Ophiacodontidae
Thien Nguyen
CSUSB
Biology 680 - 2009
Introduction
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Kingdom: Animalia
Phylum: Chordata
Superclass: Tetrapoda
Class: Synapsida
Order: Pelycosauria
Sub-Order: Ophiacodontia
Family: Ophiacodontidae
Ophiacodontia
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Ophiacodontidae
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Which include pelycosaurs with features once
considered as primitive and close to the basal stock of
the order
There is a fairly complete knowledge of
Ophiacodontidae anatomy, particularly on Ophiacodon
Members of the family include
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Archeothyris
Clepsydrops
Ophiacodon
Varanosaurus
Introduction
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Ophiacodonts first appeared in the late Carboniferous
period.
Many were possibly semi- or fully aquatic animals.
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They have piscivorous habits (feeding on fishes) and
amphibious adaptations
Fed on food items which required little mastication; this is
due to features such as their long snout, lightly built skulls
and jaws, and undifferentiated dentitions
Ophiacodontia
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These animals had low and relatively broad skulls with a
moderately elongated snout
Concaved dorsal borders of the orbit
Lower margin of skull is nearly straight
Occiput slants strongly forward dorsally
Slender marginal teeth
Canines are always distinct
Palatal teeth present but
not greatly developed
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Jaw articulation is almost in-line or on the same level as the row of
teeth
The jaw is slender
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Symphasis is confined for the most part to the dentary
Coronoid is elevated
Developed pterygoid flange (although not thickened)
Lacrimal reaches the naris
Basal portion of quadrate
is broad transversely
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Vertebrae is primitively short but tends to elongate in some
forms
Presacral Centra tends to be flattened ventrally and keel in dorsal
region is never sharp
Transverse processes are short while the neural arch tends to be
broad and heavy
The cervical ribs are dialated
Abdominal ribs are highly developed
Clavicals are narrow distally and
head of interclavical is short →
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Scapula is short and broad
The Supraglenoid foramen occupies primitive position
Coracoid does not lag in ossification
Process for coracoid head of the triceps is slightly developed
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The ilium is long but unexpanded dorsally but retains dorsal
trough for axial muscle attachment
Pubic tubercle is usually present
Internal shelf for the puboishiofemoralis internus is present on the
pubis
Ophiacodontidae
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Features of the Skull
Always large and relatively narrow
 Moderately to greatly elongated facial region
 Numerous marginal teeth
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40-55 in upper jaw
Moderately developed canines
 Stapes is a massive rod
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Ophiacodontidae
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Physical features
Short vertebrae
 Hind legs are longer than the fore legs
 The atlas centrum doesn’t reach ventral surface of
the column
 Primitive adductor ridge in femur has disappeared.
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Caudal muscles have no prominent area for attachment
Ophiacodontidae
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Members of the family include:
Ophiacodon
 Varanosaurus
 Clepsydrops
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*These three are strikingly similar with only slight differences in
their skull and vertebrae proportions and a few others.
