Three basic types of Hunter-Schreger bands (HSB) in rodent tooth enamel© June 1, 1999 Thomas Martin
Pauciserial Hunter-Schreger Bands
Pauciserial HSB characterize the most primitive rodents independent of their systematic affinities. Pauciserial HSB is structurally similar to the primitive mammalian condition that is seen in Paleocene condylarths, but pauciserial enamel is somewhat thinner. |
| Hunter-Schreger bands (HSB) |
| Band width |
Band inclination |
Transition between bands |
| Variable and few prisms (1 to 6 prisms; 1 to 3 is usual) |
Not inclined or slightly inclined |
No transition zone |
| Interprismatic matrix (IPM) |
| Relationship to prisms |
Orientation |
Thickness |
| Completely surrounds prisms and is separated from them by prism sheath |
Always parallel to prism direction |
Much thicker than in multiserial HSB and Portio Externa |
| Prisms |
| Cross sections |
Inclination in Portio Externa |
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Portio Interna: Irregularly rounded and not flattened laterally; prism sheath forming gap is unique to pauciserial HSB
Portio Externa: Usually oval, more rounded in the earliest examples; laterally flattened in a few cases |
Comparatively low, usually 20° - 30° |
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Uniserial Hunter-Schreger Bands
Primitive uniserial HSB in which the interprismatic matrix is parallel to the prisms may have been derived from pauciserial enamel by thinning of the bands to one prism wide.
|
| Hunter-Schreger Bands (HSB) |
| Band width |
Band inclination |
Transitions between bands |
| One prism thick; occasionally bands 2 prisms thick may occur |
Primitively low
Derived: Up to 50° |
No transition zone |
| Interprismatic matrix |
| Relationship to prisms |
Orientation |
Thickness |
| Primitive: Surrounds prisms but appears thicker between bands |
Primitive: Parallel to prisms |
Thinner than in pauciserial enamel HSB |
| Derived: Separates prisms within HSB, but prisms of adjacent HSB touch |
Derived: acute angular
Most derived: Rectangular to prisms |
|
| Prisms |
| Cross sections |
Inclination in Portio Externa |
|
Portio Interna: Oval to laterally flattened, no visible prism sheath
Portio Externa: strongly laterally flattened |
Up to 80° |
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Multiserial Hunter-Schreger Bands
|
| Hunter-Schreger bands (HSB) |
| Band width |
Band inclination |
Transition between bands |
3 to 10 prisms per band;
mostly between 3 and 7 |
Usually more than 20°, up to 50° |
Transition zone present where prisms switch apically from one HSB to the next |
| Interprismatic matrix (IPM) |
| Relationship to prisms |
Orientation |
Thickness |
| Primitive: Cannot be distinguished from prisms |
Primitive: parallel to prisms (e.g., some Caviidae) |
Much thinner than in pausiserial HSB |
| Derived: Extends between rows of prisms in HSB but does not surround individual prisms |
Derived: At a slight angle to prism direction
More derived: At an acute angle to prism direction
Most derived: Rectangular and forming interrow sheets | |
| Prisms |
| Cross sections |
Inclination in Portio Externa |
|
Portio Interna: Oval to laterally flattened, no visible prism sheath
Portio Externa: Strongly laterally flattened |
Usually very steep: up to 80°
Exception: Bathyergoidea, prisms bend to horizontal |
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References:
Martin, Thomas. 1997. Incisor enamel microstructure and systematics in rodents. Chapter 9, pp. 163-175, in W. v. Koenigswald & P. M. Sander, eds., Tooth enamel microstructure. Amsterdam, A. A. Balkema.
Martin, Thomas. 1993. Early rodent incisor enamel evolution: Phylogenetic implications. J. Mammal. Evol., 1: 227-254.
Thomas Martin's tooth preparation method for SEM viewing.
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Last updated 2 June 1999 (TM/JHW)
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