Non Avian Theropods And Early Birds example essay topic

As promised, here are the derived characters with which Gauthier (in his 1986 paper) unites Archaeopteryx with modern birds, outside of all other theropods (with Gauthier's original clarifier's in parens) [and with my editorial comments in brackets]: Premaxilla e elongate, narrow, and more pointed anteriorly, with longer nasal processes [similar condition in bullatosaurs, and in the non dinosaurian Megalancosaurus, but unique to Archie and later birds in Maniraptora]. Maxillary process of premaxilla reduced so that maxilla participates broadly in external naris (also in troodontids). Enlarged brain / basi cranium (temporal musculature fails to extend origin onto frontal bones [to a certain degree in bullatosaurs and therizinosauroids, and perhaps in some of the newer, "brainier" dromaeosaurids]. Double-condyled quadrate displaced from distal position on opisthotic to more anteromedial position in contact with pro otic (Currie, pers. comm. and Walker, pers. comm., disagree with Whetstone's interpretation of the quadrate: Currie notes the anterior displacement of the quadrate in troodontids [maybe Nino can comment on the condition in Pelecanimimus], and Walker does not consider the quadrate to be double-condyled in Archaeopteryx).

Maxillary and dentry teeth reduced in size and number (or lost), with unserrated crowns and enlarged roots that completely enclose replacement teeth within them [many of the smallest theropod teeth are unserrated, which may be a developmental constraint. The pinched roots of bird teeth are similar to those of troodontids, basal ornithomimosaurs, and (in at least a couple of cases) dromaeosaurids]. Robust furcula for hypertrophied flight musculature [true to a certain extent, although oviraptorids and (perhaps) some dromaeosaurids have substantial furcula as well, and even the new Morrison allosaurid seems to have a primitive furcula! ].

Scapula with more o less prominent acromion process for ligamentous connection to clavicle. Lenght / breath ratio of scapula at mid length exceeds nine (not in penguins) and scapula tapers distally. Acro coracoid tuberosity larger than in other coelurosaurs. Coracoid enlarged and inflected posteromedially more so than in other coelurosaurs. Very long forelimb and hands (e. g., in Archaeopteryx forelimb is 120-140% of hind limb length, and more than twice as long as distance between glenoid and acetabulum), with forearm more than 87% of humerus length and mcI I approaching or exceeding one-half of humerus length. Ischium compressed and dorsoventral ly deep.

Compared to other theropods, tibia, fibula, and metatarsals relatively more elongate with respect to femur, regardless of body size (mts short in penguins and some other birds) [Actually, as S. Gatsby and I have shown elsewhere, what actually is happening is a difference in the allometry of bird vs. nonavian theropod hind limbs. In nonavian theropods, the tibia / fibula and the metatarsus become relatively smaller as body size (and femur size) increases; in birds, the tibia / fibula and the me tarsus become relatively longer as body size (and femur size) increases. Unfortunately, Archaeopteryx lies very close to the points at which the "bird" and "non bird" allo metric lines cross, so it is not possible to say at present to which of these curves the Ur vogel belongs]. Fibula attenuate distally, and may not extend to end of tibia.

Proximal tarsals fused to tibia / fibula and to one another in adults [also in some ceratosaurs]. Distal tarsals and metatarsals fused at least distally in fully adult individuals (convergent in some ceratosaurs, elmisaurids, and Hulsanpes) [future work may show why this is no surprise for Hulsanpes... ; also found in Avimimus]. First pedal digit elongate and reversed (may be reversed in some extant birds) [the first "reversed" he uses is "reverted"; the second is "reversed" in the evolutionary sense]. Metatarsal I attached on the distal quarter of metatarsal II.

Tail reduced to no more than 23 free caudal vertebrae. Feathers cover limbs and tail, feathers on lateral margin of tail and posterior margin of arms enlarged, curved, and asymmetrically vane d, indicating aerodynamic function [While it is true these features are currently only known in Archaeopteryx and later birds, there is only negative evidence with regards to this character in other theropods, as discussed in the paragraph immediately following his character list]. Thus, there are derived features linking Archaeopteryx to modern birds. In order to falsify this hypothesis, additional analyses must be conducted which: a) add new characters, or demonstrate that the above are not coded properly; and b) add new taxa, or demonstrate that the taxa previously used were not coded properly. Abundant new discoveries of Mesozoic birds and new bird-like theropods will help on both these counts. With several teams working on just this problem (thankfully not me: nonavian theropods are a problem enough! ), we should get some interesting results.

Dinosaurian Synapomorphies Found In Archaeopteryx From: Here are 20 to get you started (characters shared with / retained from dromaeosaurids and other related theropods and dinosaurs): 1. Tridactyl manus with manual digits IV, V lost 2. Manual digit I robust 3. Manual digit II longest in hand 4. Manual digit slender, with phalanges 3, 4 both short 5. Semilunate carpal 6.

V-shaped furcula present 7. Strap like scapula 8. Functionally tridactyl pes with retroverted hallux 9. Advanced meso tarsal ankle 10. Splint like metatarsal V 11. Ascending process on astragalus 12.

Slender fibula 13. Femur with orthogonally in turned head 14. Perforate acetabulum 15. Pelvis moderately opisthopubic 16. Pubis long, rod like with distal expansion 17. Blade like ilium 18.

Sacrum with at least 5 vertebrae (A. has six) 19. Long tail, distally stiffened 20. Jaws with teeth There are dozens more-I've scarcely touched the skull in this list. But you get the idea, yes Dromaeosaurids Archaeopteryx Gregory S. Paul Getting ready for the Soc Avian Paleo & Evol conference on Mesozoic birds in June in DC has caused me to restudy Archaeopteryx and proto avian (sensu Paul 1988 PDF) theropods.

