Diplodetus americanus (Stephenson, 1941)
Plate: DiAm-10
Series: Upper Cretaceous Group: Navarro Formation: Corsicana
Locale: San Antonio County: Bexar Stage: Maastrichtian
Length: 35.3 mm Width: 31.9 mm Height: 22.9 mm
Specimen in photo: NPL 83001 (Hypotype)
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: USNM 76253 — National Museum of Natural History, Smithsonian Institution (Stephenson, 1941)
Locality: 2.5 miles north of Tlevallie, Falls County, Texas (Stephenson, 1941)
SYNONYMY
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Atelostomata Zittel, 1879
Order: Spatangoida L. Agassiz, 1840
Suborder: Micrasterina Fischer, 1966
Family: Micrasteridae Lambert, 1920
Genus: DIPLODETUS Schlüter, 1900
Species: Diplodetus americanus (Stephenson, 1941)
TYPE SPECIES: Diplodetus brevistella (Schlüter, 1869)
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Navarro (Stephenson, 1941)
Formations: Corsicana Formation (Stephenson, 1941)
Stratigraphic Units: Upper Cretaceous, Maastrichtian
Counties: Bexar; Falls (Stephenson, 1941)
DESCRIPTION
TOP: Length, width, height: 35.3 mm L × 31.9 mm W × 22.9 mm H
Top shape: Subcordate; with rounded lateral and anterior margins (Cooke, 1953)
Top domed: Higher behind than in front (Cooke, 1953)
SIDE: Side shape: Higher behind than in front (Cooke, 1953)
Truncation: Truncated behind (Cooke, 1953)
AMB: Amb shape: Anterior ambulacrum broadly depressed, depression extending to peristome and indenting margin (Cooke, 1953)
Amb primary zones: Petaliferous part of anterior amb extends about halfway to margin. Paired petals depressed, extending more than halfway to margin. Anterior pair longer, nearly straight, widely diverging; posterior pair slightly curved backward (Cooke, 1953)
Amb width: Poriferous zones somewhat narrower than interporiferous zones in paired petals (Cooke, 1953)
PORE PAIRS: Shape: Anterior amb pores small, round. Paired petal pores elongate oval, similar in all zones (Cooke, 1953)
Conjugate vs Nonconjugate: Anterior amb zygopores inclined, divided by a bead (Cooke, 1953)
TUBERCLES: Primary tubercles: Crenulated, perforated (Cooke, 1953)
FASCIOLE: Subanal fasciole complete; peripetalous fasciole extending around the paired petals but indistinct or wanting at the anterior end (Cooke, 1953)
APICAL SYSTEM: Location: Slightly behind the center (Cooke, 1953)
Genital pores: Four genital pores (Cooke, 1953)
Shape: Ethmophract (Cooke, 1953)
PERIPROCT (ANUS): Shape & Size: Vertically elongated; small (Cooke, 1953)
Location: Well up on a vertical posterior truncation (Cooke, 1953)
Visibility: Barely visible from above (Cooke, 1953)
PERISTOME (MOUTH): Location: At the anterior third (Cooke, 1953)
Lip: Surrounded by a rim; strongly lipped behind (Cooke, 1953)
SPECIMENS STUDIED & CONDITION: Hypotype NPL 83001 .
ETYMOLOGY: Named for North America, distinguishing it from the European type species of the genus.
REMARKS & COMPARISONS
Remarks: Cooke (1953) noted that Arkansas specimens are nearly twice as large as the type. He originally classified it as Micraster americanus, distinguishing it from the type species Micraster coranguinum by the presence of a "fairly distinct partial peripetalous fasciole." He suggested the species might be more like Diplodetus due to the fasciole but noted the ethmophract apical system excluded it from Brissidae. Modern classification places Diplodetus in Micrasteridae, accommodating the ethmophract system.
Comparisons: Differs from Micraster coranguinum by having a partial peripetalous fasciole. Plesiaster peini has different pore structure in the unpaired ambulacrum (Cooke, 1953).
