Transitional fossils: Eochrysochloris, an early golden mole

African golden moles (Chrysochloridae), are mole-like mammals that live in Africa. Unlike the “true moles” that one might be familiar with in North America or Europe, these mammals are genetically more similar to fellow endemic African fauna such as elephants, hyraxes and the aardvark.

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Golden moles, as their name implies, are highly subterranean mammals, spending most of the their time underground. The earliest known golden mole fossil, Eochrysochloris, does not show any evidence of subterranean living, but this is due to the fact that all that remains of this organism are parts of the mandible (lower jaw) and teeth. The teeth, however, show evidence of an evolutionary transition.

It’s thought that present day mammals descended from mammals with tribosphenic teeth, a trait that’s found in mammals located in Mesozoic rocks that are dated earlier than 66 million years ago. Tribosphenic teeth include upper cheek teeth that have three cusps, termed the paracone, metacone and protocone. The lower cheek teeth have structures called the trigonid and talonid basin.

Upper tribosphenic teeth

Extant golden moles (i.e., those alive today) have cheek that are shaped in an uncommon pattern that is termed zalambdodonty, characterized by the reduction or absence of metacones and enlarged paracones. Since the metacones are reduced or absent, the place that they articulate with the lower cheek teeth, the talonid basin, is also reduced. Other zalambdodonts include the unrelated marsupial mole and solenodons.

Upper zalambdodont teeth

In addition to extant golden moles, an extinct golden mole known as Prochrysochloris possesses the zalambdodont condition. This species is found in Early Miocene rocks which date to 23-16 million years ago. Eochrysochloris, which is found in early Oligocene rocks (33.9-28.4 million years ago), has molars that are similar to zalambdodonty, but haven’t quite reached their fully developed form [1]. In particular, the talonid basin is still relatively well developed, implying that the metacone is still present in their cheek teeth.

 

This intermediate zalambdodonty in Eochrysochloris provides evidences of a transition from tribospheny, as present in early mammals, to full zalambdodonty in Prochrysochloris and modern golden moles.

Questions for Creationists

Is this sequence of fossils just a coincidence ? Or could it be that it reflects an evolutionary transition from one tooth type to another? Why do we no longer see Eochrysochloris or Prochrysochloris today?

References

1. Seiffert E, Simons E, Ryan TM, Bown TM, Attia Y. 2007. New remains of Eocene and Oligocene Afrosoricida (Afrotheria) from Egypt, with implications for the origin(s) of afrosoricid zalambdodonty. J Vertebr Paleontol 27: 963–972.

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One thought on “Transitional fossils: Eochrysochloris, an early golden mole

  1. Pingback: Pseudogenes: Subterranean mammals lose vision genes | Evolution For Skeptics

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