Ring-tailed Lemur - Evolutionary History

Evolutionary History

All mammalian fossils from Madagascar come from recent times. Thus, little is known about the evolution of the ring-tailed lemur, let alone the rest of the lemur clade, which comprises the entire endemic primate population of the island. However, chromosomal and molecular evidence suggest that lemurs are more closely related to each other than to other Strepsirrhine primates. For this to have happened, it is thought that a very small ancestral population came to Madagascar via a single rafting event between 50 and 80 million years ago. Subsequent evolutionary radiation and speciation has created the diversity of Malagasy lemurs seen today.

According to analysis of amino acid sequences, the branching of the family Lemuridae has been dated to 26.1 ±3.3 mya while rRNA sequences of mtDNA place the split at 24.9 ±3.6 mya. The ruffed lemurs are the first genus to split away (most basal) in the family, a view that is further supported by analysis of DNA sequences and karyotypes. Additionally, Molecular data suggests a deep genetic divergence and sister group relationship between the true lemurs (Eulemur) and the remaining three genera: Lemur, Hapalemur, and Prolemur.

The ring-tailed lemur is thought to share closer affinities to the bamboo lemurs of the genera Hapalemur and Prolemur than to the other two genera in its family. This has been supported by comparisons in communication, chromosomes, genetics, and several morphological traits, such as scent gland similarities. However, other data concerning immunology and other morphological traits fail to support this close relationship. For example, Hapalemur and Prolemur have short snouts, while the ring-tailed lemur and the rest of Lemuridae have long snouts. However, differences in the relationship between the orbit (eye socket) and the muzzle suggest that the ring-tailed lemur and the true lemurs evolved their elongated faces independently.

The relationship between the ring-tailed lemur and bamboo lemurs (both Hapalemur and Prolemur) is the least understood. Molecular analysis suggests that either the bamboo lemurs diverged from the ring-tailed lemur, making the group monophyletic and supporting the current 3-genera taxonomy, or that the ring-tailed lemur is nested in with the bamboo lemurs.

The karyotype of the ring-tailed lemur has 56 chromosomes, of which four are metacentric (arms of nearly equal length), four are submetacentric (arms of unequal length), and 46 are acrocentric (the short arm is hardly observable). The X chromosome is metacentric and the Y chromosome is acrocentric.