Marine Myalinidae (Bivalvia: Pterioida) from the Permian of West Texas

2005·0.67 MB·English

by  Christopher A. Mcroberts

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3469, 15 pp., 9 figures, 3 tables March 24, 2005
Marine Myalinidae (Bivalvia: Pterioida) from the
Permian of West Texas
CHRISTOPHER A. McROBERTS1 AND NORMAN D. NEWELL2
ABSTRACT
Marine bivalvesofthefamilyMyalinidaeareanimportantbenthicconstituentofthePerm-
ianReefComplexofWestTexasandNewMexico.Wedescribeandsummarizethemyalinids
from Lower and Middle Permian reef and near-reef settings and infer living habits as either
epifaunal or semi-infaunal byssally attached suspension feeders. The six myalinid species
described are exceptionally preserved as silica pseudomorphs. Included in the fauna are two
new taxa: Myalina lamellosa, a species with distinctive commarginal lamellae, and Myalina
plicata, the only known myalinid with prominent radial plicae. The family Myalinidae is
placed in the Ambonychioidea (Order Pterioida) and an emended diagnosis incorporates lig-
ament characters and details of shell ultrastructure.
INTRODUCTION species.Followingtheend-Permianmassex-
tinction, the marine Myalinidae were greatly
In terms of taxonomic richness and mor-
diminished in taxonomic and ecological di-
phologic innovation, the marine Myalinidae
versity but persisted until possibly the Mid-
is one of the most successful of Late Paleo-
dle Triassic, when the group became extinct.
zoic–Early Mesozoic bivalve families. Al-
Their resilience, however, is underscored by
thoughmyalinidsareknownfromasfarback the fact that several myalinid species com-
as the early Carboniferous, and perhapseven prise a significant component of the Early
to the Devonian if Myalina squamosa Sow- Triassic recovery fauna (e.g., Schubert and
erby is considered a true myalinid, they did Bottjer, 1995).
not reach their glory until the Permian, Marine myalinids are an abundant and
where richness exceeds 10 genera and 25 conspicuous component in near-reef andlev-
1StateUniversityofNewYorkatCortland,P.O.Box2000,Cortland,NewYork13045([email protected]).
2DivisionofPaleontology(Invertebrates),AmericanMuseumofNaturalHistory([email protected]).
Copyright(cid:113)AmericanMuseumofNaturalHistory2005 ISSN0003-0082
2 AMERICAN MUSEUM NOVITATES NO. 3469
Fig.1. GeneralizedWolfcampiantoDzhulfianPermianstratigraphyofGlassMountainsregionWest
Texas. Modified from Rohr and others (2000).
el-bottom paleocommunities associated with MATERIAL AND COLLECTIONS
the spectacular Permian reef complex of Most of the material described herein
West Texas and southern New Mexico. Al- comes from the Glass Mountains of West
though several myalinid taxa have been de- Texas situated on the south margin of the
scribed fromthePermianreefcomplexinre- Permian Delaware Basin. The bulk of the
cent years (McRoberts and Newell, 1997, specimens come from the Leonardian-Guad-
2001), this contribution represents a more alupian Cathedral Mountain, Road Canyon
complete account of the taxonomic and mor- andWordFormations(fig.1).Theywerecol-
phological richness of the family from the lected and processed by G.A. Cooper as a
Permian of West Texas. Furthermore, we byproduct of his work on Permian brachio-
provide a revised account of themorphology pods (e.g., Cooper and Grant, 1972). More
of the family, with a reviseddiagnosiswhich completegeographicandstratigraphicdetails
will complementNewell’smonographonthe of the listed U.S. Geological Survey locality
Myalinidae published more than a half cen- numbers can be found in Cooper and Grant
tury ago (Newell, 1942). (1972).
