OphiacodontidaeOphiacodontidae

Thien NguyenThien Nguyen

CSUSBCSUSB

Biology 680 - 2009Biology 680 - 2009

IntroductionIntroduction

KingdomKingdom: Animalia: Animalia PhylumPhylum: Chordata: Chordata SuperclassSuperclass: Tetrapoda: Tetrapoda ClassClass: Synapsida: Synapsida OrderOrder: Pelycosauria: Pelycosauria Sub-OrderSub-Order: Ophiacodontia: Ophiacodontia FamilyFamily: Ophiacodontidae: Ophiacodontidae

OphiacodontiaOphiacodontia OphiacodontidaeOphiacodontidae

Which include pelycosaurs with features once Which include pelycosaurs with features once considered as primitive and close to the basal considered as primitive and close to the basal stock of the orderstock of the order

There is a fairly complete knowledge of There is a fairly complete knowledge of Ophiacodontidae anatomy, particularly on Ophiacodontidae anatomy, particularly on OphiacodonOphiacodon

Members of the family includeMembers of the family include ArcheothyrisArcheothyris ClepsydropsClepsydrops OphiacodonOphiacodon VaranosaurusVaranosaurus

IntroductionIntroduction

Ophiacodonts first appeared in the late Ophiacodonts first appeared in the late Carboniferous period.Carboniferous period.

Many were possibly semi- or fully aquatic Many were possibly semi- or fully aquatic animals.animals. They have piscivorous habits (feeding on They have piscivorous habits (feeding on

fishes) and amphibious adaptationsfishes) and amphibious adaptations Fed on food items which required little Fed on food items which required little

mastication; this is due to features such as mastication; this is due to features such as their long snout, lightly built skulls and jaws, their long snout, lightly built skulls and jaws, and undifferentiated dentitions and undifferentiated dentitions

OphiacodontiaOphiacodontia These animals had low and relatively broad skulls These animals had low and relatively broad skulls

with a moderately elongated snoutwith a moderately elongated snout Concaved dorsal borders of the orbitConcaved dorsal borders of the orbit Lower margin of skull is nearly straightLower margin of skull is nearly straight Occiput slants strongly forward dorsallyOcciput slants strongly forward dorsally Slender marginal teethSlender marginal teeth Canines are always distinctCanines are always distinct Palatal teeth present butPalatal teeth present but

not greatly developednot greatly developed

Jaw articulation is almost in-line or on the same Jaw articulation is almost in-line or on the same level as the row of teethlevel as the row of teeth

The jaw is slender The jaw is slender Symphasis is confined for the most part to the dentarySymphasis is confined for the most part to the dentary Coronoid is elevatedCoronoid is elevated

Developed pterygoid flange (although not Developed pterygoid flange (although not thickened)thickened)

Lacrimal reaches the narisLacrimal reaches the naris Basal portion of quadrateBasal portion of quadrate

is broad transverselyis broad transversely

Vertebrae is primitively short but tends to Vertebrae is primitively short but tends to elongate in some formselongate in some forms

Presacral Centra tends to be flattened ventrally Presacral Centra tends to be flattened ventrally and keel in dorsal region is never sharpand keel in dorsal region is never sharp

Transverse processes are short while the neural Transverse processes are short while the neural arch tends to be broad and heavyarch tends to be broad and heavy

The cervical ribs are dialatedThe cervical ribs are dialated Abdominal ribs are highly developedAbdominal ribs are highly developed Clavicals are narrow distally andClavicals are narrow distally and

head of interclavical is short head of interclavical is short →→

Scapula is short and broadScapula is short and broad The Supraglenoid foramen occupies primitive The Supraglenoid foramen occupies primitive

positionposition CoracoidCoracoid does not lag in ossification does not lag in ossification Process for coracoid head of the triceps is Process for coracoid head of the triceps is

slightly developedslightly developed

The The iliumilium is long but unexpanded dorsally but is long but unexpanded dorsally but retains dorsal trough for axial muscle attachmentretains dorsal trough for axial muscle attachment

PubicPubic tubercle is usually present tubercle is usually present Internal shelf for the puboishio-Internal shelf for the puboishio-

femoralis internus is present on thefemoralis internus is present on the

pubispubis

OphiacodontidaeOphiacodontidae Features of the SkullFeatures of the Skull

Always large and relatively narrowAlways large and relatively narrow Moderately to greatly elongated facial Moderately to greatly elongated facial

regionregion Numerous marginal teethNumerous marginal teeth

40-55 in upper jaw40-55 in upper jaw Moderately developed caninesModerately developed canines Stapes is a massive rodStapes is a massive rod

OphiacodontidaeOphiacodontidae Physical featuresPhysical features

Short vertebraeShort vertebrae Hind legs are longer than the fore legsHind legs are longer than the fore legs The atlas centrum doesn’t reach ventral The atlas centrum doesn’t reach ventral

surface of the columnsurface of the column Primitive adductor ridge in femur has Primitive adductor ridge in femur has

disappeared.disappeared. Caudal muscles have no prominent area for Caudal muscles have no prominent area for

attachmentattachment

OphiacodontidaeOphiacodontidae Members of the family include:Members of the family include:

OphiacodonOphiacodon VaranosaurusVaranosaurus ClepsydropsClepsydrops

**These three are strikingly similar with only These three are strikingly similar with only slight differences in their skull and vertebrae slight differences in their skull and vertebrae proportions and a few others.proportions and a few others.

