Box Relationships Of The Dinosaurs

The Dinosauria (see cladogram) consist of two main clades (Gauthier, 1986; Benton, 1990a; Sereno, 1999), the Saurischia and Ornithischia. The Saurischia fall into two main clades, the Theropoda and Sauropodomorpha. Within Theropoda, the main outlines are widely agreed, with the coelophysoids and ceratosaurs near the base, then various larger flesh-eating groups (e.g. megalosaurids, allosaurids, spinosaurids), then tyrannosaurids and maniraptorans (troodontids, dro-maeosaurids, birds). Much of the detail is controversial.

We use here the most thorough recent analyses of theropod relationships: Rauhut (2003), for the outline of major theropod groups, and Clark etal. (2002) and Maryanska et al. (2002) for maniraptorans and basal birds. Sereno (1999) regards herrerasaurids as basal theropods, whereas they are indicated as basal saurischi-ans here (Langer et al., 1999). Earlier authors (e.g. Gauthier, 1986; Holtz, 1994; Sereno, 1999) recognized a broad-based ceratosaur clade, whereas Rauhut (2003) finds that coelophysoids and ceratosaurs are successive outgroups. Holtz (1994) identified a major theropod clade, termed the Arctometatarsalia, that included tyrannosaurids, ornithomimids and troodontids. This is not accepted here (Rauhut, 2003). Among Maniraptora (Gauthier, 1986), major changes have been the move down the tree of the alvarezsaurids (Chiappe et al., 2002), formerly regarded as fully-fledged birds, and the move of oviraptorosaurs into Aves (Maryanska et al., 2002). Sereno (2001) pairs alvarezsaurids with ornithomimids, but we retain them simply as an outgroup on the main stem to birds.

The Sauropodomorpha includes the Triassic and Jurassic Prosauropoda, possibly a clade, or more probably a sequence of outgroups to Sauropoda (Yates, y 2003b). Within Sauropoda (Upchurch, 1998; Curry Rogers and Forster, 2001; Wilson, 2002), the Early and Middle Jurassic vulcanodontids and euhelopodids are outgroups to six major families of giant sauropods, mainly Late Jurassic to Cretaceous in age.

The Ornithischia (Sereno, 1986, 1999) have a possible primitive member, Pisanosaurus, and two main clades, the Cerapoda and the armoured Thyreophora, jointly the Genasauria. The Early Jurassic fabrosaurid Lesothosaurus is an outgroup to the Genasauria. The Cerapoda include a series of unarmoured bipedal or-nithopods of the Jurassic and Cretaceous, leading to the hadrosaurs, as well as the horned ceratopsians and bone-headed pachycephalosaurs, which together make up the Marginocephalia. The Thyreophora consists essentially of the Stegosauria and the Ankylosauria, with Scelidosaurus and Scutellosaurus, Early Jurassic forms, as basal representatives.