Ophiacodon
Ophiacodon
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Ophiacodontids were generally moderate to very large in size
Skull is large, long, and high
Vertebrae are more slender than smaller members of the family
Pubic tubercle is reduced or absent
There is a development of a secondary adductor ridge on the
femur
Unguals (or claws) are flattened
Ophiacodons have a distinctive feature in that they have slow
ossification of replacement bones, both in the skull and
postcranial skeleton
Ophiacodon
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Greatly elongated skull (Due to elongated nasal, lacrimal, maxillae,
frontal and pre-frontal elements)
Disappearance of the palaeorbital connection of pre and
postfrontals (a primitive feature)
Moderately long post orbital region
Lacrimal (L) is very thin
Lacrimal duct can extend as
as far as level of canines
Small supratemporal (ST)
Anterior margin of orbit is
thin ventrally and thickened
dorsally
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Parietal bone is a single structure. Although in some Ophiacodon
and Varanosaurus specimens, the interparietal is divided in two by
a longitudinal fissure
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Debate as to whether it is a crack or suture
Slender connection between maxilla and premaxilla
Ascending bar on inner surface of the maxilla (also present in
Clepsydrops) above the canines; possibly to brace the tooth row
to the skull roof
Post orbital (PO) and jugal (J)
forms a broad bar extending
medially behind the orbit
Palate (PAL) is lightly built
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The quadratojugal is well developed and extends almost to the
maxilla. It is also fused to the quadrate and has an articulation
with pterygoid ramus above the quadrate foramen
Squamosal (SQ) has a well-developed reflected lamina which
provides an attachment to the tip of the paraoccipital process
Choanae are long and narrow while prevomers are slender and
toothless
Row of teeth present which runs forward along the margin of
the narrow interpterygoid vacuity
Second line of teeth runs along
palatal ramus of the pterygoid
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Articular area for the basipterygoid process is large and deep and
is situated far ventrally
The stapes is situated on a cavity formed by the quadrate ramus
of the pterygoid and the adjacent portion of the quadrate
Quadrate (Q) is transversely expanded with its articular surface
situated in a nearly horizontal plane
Its believed that the quadrate bone is built to aid the pterygoid
in enclosing the middle ear chamber
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Ophiacodon Braincase is adequately studied
The sutures between all of the braincase elements can be seen
due to the slow ossification process in Ophiacodon
Outline of supraoccipital is subquadrate
Venous depression present on inner surface of supraoccipital
The opisthotic (op) occupies the latero-ventral portion of the
occipital plate and is clearly separable from the other elements
Opisthotic is incompletely ossified ventrally at the area where it
borders the fenestra ovalis
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Jaw
Slender and shallow dorso-ventrally at the anterior end
Symphysis of bones is weakly developed and primarily confined
in the dentary
Dentary (D) is elongated
Oval external opening is present in between the dentary, angular,
and subangular1
The postero-dorsal expansion of the Dentary covers much of the
outer side of the surangular (SANG)
Maxillary (MX) region is slightly
concaved
Coronoid (C) region is slightly
convexed
Upper margin of surangular
is thin
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The angular has a prominent ventral keel
Splenial (SP) is broad on the internal surface but is
barely visible from the outer view
Prominent ventral keel present on articular (A) and is
continuous with the angular; Internal processes for
muscle attachments are not present on the articular
Articular surface is gently tilted inward and appear to be
primitive in construction
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Both cavities are short anteroposterioly
Lateral cavity is deeply concaved
Medial cavity is flat
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Marginal teeth are rounded in section, sharply pointed, and
slightly recurved
The bases of each tooth are subquadrate and have longitudinal
striations
Tooth replacement is believed to be slow, resulting in frequent
gaps in the tooth row
Total number of maxillary teeth generally range from 29-46
6-7 precanines are always present
Canines are not very projecting but are distinct
Dentary teeth are generally more numerous, crowded, and
smaller in size
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Vertebrae
There are generally 27 pre-sacral vertebrae, 2 sacrals, and an
elongated tail present
The vertabrae and the body as a whole is short which is believed
to be a primitive feature
Presence of 5 nonmovable ribs in front of the sacrum; possibly
lumbars
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Transverse processes of the cervical and dorsal vertebrae are
short (compared to other suborders)
The dorsal transverse processes is semicircular in section
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Posterior surface is flat while the anterior surface is convex
The arch of the transverse processes of the cervical emerges
further down and slants sharply backwards and downwards
The dorsal neural spines are thin transversely and broad anteroposteriorly; cervical neural spines have stouter bases; spines in
both cases have blunt tips and are never elongated
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Atlanto-axial complex indicate a common and distinctive
structure
Proatlas is present
Atlantal centrum may be fused with the axial intercentrum and is
thick antero-posteriorly and has a well developed dorsal portion
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Highly characteristic feature of Ophiacodontidae
Atlantal intercentrum is large and underlains the atalantal
centrum
Spine of axis expands anteroposteriorly and is thin anteriorly
and thickened at the posterior edge
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The cervical ribs are two-headed and although lumbar ribs are
present, they are often small
Two sacrals are present
The first sacral rib is large and has a fan shaped surface which
fits into a hollow in the ilium
The second rib is much smaller and has little contact w/the
ilium; seems that its purpose was just to prop the first rib
Caudal ribs (approx. 11) were present and well developed
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The blade of the clavicle is extremely narrow
Shaft of clavicle is flattened and groove for attachment to the
scapula is extremely underdeveloped
Distal ends are heavily striated
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Believed that this is to compensate for the small area it has that contacts
with the interclavicle
The bowl of the interclavical is
short and the anterior quadrants
are only slightly developed; the
blade is nearly uniform in width
but broadens at mid-length
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Scapulocoracoid
Scapular blade is generally low in correlation with the low build
of the body
The scapula is broad; the posterior margin of scapula curves
backwards to a slight degree
Coracoid surface below the glenoid is slightly concave in dorsoventral section
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Pelvic Girdle
Primitive in regards to the construction of the iliac blade
Outer surface of ilium associated only with appendicular muscles
Iliac blade is elongated and points posteriorly (which is believed
to be a primitive feature); blade increases in height anteriorly
Dorsal margin of iliac blade is characteristically concave in
outline while it is convex posteriorly
Lower front margin of ilium forms a sharp ridge
Iliac component in the formation of
the acetabulum is greatest in size
Acetabulum has a thick posterior
margin
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Pelvic Girdle (cont.)
