Heteraster mexicanus (Cotteau, 1890)
Plate: HeMe-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Edwards
Locale: Harker Heights County: Bell Stage: Albian
Length: 47.9 mm Width: 43.5 mm Height: 33.2 mm
Specimen in photo: Collection of Terry Stephenson
Repository: Collection of Terry Stephenson
HOLOTYPE INFO:
Holotype: Cotteau's original specimen. Current location unknown; possibly in the École des Mines (Paris) or lost.
Locality: Colima, Mexico (Cotteau, 1890)
Stratigraphy: Cretaceous (Albian)
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: Toxasteridae Lambert, 1920
Genus: HETERASTER d'Orbigny, 1853
Species: Heteraster mexicanus (Cotteau, 1890)
TYPE SPECIES: Spatangus oblongus Brongniart, 1821
DIAGNOSIS
Species rather large, oval, elongate, notched in front, vertically truncate behind. Upper face swollen, highest near the apical center. Unpaired ambulacrum pores heterogeneous, with long narrow pores alternating with shorter pairs. Apical system eccentric posterior (Cotteau, 1890; Cooke, 1955).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Edwards Formation; Comanche Peak Limestone, Goodland Limestone (Cooke, 1955).
Stratigraphic Units: Lower Cretaceous, Middle Albian (Cooke, 1955).
Counties: Bell, Menard, Hood, Williamson, Tarrant, Bosque, Gillespie, Upton (Cooke, 1955). Also Mexico (Colima, Chihuahua).
DESCRIPTION
TOP: Length, width, height: 47.9 mm L × 43.5 mm W × 33.2 mm H.
Top shape: Cordate, angular; margin has flat sections on either side of the sulcus. Widest point midway (Book Author); oval, elongate, notched in front (Cotteau, 1890).
Top domed: Upper face swollen, highest near the apical center (Cooke, 1955). From either end, the apex creates a small flat platform.
SIDE: Ambitus: Low, about 25% from bottom.
Side shape: Very inflated. Posterior end truncated and sloping long (Book Author); vertically truncate behind (Cotteau, 1890). Anterior end curved; obliquely sloping in the anterior region (Cotteau, 1890).
BOTTOM: Bottom shape: Curved (Book Author); almost flat, depressed around the mouth, slightly arched in the posterior interambulacral area (Cotteau, 1890).
AMB: Amb shape: Unpaired ambulacrum (III) in a wide, quite deep sulcus extending from apex to peristome (Cooke, 1955).
Amb arrangement: Paired ambulacra flush, subflexuous. Anterior paired ambs rounded at start, slightly bent outward at tips. Posterior paired ambs short, subflexuous, slightly diverging, almost closed at the end (Cotteau, 1890). Anterior pair less than two times longer than posterior pair. Interporiferous zones very narrow.
PORE PAIRS: Arrangement: Unpaired ambulacrum pores heterogeneous (Enallaster-type): near summit, 8-10 pairs of small narrow pores; below this, pores alternate between a pair of long narrow pores and a pair of much shorter pores. The alternation is usual (1:1), but sometimes two long pairs occur beside one short pair (Cotteau, 1890).
Paired ambs: Anterior poriferous zone of anterior petals composed of very small, rounded pores; posterior zone very wide with unequal pores (outer comma-shaped, inner rounded). Eight pairs of posterior zone pores correspond to five pairs of anterior zone pores (Cooke, 1955).
TUBERCLES: Primary Areola shape: Depressed; widely scrobiculate (Cotteau, 1890).
Distribution: Tubercles quite large, scattered. More plentiful around unpaired ambulacrum and on bottom. Tubercles on plastron smaller.
APICAL SYSTEM: Location: Slightly posterior of center; very eccentric behind (Cotteau, 1890).
Genital pores: Four gonopores, almost equally spaced (Cooke, 1955).
Plating: Madreporite somewhat elongated, reaching center but not extending beyond the two posterior genital plates (Cotteau, 1890). Ocular plates subpentagonal.
PERIPROCT (ANUS): Shape & Size: Slightly vertically oval with point at bottom (Book Author); rounded sub-transverse (Cotteau, 1890).
Location: Placed at the top of the posterior truncation (Cotteau, 1890); above midpoint.
Visibility: Visible from above.
PERISTOME (MOUTH): Shape: Small, kidney-shaped (Book Author).
Location: Very eccentric in front (Cotteau, 1890); located about 20% from anterior end.
Plastron: Large.
Visibility: Visible from posterior end.
SPECIMENS STUDIED & CONDITION: Specimen in photo from Collection of Terry Stephenson. (Note: NPL number likely assigned if deposited).
ETYMOLOGY
Named for the country of Mexico, where the type specimen was found (Cotteau, 1890).
REMARKS & COMPARISONS
Remarks: Miller (2009) states that H. mexicanus is a synonym of Heteraster texanus. Cooke (1955) noted that H. mexicanus has often passed as Enallaster texanus (Roemer), but he preferred retaining mexicanus for Fredericksburg specimens due to the uncertainty of Roemer's species identity.
Comparisons:
Plate: HeMe-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Edwards
Locale: Harker Heights County: Bell Stage: Albian
Length: 47.9 mm Width: 43.5 mm Height: 33.2 mm
Specimen in photo: Collection of Terry Stephenson
Repository: Collection of Terry Stephenson
HOLOTYPE INFO:
Holotype: Cotteau's original specimen. Current location unknown; possibly in the École des Mines (Paris) or lost.
