Tetragramma hammerschmidti Thompson, 2016
Plate: TeHa-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Spring Branch County: Comal Stage: Albian
Length: 20.5 mm Height: 6.2 mm
Specimen in photo: NPL 70932 Holotype
Collector: William R. Thompson, Jr.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 70942.
Locality: West of Bergheim/Spring Branch, Comal County, Texas.
Stratigraphy: Glen Rose Formation (Soft yellow matrix), Trinity Group.
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 hammerschmidti Thompson, 2016
TYPE SPECIES: Cidarites variolare Brongniart, 1822
DIAGNOSIS
A medium Tetragramma with a moderately inflated test and a round outline. Interambulacra bear six rows of perforated, crenulate primary tubercles, with 15–16 tubercles per row at the ambitus, decreasing toward both poles. Ambulacra narrow 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 dense aborally and adorally. Apical system round, cutting shallowly into the interambulacra. Peristome circular with shallow buccal notches.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity
Formations: Glen Rose Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Comal.
Abundance: Rare; two specimens known.
Associated Fauna: Found with Heteraster obliquatus and Coenholectypus planatus.
DESCRIPTION
TOP: Length, width, height: 20.5 mm L × 6.2 mm H. Top shape: Round to slightly pentagonal. Top domed: Flattened upper surface.
SIDE: Ambitus: Positioned at midpoint. Side shape: Margin rounded; flattened upper and lower surfaces.
BOTTOM: Bottom shape: Flattened.
AMB: Amb shape: Widest at ambitus; slightly narrower at peristome; narrower at apical system. Amb arrangement: Two rows of 15–16 tubercles. Width: Interambulacra are just over twice the size of ambulacra at the margin. Plating: Quinquegeminate aborally; quadrigeminate adorally.
PORE PAIRS: Arrangement: Uniserial below margin; biserial above margin. Condition: Become crowded at peristome.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: Yes. Size: Small. Ambulacral Tubercles: 15–16 per row. Interambulacral Tubercles: Total of 6 rows below ambitus. Two inner rows (16 tubercles) run the entire length perpendicular to each other. Two intermediate rows (12 tubercles) run from 1/4 below the apical system to near the peristome. Two outer/adradial rows (8 tubercles) run from slightly above the ambitus to halfway to the peristome. Tubercles are largest at the ambitus and decrease in size in both directions; outer rows decrease more quickly.
GRANULES: Distribution: In ambulacra, granules run between tubercles. In interambulacra, miliary tubercles and granulation run the length of the interradial suture; sparse above ambitus and near apical system.
FASCIOLE: Absent.
APICAL SYSTEM: Size: Large; diameter about 48% of test. Shape: Round.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Diameter 33% (1/3) of test. Shape: Circular. Lip: Buccal notches very small.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION:
ETYMOLOGY
Named after Paul Hammerschmidt, a fossil collector and friend of the author.
REMARKS & COMPARISONS
Remarks:
Tetragramma hammerschmidti is readily distinguished from other Glen Rose Tetragramma by its high tubercle counts in both the ambulacra and interambulacra, with 15–16 tubercles per row at the ambitus, a value exceeded only by the much larger T. taffi. The species also shows a consistently round apical system, unlike the pentagonal systems seen in T. tenerum, T. cranei, and T. glenrosense. Granulation is present but reduced compared to T. tenerum, and the pore pairs show less crowding at the peristome than in other Glen Rose species. The combination of six rows, high tubercle counts, round apical system, and moderate inflation makes T. hammerschmidti morphologically stable and easily recognized.
Comparisons:
• Tetragramma tenerum — T. hammerschmidti is less inflated, has fewer granules, and possesses a round apical system rather than the pentagonal system of T. tenerum. Pore pairs in T. hammerschmidti are less crowded at the peristome, and tubercle counts are significantly higher.
• Tetragramma cranei — T. cranei has six rows but with a 12–9–5 pattern and far fewer tubercles per row. T. cranei also has a pentagonal apical system and only 8 ambulacral tubercles, making it much smaller and more flattened.
• Tetragramma glenrosense — T. glenrosense has only four rows of interambulacral tubercles and a larger, more pentagonal apical system. It is also more flattened and has lower tubercle counts.
• Tetragramma goodlandense — Although both species have six rows, T. goodlandense has secondary rows, a more flattened test, and different row‑length patterns. T. hammerschmidti has higher tubercle counts and a round apical system.
• Tetragramma taffi — T. taffi is much larger and has 8–10 rows of tubercles, making it the most heavily ornamented of the Glen Rose species. T. hammerschmidti is smaller and has only six rows.
• Tetragramma donaldtrumpi — T. donaldtrumpi has more complex ambulacral plating (tri‑ to quadri‑ to quinquegeminate), a larger apical system, and different tubercle spacing. T. hammerschmidti is simpler in plating and has a round apical system.
