Question

Bony no using the following characteristics, build a cladogram that is the most parsimonious to represent the relationships between these organisms. Vertebrae? Four Amniotic Hair? Fused Two post skeleton? limbs? egg? orbital bones in temporal forelimb? fenestra? Lampreys no no no no no Sharks yes no no no no Ray-finned fishes yes yes no no no Amphibians yes no no Mammals yes yes yes no Crocodiles and yes yes yes yes yes no relatives Dinosaurs yes yes yes Birds yes yes yes yes no yes yes no yes yes no a yes no yes no yes What is the function of having the lampreys in this cladogram?

Answer 1

A cladogram is a phylogenetic diagram that explains the relationships between groups on organisms based on certain data. There are various ways to build a cladogram, however, scientists prefer the easiest visualization obtained by the parsimony model. The parsimony model involves building a cladogram with the least number of jumps.

For the given data, we can build a cladogram as follows:

Lampreys Sharks Ray-finned fishes Amphibians Mammals Vertebrae Bony Skeleton Four limbs Crocodiles and relatives Hair Dinosaurs Amniotic egg Two post-orbital temporal fenestra Fused bones in Birds limbs

This cladogram is based on the parsimony model since it involves the least jumps. This tree can be built simply from the given table, by following the yes and no's. Each node needs to be added for an increased number of yes. This can be followed until all the yes's are exhausted.

The lampreys here have none of the characteristics mentioned in the table. Thus, it forms an outgroup. A cladogram often uses an outgroup as a reference for the remaining ingroups. The outgroup serves as a reference to estimate the evolutionary relationships of the other organisms.