Tetragramma texanum (Roemer, 1852)
Plate: TeTex-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Comanche Peak
Locale: unsure County: Mills Stage: Albian
Length: 31.4 mm Height: 12.7 mm
Specimen in photos: Collection of Terry Stephenson
Plate: TeTex-20
Series: Lower Cretaceous Group: Fredericksburg? Formation: Comanche Peak?
Locale: unsure County: unsure Stage: Albian
Length: 1 & 3/4 inch Height: 7/8 inch
Specimen in drawings: Drawings of Holotype - Roemer
Plate: TeTex-30
Series: Lower Cretaceous Group: Fredericksburg Formation: Walnut
Locale: unknown County: Mills European Stage: Albian
Length: 14.4 mm Height: 5.9 mm
Collection: William Thompson NPL ###### Juvenile
Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: Roemer's original specimen. Repository: Likely Geological Museum of the University of Bonn, Germany.
Locality: "Fredericksburg and near the head of the San Saba River," Texas (Roemer, 1852).
Stratigraphy: Fredericksburg Group (Comanche Peak Limestone).
SYNONYMY
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Carinacea Kroh & Smith, 2010
Superorder: Calycina Gregory, 1900
Order: Phymosomatoida Mortensen, 1904
Family: Diplopodiidae Smith & Wright, 1993
Genus: TETRAGRAMMA L. Agassiz, 1838
Species: Tetragramma texanum (Roemer, 1852)
TYPE SPECIES: Cidarites variolare Brongniart, 1822
DIAGNOSIS
A large, subcircular, elevated Tetragramma. Ambulacra with two rows of primary tubercles; pore zones broad and biserial above the ambitus, becoming narrow and uniserial below. Interambulacra with four rows of primary tubercles at the ambitus, reducing to two rows near both poles. Juveniles show only two rows. Test moderately inflated with a large peristome and a broad, subpentagonal apical system.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Comanche Peak Limestone; Walnut Formation; Goodland Limestone.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Mills, Gillespie, Travis, Williamson.
Abundance: Common.
DESCRIPTION
TOP: Length, width, height: 31.4 mm L × 12.7 mm H (Adult TeTex-10). Type measures ~44.5 mm diameter. Top shape: Subcircular (Clark, 1893). Top domed: Elevated and convex.
SIDE: Ambitus: Positioned at midpoint. Side shape: Inflated.
BOTTOM: Bottom shape: Depressed and concave (Clark, 1893).
AMB: Amb shape: Broad and lanceolate; prominent. Amb arrangement: Two rows of primary tubercles (14–15 in each series). Tubercles are large at the ambitus and decrease gradually toward the poles. Plating: Juveniles show quadrigeminate plating with the first two sets of 4 pairs almost biserial (biserial tendencies.)
PORE PAIRS: Arrangement: Biserial (bigeminal) from the ambitus to the apical disk. Uniserial (single pairs) from the peristome to the ambitus. Condition: Greatly increased/crowded at the mouth edges (Clark, 1893). Juveniles biserial pore areas short.
TUBERCLES: Primary Perforated: Yes (Mamelons perforated, though sometimes distinctness varies with preservation). Primary Crenulate: Yes. Interambulacral Tubercles: Four rows at the ambitus. Reduced to two rows near the apical disk and mouth. In the center of the column, the four rows are of equal size; outer rows reduce rapidly toward poles. Juveniles have 2 rows of tubercles in interamb.
GRANULES: Distribution: Irregularly scattered granules cover the space between tubercles. A circle of scattered granules surrounds the narrow ambulacral areolas (Clark, 1893).
APICAL SYSTEM: Size: Large discal opening. Shape: Subpentagonal. Juvenile: Apical scar is 10-sided, cutting into each interradial and perradial suture; diameter 33.3% of test.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Wide; about two-fifths (40%) the diameter of the test (Clark, 1893). Shape: Circular, broken by distinct incisions.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION:
ETYMOLOGY
Named for the state of Texas.
REMARKS & COMPARISONS
Remarks: Roemer’s locality description (“Fredericksburg and near the head of the San Saba River”) is geographically inconsistent, but likely refers to Fredericksburg‑area Comanche Peak exposures on the Edwards Plateau. T. texanum is the common Fredericksburg‑Group four‑row species, distinct from the larger, multi‑row T. taffi and the smaller, depressed T. tenerum. Juveniles show only two rows of interambulacral tubercles, confirming that the four‑row condition is ontogenetically derived rather than primary. The species is consistent across Comanche Peak, Walnut, and Goodland material, with only minor variation in pore‑pair length and apical system breadth.
Comparisons:
Plate: TeTex-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Comanche Peak
Locale: unsure County: Mills Stage: Albian
Length: 31.4 mm Height: 12.7 mm
Specimen in photos: Collection of Terry Stephenson
Plate: TeTex-20
Series: Lower Cretaceous Group: Fredericksburg? Formation: Comanche Peak?
Locale: unsure County: unsure Stage: Albian
Length: 1 & 3/4 inch Height: 7/8 inch
Specimen in drawings: Drawings of Holotype - Roemer
Plate: TeTex-30
Series: Lower Cretaceous Group: Fredericksburg Formation: Walnut
Locale: unknown County: Mills European Stage: Albian
Length: 14.4 mm Height: 5.9 mm
Collection: William Thompson NPL ###### Juvenile
Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: Roemer's original specimen. Repository: Likely Geological Museum of the University of Bonn, Germany.