Plate: TeHa-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Spring Branch County: Comal Stage: Albian
Length: 20.5 mm Height: 6.2 mm
Specimen in photo: NPL 70932 Holotype
Collector: William R. Thompson, Jr.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 70942.
Locality: West of Bergheim/Spring Branch, Comal County, Texas.
Stratigraphy: Glen Rose Formation (Soft yellow matrix), Trinity Group.
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 hammerschmidti Thompson, 2016
TYPE SPECIES: Cidarites variolare Brongniart, 1822
DIAGNOSIS
A medium Tetragramma with a moderately inflated test and a round outline. Interambulacra bear six rows of perforated, crenulate primary tubercles, with 15–16 tubercles per row at the ambitus, decreasing toward both poles. Ambulacra narrow 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 dense aborally and adorally. Apical system round, cutting shallowly into the interambulacra. Peristome circular with shallow buccal notches.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity
Formations: Glen Rose Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Comal.
Abundance: Rare; two specimens known.
Associated Fauna: Found with Heteraster obliquatus and Coenholectypus planatus.
DESCRIPTION
TOP: Length, width, height: 20.5 mm L × 6.2 mm H. Top shape: Round to slightly pentagonal. Top domed: Flattened upper surface.
SIDE: Ambitus: Positioned at midpoint. Side shape: Margin rounded; flattened upper and lower surfaces.
BOTTOM: Bottom shape: Flattened.
AMB: Amb shape: Widest at ambitus; slightly narrower at peristome; narrower at apical system. Amb arrangement: Two rows of 15–16 tubercles. Width: Interambulacra are just over twice the size of ambulacra at the margin. Plating: Quinquegeminate aborally; quadrigeminate adorally.
PORE PAIRS: Arrangement: Uniserial below margin; biserial above margin. Condition: Become crowded at peristome.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: Yes. Size: Small. Ambulacral Tubercles: 15–16 per row. Interambulacral Tubercles: Total of 6 rows below ambitus. Two inner rows (16 tubercles) run the entire length perpendicular to each other. Two intermediate rows (12 tubercles) run from 1/4 below the apical system to near the peristome. Two outer/adradial rows (8 tubercles) run from slightly above the ambitus to halfway to the peristome. Tubercles are largest at the ambitus and decrease in size in both directions; outer rows decrease more quickly.
GRANULES: Distribution: In ambulacra, granules run between tubercles. In interambulacra, miliary tubercles and granulation run the length of the interradial suture; sparse above ambitus and near apical system.
FASCIOLE: Absent.
APICAL SYSTEM: Size: Large; diameter about 48% of test. Shape: Round.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Diameter 33% (1/3) of test. Shape: Circular. Lip: Buccal notches very small.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION:
- Holotype NPL 70942: Spring Branch, Comal Co.
- Specimen 2: Worn specimen (28.6 mm) found east of Hwy 281 and north of FM 306, Comal Co.
ETYMOLOGY
Named after Paul Hammerschmidt, a fossil collector and friend of the author.
REMARKS & COMPARISONS
Remarks:
Tetragramma hammerschmidti is readily distinguished from other Glen Rose Tetragramma by its high tubercle counts in both the ambulacra and interambulacra, with 15–16 tubercles per row at the ambitus, a value exceeded only by the much larger T. taffi. The species also shows a consistently round apical system, unlike the pentagonal systems seen in T. tenerum, T. cranei, and T. glenrosense. Granulation is present but reduced compared to T. tenerum, and the pore pairs show less crowding at the peristome than in other Glen Rose species. The combination of six rows, high tubercle counts, round apical system, and moderate inflation makes T. hammerschmidti morphologically stable and easily recognized.
Comparisons:
• Tetragramma tenerum — T. hammerschmidti is less inflated, has fewer granules, and possesses a round apical system rather than the pentagonal system of T. tenerum. Pore pairs in T. hammerschmidti are less crowded at the peristome, and tubercle counts are significantly higher.
• Tetragramma cranei — T. cranei has six rows but with a 12–9–5 pattern and far fewer tubercles per row. T. cranei also has a pentagonal apical system and only 8 ambulacral tubercles, making it much smaller and more flattened.
• Tetragramma glenrosense — T. glenrosense has only four rows of interambulacral tubercles and a larger, more pentagonal apical system. It is also more flattened and has lower tubercle counts.
• Tetragramma goodlandense — Although both species have six rows, T. goodlandense has secondary rows, a more flattened test, and different row‑length patterns. T. hammerschmidti has higher tubercle counts and a round apical system.
• Tetragramma taffi — T. taffi is much larger and has 8–10 rows of tubercles, making it the most heavily ornamented of the Glen Rose species. T. hammerschmidti is smaller and has only six rows.
• Tetragramma donaldtrumpi — T. donaldtrumpi has more complex ambulacral plating (tri‑ to quadri‑ to quinquegeminate), a larger apical system, and different tubercle spacing. T. hammerschmidti is simpler in plating and has a round apical system.
