Macraster elegans (Shumard, 1853)
Plate: MaEl-10
Series: Lower Cretaceous Group: Washita Formation: Fort Worth
Locale: Denison County: Grayson Stage: Albian
Length: 74.8 mm Width: 69.9 mm Height: 47.2 mm
Specimen in photos: Collection of Ed Elliott
Repository: Private Collection
HOLOTYPE INFO:
Holotype: Originally described by Shumard (1853). Type material likely lost (common for Shumard's collections).
Locality: Fort Washita, near Durant, Oklahoma (Shumard, 1853).
Stratigraphy: Fort Worth Limestone (or equivalent "marly clay"), 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 elegans (Shumard, 1853)
TYPE SPECIES: Macraster texanus Roemer, 1888
DIAGNOSIS
Test very large, oblong-cordiform, and flattened above and below. Ambulacra are long, depressed, and subpetaloid, reaching nearly to the margin. Distinguished from Hemiaster by the absence of a distinct peripetalous fasciole and larger size.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Fort Worth Limestone; Duck Creek, Denton, Weno (Adkins, 1928).
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Grayson, Tarrant, Bosque, Pecos.
Abundance: Common in the Fort Worth Limestone; one of the largest echinoids in the Texas Cretaceous.
DESCRIPTION
TOP: Length, width, height: 74.8 mm L × 69.9 mm W × 47.2 mm H.
Top shape: Oblong, cordiform (Clark & Twitchell, 1915).
Top domed: Flattened on the upper surface. A shallow groove occupies the anterior face, cutting the margin lightly.
SIDE: Ambitus: Rounded sides.
Side shape: Flattened above and below.
Profile: Posterior face is obliquely but not broadly truncated (Clark & Twitchell, 1915).
BOTTOM: Bottom shape: Flattened.
AMB: Amb shape: Ambulacral areas are nearly equal and depressed, with a distinct furrow on the upper surface. Subpetaloidal on the upper surface, reaching quite to the upper margin of the rounded sides (Clark & Twitchell, 1915).
Amb arrangement: Unpaired ambulacrum is narrower than the others.
PORE PAIRS: Shape: Pores consist of elongated, slit-like openings.
Arrangement: Poriferous zones are long, wide, and straight (Clark & Twitchell, 1915). Pores in the unpaired ambulacrum are smaller and more closely approximated.
TUBERCLES: Distribution: Surface of both areas covered with minute tubercles.
GRANULES: Distribution: Microscopic granules located between the tubercles (Clark & Twitchell, 1915).
FASCIOLE: Absent. (Note: Clark & Twitchell, 1915 claimed peripetalous fascioles were "present although poorly developed," but Roemer (1888) and Cooke (1946) define Macraster specifically by the absence of fascioles).
APICAL SYSTEM: Size: Small and compact.
Plating: Consists of four large perforated genital plates and five small oculars (Clark & Twitchell, 1915).
PERIPROCT (ANUS): Shape: Large and oval.
Location: Situated on the obliquely truncated face of the posterior margin; opens downward (Clark & Twitchell, 1915).
PERISTOME (MOUTH): Shape: Transversely oval.
Location: Situated near the anterior margin.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: One specimen studied from the Collection of Ed Elliott.
ETYMOLOGY
From the Latin elegans (elegant, fine), referring to the symmetry and form of the test.
REMARKS & COMPARISONS
Remarks: Roemer (1888) established the genus Macraster (with M. texanus as type) for forms identical to Hemiaster elegans. While Clark (1915) rejected Macraster believing the species possessed fascioles, modern workers (e.g., Cooke, 1946) accept Macraster as a valid genus for these large, fasciole-less spatangoids. M. texanus is generally considered a synonym of M. elegans.
Comparisons:
Plate: MaEl-10
Series: Lower Cretaceous Group: Washita Formation: Fort Worth
Locale: Denison County: Grayson Stage: Albian
Length: 74.8 mm Width: 69.9 mm Height: 47.2 mm
Specimen in photos: Collection of Ed Elliott
Repository: Private Collection
HOLOTYPE INFO:
Holotype: Originally described by Shumard (1853). Type material likely lost (common for Shumard's collections).
