Name Meaning:  Tully Monster

Geologic Era:  Late Carboniferous

Location Found:  Mazon Creek Formation (Braidwood, IL area)

Estimated Range:  Modern Illinois

Size:  8-35 cm in length

Extinction:  299 million years ago

This little animal is the state fossil of Illinois.  Ours is just a partial specimen in an ironstone nodule.  The parts that are preserved are a good portion of the head, the eyestalks, and the beginnings of the proboscis.  If I had to guess, if our Tully Monster was complete, it would probably measure about 20 centimeters long (including the proboscis).  The nodule is in two halves, one a positive impression and the other a negative impression.  The eyestalks are pronounced enough that one can feel them if one ran a finger along their location.  Tullymonstrum lived in what is now Illinois, which as the time was a shallow sea connected to a river delta, probably similar in climate and appearance to modern Louisiana.    

Until 2016, Tullymonstrum was classified as an invertebrate, though where it fell in among invertebrates was not very clear.  Ideas ranged anywhere from a type of conodont to a worm to an as-yet unidentified group of animals.  The most recent analysis, however, showed the presence of a notochord.  This structure is the basis for the spinal cord, which places Tullymonstrum firmly in the vertebrate category.  While clearly unlike any vertebrate alive today, it is possibly related to modern lampreys and hagfish, which are some of the most primitive vertebrates still in existence.  So, while not looking fish-like in the slightest, the Tully Monster was actually a very early fish.  

Further evidence for Tullymonstrum being a vertebrate was found in further analysis of its eyes.  Particles called melanosomes were detected in the remnants of the eyes.  These particles are only found in the eyes of vertebrates.  The Carboniferous period is well known for evolution experimenting with some rather bizarre forms; Tullymonstrum was no exception.

Image Credits:

Life Restoration:  By Nobu Tamura email:nobu.tamura@yahoo.com http://spinops.blogspot.com/ http://paleoexhibit.blogspot.com/ – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=49352908