Mecaster texanus (Roemer, 1852)
Plate: MeTe-10
Series: Upper Cretaceous Group: Taylor Formation: Anacacho Limestone
Locale: Sabinal County: Uvalde Stage: Campanian
Length: 37.4 mm Width: 36.5 mm Height: 22.9 mm
Specimen in photos: U.S.N.M. 108399 Hypotype?
Repository: Paleobiology Dept., NMNH, Smithsonian Institution Red Ink
HOLOTYPE INFO:
Holotype: Originally described as Diadema texanum by Roemer (1852). (Note: This is considered a homonym for a different species). Roemer's original type material is likely housed in the University of Bonn, Germany.
Referred Specimen: USNM 108399 (Figured by Cooke, 1953).
Locality: Waterfall of the Guadalupe at New Braunfels, Comal County, Texas (Roemer, 1852).
Stratigraphy: Austin Chalk (type locality); Anacacho Limestone and Taylor Marl (Cooke, 1953).
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: Hemiasteridae H. L. Clark, 1917
Genus: MECASTER Pomel, 1883
Species: Mecaster texanus (Roemer, 1852 sensu Cooke, 1953)
TYPE SPECIES: Hemiaster fourneli Agassiz & Desor, 1847
DIAGNOSIS
Test cordate-subquadrate, with a moderately high upper surface and slightly inflated lower surface. Characterized by long, straight, deeply indented petals where the anterior pair is longer. The anterior ambulacrum is subpetaloid, and a peripetalous fasciole is typically present (Cooke, 1953).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Taylor, Austin
Formations: Anacacho Limestone, Austin Chalk, Taylor Marl.
Stratigraphic Units: Upper Cretaceous, Campanian (Senonian age).
Counties: Uvalde, Comal, Travis.
Abundance: Plentiful and in good condition in the Anacacho Limestone (Cooke, 1953).
DESCRIPTION
TOP: Length, width, height: 37.4 mm L × 36.5 mm W × 22.9 mm H.
Top shape: Cordate-subquadrate; indented in front, truncated behind (Cooke, 1953). Very angular margin; wide, narrowing posteriorly.
Top domed: Upper surface rather high.
SIDE: Ambitus: Positioned about 40% from the base.
Side shape: Inflated; posterior end long and truncated, almost perpendicular. Anterior end sloping.
Profile: From the ends, test appears broad and very rounded.
BOTTOM: Bottom shape: Lower surface slightly inflated (Cooke, 1953); mostly flat, slightly curved.
AMB: Amb shape: All 5 ambulacra are sunken; the unpaired ambulacrum (III) is more deeply sunken and narrower than the paired ambulacra. Petals long, straight, deeply indented (depressed) (Cooke, 1953).
Amb arrangement: Paired petals are open distally. Anterior paired ambulacra are slightly longer than the posterior pair and almost reach the margin.
Unpaired Amb: Subpetaloid; plates long and narrow; deep, rounded ambulacral furrow extending to the peristome (Cooke, 1953).
PORE PAIRS: Shape: Pores elongated, conjugate (Cooke, 1953).
Unpaired Amb: Pores of each zygopore are round, close together, and separated by a small flattened bead (Cooke, 1953).
Paired Amb: Pores in paired ambulacra are elongated.
TUBERCLES: Primary Perforated: Yes.
Primary Crenulate: Yes.
Areolas: Sunken.
Distribution: Small. Tubercles at anterior end surrounded by fine granulation. Tubercles on plastron resting on scaly socles (Cooke, 1953). More pronounced on adoral surface and at margin on aboral surface.
GRANULES: Distribution: Fine granulation around anterior tubercles (Cooke, 1953).
FASCIOLE: Peripetalous: Slightly indented between the lateral petals (Cooke, 1953).
APICAL SYSTEM: Location: Nearly central.
Type: Ethmolytic; the madreporite separates the posterior oculars (which are otherwise in contact).
Genital Pores: Four perforated genital plates; lateral perforations much closer together than the front or back (Cooke, 1953).
Condition: Mostly missing in figured specimen.
PERIPROCT (ANUS): Shape: Oval.
