Tetragramma tenerum Smith and Rader, 2009
Plate: TeTen-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Canyon Lake County: Comal Stage: Albian
Length: 16.1 mm Height: 5.8 mm
Specimen in photo: NPL 70942 Hypotype
Collector: William R. Thompson, Jr.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: BMNH EE13460 (Natural History Museum, London) (Smith & Rader, 2009).
Locality: Rancho del Lago, Comal County, Texas.
Stratigraphy: Unit 4, Upper Member, Glen Rose Formation.
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 tenerum Smith & Rader, 2009
TYPE SPECIES: Cidarites variolare Brongniart, 1822
DIAGNOSIS
A small, depressed Tetragramma with flattened upper and lower surfaces. Interambulacral plates bear two subequal primary tubercles at the ambitus (four rows total). Pore pairs are strictly biserial over most of the adapical surface, becoming offset to uniserial adorally near the peristome. Ambulacral plating trigeminate below the ambitus and quadrigeminate above. Interradial granulation is dense and well developed. (Smith & Rader, 2009).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity
Formations: Glen Rose Formation (Upper Member).
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Comal, Travis.
Abundance: Uncommon.
DESCRIPTION
TOP: Length, width, height: 16.1 mm L × 5.8 mm H. Top shape: Round, slightly pentagonal. Top domed: Depressed; very flat top.
SIDE: Ambitus: Positioned at midpoint. Side shape: Evenly rounded.
BOTTOM: Bottom shape: Very flat; adoral surface slightly concave.
AMB: Amb shape: Widest at ambitus. Amb arrangement: Two rows of 10 tubercles. Tubercles are large, round, perforate, and crenulate with large raised areoles. Width: Interambulacra are less than twice the width of the ambulacra at the ambitus.
PORE PAIRS: Arrangement: Uniserial and offset adorally; becoming biserial near the apical system (Book Author). Smith & Rader (2009) describe them as strictly biserially arranged over most of the adapical surface. Condition: Crowded at the peristome to form phyllodes. Trigeminate plating below ambitus, quadrigeminate above ambitus.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: Yes. Interambulacral Tubercles: Two rows of 10 alternating plates. Tubercles equal in size to ambulacral tubercles. Two inner rows run perpendicular to each other from the peristome to the apical system. Two outer (adradial) rows start just above the ambitus and run downward, reducing in size quickly near the peristome. Scrobicular Tubercles: Ring the primary tubercles.
GRANULES: Distribution: Secondary tubercles and granules are dense. Tubercles and granulation reduced at the apical system.
FASCIOLE: Absent.
APICAL SYSTEM: Size: Diameter about 45% of test. Shape: Subpentagonal; points of the pentagon cut into interambulacra equally.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Diameter 50% of test. Shape: Circular. Lip: Buccal notches deep; small lips closer together in interambulacra.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Hypotype NPL 70942. Found by William R. Thompson, Jr.
ETYMOLOGY
From the Latin tener (delicate/soft), possibly referring to the small size or fine granulation (Smith & Rader, 2009).
REMARKS & COMPARISONS
Remarks: Tetragramma tenerum represents the smallest and most delicate of the Glen Rose Tetragramma species. It differs from the larger T. taffi and T. malbosii by its strictly biserial adapical pore pairs, dense interradial granulation, and four‑row interambulacral pattern. The species is consistently depressed, with a broad peristome and a well‑defined pentagonal apical system. Smith & Rader (2009) established the species to accommodate small Glen Rose specimens that had previously been misassigned to juvenile T. taffi or T. malbosii.
Comparisons:
Plate: TeTen-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Canyon Lake County: Comal Stage: Albian
Length: 16.1 mm Height: 5.8 mm
Specimen in photo: NPL 70942 Hypotype
Collector: William R. Thompson, Jr.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: BMNH EE13460 (Natural History Museum, London) (Smith & Rader, 2009).
Locality: Rancho del Lago, Comal County, Texas.
Stratigraphy: Unit 4, Upper Member, Glen Rose Formation.
