Tiaromma magilla Thompson, 2020
Plate: TeMa-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Walnut
Locale: Clifton County: Bosque Stage: Albian
Width: 8.4 mm Height: 3.4 mm
Collector: William Thompson
Holotype: NPL 94367
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 94367.
Paratypes: NPL 94368.
Locality: Clifton, Bosque County, Texas.
Stratigraphy: Upper part of the Walnut Formation, Fredericksburg 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: Diplopodiidae Smith & Wright, 1993
Genus: TIAROMMA Pomel, 1883
Species: Tiaromma magilla Thompson, 2020
TYPE SPECIES: Diadema michelini Agassiz & Desor, 1846
DIAGNOSIS
A small Tiaromma from the Albian of Texas characterized by 2 rows of 7 tubercles in both the ambulacral and interambulacral areas. Range of width of known specimens ranges from 6.5 mm to 12.9 mm.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Walnut Formation (Upper).
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Bosque.
Abundance: Common; 70 specimens studied.
Associated Fauna: Found in association with juvenile Heteraster bosei, juvenile Heteraster electus, juvenile Salenia sp., and shark teeth.
DESCRIPTION
TOP: Length/Width: 8.4 mm W × 3.4 mm H (Holotype). Top shape: Round. Top domed: Flat top; apical scar is 53% of diameter.
SIDE: Ambitus: Positioned at midpoint (50% from base). Side shape: Inflated.
BOTTOM: Bottom shape: Flat; concave depression near peristome.
AMB: Amb shape: Pentagonal plating, taller than wide. Amb arrangement: Two alternating rows of 7 tubercles; one primary tubercle per plate. Width: Interambulacra are 1.7 times wider than ambulacra. Plating: Plates have 3 pore pairs at the ambitus and above; 4 pore pairs adorally.
PORE PAIRS: Arrangement: Uniserial; straight with a slight zigzag pattern. Pairs are widely separated on ambulacral plates.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: Yes. Distribution: Decrease in size adapically and adorally. Tubercles slightly larger in interambulacra. Mamelons pronounced, bosses raised.
GRANULES: Distribution: Thick granulation runs vertically along adradial sutures. Adorally, a row of small secondary tubercles runs along the adradial sutures. Granulation present at interradial sutures; less granulation near apical system and peristome.
FASCIOLE: Absent.
INTERAMB: Shape: Pentagonal plating, wider than tall. Arrangement: Two rows of 7 tubercles. Interradial suture pronounced.
APICAL SYSTEM: Size: Scar diameter 53% of test. Shape: Subpentagonal; points at both interambulacra and ambulacra. Condition: Plating caducous (lost).
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Diameter 46% of test. Lip: Buccal notches wide, not deep, invaginated.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: 70 specimens studied. Holotype NPL 94367; Paratypes NPL 94368.
ETYMOLOGY
Named for Annette Magill Crane of Dallas, Texas, wife of Dr. Stephen Crane.
REMARKS & COMPARISONS
Remarks: Tiaromma magilla possesses fewer tubercles (7 per row) in both the ambulacra and interambulacra than other known Tiaromma species, which typically have 12 to 14.
Comparisons:
Plate: TeMa-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Walnut
Locale: Clifton County: Bosque Stage: Albian
Width: 8.4 mm Height: 3.4 mm
Collector: William Thompson
Holotype: NPL 94367
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 94367.
Paratypes: NPL 94368.
Locality: Clifton, Bosque County, Texas.
Stratigraphy: Upper part of the Walnut Formation, Fredericksburg 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: Diplopodiidae Smith & Wright, 1993
Genus: TIAROMMA Pomel, 1883
Species: Tiaromma magilla Thompson, 2020
TYPE SPECIES: Diadema michelini Agassiz & Desor, 1846
DIAGNOSIS
A small Tiaromma from the Albian of Texas characterized by 2 rows of 7 tubercles in both the ambulacral and interambulacral areas. Range of width of known specimens ranges from 6.5 mm to 12.9 mm.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Walnut Formation (Upper).
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Bosque.
Abundance: Common; 70 specimens studied.
Associated Fauna: Found in association with juvenile Heteraster bosei, juvenile Heteraster electus, juvenile Salenia sp., and shark teeth.
DESCRIPTION
TOP: Length/Width: 8.4 mm W × 3.4 mm H (Holotype). Top shape: Round. Top domed: Flat top; apical scar is 53% of diameter.
SIDE: Ambitus: Positioned at midpoint (50% from base). Side shape: Inflated.
BOTTOM: Bottom shape: Flat; concave depression near peristome.
AMB: Amb shape: Pentagonal plating, taller than wide. Amb arrangement: Two alternating rows of 7 tubercles; one primary tubercle per plate. Width: Interambulacra are 1.7 times wider than ambulacra. Plating: Plates have 3 pore pairs at the ambitus and above; 4 pore pairs adorally.
PORE PAIRS: Arrangement: Uniserial; straight with a slight zigzag pattern. Pairs are widely separated on ambulacral plates.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: Yes. Distribution: Decrease in size adapically and adorally. Tubercles slightly larger in interambulacra. Mamelons pronounced, bosses raised.
GRANULES: Distribution: Thick granulation runs vertically along adradial sutures. Adorally, a row of small secondary tubercles runs along the adradial sutures. Granulation present at interradial sutures; less granulation near apical system and peristome.
FASCIOLE: Absent.
INTERAMB: Shape: Pentagonal plating, wider than tall. Arrangement: Two rows of 7 tubercles. Interradial suture pronounced.
APICAL SYSTEM: Size: Scar diameter 53% of test. Shape: Subpentagonal; points at both interambulacra and ambulacra. Condition: Plating caducous (lost).
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Diameter 46% of test. Lip: Buccal notches wide, not deep, invaginated.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: 70 specimens studied. Holotype NPL 94367; Paratypes NPL 94368.
ETYMOLOGY
Named for Annette Magill Crane of Dallas, Texas, wife of Dr. Stephen Crane.
REMARKS & COMPARISONS
Remarks: Tiaromma magilla possesses fewer tubercles (7 per row) in both the ambulacra and interambulacra than other known Tiaromma species, which typically have 12 to 14.
Comparisons:
- Tiaromma michelini: T. magilla lacks the large secondary tubercles along the adradial suture adorally and the thick granules at the interradial suture seen in T. michelini.
