Macraster denisonensis Smiser, 1936
Plate: MaDe-10
Series: Lower Cretaceous Group: Washita Formation: Duck Creek
Locale: Denison County: Grayson Stage: Albian
Length: 44.7 mm Width: 42.6 mm Height: 30.1 mm
Specimen in photos: BEG 21263 Holotype
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: BEG 21263 (Cragin, 1893).
Locality: Denison, Grayson 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 denisonensis (Cragin, 1893)
TYPE SPECIES: Macraster texanus Roemer, 1888
DIAGNOSIS
Test large, elevated, and cordate with a very angular margin. Ambulacra are deeply sunken. Distinguished by a noticeable raised keel between the apical system and the posterior end.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Duck Creek Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Grayson.
Abundance: Rare.
DESCRIPTION
TOP: Length, width, height: 44.7 mm L × 42.6 mm W × 30.1 mm H.
Top shape: Cordate with a very angular margin. Anterior end features a wide sulcus.
Top domed: Very inflated; apex is located at the posterior third (1/3 from posterior end).
SIDE: Ambitus: Positioned low, about 1/3 from the base.
Side shape: Test very inflated with a sloping bottom. Posterior end is truncated.
Profile: A noticeable raised keel is present between the apical system and the posterior end.
BOTTOM: Bottom shape: Sloping.
AMB: Amb shape: All 5 ambulacra are sunken. Paired ambulacra are wide, petaloid, and open at the outer ends.
Amb arrangement: Both sets of paired ambulacra are equal in length.
Unpaired Amb: Pore pairs in the unpaired ambulacrum are slightly elongated with a granule between each pair.
PORE PAIRS: Shape: Pores in paired ambulacra are elongated.
TUBERCLES: Primary Perforated: Yes.
Primary Crenulate: Yes.
Distribution: Tubercles and granulation cover most of the test but thin out below the anterior paired ambulacra.
INTERAMB: Shape: All interambulacra are slightly raised from the surface.
FASCIOLE: Absent in Macraster.
APICAL SYSTEM: Location: Central to slightly posterior (apex is 1/3 from posterior).
Size: Small.
PERIPROCT (ANUS): Shape: Small, longitudinally oval.
Location: Situated on the small truncated posterior end, about 60% from the base.
Visibility: Cannot be seen from above.
PERISTOME (MOUTH): Shape: Subpentagonal.
Size: Depressed; about equal in size to the periproct.
Visibility: Visible from the anterior end.
Plastron: Large.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype BEG 21263.
ETYMOLOGY
Named for the city of Denison, Texas, the type locality.
REMARKS & COMPARISONS
Remarks: Cooke (1946) considered Macraster denisonensis to be a synonym of Macraster elegans washitae (Lambert). However, the specific characters described by Cragin (1893) regarding the uneven convexity and deep ambulacral impressions support its distinction in some classifications. Macraster is distinguished from Hemiaster primarily by the absence of a peripetalous fasciole.
Plate: MaDe-10
Series: Lower Cretaceous Group: Washita Formation: Duck Creek
Locale: Denison County: Grayson Stage: Albian
Length: 44.7 mm Width: 42.6 mm Height: 30.1 mm
Specimen in photos: BEG 21263 Holotype
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: BEG 21263 (Cragin, 1893).
Locality: Denison, Grayson County, Texas.
Stratigraphy: Duck Creek Formation, Washita Group.
SYNONYMY
- Hemiaster denisonensis Cragin, 1893
- Macraster elegans washitae (Lambert, 1920) (fide Cooke, 1946)
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 denisonensis (Cragin, 1893)
TYPE SPECIES: Macraster texanus Roemer, 1888
DIAGNOSIS
Test large, elevated, and cordate with a very angular margin. Ambulacra are deeply sunken. Distinguished by a noticeable raised keel between the apical system and the posterior end.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Duck Creek Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Grayson.
Abundance: Rare.
DESCRIPTION
TOP: Length, width, height: 44.7 mm L × 42.6 mm W × 30.1 mm H.
Top shape: Cordate with a very angular margin. Anterior end features a wide sulcus.
Top domed: Very inflated; apex is located at the posterior third (1/3 from posterior end).
SIDE: Ambitus: Positioned low, about 1/3 from the base.
Side shape: Test very inflated with a sloping bottom. Posterior end is truncated.
Profile: A noticeable raised keel is present between the apical system and the posterior end.
BOTTOM: Bottom shape: Sloping.
AMB: Amb shape: All 5 ambulacra are sunken. Paired ambulacra are wide, petaloid, and open at the outer ends.
Amb arrangement: Both sets of paired ambulacra are equal in length.
Unpaired Amb: Pore pairs in the unpaired ambulacrum are slightly elongated with a granule between each pair.
PORE PAIRS: Shape: Pores in paired ambulacra are elongated.
TUBERCLES: Primary Perforated: Yes.
Primary Crenulate: Yes.
Distribution: Tubercles and granulation cover most of the test but thin out below the anterior paired ambulacra.
INTERAMB: Shape: All interambulacra are slightly raised from the surface.
FASCIOLE: Absent in Macraster.
APICAL SYSTEM: Location: Central to slightly posterior (apex is 1/3 from posterior).
Size: Small.
PERIPROCT (ANUS): Shape: Small, longitudinally oval.
Location: Situated on the small truncated posterior end, about 60% from the base.
Visibility: Cannot be seen from above.
PERISTOME (MOUTH): Shape: Subpentagonal.
Size: Depressed; about equal in size to the periproct.
Visibility: Visible from the anterior end.
Plastron: Large.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype BEG 21263.
ETYMOLOGY
Named for the city of Denison, Texas, the type locality.
REMARKS & COMPARISONS
Remarks: Cooke (1946) considered Macraster denisonensis to be a synonym of Macraster elegans washitae (Lambert). However, the specific characters described by Cragin (1893) regarding the uneven convexity and deep ambulacral impressions support its distinction in some classifications. Macraster is distinguished from Hemiaster primarily by the absence of a peripetalous fasciole.
