Let me introduce you to graptolites. These odd little prehistoric creatures were colonies of tiny marine animals which formed protective cup-like structures around their bodies and filter-fed on microscopic plankton. They’re classified as hemichordates, and their closest living relatives are a similar member of that group called pterobranchs.

They appeared in the fossil record between about 490 and 320 million years ago, and came in a wide range of shapes and sizes. There were single rows, double rows, branches, spirals, forks, and even net-like forms. The earliest types lived attached to the sea floor, but later ones floated around freely near the surface of the ocean and could reach lengths of up to 1.5m (~5ft). Some may have attached themselves to seaweed and floating debris, others are thought to have dangled from their own little bubble-like flotation rafts.

Their remains are so numerous and widespread that they’re very useful as “index fossils”, allowing paleontologists to precisely date the age of the rocks they’re found in.

Yuknessia Cambrian Explosion Hemichordate Fossil

Name: Yuknessia sp
Superphylum Deuterostomia, Phylum Hemichordata, Class Pterobranchia
Geological Time: Middle Cambrian, more than 500 million years old
Size: 16 by 28 mm
Fossil Site: Wheeler Shale Formation, Millard County, Utah

This is as particularly well preserved specimen of the genus Yuknessia from the famous Wheeler Formation of Utah. Once thought to be fossil algaea, Yuknessia from the Cambrian is now interpreted as an early deuterostome metazoan, a group that includes Chordates, Hemichordata, Echinodermata, Xenoturbellida and Vetulicolia, and is placed in Class Pterobranchia.

The secret to an Oesia life: Prehistoric worm built tube-like 'houses' on sea floor
The fossilised remnants of tube-like 'dwellings' which housed a primitive type of prehistoric sea worm on the ocean floor have been identified in a new study. The long, perforated tubes may have looked like narrow chimneys reaching up from the sea bed, and were made by a creature called Oesia, which lived a solitary existence inside them about 500 million years ago.

Yannanozoon lividum, Putative Earliest Known Hemichordate from the Chengjiang Biota

“a fossil of the Cambrian Explosion from Yunnan Province, China”

Yannanozoon lividum 

Phylum Hemichordata
Geological Time: Early Cambrian (~525 million years ago)
Size: 23 mm long on a 75 mm by 65 mm matrix
Fossil Site: Chengjiang Maotianshan Hill, Quiongzhusi Section, Yu'anshan Member, Heilinpu FormationYuxi, Chengjiang County, Yunnan Province, China

Yannanozoon bear resemblance and traits to Haikouella lanceolata, a chordate from the same Maotianshan Shales.

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