Isomicraster danei Cooke, 1953
Plate: IsDa-10
Series: Upper Cretaceous Group: Austin Formation: Austin Chalk (Gober Tongue)
Locale: Bailey, Texas County: Fannin, Texas Stage: Santonian
Length: 58.8 mm Width: 56.1 mm Height: 28.7 mm
Specimen in photo: U.S.N.M. 108391 Holotype
Collector: (USGS Survey)
Repository: Paleobiology Dept., NMNH, Smithsonian Institution Plate: IsDa-10
HOLOTYPE INFO:
Holotype: USNM 108391 (Cooke, 1953).
Locality: USGS 17878, 2 miles northwest of Bailey, Fannin County, Texas.
Stratigraphy: Top of the Gober Tongue of the Austin Chalk.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Atelostomata Zittel, 1879
Order: Spatangoida L. Agassiz, 1840
Family: Epiasteridae Lambert, 1920
Genus: ISOMICRASTER Lambert, 1901
Species: Isomicraster danei Cooke, 1953
TYPE SPECIES: Isomicraster stolleyi Lambert, 1901
DIAGNOSIS
Test sub-conical or dome-shaped with a steep anterior slope and rostrate posterior. Petals are long, depressed, and non-expanding; the unpaired anterior petal is similar in structure to the paired petals. Fascioles are absent (Cooke, 1953).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Austin
Formations: Austin Chalk (Gober Tongue).
Stratigraphic Units: Upper Cretaceous, Santonian.
Counties: Fannin.
Abundance: Rare; known definitively only from the holotype.
DESCRIPTION
TOP: Length, width, height: 58.8 mm L × 56.1 mm W × 28.7 mm H.
Top shape: Sub-conical or dome-shaped (Cooke, 1953).
Top domed: Steeply sloping forward into a sulcus.
SIDE: Side shape: Rostrate (beaked) behind.
BOTTOM: (Lower surface mostly missing in Holotype).
AMB: Amb shape: Petals long, depressed, not expanding, extending almost to the margin.
Amb arrangement: Anterior paired petals are straight and widely spreading. Posterior paired petals are slightly curved backward.
Unpaired Amb: The anterior petal (III) is "like the others" (petaloid/subpetaloid), not distinct as in Micraster.
PORE PAIRS: Arrangement: Poriferous zones equal the interporiferous zone in width.
Shape: Pores conjugate; outer pores slightly longer than the inner pores (Cooke, 1953).
TUBERCLES: Distribution: Small, evenly spaced.
GRANULES: Distribution: Surface is finely granulated (Cooke, 1953).
FASCIOLE: No fascioles (Cooke, 1953). This absence distinguishes the genus from Micraster.
APICAL SYSTEM: Location: Central.
PERIPROCT (ANUS): Shape: Circular.
Location: At the top of a slightly overhanging V-shaped truncation.
Visibility: Not visible from above.
PERISTOME (MOUTH): Condition: Not preserved in the holotype.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype USNM 108391. The holotype lacks most of the lower surface. A second internal mold from Texas was mentioned by Cooke but not surely identified.
ETYMOLOGY
Named for Carle Hamilton Dane (1900–1971), USGS geologist who worked extensively on the Upper Cretaceous of the Gulf Coastal Plain.
REMARKS & COMPARISONS
Comparisons:
Plate: IsDa-10
Series: Upper Cretaceous Group: Austin Formation: Austin Chalk (Gober Tongue)
Locale: Bailey, Texas County: Fannin, Texas Stage: Santonian
Length: 58.8 mm Width: 56.1 mm Height: 28.7 mm
Specimen in photo: U.S.N.M. 108391 Holotype
Collector: (USGS Survey)
Repository: Paleobiology Dept., NMNH, Smithsonian Institution Plate: IsDa-10
HOLOTYPE INFO:
Holotype: USNM 108391 (Cooke, 1953).
Locality: USGS 17878, 2 miles northwest of Bailey, Fannin County, Texas.
Stratigraphy: Top of the Gober Tongue of the Austin Chalk.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Atelostomata Zittel, 1879
Order: Spatangoida L. Agassiz, 1840
Family: Epiasteridae Lambert, 1920
Genus: ISOMICRASTER Lambert, 1901
Species: Isomicraster danei Cooke, 1953
TYPE SPECIES: Isomicraster stolleyi Lambert, 1901
DIAGNOSIS
Test sub-conical or dome-shaped with a steep anterior slope and rostrate posterior. Petals are long, depressed, and non-expanding; the unpaired anterior petal is similar in structure to the paired petals. Fascioles are absent (Cooke, 1953).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Austin
Formations: Austin Chalk (Gober Tongue).
Stratigraphic Units: Upper Cretaceous, Santonian.
Counties: Fannin.
Abundance: Rare; known definitively only from the holotype.
DESCRIPTION
TOP: Length, width, height: 58.8 mm L × 56.1 mm W × 28.7 mm H.
Top shape: Sub-conical or dome-shaped (Cooke, 1953).
Top domed: Steeply sloping forward into a sulcus.
SIDE: Side shape: Rostrate (beaked) behind.
BOTTOM: (Lower surface mostly missing in Holotype).
AMB: Amb shape: Petals long, depressed, not expanding, extending almost to the margin.
Amb arrangement: Anterior paired petals are straight and widely spreading. Posterior paired petals are slightly curved backward.
Unpaired Amb: The anterior petal (III) is "like the others" (petaloid/subpetaloid), not distinct as in Micraster.
PORE PAIRS: Arrangement: Poriferous zones equal the interporiferous zone in width.
Shape: Pores conjugate; outer pores slightly longer than the inner pores (Cooke, 1953).
TUBERCLES: Distribution: Small, evenly spaced.
GRANULES: Distribution: Surface is finely granulated (Cooke, 1953).
FASCIOLE: No fascioles (Cooke, 1953). This absence distinguishes the genus from Micraster.
APICAL SYSTEM: Location: Central.
PERIPROCT (ANUS): Shape: Circular.
Location: At the top of a slightly overhanging V-shaped truncation.
Visibility: Not visible from above.
PERISTOME (MOUTH): Condition: Not preserved in the holotype.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype USNM 108391. The holotype lacks most of the lower surface. A second internal mold from Texas was mentioned by Cooke but not surely identified.
ETYMOLOGY
Named for Carle Hamilton Dane (1900–1971), USGS geologist who worked extensively on the Upper Cretaceous of the Gulf Coastal Plain.
REMARKS & COMPARISONS
Comparisons:
- Isomicraster rossi: I. danei has deeper petals, a deeper anterior sulcus, and finer granulation than I. rossi (Cooke, 1953), which is found in the Ozan Formation (Campanian) of Arkansas.
- Micraster: Isomicraster superficially resembles Micraster but is distinguished by the absence of a subanal fasciole and by the anterior ambulacrum being similar in structure to the paired petals (petaloid) rather than distinct.
