Strictotiara adami (Thompson 2016)
Plate: StAd-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Bergheim County: Comal Stage: Albian
Length: 20.6 mm Height: 7.9 mm
Collector: William R. Thompson, Jr.
Holotype: NPL 70941
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 70941 .
Locality: Near Bergheim, Comal County, Texas.
Stratigraphy: Glen Rose Formation (Softer yellow matrix above Toucasia hardground).
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: STRICTOTIARA Lambert & Thiéry, 1925
Species: Strictotiara adami
TYPE SPECIES: Diadema tenui-stria Agassiz & Desor, 1846
DIAGNOSIS
A small, moderately inflated Strictotiara with six rows of interambulacral tubercles at the ambitus, the two inner rows extending the full length of the column. Ambulacra narrow with two rows of 16 primary tubercles, matching the vertical distribution of the interambulacral series. Pore pairs strictly biserial adapically, becoming offset to uniserial adorally. Apical system pentagonal, with the posterior angle only slightly produced into the interambulacrum. Peristome circular with shallow, distinct buccal notches. Originally assigned to Tetragramma (Thompson, 2016), a rigorous anatomical audit of the holotype corona (NPL 70941) necessitates its systematic assignment to Strictotiara based on four independent macro- and micro-structural parameters: oral-biased morphometric asymmetry (0.36D peristome vs. 0.32D apical system), a non-elongated subpentagonal apical scar, strictly trigeminate adoral plating architecture, and a stepped ontogenetic dropout pattern of the auxiliary interambulacral columns flanking the ambitus.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity
Formations: Glen Rose Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Comal.
Abundance: Rare; only one specimen found.
Associated Fauna: Found above a hard bed of Toucasia hancockensis. Associated with Loriolia rosana, Parorthopsis comalensis, Heteraster obliquatus, and Coenholectypus planatus.
DESCRIPTION
TOP: Length, width, height: 20.6 mm L × 7.9 mm H. Top shape: Subcircular. Top domed: Moderately inflated; slight swelling around apical system.
SIDE: Ambitus: Positioned at midpoint. Side shape: Margin evenly rounded; upper surface gently arched, flattened lower surface.
BOTTOM: Bottom shape: Flattened to slightly concave around peristome.
AMB: Amb shape: Widest at ambitus; narrow at peristome and apical system. Amb arrangement: Two rows of 16 tubercles. Plating: Trigeminate adorally.
PORE PAIRS: Arrangement: Uniserial below the margin; biserial above the margin.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: Yes. Mamelons: Small. Interambulacral Tubercles: Two rows of 12–13 tubercles run the entire length. Another two rows (9–10 tubercles) run from 1/4 below the apical system to the peristome. A third set of two rows (6–7 tubercles) runs from slightly above the margin to halfway below the margin. Tubercles are largest at the ambitus.
GRANULES: Distribution: Miliary tubercles and granulation run the length of the ambulacra between tubercles. In the interambulacra, granulation runs the length of the interradial suture but is sparse near the apical system.
FASCIOLE: Absent.
INTERAMB: Width: Over 2 times the width of ambulacra at the margin.
APICAL SYSTEM: Size: Diameter 32% of test diameter. Shape: Rounded to subpentagonal; cuts slightly into each ambulacrum and interambulacrum.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Diameter 36% of test diameter. Shape: Circular. Lip: Buccal notches very small but pronounced.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype NPL 70941.
ETYMOLOGY
Named after Adam Ray Thompson of Austin, TX, son of the author.
REMARKS & COMPARISONS
Remarks: This species resembles Tetragramma species found in Texas but is assigned to Strictotiara based on the circular apical scar (vs. pentagonal/elongate in Tetragramma).
Periproctal and Peristomial Morphometrics: A diagnostic hallmark of the family Diplopodiidae is the proportional relationship between the aboral apical aperture and the oral peristome relative to total test diameter.
