Miocyphosoma bexarense Thompson 2016
Plate: MiBe-10
Series: Upper Cretaceous Group: Navarro Formation: Corsicana
Locale: San Antonio County: Bexar Stage: Maestrichtian
Width: 24.3 mm Height: 11.3 mm
Collector: William Thompson
Holotype: NPL 94347 Non-vertebrate Paleo. Lab., Univ. of Texas
Plate: MiBe-20
Series: Upper Cretaceous Group: Navarro Formation: Corsicana
Locale: San Antonio County: Bexar Stage: Maestrichtian
Width: 20.5 mm Height: 9.5 mm
Collector: Kevin Durney
Plate: MiBe-30
Series: Upper Cretaceous Group: Taylor or Navarro Formation: Anacacho? or Escondito?
Locale: unsure County: unsure Stage: Campanian? or Maestrichtian?
Width: 26.7 mm Height: 11.8 mm
Collector: Dr. Stephen Crane
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 94347.
Locality: San Antonio, Bexar County, Texas.
Stratigraphy: Corsicana Formation, Navarro 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: Phymosomatidae Pomel, 1883
Genus: MIOCYPHOSOMA Pomel, 1883
Species: Miocyphosoma bexarense
TYPE SPECIES: Cidaris wetherelli Forbes, 1850 (by subsequent designation of Lambert & Thiéry, 1911)
DIAGNOSIS
A medium-sized Miocyphosoma from the Maastrichtian of Texas characterized by uniserial pore pairs arranged in arcs adorally. Ambulacral plating is quinqueminate (5 elements) aborally and trigeminate adorally. Distinguished by distinct adradial and interradial bands of granules.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Navarro; Taylor (?)
Formations: Corsicana Formation; possibly Anacacho or Escondito.
Stratigraphic Units: Upper Cretaceous, Maastrichtian.
Counties: Bexar.
Abundance: Rare; three specimens studied.
DESCRIPTION
TOP: Length, width, height: 24.3 mm L × 11.3 mm H (Holotype).
Top shape: Circular outline.
Top domed: Domed profile.
SIDE: Ambitus: Rounded; positioned at 47% of height from the adoral surface.
Side shape: Domed.
BOTTOM: Bottom shape: Adoral surface very slightly concave.
AMB: Amb shape: Lanceolate; width at apical system is almost twice the width at the peristome.
Amb arrangement: Ambulacra are 46% the width of the interambulacra at the ambitus. Two rows of medium tubercles (10–11 per row) gradually diminish in size toward the poles.
Plating: Phymosomatid plate compounding; composed of 5 elements (quinqueminate) except adorally where plating becomes trigeminate (3 elements).
PORE PAIRS: Arrangement: Uniserial; mostly straight with arcs aborally, forming arcs adorally.
TUBERCLES: Primary Perforated: No (Imperforate).
Primary Crenulate: Yes (very slightly).
Interambulacral Tubercles: Two rows of medium tubercles (10–11 per row) equal in size to ambulacral tubercles. At the ambitus, two rows of smaller secondary tubercles are present.
Areolas: Large; dominate the plates.
GRANULES: Distribution: Rows of granules present at adradial and interradial margins.
FASCIOLE: Absent.
APICAL SYSTEM: Size: Diameter 1/3 of test.
Shape: Angular, pentagonal.
Condition: Plating lost in holotype.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Diameter 45% of test.
Shape: Circular.
Lip: Buccal notches present with adradial tags.
SPINES: Shape: Lanceolate and smooth (based on fragment in matrix).
SPECIMENS STUDIED & CONDITION:
ETYMOLOGY
Named after Bexar County, Texas, the type locality.
REMARKS & COMPARISONS
Remarks: This species represents a rare occurrence of Miocyphosoma in the Navarro Group.
Comparisons:
Plate: MiBe-10
Series: Upper Cretaceous Group: Navarro Formation: Corsicana
Locale: San Antonio County: Bexar Stage: Maestrichtian
Width: 24.3 mm Height: 11.3 mm
Collector: William Thompson
Holotype: NPL 94347 Non-vertebrate Paleo. Lab., Univ. of Texas
Plate: MiBe-20
Series: Upper Cretaceous Group: Navarro Formation: Corsicana
Locale: San Antonio County: Bexar Stage: Maestrichtian
Width: 20.5 mm Height: 9.5 mm
Collector: Kevin Durney
Plate: MiBe-30
Series: Upper Cretaceous Group: Taylor or Navarro Formation: Anacacho? or Escondito?
