Macraster roberti var ovatus Smiser, 1936
Plate: MaRovOv-10
Series: Lower Cretaceous Group: Washita Formation: Duck Creek
Locale: Alpine County: Brewster Stage: Albian
Length: 29 mm Width: 30 mm Height: 18 mm
Specimen in photo: Smiser Collection
Repository: Paleobiology Dept., NMNH, Smithsonian Institution
HOLOTYPE INFO:
Holotype: USNM (Originally BEG/UT 1734 per Smiser, 1936).
Locality: Georgetown Road, 4 miles north of Alpine, Brewster County, Texas.
Stratigraphy: Duck Creek Formation, Washita Group.
SYNONYMY
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: Macrasteridae Lambert, 1920
Genus: MACRASTER Roemer, 1888
Species: Macraster roberti Lambert, 1924
Variety: Macraster roberti var. ovatus Smiser, 1936
TYPE SPECIES: Macraster texanus Roemer, 1888
DIAGNOSIS
A variety of Macraster roberti characterized by a broad, rounded, cordate test (width slightly exceeding length). The posterior face is vertically truncated and perpendicular to the base. Ambulacra are narrow and lanceolate (Smiser, 1936).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Duck Creek Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Brewster.
Abundance: Rare.
DESCRIPTION
TOP: Length, width, height: 29.0 mm L × 30.0 mm W × 18.0 mm H.
Top shape: Cordate, rounded, and broad. Widest part is 60% from the posterior end.
Top domed: Apex positioned posterior of center. Anterior end features a small furrow.
SIDE: Ambitus: Positioned about 35–40% of the distance from the adoral surface.
Side shape: Posterior end is truncated and perpendicular to the base.
Profile: Apex is posterior.
BOTTOM: Bottom shape: Base flat.
AMB: Amb shape: All ambulacra are lanceolate, narrow, and equal in size.
Amb arrangement: Unpaired ambulacrum is straight. Paired ambulacra are slightly petaloid with open ends; anterior pair is slightly longer than the posterior pair. Posterior paired ambulacra do not reach the margins.
PORE PAIRS: Arrangement: Unpaired ambulacrum pores are slit-shaped, closely spaced, and arranged slightly en chevron.
Shape: Pores in paired ambulacra are slit-like.
TUBERCLES: Distribution: Sparse; larger adorally.
Features: Small and slightly crenulate.
GRANULES: Not specified.
FASCIOLE: Absent in Macraster.
APICAL SYSTEM: Size: Small.
Genital pores: 4 gonopores.
Plating: Genital plates are hexagonal. Ocular plates are C-shaped with the indentation facing toward the ambulacra.
PERIPROCT (ANUS): Shape: Vertically oval.
Location: Located above the midpoint on the posterior truncation.
Visibility: Slightly visible from above; clearly visible from the posterior end.
PERISTOME (MOUTH): Location: Anterior of center.
Visibility: Visible from the anterior end.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype studied (Smiser Collection/USNM).
ETYMOLOGY
Named for its ovate shape, distinguishing it as a variety of M. roberti.
REMARKS & COMPARISONS
Remarks: Kamyabi Shadan et al. (2014) reviewed the genus and noted that Macraster solitariensis (Smiser, 1936) is a synonym of Macraster roberti (Lambert & Thiéry, 1924). The high number of species names for Macraster in the region is likely an overestimation of biological diversity due to ecophenotypic variation.
Comparisons:
Plate: MaRovOv-10
Series: Lower Cretaceous Group: Washita Formation: Duck Creek
Locale: Alpine County: Brewster Stage: Albian
Length: 29 mm Width: 30 mm Height: 18 mm
Specimen in photo: Smiser Collection
Repository: Paleobiology Dept., NMNH, Smithsonian Institution
HOLOTYPE INFO:
Holotype: USNM (Originally BEG/UT 1734 per Smiser, 1936).
Locality: Georgetown Road, 4 miles north of Alpine, Brewster County, Texas.
Stratigraphy: Duck Creek Formation, Washita Group.
SYNONYMY
- Macraster roberti var. ovatus Smiser, 1936
- Macraster roberti Lambert, 1924 (fide Kamyabi Shadan et al., 2014)
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: Macrasteridae Lambert, 1920
Genus: MACRASTER Roemer, 1888
Species: Macraster roberti Lambert, 1924
Variety: Macraster roberti var. ovatus Smiser, 1936
TYPE SPECIES: Macraster texanus Roemer, 1888
DIAGNOSIS
A variety of Macraster roberti characterized by a broad, rounded, cordate test (width slightly exceeding length). The posterior face is vertically truncated and perpendicular to the base. Ambulacra are narrow and lanceolate (Smiser, 1936).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Duck Creek Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Brewster.
Abundance: Rare.
DESCRIPTION
TOP: Length, width, height: 29.0 mm L × 30.0 mm W × 18.0 mm H.
Top shape: Cordate, rounded, and broad. Widest part is 60% from the posterior end.
Top domed: Apex positioned posterior of center. Anterior end features a small furrow.
SIDE: Ambitus: Positioned about 35–40% of the distance from the adoral surface.
Side shape: Posterior end is truncated and perpendicular to the base.
Profile: Apex is posterior.
BOTTOM: Bottom shape: Base flat.
AMB: Amb shape: All ambulacra are lanceolate, narrow, and equal in size.
Amb arrangement: Unpaired ambulacrum is straight. Paired ambulacra are slightly petaloid with open ends; anterior pair is slightly longer than the posterior pair. Posterior paired ambulacra do not reach the margins.
PORE PAIRS: Arrangement: Unpaired ambulacrum pores are slit-shaped, closely spaced, and arranged slightly en chevron.
Shape: Pores in paired ambulacra are slit-like.
TUBERCLES: Distribution: Sparse; larger adorally.
Features: Small and slightly crenulate.
GRANULES: Not specified.
FASCIOLE: Absent in Macraster.
APICAL SYSTEM: Size: Small.
Genital pores: 4 gonopores.
Plating: Genital plates are hexagonal. Ocular plates are C-shaped with the indentation facing toward the ambulacra.
PERIPROCT (ANUS): Shape: Vertically oval.
Location: Located above the midpoint on the posterior truncation.
Visibility: Slightly visible from above; clearly visible from the posterior end.
PERISTOME (MOUTH): Location: Anterior of center.
Visibility: Visible from the anterior end.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype studied (Smiser Collection/USNM).
ETYMOLOGY
Named for its ovate shape, distinguishing it as a variety of M. roberti.
REMARKS & COMPARISONS
Remarks: Kamyabi Shadan et al. (2014) reviewed the genus and noted that Macraster solitariensis (Smiser, 1936) is a synonym of Macraster roberti (Lambert & Thiéry, 1924). The high number of species names for Macraster in the region is likely an overestimation of biological diversity due to ecophenotypic variation.
Comparisons:
- Macraster solitariensis: M. roberti ovatus is very similar to M. solitariensis in dorsal outline. However, M. roberti ovatus differs by having a vertically truncated posterior end (perpendicular to base), whereas M. solitariensis is not vertically truncated. Additionally, the ambitus is much lower on M. solitariensis.
