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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

http://www.divebums.com/FishID/Pages/butterfly_ray.html

Myliobatoidea

myliobatoidea species studied
Myliobatoidea Species Studied:

Gymnura marmorata (GMA)

California Butterfly Ray

http://www.fishbase.org.ph/Summary/SpeciesSummary.cfm?id=2578

Gymnura micrura (GMI)

Smooth Butterfly Ray

http://filaman.uni-kiel.de/Summary/SpeciesSummary.cfm?ID=257

slide4

Aetobatus narinari (AN)

Spotted Eagle Ray

http://www.fishbase.org

Mobula munkiana (MM)

Munk’s Devil Ray

http://www.fishbase.org

Mobula thurstoni (MT)

Bentfin Devil Ray

http://www.fishbase.org

slide5

Myliobatis californica (MC)

Bat Eagle Ray

http://www.fishbase.org

Myliobatis longirostris (ML)

Snouted Eagle Ray

http://www.fishbase.org

Rhinoptera steindachneri (RS)

Pacific Cownose Ray

Http://www.fishbase.org

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.
methods
Methods:
  • 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
methods1
Methods:
  • Conventional techniques were used for dissection, focusing on dorsal and ventral cranial musculature

Dorsal View

Ventral View

methods2
Methods:
  • 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

discussion
Discussion:
  • 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

Myliobatids

Rhinoptera

Mobula

Proposed Phylogeny from data of this paper

conclusions
Conclusions:
  • 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.