With all the specimens old and new now available, virtually the entire skull and skeleton is now known for Archaeopteryx. Conclusions are as follows. Archaeopteryx truly is a flying theropod that shows virtually no avian characters not observed in other theropods (the large, distal, fully reversed hallux may be the only exception). Contrary to reports otherwise, there is no evidence for avian skull kinetics, and the postorbital bar was probably complete.

The palate and brain case are entirely theropod ian in structure. Archaeopteryx is not only a theropod, it is a dromaeosaur because it shares a number of detailed characters only with dromaeosaurs. Some other characters are found only in the two forms and some basal birds. Some of the Archaeopteryx-dromaeosaur characters are as follows. nasal depressed nasal and snout upturned oDorsal process of maxilla almost reaches preorbital bar preorbital bar slender & straight preorbital in lateral view oDorsal depression on the ectopterygoid o Diamond shaped supra occipital o Strongly twisted para occipital process (noted by Currie) o Highly modified tail with hyperdorso-flexible base (condition approached in troodonts) o Middle finger most robust o Ilium parallelogram shaped (also basal birds) oPubic peduncle very large & reversed o Ilio-pubic articulation inverted V shape oPubic shafts are flat plates oriented 140 degrees to each other In addition, the foot of Archaeopteryx is functionally two toed, with a short toe II that is hyper extendable. Many Cretaceous theropods - dromaeosaurs, troodonts, ovi raptors - are more bird-like than Archaeopteryx in many respects, and have a shoulder girdle that is similar to secondarily flightless birds. All this suggests that avian flight first evolved in arboreal theropods (where they developed big brains and forward facing eyes, features not found in flying insects and pterosaurs), and that some of the flying theropods lost flight.

Not knowable at this time is whether Archaeopteryx was a member of the true bird clade, or was an independent experiment in flight, or where theropods end and birds begin, among other matters. Copyright 1996 respective authors. This document was a public post to the Dinosaur Mailing List. Feathered non-avian theropods found Jeff Poling Scientists reported in the June 25, 1998, edition of the journal Nature the discovery of two new fossils from Liaoning, China. The early Cretaceous Liaoning site is already known for its spectacularly preserved fossils of soft tissue including feathers on specimens of Confucius ornis and possible proto feathers on Sinosauropteryx. The two new animals, named Protarchaeopteryx robusta (robust first ancient-wing) and Caudipteryx zou i (Zou Jiahua's tail feather), also have feathers preserved but add to the list of incredible Liaoning discoveries for a different reason: they are, according to the authors, the first dinosaurs preserved with unambiguous feathers that are not in the clade Aves, the clade commonly referred to as "birds".

The animals were covered with feathers, including down, like those of Archaeopteryx and modern birds, with central rachis, radiating vanes and barbule's. Unlike those of Archaeopteryx and all flying birds, the primary feathers of Protarchaeopteryx and Caudipteryx were symmetrical, indicating they were incapable of sustained powered flight. The feathers covered their bodies and formed "wings" on their forelimbs and large fans on their tails. Protarchaeopteryx and Caudipteryx were approximately turkey-sized with long legs suitable for swift running.

Neither animal had the fully reversed first toe held close to the ground that Archaeopteryx and modern birds have, an adaptation for perching. Instead, the toe was farther up the foot in a position typical of non-avian theropod dinosaurs. Both animals had U-shaped furculas typical of those known from both avian and non-avian theropods. Both fossils were found with gastrolith's, or "stomach stones", like those found in modern birds and some predentatan dinosaurs, but never before found in theropods.

Both animals had gastralgia, or belly ribs, typical of those of non-avian theropods and early birds. The teeth of Protarchaeopteryx were serrated, unlike those of all known birds, including Archaeopteryx. The teeth of Caudipteryx were confined to the pre maxillary, and were elongate and spike-like, unique among all theropods. Both animals had the semilunate (half-moon) shaped bone in the wrist typical of birds and other maniraptoran theropods such as the dromaeosaurs, which includes animals like Velociraptor.

Their unf used fingers also had the typical theropod and early bird phalangeal formula (number of bones in the fingers) of 2-3-4-x-x. All fingers supported claws, with keratinous sheaths preserved on two claws of Protarchaeopteryx. The tail of Protarchaeopteryx was comprised of up to 28 vertebrae, similar to non-avian theropods, while Caudipteryx's tail was comprised of 22 vertebrae like that of Archaeopteryx. The forelimbs of Protarchaeopteryx were shorter, compared with the femur, than in birds but was longer than those of long-armed non-avian coelurosaurs theropods such as the dromaeosaurs. The forelimbs of Caudipteryx were shorter relative to the femur than in both birds and non-avian coelurosaurs.

Because of the lack of the perching adaptation and the other synapomorphies that uniquely identify Aves (not listed here for brevity), both animals have been placed outside of the birds. The fossils do, however, have the characters typical of theropod dinosaurs. On the dinosaur family tree, Caudipteryx is placed very close to, but more primitive than, Archaeopteryx and all other birds while Protarchaeopteryx is considered to be closely related to the dromaeosaurs. Many paleontologists and enthusiasts feel the presence of confirmed feathers on non-avian dinosaurs should remove any lingering doubts that birds are dinosaurs. "It is a historic moment when a controversy is resolved", Dr. Phil Currie of the Royal Tyrrell museum in Alberta, Canada, said at a National Geographic Society news conference. "This shows that dinosaurs are not extinct, but are well-represented by 10,000 species of birds".

Bibliography

Qiang, Ji, Phillip J. Currie, Mark A. Norell and Ji Shu-An. 1998.
Two feathered dinosaurs from northeastern China. Nature June 25, 1998.
Copyright 1998 by Jeff Poling.