OphiacodonOphiacodon

OphiacodonOphiacodon Ophiacodontids were generally moderate to very Ophiacodontids were generally moderate to very

large in sizelarge in size Skull is large, long, and highSkull is large, long, and high Vertebrae are more slender than smaller Vertebrae are more slender than smaller

members of the familymembers of the family Pubic tubercle is reduced or absentPubic tubercle is reduced or absent There is a development of a secondary adductor There is a development of a secondary adductor

ridge on the femurridge on the femur Unguals (or claws) are flattenedUnguals (or claws) are flattened Ophiacodons have a distinctive feature in that Ophiacodons have a distinctive feature in that

they have slow ossification of replacement bones, they have slow ossification of replacement bones, both in the skull and postcranial skeletonboth in the skull and postcranial skeleton

OphiacodonOphiacodon Greatly elongated skull (Due to elongated nasal, Greatly elongated skull (Due to elongated nasal,

lacrimal, maxillae, frontal and pre-frontal lacrimal, maxillae, frontal and pre-frontal elements)elements)

Disappearance of the palaeorbital connection of Disappearance of the palaeorbital connection of pre and postfrontals (a primitive feature)pre and postfrontals (a primitive feature)

Moderately long post orbital regionModerately long post orbital region Lacrimal (L) is very thinLacrimal (L) is very thin Lacrimal duct can extend asLacrimal duct can extend as

as far as level of caninesas far as level of canines Small supratemporal (ST)Small supratemporal (ST) Anterior margin of orbit isAnterior margin of orbit is

thin ventrally and thickened thin ventrally and thickened

dorsallydorsally

Parietal bone is a single structure. Although in Parietal bone is a single structure. Although in some some OphiacodonOphiacodon and and VaranosaurusVaranosaurus specimens, specimens, the interparietal is divided in two by a the interparietal is divided in two by a longitudinal fissurelongitudinal fissure

Debate as to whether it is a crack or sutureDebate as to whether it is a crack or suture Slender connection between maxilla and Slender connection between maxilla and

premaxillapremaxilla Ascending bar on inner surface of the maxilla Ascending bar on inner surface of the maxilla

(also present in Clepsydrops) above the canines; (also present in Clepsydrops) above the canines; possibly to brace the tooth row to the skull roofpossibly to brace the tooth row to the skull roof

Post orbital (PO)Post orbital (PO) and and jugal (J)jugal (J)

forms a broad bar extending forms a broad bar extending

medially behind the orbitmedially behind the orbit Palate (PAL)Palate (PAL) is lightly built is lightly built

The quadratojugal is well developed and extends The quadratojugal is well developed and extends almost to the maxilla. It is also fused to the almost to the maxilla. It is also fused to the quadrate and has an articulation with pterygoid quadrate and has an articulation with pterygoid ramus above the quadrate foramenramus above the quadrate foramen

Squamosal (SQ) has a well-developed reflected Squamosal (SQ) has a well-developed reflected lamina which provides an attachment to the tip lamina which provides an attachment to the tip of the paraoccipital processof the paraoccipital process

Choanae are long and narrow while prevomers Choanae are long and narrow while prevomers are slender and toothlessare slender and toothless

Row of teeth present which runs forward along Row of teeth present which runs forward along the margin of the narrow interpterygoid vacuitythe margin of the narrow interpterygoid vacuity

Second line of teeth runs alongSecond line of teeth runs alongpalatal ramus of the pterygoidpalatal ramus of the pterygoid

Articular area for the basipterygoid process is Articular area for the basipterygoid process is large and deep and is situated far ventrallylarge and deep and is situated far ventrally

The stapes is situated on a cavity formed by the The stapes is situated on a cavity formed by the quadrate ramus of the pterygoid and the quadrate ramus of the pterygoid and the adjacent portion of the quadrateadjacent portion of the quadrate

Quadrate (Q) is transversely expanded with its Quadrate (Q) is transversely expanded with its articular surface situated in a nearly horizontal articular surface situated in a nearly horizontal planeplane

Its believed that the quadrate bone is built to aid Its believed that the quadrate bone is built to aid the pterygoid in enclosing the middle ear the pterygoid in enclosing the middle ear chamberchamber

OphiacodonOphiacodon Braincase is adequately studied Braincase is adequately studied The sutures between all of the braincase The sutures between all of the braincase

elements can be seen due to the slow ossification elements can be seen due to the slow ossification process in Ophiacodonprocess in Ophiacodon

Outline of supraoccipital is subquadrateOutline of supraoccipital is subquadrate Venous depression present on inner surface of Venous depression present on inner surface of

supraoccipitalsupraoccipital The The opisthotic (op)opisthotic (op) occupies the latero-ventral occupies the latero-ventral

portion of the occipital plate and is clearly portion of the occipital plate and is clearly separable from the other elementsseparable from the other elements

Opisthotic is incompletely ossified ventrally at Opisthotic is incompletely ossified ventrally at the area where it borders the fenestra ovalisthe area where it borders the fenestra ovalis

JawJaw Slender and shallow dorso-ventrally at the anterior Slender and shallow dorso-ventrally at the anterior

endend Symphysis of bones is weakly developed and Symphysis of bones is weakly developed and

primarily confined in the dentaryprimarily confined in the dentary Dentary (D)Dentary (D) is elongated is elongated Oval external opening is present in between the Oval external opening is present in between the

dentary, angular, and subangulardentary, angular, and subangular11

The postero-dorsal expansion of the Dentary covers The postero-dorsal expansion of the Dentary covers much of the outer side of the much of the outer side of the surangular (SANG)surangular (SANG)

Maxillary (MX)Maxillary (MX) region is slightly region is slightly concavedconcaved

Coronoid (C)Coronoid (C) region is slightly region is slightly convexedconvexed

Upper margin of surangularUpper margin of surangularis thinis thin

The angular has a prominent ventral keelThe angular has a prominent ventral keel Splenial (SP)Splenial (SP) is broad on the internal is broad on the internal

surface but is barely visible from the outer surface but is barely visible from the outer viewview

Prominent ventral keel present on Prominent ventral keel present on articular articular (A)(A) and is continuous with the angular; and is continuous with the angular; Internal processes for muscle attachments Internal processes for muscle attachments are not present on the articularare not present on the articular

Articular surface is gently tilted inward Articular surface is gently tilted inward and appear to be primitive in constructionand appear to be primitive in construction Both cavities are short antero-Both cavities are short antero-

posteriolyposterioly Lateral cavity is deeply concavedLateral cavity is deeply concaved Medial cavity is flatMedial cavity is flat