continued i

ro 4












Cladogram showing the postulated phylogenetic relationships of the main groups of dinosaurs. Synapomorphies from Rauhut (2003) and Clark etal. (2002) on theropods, Yates (2003b) on basal saurischians and basal sauropodomorphs, Upchurch (1998), Curry Rogers and Forster (2001) and Wilson (2002) on sauropods and Sereno (1986, 1999) on ornithischians. Synapomorphies: A DINOSAURIA, exposed quadrate head in lateral aspect, ectopterygoid lies dorsal to pterygoid, elongate deltopectoral crest on the humerus, brevis shelf on ventral surface of postacetabular part of ilium, extensively perforated acetabulum, tibia with a posterolateral flange, ascending astragalar flange on anterior face of tibia; B SAURISCHIA, lacrimal exposed on the dorsal skull roof, cervicals 3-6 longer than the axis, accessory articulations between vertebrae (hyposphene-hypantrum), hand more than 45% of humerus + radius, first phalanx of thumb longer than metacarpal I, hand digits 1 and 2 reduced to two and one phalanges respectively, prominent supraacetabular-preacetabular buttress on the ilium; C, premaxilla-nasal suture below naris absent, large subnarial foramen, erect L-shaped lacrimal, cervicals 7-9 longer than the axis, radius less than 80% of the humerus, thumb claw at least as long as claw of digit 2, digit 2 in he eg hand longer than digit 3, posterior margin of Iliac blade Is square In outline, large expansion of distal end of Ischium; D THEROPODA, anterior tympanic recess In braincase, 4-branched palatine bone, additional articulation In middle of lower jaw, pleurocoels In cervicals, elongate and curved anterior wing on Iliac blade, tibia bears a ridge at the proximal end for contact with fibula, metatarsal I reduced and attached to metatarsal II and does not reach the ankle joint proximally; E, tooth row ends at anterior rim of the orbit, pleurocoels In cervicals developed as foramina that Invade the vertebral body; F, lesser trochanter In femur broadened and wing-like, distal end of femur well rounded, distal articular facet of tibia broadly triangular In outline, facet for the tibia on the calcaneum; G CERATOSAURIA, external nares face anterolaterally, upper temporal fenestrae almost meet In front, quadrate foramen absent, neural spines of mid-caudals rod-like and vertical; H TETANURAE, maxillary fenestra In antorbital fossa, lesser trochanter proximally placed but lower than greater trochanter, sharp ridge on tibia for close attachment to fibula offset from proximal end; I CARNOSAURIA, ascending process of maxilla offset from anterior rim of maxilla, cervical centra strongly opisthocoelous, metacarpal I very stout and about as broad as long; J SPINOSAUROIDEA, premaxilla In front of naris elongate and rounded snout, enlarged fang-like teeth In the dentary; K ALLOSAUROIDEA, antorbital fossa extends on to the nasals, distal ends of paroccipital processes entirely below the foramen magnum; L COELUROSAURIA, maxillary antorbital fenestra more than 40% the length of the external antorbital fenestra, no serrations on premaxillary teeth, feathers; M MANIRAPTORIFORMES, upper temporal fenestrae confluent over the parietals and parietals form a sagittal crest, fewer than 41 caudals, medial side of metacarpal II straight and without proximal expansion, femoral head separated from the greater trochanter by a cleft, lesser trochanter as high as or higher than greater trochanter; N, jugal antorbital fossa absent or a slight depression, lacrimal fenestra absent, more than five sacral vertebrae; O MANIRAPTORA, fewer than 35 caudals, coracoid longer than high, Internal tuberosity on humerus rectangular, semilunate carpal, obturator process of Ischium distally placed, distal end of tibia broadly rectangular and more than three times wider than long, fibular shaft narrows to a thin splint, metatarsal V reduced and rod-like, contour feathers; P, ossified ventral rib segments, sternum with lateral process, glenoid facet on scapula faces ventrolaterally; Q, hyposphene wide, ten or fewer caudals with transverse processes, fewer than 11 caudals with well developed neural spines, anterior caudals box-like, acromion process of scapula low, coracoid subrectangular In outline, shaft of metacarpal III bowed laterally, anterior process of Ilium longer than posterior; R DEINONYCHOSAURIA, premaxillary teeth with serrated carinae, digit IV of the foot much longer than II and only slightly shorter than III; S SAUROPODOMORPHA, skull less than 50% length of the femur, anterior end of premaxilla deflected, lanceolate teeth with coarse serrations, at least ten cervical vertebrae forming elongate neck, dorsal and caudal vertebrae added to sacrum, forelimb at least 50% length of hindlimb, enormous thumb equipped with an enlarged claw; T, five premaxillary teeth, hand claw II Is less than 75% the size of claw I In all dimensions; U, short hand, femur straight In anterior view, femoral head not offset; V, short lacrimal and triangular antorbital fenestra, jugal excluded from margin of antorbital fenestra, four premaxillary teeth, digit I Is longest In the hand, phalanges In digits II and III shortened; W SAUROPODA, four or more sacral vertebrae, forelimb Is two-thirds the length of the hindlimb or more, metacarpal V enlarged and robust, femur Is straight and lesser trochanter Is reduced or absent, distal tarsals not ossified, foot claws deep and narrow, digit V of foot weight-bearing; X, fourth trochanter reduced to a low rounded ridge; Y NEOSAUROPODA, upper temporal fenestrae separated by broad bone bar, external mandibular fenestra closed, marginal tooth denticles absent, two or fewer carpal bones; Z MACRONARIA, external naris broader than orbit, coronoid H

