Ordovician (Late Llandeilo – Early Ashgill)
Holtedahlina is an extinct genus of stationary epifaunal suspension feeders
Identification in Hand Sample:
- Strong ventral sulcus, dorsal fold anteriorly
- Unequally costellate
- Large pseudodeltidium
- Semicircular outline truncated by straight hinge line
Treatise on Invertebrate Paleontology, Part H, Vol. 2 (2000)::
- Profile gently dorsibiconvex with strong ventral sulcus, dorsal fold anteriorly; ornament of unequal costellate; large pseudodeltidium; small Chilidial plates; interior as in Strophomena, but dorsal transmuscle ridges weakly developed.
Fossils of Ohio (1998):
- A small to medium sized strophomenid brachiopod that has an unequally biconvex profile. Its semicircular outline is truncated by a straight hinge line. Fine ribs radiate from the umbones of both vaves. One of the characteristics that helps to distinguish this genus from others is the deep sulcus of the pedicle valve. Holtedahlina is recorded from the Waynesville Formation to the Drakes Formation.
- Schuchert distinguished two groups of Strophomena: (1) those in which the pedicle (ventral) valve is concave anteirorly and antero-laterally, and (2) those in which the convexity of the umbonal part of the pedicle (ventral) valve continues almost or altogether as far as the anterior margin, though in a diminishing degree.
- In the second group he included those in which the median part of the brachial (dorsal) valve tends to be elevated into a somewhat conspicuous fold anteriorly, and the corresponding part of the pedicle valve tends to be depressed into a sinus. The latter are here selected as the more typically forms of the proposed new generic group Holtedahlina, with Strophomena sulcata Verneuil as the genotype. This species is characterized by relatively coarse, radiating striae, coarse enough to be called plications, and the anterior part of the muscle scar of the pedicle valve is weakly defined.
- S. sinuata Meek, a closely similar species, occurs in the middle of the Fairmount and S. sulcata ranges from the Clarksville division of the Waynesville to the top of the Whitewater group, but the former may not be ancestral to the latter, since the anterior fold and sinus may have originated independently in a number of species from ancestors more nearly resembling S. planoconvexa Hall. S. sinuata, at least, appears to have originated directly form S. planoconvexa, whereas the immediate ancestors of S. sulcata are unknown.
- Strophomena scofieldi Winchell and Schuchert, from the Prosser member of the Trenton of the upper Mississippi valley resembles the preceding in having a median fold and sinus, but the radiating striae are much finer. It may not be as closely related as its general form suggests, but, for the present, it is regarded as possible that the more coarsely striated species originated from the more finely striated ones, and S. scofieldi is regarded as an early form of Holtedahlina.
- Provisionally S. planoconvexa Hall and S. maysvillensis also are included in Holtedahlina, being regarded as ancestral to S. sinuata. S. maysvillensis ranges from the lower Mount Hope to the upper Fairmount in various parts of Kentucky, and S. planoconvexa appears merely to be a local depauperated variety of the former, confined to a single layer between the top of the Mount Hope and the base of the Fairmount. The convexity of the median part of the brachial (dorsal) valveof S. maysvillensis anteriorly, with a corresponding concave flexure of the pedicle (ventral) valve, appears to be preliminary to the median fold and sinus of S. sinuata. S. planoconvexa, S. maysvillensis, and S. sinuata agree in the coarseness of the radiating striae and in the character of the muscle scar of the pedicle (ventral) valve.
- Strophomena hallie, Miller, from the Economy and Southgate members of the Eden, is less coarsely striated than typical S. maysvillensis, but may be regarded as intermediate between S. scofieldi and S. maysvillensis. In its tendency toward a nasute form, it simulates S. maysvillensis more closely than S. planoconvexa.
- In the same manner as S. sinuata may be regarded as a derivative of S. maysvillensis, S. millionensis may be a derivative of the same stock as S. hallie.
- Schuchert regarded S. scofieldi as closely related to S. billingsi Winchell and Schuchert, though the latter has a less defined sinus and fold, finer radiating striae, and concentric growth lines more delicate and closely crowded.
- Species resembling S. sulcata in having a median fold and sinus, and coarse, radiating striae, are figured by Holtedahl from the Christiania area. They appear to have a wide range in northern areas. In Canada, S. sulcata occurs on Manitoulin island, and similar forms occur in the Ottawa basin and as far northeast as lake St. John.
- Among the forms figured from the Girven district of Scotland, S. antiquata woodslandensis Reed may belong here.