Phymosoma texanum (Roemer, 1852)
Plate: PhTe-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Comanche Peak
Locale: Harker Heights County: Bell Stage: Albian
Length: 43.8 mm Height: 20.6 mm
Specimen in photo: NPL 83031 Hypotype
Collector: William R. Thompson, Jr.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
Plate: PhTe-20
Series: Lower Cretaceous Group: Fredericksburg Formation: Comanche Peak
Locale: Unknown County: Unknown Stage: Albian
Length: 38 mm
Specimen in photos: Collection of Chris Garvie
Plate: PhTe-30
Length: 45.8 mm Height: 19.6 mm
Illustrations from original description.
HOLOTYPE INFO:
Holotype: Roemer’s original specimens are likely housed in the Geological Museum of the University of Bonn, Germany.
Locality: Fredericksburg or San Saba River, Texas (Roemer, 1852).
Stratigraphy: Comanche Peak Limestone (Fredericksburg Group).
SYNONYMY
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: PHYMOSOMA Haime, 1853
Species: Phymosoma texanum (Roemer, 1852)
TYPE SPECIES: Diadema priscum Agassiz, 1840
DIAGNOSIS
Test large, subcircular, and elevated. Characterized by four rows of primary tubercles in the interambulacra at the ambitus (reducing to two at the poles). Pore zones are biserial on the upper surface (from ambitus to apex) and uniserial below the ambitus (Clark & Twitchell, 1915; Cooke, 1953).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Comanche Peak Limestone; Walnut Formation; Goodland Limestone (Adkins, 1928).
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Bell, Travis, Williamson, Gillespie, Comal.
Abundance: Common index fossil for the Fredericksburg Group.
DESCRIPTION
TOP: Length, width, height: 43.8 mm L × 20.6 mm H (NPL 83031). Top shape: Subcircular to subpentagonal (Clark & Twitchell, 1915). Top domed: Upper surface elevated (Clark & Twitchell, 1915).
SIDE: Ambitus: Inflated. Side shape: Sides inflated; adoral surface elevated and convex (Clark & Twitchell, 1915).
BOTTOM: Bottom shape: Depressed and concave (Clark & Twitchell, 1915).
AMB: Amb shape: Broad, prominent, and lanceolate. Amb arrangement: Two rows of primary tubercles (14 or 15 in each series); large at the ambitus, decreasing gradually toward the poles. A circle of scattered granules surrounds the narrow areolas (Clark & Twitchell, 1915).
PORE PAIRS: Arrangement: Uniserial below the ambitus (except directly at the peristome where they increase). Biserial (bigeminal) from the ambitus to the apical system. Poriferous zones are broad upon the upper surface but very narrowed below (Clark & Twitchell, 1915).
TUBERCLES: Primary Perforated: No (Imperforate) (Cooke, 1953). Primary Crenulate: Yes. Interambulacral Tubercles: Four rows of primary tubercles at the ambitus; reduced to two near the apical system and peristome. In the center of the column, the four rows are of equal size; outer rows reduce rapidly toward the poles. Distribution: Small secondary tubercles on outer margins; irregularly scattered granules cover spaces between tubercles (Clark & Twitchell, 1915).
GRANULES: Distribution: See Tubercles.
FASCIOLE: Absent.
INTERAMB: Width: About 1.5 times the width of the ambulacra at the ambitus. Features: A slight depression occurs along the median suture (Clark & Twitchell, 1915).
APICAL SYSTEM: Condition: Caducous (often missing). Shape: Large and subpentagonal (Clark & Twitchell, 1915).
PERIPROCT (ANUS): Shape: Large and subpentagonal (Clark & Twitchell, 1915).
PERISTOME (MOUTH): Shape: Circular; broken by distinct incisions (buccal notches). Size: Wide; about two-fifths (40%) the diameter of the test (Clark & Twitchell, 1915). Lantern: Stirodont; upright, keeled teeth with deep V-shaped foramen magnum in pyramids .
SPINES: Shape: No ornamentation; wide collar; tapered ends .
SPECIMENS STUDIED & CONDITION:
Named for the state of Texas, the type locality (Roemer, 1849).
REMARKS & COMPARISONS
Remarks: This species was historically confused with Diplopodia due to early misinterpretations of the pore arrangement. Clark (1915) clarified that the pores are biserial only on the upper surface, placing it in Cyphosoma (now Phymosoma).
Comparisons:
Plate: PhTe-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Comanche Peak
Locale: Harker Heights County: Bell Stage: Albian
Length: 43.8 mm Height: 20.6 mm
Specimen in photo: NPL 83031 Hypotype
Collector: William R. Thompson, Jr.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
Plate: PhTe-20
Series: Lower Cretaceous Group: Fredericksburg Formation: Comanche Peak
Locale: Unknown County: Unknown Stage: Albian
Length: 38 mm
Specimen in photos: Collection of Chris Garvie
Plate: PhTe-30
Length: 45.8 mm Height: 19.6 mm
Illustrations from original description.