2005 McROBERTS AND NEWELL: MARINE MYALINIDAE 3
The bivalve specimens are preserved as
silica pseudomorphs which preserve the fine
details of the outer calcite shell layers and
external surface ornamentation.Unfortunate-
ly, the inner shell layers of the bivalves,
which were presumably composed of ara-
gonite and would exhibit muscle scars, were
most often not silicified and are typicallynot
preserved. A few of the better preserved
specimens, however, exhibit coarse silicifi-
cation of the inner aragonticshelllayers,and
therefore preserve interior adductor muscle
scars. A more complete description of the
unique mode of preservation can befoundin
Cooper and Grant (1972) and Newell et al.
(1953).
Institutional repository abbreviations for
Fig. 2. Generalized internal morphologic fea-
typeandfiguredspecimensandlocalitiesare:
tures. DL, duplivincular ligament grooves; BS,
AMNH, American Museum of Natural His-
byssal sinus; PL, pallial line; PA, posterior ad-
tory; USNM, Museum of Natural History, ductor insertion scar; AA, anterior adductor in-
Smithsonian Institution; KU, University of sertion scar.
Kansas Paleontological Collections; UWM,
Geological Museum of the University of
SYSTEMATIC PALEONTOLOGY
Wisconsin, Madison.
ORDER PTERIOIDA NEWELL, 1965
MORPHOLOGY SUPERFAMILY AMBONYCHIOIDEA MILLER, 1877
The shell morphology of myalinid bi- FAMILY MYALINIDAE FRECH, 1891
valves has been the subject of much discus- emended McRoberts and Newell
sion which has led to greatly different views
REVISED DIAGNOSIS: Mostly inequivalved
on the structure and significance of many
Ambonychiaceawith rightvalveslightlyless
morphologic features. Because descriptive
convex than left valve; inequilateral; eden-
terms for myalinid morphology are mostly
tulous or with cardinal tooth or boss beneath
available elsewhere, the reader is referred to
beakofrightvalveandcorrespondingfurrow
Newell (1942) for a summary.
in left valve; pallial line entire,generallypit-
Although many morphologic features, in-
ted; anisomyarian; ligament duplivincular
cluding shell outlines, have proven useful in
continuous, not extending to calcitic shell
discriminating myalinid genera and species, layer; inner shell layer in both valves nacre-
itisnoteworthythatshapeisoftencontrolled ous aragonite; outer shell layers either pris-
by environmental factors such as the grain matic calcite in both valves or prismatic cal-
size and stability of substrate, water chem- cite in right valve and homogeneous calcite
istry, and water temperature (e.g., Hickey, or homogeneous calcite with mosaic struc-
1987) and should not in itself be a single ture in outer shell layer in left valve.
criterion for species definition. While rec- REMARKS: Newell (1942: 44) revised the
ognizing the value of shell shapes and sizes family as:‘‘Shellinequivalve,therightvalve
in discriminating between different popula- slightly less convex and slightly smaller at
tions, our approach isto maximizetheuseof the margin than the left; beaks at or near the
discrete character traits in defining new taxa. small and projecting anterior end; posterior
A summary of internal features used in the margin sub-ovate, quadrate, or extended in a
descriptions is provided in figure 2 and gen- posterodorsal auricle; ligament external, du-
eral conventions of measurement axes and plivincular, mainly opisthodetic, but with
orientation are shown in figure 3. amphideticremnantbeforethebeaksinsome
4 AMERICAN MUSEUM NOVITATES NO. 3469
Fig. 3. Measurement axis conventions and orientations for extreme forms a and b. H, height; L,
length; HL, hinge length; LG, number of ligament grooves; MGV, maximum growth vector (umbonal
ridge); PAV, posterior auricle vector; (cid:97), angle subtended by the posterio-ventral terminus of maximum
growthvectorandhingeline;(cid:98),anglesubtendedbyhingelineandposteriormargin;(cid:103),anglesubtended
by PAV and MGV.
genera; hinge edentulous or with weak car- sublayer per ligament ridge, and with each
dinal teeth 1/2a, 2b at the front end of hinge; fibrous sublayer initially spanning the two
innershelllayerlamellar,probablyaragonite; valves.