Location: Well up on a sloping, slightly concave posterior truncation.
Visibility: Visible from above (Cooke, 1953).
PERISTOME (MOUTH): Shape: Reniform, sunken (Cooke, 1953). Subpentagonal; wide.
Location: Anterior.
Lip: Strongly labiate (protruding lip) posteriorly (Cooke, 1953). Surrounded by four paired ambulacral furrows with small beaded zygopores.
Visibility: Barely visible from anterior end.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Hypotype USNM 108399. (Note: Original label had "Red Ink").
ETYMOLOGY
Named for the state of Texas.
REMARKS & COMPARISONS
Remarks: This species has a complex taxonomic history. Roemer (1852) originally described Diadema texanum (which Cooke (1946) renamed Loriolia rosana due to homonymy). However, Cooke (1953) explicitly identified specimens as Hemiaster texanus (Roemer, 1852), basing his description on Roemer's original figures. Cooke noted that while Austin Chalk specimens were poorly preserved, numerous, well-preserved Anacacho Limestone specimens agreed well with Roemer's figures, making identification certain. The species is widely regarded as a junior synonym of Mecaster texanus (Roemer, 1888), or Mecaster elegans (Shumard, 1853) by others (Kamyabi Shadan et al., 2014).
Comparisons:
Remarks (01-2026): USNM 108399 is labeled "Type," but since Roemer's (1852) actual type is likely European, this is treated as a Hypotype (figured specimen) by Cooke.
Remarks (01-2026): The Holotype is the type found in the Anacacho Limestone of Uvalde County. The Mecasters found in the Austin Chalk are now Mecaster austensis (Thompson 2020). The literature says it is from the Austin Chalk in New Bruanfels. I challenge this due to the differences in the specimens.
Plate: MeTe-10
Series: Upper Cretaceous Group: Taylor Formation: Anacacho Limestone
Locale: Sabinal County: Uvalde Stage: Campanian
Length: 37.4 mm Width: 36.5 mm Height: 22.9 mm
Specimen in photos: U.S.N.M. 108399 Hypotype?
Repository: Paleobiology Dept., NMNH, Smithsonian Institution Red Ink
HOLOTYPE INFO:
Holotype: Originally described as Diadema texanum by Roemer (1852). (Note: This is considered a homonym for a different species). Roemer's original type material is likely housed in the University of Bonn, Germany.
Referred Specimen: USNM 108399 (Figured by Cooke, 1953).
Locality: Waterfall of the Guadalupe at New Braunfels, Comal County, Texas (Roemer, 1852).
Stratigraphy: Austin Chalk (type locality); Anacacho Limestone and Taylor Marl (Cooke, 1953).
SYNONYMY
- Diadema texanum Roemer, 1852 (non Diadema texanum Roemer, 1849)
- Hemiaster texanus (Roemer) Cooke, 1953
- Macraster texanus Roemer, 1888 (regarded as Type Species of Macraster; frequently confused with this species, but morphologically distinct (no fasciole))
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: Hemiasteridae H. L. Clark, 1917
Genus: MECASTER Pomel, 1883
Species: Mecaster texanus (Roemer, 1852 sensu Cooke, 1953)
TYPE SPECIES: Hemiaster fourneli Agassiz & Desor, 1847
DIAGNOSIS
Test cordate-subquadrate, with a moderately high upper surface and slightly inflated lower surface. Characterized by long, straight, deeply indented petals where the anterior pair is longer. The anterior ambulacrum is subpetaloid, and a peripetalous fasciole is typically present (Cooke, 1953).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Taylor, Austin
Formations: Anacacho Limestone, Austin Chalk, Taylor Marl.
Stratigraphic Units: Upper Cretaceous, Campanian (Senonian age).
Counties: Uvalde, Comal, Travis.
Abundance: Plentiful and in good condition in the Anacacho Limestone (Cooke, 1953).
DESCRIPTION
TOP: Length, width, height: 37.4 mm L × 36.5 mm W × 22.9 mm H.
Top shape: Cordate-subquadrate; indented in front, truncated behind (Cooke, 1953). Very angular margin; wide, narrowing posteriorly.