process on lower jaw, 17 or fewer dentary teeth, posterior dorsal centra opisthocoelous, metacarpal I longer than metacarpal IV; AATITANOSAURIFORMES, mid-cervical centra elongate, dorsal ribs with pneumatic cavities, metacarpal I distal condyle undivided and perpendicular to shaft, Iliac preacetabular process semicircular; AB ORNITHISCHIA, cheek teeth with low subtriangular crowns, muscular cheeks [?or at V]; AC, reduced antorbital opening, palpebral bone, toothless and roughened tip of snout, predentary bone, jaw joint set below level of upper tooth row, at least five sacral vertebrae, ossified tendons above the sacral region, pelvis with pubis directed backwards, small prepubic process on pubis, long thin anterior process on Ilium; AD GENASAURIA, muscular cheeks, spout-shaped front to mandibles, reduction In size of mandibular foramen; AE THYREOPHORA, transversely broad postorbital provess of jugal, parallel rows of keeled scutes on the back and sides; AF, additional bones In margins of orbit, posterior process of Ilium reduced and anterior part enlarged, fourth trochanter on femur reduced, short and O

stocky metacarpals and metatarsals, loss of phalanx In digit 4 of foot; AGCERAPODA, gap between teeth of the premaxilla and maxilla, five or fewer premaxillary teeth, finger-like lesser trochanter on femur; AH MARGINOCEPHALIA, narrow shelf formed from parietal and squamosal bones that extends over the back of the skull, reduced contribution of premaxilla to palate short pubis; AI ORNITHOPODA, elongation of lateral process of premaxilla to contact lacrimal and/ or prefrontal, premaxillary tooth row offset ventrally compared with maxillary tooth row, crescentic paroccipital process, jaw joint set well below level of tooth rows; AJ EUORNITHOPODA, absence of prominent boss In cheek region, high angle between prepubic process and body of S

pubis; AK, external naris enlarged, antorbital fenestra reduced, back of skull narrow, close-packed teeth, premaxillary teeth absent, maxillary teeth with relatively high crowns and prominent ^

ridge on outside, wrist bones fused, spiked thumb, digits 1-4 of hand reduced, digit 5 of foot absent, ossified tendons extend from base of neck to middle of tail.

Nasal Bone And Jaw Fossil
Fig. 8.17 The ceratopsians: (a) skeleton ofPsittacosaurus; (b,c) skull ofProtoceratopsin lateral and dorsal views,with the cheek and major muscles restored; (d) skeleton of Centrosaurus. [Figure (a) after Zittel, 1932; (b, c) modified from Ostrom, 1966; (d) after Brown, 1917.]

trunk have high neural spines for the attachment of powerful muscles to hold the head up and there are bundles of ossified tendons over the hips. The real variation is seen in the skulls: some forms such as Centrosaurus (Figure 8.17(d)) have a simple horn formed by fused nasal bones, whereas others have this and a pair of'horns' on the jugals. The frill may be short or long and indeed Torosaurus had a skull 2.6 m long in which the frill is longer than the rest of the skull, the largest skull known from any land animal. The frills and horns may have been used in defence and as visual species-signalling structures as well as in threat dis plays. Male ceratopsians may have engaged in head wrestling with the horns interlocked, just as deer do today.

