Paracidaris tysoni Whitney & Kellum, 1966
Plate: PhTy-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Canyon Texas County: Comal Stage: Albian
Width: 40 mm Height: 30 mm
Specimen in photo: UMMP 52162 Holotype
Collector: (Not specified)
Repository: University of Michigan Museum of Paleontology
HOLOTYPE INFO:
Holotype: UMMP 52162 (Whitney & Kellum, 1966).
Locality: 2 miles southwest of Wimberley, Hays County, Texas.
Stratigraphy: Glen Rose Limestone (Lower Member).
SYNONYMY
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Cidaroidea Smith, 1984
Order: Cidaroida Claus, 1880
Family: Cidaridae Gray, 1825
Genus: PARACIDARIS Pomel, 1883
Species: Paracidaris tysoni (Whitney & Kellum, 1966)
TYPE SPECIES: Cidaris florigemma Phillips, 1829
DIAGNOSIS
Test large, inflated, and subglobular. Ambulacra are extremely narrow and sinuous (flexuous). Interambulacra are very wide, composed of large hexagonal plates with large, perforate, non-crenulate primary tubercles. Scrobicular tubercles form a distinct ring at the margins of the areolas (Whitney & Kellum, 1966).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity
Formations: Glen Rose Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Comal, Hays.
Abundance: Rare. Only known form Holotype
DESCRIPTION
TOP: Length/Width: 40.0 mm diameter. Top shape: Circular.
SIDE: Side shape: Inflated; ball-like. Ambitus: Positioned at midpoint.
BOTTOM: Bottom shape: Slightly flattened adorally.
AMB: Amb shape: Extremely narrow and very flexuous (sinuous). Amb arrangement: Pore pairs are uniserial. Small tubercles are set between the pore pairs, set against them. Dense granulation fills the space between these tubercles.
PORE PAIRS: Arrangement: Uniserial.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: No (Implied by assignment to Phyllacanthus/Paracidaris). Interambulacral Tubercles: One large, prominent primary tubercle on each plate. Areolas: Large, circular, and depressed. Mamelons: Round and perforated.
SCROBICULAR TUBERCLES: Primary tubercles are surrounded at the margins by scrobicular tubercles.
GRANULES: Distribution: Great amount of granulation present on the outside of each plate and along the interradial ridge.
FASCIOLE: Absent in Cidaroida.
INTERAMB: Width: Very wide (four times wider than ambulacra). Arrangement: Made up of two rows of large prominent plates; center plates are very large. Plates near the peristome and apical system are much smaller. Shape: Plates are hexagonal with sides nearly equal.
APICAL SYSTEM: Condition: Missing in the specimen studied.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Large. Shape: 5-sided (Pentagonal).
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Viewed photos of the Holotype (UMMP 52162), which is noted as being a crushed specimen.
ETYMOLOGY
Named in honor of Alfred Woods Tyson (1913–2002), a Texas geologist who collected the holotype specimen. (Whitney & Kellum, 1966).
REMARKS & COMPARISONS
Remarks: Originally described as Phyllacanthus tysoni. As with P. texana, this species is reassigned to Paracidaris because Phyllacanthus is a Cenozoic/Recent genus.
Comparisons:
Remarks (01-2026): Updated Genus to Paracidaris to align with Cretaceous Cidarid taxonomy (per Smith & Rader, 2009 logic for Glen Rose cidaroids), replacing the Cenozoic genus Phyllacanthus.
Plate: PhTy-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Canyon Texas County: Comal Stage: Albian
Width: 40 mm Height: 30 mm
Specimen in photo: UMMP 52162 Holotype
Collector: (Not specified)
Repository: University of Michigan Museum of Paleontology
HOLOTYPE INFO:
Holotype: UMMP 52162 (Whitney & Kellum, 1966).
Locality: 2 miles southwest of Wimberley, Hays County, Texas.
Stratigraphy: Glen Rose Limestone (Lower Member).
SYNONYMY
- Phyllacanthus tysoni Whitney & Kellum, 1966
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Cidaroidea Smith, 1984
Order: Cidaroida Claus, 1880
Family: Cidaridae Gray, 1825
Genus: PARACIDARIS Pomel, 1883
Species: Paracidaris tysoni (Whitney & Kellum, 1966)
TYPE SPECIES: Cidaris florigemma Phillips, 1829
DIAGNOSIS
Test large, inflated, and subglobular. Ambulacra are extremely narrow and sinuous (flexuous). Interambulacra are very wide, composed of large hexagonal plates with large, perforate, non-crenulate primary tubercles. Scrobicular tubercles form a distinct ring at the margins of the areolas (Whitney & Kellum, 1966).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity
Formations: Glen Rose Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Comal, Hays.
Abundance: Rare. Only known form Holotype
DESCRIPTION
TOP: Length/Width: 40.0 mm diameter. Top shape: Circular.
SIDE: Side shape: Inflated; ball-like. Ambitus: Positioned at midpoint.
BOTTOM: Bottom shape: Slightly flattened adorally.
AMB: Amb shape: Extremely narrow and very flexuous (sinuous). Amb arrangement: Pore pairs are uniserial. Small tubercles are set between the pore pairs, set against them. Dense granulation fills the space between these tubercles.
PORE PAIRS: Arrangement: Uniserial.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: No (Implied by assignment to Phyllacanthus/Paracidaris). Interambulacral Tubercles: One large, prominent primary tubercle on each plate. Areolas: Large, circular, and depressed. Mamelons: Round and perforated.
SCROBICULAR TUBERCLES: Primary tubercles are surrounded at the margins by scrobicular tubercles.
GRANULES: Distribution: Great amount of granulation present on the outside of each plate and along the interradial ridge.
FASCIOLE: Absent in Cidaroida.
INTERAMB: Width: Very wide (four times wider than ambulacra). Arrangement: Made up of two rows of large prominent plates; center plates are very large. Plates near the peristome and apical system are much smaller. Shape: Plates are hexagonal with sides nearly equal.
APICAL SYSTEM: Condition: Missing in the specimen studied.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Large. Shape: 5-sided (Pentagonal).
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Viewed photos of the Holotype (UMMP 52162), which is noted as being a crushed specimen.
ETYMOLOGY
Named in honor of Alfred Woods Tyson (1913–2002), a Texas geologist who collected the holotype specimen. (Whitney & Kellum, 1966).
REMARKS & COMPARISONS
Remarks: Originally described as Phyllacanthus tysoni. As with P. texana, this species is reassigned to Paracidaris because Phyllacanthus is a Cenozoic/Recent genus.
Comparisons:
- Paracidaris texana: P. tysoni is distinguished by having larger and fewer interambulacral plates and a different proportion of ambulacral to interambulacral width. The granulation pattern also differs between the two species (Whitney & Kellum, 1966).
Remarks (01-2026): Updated Genus to Paracidaris to align with Cretaceous Cidarid taxonomy (per Smith & Rader, 2009 logic for Glen Rose cidaroids), replacing the Cenozoic genus Phyllacanthus.
