Theropoda: Avetheropoda: Allosauridae

Allosauridae: Allosaurus. Allosaurus > Sinraptor. Padian et al. (1999). 

Introduction: The Allosaurids evolved from something close to the Sinraptorids, and replaced them as the top carnivores of the Kimmeridgian and Tithonian ages (latest Jurassic period). The two groups are pretty similiar in size and appearance, and differ only in detail. Representatives of this family include Allosaurus, Neovenator, Valdoraptor, Acrocanthosaurus (although this genus is sometimes considered a Carcharodontosaurid), and probably Wakinosaurus and the poorly known Mongolian form "Chilantaisaurus maortuensis." (adapted from MAK)

Range: Middle Jurassic-mid-Cretaceous. 

Phylogeny: Allosauroidea:: Carcharodontosauridae + *. 

Characters: Most of the following applies to Allosaurus, the only certain member of the taxon. Up to 12 m for Allosaurus, but * may also include the larger Giganotosaurus (more probably a Carcharodontosaur); skull large but very narrow (indeed the entire animal is extraordinarily narrow in anterior view); skull is largely composed of buttressed arches, rather than plates, except for the nasal-lacrimal shield along the dorsal midline; skull apparently had ability to expand laterally; in Allosaurus, the lacrimal seems remarkably fragile above the orbits and may have been protected by a crest or horn-like structure attached to rugose flanges of the lacrimals on the postero-dorsal margin of the pre-orbital fenestrae. Premaxilla with 5 pairs of teeth; "tooth plates" (modified cingula?) at base of teeth; all tooth plates fused together; posterior end of angular not anterior to articular; unique, neomorphic anarticular bone present; vomers do not contact pterygoid; $ single mandibular fenestra small externally; upper jaw with about 20 teeth, lower jaw with 13; $ deep anterior ramus of surangular; nasal with 1-3 pneumatic openings; dorsolateral horn of lacrimal high; ventral process of lacrimal uniformly convex; lacrimal may contact maxilla externally; small, triangular prefrontal; small rugose anterior projection on post-orbital; $ short quadrate, with head at the level of middle of orbit; separate exit from braincase for opthalmic branch of trigeminal (Vth) nerve; large basal tubera below occiput; paroccipital process turns strongly downward; hyposphene hypantrum articulation present only from 6th dorsal vertebra; caudal vertebrae without hyposphenes; furcula present; sacrum massive; manus bears 3 strongly recurved unguals, although arm is short and slender; brevis shelf narrow; pubic boot is very prominent; $ pubic boot longer anteriorly than posteriorly & triangular in ventral view; ribs and distal elements of hind limb are oddly delicate and slender; tall ascending process of astragalus; astragalus lacks extensive contact with fibula. 

Links: DD: Allosauridae. 

References: Currie & Carpenter (2000); Currie & Zhao (1993) . ATW010426.

Acrocanthosaurus: Stovall & Langston, 1950.  A. atokensis Stovall & Langston, 1950.  

Range: Early Cretaceous (Aptian-Albian) of North America (Oklahoma)

Phylogeny: Allosauridae : Carcharodontosauridae + *.  [CC00].

