot the three measurement against one another. All the land tortoise species formed a tight cluster of points in the upper part of the triangle; all the water turtles cluster in the lower part of the triangular garph.There was no overlap,except when they added some species that spend time both in water and an land.Sure enough,these anphibious species show up on the triangular graph approximately half way between the ‘wet cluster' of sea turtles and the‘dry cluster’of land tortoises. The next step was to determine where the fossils fell. The bones of P. quenstedti and P.talampayensis leave us in no doubt.Their points on the graph are right in the thick of the dry cluster.Both these fossils were dry-land tortoises .They come from the erabefore our turtles returned to the water.
Complete the flow-chart below.
Choose NO MORE THAN TWO WORDS AND/OR A NUMBER from the passage for each answer.Write your answers in boxes 34-39 on your answer sheet.
Method of determining where the ancestors of turtles and tortoises come from
Step1：71 species of living turtles and tortoises were examined and a total of 17_____ were taken from the bones of their forelimbs.
Step 2：The data was recorded on a 18______(necessary for comparing the information).Outcome:Land tortoises were represented by a dense 19_______ of points towards the top.
Sea turtles were grouped together in the bottom part.
Step 3：The same data was collected from some living 20_____species and added to the other results.