Marginal teeth are rounded in section, sharply Marginal teeth are rounded in section, sharply pointed, and slightly recurvedpointed, and slightly recurved

The bases of each tooth are subquadrate and The bases of each tooth are subquadrate and have longitudinal striationshave longitudinal striations

Tooth replacement is believed to be slow, Tooth replacement is believed to be slow, resulting in frequent gaps in the tooth rowresulting in frequent gaps in the tooth row

Total number of maxillary teeth generally range Total number of maxillary teeth generally range from 29-46from 29-46

6-7 precanines are always present6-7 precanines are always present Canines are not very projecting but are distinctCanines are not very projecting but are distinct Dentary teeth are generally more numerous, Dentary teeth are generally more numerous,

crowded, and smaller in sizecrowded, and smaller in size

VertebraeVertebrae There are generally 27 pre-sacral vertebrae, 2 There are generally 27 pre-sacral vertebrae, 2

sacrals, and an elongated tail presentsacrals, and an elongated tail present The vertabrae and the body as a whole is short The vertabrae and the body as a whole is short

which is believed to be a primitive featurewhich is believed to be a primitive feature Presence of 5 nonmovable ribs in front of the Presence of 5 nonmovable ribs in front of the

sacrum; possibly lumbarssacrum; possibly lumbars

Transverse processes of the cervical and dorsal Transverse processes of the cervical and dorsal vertebrae are short (compared to other vertebrae are short (compared to other suborders)suborders)

The The dorsal transverse processesdorsal transverse processes is semicircular is semicircular in sectionin section Posterior surface is flat while the anterior surface is Posterior surface is flat while the anterior surface is

convexconvex The arch of the The arch of the transverse processes of the transverse processes of the

cervicalcervical emerges further down and slants sharply emerges further down and slants sharply backwards and downwardsbackwards and downwards

The dorsal neural spines are thin transversely The dorsal neural spines are thin transversely and broad antero-posteriorly; cervical neural and broad antero-posteriorly; cervical neural spines have stouter bases; spines in both cases spines have stouter bases; spines in both cases have blunt tips and are never elongatedhave blunt tips and are never elongated

Atlanto-axial complex indicate a common and Atlanto-axial complex indicate a common and distinctive structuredistinctive structure

ProatlasProatlas is present is present Atlantal centrum may be fused with the axial Atlantal centrum may be fused with the axial

intercentrum intercentrum and is thick antero-posteriorly and and is thick antero-posteriorly and has a well developed dorsal portionhas a well developed dorsal portion Highly characteristic feature of OphiacodontidaeHighly characteristic feature of Ophiacodontidae

Atlantal intercentrumAtlantal intercentrum is large and underlains the is large and underlains the atalantal centrumatalantal centrum

Spine of axis expands antero-Spine of axis expands antero-

posteriorly and is thin anteriorly posteriorly and is thin anteriorly

and thickened at the posterior edgeand thickened at the posterior edge

The cervical ribs are two-headed and although The cervical ribs are two-headed and although lumbar ribs are present, they are often smalllumbar ribs are present, they are often small

Two Two sacralssacrals are present are present The The first sacral ribfirst sacral rib is large and has a fan shaped is large and has a fan shaped

surface which fits into a hollow in the iliumsurface which fits into a hollow in the ilium The second rib is much smaller and has little The second rib is much smaller and has little

contact w/the ilium; seems that its purpose was contact w/the ilium; seems that its purpose was just to prop the first ribjust to prop the first rib

Caudal ribs (approx. 11) were present and well Caudal ribs (approx. 11) were present and well developeddeveloped

The blade of the clavicle is extremely narrowThe blade of the clavicle is extremely narrow Shaft of clavicle is flattened and groove for Shaft of clavicle is flattened and groove for

attachment to the scapula is extremely attachment to the scapula is extremely underdevelopedunderdeveloped

Distal ends are heavily striatedDistal ends are heavily striated Believed that this is to compensate for the small area it Believed that this is to compensate for the small area it

has that contacts with the interclaviclehas that contacts with the interclavicle The bowl of the interclavical is The bowl of the interclavical is

short and the anterior quadrants short and the anterior quadrants

are only slightly developed; the are only slightly developed; the

blade is nearly uniform in width blade is nearly uniform in width

but broadens at mid-lengthbut broadens at mid-length

ScapulocoracoidScapulocoracoid Scapular blade is generally low in correlation Scapular blade is generally low in correlation

with the low build of the bodywith the low build of the body The scapula is broad; the The scapula is broad; the posterior margin of posterior margin of

scapulascapula curves backwards to a slight degree curves backwards to a slight degree Coracoid surface below the Coracoid surface below the glenoidglenoid is slightly is slightly

concave in dorso-ventral sectionconcave in dorso-ventral section

Pelvic GirdlePelvic Girdle Primitive in regards to the construction of the iliac Primitive in regards to the construction of the iliac

bladeblade Outer surface of Outer surface of iliumilium associated only with associated only with

appendicular musclesappendicular muscles Iliac blade is elongated and points posteriorly Iliac blade is elongated and points posteriorly

(which is believed to be a primitive feature); blade (which is believed to be a primitive feature); blade increases in height anteriorlyincreases in height anteriorly

Dorsal margin of iliac blade is characteristically Dorsal margin of iliac blade is characteristically concave in outline while it is convex posteriorlyconcave in outline while it is convex posteriorly

Lower front margin of ilium forms a sharp ridgeLower front margin of ilium forms a sharp ridge Iliac component in the formation of Iliac component in the formation of

the acetabulum is greatest in sizethe acetabulum is greatest in size Acetabulum has a thick posterior Acetabulum has a thick posterior

marginmargin

Pelvic Girdle (cont.)Pelvic Girdle (cont.) Acetabulum is more dorsally facing (its deepest Acetabulum is more dorsally facing (its deepest

portion lies near the ischiadic component of the portion lies near the ischiadic component of the acetabulumacetabulum