Characters: 6+m [CC00]; Dermal skull: skull 129cm long [CC00]; facial horns absent [CC00]; premaxillae meet at acute angle, forming sharp, narrow anterior margin [CC00];  subnarial foramen between premaxilla & maxilla [CC00]; antorbital fenestra very large & triangular [CC00]; antorbital fenestra with overhanging anterioventral rim, covering small promaxillary fenestra [CC00]; nares small & elongate [CC00]; naris formed by premaxilla & nasal, excluding maxilla [CC00]; maxilla with 2 accessory fenestra [CC00]; maxilla taller than long [CC00]; maxilla, anterior margin slopes posterodorsally [CC00]; maxilla forms most of anterior margin of antorbital fenestra [CC00]; maxilla rugose only anteriorly & near tooth row [CC00]; maxilla posterodorsal process passes between nasal and antorbital fenestra, bifurcating distally to embrace anteroventral process of lacrimal.[CC00]; maxillary fenestra between naris & antorbital fenestra [CC00]; nasal flat, narrow, 4x length of frontal [CC00]; nasal with groove for maxilla articulation, allowing some lateral rotation of maxilla [CC00]; nasal overlaps lacrimal & frontal [CC00]; lacrimal forming low ridge anterior to orbit (but not horn as in Sinraptor) [CC00]; lacrimal contacts postorbital under lappet of prefrontal [CC00]; "the posterior margin of the ventral (preorbital) process of the lacrimal has a double concavity separated by a short process (for attachment of the ligamentum suborbitale) that marks the anteroventral extent of the eyeball itself (diameter was about 11 cm)" [CC00]; nasal & lacrimal with straight, slightly rugose ridge separating dorsal & lateral exposures [CC00]; prefrontal large & triangular [CC00]; prefrontal contacts postorbital & may participate in orbit, excluding frontal [CC00]; frontals "more or less" fused, as is frontal-parietal suture [CC00]; skull roof narrow [CC00]; parietals perpendicular to vertical occiput [CC00]; sagittal crest absent [CC00]; jugal participates in antorbital fenestra [CC00]; jugal overlaps lacrimal so that lacrimal-maxilla contact absent [CC00]; jugal form posteroventral margin of orbit [CC00]; jugal, postorbital process huge & triangular [CC00]; orbit key-hole shaped & narrow [CC00]; cheek flat, vertical, at sharp angle to skull roof [CC00]; postorbital with thick, rugose rim [CC00]; postorbital, intertemporal ramus short and almost vertical [CC00]; postorbital forming wide postorbital bar [CC00]; lower temporal fenestra piriform & bordered dorsally by short intertemporal bar [CC00]; jugal & quadratojugal moderately invade lateral temporal fenestra [CC00]; quadratojugal overlaps quadrate, curving onto occipital surface [CC00]; squamosal with deep quadrate cotylus, probably exposing head of quadrate in lateral view [CC00]; "Posteroventrally, the squamosal extended along the dorsal surface of the paroccipital process, covering up the ventrolateral process of the parietal and wrapping around onto the anterodorsal surface of the distal end of the paroccipital process. The squamosal was inclined in such a manner that it would have roofed over the posterior temporal musculature" [CC00: 217]; Occiput: supraoccipital forms double boss behind low nuchal crest [CC00]; supraoccipital with strong midline ridge [CC00]; paroccipital process broad & shallow, turning ventrally at lateral ends, without distal posterior projection [CC00]; occipital condyle circular, not flattened [CC00]; Mandible: jaw with large external mandibular fenestra [CC00]; dentary long and low, laterally smooth with large mental foramina [CC00]; dentary with ventral process under symphysis [CC00]; angular with thickened ventral rim [CC00]; angular having sliding contact with dentary [CC00]; retroarticular process oriented posteromedially [CC00]; supradentary present, unknown if fused to coronoid [CC00];  Dentition: premaxilla with 4 teeth, maxilla with 15 teeth (dentary count unknown) [CC00]; teeth without wrinkled enamel [CC00]; premaxillary teeth blade-like, not D-shaped [CC00]; Axial: body high and narrow [CC00]; neural spines >2.5x length of centra [CC00]; precaudal centra strongly excavated with complex pleurocoels [CC00]; cervical neural spines with triangular anterior processes inserting into depressions under overhanging processes on preceding neural spines [CC00]; mid- and distal caudals with posteriorly placed neural spines [CC00]; mid-caudal vertebrae with accessory transverse processes [CC00]; Appendicular: arm short (81% femur length) [CC00]; scapula long slender, gently curved [CC00]; deltopectoral crest large, quadralateral [C00].  

References: Currie & Carpenter (2000) [CC00]; Franzosa & Rowe (2005) [FR05].  ATW060217.

Carcharodontosauridae: Giganotosaurus. Carcharodontosaurus > Allosaurus

Introduction: Carcharodontosaurids are Allosaurid cousins that flourished in Gondwanaland (but not, strangely enough, in the north). They include the largest ever land carnivores, and some even exceeded Tyrannosaurus rex in size (although not by much). The skull of carcharodontosaurids is long and narrow. Unlike the tyrannosaurs, these animals could not have possessed binocular vision if they normally looked down the length of the snout. This assumption about the direction of theropod vision may itself be flawed. Many theropods have frontated orbits, eyes which were separated only by a narrow strip of frontal. They may, therefore have looked at the world over the bridge of the nose (like humans) with the mouth directed downwards.

This group includes Bahariasaurus, Carcharodontosaurus, Giganotosaurus, and possibly Acrocanthosaurus (although this form is generally considered an Allosaurid). They show some unusual convergences with the abelisaurids, another group of Gondwana theropods. As yet it is not clear whether this means the abelisaurs, despite their many very primitive features, are actually allosaurs, or whether the two lineages had to evolve in similiar ways to similiar unique environmental conditions. (ATW & MAK)

Range: Early Cretaceous-Late Cretaceous of Afr. NAm & SAm. 

Phylogeny: Allosauridae : Acrocanthasaurus + *. 

Characters: Very large allosauroids; maxilla with strongly rugose lateral face [CC00]; lacrimal forming low ridge anterior to orbit [CC00]; horizontal shelf of bone covering each eye; parietal forms obtuse angle with occiput [CC00]; paroccipital process with distal posterior projection [CC00]; eustachian system tripartite as in crocodiles; teeth with wrinkled enamel [CC00]; teeth not curved; horizontal undulations on compressed, blade-like teeth; undulations curved toward the tip of tooth near its cutting edges; lowest tibia / femur ratio of non-avian theropods; 

Note: Acrocanthosaurus is usually placed in this taxon. But see, Currie & Carpenter (2000). 

Links: DD: Carcharodontosauridae; Carcharodontosaurids; Giganotosaurus - Enchanted Learning Software; Discussion of Deltadromeus and Carcharodontosaurus; g00n2a3.pdf; MEA592D Dinosaur Osteology: Lecture 4. 

References: Currie & Carpenter (2000) [CC00].  ATW060214.

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