Tetragramma dentonense Thompson Date?
Plate: TeDe-10
Series: Lower Cretaceous Group: Washita Formation: Denton
Locale: Denison County: Grayson Stage: Albian
Length: 18.5 mm Height: 7.0 mm
Specimen in photo: NPL 70943 Holotype
Collector: Ed Elliott
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 70943.
Locality: Denison, Grayson County, Texas.
Stratigraphy: Denton Formation, Washita Group.
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 dentonense Thompson, 2016
TYPE SPECIES: Cidarites variolare Brongniart, 1822
DIAGNOSIS
A medium Tetragramma with a moderately inflated test and a round to slightly pentagonal outline. Interambulacra bear four rows of perforated, crenulate primary tubercles, with the two inner rows running the full length and the two outer rows diminishing toward both poles. Ambulacra are lanceolate with two rows of 10–12 tubercles, largest at the ambitus. Ambulacral plating quinquegeminate aborally and quadrigeminate adorally. Pore pairs uniserial below the ambitus and biserial above. Granulation moderate, thinning near the apical system. Apical system large and pentagonal; peristome circular with shallow buccal notches.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Denton Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Grayson.
Abundance: Rare; only two specimens found.
DESCRIPTION
TOP: Length, width, height: 18.5 mm L × 7.0 mm H. Top shape: Round. Top domed: Moderately inflated upper surface; slight concavity around apical system.
SIDE: Ambitus: Positioned at midpoint. Side shape: Margin rounded; upper and lower surfaces gently inflated.
BOTTOM: Bottom shape: Flattened to slightly concave around peristome.
AMB: Amb shape: Lanceolate; widest at ambitus, narrowing toward apical system and peristome. Amb arrangement: Two rows of 10–12 tubercles, largest at ambitus. Width: Interambulacra are just under twice the width of ambulacra at the margin. Plating: Quinquegeminate (5 elements) aborally; quadrigeminate (4 elements) adorally.
PORE PAIRS: Arrangement: Uniserial below margin; biserial above margin. Condition: Become crowded at peristome.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: Yes. Bosses: Medium.
Ambulacral Tubercles: Largest at ambitus, decreasing in size moving away.
Interambulacral Tubercles: Four rows total. Two inner rows run the entire length, widest near the apical system and narrowing toward the peristome. Two outer rows begin below the apical system and run to the peristome, diminishing rapidly toward both poles. Center rows maintain size until close to the apical system. Scrobicular tubercles present above and below the margin, fading toward the poles.
GRANULES: Distribution: Granulation present aborally and adorally; thins near the apical system and peristome. Interradial sutures lightly granulated.
APICAL SYSTEM: Size: Small; diameter 32% of test. Shape: Subpentagonal; cuts into each interambulacrum and ambulacrum.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Diameter 33% (1/3) of test. Shape: Circular. Lip: Buccal notches small.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: One specimen: Holotype NPL 70943. Found by Ed Elliott.
ETYMOLOGY
Named after the Denton Formation, the stratigraphic unit where the holotype was found.
REMARKS & COMPARISONS
Remarks:
Tetragramma dentonense is distinguished by its four‑row interambulacral pattern, moderate inflation, and 10–12 ambulacral tubercles, placing it between the smaller, flatter T. cranei and the larger, more inflated T. glenrosense. The species is consistent across known specimens, with no evidence of additional tubercle rows developing in larger individuals.
Comparisons:
• T. glenrosense — T. glenrosense is more flattened and has fewer ambulacral tubercles.
• T. cranei — T. cranei has six rows at the margin and only 8 ambulacral tubercles.
• T. donaldtrumpi — T. donaldtrumpi is larger, more inflated, and has more complex ambulacral plating
• T. hammerschmidti — T. hammerschmidti has six rows with much higher tubercle counts.
• T. taffi — T. taffi is significantly larger and has 8–10 rows of tubercles
• T. goodlandense — T. goodlandense is more flattened and has six rows plus secondary rows.
Gender Emendation: The specific epithet dentonensis (masculine/feminine) was emended to dentonense (neuter) to comply with the gender of the genus Tetragramma.
