GEOL 104 Dinosaurs: A Natural History

Fall Semester 2014
Theropoda III, Eumaniraptora: Dinosaurs of the Air


Simplified cladogram of Eumaniraptora


More detailed phylogeny of Eumaniraptora

MAJOR GROUPS OF EUMANIRAPTORANS

Eumaniraptora is just one clade within Pennoraptora (and thus Maniraptora). The actual shared derived characters that unite them as a whole are a bit problematic, due to the uncertainty of the position of Archaeopteryx and its kin and the discovery that basal deinonychosaurs are far more Archaeopteryx-like than are the "classic" deinonychosaurs. Some probable transformations at the base of Eumaniraptora include:

The two major groups of eumaniraptorans belong to either Deinonychosauria or to Avialae. However, there are several eumaniraptorans whose exact placement is uncertain. For example, it is uncertain where the late Middle Jurassic (or early Late Jurassic) Pedopenna fits. It might be a basal avialian, or it might be outside eumaniraptora. The most significant of these early eumaniraptoras is Archaeopteryx and its kin.

ARCHAEOPTERYGIDAE
The best-studied, and longest-known, eumaniraptoran of the Late Jurassic is Archaeopteryx. Some paleontologists regard this as a single genus and species (A. lithographica); others divide it up into several genera (Archaeornis, Jurapteryx, Wellnhoferia, as well as Archaeopteryx). (For this course, we'll provisionally regard them as a single genus.)

The first and second specimens of this theropod were the first fossil skeletons with feathers ever discovered (in the 1860s and 1870s). Indeed, these were the first good maniraptoran fossils of the Mesozoic ever found. Consequently, Archaeopteryx has spent most of the last century and a half being considered a "bird". But as feathers have been found in other theropods, and the skeletons of basal deinonychosaurs have been discovered, the "birdiness" of Archaeopteryx has decreased.

Archaeopteryx came from the Late Jurassic of Europe. Isolated bones from western North America of the same age might be from a same or similar taxon.

There remain a few features that Archaeopteryx shares with Avialae (modern birds and the theropods closer to birds than to deinonychosaurs), but a new specimen also shows some features more similar to deinonychosaurs than to avialians. So at present, we can't be certain of the position of this little crow-sized dinosaur: indeed, addition of characters from what seem to be its closest relatives have really confused the issue!

In recent years new taxa have been found in China which seem to be closer to Archaeopteryx than to all other known taxa, forming a clade Archaeopterygidae. These are the latest Middle Jurassic/earliest Late Jurassic Anchiornis, which shows the presence of long leg feathers as in Archaeopteryx, basal dromaeosaurids, and various basal birds; Xiaotingia, Aurornis, and Eosinopteryx. Anchiornis was first thought to be an avialian basal to Archaeopteryx, then to be a basal troodontid; however, addition of the data from Xiaotingia pulls the archaeopterygids together and places them (although without strong statistical support) as basal members of Deinonychosauria. On the other hand, some studies do NOT find them as a monophyletic group, but instead place Archaeopteryx as a basal bird and a Xiaotingia+Anchiornis clade in Deinonychosauria; OR with that last clade as basal avialians, but outside an Archaeopteryx + more derived avialian clade; or other alternatives.

At present, it appears that the following three positions for Archaeopterygidae are quite possible, and there is not strong evidence to discount any of these:

So in some ways, the safest position at present is an unresolved three-way split between Deinonychosauria, Archaeopterygidae, and Avialae.

One comforting aspect of this uncertainty: archaeoptergyids are probably our best model for what the common ancestor of all Eumaniraptora looked like.

(A note on the use of the word "bird": this English term unfortunately carries with it a lot of intellectual baggage. If we hear that a fossil was from a "bird" we might assume that it had modern "bird" habits and adaptations (flight, song, tree nests, seed or insect diets, etc.). However, not all these characteristics are even true of all modern birds, much less of earlier branches of the lineage. So let's avoid calling Archaeopteryx a "Jurassic bird". There is no evidence that it was a seed eater; there is no evidence for song; it almost certainly nested on the ground; and as we will see it might not have been able to fly any better than early dromaeosaurids.)

DEINONYCHOSAURIA
The "raptor dinosaurs", broadly defined. Deinonychosauria ("Deinonychus lizards") were one of the two main branches of Eumaniraptora. Deinonychosaurs first appear in the Middle Jurassic (possibly; definitely by the Late Jurassic) and die out at the end of the Cretaceous. They are known from all over the world, and in habitats from deserts to coasts.

Deinonychosaurs show the following transformations from the ancestral condition:

In addition (possibly) to Archaeopterygidae, Deinonychosauria divides into two clades (at least in our present understanding): Dromaeosauridae and Troodontidae. The basal members of both groups are only about crow-sized (similar in size to Archaeopteryx, Pedopenna, and basal avialians).