Locale: unsure County: unsure Stage: Campanian? or Maestrichtian?
Width: 26.7 mm Height: 11.8 mm
Collector: Dr. Stephen Crane
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 94347.
Locality: San Antonio, Bexar County, Texas.
Stratigraphy: Corsicana Formation, Navarro 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: Phymosomatidae Pomel, 1883
Genus: MIOCYPHOSOMA Pomel, 1883
Species: Miocyphosoma bexarense
TYPE SPECIES: Cidaris wetherelli Forbes, 1850 (by subsequent designation of Lambert & Thiéry, 1911)
DIAGNOSIS
A medium-sized Miocyphosoma from the Maastrichtian of Texas characterized by uniserial pore pairs arranged in arcs adorally. Ambulacral plating is quinqueminate (5 elements) aborally and trigeminate adorally. Distinguished by distinct adradial and interradial bands of granules.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Navarro; Taylor (?)
Formations: Corsicana Formation; possibly Anacacho or Escondito.
Stratigraphic Units: Upper Cretaceous, Maastrichtian.
Counties: Bexar.
Abundance: Rare; three specimens studied.
DESCRIPTION
TOP: Length, width, height: 24.3 mm L × 11.3 mm H (Holotype).
Top shape: Circular outline.
Top domed: Domed profile.
SIDE: Ambitus: Rounded; positioned at 47% of height from the adoral surface.
Side shape: Domed.
BOTTOM: Bottom shape: Adoral surface very slightly concave.
AMB: Amb shape: Lanceolate; width at apical system is almost twice the width at the peristome.
Amb arrangement: Ambulacra are 46% the width of the interambulacra at the ambitus. Two rows of medium tubercles (10–11 per row) gradually diminish in size toward the poles.
Plating: Phymosomatid plate compounding; composed of 5 elements (quinqueminate) except adorally where plating becomes trigeminate (3 elements).
PORE PAIRS: Arrangement: Uniserial; mostly straight with arcs aborally, forming arcs adorally.
TUBERCLES: Primary Perforated: No (Imperforate).
Primary Crenulate: Yes (very slightly).
Interambulacral Tubercles: Two rows of medium tubercles (10–11 per row) equal in size to ambulacral tubercles. At the ambitus, two rows of smaller secondary tubercles are present.
Areolas: Large; dominate the plates.
GRANULES: Distribution: Rows of granules present at adradial and interradial margins.
FASCIOLE: Absent.
APICAL SYSTEM: Size: Diameter 1/3 of test.
Shape: Angular, pentagonal.
Condition: Plating lost in holotype.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Diameter 45% of test.
Shape: Circular.
Lip: Buccal notches present with adradial tags.
SPINES: Shape: Lanceolate and smooth (based on fragment in matrix).
SPECIMENS STUDIED & CONDITION:
- Holotype NPL 94347: Bexar County.
- Specimen 2 (MiBe-20): Kevin Durney Collection (Width 20.5 mm).
- Specimen 3 (MiBe-30): Dr. Stephen Crane Collection (Width 26.7 mm). Locality/Stratigraphy uncertain (Anacacho/Escondito?).
ETYMOLOGY
Named after Bexar County, Texas, the type locality.
REMARKS & COMPARISONS
Remarks: This species represents a rare occurrence of Miocyphosoma in the Navarro Group.
Comparisons:
- Rachiosoma hondoense: M. bexarense resembles R. hondoense (Cooke, 1953) but differs in plating; R. hondoense has 5 elements throughout, whereas M. bexarensis is trigeminate adorally.
- Gauthieria paucituberculata: M. bexarense has a much larger peristome.
- Miocyphosoma wetherelli: M. bexarense is more dome-shaped than M. wetherelli.
- Miocyphosoma sp. (Undescribed): Distinguished from another undescribed form (referred to in notes as M. occultatum) by having a much more angular and pentagonal peristome and lacking the distinctive crenulation of that form.
