Ophiacodontidae

1. Ophiacodontidae Thien Nguyen CSUSB Biology 680 - 2009

2. Introduction • Kingdom: Animalia • Phylum: Chordata • Superclass: Tetrapoda • Class: Synapsida • Order: Pelycosauria • Sub-Order: Ophiacodontia • Family: Ophiacodontidae

3. Ophiacodontia • Ophiacodontidae • 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 • Archeothyris • Clepsydrops • Ophiacodon • Varanosaurus

4. Introduction • Ophiacodonts first appeared in the late Carboniferous period. • Many were possibly semi- or fully aquatic animals. • 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

5. Ophiacodontia • 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

6. Jaw articulation is almost in-line or on the same level as the row of teeth • The jaw is slender • 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

7. 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 →

8. 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

9. The ilium is long but unexpanded dorsally but retains dorsal trough for axial muscle attachment • Pubic tubercle is usually present • Internal shelf for the puboishio- femoralis internus is present on the pubis

10. Ophiacodontidae • Features of the Skull • Always large and relatively narrow • Moderately to greatly elongated facial region • Numerous marginal teeth • 40-55 in upper jaw • Moderately developed canines • Stapes is a massive rod

11. Ophiacodontidae • 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. • Caudal muscles have no prominent area for attachment

12. Ophiacodontidae • Members of the family include: • Ophiacodon • Varanosaurus • Clepsydrops *These three are strikingly similar with only slight differences in their skull and vertebrae proportions and a few others.

13. Ophiacodon

14. Ophiacodon • 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

15. Ophiacodon • 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

16. Parietal bone is a single structure. Although in some Ophiacodon and Varanosaurus specimens, the interparietal is divided in two by a longitudinal fissure • 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

17. 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

18. 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

19. 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 fenestraovalis

20. 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

21. 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 • Both cavities are short antero- posterioly • Lateral cavity is deeply concaved • Medial cavity is flat

22. 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

23. 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

24. Transverse processes of the cervical and dorsal vertebrae are short (compared to other suborders) • The dorsal transverse processes is semicircular in section • 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 antero-posteriorly; cervical neural spines have stouter bases; spines in both cases have blunt tips and are never elongated

25. 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 • Highly characteristic feature of Ophiacodontidae • Atlantal intercentrum is large and underlains the atalantal centrum • Spine of axis expands antero- posteriorly and is thin anteriorly and thickened at the posterior edge

26. 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

27. 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 • 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

28. 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 dorso-ventral section

29. 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

30. 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 • Tubercle is reduced in Ophiacodon • The puboischiadic plate is relatively narrow dorso-ventrally

31. Appendages • Proximal segments of the limbs were short in comparison to the sphenacodontids or edaphosaurs • Front legs are smaller than hind legs • 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

32. 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

33. 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

34. 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 • 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 dorso- ventrally

35. 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

36. 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

37. 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

38. 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

39. 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

40. Manus & Pes • Complete data available for Ophiacodon; data incomplete in Varanosaurus and only isolated elements are available for Clepsydrops • 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

41. 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; • Its articulation with the first distal carpal is relatively broad • Has a small contact area with the third distal carpal • Primitive phalangeal formula retained • 2-3-4-5-3

42. 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 • Positioned side by side distal to the astragalus and medial to the fourth distal tarsal • Primitive phalangeal formula retained • 2-3-4-5-4

43. Varanosaurus

44. 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 • 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

45. 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 • Temp. fenestra has the outline of a right triangle w/rounded corners

46. 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

47. 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 • 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

48. The premaxilla is small and lightly built; It has room for 6 teeth • 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

49. 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

50. 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) • 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