Top domed: Upper surface rather high.
SIDE: Ambitus: Positioned about 40% from the base.
Side shape: Inflated; posterior end long and truncated, almost perpendicular. Anterior end sloping.
Profile: From the ends, test appears broad and very rounded.
BOTTOM: Bottom shape: Lower surface slightly inflated (Cooke, 1953); mostly flat, slightly curved.
AMB: Amb shape: All 5 ambulacra are sunken; the unpaired ambulacrum (III) is more deeply sunken and narrower than the paired ambulacra. Petals long, straight, deeply indented (depressed) (Cooke, 1953).
Amb arrangement: Paired petals are open distally. Anterior paired ambulacra are slightly longer than the posterior pair and almost reach the margin.
Unpaired Amb: Subpetaloid; plates long and narrow; deep, rounded ambulacral furrow extending to the peristome (Cooke, 1953).
PORE PAIRS: Shape: Pores elongated, conjugate (Cooke, 1953).
Unpaired Amb: Pores of each zygopore are round, close together, and separated by a small flattened bead (Cooke, 1953).
Paired Amb: Pores in paired ambulacra are elongated.
TUBERCLES: Primary Perforated: Yes.
Primary Crenulate: Yes.
Areolas: Sunken.
Distribution: Small. Tubercles at anterior end surrounded by fine granulation. Tubercles on plastron resting on scaly socles (Cooke, 1953). More pronounced on adoral surface and at margin on aboral surface.
GRANULES: Distribution: Fine granulation around anterior tubercles (Cooke, 1953).
FASCIOLE: Peripetalous: Slightly indented between the lateral petals (Cooke, 1953).
APICAL SYSTEM: Location: Nearly central.
Type: Ethmolytic; the madreporite separates the posterior oculars (which are otherwise in contact).
Genital Pores: Four perforated genital plates; lateral perforations much closer together than the front or back (Cooke, 1953).
Condition: Mostly missing in figured specimen.
PERIPROCT (ANUS): Shape: Oval.
Location: Well up on a sloping, slightly concave posterior truncation.
Visibility: Visible from above (Cooke, 1953).
PERISTOME (MOUTH): Shape: Reniform, sunken (Cooke, 1953). Subpentagonal; wide.
Location: Anterior.
Lip: Strongly labiate (protruding lip) posteriorly (Cooke, 1953). Surrounded by four paired ambulacral furrows with small beaded zygopores.
Visibility: Barely visible from anterior end.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Hypotype USNM 108399. (Note: Original label had "Red Ink").
ETYMOLOGY
Named for the state of Texas.
REMARKS & COMPARISONS
Remarks: This species has a complex taxonomic history. Roemer (1852) originally described Diadema texanum (which Cooke (1946) renamed Loriolia rosana due to homonymy). However, Cooke (1953) explicitly identified specimens as Hemiaster texanus (Roemer, 1852), basing his description on Roemer's original figures. Cooke noted that while Austin Chalk specimens were poorly preserved, numerous, well-preserved Anacacho Limestone specimens agreed well with Roemer's figures, making identification certain. The species is widely regarded as a junior synonym of Mecaster texanus (Roemer, 1888), or Mecaster elegans (Shumard, 1853) by others (Kamyabi Shadan et al., 2014).
Comparisons:
- Mecaster austinensis: M. texanus is distinguished by having its widest part of the test located slightly above the midpoint (vs. further anterior in M. austinensis). Its petals are broader and more deeply sunken. The posterior truncation below the periproct is more deeply depressed. The peristome is very deeply sunken with a sunken lip, contrasting with the slightly sunken peristome and nearly flush lip of M. austinensis.
Remarks (01-2026): USNM 108399 is labeled "Type," but since Roemer's (1852) actual type is likely European, this is treated as a Hypotype (figured specimen) by Cooke.
Remarks (01-2026): The Holotype is the type found in the Anacacho Limestone of Uvalde County. The Mecasters found in the Austin Chalk are now Mecaster austensis (Thompson 2020). The literature says it is from the Austin Chalk in New Bruanfels. I challenge this due to the differences in the specimens.