Plate: TeDe-10
Series: Lower Cretaceous Group: Washita Formation: Denton
Locale: Denison County: Grayson Stage: Albian
Length: 18.5 mm Height: 7.0 mm
Specimen in photo: NPL 70943 Holotype
Collector: Ed Elliott
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 70943.
Locality: Denison, Grayson County, Texas.
Stratigraphy: Denton Formation, Washita Group.
SYNONYMY
- Tetragramma dentonensis Thompson, 2016
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 dentonense Thompson, 2016
TYPE SPECIES: Cidarites variolare Brongniart, 1822
DIAGNOSIS
A medium Tetragramma with a moderately inflated test and a round to slightly pentagonal outline. Interambulacra bear four rows of perforated, crenulate primary tubercles, with the two inner rows running the full length and the two outer rows diminishing toward both poles. Ambulacra are lanceolate with two rows of 10–12 tubercles, largest at the ambitus. Ambulacral plating quinquegeminate aborally and quadrigeminate adorally. Pore pairs uniserial below the ambitus and biserial above. Granulation moderate, thinning near the apical system. Apical system large and pentagonal; peristome circular with shallow buccal notches.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Denton Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Grayson.
Abundance: Rare; only two specimens found.
DESCRIPTION
TOP: Length, width, height: 18.5 mm L × 7.0 mm H. Top shape: Round. Top domed: Moderately inflated upper surface; slight concavity around apical system.
SIDE: Ambitus: Positioned at midpoint. Side shape: Margin rounded; upper and lower surfaces gently inflated.
BOTTOM: Bottom shape: Flattened to slightly concave around peristome.
AMB: Amb shape: Lanceolate; widest at ambitus, narrowing toward apical system and peristome. Amb arrangement: Two rows of 10–12 tubercles, largest at ambitus. Width: Interambulacra are just under twice the width of ambulacra at the margin. Plating: Quinquegeminate (5 elements) aborally; quadrigeminate (4 elements) adorally.
PORE PAIRS: Arrangement: Uniserial below margin; biserial above margin. Condition: Become crowded at peristome.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: Yes. Bosses: Medium.
Ambulacral Tubercles: Largest at ambitus, decreasing in size moving away.
Interambulacral Tubercles: Four rows total. Two inner rows run the entire length, widest near the apical system and narrowing toward the peristome. Two outer rows begin below the apical system and run to the peristome, diminishing rapidly toward both poles. Center rows maintain size until close to the apical system. Scrobicular tubercles present above and below the margin, fading toward the poles.
GRANULES: Distribution: Granulation present aborally and adorally; thins near the apical system and peristome. Interradial sutures lightly granulated.
APICAL SYSTEM: Size: Small; diameter 32% of test. Shape: Subpentagonal; cuts into each interambulacrum and ambulacrum.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Diameter 33% (1/3) of test. Shape: Circular. Lip: Buccal notches small.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: One specimen: Holotype NPL 70943. Found by Ed Elliott.
ETYMOLOGY
Named after the Denton Formation, the stratigraphic unit where the holotype was found.
REMARKS & COMPARISONS
Remarks:
Tetragramma dentonense is distinguished by its four‑row interambulacral pattern, moderate inflation, and 10–12 ambulacral tubercles, placing it between the smaller, flatter T. cranei and the larger, more inflated T. glenrosense. The species is consistent across known specimens, with no evidence of additional tubercle rows developing in larger individuals.
Comparisons:
• T. glenrosense — T. glenrosense is more flattened and has fewer ambulacral tubercles.
• T. cranei — T. cranei has six rows at the margin and only 8 ambulacral tubercles.
• T. donaldtrumpi — T. donaldtrumpi is larger, more inflated, and has more complex ambulacral plating
• T. hammerschmidti — T. hammerschmidti has six rows with much higher tubercle counts.
• T. taffi — T. taffi is significantly larger and has 8–10 rows of tubercles
• T. goodlandense — T. goodlandense is more flattened and has six rows plus secondary rows.
Gender Emendation: The specific epithet dentonensis (masculine/feminine) was emended to dentonense (neuter) to comply with the gender of the genus Tetragramma.
