The Four Mile Dam Formation, also called the Four Mile Dam Limestone, is a geologic formation in Michigan. It preserves fossils dating back to the middle Devonian period.

Fossil content Vertebrates Acanthodians Acanthodians reported from the Four Mile Dam Formation Genus Species Presence Material Notes Images 'Acanthodii'Unidentified "Two partial fin spines (JS 120, JS 121)". "Distinct from named acanthodians (Gyracanthus, Machaeracanthus, and Oracanthus) and chondrichthyans (Tamiobatis and Acondylacanthus) reported from Michigan".

Conodonts Conodonts reported from the Four Mile Dam Formation Genus Species Presence Material Notes Images AcodinaA. formosa Also found in the Detroit River, Traverse, Dundee, Bell, Alpena and Norway Point formations. BelodellaB. devonicusAlso found in the Detroit River, Traverse, Antrim, Alpena and Norway Point formations.IcriodusI. latericrescens latericrescensAlso found in the Traverse, Bell, Ferron Point, Genshaw, Newton Creek, Alpena, Norway Point, Potter Farm and Thunder Bay formations.OzarkodinaO. willsiAlso found in the Detroit River, Traverse, Antrim, Dundee, Alpena and Norway Point formations.PolygnathusP. varcusAlso found in the Traverse, Antrim, Alpena, Norway Point and Thunder Bay formations.

Placoderms Placoderms reported from the Four Mile Dam Formation Genus Species Presence Material Notes Images?Macropetalichthys?M. sp."A partial head shield (32M)".A petalichthyid. ?Mylostoma?M. sp.39 specimens, including potential juveniles.'Placodermi'Unidentified"One specimen of an armour plate (JS 4)".ProtitanichthysP. rockportensis"One specimen of an armor fragment (JS 101)".A coccosteid.

Invertebrates

Brachiopods Brachiopods reported from the Four Mile Dam Formation Genus Species Presence Material Notes ImagesDouvillinaD. distansFour Mile Dam, Thunder Bay River, Alpena County, Michigan.Also found in the Hungry Hollow Formation and Logansport Formation.LeptalosiaL. radicansFour Mile Dam, Thunder Bay River, Alpena County, Michigan.Also found in the Norway Point, Gravel Point, Alpena and Genshaw formations.LongispinaL. emmetensisDock Street clay member.Also found in the Alpena Limestone and Gravel Point Formation.MegastrophiaM. gibbosaFour Mile Dam, Thunder Bay River, Alpena County, Michigan.Also found in the Hungry Hollow Formation and Logansport Formation.OligorhachisO. oligorhachisFour Mile Dam, Thunder Bay River, Alpena County, Michigan.Also found in the Gravel Point Formation.PentamerellaP. alpenensisDock Street clay member.Also found in the Alpena Limestone and Gravel Point Formation.P. sp. CDock Street clay.A complete specimen.ProtoleptostrophiaP. lirellaDock Street clay member.Also found in the Norway Point Formation and Alpena Limestone.SchuchertellaS. anomalaPossibly the Dock Street clay member.Also found in the Gravel Point Formation.S. sp.Four Mile Dam, Thunder Bay River, Alpena County, Michigan.SpinulicostaS. mutocostaFour Mile Dam, Thunder Bay River, Alpena County, Michigan.Also found in the Bell, Rockport Quarry, Ferron Point, Beebe School, Thunder Bay and Potter Farm formations.StrophodontaS. erraticaDock Street clay member.Also found in the Alpena Limestone and Gravel Point Formation.S. fissicostaDock Street clay member.Also found in the upper Gravel Point Formation.S. nanusDock Street clay member.Also found in the Alpena Limestone and Gravel Point Formation.S. paulaDock Street clay member.Also found in the Alpena Limestone.S. sp. BDock Street clay member and overlying crystalline limestone beds.Several specimens. RhipidomellaR. penelope traversensis Thunder Bay River, Alpena County, Michigan.

Corals Corals reported from the Four Mile Dam Formation Genus Species Presence Material Notes ImagesAulocystisA. cooperiAlso found in the Plum Brook shale, Silica shale and Potter Farm Formation.A. jacksoni Dock Street clay member. Also found in the Silica Shale, Ferron Point Formation, Petoskey Formation, Hungry Hollow Formation, Widder Shale, Wanakah shale and Centerfield Limestone. AuloporaA. confertaAlso found in the Bell, Ferron Point, Gravel Point, Genshaw, Alpena, Potter Farm, Petoskey and Hungry Hollow formations.A. gregariaAlso found in the Genshaw Formation, Alpena Limestone and Petoskey Formation.PachyphragmaP. concentricumDock Street clay member.Also found in the Ferron Point Formation, Gravel Point Formation and Alpena Limestone.

Gastropods Gastropods reported from the Four Mile Dam Formation Genus Species Presence Material Notes ImagesAnematinaA. conicaUpper limestone unit.An elasmonematid.A. mellariaUpper limestone unit.An elasmonematid, very rare in the Four Mile Dam Limestone.BembexiaB. (Genuspira) nodosaUpper limestone unit.About 35 specimens.An eotomariid and the most abundant gastropod in the formation.DictyobembixD. bellaUpper limestone unit.5 specimens.An eotomariid.MourloniaM. lirataUpper limestone unit.An eotomariid.MurchisoniaM. (Murchisonia) subulataUpper limestone unit.A murchisoniid, extremely rare in the formation.NaticopsisN. sp.Upper limestone unit.A neritopsid, extremely rare in the formation.Palaeoscurria?P.? sp.Upper limestone unit.3 poorly preserved ventral molds.A metoptomatid.PlatycerasP. (Platyceras) bartlettenseDock Street Clay Member.A platyceratid.P. (Euthyrachis) indianenseDock Street Clay Member.A platyceratid.P. (Orthonychia) variabilisUpper limestone unit.A platyceratid.Pseudozygopleuridae? Genus AGenus A sp. AUpper limestone unit.Relatively numerous steinkerns.Pseudozygopleuridae? Genus BGenus B sp. BUpper limestone unit.One very poorly preserved steinkern with a few small shell patches (YPM 23684).SpiroscalaS. sp.Upper limestone unit.One specimen (UMMP 47377).An eotomariid. StraparollusS. (Philoxene) sp.Upper limestone unit.3 poorly preserved specimens. An euomphalid.TrepospiraT. (Angyomphalus) bellaUpper limestone unit.A raphistomatid, very rare in the Four Mile Dam Limestone.TurbinilopsisT. anacarinaUpper limestone unit.Abundant specimens.An anomphalid.

Sponges Sponges reported from the Four Mile Dam Formation Genus Species Presence Material Notes Images AnostylostromaA. anacolumna On Thunder Bay River. A stromatoporoid.

Trilobites Trilobites reported from the Four Mile Dam Formation Genus Species Presence Material Notes ImagesCordaniaC. raraDechenellaD. (Monodechenella) macrocephalaAlso found in the Hamilton Group.D. (Basidechenella) rowiAlso known from the Hamilton Group.EldredgeopsE. ranaOriginally reported as Phacops rana. Also found in the Hamilton, Hungry Hollow, Widder, Plum Brook, Prout, Ten Mile Creek, Alpena, Norway Point and Gravel Point formations.GreenopsG. aequituberculatusDock Street clay member.Also found in the Norway Point and Gravel Point formations.G. traversensisDock Street clay member.Also found in the Gravel Point Formation.PhacopsP. ranaReassigned to the genus Eldredgeops. ProetusP. (Crassiproetus) traversensis Also known from the Gravel Point Formation.

See also

List of fossiliferous stratigraphic units in Michigan

References