Pygaster borachoensis Thompson, 2016
Plate: PyBo-10
Series: Upper Cretaceous Group: Washita Formation: Boracho
Locale: McCamey County: Upton Stage: Cenomanian
Width: 86.6 mm Height: 31.9 mm
Specimen in photo: NPL 71462 Holotype
Collector: Frank Crane
University of Texas Non-vertebrate Paleo. Lab.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 71462.
Locality: McCamey, Upton County, Texas.
Stratigraphy: Boracho Formation, Washita Group.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Order: Pygasteroida Durham & Melville, 1957
Family: Pygasteridae Lambert, 1900
Genus: PYGASTER L. Agassiz, 1836
Species: Pygaster borachoensis Thompson, 2016
TYPE SPECIES: Clypeus semisulcatus Phillips, 1829
DIAGNOSIS
A Pygaster from the Upper Cretaceous of West Texas characterized by a low dome profile and a large, teardrop-shaped periproct that points toward the apical system.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Boracho Formation.
Stratigraphic Units: Upper Cretaceous, Cenomanian.
Counties: Upton.
Abundance: Rare; only one specimen known.
DESCRIPTION
TOP: Length, width, height: 86.6 mm W × 31.9 mm H. Top shape: Pentagonal; very large. Top domed: Low dome-shaped; apex central.
SIDE: Ambitus: Rounded; positioned low. Side shape: Curved sides; posterior end truncated.
BOTTOM: Bottom shape: Flat; adoral surface concave.
AMB: Amb shape: Lanceolate from above and below; pointed at both ends, widest at the margin. Amb arrangement: Protruding from the test outline. Plating: Trigeminate throughout.
PORE PAIRS: Arrangement: Uniserial. Shape: Small and round.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: Yes (Implied by genus, text says bosses protruding). Ambulacral Tubercles: A row of primary tubercles runs the entire length of the ambulacra next to the granule row. Interambulacral Tubercles: Dense; each interambulacrum filled with primary tubercles (13–14 wide) in a consistent pattern. Tubercles are very dense adorally and near the margin; less dense and more randomly placed near the peristome. Areolas: Sunken. Bosses: Protruding.
GRANULES: Distribution: Aborally in ambulacra, a row of granules sits next to the pore pairs. Inside the primary rows, granules of varying sizes are arranged in a somewhat random pattern. Randomly spaced in interambulacra.
FASCIOLE: Absent in Pygasteridae.
INTERAMB: Width: Four times wider than ambulacra at the margin. Shape: Plates much wider than tall.
APICAL SYSTEM: Location: Central. Condition: Incomplete in specimen.
PERIPROCT (ANUS): Shape: Large, teardrop-shaped; length almost twice the width. Location: Aboral; pointed at the apical system (characteristic of the genus where the periproct is typically continuous with the apical disc).
PERISTOME (MOUTH): Shape: Sub-pentagonal. Size: Near equal in size to the apical system. Lip: Notches present.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype NPL 71462. A second specimen from the Crane Collection was also studied.
ETYMOLOGY
Named after the Boracho Formation, the stratigraphic unit where the holotype was found.
REMARKS & COMPARISONS
Remarks: The genus Pygaster is predominantly Jurassic in occurrence. This specimen represents a significant Cretaceous occurrence in North America.
Comparisons:
Plate: PyBo-10
Series: Upper Cretaceous Group: Washita Formation: Boracho
Locale: McCamey County: Upton Stage: Cenomanian
Width: 86.6 mm Height: 31.9 mm
Specimen in photo: NPL 71462 Holotype
Collector: Frank Crane
University of Texas Non-vertebrate Paleo. Lab.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 71462.
Locality: McCamey, Upton County, Texas.
Stratigraphy: Boracho Formation, Washita Group.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Order: Pygasteroida Durham & Melville, 1957
Family: Pygasteridae Lambert, 1900
Genus: PYGASTER L. Agassiz, 1836
Species: Pygaster borachoensis Thompson, 2016
TYPE SPECIES: Clypeus semisulcatus Phillips, 1829
DIAGNOSIS
A Pygaster from the Upper Cretaceous of West Texas characterized by a low dome profile and a large, teardrop-shaped periproct that points toward the apical system.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Boracho Formation.
Stratigraphic Units: Upper Cretaceous, Cenomanian.
Counties: Upton.
Abundance: Rare; only one specimen known.
DESCRIPTION
TOP: Length, width, height: 86.6 mm W × 31.9 mm H. Top shape: Pentagonal; very large. Top domed: Low dome-shaped; apex central.
SIDE: Ambitus: Rounded; positioned low. Side shape: Curved sides; posterior end truncated.
BOTTOM: Bottom shape: Flat; adoral surface concave.
AMB: Amb shape: Lanceolate from above and below; pointed at both ends, widest at the margin. Amb arrangement: Protruding from the test outline. Plating: Trigeminate throughout.
PORE PAIRS: Arrangement: Uniserial. Shape: Small and round.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: Yes (Implied by genus, text says bosses protruding). Ambulacral Tubercles: A row of primary tubercles runs the entire length of the ambulacra next to the granule row. Interambulacral Tubercles: Dense; each interambulacrum filled with primary tubercles (13–14 wide) in a consistent pattern. Tubercles are very dense adorally and near the margin; less dense and more randomly placed near the peristome. Areolas: Sunken. Bosses: Protruding.
GRANULES: Distribution: Aborally in ambulacra, a row of granules sits next to the pore pairs. Inside the primary rows, granules of varying sizes are arranged in a somewhat random pattern. Randomly spaced in interambulacra.
FASCIOLE: Absent in Pygasteridae.
INTERAMB: Width: Four times wider than ambulacra at the margin. Shape: Plates much wider than tall.
APICAL SYSTEM: Location: Central. Condition: Incomplete in specimen.
PERIPROCT (ANUS): Shape: Large, teardrop-shaped; length almost twice the width. Location: Aboral; pointed at the apical system (characteristic of the genus where the periproct is typically continuous with the apical disc).
PERISTOME (MOUTH): Shape: Sub-pentagonal. Size: Near equal in size to the apical system. Lip: Notches present.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype NPL 71462. A second specimen from the Crane Collection was also studied.
ETYMOLOGY
Named after the Boracho Formation, the stratigraphic unit where the holotype was found.
REMARKS & COMPARISONS
Remarks: The genus Pygaster is predominantly Jurassic in occurrence. This specimen represents a significant Cretaceous occurrence in North America.
Comparisons:
- Pygaster truncatus: P. borachoensis is less inflated and has a more teardrop-shaped periproct (vs. elliptical in P. truncatus).
