Schizaster caddoensis Zachos and Molineux, 2003
Plate: ScCa-10
Series: Early Middle Eocene Group: Claiborne Formation: Weches
Locale: Melrose County: Nacogdoches Stage: Lutetian
Length: 21.0 mm Width: 20.5 mm Height: 14.5 mm
Specimen in photos: TX 2000.1 Holotype
Collector: (Not specified)
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: TX 2000.1 (Zachos & Molineux, 2003).
Locality: Melrose, Nacogdoches County, Texas.
Stratigraphy: Weches Formation, Claiborne Group.
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: Schizasteridae Lambert, 1905
Genus: SCHIZASTER L. Agassiz, 1836
Species: Schizaster caddoensis Zachos & Molineux, 2003
TYPE SPECIES: Schizaster studeri L. Agassiz, 1836
DIAGNOSIS
A small Schizaster from the Middle Eocene of Texas. Characterized by a very deep anterior sulcus that cuts down for 2/3 of the test height and a posterior apical system. The anterior paired petals are approximately twice the length of the posterior pair.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Claiborne
Formations: Weches Formation; Reklaw Formation (Zachos & Molineux, 2003).
Stratigraphic Units: Paleogene, Middle Eocene, Lutetian.
Counties: Nacogdoches, Bastrop (Reklaw).
Abundance: Rare.
DESCRIPTION
TOP: Length, width, height: 21.0 mm L × 20.5 mm W × 14.5 mm H. Top shape: Cordate; angular shoulders with a slight posterior point. Widest spot is at the midpoint. Top domed: Inflated; deep anterior sulcus.
SIDE: Ambitus: Positioned slightly posterior of the midpoint. Side shape: Rounded sides that curve less above the ambitus to create a posterior peak (keel). Profile: Very inflated. The anterior sulcus is deeply incised, cutting down 2/3 of the test height.
BOTTOM: Bottom shape: Not detailed, implied convex/plastronate.
AMB: Amb shape: All ambulacra are petaloid and deeply sunken. Amb arrangement: Anterior paired petals depress slightly over 1/3 of the test height. Posterior paired petals are very short (half the length of anterior pair) and depress about 1/7 of the height. Interambulacra between the anterior and posterior petals form a 90-degree angle.
PORE PAIRS: Shape: Slit-like.
TUBERCLES: Distribution: Very small and dense.
GRANULES: See Tubercles.
FASCIOLE: (Not preserved in specimen, but peripetalous and latero-anal fascioles are generic traits of Schizaster).
APICAL SYSTEM: Location: Small; situated at the posterior third (1/3 of test length from posterior end).
PERIPROCT (ANUS): Shape: Small and round. Location: Situated slightly above the midpoint on the posterior face.
PERISTOME (MOUTH): Shape: Reniform ("drooping kidney shape"). Location: Very anterior (1/6th from anterior end). Condition: Mostly missing in holotype.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype TX 2000.1.
ETYMOLOGY
Named for the Caddo Native American tribe, indigenous to the region where the holotype was found (Zachos & Molineux, 2003).
REMARKS & COMPARISONS
Remarks: This species is one of four new taxa described by Zachos & Molineux (2003). It is distinct from the contemporaneous Schizaster stenzeli (also Weches Fm) and the younger Schizaster (Paraster) susana (Caddell Fm).
Comparisons:
Plate: ScCa-10
Series: Early Middle Eocene Group: Claiborne Formation: Weches
Locale: Melrose County: Nacogdoches Stage: Lutetian
Length: 21.0 mm Width: 20.5 mm Height: 14.5 mm
Specimen in photos: TX 2000.1 Holotype
Collector: (Not specified)
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: TX 2000.1 (Zachos & Molineux, 2003).
Locality: Melrose, Nacogdoches County, Texas.
Stratigraphy: Weches Formation, Claiborne Group.
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: Schizasteridae Lambert, 1905
Genus: SCHIZASTER L. Agassiz, 1836
Species: Schizaster caddoensis Zachos & Molineux, 2003
TYPE SPECIES: Schizaster studeri L. Agassiz, 1836
DIAGNOSIS
A small Schizaster from the Middle Eocene of Texas. Characterized by a very deep anterior sulcus that cuts down for 2/3 of the test height and a posterior apical system. The anterior paired petals are approximately twice the length of the posterior pair.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Claiborne
Formations: Weches Formation; Reklaw Formation (Zachos & Molineux, 2003).
Stratigraphic Units: Paleogene, Middle Eocene, Lutetian.
Counties: Nacogdoches, Bastrop (Reklaw).
Abundance: Rare.
DESCRIPTION
TOP: Length, width, height: 21.0 mm L × 20.5 mm W × 14.5 mm H. Top shape: Cordate; angular shoulders with a slight posterior point. Widest spot is at the midpoint. Top domed: Inflated; deep anterior sulcus.
SIDE: Ambitus: Positioned slightly posterior of the midpoint. Side shape: Rounded sides that curve less above the ambitus to create a posterior peak (keel). Profile: Very inflated. The anterior sulcus is deeply incised, cutting down 2/3 of the test height.
BOTTOM: Bottom shape: Not detailed, implied convex/plastronate.
AMB: Amb shape: All ambulacra are petaloid and deeply sunken. Amb arrangement: Anterior paired petals depress slightly over 1/3 of the test height. Posterior paired petals are very short (half the length of anterior pair) and depress about 1/7 of the height. Interambulacra between the anterior and posterior petals form a 90-degree angle.
PORE PAIRS: Shape: Slit-like.
TUBERCLES: Distribution: Very small and dense.
GRANULES: See Tubercles.
FASCIOLE: (Not preserved in specimen, but peripetalous and latero-anal fascioles are generic traits of Schizaster).
APICAL SYSTEM: Location: Small; situated at the posterior third (1/3 of test length from posterior end).
PERIPROCT (ANUS): Shape: Small and round. Location: Situated slightly above the midpoint on the posterior face.
PERISTOME (MOUTH): Shape: Reniform ("drooping kidney shape"). Location: Very anterior (1/6th from anterior end). Condition: Mostly missing in holotype.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype TX 2000.1.
ETYMOLOGY
Named for the Caddo Native American tribe, indigenous to the region where the holotype was found (Zachos & Molineux, 2003).
REMARKS & COMPARISONS
Remarks: This species is one of four new taxa described by Zachos & Molineux (2003). It is distinct from the contemporaneous Schizaster stenzeli (also Weches Fm) and the younger Schizaster (Paraster) susana (Caddell Fm).
Comparisons:
- Schizaster susana: S. caddoensis is from the Middle Eocene (Weches), while S. susana is Upper Eocene (Caddell). S. caddoensis is typically smaller and has different petal proportions.