DROMAEOSAURIDAE
The unquestionably carnivorous dromaeosaurids are known throughout the Cretaceous and from North and South America, Europe, Asia, Africa, and Madagascar.

Basal dromaeosaurs (Unenlagiinae and Microraptorinae) include some crow- to turkey-sized taxa: Rahonavis of the Late Cretaceous of Madagascar (and initially thought to be a bird); Microraptor of the Early Cretaceous of China (the first eumaniptoran for which the tail feathers were known); long-snouted Buitreraptor of Late Cretaceous Argentina; and others. Not all of these were small, however. One of the most unusual of these basal dromaeosaurids is giant Austroraptor of the mid Late Cretaceous of Argentina: a long-snouted, short-armed polar bear-sized unenlagiine. The very small size of unenlagiine teeth suggest that they ate only small bodied animals; we have definite evidence that at least some microraptorines ate their avialian cousins.

The more derived dromaeosaurids form a group called Eudromaeosauria. These were coyote-to-grizzly bear sized. Eudromaeosaurs include two major subclades. The more robust Dromaeosaurinae includes coyote-sized Dromaeosaurus of Late Cretaceous western North America; lion-sized Achillobator of mid-Late Cretaceous Asia; and grizzly-sized Utahraptor of the Early Cretaceous of western North America, at present the largest known eumaniraptoran. Well-studied examples of Velociraptorinae include coyote-sized Velociraptor of the Late Cretaceous deserts of Mongolia; wolf-sized Deinonychus of the Early Cretaceous of western North America; Acheroraptor of latest Cretaceous western North America, and bizarre double-sickle-clawed Balaur of Late Cretaceous Transylvania.

Dromaeosaurid caudals were more tightly interlocked than in typical theropods, and in microraptorines and eudromaeosaurs extensions from the chevrons and neural arches grew extremely long. The tail was thus an extreme dynamic stabilizer.

Some basal dromaeosaurids had elongate metatarsi (indeed, they have a primitive form of the arctometatarsus), but the majority had relatively short stout metatarsi and tibiae. This suggests that they had sacrificed speed, perhaps for agility (better able to turn quickly while pursuing prey or escaping predators, especially with the help of the stiffened tail). Despite certain books and movies to the contrary, the dromaeosaurids show no signs of being speed specialists.

While the small primitive forms may have eaten small prey (skewering it with the sickle claw in the manner of modern secretary birds, perhaps), the larger forms were predators of dinosaurs. The "Fighting Dinosaurs" specimen of Velociraptor shows it in combat with Protoceratops, the hands used to grasp the head of the herbivore while the sickle claw was ripping into the throat: very similar to the attacks used by large cats. Some (contraversial) evidence suggest that Deinonychus may have attacked the much larger iguanodontian Tenontosaurus in groups (packs or mobs).

Note that the sickle claw may have also been used to climb: either up trees, or up the sides of victims! Additionally, they may have been used to pin smaller prey down on the ground while the jaws and hand claws were used to kill it.

As discussed next lecture, at least some of the smaller basal forms may have had limited flight capability: indeed, they show somewhat better flight adaptations than Archaeopteryx and other archaeopterygids! The majority of dromaeosaurids, however, probably lived their lives on the ground (although hiding/sleeping in the trees may have been possible, especially for juveniles).

In the Early Cretaceous dromaeosaurids were major mid-sized predators, and in the deserts of Late Cretaceous Asia they were among the largest carnivorous dinosaurs present. However, with the rise of the tyrannosaurids large-bodied dromaeosaurids disappear in the Northern Hemisphere, and the Late Cretaceous dromaeosaurids of Asia and North America were fairly small animals.

[Hey, want to make eumaniraptoran systematics MORE confusing! Some studies suggest that microraptorines, unenlagiines, and/or troodontids might be more closely related to Aves than to the eudromaeosaurs; this would make microraptorines, unenlagiines, and/or troodontids members of Avialae!]

TROODONTIDAE
Troodontids were crow-to-deer sized theropods. The oldest troodontid may be Jinfengopteryx of China: described originally as a bird, but now recognized as a troodontid. It might be from the Middle Jurassic; but because the rocks it was found in are not well-dated, it could be as young as earliest Cretaceous. Like Archaeopteryx, Jinfengopteryx had long tail feathers all along its tail. Additionally, a Late Jurassic troodontid is known from western North America, but has not yet been named or fully described. The last troodontids are from the very end of the Cretaceous.