outer layer composed of calcite, either ho- There has been much discussion concern-
mogeneous or finely prismatic, the prisms ing the taxonomic content and systematic
and optic axes nearly normaltotheshellsur- placement of the Myalinidae within higher
face; musculature characteristically aniso- categoriesoftheBivalvia.Contrarytoearlier
myarian, but monomyarian in a few species. workers who have aligned them with the
The genera that unquestionably belong here Pterioidea, Newell (1942) was impressed
do not possess well-defined radial ornamen- with the similarities, especially in muscula-
tation, and all pass through a form stage in ture, with the Mytiloidea. However, it was
the early ontogeny similar to adult Modiol- later determined that similarities in ligament
opsis.’’ indicate placement into the superfamilyAm-
Later, Newell (1969: N289) defined the bonychoidea (Newell, 1965; Pojeta, 1966).
family as: ‘‘Inequivalved, with RV slightly Furthermore, it is likely that based on simi-
lessconvexthanLV;edentulous,orwithcar- larities in ligament, the Alatoconchidae, a
dinal tooth or boss beneath beak of RV and group of aberrant giant clams, are closelyre-
corresponding furrow in LV; pallial line en- lated to, or descended from, the Myalinidae
tire, generally pitted.’’ (Yancey and Boyd, 1983).
Tothisdiscussion,Carter(1990:201)add- Currently, the following genera and their
ed that myalinids have a simple prismatic ranges are here considered to be marine My-
calcite or both simple prismatic and homo- alinidae: Myalina (?Devonian, Carbonifer-
geneous calcite outer shell layer with theho- ous–L. Triassic,? M. Triassic), Septimyalina
mogeneous structure commonly restricted to (Carboniferous–L. Permian), Orthomyalina
the left valve; the middle and innershelllay- (U. Carboniferous–L. Permian), Myalinella
ers are nacreous and aragonitic prismatic. (U. Carboniferous–L. Triassic), Arctomyali-
Carter (1990) also noted that the ligament in na (U. Carboniferous), Elversella (M. Perm-
Myalinidae is duplivincular with one fibrous ian), Pseudomyalina (L. Permian), Seleni-
2005 McROBERTS AND NEWELL: MARINE MYALINIDAE 5
TABLE1
Myalina lamellosa McRoberts and Newell, new species
(Measurements in millimeters; see fig. 3 caption for abbreviations.)
Specimen Valve H L HL MGV (cid:97) (cid:98) LG
USNM431335a LV 17.3 22.1 18.3 23.7 42 69 4
USNM431336 LV 21.3 26.3 19.9 28.1 41 63 5
USNM431337a RV 16.8 19.7 17.2 23.1 36 80 4
USNM431338a LV 13.7 16.5 17.2 18.8 38 85 5
USNM431339 LV 10.5 11.5 11.6 13.6 42 92 —
USNM431340 LV 19.2 16.9 22.4 28.4 36 67 —
USNM431341a LV 14.1 17.8 16.3 21.5 38 79 4
USNM431342a LV 12.3 15 14.7 17.1 37 71 —
USNM431343a LV 17.2 23.3 19.1 25.2 35 52 —
USNM431344a LV 28.6 30.5 28.9 35.2 41 97 7
USNM431345a LV 13.5 16.2 14.3 17.1 43 80 12
USNM431346a LV 8.8 10.1 9.3 10.9 49 89 —
USNM431347 RV 15.6 23.2 20.7 23.8 38 102 —
USNM431348a LV 12.1 16.7 15.8 16.5 41 89 —
USNM431348a RV 16.8 19.2 18.5 23.2 44 69 —
USNM431349a LV 37.4 41.3 36.2 45.2 37 96 —
USNM431349a RV 35.3 37.6 33.3 43.4 36 92 —
USNM431350a LV 17.5 21.6 17.9 23.4 34 97 —
USNM431350a RV 17.6 20.3 17.8 23.9 42 103 na
aMeasurementstakenon commarginalgrowthlamellae.
