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Abstract

The Cleveland Shale fauna represents a unique view of the time after a major Devonian extinction event

(Frasnian–Famenian) with the recovery of arthrodires (Placodermi) best represented by this most specious

North American fauna. This time was followed by an additional event (Hangenberg Biocrisis) leading to the

extinction of arthrodires (and all other placoderms). An understanding of the diversity and interrelationships of

North American arthrodires can aid our understanding of this critical time in vertebrate evolution. A new aspinothoracid

arthrodire Hlavinichthys jacksoni gen. et sp. nov. is described from the Late Devonian of northern

Ohio, U.S.A., which adds to our knowledge of this group. It provides a point of comparison to other members

of the fauna whose interrelationships are poorly known. A phylogenetic analysis supports an assignment of

Hlavinichthys jacksoni gen. et sp. nov. among the aspinothoracid arthrodires. This work has drawn attention to

the continued need for descriptive and phylogenetic analyses of this unique fauna. Decades old species descriptions

need revision along with preparation and description of new taxa. The work on Hlavinichthys jacksoni

gen. et sp. nov. here is one step in that process.

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Authors and Affiliations

Robert K. Carr
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Abstract

Six enigmatic fossils from the Famennian (Devonian) Cleveland Shale in Ohio, U.S.A., are interpreted here as

arthrodiran (Placodermi) egg cases. Recognition as egg cases is confirmed based on the observation of layered

collagen fibers. The presence of a tuberculated bone fragment preserved within one case confirms a vertebrate

source. The nature of the tubercles and the unique morphology of the egg cases supports the interpretation of

an arthrodiran source. Reports of Devonian egg cases are limited to either assumed chondrichthyan producers

or a putative ‘egg sac’ with a morphology atypical for any vertebrate. The Cleveland Shale egg cases thus

represent the first record for a non-chondrichthyan producer. Among placoderms, behaviors of a pelagic life

style with obligate nesting sites, reef fishes with live birth, and estuarine and fluvial nurseries, along with eggcase

oviparity testifies to the diversity of reproductive strategies. As with modern fishes these strategies may

be ecologically driven and the derived and variable reproductive biology of extant chondrichthyans is actually

a primitive condition among gnathostomes. One consequence of the diversity of reproductive strategies (dependent

on the topology of relationships) is the independent origin of internal fertilization within placoderms,

possibly suggesting external fertilization as the primitive gnathostome reproductive mode.

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Authors and Affiliations

Robert K. Carr
Gary Jackson

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