Troodontids differ from other eumaniraptorans by an increase in the number of teeth, reduced arm length, and increased distal hindlimb length. Tiny Sinovenator of the Early Cretaceous of China has a backwards-pointing pubis and lacks an arctometatarsus; later troodontids show a reversal to a forward-pointing pubis and have an arctometatarsus.

Troodontids have relatively lightly built snouts, suggesting that they did not tackle very large prey (particularly as their forelimbs were fairly short and lightly-built as well). The largest and most derived troodontids are not particularly large (turkey-to-deer sized), and had forward-facing eyes and leaf-shaped teeth with large denticles on the back. They may have had some plants in their diet, but toothmarked bones show that they definitely ate meat. (NOTE: if troodontids were omnivores, this would make Dromaeosauridae the only primarily carnivorous group of maniraptoriform. If true, this would almost certain be an evolutionary reversal, and indicate that Velociraptor and Deinonychus were descendents of omnivores or even herbivores!)

The more completely known troodontids include Mei and Sinornithoides of the Early Cretaceous of Asia (and both known from specimens buried in sleeping position!); Saurornithoides, Xixiasaurus, and Zanabazar of the Late Cretaceous of Asia; and Talos and Troodon (sometimes called Stenonychosaurus) of the Late Cretaceous of western North America, largest of the Troodontidae.

The large eyes of troodontids suggests to some that they may have been nocturnal. Possibly related to that, troodontids are by far the most common dinosaur in polar Late Cretaceous North American fossil sites (where light levels would have been very low during the winter), while they were no more common than dromaeosaurids in the rest of their range. Troodon is particularly notable by having the largest brain/body size of the non-pygostylian dinosaurs, and thus likely the "smartest" of the traditional dinosaurs.

AVIALAE
The remaining eumaniraptorans are the Avialae ("bird wings"), or "birds, broadly defined". (See note above, though, about the cautions of using the word "bird" for these early members of the lineage). If Archaeopterygidae is an avialian group (which remains a distinct possibility), than this clade is known from the Late Jurassic. If not (and if the scansoriopterygids are not avialians as well), than all our fossils of them are from the Cretaceous (but the lineage would have been present in the Middle and Late Jurassic, though, because of minimum divergence time with Deinonychosauria).

In addition to Archaeopterygidae, another possible set of Jurassic avialians are Scansoriopterygidae. Known from the poorly dated (possibly Middle Jurassic, possibly Late Jurassic, possibly even earliest Cretaceous!) Epidendrosaurus (also known as "Scansoriopteryx") and Epidexipteryx (which may just be the adult form of Epidendrosaurus!) these are among the smallest Mesozoic dinosaurs (pigeon-sized). As they are small enough, and have the distally-placed pedal digit I, it may be that they may have spent some time up in the trees. The skull shape and tiny teeth of the scansoriopterygids suggest that they might have been insect eaters or omnivores. Nearly all recent studies place these dinosaurs as the basalmost members of Avialae, but it is not inconceivable that they might wind out outside Eumaniraptora proper, or even some sort of tiny oviraptorosaurs.

Once upon a time (i.e., before the discovery of basal deinonychosaurs and new archaeopterygids) it was easy to distinguish Deinonychosauria and Avialae; now, not so much... Possible avialian shared derived features might be:

(A reduction in the number of caudals was once a likely avialian trait, but the primitive avialian Jeholornis has as many caudals as do basal dromaeosaurids...).

Despite some artistic and scientific reconstructions, there is at present no strong evidence that basal avialians were any better at flight than were dromaeosaurids like Microraptor and Rahonavis. Indeed, based on the shape and orientation of the shoulder joints, there is positive evidence that the basal avialians (and archaeopterygids) were in fact not very good at powered flight.

Much of our knowledge of the basalmost avialians comes from China. Jeholornis (also called "Shenzhouraptor": both names were proposed within weeks of each other) may be the most primitive avialian (other than Scansioropterygidae and Archaeopterygidae, perhaps). It was chicken-to-turkey sized, and gut contents show that it ate both seeds and fish. Like the dromaeosaurid Microraptor, Jeholornis had long tail feathers only at the end of its tail.

Larger still are the Omnivoropterygidae (sometimes called "Sapeornithidae"), which are the basalmost avialians to show a reduction and fusion of the distalmost caudals into a pygostyle (convergently evovled in the oviraptorosaur Nomingia and the therizinosauroid Beipiaosaurus). At present, all known omnivoropterygids are from a single formation (Jiufotang Fm. of China). At least some have stubby blunt teeth at the front of their snouts, suggesting a diet of seeds, fleshy parts of plants, and/or small invertebrates. In some recent studies omnivopterygids were found to be even more basal: more distantly related to modern birds than is Jeholornis.