Acetabulum is more dorsally facing (its deepest portion lies near
the ischiadic component of the acetabulum
Ischium points posteriorly
The pubis is generally short; a thick dorsal margin descends
sharply downward and outward from the acetabulum
In primitive forms, there is a prominent pubic tubercle
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Tubercle is reduced in Ophiacodon
The puboischiadic plate is relatively
narrow dorso-ventrally
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Appendages
Proximal segments of the limbs were short in comparison to the
sphenacodontids or edaphosaurs
Front legs are smaller than hind legs
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Humerus was ~20% shorter than the femur; Humerus only ~10% shorter
than femur in sphenacodontids and edaphosaurs
Radius and ulna were noticeably shorter than tibia and fibula; These
bones were approx. equal in size in sphenacodontids and edaphosaurs
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Humerus
Articular surface occupies nearly the entire extent of the
proximal end
Anterior margin of supinator process curves out sharply beyond
the middle of the humerus; distal surface is blunt and faces
directly forward
Supinator process positioned at a lower level than the
ectepicondyle and is separated from it by a deep groove and
notch
The proximal dorsal surface is
essentially flat
The latissimus tubercle is small
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Humerus (cont.)
Surface for the coracobrachialis is tilted ventrally
The deltopectoral crest is greatly developed; the proximal edge
of the crest is thickened
The radial articulation is nearly circular in outline
The radial and ulnar articulations combined occupies a relatively
broad area along the distal end of the bone
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Radius & Ulna
The radius is very short and has less of an arch compared to
those seen in spenacodonts; radius shaft is thick and convex
dorsally in section
A ridge is present not far below the head on the ventral side of
the lateral margin
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Ridge slants out to the margin towards the distal end of the bone
Distal portion of the flexor surface is nearly flat
The proximal articulation is semicircular
The distal articulation is wide dorsoventrally
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Like the radius, the ulna is also very short
In general, the bone is flat dorso-ventrally
The lateral margin of the shaft has a rounded edge but becomes
thin and ridge-like distally
Dorsal surface of the head region is slightly concave
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Femur
The femur is short and nearly straight
Articular surface of the head is broad anteriorly
The dorsal margin of the articular area is somewhat convex in
outline
The anterior tibial condyle flares out anteriorly to a moderate
degree
Dorsal surface tilts strongly posteriorly
The anterior margin descends abruptly into the intercondylar
fossa
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Femur (cont.)
Intertrochanteric fossa is long, broad, and relatively shallow
The ridge posterior to the intertrochanteric fossa is moderately
developed
The popliteal area is flattened
Tibial articular areas faces more distally than seen in other
pelycosaurs; indicates that the knee was less flexible
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Tibia & Fibula
Like the femur, the tibia and fibula are also short
The lateral area of the tibia head (area of articulation with the
femur) is broad dorso-ventrally; this suggest that the articulation
had limited rotation
The proximo-medial portion of the bone is thick with a rounded
lateral margin; medial portion is broad and convex
The distal end of the shaft tends to curve laterally
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Head of fibula is narrow; pair of tubercles present, one below the
other
Articular areas for astragalus and calcaneum are elongated
transversely and thin dorso-ventrally
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Manus & Pes
Complete data available for Ophiacodon; data incomplete in
Varanosaurus and only isolated elements are available for
Clepsydrops
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Data on Manus and Pes seems to be consistent across the genera
Broadness of the feet suggest a webbed condition
The face on the radiale is larger than
that for the lateral centrale in the
carpus
Short contact between radiale
and intermedium distally
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Manus & Pes (cont.)
