Transitional Vertebrate Fossil2

Transitional Vertebrate Fossil2 - Transitional Vertebrate...

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Transitional Vertebrate Fossils Artiodactyls (cloven-hoofed animals) "The early evolution of the artiodactyls is fairly well documented by both the dentition and the skeletal material and provides the basis for fairly detailed analysis of evolutionary patterns. ...the origin of nearly all the recognized families can be traced to the late Middle Eocene or the Upper Eocene. .." (Carroll, 1988) Chriacus (early Paleocene) -- A primitive oxyclaenid condylarth from the Lower Paleocene. Has many tooth features linking it to later Diacodexis ; but in all other ways, including the legs, it was an unspecialized condylarth. GAP: No artiodactyl fossils known from the late Paleocene. Similar late Paleocene gaps in rodents, lagomorphs, and perissodactyls are currently being filled with newly discovered Asian fossils, so apparently much late Paleocene herbivore evolution occurred in central Asia. Perhaps the new Asian expeditions will find Paleocene artiodactyl fossils too. At any rate, somewhere between Chriacus & Diacodexis, the hind leg changed, particularly the ankle, to allow smooth running. Diacodexis (early Eocene) -- A rabbit-sized with longer limbs than the condylarths. The fibula was reduced to a splint, and in some (but not all!) individuals, fused partially to the tibia. Artiodactyl-like "double pulley" ankle (because of this feature, Diacodexis is automatically classified as the first artiodactyl). The feet were very elongated, and the 3rd and 4th toes bore the most weight. Many primitive, non-artiodactyl features retained: collarbone, unfused ulna, primitive femur, unfused foot bones with all 5 toes, could still spread hind limb out to the side, very primitive skull & teeth (all teeth present, no gaps, simple cusps). In fact, in most ways, Diacodexis is just a leggy condylarth. Only the ankle shows that it was in fact the ancestor of all our modern cloven-hoofed animals (possible exception: the hippos & pigs may have split off earlier). There are abundant species-to- species transitions linking Diacodexis to various artiodactyl familes (see below). Hippos & pigs: Helohyus or a similar helohyid (mid-Eocene) -- Primitive artiodactyl, larger than Diacodexis Anthracotherium and later anthracotheriids (late Eocene) -- A group of heavy artiodactyls that started out dog-size and increased to be hippo-size. Later species became amphibious with hippo-like teeth. Led to the modern hippos in the early Miocene, 18 Ma. Propalaeochoerus or a similar cebochoerid/choeropotamid (late Eocene) -- Primitive piglike artiodactyls derived from the helohyids (see above). Perchoerus
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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 Fossil2 - Transitional Vertebrate...

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