The several species of the family Caenagnathidae, “recent jawless”, had birdlike toes and fusion of the bones of the foot.  They were about 2 meters in length and had a toothless beak (Lambert, 1990, Fastovsky, 1996).


    Troodon, “wounding teeth”, measured 2 meters in length and had the largest known dinosaur brain relative to its body size.  Because of its large eyes, some have suggested that it was nocturnal or at least able to hunt at twilight.  Troodon had a retractable claw on second toe; weaker and smaller claw than in dromaeosaurids (discussed next) (Lambert, 1990, Fastovsky, 1996).  An adult Troodon is preserved over one nest, suggesting that Troodon cared for their young.  The eggs were more similar to birds than to crocodiles and the eggs of the nests seem to have been laid over a series of days (Prum, 2002; Varricchio, 1997).  A troodontid fossil was found in a position typical of birds when they are asleep (Lemonick, 2004).

A tooth from a troodontid was found embedded in the fossil of a pterosaur thigh, indicating that pterosaurs were included in troodontid diets (Buffetaut, 2004).


Noasaurus is known from the Late Cretaceous of Argentina.  It had a retractable claw on its second toe.


     Segnosaurs, slow lizards”, were strange dinosaurs known from North America and Asia

.  They range in size from 2-9 meters in length and are known from the Late Cretaceous.  At first, incomplete fossils suggested that they belonged to a third order of dinosaurs, not Saurischia or Ornithischia. Falcarius was a basal therizinosauroid (segnosaur) theropod known from the early Cretaceous.

The segnosaurs (therinizosauroids) possessed leaf-shaped teeth and presumably made the transition from carnivory to herbivory. The feature of leaf-shaped teeth was already present in the earliest known member of the lineages, Falcarius, a 4 meter long theropod from the Early Cretaceous ( Kirkland, 2005).

Some members of the group possess 5 sacral vertebrae while others possess 6 ( Kirkland, 2005).A more recent segnosaur find of Beipiaosaurus resulted in 2 great observations: segnosaurs were coelurosaurian tetanurans and at least some of them had feathers (as did some other coeulurosaurs as will be discussed in the chapter with birds).



 They possessed lightly built bodies with a toothless beak, small sharp cheek teeth, and fleshy cheeks.  Their long legs bore 4 toes with claws and were perhaps webbed.  The skull is similar to that of ornithischians but lack a predentary bone.  The unconsolidated foot is similar to that of Plateosaurus but even more primitive than the earliest theropods.  The pelvis is unique as is depicted in the image below.

    Alxasaurus had claws as long as 28 cm, some tetanuran characteristics, prosauropod teeth, and may even have eaten plants.   (Lambert, 1990, Fastovsky, 1996).








There are several species of Oviraptoridae, “egg thieves”, known from Mongolia.  Because their jaws lacked teeth and they fossils have been found near aquatic environments, it has been proposed that Oviraptorids fed on eggs or shellfish.  Its name meaning “egg thief” resulted from in which an adult was found with eggs.  More recently, an Oviraptor fossil was discovered in which an adult was preserved sitting on its own eggs, in a brooding position similar to that of birds.   This adult stayed with its nest during a sandstorm and was buried along with the nest.  Instead of being an egg thief, evidence now suggests Oviraptor was a good parent (Lambert, 1990, Fastovsky, 1996).


Oviraptor resembled birds in its wrist, hips, and furcula (wishbone) and measured under 2 meters in length. Other oviraptorids, such as Concharaptor and Ingenia (whose hip is pictured below) are known.  Ingenia’s hip is unique in its outward curvature of pubis (Weishampel, p. 255).


  Avimimus, “bird mimic”, was a very birdlike theropod.  It possessed fused wrist bones and a toothless beak.  Avimimus possessed large orbits and fusion of its tibia, fibula, and proximal tarsals. It is unusual in that it retained its fifth metatarsal which have been lost in most theropods.  Evidence suggests that it possessed feathers on its short arms.  These feathers might have functioned for thermoregulation or display; Avimimus would not have been able to fly or even flutter with its feathered arms.   (Lambert, 1990, Fastovsky, 1996).


