Transitional Vertebrate Fossil9

Transitional Vertebrate Fossil9 - Transitional Vertebrate...

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Transitional Vertebrate Fossils Overview of the Cenozoic The Cenozoic fossil record is much better than the older Mesozoic record, and much better than the very much older Paleozoic record. The most extensive Cenozoic gaps are early on, in the Paleocene and in the Oligocene. From the Miocene on it gets better and better, though it's still never perfect. Not surprisingly, the very recent Pleistocene has the best record of all, with the most precisely known lineages and most of the known species-to-species transitions. For instance, of the 111 modern mammal species that appeared in Europe during the Pleistocene, at least 25 can be linked to earlier European ancestors by species-to-species transitional morphologies (see Kurten, 1968, and Barnosky, 1987, for discussion). Timescale Pleistocene 2.5-0.01 Ma Excellent mammal record Pliocene 5.3-2.5 Ma Very good mammal record Miocene 24-5.3 Ma Pretty good mammal record Oligocene 34-24 Ma Spotty mammal record. Many gaps in various lineages Eocene 54-34 Ma Surprisingly good mammal record, due to uplift and exposure of fossil- bearing strata in the Rockies Paleocene 67-54 Ma Fair record early on, but late Paleocene is lousy For the rest of this FAQ, I'll walk through the known fossil records for the major orders of modern placental mammals. For each order, I'll describe the known lineages leading from early unspecialized placentals to the modern animals, point out some of the remaining gaps, and list several of the known species-to-species transitions. I left out some of the obscure orders (e.g. hyraxes, anteaters), groups that went completely extinct, and some of the families of particularly diverse orders. Primates I'll outline here the lineage that led to humans. Notice that there were many other large, successful branches (particularly the lemurs, New World monkeys, and Old World monkeys) that I will only mention in passing. Also see Jim Foley's fossil hominid FAQ for detailed information on hominid fossils. GAP: "The modern assemblage can be traced with little question to the base of the Eocene" says Carroll (1988). But before that, the origins of the very earliest primates are fuzzy. There is a group of Paleocene primitive primate-like animals called "plesiadapids" that may be ancestral to primates, or may be "cousins" to primates. (see Beard, in Szalay et al., 1993.) Palaechthon , Purgatorius (middle Paleocene) -- Very primitive plesiadapids. To modern eyes they looks nothing like primates, being simply pointy-faced, small early mammals with mostly primitive teeth, and claws instead of nails. But they show the first signs of primate-like teeth; lost an incisor and a premolar, and had relatively blunt-cusped, squarish molars.
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Cantius (early Eocene) -- One of the first true primates (or "primates of modern aspect"), more advanced than the plesiadapids (more teeth lost, bar behind the eye, grasping hand Pelycodus
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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 Fossil9 - Transitional Vertebrate...

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