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Anatomical Comparison of the Cephalic Musculature of Some Members of the Superfamily Myliobatoidea (Chondrichthyes): Implications for Evolutionary Understanding.

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Anatomical Comparison of the Cephalic Musculature of Some Members of the Superfamily Myliobatoidea (Chondrichthyes): Implications for Evolutionary Understanding

Gonzalez-Isais M. 2003. Anatomical Comparison of the Cephalic Musculature of Some Members of the Superfamily Myliobatoidea (Chondrichthyes): Implications for Evolutionary Understanding. The Anatomical Record Part A 271A: 259-272.

background information
Background Information:

© Tracy Clark


myliobatoidea species studied
Myliobatoidea Species Studied:

Gymnura marmorata (GMA)

California Butterfly Ray

Gymnura micrura (GMI)

Smooth Butterfly Ray


Aetobatus narinari (AN)

Spotted Eagle Ray

Mobula munkiana (MM)

Munk’s Devil Ray

Mobula thurstoni (MT)

Bentfin Devil Ray


Myliobatis californica (MC)

Bat Eagle Ray

Myliobatis longirostris (ML)

Snouted Eagle Ray

Rhinoptera steindachneri (RS)

Pacific Cownose Ray


muscles of the dorsal cephalic region
Muscles of the Dorsal Cephalic Region
  • Precranial muscle (PM)
  • Ethmoideo-parethmoidalis muscle (EPE)
  • *Dorsal longitudinal bundles (DLB)
  • Levator hyomandibulae muscle (LHM)
  • Levator spiracularis muscle (LS)
  • Superficial dorsal constrictor muscles 1-5 (DC1-DC5)
  • Constrictor hyoideus dorsalis (CHD)
  • *Cucullaris muscle (CC)
muscles of the cephalic ventral region
Depressor rostri muscle (DR)

*Superficial transverse (ST) muscle and superficial ventral constrictors (VC1-VC5)

Coracoarcualis muscle (CA)

*Coracomandibular muscle (CM)

Suborbitalis muscle (SB)

Adductor mandibulae medialis muscle (AMM)

*Mandibular adductor muscles (AM, AML1, and AML2)

Coracohyomandibularis muscle (CHM)

*Depressor hyomandibulae (DH)

Constrictor hyoideus ventralis (CHV)

Coracobranchiales muscles (CB)

*Y muscle (Y)

*Z muscle (Z)

M muscle (M)

Coracohyoideus muscle (CH)

*Quadratomandibularis ventral (QV)

Muscles of the Cephalic Ventral Region
objective of the study
Objective of the Study:
  • The researchers attempted to describe the anatomy of the cephalic dorsal and ventral musculature of myliobatoids, as a basis for future phylogenetic genus research.
  • Specimens were collected from areas along the Gulf of Mexico, Gulf of California, and the Pacific Ocean
  • Larger specimens were dissected in the field
  • Smaller specimens were fixed in formaldehyde 10% to be transported to a laboratory and dissected at a later time
  • Conventional techniques were used for dissection, focusing on dorsal and ventral cranial musculature

Dorsal View

Ventral View

  • For each muscle the following characteristics were analyzed:

1. form disposition

2. fiber orientation

3. origin-point of attachment of a muscle; end not easily movable

4. insertion-point of attachment of a muscle; end that is easily movable

results dorsal musculature
Results: Dorsal Musculature
  • Overall, all taxa was fairly consistent with the exception of some variation in two of the muscles analyzed:

1. Dorsal Longitudinal Bundles

2. Cucullaris Muscle

results cucullaris muscle
Results: Cucullaris muscle

M. longitostris

A. narinari

*Absent in A. narinari, M. thurstoni, and M. munkiana

results ventral musculature
Results: Ventral Musculature
  • Variations were found in the following muscles:

1. Depressor hyomandibulae

2. Quadratomandibularis muscle

3. Mandibular Adductor

4. Dorsal and Ventral Superficial Constrictor Muscles

5. Coracomandibular Muscle

6. Y muscle

7. Z muscle

results depressor hyomandibulae
Results: Depressor hyomandibulae

Reduced in: MC, ML, and AN; Absent in: MM, MT

G. micrura

M. californica

results quadratomandibularis muscle
Results: Quadratomandibularis Muscle
  • Found only in GMi and GMa
    • Plesiomorphic Characteristic

G. marmorata

*Absence of Quad. Muscle considered derived characteristic

results mandibular adductor muscles
Results: Mandibular adductor muscles
  • Increased size in ML, MC, AN, and RS

M. californica

G. micrura

results superficial constrictor muscles
Results: Superficial Constrictor Muscles
  • Reduced in MT and MM
  • Fused in AN, MC, and ML
    • Considered synapmorphy

G. Marmorata

M. Californica

M. munkiana

results coracomandibularis muscle
Results: Coracomandibularis Muscle

-In MC, Ml, AN, and RS the muscle originates in the pectoral girdle

-In GMI, GMA, MT, and MM the muscle originates in the membrane where the coracoarcualis muscle inserts

A. narinari M. munkiana

results y muscle and z muscle
Results: Y muscle and Z muscle
  • These muscles were found in MC, ML, AN, and RS

M. californica

  • Differences in the ventral musculature are related to feeding habits:
    • AN, MC, ML, and RS hard-shelled mollusks and crustaceans
    • MM and MT are filtering species that feed mainly on small crustaceans
discussion phylogenetic studies1
Discussion: Phylogenetic Studies




Proposed Phylogeny from data of this paper

  • Rhinoptera is the myliobatids’ sister group.
  • The results from this study alone are too general to base a phylogeny on, but the results should be used for future phylogeny research.
  • Overall, a phylogeny can change drastically depending on what aspect(s) of the specimen a specific study is analyzing.