Download Lab 3 Osteology of reptiles, mammals and birds (amniotes)

G404 Geobiology
Fall 2011
Name __________________________________
Lab 3
Osteology of reptiles, mammals and birds (amniotes)
Use the materials in this lab to familiarize yourself with the skull and skeleton of living
amniotes. In addition to studying the bones, pay special attention to the following openings
in the cranium. These descriptions apply primarily to mammals, but many of them have
variants in other vertebrate groups.
1. Foramen magnum (“big hole”) – opening in the posterior braincase between the
occipital bones through which spinal cord exits and through which vertebral arteries
enter.
2. Posterior lacerate foramen (“jagged hole in the back”) – variably shaped
opening forming a gap behind the otic/petrosal bones, between them and the
occipitals. Many structures pass through this opening, one of them the internal
jugular vein, which drains blood out of the braincase and back to the heart. In some
clades the plf is a single opening, in others it is subdivided into several smaller
openings. Sometimes this opening is called the jugular foram en.
3. M iddle lacerate foramen (“jagged hole in the middle”) – variably shaped opening
forming a gap in front of the otic/petrosal bones, between them and the sphenoids.
Many structures pass through this opening as well, including the internal carotid
artery (ica), which is one of the primary arteries supplying the brain. Like the plf,
this opening is variable and is divided into several smaller openings in many clades.
4. Optic foramen – almost perfectly round hole in the back of the orbit that carries
the optic nerve (CN II) from the braincase to the back of the eye. Of the several
openings in the orbit, this one is the most dorsal and medial of them.
5. Infraorbital foramen (“hole below the eye”) – oval or round opening in the maxilla
that transmits the maxillary division of the trigeminal nerve (CN V2) from the floor of
the orbit forward onto the face. Typically this opening is larger in clades with welldeveloped sensory organs around the nose, such as the whiskers of cats. It is
comparatively small in humans.
6. Incisive foramen (“hole behind the incisor teeth”) – opening in the anterior part
of the roof of the mouth bounded by the premaxillae, maxilla, and vomer. Nerves and
blood vessels supplying the soft tissues pass through it. Above it lies the
vomeronasal organ (also known as Jacobson’s organ), which is a type of olfactory
(chemical) sensory structure that detects pheromones and other chemicals. It is
typically larger in clades with well-developed chemical cues for reproduction, such as
horses.
7. External auditory m eatus (“exterior tube for the ear”) – opening from the ear
into the middle ear. The base of this tube is ringed by the ectotympanic bone, which
supports the eardrum (aka., tympanic membrane). Look deep into the middle ear on
the dorsal side of the cavity and you can see the tiny openings to the inner ear and,
in some specimens, the bones of the middle ear (in mammals there are three:
stapes, incus, and malleus).
Assignment
Continue compiling your list of ten characters. We will use this information in later labs to
perform your own phylogenetic analysis of selected living vertebrates. The kind of
information useful at this broad level is the gain and loss of bones or major transformations
in homologous bones.
Typical examples of phylogenetic characters are “tabular bone (1) present or (2) absent” or
“jaw joint (1) between quadrate and articular bones or (2) between dentary and squamosal
bones” or “occipital condyle (1) single or (2) double”. For each taxon in your analysis you will
eventually need to record the condition of these characters by assigning each variant (state)
a number and recording the appropriate number for each taxon. To be useful, the character
must vary among taxa being considered. Ideally each variant will be shared by at least two
taxa.
For this lab, identify at least ten characters that vary among the taxa you have seen in the
osteology labs. Add at least four new mammal or bird taxa to the four from last week:
1.
2.
3.
Describe each character and its variants using similar format as above.
Record the species name, class name, and specimen number for your four taxa
(plus four from last week).
For each species, record the character state (variant) for each of your ten
characters.
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Turtle Carotid Arteries (ventral view)
(Gaffney, 1979, Comparative cranial morphology of recent and fossil turtles.)
Lizard Skull (posterior view)
jf = jugular foramen. pa = ascending process of the supraoccipital. po = paroccipital process
of otoociptial.
Head et al., 2009, Zool J. Linn Soc.)
Bird Skull (lateral and ventral views)
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Mammal Skull (lateral view)
(after Evans, Anatomy of the Dog)
(from Kardong 1995, Vertebrates)
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Sagittal crest, point of attachment for temporalis muscles which help close the jaw.
Infraorbital foramen, passage for the branch of the trigeminal nerve that innervates the face,
especially the vibrissae. Optic canal, passage from the braincase to the eye carrying the optic
nerve. External Acoustic Meatus, opening of the ear canal, which ends in the tympanic
membrane. Occipital Condyle, joint surface for attachment of the skull to the first cervical
vertebra (atlas). Foramen magnum, opening into the brain case through which the spinal
cord passes.
(Evans, Miller’s Anatomy of the Dog)
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(Evans, Miller’s Anatomy of the Dog)
Palatine fissure = incisive foramen, opening for passage of nerves onto the palate and
related to chemical sensation by the vomeronasal organ. Jugular foramen, large passage
through which the jugular vein drains blood from the braincase and through which several
cranial nerves pass. Hypoglossal foramen, and easily identifiable opening for the
hypoglossal nerve (a cranial nerve).
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