Locality: "Fredericksburg and near the head of the San Saba River," Texas (Roemer, 1852).
Stratigraphy: Fredericksburg Group (Comanche Peak Limestone).
SYNONYMY
- Diadema texanum Roemer, 1849
- Cyphosoma texanum (Roemer) Roemer, 1852
- Diplopodia texanum (Roemer) Clark, 1893
- Tetragramma texanum (Roemer) Cooke, 1946
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Carinacea Kroh & Smith, 2010
Superorder: Calycina Gregory, 1900
Order: Phymosomatoida Mortensen, 1904
Family: Diplopodiidae Smith & Wright, 1993
Genus: TETRAGRAMMA L. Agassiz, 1838
Species: Tetragramma texanum (Roemer, 1852)
TYPE SPECIES: Cidarites variolare Brongniart, 1822
DIAGNOSIS
A large, subcircular, elevated Tetragramma. Ambulacra with two rows of primary tubercles; pore zones broad and biserial above the ambitus, becoming narrow and uniserial below. Interambulacra with four rows of primary tubercles at the ambitus, reducing to two rows near both poles. Juveniles show only two rows. Test moderately inflated with a large peristome and a broad, subpentagonal apical system.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Comanche Peak Limestone; Walnut Formation; Goodland Limestone.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Mills, Gillespie, Travis, Williamson.
Abundance: Common.
DESCRIPTION
TOP: Length, width, height: 31.4 mm L × 12.7 mm H (Adult TeTex-10). Type measures ~44.5 mm diameter. Top shape: Subcircular (Clark, 1893). Top domed: Elevated and convex.
SIDE: Ambitus: Positioned at midpoint. Side shape: Inflated.
BOTTOM: Bottom shape: Depressed and concave (Clark, 1893).
AMB: Amb shape: Broad and lanceolate; prominent. Amb arrangement: Two rows of primary tubercles (14–15 in each series). Tubercles are large at the ambitus and decrease gradually toward the poles. Plating: Juveniles show quadrigeminate plating with the first two sets of 4 pairs almost biserial (biserial tendencies.)
PORE PAIRS: Arrangement: Biserial (bigeminal) from the ambitus to the apical disk. Uniserial (single pairs) from the peristome to the ambitus. Condition: Greatly increased/crowded at the mouth edges (Clark, 1893). Juveniles biserial pore areas short.
TUBERCLES: Primary Perforated: Yes (Mamelons perforated, though sometimes distinctness varies with preservation). Primary Crenulate: Yes. Interambulacral Tubercles: Four rows at the ambitus. Reduced to two rows near the apical disk and mouth. In the center of the column, the four rows are of equal size; outer rows reduce rapidly toward poles. Juveniles have 2 rows of tubercles in interamb.
GRANULES: Distribution: Irregularly scattered granules cover the space between tubercles. A circle of scattered granules surrounds the narrow ambulacral areolas (Clark, 1893).
APICAL SYSTEM: Size: Large discal opening. Shape: Subpentagonal. Juvenile: Apical scar is 10-sided, cutting into each interradial and perradial suture; diameter 33.3% of test.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Wide; about two-fifths (40%) the diameter of the test (Clark, 1893). Shape: Circular, broken by distinct incisions.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION:
- Plate TeTex-10: Collection of Terry Stephenson. Mills County.
- Plate TeTex-20: Drawings of Holotype.
- Plate TeTex-30 (Juvenile): Collection from William Thompson.
ETYMOLOGY
Named for the state of Texas.
REMARKS & COMPARISONS
Remarks: Roemer’s locality description (“Fredericksburg and near the head of the San Saba River”) is geographically inconsistent, but likely refers to Fredericksburg‑area Comanche Peak exposures on the Edwards Plateau. T. texanum is the common Fredericksburg‑Group four‑row species, distinct from the larger, multi‑row T. taffi and the smaller, depressed T. tenerum. Juveniles show only two rows of interambulacral tubercles, confirming that the four‑row condition is ontogenetically derived rather than primary. The species is consistent across Comanche Peak, Walnut, and Goodland material, with only minor variation in pore‑pair length and apical system breadth.
Comparisons:
- Tetragramma taffi — T. taffi is much larger, lower, and has 8–10 rows of interambulacral tubercles. T. texanum has only four rows, is more elevated, and has a proportionally larger peristome.
- Tetragramma tenerum — T. tenerum is smaller, more depressed, and has four rows but with a different plating pattern and strictly biserial adapical pore pairs. T. texanum is larger, more inflated, and has a broader apical system.
- Tetragramma hammerschmidti — T. hammerschmidti has six rows with high tubercle counts and a round apical system. T. texanum has four rows and a subpentagonal apical system.
- Tetragramma glenrosense — T. glenrosense is more flattened, with four rows but a smaller peristome and different pore‑pair proportions. T. texanum is more inflated and has a larger apical system.
- Tetragramma cranei — T. cranei has six rows arranged in a 12–9–5 pattern and is much smaller and more flattened. T. texanum is larger, more inflated, and has only four rows.
- Juveniles (TeTex‑30) — Juveniles have two rows of interambulacral tubercles and short biserial pore zones; adults have four rows and long biserial zones.
