The tetanurans, the “fused tails”, make up the second clade of theropods.  They lack a fang-like tooth in the gap between maxillary and premaxillary bones of the upper jaw that most ceratosaurs had.  One tetanuran, Protoceratosaurus bradleyi, possessed a nasal horn (Weishampel, p. 165). The end of the pubis expanded to form a pubic “boot” which anchored large leg muscles. The crested Antarctic dinosaur Cryolophosaurus seems to be a primitive tetanuran but its skeleton includes some features associated with ceratosaurs (Hammer, 1994). tetanuran characteristics
    Torvosaurus is the most basal tetanuran known whose relatives, such as Yangchuanosaurus, are known from various parts of the world (Lambert, 1990, Fastovsky, 1996).
Torvosaurus Yangchuanosaurus
Two interesting theropods, Baryonx and Spinosaurus are related to the torvosaurids. The early tetanurans (such as Torvisaurus and Spinosaurids) were large while most of the later coelurosaurs were small to medium sized, although two lineages, therizinosaurids and tyrannosaurs, evolved to large sizes (Serreno, 1999). Baryonyx, “heavy claws”, resembled a large crocodile.  One fossil specimen was found with a partially digested one meter long fish in its abdomen.  Baryonyx is unlike most other theropods in its long snout, its long and low nostril, its large hand claw, its large number of teeth, and a longer, straighter neck than most theropods.  Its large thumb claws would have been useful in grabbing fish.  It may have been capable of both bipedal and quadrupedal locomotion (Charig, 1997).  (Charig, 1986).
Baryonx 2
Spinosaurus ,“thorn lizard”, possessed a spinal frill, possibly for thermoregulation or display.   It was a fish eating theropod.  Suchomimus, an early spinosaurid, has a lower sail than Spinosaurus and has a thumb claw and other features which link it to Baryonx.

One find of Baryonyx included bones of a young iguanodont, indicating that its diet was not limited to fish. A spinosaurid tooth (similar to the spinosaurid Irritator) was found in the neck vertebrae of a pterosaur fossil, indicating that spinosaurids included pterosaurs in their diets (Buffetaut, 2004).

spinosaurus Suchomimus
There are a number of species of the family Megalosauridae,  great lizards”, known from Europe and Asia (and perhaps Africa).  They possessed three large clawed digits on both hands and feet.  On their feet, one small toe faced backwards. Poekilopleuron was one of the first known dinosaurs, described in 1838 but the original specimen was destroyed in World War II.  Megalosaurus may be a synonomous name for Poekilopleuron (Allain, 2002).  Altispinax possessed lengthened vertebral neural arches which formed a low sail.
Dryptosaurus is the only known member of a group that may be related to Megalosaurus.

    The Allosauridae, “different lizards”, were the top predators of the Jurassic.  Their neck had an S-shaped curve and they had small hornlets on their heads.  They were the most common predators of the Late Jurassic.   Perhaps a group of allosaurs could have hunted the large sauropods.  The various species of this group are known from every continent except Antarctica.

     Allosaurus was the largest allosaur, reaching 12 meters in length.  It possessed short arms. One fossil site in Utah includes more than 10,000 disarticulated bones with individuals of every age group, including young.  This suggests that allosaurs lived in groups and perhaps hunted in packs.

     Eustreptospondylus  was similar to Allosaurus but was smaller and lived on the island which is now England (Lambert, 1990, Fastovsky, 1996). The 4 meter long Gasosaurus and the similar Piatnitzkysaurus may represent ancestors of the allosaurs (Czerkas, 1990).

Allosaurus skull Allosaurus skeleton
     Tyrannosaurus rex was the largest known terrestrial predator for about 90 years but, in recent years, finds of Gigantosaurus and Carcharodontosaurus have challenged this title.  Gigantosaurus “gigantic lizard” had a skull which measured1.5 meters and its body estimated 12.5 meters making it larger than Tyrannosaurus (its femur was 2 inches longer than that of the largest known T. rex) and heavier (weighing 8 tons). Carcharodontosaurus possessed a 62 inch skull—3 inches longer than that of T. rex and about the size of Gigantosaurus.  Unfortunately, the leg bones are unknown so that estimating its body size is not possible.  T. rex is known from North America, Gigantosaurus from South America, and Carcharodontosaurus from Northern Africa.  Saurophaganax, Spinosaurus, and Acrocanthosaurus are also about the same size (Zimmer, 1997)  .
gigantosaurus Carcharadontosaurus
Acrocantosaurus Acrocanthosaurus skull
Compsognathus foot

     The first known member of the family Compsognathidae was Compsognathus, “pretty jaws”. Measuring 2-3 feet in length, it was the smallest known dinosaur until the discovery of Microraptor. It lived in the Late Jurassic.  One fossil specimen died with a lizard in its stomach.  Compsognathus had only 2 fingers and resembled birds in the structure of its ribs, shoulders, and wrists (Lambert, 1990, Fastovsky, 1996).

   In 1996, a compsognath named Sinosauropteryx from China was found with feathers.  Sinosauropteryx possessed downy feathers that were only about 2 cm long-- some had quills and they were not suited for flight.  Most of the feathers were on the neck, back, and tail and were not observed on limbs.  Sinosauropteryx is the only dinosaur that has been preserved with a mammal in its gut.  (Chen, 1998; Padian, 1998;).

The theropod Irenichnites was about the size of a chicken (Russell, 1989).