Locality: Colima, Mexico (Cotteau, 1890)
Stratigraphy: Cretaceous (Albian)
SYNONYMY
- Enallaster mexicanus Cotteau, 1890
- Enallaster texanus (Roemer) (misidentification in some collections per Cooke, 1955)
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: Toxasteridae Lambert, 1920
Genus: HETERASTER d'Orbigny, 1853
Species: Heteraster mexicanus (Cotteau, 1890)
TYPE SPECIES: Spatangus oblongus Brongniart, 1821
DIAGNOSIS
Species rather large, oval, elongate, notched in front, vertically truncate behind. Upper face swollen, highest near the apical center. Unpaired ambulacrum pores heterogeneous, with long narrow pores alternating with shorter pairs. Apical system eccentric posterior (Cotteau, 1890; Cooke, 1955).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Edwards Formation; Comanche Peak Limestone, Goodland Limestone (Cooke, 1955).
Stratigraphic Units: Lower Cretaceous, Middle Albian (Cooke, 1955).
Counties: Bell, Menard, Hood, Williamson, Tarrant, Bosque, Gillespie, Upton (Cooke, 1955). Also Mexico (Colima, Chihuahua).
DESCRIPTION
TOP: Length, width, height: 47.9 mm L × 43.5 mm W × 33.2 mm H.
Top shape: Cordate, angular; margin has flat sections on either side of the sulcus. Widest point midway (Book Author); oval, elongate, notched in front (Cotteau, 1890).
Top domed: Upper face swollen, highest near the apical center (Cooke, 1955). From either end, the apex creates a small flat platform.
SIDE: Ambitus: Low, about 25% from bottom.
Side shape: Very inflated. Posterior end truncated and sloping long (Book Author); vertically truncate behind (Cotteau, 1890). Anterior end curved; obliquely sloping in the anterior region (Cotteau, 1890).
BOTTOM: Bottom shape: Curved (Book Author); almost flat, depressed around the mouth, slightly arched in the posterior interambulacral area (Cotteau, 1890).
AMB: Amb shape: Unpaired ambulacrum (III) in a wide, quite deep sulcus extending from apex to peristome (Cooke, 1955).
Amb arrangement: Paired ambulacra flush, subflexuous. Anterior paired ambs rounded at start, slightly bent outward at tips. Posterior paired ambs short, subflexuous, slightly diverging, almost closed at the end (Cotteau, 1890). Anterior pair less than two times longer than posterior pair. Interporiferous zones very narrow.
PORE PAIRS: Arrangement: Unpaired ambulacrum pores heterogeneous (Enallaster-type): near summit, 8-10 pairs of small narrow pores; below this, pores alternate between a pair of long narrow pores and a pair of much shorter pores. The alternation is usual (1:1), but sometimes two long pairs occur beside one short pair (Cotteau, 1890).
Paired ambs: Anterior poriferous zone of anterior petals composed of very small, rounded pores; posterior zone very wide with unequal pores (outer comma-shaped, inner rounded). Eight pairs of posterior zone pores correspond to five pairs of anterior zone pores (Cooke, 1955).
TUBERCLES: Primary Areola shape: Depressed; widely scrobiculate (Cotteau, 1890).
Distribution: Tubercles quite large, scattered. More plentiful around unpaired ambulacrum and on bottom. Tubercles on plastron smaller.
APICAL SYSTEM: Location: Slightly posterior of center; very eccentric behind (Cotteau, 1890).
Genital pores: Four gonopores, almost equally spaced (Cooke, 1955).
Plating: Madreporite somewhat elongated, reaching center but not extending beyond the two posterior genital plates (Cotteau, 1890). Ocular plates subpentagonal.
PERIPROCT (ANUS): Shape & Size: Slightly vertically oval with point at bottom (Book Author); rounded sub-transverse (Cotteau, 1890).
Location: Placed at the top of the posterior truncation (Cotteau, 1890); above midpoint.
Visibility: Visible from above.
PERISTOME (MOUTH): Shape: Small, kidney-shaped (Book Author).
Location: Very eccentric in front (Cotteau, 1890); located about 20% from anterior end.
Plastron: Large.
Visibility: Visible from posterior end.
SPECIMENS STUDIED & CONDITION: Specimen in photo from Collection of Terry Stephenson. (Note: NPL number likely assigned if deposited).
ETYMOLOGY
Named for the country of Mexico, where the type specimen was found (Cotteau, 1890).
REMARKS & COMPARISONS
Remarks: Miller (2009) states that H. mexicanus is a synonym of Heteraster texanus. Cooke (1955) noted that H. mexicanus has often passed as Enallaster texanus (Roemer), but he preferred retaining mexicanus for Fredericksburg specimens due to the uncertainty of Roemer's species identity.
Comparisons:
- E. obliquatus: H. mexicanus is higher and narrower in front and broader behind than E. obliquatus from the Trinity Group (Cooke, 1955).
- E. bravoensis: It is commonly higher than E. bravoensis from the Washita Group (Cooke, 1955).
- Washitaster: It lacks the narrow branching fascioles distinctive of the subgenus Washitaster (Cooke, 1955).
