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Fossil Spotlight

Fossil Spotlight: Mesosaur Embryo

Pictures, Diagram, and Drawings of the Mesosaur Embryo.  Image by Piñeiro et al. 2012
Picture, diagram, and drawing of the Mesosaur embryo. Image from Piñeiro et al. 2012

Who: Mesosaur embryo
Lagerstätte: Mangrullo Formation in Uruguay
What: Mesosaurs were an Early Permian group of reptiles that swam in the seas. They were the first reptiles to return to the oceans starting a marine reptile trend that would continue to this day. Many ancient marine reptiles like mosasaurs, ichthyosaurs, and plesiosaurs have evolved to give live birth, called viviparity, which was crucial in their marine domination. This mesosaur embryo is the oldest known amniotic (which includes mammals, reptiles, and birds) embryo. The advance stage of the embryo suggests that mesosaurs were also viviparous or laid eggs on land which quickly hatched. Mesosaurs may have even tended to their young in a nurturing behavior. In general, eggs and embryos are rare in the fossil record due to their low fossil potential but every now and then we get lucky with a truly remarkable find like this one.

References
Piñeiro, Graciela, et al. “The oldest known amniotic embryos suggest viviparity in mesosaurs.” Historical Biology 24.6 (2012): 620-630.

Categories
Fossil Spotlight

Fossil Spotlight: The Dire Wolf

Image by Bill Abbott. Taken at The La Brea Tar Pits and Museum

Who: The Dire Wolf, Canis dirus
Lagerstätte: La Brea Tar Pits
What: With over 3,600 individuals found, the Dire Wolf is the most common mammal at La Brea Tar Pits. It was the dominant predator at this ecosystem hunting the likes of ground sloths, American camels and horses, and ancient bison. It was larger than modern timber wolves and its massive jaws and teeth point to an adept scavenger, able to crush bones with their powerful bite. There are quite a few specimens that experience tooth breakage from these bone-biting behaviors. Their extinction may have stemmed from a loss of large and slow prey. Their stout build favored power over speed and as such couldn’t keep up with the surviving faster prey.

The image seen here is from The La Brea Tar Pits and Museum. 400 skulls of Dire Wolves are on display!

References
https://www.sdnhm.org/exhibitions/fossil-mysteries/fossil-field-guide-a-z/dire-wolf/
Coltrain, Joan Brenner, et al. “Rancho La Brea stable isotope biogeochemistry and its implications for the palaeoecology of late Pleistocene, coastal southern California.” Palaeogeography, Palaeoclimatology, Palaeoecology 205.3-4 (2004): 199-219.

Categories
Fossil Spotlight

Fossil Spotlight: Orb-Weaver Spider in Amber

Who: Pulchellaranea pedunculata
Lagerstätte: Dominican Amber
What: Pulchellaranea is an orb-weaver spider encased in amber from the Dominican Republic. Orb-weavers are the most common group of spiders who spin the wheel-shaped webs you see in your backyard, forests, and parks. Spiders are notoriously rare in the fossil record and over 90% of spider fossils are found in amber. Their rarity is due to their fragile nature and burial difficulties as their corpses tend to float on water and not sink. Spiders are more common in amber as it gently entombs them and minimizes decay. An ant, which are quite common in the Dominican Amber, joins this spider. Their proximity indicates they fell into the amber at the same time probably after a brief interaction.

Reference
-High def image from the New Yorker
-The same image can also be found in black and white along with a description of this species here
Poinar Jr, George. “Pulchellaranea pedunculata n. gen. n. sp.(Araneae: Araneidae), a new genus of spiders with a review of araneid spiders in Cenozoic Dominican amber.” Historical Biology 27.1 (2015): 103-108.