SYNONYMY
- Tetragramma tenerum Smith & Rader, 2009
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 tenerum Smith & Rader, 2009
TYPE SPECIES: Cidarites variolare Brongniart, 1822
DIAGNOSIS
A small, depressed Tetragramma with flattened upper and lower surfaces. Interambulacral plates bear two subequal primary tubercles at the ambitus (four rows total). Pore pairs are strictly biserial over most of the adapical surface, becoming offset to uniserial adorally near the peristome. Ambulacral plating trigeminate below the ambitus and quadrigeminate above. Interradial granulation is dense and well developed. (Smith & Rader, 2009).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity
Formations: Glen Rose Formation (Upper Member).
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Comal, Travis.
Abundance: Uncommon.
DESCRIPTION
TOP: Length, width, height: 16.1 mm L × 5.8 mm H. Top shape: Round, slightly pentagonal. Top domed: Depressed; very flat top.
SIDE: Ambitus: Positioned at midpoint. Side shape: Evenly rounded.
BOTTOM: Bottom shape: Very flat; adoral surface slightly concave.
AMB: Amb shape: Widest at ambitus. Amb arrangement: Two rows of 10 tubercles. Tubercles are large, round, perforate, and crenulate with large raised areoles. Width: Interambulacra are less than twice the width of the ambulacra at the ambitus.
PORE PAIRS: Arrangement: Uniserial and offset adorally; becoming biserial near the apical system (Book Author). Smith & Rader (2009) describe them as strictly biserially arranged over most of the adapical surface. Condition: Crowded at the peristome to form phyllodes. Trigeminate plating below ambitus, quadrigeminate above ambitus.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: Yes. Interambulacral Tubercles: Two rows of 10 alternating plates. Tubercles equal in size to ambulacral tubercles. Two inner rows run perpendicular to each other from the peristome to the apical system. Two outer (adradial) rows start just above the ambitus and run downward, reducing in size quickly near the peristome. Scrobicular Tubercles: Ring the primary tubercles.
GRANULES: Distribution: Secondary tubercles and granules are dense. Tubercles and granulation reduced at the apical system.
FASCIOLE: Absent.
APICAL SYSTEM: Size: Diameter about 45% of test. Shape: Subpentagonal; points of the pentagon cut into interambulacra equally.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Diameter 50% of test. Shape: Circular. Lip: Buccal notches deep; small lips closer together in interambulacra.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Hypotype NPL 70942. Found by William R. Thompson, Jr.
ETYMOLOGY
From the Latin tener (delicate/soft), possibly referring to the small size or fine granulation (Smith & Rader, 2009).
REMARKS & COMPARISONS
Remarks: Tetragramma tenerum represents the smallest and most delicate of the Glen Rose Tetragramma species. It differs from the larger T. taffi and T. malbosii by its strictly biserial adapical pore pairs, dense interradial granulation, and four‑row interambulacral pattern. The species is consistently depressed, with a broad peristome and a well‑defined pentagonal apical system. Smith & Rader (2009) established the species to accommodate small Glen Rose specimens that had previously been misassigned to juvenile T. taffi or T. malbosii.
Comparisons:
- Polydiadema travisensis — T. tenerum resembles P. travisensis in overall shape and in having a pentagonal apical disc, but differs by having strictly biserial adapical pore pairs, trigeminate–quadrigeminate plating, and a much more developed interradial granulation.
- Tetragramma hammerschmidti — T. tenerum is more depressed, has denser granulation, and has a pentagonal apical system (vs. round in hammerschmidti). T. hammerschmidti has six rows with higher tubercle counts and is more inflated.
- Tetragramma taffi — T. taffi is much larger, more inflated, and has 8–10 rows of interambulacral tubercles. T. tenerum has only four rows and a much smaller, more delicate test.
- Tetragramma glenrosense — T. glenrosense is larger, more inflated, and has a different plating pattern. T. tenerum is smaller, flatter, and has denser granulation.
- Tetragramma cranei — T. cranei has six rows arranged in a 12–9–5 pattern and a pentagonal apical system. T. tenerum is smaller, more depressed, and has only four rows.
