Dalmanella emacerata

Classification
Phylum: Brachiopoda
Class: Rhynchonellata
Order: Orthida
Family: Dalmanellidae
Genus: Dalmanella
Species: Dalmanella emacerata (Hall, 1860)

Taxonomic Details

Holland (UGA Strat Lab, 2013)

  • NOTE: Dr. Jisuo Jin n is currently studying Dalmanella and believes that this species actually belongs to Heterorthina. “Heterorthina can be recognized based on the presence of a dorsal medial groove or medial interspace (as opposed to medial rib) and a prominently trilobite cardinal process. These species have not yet been formally assigned to Heterorthina.”

Stratigraphic Occurrences

D.emacerata_strat

Geographic Occurrences

		
Map point data provided by iDigBio.

Stratigraphic Description

Sequences (Formations)

  • C1 Sequence (Clays Ferry/Kope: Southgate, Economy/Fulton)

Identification in Hand Sample

  • Width about 1.1 times the length, greatest width noted at the shell middle
  • Outline varying from transversely subquadrate to transversely subelliptical to subcircular
  • Pedicle valve moderately convex in lateral profile, greatest convexity observed between the shell middle and the umbo
  • Adjustor muscle impressions small, situated at base and sides of the dental plates
  • Brachial valve nearly plane in lateral profile; sulcus narrow on the umbo, becoming weak or obsolete near the front margin

Dalmanella emacerata from the McMillan formation of Cincinnati, Ohio (OUIP 478)

Published Description

Davis (1998):

  • (as Onniella) Articulate brachiopod. Differs from the next species (O. multisecta) by greater size, flatter valves, more rectangular outline, and lack of median sinus in the brachial valve. Fulton through Southgate.

Howe and Reso (1967):

  • Shell of average size for the genus; width about 1.1 times the length, greatest width noted at the shell middle. Outline varying from transversely subquadrate to transversely subelliptical to subcircular; cardinal and antero-lateral extremities broadly rounded, sides nearly straight or gently curved. Anterior commissure rectimarginate. Ornamentation costellate, about two or three costellae spaced in 1 mm. along the front margin; concentric growth lines developed in a few specimens.
  • Pedicle valve moderately convex in lateral profile, greatest convexity observed between the shell middle and the umbo in most specimens; anterior profile triangular. Fold narrow on the umbo, continuing as a progressively wider fold anteriorly. Posterolateral flanks bounding fold gently depressed. Interarea short, less than one-half of the maximum shell width, apsacline, and curved in lateral profile. Interior of pedicle valve: Delthyrium open, triangular; delthyrial cavity deep; pedicle callist small; teeth large, crural fossettes deep, oblique; dental plates advancing. Muscle field showing wide variations; adductor muscle scars small, ovate, situated between delthyrial cavity and middle of shell; adductor muscle track linear, much narrower and shorter than the diductor impressions. Diductor scars large, greatly elongated, averaging about two-thirds of shell length, generally multilobate, lateral lobes smaller than submedian pair; primary diductor impressions commonly separated by a median septum in front of adductor muscle track; in some specimens diductor scars diverging and separated by a broad platform as in Onniella Bancroft and Paucicrura Cooper. Adjustor muscle impressions small, situated at base and sides of the dental plates.
  • Brachial valve nearly plane in lateral profile; sulcus narrow on the umbo, becoming weak or obsolete near the front margin; flanks bounding sulcus somewhat swollen. Interior of brachial valve: Brachiophores bladelike plates; cardinal shaft elongate, generally expanded posteriorly, bulbous in some specimens; myophore differentially trilobate; sockets wide, generally deep, bounded laterally by low ridges (possibly rudimentary fulcral plates). Median ridge thick, ex-tending to anterior margin of muscle field; muscle field subpentagonal in outline; anterior adductor scars much larger than posterior pair, separated from latter by weak transverse ridge.

McFarland (1931):

  • D. emacerata is a semi-elliptical or subquadrate, finely striated, thin shelled species. Typically width about 20 mm., length about 0.75 width. Anteriorly 16-17 striae in 5 mm. Pedicle valve depressed convex, brachial flat, with faintly developed sinus.

Foerste (1912):

  • In the original description the shell is stated to be “semi-elliptical, length and width about as five to seven; hinge-line nearly equalling the width of the shell.” Fig. 1, on plate II, of the Fifteenth Report, represents a brachial valve 15 mm. in length and 20.5 mm in width; the ratio of length to width being as three to four. Fig.2 on the same plate represents a pedicel valve almost 14 mm. in length and 21 mm. in width, the ratio being as two to three.
  • In typical Dalmanella emacerata, there is a tendency toward the greatest width lying near the line across the middle of the shell and a tendency toward a more angular postero-lateral outline. In the type Dalmanella emacerata, Hall, as preserved in the American Museum of Natural History, many of the finer striae are more or less obscured by the clay which still adheres to the specimen, but sufficient evidence is presented under a lens to make it certain that the striae of the type are very fine and close. It is now evident that the typical Dalmanella emacerata must not be identified with the much more coarsely striated form found in the Fulton bed, 2 feet above the crinoidal top of the so-called Trenton rock as exposed in the First Ward, in Cincinnati, Ohio.
  • The horizon of the typical Dalmanella emacerata is in the Southgate bed, about 160 feet above the low-water in the Ohio River, at Cincinnati, Ohio. The lower forms, about 60 feet above the base of the Eden, are somewhat coarsely striated.

Foerste (1903):

  • The Saltillo limestone contains comparatively few species of fossils, and most of these are not abundant. The most widely distributed species is a variety of Dalmanella emacerata,’ 20mm in width, which is abundant at Clifton and on Beech creek, north- west of Waynesboro.