Ischium Ischium points posteriorlypoints posteriorly The pubis is generally short; a thick dorsal The pubis is generally short; a thick dorsal

margin descends sharply downward and outward margin descends sharply downward and outward from the acetabulumfrom the acetabulum

In primitive forms, there is a prominentIn primitive forms, there is a prominent pubic pubic tubercletubercle Tubercle is reduced in OphiacodonTubercle is reduced in Ophiacodon

The puboischiadic plate is relativelyThe puboischiadic plate is relatively

narrow dorso-ventrallynarrow dorso-ventrally

AppendagesAppendages Proximal segments of the limbs were short in Proximal segments of the limbs were short in

comparison to the sphenacodontids or comparison to the sphenacodontids or edaphosaursedaphosaurs

Front legs are smaller than hind legsFront legs are smaller than hind legs Humerus was ~20% shorter than the femur; Humerus Humerus was ~20% shorter than the femur; Humerus

only ~10% shorter than femur in sphenacodontids and only ~10% shorter than femur in sphenacodontids and edaphosaursedaphosaurs

Radius and ulna were noticeably shorter than tibia and Radius and ulna were noticeably shorter than tibia and fibula; These bones were approx. equal in size in fibula; These bones were approx. equal in size in sphenacodontids and edaphosaurssphenacodontids and edaphosaurs

HumerusHumerus Articular surfaceArticular surface occupies nearly the entire occupies nearly the entire

extent of the proximal endextent of the proximal end Anterior margin of Anterior margin of supinator processsupinator process curves out curves out

sharply beyond the middle of the humerus; distal sharply beyond the middle of the humerus; distal surface is blunt and faces directly forwardsurface is blunt and faces directly forward

Supinator process positioned at a lower level Supinator process positioned at a lower level than the than the ectepicondyleectepicondyle and is separated from it and is separated from it by a deep groove and notchby a deep groove and notch

The The proximal dorsal surfaceproximal dorsal surface is is

essentially flatessentially flat The latissimus tubercle is smallThe latissimus tubercle is small

Humerus (cont.)Humerus (cont.) Surface for the coracobrachialis is tilted Surface for the coracobrachialis is tilted

ventrallyventrally The The deltopectoral crestdeltopectoral crest is greatly developed; the is greatly developed; the

proximal edge of the crest is thickenedproximal edge of the crest is thickened The The radial articulationradial articulation is nearly circular in is nearly circular in

outlineoutline The radial and ulnar articulations combined The radial and ulnar articulations combined

occupies a relatively broad area along the distal occupies a relatively broad area along the distal end of the bone end of the bone

Radius & UlnaRadius & Ulna The radius is very short and has less of an arch The radius is very short and has less of an arch

compared to those seen in spenacodonts; radius compared to those seen in spenacodonts; radius shaft is thick and convex dorsally in sectionshaft is thick and convex dorsally in section

A A ridgeridge is present not far below the head on the is present not far below the head on the ventral side of the lateral marginventral side of the lateral margin Ridge slants out to the margin towards the distal end of Ridge slants out to the margin towards the distal end of

the bonethe bone Distal portion of the flexor surface is nearly flatDistal portion of the flexor surface is nearly flat The The proximal articulationproximal articulation is semicircular is semicircular The The distal articulationdistal articulation is wide dorso- is wide dorso-

ventrallyventrally

Like the radius, the ulna is also very shortLike the radius, the ulna is also very short In general, the bone is flat dorso-ventrallyIn general, the bone is flat dorso-ventrally The lateral margin of the shaft has a rounded The lateral margin of the shaft has a rounded

edge but becomes thin and ridge-like distallyedge but becomes thin and ridge-like distally Dorsal surface of the head region is slightly Dorsal surface of the head region is slightly

concaveconcave

FemurFemur The femur is short and nearly straightThe femur is short and nearly straight Articular surface of the head is broad anteriorlyArticular surface of the head is broad anteriorly The dorsal margin of the articular area is The dorsal margin of the articular area is

somewhat convex in outlinesomewhat convex in outline The anterior tibial condyle flares out anteriorly to The anterior tibial condyle flares out anteriorly to

a moderate degreea moderate degree Dorsal surface tilts strongly posteriorlyDorsal surface tilts strongly posteriorly The anterior margin descends abruptly into the The anterior margin descends abruptly into the

intercondylar fossaintercondylar fossa

Femur (cont.)Femur (cont.) Intertrochanteric fossa is long, broad, and Intertrochanteric fossa is long, broad, and

relatively shallowrelatively shallow The ridge posterior to the intertrochanteric fossa The ridge posterior to the intertrochanteric fossa

is moderately developedis moderately developed The popliteal area is flattenedThe popliteal area is flattened Tibial articular areas faces more distally than Tibial articular areas faces more distally than

seen in other pelycosaurs; indicates that the seen in other pelycosaurs; indicates that the knee was less flexibleknee was less flexible

Tibia & FibulaTibia & Fibula Like the femur, the tibia and fibula are also shortLike the femur, the tibia and fibula are also short The The lateral area of the tibialateral area of the tibia head (area of head (area of

articulation with the femur) is broad dorso-articulation with the femur) is broad dorso-ventrally; this suggest that the articulation had ventrally; this suggest that the articulation had limited rotationlimited rotation

The The proximo-medial portionproximo-medial portion of the bone is thick of the bone is thick with a rounded lateral margin; medial portion is with a rounded lateral margin; medial portion is broad and convexbroad and convex

The The distaldistal end of the shaft tends to curve end of the shaft tends to curve laterallylaterally

Head of fibula is narrow; pair of tubercles Head of fibula is narrow; pair of tubercles present, one below the otherpresent, one below the other

Articular areas for astragalus and calcaneum are Articular areas for astragalus and calcaneum are elongated transversely and thin dorso-ventrallyelongated transversely and thin dorso-ventrally