The ulnare is nearly as broad as it is long
Pisiform is elongated laterally
Lateral centrale is relatively short; its breadth and length about
equal
Dorsal surface of the medial centrale is nearly smooth;
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Its articulation with the first distal
carpal is relatively broad
Has a small contact area with the
third distal carpal
Primitive phalangeal formula retained
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2-3-4-5-3
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Manus & Pes (cont.)
The astragalus is nearly as broad as it is long
Astragalus has a broad fibular facet; the proximal end of the
bone is wide; upper half of the medial margin is thin and has a
sharp edge
Fibulare is broad; its length and width about equal
Centralia have primitive characteristics; they have a subquadrate
shape and are subequal in size
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Positioned side by side distal to the
astragalus and medial to the fourth
distal tarsal
Primitive phalangeal formula retained
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2-3-4-5-4
Varanosaurus
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Skull
Skull is long and narrow; in lateral view, the dorsal margin is
slightly concaved between the posterior margin of the naris and
the midlength of the orbit
Ventral margin is slightly convex from tip of the snout to the
level of the postorbital bar
External naris divided into two opening by the septomaxilla
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The naris is the larger orifice and position more anteriorly; it is subcircular
in outline
Posterior orifice has an outline of a right triangle; its function is unknown
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The dorsal rim of the orbit is flattened and is subcircular in
lateral view
Lateral temporal fenestra is located directly behind the orbit;
bordered by the postorbital, squamosal, and jugal
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Temp. fenestra has the outline of a right triangle w/rounded corners
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In dorsal view, the skull outline is narrow and triangular in shape
Dorsal skull table is nearly flat in transverse section
Orbits are semicircular notches in lateral margins of the skull
table
Antorbitally, the skull quickly narrows to about the midlength
position of the nasals
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In lateral view, the lower jaw is shallow and only slightly concave
A mandibular foramen is present on the lateral surface of the jaw
located at the intersection of the dentary, angular, and surangular
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Mandibular foramen is elongated and oval in shape and is positioned
horizontally
A smaller opening (the Meckelian fenestra) is present on the
medial surface of the jaw
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The premaxilla is small and lightly built; It has room for 6 teeth
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First 3 teeth are the largest and subequal in size, 4th & 5th are smaller and
subequal, and the 6th is the smallest
Dorsal surface of premaxilla is long and narrow
The nasal is relatively long; accounts for ~50% of the midline
length of the skull roof; bone width remains relatively constant
anteriorly
Frontals are exposed on the skull table and are subrectangular in
shape
Lacrimal is long and narrow
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Prefrontal forms the entire anterodorsal margin of the orbit
Postfrontal forms the posterodorsal rim of the orbit
Ventral end of orbital margin continues as a narrow ventral
process along anterior wall of the orbit and medial to the orbital
margin of the lacrimal
In lateral view, the anterior margin of the prefrontal ends in a
short and nearly vertical contact with the nasal bone
Postfrontal bone is in the shape of an equilateral triangle
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The maxilla has approx 55 teeth and tooth spaces; ventral margin
of the anterior end of maxilla exhibits a step-like expansion
where the first 14 teeth are located (ending with the larger
caniniform tooth pair)
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Anteriorly, the precaniniforms exhibit a steady decrease in size
The anterior 8 postcaniniform teeth are slightly smaller than the
last precaniniform tooth; followed by 8 slightly larger teeth
(subequal in size) than the last precaniniform tooth; remainder of
teeth gradually decreases in size posteriorly
Teeth have sharply pointed tips are weakly curved posteriorly
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Palate
Vomer is very narrow and forms almost all of the medial margin
of the internal naris except for a small anterior portion which is
formed by a posteriorly-directed vomerine process of the
premaxilla
A single row of small teeth is located close to and parallel with
the medial margin of the ventral surface of the posterior half of
the vomer
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Anteriorly, the palatine overlaps dorsally the vomer for a short
distance
Ectopterygoids are present and are narrowly trapezoidal in
outline
The pterygoid has a standard primitive amniote form, which
consist of an anterior (palatal) ramus, transverse flange, and a
posterior quadrate ramus