8.4.7 Stegosauria: the plated dinosaurs

The thyreophorans,the truly armoured ornithischians, are characterized by a transversely broad postorbital process of the jugal and by parallel rows of keeled scutes on the back surface of the body. The clade Thyreophora (see Box 8.5) includes some basal forms from the Early

Fig. 8.18 A basal thyreophoran (a,b) and a stegosaur (c): (a, b) skeleton of Scutellosaurus and an armour plate in lateral and dorsal views; (c) Stegosaurus. [Figures (a,b) after Colbert, 1981; (c) after Zittel,1932.]

Fig. 8.18 A basal thyreophoran (a,b) and a stegosaur (c): (a, b) skeleton of Scutellosaurus and an armour plate in lateral and dorsal views; (c) Stegosaurus. [Figures (a,b) after Colbert, 1981; (c) after Zittel,1932.]

Armor Plates For Dinosaurs

Jurassic, such as Scelidosaurus from England (and reported also from North America and China) and Scutel-losaurus from Arizona, USA (Colbert, 1981), and the more familiar larger groups Stegosauria and Anky-losauria that radiated in the Middle Jurassic. Scutel-losaurus (Figure 8.18(a)) is a modest-sized biped, with a skeleton similar to that of Lesothosaurus (Figure 8.11(c)), but it has numerous rows of keeled scutes (Figure 8.18(b)) over the back and in regular rows on the flanks.

Typical stegosaurs, such as Stegosaurus from the Upper Jurassic of North America (Figure 8.18(c)), have low, almost tubular skulls. The hindlimbs are much longer than the forelimbs, evidence of a bipedal ancestry, and the massive arched backbone supports large triangular bone plates that sit in a double row. The arrangement of the plates has been debated: was there a single row or two? This was hard to determine as the bony plates developed independently within the skin and did not meet the bones of the skeleton at all, but were presumably held firm by massive ligaments. A well-preserved specimen, with the plates in position, confirms the double, alternating row (Carpenter, 1998).

What were these plates used for? The plate surface is covered by branching grooves that probably housed blood vessels in life and they must have been covered by skin. Postulated functions for the plates include: (1) armour, (2) sexual display structures, (3) deterrent display structures and (4) thermoregulatory devices. Farlow et al. (1976) noted that the arrangement of the

Were Carpenter
Fig. 8.19 The ankylosaurs: (a) Polacanthus; (b) Euoplocephalusbody restoration; (c) Ankylosaurus tail club; (d,e) Euoplocephalus skull in lateral and dorsal views. [Figure (a) after Blows, 1987; (b) after Carpenter, 1982; (c-e) after Coombs, 1978.]

plates fitted engineering design models for heat-dissipation structures. As with the sails of the pely-cosaurs (see p. 121), Stegosaurus could have modified its body temperature by adjusting the blood flow to the fins and its orientation to the wind. An overheated animal could cool down rapidly by pumping high volumes of blood over the plates and standing broadside on to the prevailing wind.

8.4.8 Ankylosauria: armour-covered dinosaurs

Like the stegosaurs, the ankylosaurs (Coombs, 1978) arose in the Mid-Jurassic, but they are not well known until the Early Cretaceous. Polacanthus, a nodosaurid from southern England (Blows, 1987), is a typical early form with a mixture of spiny plates along the flanks and a fused mass of smaller plates over the hips (Figure 8.19(a)). The ankylosaurids such as Euoplocephalus and Ankylosaurus (Figure 8.19(b-e)) have broad armoured skulls and a body armour of plates rather than spines covering the neck, trunk and tail. Ankylosaurids also have massive bony bosses at the ends of their tails, formed by the fusion of the last caudal vertebrae and the incorporation of bony plates from the skin (Figure 8.19(c)). A blow from this club would readily disable Tyrannosaurus or any other contemporary predator.

The ankylosaur skull (Figure 8.19(d, e)) is a heavy box-like structure with massive overgrowths of the normal bones of the skull roof by a mosaic of new bone plates generated within the skin over the head. These cover the upper temporal fenestra in all genera and the lower one in most. Only a small orbit and nostril remain and even they are heavily overgrown.

0 0

Post a comment