myalina (U. Carboniferous), Novaculaper- specimens, especially in later growth stages;
mia (L. Permian), Promyalina (L. Triassic), anterior margin slightly concave, indicating
and less certainly, Liebea (U. Permian) and small byssal sinus; posterior margin broadly
Aviculomyalina (M. Triassic). convex, nearly parallel to anterior margin;
broad fold in left valve along anteroventral
Genus Myalina De Koninck 1842 margin corresponds to broad sulcus in right
valve;beaksterminal,arcuate,andprojecting
TYPE SPECIES: Myalina goldfussiana
DeKoninck, 1842, subsequently designated inwards, shell retrocrescent, with maximum
by Stoliczka, 1871. growth vector (cid:97) moderately steep ((cid:59)65(cid:56)) at
early growth stages, becoming steeper
Myalina lamellosa McRoberts and Newell, ((cid:59)75(cid:56)) at later growth stages (see fig. 5) but
new species never infracrescent; left valve slightly larger
Figure 4 than right. Surface of both valves ornament-
ed by numerous commarginal overlapping
TYPE SPECIMENS: Holotype: USNM-
growth lamellae which do not terminate in
431335; Paratypes: USNM-431336, USNM-
hemispherical spines. Lamellae becoming
431344, USNM-431348.
more pronounced and at wider spaced inter-
DIAGNOSIS: Thin-shelled and triangular-
vals by curling up and outwards in later
shaped Myalina possessing distinct irregular
growthstages.Bodycavityextendingfarinto
commarginal overlapping growth lamellae,a
broadanteroventralfoldinleftvalveandcor- the umbones, umbonal septum or deck ab-
responding sulcus in right valve, and lacking sent. Ligament opisthodetic, duplivincular;
a distinct anterior auricle. between 4 and 12 parallel grooves, slightly
DESCRIPTION: Shell medium sized (max. acute,intersectinghinge-lineatlessthan10(cid:56).
height (cid:53) 3.7 cm), triangular in outline; Musculaturecharacterizedbymoderate-sized
hinge-line straight, less than total length of ovate posterior adductor. Anterior adductor
shell; small posterior auricle present in most or other musculatureunknown.Thin-shelled,
6 AMERICAN MUSEUM NOVITATES NO. 3469
Fig. 4. Myalina lamellosa McRoberts and Newell, new species. Scale bar is 1 cm. a, holotype,
USNM 431335 (USNM loc. 702), left valve interior (a1), exterior (a2); b, paratype, articulated valve
pair, USNM 431348 (USNM loc. 702), right valve (b1), left valve (b2), dorsal view (b3); c, paratype,
left valve interior USNM 431336 (USNM loc. 702), (c1), exterior (c2); d, paratype, USNM 431344
(USNM loc. 702), left valve interior (d1), exterior (d2).
2005 McROBERTS AND NEWELL: MARINE MYALINIDAE 7
Fig. 5. Ontogenetic series showing increasing (cid:97) angle in Myalina lamellosa (a) and M. plicata (b).
ultrastructure unknown. See table 1 for mea- USNM-706-e.TothesefromtheUSNM,add
surements. Girty’s (1908, pl. 29, fig. 15) specimen from
REMARKS AND COMPARISONS: This species Delaware Mountain Formation, southern
shows similarities to forms regarded by Delaware Mountains (station 2935).
Newell (1942) as Septimyalina burmaiNew- MATERIAL: The collection consists of 10
ell 1942, yet differs from that species in the articulated valves, 23 left valves, and 8 right
absence of spinelike projections of growth valves.
lamellae and thicknessofshell.Additionally, ETYMOLOGY:Specificnamereferstoprom-
Myalina lamellosa lacks a prominent umbo- inent growth lamellae.
nal septumor deckwhichpresumablyoccurs
inS.burmaialthoughnoneisillustrated.Dif- Myalina plicata McRoberts and Newell,
fers from Myalina plicata, n.sp., in the pres- new species
ence of weak posteroventral fold and sulcus Figure 7
and absence of radial plicae.
