Mazon Creek Fossil Fauna

Tully Monsters, and the mysterious "Y" and "H" Animals

The "Tully Monster"

In 1955, a Lockport, IL, pipefitter, Francis Tully, brought a puzzling Pit 11 find to George Langford and Dr. Richardson at the Field Museum. Richardson, equally perplexed, called the discovery a “monster.” The name stuck and it was published as such: Tullimonstrum gregarium. At the time of description in 1966, critical evidence for assigning it to a specific phylum was missing or not understood. It was thought to be an annelid worm, or possibly even a shell-less swimming mollusk. However, for 60 years it remained a complete mystery!

The Tully Monster is found only in Illinois and in 1989, it became the State Fossil. Since then, it has only further captured the public’s imagination.

A study led by Yale University, in cooperation with the Field Museum, the Burpee museum and others, looked at over 1200 specimens with state-of-the-art technology. In 2016, sixty years after it was first discovered, the Tully finally has a definition. It is a jawless fish on the lineage of lampreys and hagfish.

Tullimonstrum gregarium

       Tullimonstrum gregarium, Milwaukee Public Museum collection VP365807.1 and VP365807.2 (positive and negative halves)
                  Field Museum collection (T.Testa)
                                                                                 J.Wittry collection
                  Tullimonstrum gregarium, Milwaukee Public Museum collection VP367558.1-2 (positive and negative halves)
                                                                               Field Museum collection
                  Tullimonstrum gregarium, Milwaukee Public Museum collection VP366199.1-2 (positive and negative halves)
                                                                              The Field Museum collection
                                               Tullimonstrum gregarium, A.Young collection - Pit 11, Braidwood, Illinois
                                                                   Chicago Academy of Sciences collection
                                               Tullimonstrum gregarium, A.Young collection - Pit 11, Braidwood, Illinois
                                            Tullimonstrum gregarium, Milwaukee Public Museum collection VP366202.1
                                                       Earth Science Club of Northern Illinois club member collection
                                               Tullimonstrum gregarium, Milwaukee Public Museum collection VP25859

Tullimonstrum  proboscis and "claw"

                              Tullimonstrum gregarium, Milwaukee Public Museum collection VP26070.1-2 (plus claw detail)
Field Museum collection
                                                Tullimonstrum gregarium, Milwaukee Public Museum collection VP36208
                                                                                                                                                                           J.Wittry collection

Tullimonstrum  eye-bar

                           Tullimonstrum gregarium, Milwaukee Public Museum VP366211.1-2 (positive and negative halves)
                                                                                                                             Field Museum collection

Tullimonstrum tail

                                         Tullimonstrum gregarium tail section, A.Young collection - Pit 11, Braidwood, IL

Incertae sedis "Y" and "H" Animals

Escumasia roryi 

"Y" Animal
             Escumasia roryi, MPM P360288.1-2 (positive and negative halves showing (eye?) pigment at the end of each arm)
                                                                            Milwaukee Public Museum P360292

Etacystis communis

"H" Animal
                         Etacystis communis, Milwaukee Public Museum collection P2198.1-2 (positive and negative halves)
                                                                                                                             MPM P26274.1