HOLOTYPE INFO:
Holotype: Roemer’s original specimens are likely housed in the Geological Museum of the University of Bonn, Germany.
Locality: Fredericksburg or San Saba River, Texas (Roemer, 1852).
Stratigraphy: Comanche Peak Limestone (Fredericksburg Group).
SYNONYMY
- Diadema texanum Roemer, 1849
- Cyphosoma texanum (Roemer) Agassiz & Desor, 1846
- Phymosoma texanum (Roemer) Lambert & Thiéry, 1911
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: PHYMOSOMA Haime, 1853
Species: Phymosoma texanum (Roemer, 1852)
TYPE SPECIES: Diadema priscum Agassiz, 1840
DIAGNOSIS
Test large, subcircular, and elevated. Characterized by four rows of primary tubercles in the interambulacra at the ambitus (reducing to two at the poles). Pore zones are biserial on the upper surface (from ambitus to apex) and uniserial below the ambitus (Clark & Twitchell, 1915; Cooke, 1953).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Comanche Peak Limestone; Walnut Formation; Goodland Limestone (Adkins, 1928).
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Bell, Travis, Williamson, Gillespie, Comal.
Abundance: Common index fossil for the Fredericksburg Group.
DESCRIPTION
TOP: Length, width, height: 43.8 mm L × 20.6 mm H (NPL 83031). Top shape: Subcircular to subpentagonal (Clark & Twitchell, 1915). Top domed: Upper surface elevated (Clark & Twitchell, 1915).
SIDE: Ambitus: Inflated. Side shape: Sides inflated; adoral surface elevated and convex (Clark & Twitchell, 1915).
BOTTOM: Bottom shape: Depressed and concave (Clark & Twitchell, 1915).
AMB: Amb shape: Broad, prominent, and lanceolate. Amb arrangement: Two rows of primary tubercles (14 or 15 in each series); large at the ambitus, decreasing gradually toward the poles. A circle of scattered granules surrounds the narrow areolas (Clark & Twitchell, 1915).
PORE PAIRS: Arrangement: Uniserial below the ambitus (except directly at the peristome where they increase). Biserial (bigeminal) from the ambitus to the apical system. Poriferous zones are broad upon the upper surface but very narrowed below (Clark & Twitchell, 1915).
TUBERCLES: Primary Perforated: No (Imperforate) (Cooke, 1953). Primary Crenulate: Yes. Interambulacral Tubercles: Four rows of primary tubercles at the ambitus; reduced to two near the apical system and peristome. In the center of the column, the four rows are of equal size; outer rows reduce rapidly toward the poles. Distribution: Small secondary tubercles on outer margins; irregularly scattered granules cover spaces between tubercles (Clark & Twitchell, 1915).
GRANULES: Distribution: See Tubercles.
FASCIOLE: Absent.
INTERAMB: Width: About 1.5 times the width of the ambulacra at the ambitus. Features: A slight depression occurs along the median suture (Clark & Twitchell, 1915).
APICAL SYSTEM: Condition: Caducous (often missing). Shape: Large and subpentagonal (Clark & Twitchell, 1915).
PERIPROCT (ANUS): Shape: Large and subpentagonal (Clark & Twitchell, 1915).
PERISTOME (MOUTH): Shape: Circular; broken by distinct incisions (buccal notches). Size: Wide; about two-fifths (40%) the diameter of the test (Clark & Twitchell, 1915). Lantern: Stirodont; upright, keeled teeth with deep V-shaped foramen magnum in pyramids .
SPINES: Shape: No ornamentation; wide collar; tapered ends .
SPECIMENS STUDIED & CONDITION:
- Hypotype NPL 83031: Collection of William R. Thompson, Jr.
- Specimen 2: Collection of Chris Garvie (38 mm).
- Reference: Illustrations from original description (Roemer, 1852) (Plate PhTe-30).
Named for the state of Texas, the type locality (Roemer, 1849).
REMARKS & COMPARISONS
Remarks: This species was historically confused with Diplopodia due to early misinterpretations of the pore arrangement. Clark (1915) clarified that the pores are biserial only on the upper surface, placing it in Cyphosoma (now Phymosoma).
Comparisons:
- Phymosoma volanum: P. texanum is closely related to P. volanum (Washita Group) but is taller, less subpentagonal, and has four rows of interambulacral tubercles that are more definitely developed even on small specimens (Clark & Twitchell, 1915).
- Phymosoma mexicanum: P. texanum is very similar to P. mexicanum, but P. mexicanum is distinguished by ambulacral tubercles that alternate near the apical system (unlike the opposite tubercles in texanum) and an "incomplete hexagon" granulation pattern (Böse, 1910; Cooke, 1953).
- Phymosoma hilli/bybeei: P. texanum has four rows of interambulacral tubercles, whereas P. hilli has only two rows (Clark, 1893).