PALEOAUTECOLOGY: Several features lead TYPE SPECIMENS: Holotype: KU-310505;
totheconclusionthatMyalinalamellosawas Paratypes: USNM-431351, USNM-431353.
byssally attached in an edgewise position DIAGNOSIS: Medium to thin-shelled Myali-
restingontheanteriorend(fig.6a).Although na possessing distinct commarginal growth
the two valves differ in their size, the equal- squamae, broad radial plicae, and distinct
ityintheinflationofbothvalvesandofcom- byssal sinus.
marginal lamellae suggests the animal was DESCRIPTION: Shell moderatelylarge(max.
oriented with its commissure plane nearly height (cid:53) 5.2 cm); triangular in outline;
vertical and slightly resting on its left valve. hinge-line straight, less than total length of
AGE AND OCCURRENCE: Cathedral Moun- shell; small posterior auricle present in most
tain Formation (Leonardian), localities: specimens, especially in later growth stages;
USNM-702, USNM-721-u; Road Canyon anterior margin slightly concave indicating
Formation (Guadalupian), localities: small byssal sinus; posterior margin broadly
?USNM-721-j, USNM-721-t, USNM-721-z, convex, nearly parallel to anterior margin;
USNM-724-b, USNM-726-d, USNM-726-z; beaks terminal, arcuate, and projecting in-
Word Formation (Guadalupian), localities: wards; shell retrocrescent with angle (cid:97) about
8 AMERICAN MUSEUM NOVITATES NO. 3469
Fig. 6. Hypothesized living habits of Permian Myalinidae. a, Myalina lamellosa McRoberts and
Newell, n.sp.; b, Myalina plicata McRoberts and Newell, n.sp.; c, Myalina copei; d, Elversellarugosa;
e, Novaculapermia boydi; f, Myalinella acutirostris.
40(cid:56)inearliergrowthstages,becomingnearly intersecting hinge-line at less than 10(cid:56),
infracrescent in adult stages. Surface of both grooves becoming fainter posteriorly alonga
valves ornamentedbynumerouscommargin- broadening hinge plate. Pallial line faint but
algrowthlamellae.Lamellaebecomingmore continuous, with a single large ovate raised
pronounced and at wider spaced intervalsby posterior adductor scar nearly 1 cm in di-
curling up and outwards in late growth stag- ameter. Shell moderately thin; ultrastructure
es; strong radial plications in both valves, unknown. See table 2 for measurements.
more pronounced on valve exterior, becom- REMARKS AND COMPARISONS: This being
ing fainter on posterodorsal margin. Body the only known Myalina with radial plicae,
cavity extending far into umbones; dentition it is unlike any other species known to us.In
consists of single linear tooth on right valve other characteristics, however, this species
formed by sharp fold in cardinal area, fitting resembles, especially in early growth stages,
into a narrow furrow in left valve. Ligament Myalina lamellosa in its position of raised
opisthodetic, duplivincular; between 5 and growthsquamae.However,M.plicatadiffers
10 grooves slightly acute to nearly parallel, fromM.lamellosainhavinggreater(cid:97)angles
2005 McROBERTS AND NEWELL: MARINE MYALINIDAE 9
Fig. 7. Myalina plicata McRoberts and Newell, n.sp. Scale bar is 1 cm. a, holotype KU 310505
(KU loc. 27), left valve interior (a1), exterior (a2); b, paratype, USNM 431351 (USNM loc. 706c), left
valve interior (b1), exterior (b2); c, paratype, USNM 431353 (USNM loc. 706c), right valve exterior
(c1), interior (c2).
and tending to become more infracrescentin ETYMOLOGY:Specificnamereferstoprom-
later growth stages. inent and radial plications.
MATERIAL: The collection consists of 10
left valves and 5 right valves.
Myalina copei Whitfield, 1902
AGE AND OCCURRENCE: Word Formation Figure 8
(Guadalupian), localities: USNM-706c,
USNM-721j, ?USNM-706e, University of Myalina copei Whitfield, 1902: 63–66, text fig. 2
Kansas Loc. 27. (not fig. 1).
