Isomicraster rossi Cooke, 1953
Plate: IsRo-10
Series: Upper Cretaceous Group: Eagle Ford Formation: Eagle Ford
Locale: Terlinqua Region County: Brewster Stage: Turonian
Length: 43.1 mm (smallest) Width: 45.1 mm Height: 20.7 mm
Specimen in photo: U.S.N.M. 108392 B & 108392 A Syntype
Collector: Clarence S. Ross
Paleobiology Depart. NMNH, Smithsonian Institution
HOLOTYPE INFO:
Syntypes: USNM 108392 (A and B) (Cooke, 1953).
Locality: USGS 16867, 3 miles north of Hen Egg Mountain, Brewster County, Texas (Cooke, 1953).
Stratigraphy: Eagle Ford Shale.
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 rossi Cooke, 1953
TYPE SPECIES: Isomicraster stolleyi Lambert, 1901
DIAGNOSIS
Test subcordate or dome-shaped with a slight anterior emargination. Petals are all alike, slightly sunken, and long. Surface coarsely granular. Distinguished from I. danei by coarser granulation and shallower anterior sulcus (Cooke, 1953).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Eagle Ford
Formations: Eagle Ford Shale
Stratigraphic Units: Upper Cretaceous, Turonian
Counties: Brewster
Abundance: Represented by seven individuals, all crushed and fragmentary (Cooke, 1953).
DESCRIPTION
TOP: Length, width, height: 43.1 mm L × 45.1 mm W × 20.7 mm H (Smallest Syntype).
Top shape: Subconical or dome-shaped (Cooke, 1953).
Top domed: Slight emargination in front.
AMB: Amb shape: Petaloid; petals all alike (unpaired petal similar to paired).
Amb arrangement: Slightly sunken, rather long, reaching nearly to the margin.
Interporiferous Zones: About equal in width to the poriferous zones (Cooke, 1953).
INTERAMB: Granular.
PORE PAIRS: Shape: Inner pores circular or oval; outer pores elongate.
Arrangement: Pores conjugate (Cooke, 1953).
TUBERCLES: Distribution: Scattered, small, and sunken (Cooke, 1953).
GRANULES: Distribution: Surface coarsely granular (Cooke, 1953).
FASCIOLE: Presence: Faint traces of a partial fasciole in anterior interambulacra (Cooke, 1953).
APICAL SYSTEM: Location: Apparently nearly central.
Type: Ethmophractic.
Plating: Posterior ocular plates in contact.
Genital pores: Four genital pores (Cooke, 1953).
PERIPROCT (ANUS): Location: Apparently supramarginal, on a posterior truncation.
Condition: Not preserved in type material (Cooke, 1953).
PERISTOME (MOUTH): Location: At the anterior quarter.
Lip: Strongly lipped (Cooke, 1953).
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Syntypes USNM 108392 A & B. Seven individuals total examined by Cooke, all crushed/fragmentary.
ETYMOLOGY
Named for Clarence Samuel Ross (1880–1975), the USGS geologist who collected the type material.
REMARKS & COMPARISONS
Comparisons:
Plate: IsRo-10
Series: Upper Cretaceous Group: Eagle Ford Formation: Eagle Ford
Locale: Terlinqua Region County: Brewster Stage: Turonian
Length: 43.1 mm (smallest) Width: 45.1 mm Height: 20.7 mm
Specimen in photo: U.S.N.M. 108392 B & 108392 A Syntype
Collector: Clarence S. Ross
Paleobiology Depart. NMNH, Smithsonian Institution
HOLOTYPE INFO:
Syntypes: USNM 108392 (A and B) (Cooke, 1953).
Locality: USGS 16867, 3 miles north of Hen Egg Mountain, Brewster County, Texas (Cooke, 1953).
Stratigraphy: Eagle Ford Shale.
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 rossi Cooke, 1953
TYPE SPECIES: Isomicraster stolleyi Lambert, 1901
DIAGNOSIS
Test subcordate or dome-shaped with a slight anterior emargination. Petals are all alike, slightly sunken, and long. Surface coarsely granular. Distinguished from I. danei by coarser granulation and shallower anterior sulcus (Cooke, 1953).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Eagle Ford
Formations: Eagle Ford Shale
Stratigraphic Units: Upper Cretaceous, Turonian
Counties: Brewster
Abundance: Represented by seven individuals, all crushed and fragmentary (Cooke, 1953).
DESCRIPTION
TOP: Length, width, height: 43.1 mm L × 45.1 mm W × 20.7 mm H (Smallest Syntype).
Top shape: Subconical or dome-shaped (Cooke, 1953).
Top domed: Slight emargination in front.
AMB: Amb shape: Petaloid; petals all alike (unpaired petal similar to paired).
Amb arrangement: Slightly sunken, rather long, reaching nearly to the margin.
Interporiferous Zones: About equal in width to the poriferous zones (Cooke, 1953).
INTERAMB: Granular.
PORE PAIRS: Shape: Inner pores circular or oval; outer pores elongate.
Arrangement: Pores conjugate (Cooke, 1953).
TUBERCLES: Distribution: Scattered, small, and sunken (Cooke, 1953).
GRANULES: Distribution: Surface coarsely granular (Cooke, 1953).
FASCIOLE: Presence: Faint traces of a partial fasciole in anterior interambulacra (Cooke, 1953).
APICAL SYSTEM: Location: Apparently nearly central.
Type: Ethmophractic.
Plating: Posterior ocular plates in contact.
Genital pores: Four genital pores (Cooke, 1953).
PERIPROCT (ANUS): Location: Apparently supramarginal, on a posterior truncation.
Condition: Not preserved in type material (Cooke, 1953).
PERISTOME (MOUTH): Location: At the anterior quarter.
Lip: Strongly lipped (Cooke, 1953).
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Syntypes USNM 108392 A & B. Seven individuals total examined by Cooke, all crushed/fragmentary.
ETYMOLOGY
Named for Clarence Samuel Ross (1880–1975), the USGS geologist who collected the type material.
REMARKS & COMPARISONS
Comparisons:
- Isomicraster mexicanus: I. rossi appears to have longer petals than I. mexicanus Lambert, 1936, from the Lower Senonian of Chiapas (Cooke, 1953).
- Isomicraster danei: I. rossi has somewhat coarser granulation than I. danei Cooke, 1953. Additionally, I. danei (from the Santonian) lacks the partial fasciole traces seen in I. rossi and possesses a deeper anterior emargination (Cooke, 1953).
