Transitional Vertebrate Fossil7

Transitional Vertebrate Fossil7 - Transitional Vertebrate...

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Transitional Vertebrate Fossils Rodents Lagomorphs and rodents are two modern orders that look superficially similar but have long been thought to be unrelated. Until recently, the origins of both groups were a mystery. They popped into the late Paleocene fossil record fully formed -- in North America & Europe, that is. New discoveries of earlier fossils from previously unstudied deposits in Asia have finally revealed the probable ancestors of both rodents and lagomorphs -- surprise, they're related after all. (see Chuankuei-Li et al., 1987) Anagale , Barunlestes , or a similar anagalid (mid-late Paleocene) -- A recently discovered order of primitive rodent/lagomorph ancestors from Asia. Rabbit-like lower cheek teeth, with cusps in a pattern that finally explains where the rabbits' central cusp came from (it's the old anagalid protocone). Primitive skeleton not yet specialized for leaping, with unfused leg bones, but has a rabbit-like heel. No gap yet in the teeth. These fossils have just been found in the last decade, and are still being described and analyzed. Barunlestes in particular (known so far from just one specimen) has both rodent-like and rabbit-like features, and may be ancestral to both the rodents and the lagomorphs. This lineage then apparently split into two groups, a eurymyloid/rodent-like group and a mymotonid/rabbit- like group. Heomys (mid-late Paleocene, China) -- An early rodent-like eurymyloid. Similar overall to Barunlestes but with added rodent/lagomorph features (enamel only on front of incisors, loss of canines and some premolars, long tooth gap) plus various rodent-like facial features and rodent-like cheek teeth. Probably a "cousin" to the rodents, though Chuankuei-Li et al (1987, and in Szalay et al. 1993) think it is "very close to the ancestral stem of the order Rodentia." News flash Tribosphenomys minutus (late Paleocene, 55 Ma) -- A just-announced discovery; it's a small Asian anagalid known from a single jaw found in some fossilized dung (well, we all have to die somehow). It still had rabbit-like cheek teeth, but had fully
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This note was uploaded on 11/22/2011 for the course GLY GLY1100 taught by Professor Jaymuza during the Spring '10 term at Broward College.

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Transitional Vertebrate Fossil7 - Transitional Vertebrate...

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