Plate: DiAm-10
Series: Upper Cretaceous Group: Navarro Formation: Corsicana
Locale: San Antonio County: Bexar Stage: Maastrichtian
Length: 35.3 mm Width: 31.9 mm Height: 22.9 mm
Specimen in photo: NPL 83001 (Hypotype)
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: USNM 76253 — National Museum of Natural History, Smithsonian Institution (Stephenson, 1941)
Locality: 2.5 miles north of Tlevallie, Falls County, Texas (Stephenson, 1941)
SYNONYMY
- Micraster (Plesiaster) americanus Stephenson, 1941
- Micraster americanus (Stephenson, 1941) (Cooke, 1953)
- Plesiaster americanus (Stephenson, 1941)
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Atelostomata Zittel, 1879
Order: Spatangoida L. Agassiz, 1840
Suborder: Micrasterina Fischer, 1966
Family: Micrasteridae Lambert, 1920
Genus: DIPLODETUS Schlüter, 1900
Species: Diplodetus americanus (Stephenson, 1941)
TYPE SPECIES: Diplodetus brevistella (Schlüter, 1869)
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Navarro (Stephenson, 1941)
Formations: Corsicana Formation (Stephenson, 1941)
Stratigraphic Units: Upper Cretaceous, Maastrichtian
Counties: Bexar; Falls (Stephenson, 1941)
DESCRIPTION
TOP: Length, width, height: 35.3 mm L × 31.9 mm W × 22.9 mm H
Top shape: Subcordate; with rounded lateral and anterior margins (Cooke, 1953)
Top domed: Higher behind than in front (Cooke, 1953)
SIDE: Side shape: Higher behind than in front (Cooke, 1953)
Truncation: Truncated behind (Cooke, 1953)
AMB: Amb shape: Anterior ambulacrum broadly depressed, depression extending to peristome and indenting margin (Cooke, 1953)
Amb primary zones: Petaliferous part of anterior amb extends about halfway to margin. Paired petals depressed, extending more than halfway to margin. Anterior pair longer, nearly straight, widely diverging; posterior pair slightly curved backward (Cooke, 1953)
Amb width: Poriferous zones somewhat narrower than interporiferous zones in paired petals (Cooke, 1953)
PORE PAIRS: Shape: Anterior amb pores small, round. Paired petal pores elongate oval, similar in all zones (Cooke, 1953)
Conjugate vs Nonconjugate: Anterior amb zygopores inclined, divided by a bead (Cooke, 1953)
TUBERCLES: Primary tubercles: Crenulated, perforated (Cooke, 1953)
FASCIOLE: Subanal fasciole complete; peripetalous fasciole extending around the paired petals but indistinct or wanting at the anterior end (Cooke, 1953)
APICAL SYSTEM: Location: Slightly behind the center (Cooke, 1953)
Genital pores: Four genital pores (Cooke, 1953)
Shape: Ethmophract (Cooke, 1953)
PERIPROCT (ANUS): Shape & Size: Vertically elongated; small (Cooke, 1953)
Location: Well up on a vertical posterior truncation (Cooke, 1953)
Visibility: Barely visible from above (Cooke, 1953)
PERISTOME (MOUTH): Location: At the anterior third (Cooke, 1953)
Lip: Surrounded by a rim; strongly lipped behind (Cooke, 1953)
SPECIMENS STUDIED & CONDITION: Hypotype NPL 83001 .
ETYMOLOGY: Named for North America, distinguishing it from the European type species of the genus.
REMARKS & COMPARISONS
Remarks: Cooke (1953) noted that Arkansas specimens are nearly twice as large as the type. He originally classified it as Micraster americanus, distinguishing it from the type species Micraster coranguinum by the presence of a "fairly distinct partial peripetalous fasciole." He suggested the species might be more like Diplodetus due to the fasciole but noted the ethmophract apical system excluded it from Brissidae. Modern classification places Diplodetus in Micrasteridae, accommodating the ethmophract system.
Comparisons: Differs from Micraster coranguinum by having a partial peripetalous fasciole. Plesiaster peini has different pore structure in the unpaired ambulacrum (Cooke, 1953).