Manus & PesManus & Pes Complete data available for Complete data available for OphiacodonOphiacodon; data ; data

incomplete in incomplete in VaranosaurusVaranosaurus and only isolated and only isolated elements are available for elements are available for ClepsydropsClepsydrops Data on Manus and Pes seems to be consistent across Data on Manus and Pes seems to be consistent across

the generathe genera Broadness of the feet suggest a webbed Broadness of the feet suggest a webbed

conditioncondition The face on the The face on the radialeradiale is larger than is larger than

that for the that for the lateral centralelateral centrale in the in the

carpuscarpus Short contact between radiale Short contact between radiale

and and intermediumintermedium distally distally

Manus & Pes (cont.)Manus & Pes (cont.) The The ulnareulnare is nearly as broad as it is long is nearly as broad as it is long PisiformPisiform is elongated laterally is elongated laterally Lateral centraleLateral centrale is relatively short; its breadth is relatively short; its breadth

and length about equaland length about equal Dorsal surface of the Dorsal surface of the medial centralemedial centrale is nearly is nearly

smooth; smooth; Its articulation with the first distal Its articulation with the first distal

carpal is relatively broadcarpal is relatively broad Has a small contact area with the Has a small contact area with the

third distal carpalthird distal carpal Primitive phalangeal formula retainedPrimitive phalangeal formula retained

2-3-4-5-32-3-4-5-3

Manus & Pes (cont.)Manus & Pes (cont.) The The astragalusastragalus is nearly as broad as it is long is nearly as broad as it is long Astragalus has a broad fibular facet; the proximal Astragalus has a broad fibular facet; the proximal

end of the bone is wide; upper half of the medial end of the bone is wide; upper half of the medial margin is thin and has a sharp edgemargin is thin and has a sharp edge

FibulareFibulare is broad; its length and width about is broad; its length and width about equalequal

CentraliaCentralia have primitive characteristics; they have primitive characteristics; they have a subquadrate shape and are subequal in have a subquadrate shape and are subequal in sizesize Positioned side by side distal to thePositioned side by side distal to the

astragalus and medial to the astragalus and medial to the fourthfourth

distal tarsaldistal tarsal Primitive phalangeal formula retainedPrimitive phalangeal formula retained

2-3-4-5-42-3-4-5-4

VaranosaurusVaranosaurus

SkullSkull Skull is long and narrow; in lateral view, Skull is long and narrow; in lateral view, the the

dorsal margin is slightly concaved between the dorsal margin is slightly concaved between the posterior margin of the naris and the midlength posterior margin of the naris and the midlength of the orbitof the orbit

Ventral margin is slightly convex from tip of the Ventral margin is slightly convex from tip of the snout to the level of the postorbital barsnout to the level of the postorbital bar

External naris divided into two opening by the External naris divided into two opening by the septomaxillaseptomaxilla The naris is the larger orifice and position more The naris is the larger orifice and position more

anteriorly; it is subcircular in outlineanteriorly; it is subcircular in outline Posterior orifice has an outline of a right triangle; its Posterior orifice has an outline of a right triangle; its

function is unknownfunction is unknown

The dorsal rim of the orbit is flattened and is The dorsal rim of the orbit is flattened and is subcircular in lateral viewsubcircular in lateral view

Lateral temporal fenestra is located directly Lateral temporal fenestra is located directly behind the orbit; bordered by the behind the orbit; bordered by the postorbitalpostorbital, , squamosalsquamosal, and , and jugaljugal Temp. fenestra has the outline of a right triangle Temp. fenestra has the outline of a right triangle

w/rounded cornersw/rounded corners

In dorsal view, the skull outline is narrow and In dorsal view, the skull outline is narrow and triangular in shapetriangular in shape

Dorsal skull table is nearly flat in transverse Dorsal skull table is nearly flat in transverse sectionsection

Orbits are semicircular notches in lateral Orbits are semicircular notches in lateral margins of the skull tablemargins of the skull table

Antorbitally, the skull quickly narrows to about Antorbitally, the skull quickly narrows to about the midlength position of the nasalsthe midlength position of the nasals

In lateral view, the lower jaw is shallow and only In lateral view, the lower jaw is shallow and only slightly concaveslightly concave

A A mandibular foramenmandibular foramen is present on the lateral is present on the lateral surface of the jaw located at the intersection of surface of the jaw located at the intersection of the dentary, angular, and surangularthe dentary, angular, and surangular Mandibular foramen is elongated and oval in shape and Mandibular foramen is elongated and oval in shape and

is positioned horizontallyis positioned horizontally A smaller opening (the A smaller opening (the Meckelian fenestraMeckelian fenestra) is ) is

present on the medial surface of the jawpresent on the medial surface of the jaw

The The premaxillapremaxilla is small and lightly built; It has is small and lightly built; It has room for 6 teethroom for 6 teeth First 3 teeth are the largest and subequal in size, 4First 3 teeth are the largest and subequal in size, 4thth & &

55thth are smaller and subequal, and the 6 are smaller and subequal, and the 6thth is the smallest is the smallest Dorsal surface of premaxilla is long and narrowDorsal surface of premaxilla is long and narrow The The nasalnasal is relatively long; accounts for ~50% of is relatively long; accounts for ~50% of

the midline length of the skull roof; bone width the midline length of the skull roof; bone width remains relatively constant anteriorlyremains relatively constant anteriorly

FrontalsFrontals are exposed on the skull table and are are exposed on the skull table and are subrectangular in shapesubrectangular in shape

LacrimalLacrimal is long and narrow is long and narrow

PrefrontalPrefrontal forms the entire anterodorsal margin forms the entire anterodorsal margin of the orbitof the orbit

PostfrontalPostfrontal forms the posterodorsal rim of the forms the posterodorsal rim of the orbitorbit

Ventral end of orbital margin continues as a Ventral end of orbital margin continues as a narrow ventral process along anterior wall of the narrow ventral process along anterior wall of the orbit and medial to the orbital margin of the orbit and medial to the orbital margin of the lacrimallacrimal

In lateral view, the anterior margin of the In lateral view, the anterior margin of the prefrontal ends in a short and nearly vertical prefrontal ends in a short and nearly vertical contact with the contact with the nasalnasal bone bone

