Graptolites: Our Oldest Relatives
This fellow is the graptolite, Isograptus cf. maximus, from the Piranha Formation, Middle Ordovician (Dapingian), Bolivia.
Graptolites (Graptolita) are colonial animals. The biological affinities of the graptolites have always been debatable. Originally regarded as being related to the hydrozoans, graptolites are now considered to be related to the pterobranchs, a rare group of modern marine animals. They are hemichordates, phylum Hemichordata, a primitive group who share a common ancestry with the vertebrates. Yes, you're looking at one of your oldest relatives!
In life, many graptolites…