Caudipteryx was first classified as a theropod with feathers, later some concluded that it was an early flightless bird because of its longer legs and short tail.  If it were a theropod, it would be closer to the ancestry of birds that Protoarchaeopteryx.  It also had the two types of feathers seen in Protoarchaeopteryx.   Some classify Caudipteryx is a basal oviraptorosaur (Serreno, 1999; Qiang, 1998; Padian, 1998; Normile, 2000).


A fossil named Protarchaeopteryx seems to be a maniraptoran theropod.  It had gastroliths in its gut which would have prevented it from flying.  Protoarchaeopteryx had teeth, which most closely resemble those of Archaeopteryx.  It had a furcula but no significant changes to the sternum.  Not only did it possess plume feathers seen in other dinosaurs (which reached up to 2.7 cm in length) but it also had long symmetrical tail feathers over 13 cm in length.  These long feathers had a central shaft (rachis) and might have had interlocking barbs.  Its arm was shorter than that of birds but longer than other theropods (Qiang, 1998; Padian, 1998)




Microraptor is a basal dromaeosaurid, a sister taxon to all other dromaeosaurids.  It is the smallest non-avian theropod (55 cm long, weighing about 1 kg) and small size seems to be the condition of the earliest members of Deinonychosauria.  Flight feathers were found on all four limbs. It possessed a furcula  and a number of birdlike features of its teeth, hip, tail, and shoulder.  Microraptor, a basal dromaeosaur, also has a number of similarities to Sinoventor, a basal troodontid (Hwang, 2002). Its leg feathers may have been held ventral to the arms creating a "biplane" wing formation (Chatterjee, 2007). As in living raptors, the leg feathers may have had a role in prey capture (Chatterjee, 2007).


Most theropods have hips in which the pubis projects forward, unlike the condition in birds in which it projects backwards.  However, the theropods which seem to be most closely related to birds because of skeletal characteristics other than their hips, the pubis does possess the bird-like trait of projecting backwards.

Unenlagia hips

A juvenile dromaeosaur is known to have been covered in feathers. Bambiraptor was very similar to the first birds (although it is not known whether it possesed feathers or not).


  Dromaeosaurids, “running lizards”, were very fast predators with large “switchblade” second toe claws.  These claws would have been retracted while walking. 

velociraptor footvelociraptor skull

velociraptor foot

Dromaeosaurs possessed large shoulder elements to support large hands.  Dromaeosaurids possessed a large brain, 7x the size of crocodile brains (relative to body size) and within the range of birds and primitive mammals.  At one fossil site, several Deinonychus (“terrible claw”) individuals were found with a Tenontosaurus skeleton, suggesting that they traveled in packs to bring down large prey.  The position of their eye sockets suggest they had binocular vision.  This group of theropods are the closest known relatives to the bird ancestors (Lambert, 1990, Fastovsky, 1996).

Sinornithosaurus is the earliest known member of this group.  Itwas covered with 30-45 mm long and 1-3 mm wide filaments which are indistinguishable from feathers of birds preserved in the same deposits (Xu, 2001). Feathers are also known in a Sinornithosaurus-like fossil theropod which is also classified in the family Dromaeosauridae.  Its furcula is similar to that of Sinornithosaurus in its boomerang shape.  The feathers were preserved all around its body unlike Sinosauropteryx (Ji, 2001).


 Are birds dinosaurs?  This question will be examined in greater detail in the chapter on the origin of birds.  Certainly, there are few if any traits which can be used to identify a bird which cannot also be found in theropod dinosaurs, including feathers, holes in bones for lung tissue, brooding over eggs, furculas (“wishbones”), fused tailbones called furculas, and a variety of other traits.  The arms of dromaeosaurs and the wings of the first birds are virtually identical.

velociraptor arm

archaeopteryx arm

Archaeopterygids “ancient wings” are the most primitive birds but they also appear to have been modified dinosaurs.  Thus, theropods (and thus, dinosaurs) are a paraphyletic group since some of the descendants of the first dinosaurs, the birds, are not typically classified in this group.


It is unclear whether Rahona should be considered as a primitive bird or as a dromaeosaur which evolved flight independently of birds. Rahona