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Paleontology

Elephants Started Small

If elephants never forget, neither does the Earth, safeguarding the many traces of evolution–including those of elephants. For despite having only three surviving species, elephants have a strikingly long and rich history. A history even longer than previously believed, following a discovery made through a French-Moroccan program1 in the North African country's Ouled Abdoun phosphate basin: 60 million-year-old fossils of the elephant's ancestor, dating back to the Paleocene era.2 It has been named Eritherium azzouzorum, after the Ouled Azzouz villagers who helped recover the fossils.
Weighing just 4-5 kg, the marmot-like Eritherium may seem a far cry from today's large mammal, but its teeth and skull remains belie a common lineage. One such example is its prominent incisors, the forerunners of tusks. Eritherium azzouzorum has now become the oldest-known member of the elephant order (proboscideans), unseating the 55 million-year-old Phosphatherium, found in upper levels of the same basin by the same team.
Emmanuel Gheerbrant3 explains that Eritherium is one of the earliest fossil examples of modern placental orders, setting an “important milestone” for calibrating the placental tree. It is also the oldest African ungulate4 to date, suggesting ties between proboscideans and groups such as condylarths5 and elephant shrews. Eritherium's extreme primitiveness means that it is “close to the ancestral form from which the initial diversification of ungulates took place,” declares Gheerbrant.
The mammal's primitive state implies that proboscideans underwent a rapid evolution spurt, one of which in size, at the Paleocene-Eocene transition 55 million years ago. The finding further supports the idea of a swift divergence of the extant African ungulate orders from their common ancestor after the Cretaceous-Tertiary mass extinction, notably of dinosaurs, 65 million years ago, when an “extraordinary opportunity arose for other animals to evolve,” concludes Gheerbrant.

Fui Lee Luk

Notes :

1. Paris Muséum National d'Histoire Naturelle (MNHN), Moroccan Ministry of Energy and Mines, Office Chérifien des Phosphates, Universities Cadi Ayyad (Marrakech) and Chouaîb Doukkali (El Jadida).
2. E. Gheerbrant, “Paleocene emergence of elephant relatives and the rapid radiation of African ungulates,” PNAS, 2009. 106: 10717-21.
3. Centre de recherche sur la paléobiodiversité et les paléoenvironnements (MNHN / CNRS / Université Paris-VI).
4. A herbivorous mammal with hoofs, claws, or nails.
5. Primitive early Tertiary ungulates with feet that had five hoofed toes.

Contacts :

Emmanuel Gheerbrant,
MNHN, Paris.
gheerbra@mnhn.fr


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