MOTH locality

MOTH corresponds to a transitional zone between the clastic shales of the Road River Formation and the shelf carbonates of the Delorme Group.^[2] An earliest Devonian (Lochkovian) age is established by its fossil fauna, with distinctive Lochkovian fish such as Waengsjoeaspis, Canadapteraspis, Romundina, Altholepis, Polymerolepis, and Seretolepis. Brachiopod and conodont fossils also agree with this age estimate.^[8] At the time, the area would have been the tropical western continental shelf of Laurussia, fractured into many smaller basins and platforms by rifting along the Cordilleran front.^[2]

The vertebrate-bearing layers of MOTH are mainly composed of finely layered light grey argillaceous (clay-rich) limestone and dark grey silty calcareous shale. Fine grains of dolomite, calcite, and quartz are the predominant minerals in the sediment, reflecting a mixture of carbonate and siliciclastic inputs, including sharp grains sourced from airborne dust. The layers are flat-lying and undisturbed apart from subtle bioturbation, indicating perpetually calm waters. Older studies advocated for a shallow-water (tide pool or lagoon) environment, based on the assumption that its fish and invertebrates preferred coastal or freshwater habitats.^[5] A 2005 overview instead supported a more offshore environment, below storm wave base. In any case, the presence of pyrite indicates that bottom waters were anoxic (oxygen-deprived), allowing for high-fidelity fossil preservation. The exact cause of death is unknown for the fauna, as there is no evidence for turbidites (underwater mudslides) or seasonal water column disruptions.^[2] MOTH can be considered a lagerstätte.^[2]

More than 72 vertebrate species are known from MOTH as of 2015, though only around half have been formally named and described.^[7]

A few fully articulated ischnacanthiform fossils cannot be assigned to a specific species, as their diagnostic teeth are obscured by scales. Various MOTH ischnacanthid fossils have been referred to Ischnacanthus gracilis, though later studies refuted these claims.^[15][7] A 2001 UA biology dissertation by Gavin Hanke provides many new species names for MOTH specimens, but some of these names are yet to be published in a peer-reviewed journal.^[16]

Acanthodians ("spiny sharks") and acanthodian-like fish of MOTH
Genus	Species	Notes	Images
Altholepis	A. spp.	Three new species from MOTH have scales resembling Altholepis, though these species have yet to be formally named and described.[17][16][18]
Brochoadmones[6]	B. milesi	A deep-bodied acanthodian with many small spiny "finlets" on its underside.[19][1]
Cassidiceps[19]	C. vermiculatus	A deep-bodied acanthodian with a head covered in thick densely-textured scales.[19]
Erymnacanthus[7]	E. clivus	An ischnacanthid with small teeth and deep jaws.[7]
Euryacanthus[7]	E. rugosus	An ischnacanthid with large, robust teeth.[7][20]
Gladiobranchus[6]	G. probaton	A toothless gladiobranchid diplacanthiform. Potentially a junior synonym of Uraniacanthus spinosus, an English acanthodian which is exceedingly similar to Gladiobranchus.[21][22][23]
Kathemacanthus[19]	K. rosulentus	A deep-bodied acanthodian with a "necklace" of artichoke-shaped scales similar to more typical chondrichthyans.[19][24]
Lupopsyroides[25]	L. macracanthus	A toothless fish with simple scales and no apparent bony skeleton apart from fin spines.[16][25]
Lupopsyrus[6]	L. pygmaeus	An enigmatic acanthodian with simple scales and two rows of large keeled scutes on each side of its body.[26]
Nostolepis	N. striata	A weathered specimen with Nostolepis-type scales, yet to be formally described.[17][16] The specimen may be referable to Nostovicina laticristata.[27]
Obtusacanthus[25]	O. corroconis	An acanthodian-like fish with enlarged needle-like lip scales and no true teeth.[16][25][28]
Paucicanthus[29]	P. vanelsti	A narrow-bodied acanthodian lacking spines on its pectoral and pelvic fins.[29]
Polymerolepis	P. whitei	An enigmatic fish with "bradyodont"-like scales. Fossils from MOTH show that it had an anal fin spine, like acanthodians.[30]
Promesacanthus[10]	P. eppleri	A mesacanthid acanthodiform which retains small prepectoral spines, akin to "climatiiform" acanthodians.[10]
Seretolepis	S. elegans	A chondrichthyan-like fish closely related to Kathemacanthus.[24]
Tetanopsyrus[31]	T. breviacanthias[21]	A stocky diplacanthiform with broad crushing plates instead of teeth. This species has relatively short pectoral spines.[21]
	T. lindoei[31]	A stocky diplacanthiform with broad crushing plates instead of teeth.[31] This species has relatively long pectoral spines.[21]
Tricuspicanthus[7]	T. gannitus	A common but small ischnacanthid with three rows of teeth.[7][20]
	T. pisciculus	A tiny ischnacanthid with two rows of teeth.[7]

