A study recently published by the Proceedings of the National Academy of Sciences describes how modern day representatives of the Phiomorpha and Caviomorpha groups diverged approximately 37 million years ago.
The phylogeny detailed in the article was derived through combination of biogeographical, genetic and fossil evidence, and serves to demonstrate that the Caviomorpha, a group that includes modern-day guinea pigs, separated from the Phiomorpha during the early Eocene epoch between 34 and 40 million years ago.
Prior to divergence, both groups were bound by the rodent infraorder Hystricognathi and were restricted to Afro-Arabia. In sync with the rise of modern mammals during the Eocene, members of the Cavimorpha parted ways with the Phiomorpha and emmigrated to South America, possibly by rafting or other chance dispersal event. The Phiomorpha remained behind in Afro-Arabia where they radiated into a variety of genera, including the extant genus Thryonomys – commonly known as cane rats.
Key to the study’s finding was morphological examination of fossil assemblages excavated from the Fayum Depression of northeast Egypt. The mandibular and maxillary fossils recovered from the site revealed a mixture of both primitive and derived features. This fossil data was amalgamated with independently calculated genetic estimates to narrow the timing for the early Eocene divergence.
Sallam, H., Seiffert, E., Steiper, M., & Simons, E. (2009). Fossil and molecular evidence constrain scenarios for the early evolutionary and biogeographic history of hystricognathous rodents Proceedings of the National Academy of Sciences, 106 (39), 16722-16727 DOI: 10.1073/pnas.0908702106
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