Postfrontal bone is in the shape of an equilateral Postfrontal bone is in the shape of an equilateral triangletriangle

The maxilla has approx 55 teeth and tooth The maxilla has approx 55 teeth and tooth spaces; spaces; ventral margin of the anterior end of ventral margin of the anterior end of maxilla exhibits a step-like expansion where the maxilla exhibits a step-like expansion where the first 14 teeth are located (ending with the larger first 14 teeth are located (ending with the larger caniniform tooth pair)caniniform tooth pair) Anteriorly, the precaniniforms exhibit a steady decrease Anteriorly, the precaniniforms exhibit a steady decrease

in sizein size The The anterior 8 postcaniniformanterior 8 postcaniniform teeth are slightly teeth are slightly

smaller than the last precaniniform tooth; smaller than the last precaniniform tooth; followed by 8 slightly larger teeth (subequal in followed by 8 slightly larger teeth (subequal in size) than the last precaniniform toothsize) than the last precaniniform tooth;; remainder of teeth gradually decreases in size remainder of teeth gradually decreases in size posteriorlyposteriorly

Teeth have sharply pointed tips are weakly Teeth have sharply pointed tips are weakly curved posteriorly curved posteriorly

PalatePalate Vomer is very narrow and forms almost all of the Vomer is very narrow and forms almost all of the

medial margin of the internal naris except for a medial margin of the internal naris except for a small anterior portion which is formed by a small anterior portion which is formed by a posteriorly-directed vomerine process of the posteriorly-directed vomerine process of the premaxillapremaxilla

A single row of small teeth is located close to and A single row of small teeth is located close to and parallel with the medial margin of the ventral parallel with the medial margin of the ventral surface of the posterior half of the vomersurface of the posterior half of the vomer

Anteriorly, the palatine overlaps dorsally the Anteriorly, the palatine overlaps dorsally the vomer for a short distancevomer for a short distance

Ectopterygoids are present and are narrowly Ectopterygoids are present and are narrowly trapezoidal in outlinetrapezoidal in outline

The The pterygoidpterygoid has a standard primitive amniote has a standard primitive amniote form, which consist of an anterior (palatal) form, which consist of an anterior (palatal) ramus, transverse flange, and a posterior ramus, transverse flange, and a posterior quadrate ramusquadrate ramus

Although this part of the palate is incomplete, it Although this part of the palate is incomplete, it is believed that the pterygoid does not reach the is believed that the pterygoid does not reach the

internal narial borderinternal narial border The small The small interpterygoid vacuityinterpterygoid vacuity

has the outline of a narrow spadehas the outline of a narrow spade

Small teeth (appox. 0.06mm in diameter) are Small teeth (appox. 0.06mm in diameter) are distributed over most of the palatal ramus except distributed over most of the palatal ramus except in two areas; one area is a in two areas; one area is a narrow narrow anteroposterior strip near the medial marginanteroposterior strip near the medial margin and and the other is a the other is a triangular regiontriangular region anterior to the anterior to the transverse processtransverse process

Transverse flange supports a single row of ~10 Transverse flange supports a single row of ~10 teethteeth Size of teeth gradually increases mediallySize of teeth gradually increases medially Base of each tooth tends to be anteroposteriorly ovalBase of each tooth tends to be anteroposteriorly oval

MandibleMandible DentaryDentary is the dominant element in lateral view; is the dominant element in lateral view;

accounts for ~ 75% of the mandibular lengthaccounts for ~ 75% of the mandibular length Posterior end forms the anterior half of the external Posterior end forms the anterior half of the external

mandibular foramenmandibular foramen Dorsal margin continues posterodorsally on the lateral Dorsal margin continues posterodorsally on the lateral

surface of the surface of the surangularsurangular where it ends as a short, spike- where it ends as a short, spike-like processlike process

Dentary has ~60 or more tooth positions with Dentary has ~60 or more tooth positions with tooth morphology similar to that seen in the upper tooth morphology similar to that seen in the upper jaw (sharply pointed tips and weakly curved); jaw (sharply pointed tips and weakly curved); fewer size variation in teeth than seen in upper jawfewer size variation in teeth than seen in upper jaw Teeth with the greatest height Teeth with the greatest height

were located at about the were located at about the

midlength of the dentary and midlength of the dentary and

decreases in size anteiorly decreases in size anteiorly

and posteriorlyand posteriorly

In lateral view, the In lateral view, the angularangular has a large, has a large, horizonatally oval exposure on the posteroventral horizonatally oval exposure on the posteroventral angleangle

Angular forms the posterior half of the ventral Angular forms the posterior half of the ventral margin of the external mandibular foramen margin of the external mandibular foramen before continuing anteriorly under the dentary; it before continuing anteriorly under the dentary; it has a spike-like process posterodorsallyhas a spike-like process posterodorsally

The entire dorsal margin of the angular behind The entire dorsal margin of the angular behind the external mandibular foramen contacts the the external mandibular foramen contacts the surangularsurangular

Surangular forms a low, flat spike-like extension Surangular forms a low, flat spike-like extension anterodorsallyanterodorsally

In medial view, the In medial view, the splenialsplenial is the dominant is the dominant element, covering the entire anterior half of the element, covering the entire anterior half of the jawjaw

As posterior end of splenial tapers to the ventral As posterior end of splenial tapers to the ventral margin of the jaw, it contacts the narrow anterior margin of the jaw, it contacts the narrow anterior end of the posterior end of the posterior coronoid, coronoid, then broadly then broadly contacts the contacts the prearticularprearticular and and angularangular

The long and narrow prearticular forms the The long and narrow prearticular forms the broadly concave ventral border of the adductor broadly concave ventral border of the adductor fossa then continues anteriorly where it wedges fossa then continues anteriorly where it wedges between the posterior coronoid and splenialbetween the posterior coronoid and splenial

Near the posterior end of the prearticular, it Near the posterior end of the prearticular, it expands dorsally into a broadly triangular flange expands dorsally into a broadly triangular flange that underlies the articularthat underlies the articular