10 AMERICAN MUSEUM NOVITATES NO. 3469
TABLE2
Myalina plicata McRoberts and Newell, new species
(Measurements in millimeters; see fig. 3 caption for abbreviations.)
Specimen Valve H L HL MGV (cid:97) (cid:98) LG
KU310505 LV 37.6 38.9 32.9 48.7 72 74 6
USNM431351 LV 52.8 67.9 41 75.7 58 42 10
USNM431352 LV 26.1 28.5a 23.7a 32.5a 68 92 5
USNM431353 RV 43 42.1 38.6a 53.2 82 81a 8
USNM431354b RV 18.3 25.6 25.6 26.9 65 90 6
USNM431355b LV 27.1 33 30.1 39.1 59 86 na
USNM431356b LV 28.1 34.1 29.7 38.9 61 92 na
aEstimatedfrombrokenshell.
bMeasurementstakenon commarginalgrowthlamellae.
Myalina copei Whitfield, Newell, 1942: 55, pl. 4, specimens. This difference in angle (cid:97) may
figs. 1a–c, pl. be difficult to discern in immature or frag-
TYPE SPECIMEN: Lectotype AMNH-8364/2 mented specimens.
designated by Newell (1942). MATERIAL: The collection consists of five
DESCRIPTION: Shell large (max. height left valves and two right valves.
nearly 7 cm), retrocrescent becoming infra- AGE AND OCCURRENCE: Lower Hueco For-
crescent later in ontogeny. Posterior alation mation (Wolfcampian), locality AMNH 48.
moderately to strongly developed and rela- Although this Formation is not listed in fig-
tively flattened; anterior lobe small devel- ure 1 as it is known from the Hueco Moun-
oped in both valves; byssal sinus formed by tains near El Paso, Texas, according to Coo-
broad invagination on anterior-ventral mar- per and Grant (1972), it is likely age-equiv-
gin. Shell surface relatively smooth except alent to either the lower part of the Neal
for faint, evenly spaced commarginalgrowth Ranch Formation or the underlying ‘‘Uden-
lines in some specimens. Body cavity broad, ites-bearing shale member’’ of the Gaptank
extending deeply to anterior margin; liga- Formation. According to Newell (1942), M.
mentduplivincular,ligamentareabroad,pos- copei is known from the Hueco Mountains
sessing numerous deeply incised grooves es- and other localities in Texas (including the
sentially parallel to the hinge margin or in- type specimens from ShackelfordCounty)as
tersecting at a very low angle ((cid:44) 5(cid:56)); mus- well as Kansas and Nebraska.
culature unknown. Shell ultrastructure
unknown. See table 3 for measurements. Genus Myalinella Newell, 1942
REMARKS AND COMPARISONS: The outline, [nom. transl. Newell, 1969]
angular dimensions, hinge features, and es-
TYPE SPECIES: Myalina meeki Dunbar,
pecially the extended posterior auricle seem
1924, by original designation
to agree with previously illustrated speci-
mens of M. copei. Although Newell (1942)
Myalinella acutirostris
described Myalina copei as inequivalved as
(Newell and Burma, in Roth et al., 1941)
the right valve was somewhat smaller and
Figure 9d
fitting within the left valve, we have no con-
joined or disarticulated valve pairs from the Myalina squamosa Girty, 1908: 429, pl. 16, fig.
same individual to confirm this observation. 22, non pl. 29, fig. 15 ((cid:53) Myalina lamellosa).
Newell (1942) commented on the similarity Myalina sp. Newell, 1940: 286, pl. 2, fig. 1.
in shape of Myalina copei and Myalina plio- Myalina acutirostris Newell and Burma in Roth
et al., 1941: 315, pl. 45, figs. 11–15.
petina Newell. Myalina copei can be distin-
Myalina acutirostris Newell et al., 1953, pl. 22,
guished from M. pliopetina Newell in pos-
fig. 14.
sessing a somewhat thicker shell and having
a more upright form (greaterangle(cid:97)inadult TYPE SPECIMEN: Holotype UWM 20846.