Fossil Spotlight: Pyritized Trilobite

Who: Triarthrus eatoni
Lagerstätte: Beecher’s Trilobite Bed (Ordovician, New York)
What: These trilobites are preserved through pyritization which gives them a golden hue. An underwater avalanche, called a turbidity current, carried the trilobites into deep waters and buried them. The shock of the cold water killed them. Anaerobic bacteria within the soil reacted to the influx of sudden food and began to feed on them. As they feed, they released hydrogen sulfide which reacted with the soil’s iron and produced pyrite. The pyrite replaced the organic tissues preserving the legs, antennae, and internal organs. This makes these trilobites highly valuable in understanding what they looked like as most trilobite fossils do not have these soft body parts.

Briggs, Derek EG, Simon H. Bottrell, and Robert Raiswell. “Pyritization of soft-bodied fossils: Beecher’s trilobite bed, Upper Ordovician, New York State.” Geology 19.12 (1991): 1221-1224

If you would like to learn more check out my episode on Beecher’s Trilobite Bed:

Fossil Spotlight

Fossil Spotlight: Narrow-Nosed Rhinoceros

File:Stephanorhinus etruscus skull.JPG
Skull of the Narrow-Nosed Rhinoceros, Stephanorhinus etruscus. Image from Ghedoghedo.

Who: The Narrow-Nosed Rhinoceros, Stephanorhinus
Lagerstätte: Binagadi Asphalt Seep in Azerbaijan and other places
What: Tar pits containing thousands of fossils are found across the world with the most famous being La Brea Tar Pits in California. One of these is the Binagadi Asphalt Seep in Azerbaijan. This trap is thought to be older than La Brea dated up to 190,000 years old compared to La Brea’s 60,000 year age. Many species of animals are found here including the cave lion, cave hyena, and Irish elk. Among the most famous is the narrow-nosed rhinoceros Stephanorhinus. A full mounted skeleton is on display at the Hasanbey Zardabi Natural History Museum in Baku. The skeleton was made of bones from different specimens from the tar pit. Stephanorhinus itself was rather common during its heyday and could be found in Europe all the way to East Asia.

Huseynov, Said, and John M. Harris. “AZERBAIJAN’S FOSSIL CEMETERY.” Natural History 119.3 (2010): 16-21.

Fossil Spotlight

Fossil Spotlight: Maple Seed

Fossilized maple seed. Image from

Who: Maple Seed
Lagerstätte: Florissant Formation at Florissant Fossil Beds National Monument in Colorado
What: This is a maple seed preserved in shale at Florssiant Fossil Beds NM. The park is well known for its amazingly preserved insects and plants which are usually quite rare in the fossil record. It dates to the Eocene about 34 million years ago. Plant fossils like redwoods, hickory, elms, and rubber trees indicate that the area was once warm and humid; a far difference from its modern cold and drier climate. These plants were preserve in a lake which had occasional algal blooms. When plants or insects landed on the algal mat, they get entrapped and then fall to the lake’s bottom. The algae holds the leaves together and delicately buries them leaving a thin carbon film.


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.

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