BraincaseBraincase Exoccipitals and basioccipital bones remain as Exoccipitals and basioccipital bones remain as

distinct bonesdistinct bones The The supraoccipitalsupraoccipital is thick and massive; it is thick and massive; it

extends outward and forward medially to form extends outward and forward medially to form wing-like expansions; its ventrolateral corner wing-like expansions; its ventrolateral corner forms the medial wall and ventral floor of the forms the medial wall and ventral floor of the posttemporal fenestraposttemporal fenestra

Supraocciptal continues a short distance Supraocciptal continues a short distance anterodorsally beneath the anterodorsally beneath the postparietalspostparietals

A great portion of the lateral walls A great portion of the lateral walls

of the braincase is formed by theof the braincase is formed by the

prooticsprootics

The basisphenoid and parasphenoid fuse to form The basisphenoid and parasphenoid fuse to form the the basiparasphenoidbasiparasphenoid complex which expands complex which expands laterally in the posterior regionlaterally in the posterior region

The basipterygoid processes appear as stout, The basipterygoid processes appear as stout, subrectangular plugs which ventrolaterally and subrectangular plugs which ventrolaterally and slightly anteriorlyslightly anteriorly

StapesStapes StapesStapes is similar to that seen in ophiacodon but is similar to that seen in ophiacodon but

relatively smaller in size (particularly the length of relatively smaller in size (particularly the length of the shaft)the shaft)

The footplate of the stapes is large and roughly oval The footplate of the stapes is large and roughly oval in shape; it is narrow ventrally and broadly rounded in shape; it is narrow ventrally and broadly rounded dorsallydorsally

Shaft is slightly thicker ventrally than dorsally and Shaft is slightly thicker ventrally than dorsally and runs ventrolaterally and posteriorly to reach the runs ventrolaterally and posteriorly to reach the quadratequadrate

The distal end of the shaft fits into a recess in the The distal end of the shaft fits into a recess in the quadrate but falls short of the floor of the recess; this quadrate but falls short of the floor of the recess; this suggest that there is a cartilaginous continuationsuggest that there is a cartilaginous continuation

The dorsal process of the stapes The dorsal process of the stapes

contacts the underside of the contacts the underside of the

tabular tabular lateral to the tabular-lateral to the tabular-

supraoccipitalsupraoccipital contact contact

VertabraeVertabrae*There are many similarities between *There are many similarities between OphiacodonOphiacodon and and VaranosaurusVaranosaurus but the characteristics that define but the characteristics that define VaranosaurusVaranosaurus can be seen in the vertebral column can be seen in the vertebral column

There are 25-27 presacral vertebrae (which There are 25-27 presacral vertebrae (which includes the atlas and axis) and 2 sacral includes the atlas and axis) and 2 sacral vertabrae of the axial skeletonvertabrae of the axial skeleton

The atlantal centrum and axial intercentrum fuse The atlantal centrum and axial intercentrum fuse to form the Atlanto-axial complexto form the Atlanto-axial complex Degree of fusion between the elements may be due to Degree of fusion between the elements may be due to

maturity rather than taxonomic distinction; Complex maturity rather than taxonomic distinction; Complex probably not seen in juvenilesprobably not seen in juveniles

The plane of fusion between the elements runs The plane of fusion between the elements runs posteroventrally which is a direction opposite to that posteroventrally which is a direction opposite to that seen in ophiacodon (posterodorsally)seen in ophiacodon (posterodorsally)

There are small parapophyseal articulation for There are small parapophyseal articulation for the axial ribs present on the the axial ribs present on the axial intercentrumaxial intercentrum which are thinner and narrower than those in which are thinner and narrower than those in ophiacodonophiacodon

The The atlantal neural archatlantal neural arch is composed of two is composed of two elements that did not fuse dorsally; ventromedial elements that did not fuse dorsally; ventromedial facets articulate with the anterior edge of the facets articulate with the anterior edge of the atlantal centrumatlantal centrum Wing-like processes on the neural arches are smaller in Wing-like processes on the neural arches are smaller in

size than those in ophiacodon size than those in ophiacodon No dorsally directed neural spine present in No dorsally directed neural spine present in

varanosaurusvaranosaurus

The axial centrum has a shallow but well-defined The axial centrum has a shallow but well-defined ventral keelventral keel

A horizontally directed ridge runs from the A horizontally directed ridge runs from the posterior limit of each transverse process back to posterior limit of each transverse process back to the ridge of the centrumthe ridge of the centrum

The The pedicle of the neural archpedicle of the neural arch is defined by a is defined by a posterior constriction located just above the posterior constriction located just above the transverse processestransverse processes

Dorsal VertebraeDorsal Vertebrae Dorsal centra are amphicoelous (concave on both Dorsal centra are amphicoelous (concave on both

sides)sides) Anterior and posterior ends are slightly tapered Anterior and posterior ends are slightly tapered

at ventral portion for the reception of a small at ventral portion for the reception of a small intercentraintercentra

The articular facets of the The articular facets of the anterior zygopophysesanterior zygopophyses are tilted ventromedially (~20are tilted ventromedially (~20oo to the horizontal to the horizontal plane) where as those of the plane) where as those of the posterior posterior zygopophyseszygopophyses are angled dorsolaterally (~15 are angled dorsolaterally (~15oo ) )

Posterior vertebrae appear to be more tightly Posterior vertebrae appear to be more tightly articulated at both the anterior and posterior articulated at both the anterior and posterior zygopophyses than those of the anterior zygopophyses than those of the anterior vertebraevertebrae

Transverse processes are well developed Transverse processes are well developed especially in the 6especially in the 6thth and 7 and 7thth presacrals where its presacrals where its length is nearly ¾ the width of its centrumlength is nearly ¾ the width of its centrum