Placoderms of MOTH
Genus	Species	Notes	Images
Romundina	R. stellina	An acanthothoracid placoderm. A single skull found at MOTH in 1990 has yet to be fully described.[8][17][32]

A 2011 UA biology thesis by Bradley Scott provides several new species names for MOTH osteostracan specimens, but some of these names are yet to be published in a peer-reviewed journal.^[33]

All of the thelodonts present at MOTH belong to the order Furcacaudiformes, a group characterized by small heads, humpbacked bodies which are deep and laterally flattened, and equally deep fork-shaped tails.^[14][9]

Thelodonts of MOTH
Genus	Species	Notes	Images
Cometicercus[9]	C. talimaaae	A small, rare, and relatively slender furcacaudid furcacaudiform.[9]
Drepanolepis[9]	D. maerssae	A tiny drepanolepidid[40] furcacaudiform with sickle-shaped scales.[9]
Furcacauda[9]	F. fredholmae	A medium-sized furcacaudid furcacaudiform with a pronounced dorsal fin.[9]
	F. heintzae[5]	A medium-sized furcacaudid furcacaudiform with a pronounced dorsal fin. Previously considered a species of Sigurdia.[5][9]
Sphenonectris[9]	S. turnerae	A relatively large furcacaudid furcacaudiform without a dorsal fin.[9]

A 2004 UA biology thesis by Jeffrey Greeniaus provides several new species names for MOTH pteraspidomorph specimens, but these names are yet to be published in a peer-reviewed journal.^[33]

Pteraspidomorphs of MOTH
Genus	Species	Notes	Images
Aserotaspis[5]	A. canadensis	A tesselate heterostracan with many small armor plates, each bearing a mesh of irregular ridges.[5]
Canadapteraspis[5]	C. alocostomata	A medium-sized pteraspidiform.[5]
Dinaspidella	D. elizabethae	A common medium-sized irregulareaspidine cyathaspidid.[5][41][42]
Lepidaspis[5]	L. serrata	A tesselate heterostracan with many small armor plates, each bearing a single serrated ridge.[5]
Nahanniaspis	N. mackenziei[5]	A common small irregulareaspidine cyathaspidid.[5][41][42]
Pionaspis	P. amplissima[5]	A rare relatively large cyathaspidid.[5]
Poraspis	P. polaris	A medium-sized poraspidine cyathaspidid.[5]

Conodonts are found at MOTH, including the Silurian-Pragian index fossil Ozarkodina remscheidensis.^[17][16] The most abundant invertebrates at MOTH are leperditiid ostracods which cluster together in mass death assemblages, sometimes around vertebrate remains. Various brachiopods can also be found at the site. Eurypterids are rare but well-preserved.^[5][2] Conulariids and phyllocarids have also been reported.^[8] Tiny fragments of typical shallow marine invertebrates (crinoids, brachiopods, bryozoans, corals) make up a minor component of the sediment.^[2]