Macraster subobesus (Adkins, 1920)
Plate: MaSu-10
Series: Lower Cretaceous Group: Washita Formation: Weno
Locale: Rio Vista County: Johnson Stage: Albian
Length: 88.1 mm Width: 77.8 mm Height: 55.0 mm
Specimen in photos: BEG 21499 Typotype
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: USNM PAL 103883 (Adkins, 1920).
Locality: Rio Vista, Johnson County, Texas.
Stratigraphy: Top five feet of Weno Formation.
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
Family: Macrasteridae Lambert, 1920
Genus: MACRASTER Roemer, 1888
Species: Macraster subobesus (Adkins, 1920)
TYPE SPECIES: Macraster texanus Roemer, 1888
DIAGNOSIS
Test rotund, elevated, and straight-sided; tapering posteriorly to a very narrow, tall truncation. Distinguished by straight ambulacra, very long anterolateral petals (90+ pore pairs), and an extremely small, circular periproct situated relatively low on the truncation (Adkins, 1920).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Weno Formation (Top 5 feet, marl facies); Pawpaw Formation (marl facies) (Adkins, 1920).
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Johnson.
Abundance: Common in North Texas (Adkins, 1920).
DESCRIPTION
TOP: Length, width, height: 88.1 mm L × 77.8 mm W × 55.0 mm H.
Top shape: Rotund; tapering posteriorly. Contour similar to M. wenoensis but more prolonged posteriorly (Adkins, 1920).
Top domed: Much more elevated than M. wenoensis; apical system proportionately farther forward.
SIDE: Side shape: Straighter sided than M. wenoensis. Posterior truncation is very narrow, tall, and slopes forward at the bottom.
BOTTOM: Bottom shape: Base nearly flat; slightly raised on the posterior midline (less than in M. wenoensis). Excavated for the peristome.
AMB: Amb shape: Straight.
Amb arrangement: Unpaired ambulacrum (III) has about 60 similar slit-like pore pairs obliquely set.
Paired Ambs: Anterolaterals very long with 90 or more pore pairs in each zone. Posterolaterals with 80 or more pore pairs.
Interambs: Interambulacral areas notably more elevated (Adkins, 1920).
PORE PAIRS: Shape: All pores equal and similar slits in paired ambulacra. Unpaired ambulacrum pores are slit-like and obliquely set.
TUBERCLES: Not detailed.
FASCIOLE: Absent in Macraster.
APICAL SYSTEM: Location: Proportionately farther forward (anterior) than in M. wenoensis (Adkins, 1920).
PERIPROCT (ANUS): Shape: Circular; extremely small (3.5 mm diameter).
Location: Situated in the top of the posterior truncation; relatively lower than in M. wenoensis.
PERISTOME (MOUTH): Shape: Transversely oval (6.5 x 6.0 mm).
Size: Medium.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype BEG 21499.
ETYMOLOGY
Named subobesus indicating a similarity to, or a form slightly less "obese" than, Macraster obesus.
REMARKS & COMPARISONS
Remarks: Adkins (1920) noted this species might be mistaken for an old individual of M. wenoensis but is precluded by the specific differences in elevation, periproct size, and ambulacral counts. Kamyabi Shadan et al. (2014) suggest Macraster kentensis may be a synonym of this species (though they ultimately synonymize large Macraster forms with M. elegans). They note that the high number of species names for large, inflated Macraster in the USA and Mexico is likely an overestimation caused by describing local ecophenotypic variants as individual species.
Comparisons:
Plate: MaSu-10
Series: Lower Cretaceous Group: Washita Formation: Weno
Locale: Rio Vista County: Johnson Stage: Albian
Length: 88.1 mm Width: 77.8 mm Height: 55.0 mm
Specimen in photos: BEG 21499 Typotype
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: USNM PAL 103883 (Adkins, 1920).
Locality: Rio Vista, Johnson County, Texas.
Stratigraphy: Top five feet of Weno Formation.
SYNONYMY
- Epiaster subobesus Adkins, 1920
- Macraster elegans (Shumard, 1853) (fide Kamyabi Shadan et al., 2014)
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Atelostomata Zittel, 1879
Order: Spatangoida L. Agassiz, 1840
Family: Macrasteridae Lambert, 1920
Genus: MACRASTER Roemer, 1888
Species: Macraster subobesus (Adkins, 1920)
TYPE SPECIES: Macraster texanus Roemer, 1888
DIAGNOSIS
Test rotund, elevated, and straight-sided; tapering posteriorly to a very narrow, tall truncation. Distinguished by straight ambulacra, very long anterolateral petals (90+ pore pairs), and an extremely small, circular periproct situated relatively low on the truncation (Adkins, 1920).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Weno Formation (Top 5 feet, marl facies); Pawpaw Formation (marl facies) (Adkins, 1920).
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Johnson.
Abundance: Common in North Texas (Adkins, 1920).
DESCRIPTION
TOP: Length, width, height: 88.1 mm L × 77.8 mm W × 55.0 mm H.
Top shape: Rotund; tapering posteriorly. Contour similar to M. wenoensis but more prolonged posteriorly (Adkins, 1920).
Top domed: Much more elevated than M. wenoensis; apical system proportionately farther forward.
SIDE: Side shape: Straighter sided than M. wenoensis. Posterior truncation is very narrow, tall, and slopes forward at the bottom.
BOTTOM: Bottom shape: Base nearly flat; slightly raised on the posterior midline (less than in M. wenoensis). Excavated for the peristome.
AMB: Amb shape: Straight.
Amb arrangement: Unpaired ambulacrum (III) has about 60 similar slit-like pore pairs obliquely set.
Paired Ambs: Anterolaterals very long with 90 or more pore pairs in each zone. Posterolaterals with 80 or more pore pairs.
Interambs: Interambulacral areas notably more elevated (Adkins, 1920).
PORE PAIRS: Shape: All pores equal and similar slits in paired ambulacra. Unpaired ambulacrum pores are slit-like and obliquely set.
TUBERCLES: Not detailed.
FASCIOLE: Absent in Macraster.
APICAL SYSTEM: Location: Proportionately farther forward (anterior) than in M. wenoensis (Adkins, 1920).
PERIPROCT (ANUS): Shape: Circular; extremely small (3.5 mm diameter).
Location: Situated in the top of the posterior truncation; relatively lower than in M. wenoensis.
PERISTOME (MOUTH): Shape: Transversely oval (6.5 x 6.0 mm).
Size: Medium.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype BEG 21499.
ETYMOLOGY
Named subobesus indicating a similarity to, or a form slightly less "obese" than, Macraster obesus.
REMARKS & COMPARISONS
Remarks: Adkins (1920) noted this species might be mistaken for an old individual of M. wenoensis but is precluded by the specific differences in elevation, periproct size, and ambulacral counts. Kamyabi Shadan et al. (2014) suggest Macraster kentensis may be a synonym of this species (though they ultimately synonymize large Macraster forms with M. elegans). They note that the high number of species names for large, inflated Macraster in the USA and Mexico is likely an overestimation caused by describing local ecophenotypic variants as individual species.
Comparisons:
- M. wenoensis: M. subobesus is more elevated, straighter-sided, has a more anterior apical system, and a smaller, lower periproct than M. wenoensis (Adkins, 1920).