The clade Pygostylia ("pygostyle ones") is comprised of all descendants of the concestor of Confuciusornithidae and modern birds. This group is further transformed from basal avialians by:

The Confuciusornithidae of Early Cretaceous eastern Asia are best known from Chinese Confuciusornis. Literally hundreds (if not thousands) of specimens have been discovered, making this crow-sized pygostylian the most common Mesozoic dinosaur fossil. Like modern birds, confuciusornithids had a toothless beak: however, this was convergent with Aves, since the branches between Confuciusornithidae and Aves are all toothed. These may have been at least partially plant- or fruit-eating (they co-occur with the oldest fruit!), but at least some confusiusornithids have fish in their gut contents.

Unlike Aves and their closest kin (together, the clade Euornithes), there was no tail fan in the Confuciusornithidae. Instead, most specimens show no major tail feathers, while others show two very long ones. Perhaps these were sexual signals, or growth indicators, or simply lost in the tail-featherless ones.

The hand of confuciusornithids was still a perfectly good grasping organ.

ORNITHOTHORACES
Before we move on, let's take a look at the postcranium of a modern bird (courtesy of Emporia State University's Vertebrate Structure and Development course:

(You'll note a lot of special terms, some of which we've already encountered.)

The remaining pygostylians form the clade Ornithothoraces ("bird chests"). These theropods are further derived in possessing:

The hands of ornithothoracines lacked grasping ability, having become true wings.

There are two main branches of Ornithothoraces: Enantiornithes and Euornithes.

The "opposite birds", Enantiornithes have a range from the early Early Cretaceous through the end of the Cretaceous. They seem to have been the most diverse and abundant group of birds during their history. Most enantiornithines were toothed. Some may have been insect eaters, some fish eaters, some fruit or seed eaters, and possibly even some meat eaters. The smallest were sparrow-sized; the largest, eagle-sized (and thus the largest flying birds of the Mesozoic). They have been recovered from all over the world, and environments from deserts to shores.

Enantiornithes retained small claws on the manus, but these were greatly reduced compared to earlier avialians. Despite many depitctions to the contrary, enantiornithines do not seem to have the tail fan of feathers which characterize modern birds, and at most of a pair of long tail feathers (though not as long as those of confuciusornithids).

EUORNITHES
Modern birds and everything closer to them than to Enantiornithes form the clade Euornithes ("true birds": also known as "Ornithuromorpha" or "Ornithuraemorpha"). Transformations relative to basal bird groups include:

Among the early branches of euornithes are the seagull-sized fish-eating Yanornithiforms of the Early Cretaceous of China and the flightless Patagopteryx of Late Cretaceous Argentina. Limited remains of a possible very large (140 kg) flightless euornithine, Gargantuavis are known from the Late Cretaceous of Europe.

Even more derived are the Carinatae ("keeled ones"), characterized by a keeled sternum to support the powerful wing muscles, as well as by 10 or more sacrals, loss of the manual unguals, and a synsacrum (fusion of the sacrals together into a sacrum, fusion of the sacrum to the ilium, and fusion of all pelvic elements together). A notable Late Cretaceous toothed carinate is Ichthyornis of the seas of the American midwest.

Derived within the carinates are the Ornithurae ("bird tails"), one branch of which were the aquatic Hesperornithes. Early hesperornithines (such as Early Cretaceous Enaliornis) may have still had the power of flight, but later ones greatly reduced their wings. In fact, the most specialized forms lost their forearms altogher, with only stumps of humeri for wings. These latter include Hesperornis of the Late Cretaceous of the inland seas of midwestern North America. Even these advanced birds still retained teeth.

The most speciose branch of ornithurines is Aves.

AVES
"Birds" in the strictest sense: the concestor of modern birds and all of its descendants. Aves are distinguished from other carinates by toothless beaks (convergent with ornithomimids, oviraptorids, confuciusornithids, and an enantiornithine); the tibiotarsus (see above: fusion of the proximal tarsals to the tibia); 15 or more sacrals; and a number of other skeletal features.

The oldest members of Aves in this restricted sense are from the latest Cretaceous. The major groups of Aves (a clade that today contains 9000 species, and prior to the Polynesian expansion over the last 2000 years were probably at 12,000 species!) include:

with several additional branches of uncertain relation with the others.

And with Aves, we have finished our review of dinosaurian diversity!

Aves is the only clade of Dinosauria to survive the great extinction.

EVOLUTIONARY PATTERNS IN EUMANIRAPTORANS
Feeding adaptation transformations:

Terrestrial locomotory adaptations:

Miniaturization (and a little Gigantism):

Correlated Progression:
This issue is best dealt with next lecture, as one of the main selective forces seems to be that marvelous dinosaurian success story: the conquest of the air!

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Last modified: 2 July 2014