Although this part of the palate is incomplete, it is believed that
the pterygoid does not reach the
internal narial border
The small interpterygoid vacuity
has the outline of a narrow spade
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Small teeth (appox. 0.06mm in diameter) are distributed over
most of the palatal ramus except in two areas; one area is a
narrow anteroposterior strip near the medial margin and the
other is a triangular region anterior to the transverse process
Transverse flange supports a single row of ~10 teeth
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Size of teeth gradually increases medially
Base of each tooth tends to be anteroposteriorly oval
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Mandible
Dentary is the dominant element in lateral view; accounts for ~
75% of the mandibular length
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Posterior end forms the anterior half of the external mandibular foramen
Dorsal margin continues posterodorsally on the lateral surface of the
surangular where it ends as a short, spike-like process
Dentary has ~60 or more tooth positions with tooth
morphology similar to that seen in the upper jaw (sharply
pointed tips and weakly curved); fewer size variation in teeth
than seen in upper jaw
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Teeth with the greatest height
were located at about the
midlength of the dentary and
decreases in size anteiorly
and posteriorly
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In lateral view, the angular has a large, horizonatally oval
exposure on the posteroventral angle
Angular forms the posterior half of the ventral margin of the
external mandibular foramen before continuing anteriorly under
the dentary; it has a spike-like process posterodorsally
The entire dorsal margin of the angular behind the external
mandibular foramen contacts the surangular
Surangular forms a low, flat spike-like extension anterodorsally
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In medial view, the splenial is the dominant element, covering
the entire anterior half of the jaw
As posterior end of splenial tapers to the ventral margin of the
jaw, it contacts the narrow anterior end of the posterior
coronoid, then broadly contacts the prearticular and angular
The long and narrow prearticular forms the broadly concave
ventral border of the adductor fossa then continues anteriorly
where it wedges between the posterior coronoid and splenial
Near the posterior end of the prearticular, it expands dorsally
into a broadly triangular flange that underlies the articular
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Braincase
Exoccipitals and basioccipital bones remain as distinct bones
The supraoccipital is thick and massive; it extends outward and
forward medially to form wing-like expansions; its ventrolateral
corner forms the medial wall and ventral floor of the
posttemporal fenestra
Supraocciptal continues a short distance anterodorsally beneath
the postparietals
A great portion of the lateral walls
of the braincase is formed by the
prootics
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The basisphenoid and parasphenoid fuse to form the
basiparasphenoid complex which expands laterally in the
posterior region
The basipterygoid processes appear as stout, subrectangular
plugs which ventrolaterally and slightly anteriorly
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Stapes
Stapes is similar to that seen in ophiacodon but relatively smaller
in size (particularly the length of the shaft)
The footplate of the stapes is large and roughly oval in shape; it
is narrow ventrally and broadly rounded dorsally
Shaft is slightly thicker ventrally than dorsally and runs
ventrolaterally and posteriorly to reach the quadrate
The distal end of the shaft fits into a recess in the quadrate but
falls short of the floor of the recess; this suggest that there is a
cartilaginous continuation
The dorsal process of the stapes
contacts the underside of the
tabular lateral to the tabularsupraoccipital contact
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Vertabrae
*There are many similarities between Ophiacodon and Varanosaurus but the
characteristics that define Varanosaurus can be seen in the vertebral column
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There are 25-27 presacral vertebrae (which includes the atlas and
axis) and 2 sacral vertabrae of the axial skeleton
The atlantal centrum and axial intercentrum fuse to form the
Atlanto-axial complex
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Degree of fusion between the elements may be due to maturity rather
than taxonomic distinction; Complex probably not seen in juveniles
The plane of fusion between the elements runs posteroventrally which is
a direction opposite to that seen in ophiacodon (posterodorsally)
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There are small parapophyseal articulation for the axial ribs
present on the axial intercentrum which are thinner and
narrower than those in ophiacodon
The atlantal neural arch is composed of two elements that did
not fuse dorsally; ventromedial facets articulate with the anterior
edge of the atlantal centrum
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Wing-like processes on the neural arches are smaller in size than those in
ophiacodon