Neural arches seen in varanosaurus differs from Neural arches seen in varanosaurus differs from that seen in the other members of the familythat seen in the other members of the family Neural arches of the 3Neural arches of the 3rdrd & 4 & 4thth presacrals are similarly presacrals are similarly

proportionedproportioned The 5The 5thth & 6 & 6thth neural arches are wider while the 7 neural arches are wider while the 7thth, 8, 8thth, ,

and so forth are distinctively “swollen”and so forth are distinctively “swollen” There is an alternation in height of the neural There is an alternation in height of the neural

spines in some regions of the vertebral column spines in some regions of the vertebral column (mid-column)(mid-column) A feature known in a variety of Late Paleozoic tetrapodsA feature known in a variety of Late Paleozoic tetrapods

Shorter or low spines are narrow transversely Shorter or low spines are narrow transversely and elongated anteroposteriorlyand elongated anteroposteriorly Bases of the spines are long and narrowly Bases of the spines are long and narrowly

subrectangular in outlinesubrectangular in outline Shorter spines include presacrals 5, 8, 12, 14, 16, 19, Shorter spines include presacrals 5, 8, 12, 14, 16, 19,

and 22and 22 In lateral view, the taller spines are trapezoidal In lateral view, the taller spines are trapezoidal

or conical and angled slightly posteriorlyor conical and angled slightly posteriorly Bases of the spines are oval in outlineBases of the spines are oval in outline Tall spines include those not listed aboveTall spines include those not listed above Presacrals 20 and 24-26 are unknown because the Presacrals 20 and 24-26 are unknown because the

vertebrae or the spines are missingvertebrae or the spines are missing

Sacral Vertebrae and Sacral RibsSacral Vertebrae and Sacral Ribs Two Sacrals are present in vertebral columnTwo Sacrals are present in vertebral column

They are more robustly constructed than all of the They are more robustly constructed than all of the presacral vertebrae and are also generally shorter in presacral vertebrae and are also generally shorter in lengthlength

The neural arches continue smoothly up to sharp, The neural arches continue smoothly up to sharp, narrow neural spines which do not have any pattern of narrow neural spines which do not have any pattern of height alternation seen in the presacral columnheight alternation seen in the presacral column

A ridge is present in the second sacral vertebrae which A ridge is present in the second sacral vertebrae which runs parallel to the anterior marginruns parallel to the anterior margin

The proximal portion of the The proximal portion of the first sacral ribfirst sacral rib extends laterally for a short distance and then extends laterally for a short distance and then angles angles

downwards; the distal portion downwards; the distal portion

of the rib expands broadly to of the rib expands broadly to

form a fan-shaped surfaceform a fan-shaped surface

Anterior edge of first sacral rib turns sharply Anterior edge of first sacral rib turns sharply towards a vertical planetowards a vertical plane

Distal portion of Distal portion of second sacral ribsecond sacral rib is not as is not as broadly expanded as the first but is thicker broadly expanded as the first but is thicker dorsoventrallydorsoventrally

The distal expansions of both sacral ribs lay close The distal expansions of both sacral ribs lay close to the horizontal plane to the horizontal plane

Caudal Vertebrae and Caudal RibsCaudal Vertebrae and Caudal Ribs The 3 caudals following the sacral complex show The 3 caudals following the sacral complex show

little decrease in size and proportion; spines of little decrease in size and proportion; spines of these caudals appear to be narrowthese caudals appear to be narrow

The base of the tail is relatively thick; the The base of the tail is relatively thick; the proximal caudal vertebrae is stoutly built and proximal caudal vertebrae is stoutly built and lacked expanded neural archeslacked expanded neural arches

Central length of the caudal does not change Central length of the caudal does not change much by the middle of the tail but the transverse much by the middle of the tail but the transverse measure decreases substantiallymeasure decreases substantially

Haemal archesHaemal arches are clearly present beyond the 7 are clearly present beyond the 7thth caudal; in addition, the articular surfaces caudal; in addition, the articular surfaces

of the transverse processes are of the transverse processes are

circular in outlinecircular in outline Haemal arches reach as far back Haemal arches reach as far back

as the 30as the 30thth caudal caudal

By the middle of the tail, the centra are By the middle of the tail, the centra are narrower; neural arches are less built with narrower; neural arches are less built with shallow excavations at their basesshallow excavations at their bases

The posteriormost portion of the tail retains The posteriormost portion of the tail retains approximately the same length as the cauduals approximately the same length as the cauduals anterior to the sectionanterior to the section

Neural arches and spines still persist as distinct Neural arches and spines still persist as distinct structures even in the posteriormost portion of structures even in the posteriormost portion of the tail; transverse processes cannot been seen the tail; transverse processes cannot been seen in this portionin this portion

ReferencesReferences Berman, D. S, R. R. Reisz, J. R. Bolt, and D. Scott. 1995. The Berman, D. S, R. R. Reisz, J. R. Bolt, and D. Scott. 1995. The

cranial cranial anatomy and relationships of the synapsid anatomy and relationships of the synapsid VaranosaurusVaranosaurus (Eupleycosauria: (Eupleycosauria: Ophiacodontidae) from the Ophiacodontidae) from the Early Permian of Texas and Oklahoma. Early Permian of Texas and Oklahoma. Annals of Carnegie Annals of Carnegie MuseumMuseum, 64:100-133. , 64:100-133.

Palaeos.com Palaeos.com http://www.palaeos.com/Vertebrates/Units/390Synapsida/390.000.html

Romer, A.S. and L. I. Price. 1940. Review of the Pelycosauria. Romer, A.S. and L. I. Price. 1940. Review of the Pelycosauria. Bulletin of the Bulletin of the Geological Society of America Special Geological Society of America Special PapersPapers, 28: 1-538., 28: 1-538.

Sumida, S. S. 1989. Reinterpretation of vertebral structure in Sumida, S. S. 1989. Reinterpretation of vertebral structure in the Early the Early Permian pelycosaur Permian pelycosaur Varanosaurus acutirostrisVaranosaurus acutirostris (Amniota, Synapsida(Amniota, Synapsida). Journal ). Journal of Vertebrate Paleontologyof Vertebrate Paleontology, , 9:451-158. 9:451-158.