Locality: Fort Washita, near Durant, Oklahoma (Shumard, 1853).
Stratigraphy: Fort Worth Limestone (or equivalent "marly clay"), Washita Group.
SYNONYMY
- Hemiaster elegans Shumard, 1853
- Macraster texanus Roemer, 1888 (Type of Genus; considered synonym by Cooke, 1946)
- Epiaster elegans (Shumard) Böse, 1910
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 elegans (Shumard, 1853)
TYPE SPECIES: Macraster texanus Roemer, 1888
DIAGNOSIS
Test very large, oblong-cordiform, and flattened above and below. Ambulacra are long, depressed, and subpetaloid, reaching nearly to the margin. Distinguished from Hemiaster by the absence of a distinct peripetalous fasciole and larger size.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Fort Worth Limestone; Duck Creek, Denton, Weno (Adkins, 1928).
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Grayson, Tarrant, Bosque, Pecos.
Abundance: Common in the Fort Worth Limestone; one of the largest echinoids in the Texas Cretaceous.
DESCRIPTION
TOP: Length, width, height: 74.8 mm L × 69.9 mm W × 47.2 mm H.
Top shape: Oblong, cordiform (Clark & Twitchell, 1915).
Top domed: Flattened on the upper surface. A shallow groove occupies the anterior face, cutting the margin lightly.
SIDE: Ambitus: Rounded sides.
Side shape: Flattened above and below.
Profile: Posterior face is obliquely but not broadly truncated (Clark & Twitchell, 1915).
BOTTOM: Bottom shape: Flattened.
AMB: Amb shape: Ambulacral areas are nearly equal and depressed, with a distinct furrow on the upper surface. Subpetaloidal on the upper surface, reaching quite to the upper margin of the rounded sides (Clark & Twitchell, 1915).
Amb arrangement: Unpaired ambulacrum is narrower than the others.
PORE PAIRS: Shape: Pores consist of elongated, slit-like openings.
Arrangement: Poriferous zones are long, wide, and straight (Clark & Twitchell, 1915). Pores in the unpaired ambulacrum are smaller and more closely approximated.
TUBERCLES: Distribution: Surface of both areas covered with minute tubercles.
GRANULES: Distribution: Microscopic granules located between the tubercles (Clark & Twitchell, 1915).
FASCIOLE: Absent. (Note: Clark & Twitchell, 1915 claimed peripetalous fascioles were "present although poorly developed," but Roemer (1888) and Cooke (1946) define Macraster specifically by the absence of fascioles).
APICAL SYSTEM: Size: Small and compact.
Plating: Consists of four large perforated genital plates and five small oculars (Clark & Twitchell, 1915).
PERIPROCT (ANUS): Shape: Large and oval.
Location: Situated on the obliquely truncated face of the posterior margin; opens downward (Clark & Twitchell, 1915).
PERISTOME (MOUTH): Shape: Transversely oval.
Location: Situated near the anterior margin.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: One specimen studied from the Collection of Ed Elliott.
ETYMOLOGY
From the Latin elegans (elegant, fine), referring to the symmetry and form of the test.
REMARKS & COMPARISONS
Remarks: Roemer (1888) established the genus Macraster (with M. texanus as type) for forms identical to Hemiaster elegans. While Clark (1915) rejected Macraster believing the species possessed fascioles, modern workers (e.g., Cooke, 1946) accept Macraster as a valid genus for these large, fasciole-less spatangoids. M. texanus is generally considered a synonym of M. elegans.
Comparisons:
- Hemiaster whitei: M. elegans is separated from H. whitei by its much greater size, excessively long subpetaloidal areas, and the position of the periproct (on an obliquely truncated surface opening downward, vs. a vertical face opening upward in whitei) (Clark & Twitchell, 1915).
- Macraster denisonensis: M. elegans lacks the raised posterior keel and angular margin seen in M. denisonensis.