In Tetragramma, the apical system typically dominates or equals the peristomial dimensions. Conversely, S. adami exhibits a clear oral-biased asymmetry: Apical System Diameter = 0.32D vs. Peristome Diameter = 0.36D
This structural bias toward an expanded oral aperture relative to the apical scar aligns precisely with the generic constraints of Strictotiara and strongly diverges from Tetragramma.
Apical System Geometry
The periproctal opening of Tetragramma is widely characterized by a deeply elongated, starkly pentagonal insertion track that extends conspicuously into the posterior interambulacrum.
The S. adami apical scar is sharply geometric but fundamentally rounded-subpentagonal. The posterior angle is only faintly produced and lacks the slit-like, elongated configuration seen in co-occurring Texas diplopodiids, such as Tetragramma texanum.
Adoral Plating Architecture
The mechanism of compound plate calcification near the oral margin provides an ironclad generic boundary between these groups:
Interambulacral Tuberculation Ontogeny
While both genera can develop multiple rows of interambulacral tubercles, the vertical continuity of these columns differs across the corona. Multi-rowed Tetragramma retain broad, continuous vertical bands that span almost the entire height of the side wall.
In S. adami, the six vertical columns display a restricted, stepped dropout pattern flanking the ambitus:
Comparisons:
Plate: StAd-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Bergheim County: Comal Stage: Albian
Length: 20.6 mm Height: 7.9 mm
Collector: William R. Thompson, Jr.
Holotype: NPL 70941
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 70941 .
Locality: Near Bergheim, Comal County, Texas.
Stratigraphy: Glen Rose Formation (Softer yellow matrix above Toucasia hardground).
SYNONYMY
- Tetragramma adami 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: STRICTOTIARA Lambert & Thiéry, 1925
Species: Strictotiara adami
TYPE SPECIES: Diadema tenui-stria Agassiz & Desor, 1846
DIAGNOSIS
A small, moderately inflated Strictotiara with six rows of interambulacral tubercles at the ambitus, the two inner rows extending the full length of the column. Ambulacra narrow with two rows of 16 primary tubercles, matching the vertical distribution of the interambulacral series. Pore pairs strictly biserial adapically, becoming offset to uniserial adorally. Apical system pentagonal, with the posterior angle only slightly produced into the interambulacrum. Peristome circular with shallow, distinct buccal notches. Originally assigned to Tetragramma (Thompson, 2016), a rigorous anatomical audit of the holotype corona (NPL 70941) necessitates its systematic assignment to Strictotiara based on four independent macro- and micro-structural parameters: oral-biased morphometric asymmetry (0.36D peristome vs. 0.32D apical system), a non-elongated subpentagonal apical scar, strictly trigeminate adoral plating architecture, and a stepped ontogenetic dropout pattern of the auxiliary interambulacral columns flanking the ambitus.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity
Formations: Glen Rose Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Comal.
Abundance: Rare; only one specimen found.
Associated Fauna: Found above a hard bed of Toucasia hancockensis. Associated with Loriolia rosana, Parorthopsis comalensis, Heteraster obliquatus, and Coenholectypus planatus.
DESCRIPTION
TOP: Length, width, height: 20.6 mm L × 7.9 mm H. Top shape: Subcircular. Top domed: Moderately inflated; slight swelling around apical system.
SIDE: Ambitus: Positioned at midpoint. Side shape: Margin evenly rounded; upper surface gently arched, flattened lower surface.
BOTTOM: Bottom shape: Flattened to slightly concave around peristome.
AMB: Amb shape: Widest at ambitus; narrow at peristome and apical system. Amb arrangement: Two rows of 16 tubercles. Plating: Trigeminate adorally.
PORE PAIRS: Arrangement: Uniserial below the margin; biserial above the margin.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: Yes. Mamelons: Small. Interambulacral Tubercles: Two rows of 12–13 tubercles run the entire length. Another two rows (9–10 tubercles) run from 1/4 below the apical system to the peristome. A third set of two rows (6–7 tubercles) runs from slightly above the margin to halfway below the margin. Tubercles are largest at the ambitus.