No dorsally directed neural spine present in varanosaurus
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The axial centrum has a shallow but well-defined ventral keel
A horizontally directed ridge runs from the posterior limit of
each transverse process back to the ridge of the centrum
The pedicle of the neural arch is defined by a posterior
constriction located just above the transverse processes
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Dorsal Vertebrae
Dorsal centra are amphicoelous (concave on both sides)
Anterior and posterior ends are slightly tapered at ventral portion
for the reception of a small intercentra
The articular facets of the anterior zygopophyses are tilted
ventromedially (~20o to the horizontal plane) where as those of
the posterior zygopophyses are angled dorsolaterally (~15o )
Posterior vertebrae appear to be more tightly articulated at both
the anterior and posterior zygopophyses than those of the
anterior vertebrae
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Transverse processes are well developed especially in the 6th and
7th presacrals where its length is nearly ¾ the width of its
centrum
Neural arches seen in varanosaurus differs from that seen in the
other members of the family
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Neural arches of the 3rd & 4th presacrals are similarly proportioned
The 5th & 6th neural arches are wider while the 7th, 8th, and so forth are
distinctively “swollen”
There is an alternation in height of the neural spines in some
regions of the vertebral column (mid-column)
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A feature known in a variety of Late Paleozoic tetrapods
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Shorter or low spines are narrow transversely and elongated
anteroposteriorly
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Bases of the spines are long and narrowly subrectangular in outline
Shorter spines include presacrals 5, 8, 12, 14, 16, 19, and 22
In lateral view, the taller spines are trapezoidal or conical and
angled slightly posteriorly
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Bases of the spines are oval in outline
Tall spines include those not listed above
Presacrals 20 and 24-26 are unknown because the vertebrae or the spines
are missing
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Sacral Vertebrae and Sacral Ribs
Two Sacrals are present in vertebral column
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They are more robustly constructed than all of the presacral vertebrae and
are also generally shorter in length
The neural arches continue smoothly up to sharp, narrow neural spines
which do not have any pattern of height alternation seen in the presacral
column
A ridge is present in the second sacral vertebrae which runs parallel to the
anterior margin
The proximal portion of the first sacral rib extends laterally for a
short distance and then angles
downwards; the distal portion
of the rib expands broadly to
form a fan-shaped surface
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Anterior edge of first sacral rib turns sharply towards a vertical
plane
Distal portion of second sacral rib is not as broadly expanded as
the first but is thicker dorsoventrally
The distal expansions of both sacral ribs lay close to the
horizontal plane
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Caudal Vertebrae and Caudal Ribs
The 3 caudals following the sacral complex show little decrease
in size and proportion; spines of these caudals appear to be
narrow
The base of the tail is relatively thick; the proximal caudal
vertebrae is stoutly built and lacked expanded neural arches
Central length of the caudal does not change much by the middle
of the tail but the transverse measure decreases substantially
Haemal arches are clearly present beyond the 7th caudal; in
addition, the articular surfaces
of the transverse processes are
circular in outline
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Haemal arches reach as far back
as the 30th caudal
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By the middle of the tail, the centra are narrower; neural arches
are less built with shallow excavations at their bases
The posteriormost portion of the tail retains approximately the
same length as the cauduals anterior to the section
Neural arches and spines still persist as distinct structures even in
the posteriormost portion of the tail; transverse processes cannot
been seen in this portion
References
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Berman, D. S, R. R. Reisz, J. R. Bolt, and D. Scott. 1995. The cranial
anatomy and relationships of the synapsid Varanosaurus (Eupleycosauria:
Ophiacodontidae) from the Early Permian of Texas and Oklahoma.
Annals of Carnegie Museum, 64:100-133.
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Palaeos.com
http://www.palaeos.com/Vertebrates/Units/390Synapsida/390.000.html
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Romer, A.S. and L. I. Price. 1940. Review of the Pelycosauria. Bulletin of the
Geological Society of America Special Papers, 28: 1-538.
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Sumida, S. S. 1989. Reinterpretation of vertebral structure in the Early
Permian pelycosaur Varanosaurus acutirostris (Amniota, Synapsida). Journal
of Vertebrate Paleontology, 9:451-158.