GRANULES: Distribution: Miliary tubercles and granulation run the length of the ambulacra between tubercles. In the interambulacra, granulation runs the length of the interradial suture but is sparse near the apical system.
FASCIOLE: Absent.
INTERAMB: Width: Over 2 times the width of ambulacra at the margin.
APICAL SYSTEM: Size: Diameter 32% of test diameter. Shape: Rounded to subpentagonal; cuts slightly into each ambulacrum and interambulacrum.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Diameter 36% of test diameter. Shape: Circular. Lip: Buccal notches very small but pronounced.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype NPL 70941.
ETYMOLOGY
Named after Adam Ray Thompson of Austin, TX, son of the author.
REMARKS & COMPARISONS
Remarks: This species resembles Tetragramma species found in Texas but is assigned to Strictotiara based on the circular apical scar (vs. pentagonal/elongate in Tetragramma).
Periproctal and Peristomial Morphometrics: A diagnostic hallmark of the family Diplopodiidae is the proportional relationship between the aboral apical aperture and the oral peristome relative to total test diameter.
In Tetragramma, the apical system typically dominates or equals the peristomial dimensions. Conversely, S. adami exhibits a clear oral-biased asymmetry: Apical System Diameter = 0.32D vs. Peristome Diameter = 0.36D
This structural bias toward an expanded oral aperture relative to the apical scar aligns precisely with the generic constraints of Strictotiara and strongly diverges from Tetragramma.
Apical System Geometry
The periproctal opening of Tetragramma is widely characterized by a deeply elongated, starkly pentagonal insertion track that extends conspicuously into the posterior interambulacrum.
The S. adami apical scar is sharply geometric but fundamentally rounded-subpentagonal. The posterior angle is only faintly produced and lacks the slit-like, elongated configuration seen in co-occurring Texas diplopodiids, such as Tetragramma texanum.
Adoral Plating Architecture
The mechanism of compound plate calcification near the oral margin provides an ironclad generic boundary between these groups:
- The Polyplicate Condition: Tetragramma exhibits highly complex polyplicate adoral plating, where four or more primary plates fuse to carry dense, clustered pore-pair bands at the peristomial rim.
- The Trigeminate Condition: S. adami, the plating transition to the peristome is strictly trigeminate. Individual compound elements consist of exactly three fused primary plates, each bearing a single pore-pair. This triad grouping is an immutable diagnostic criterion for Strictotiara.
Interambulacral Tuberculation Ontogeny
While both genera can develop multiple rows of interambulacral tubercles, the vertical continuity of these columns differs across the corona. Multi-rowed Tetragramma retain broad, continuous vertical bands that span almost the entire height of the side wall.
In S. adami, the six vertical columns display a restricted, stepped dropout pattern flanking the ambitus:
- The inner primary pair spans the full vertical column length (12 - 13 tubercles).
- The secondary columns truncate abruptly at approximately 0.25 distance from the apical system (9 – 10 tubercles).
- The tertiary outermost rows are restricted to a tight band immediately adjacent to the ambitus (6 - 7 tubercles).
Comparisons:
- Strictotiara argonnensis (Lambert, 1927): Globally, the most morphologically proximate congeneric is S. argonnensis (Lambert, 1927) from the Aptian sequence of Grandpré, France. S. adami is fundamentally distinguished from the European type by its advanced interambulacral plating and tuberculation density. While S. argonnensis is strictly constrained to a four-row primary tubercle layout at the ambitus, S. adami develops a highly dense six-row configuration. Furthermore, the auxiliary outer rows in S. adami exhibit an abrupt vertical dropout pattern flanking the ambitus, a trait markedly more pronounced than the gradual column tapering observed in S. argonnensis.
- Strictotiara tenui-stria (Agassiz & Desor, 1846): These Western European forms display a much narrower apical scar profile relative to total test diameter (<28% D). S. adami stands distinct with its remarkably expansive, geometric apical scar (32% D), suggesting a regional evolutionary widening of the aboral ring within Gulf Coast populations.
