Editing Protoavis (section)

==Description==
''Protoavis'' is usually depicted as being a [[Bipedalism|bipedal]] [[archosaur]], similar to several [[poposaurid]]s and [[rauisuchid]]s that lived during roughly the same time as ''Protoavis''.<ref name="DMLMartzjeff1">{{cite mailing list|url=http://dml.cmnh.org/1997Oct/msg00571.html|title=Re: Protoavis?|date=20 October 1997|access-date=2009-08-11|mailing-list=Dinosaur|last=Martz|first=Jeffrey|archive-date=24 May 2021|archive-url=https://web.archive.org/web/20210524153050/http://dml.cmnh.org/1997Oct/msg00571.html|url-status=dead}}</ref> In a description published by [[Sankar Chatterjee]], structures were identified as quill knobs,<ref name="Chatterjee1995">{{cite journal |last1=Chatterjee |first1=S |year=1995 |title=The Triassic bird ''Protoavis'' |journal=Archaeopteryx |volume=13 |pages=15–31}}</ref> although there has been debate as to whether these are actually quill knobs or not.<ref name="Ostrom1996" />

===Skull and braincase===
The [[Endocast|braincase]] of ''Protoavis'' is similar in some respects to ''[[Troodon]]'', with an enlarged cerebellum that shifted the optic lobes ventrolaterally, and also has a large floccular lobe.<ref name="CurrieZhao93" /> The inner ear is also pretty similar and bird-like in both taxa. The canalicular systems and the cochlear process differ in both taxa, and the vestibular region is relatively small and located in a ventral position to most of the anterior and posterior semicircular canals. The anterior semicircular canal is significantly longer than the others, and the cochlear process is a relatively long, vertically oriented tube.<ref name="CurrieZhao93" />{{rp|2244}} However, ''Protoavis'' is also remarkedly non-bird like in that it possess only a single exit for the trigeminal.<ref name="CurrieZhao93" />{{rp|2244}} However, these characters are not robust enough to identify ''Protoavis'' as a bird.<ref name="CurrieZhao93" />

The skull has an extremely narrow [[parietal bone|parietal]] with block like dorsal aspect, very broad, T-shaped frontals that form the "lateral wings" that Chatterjee applies to the lack of postorbitals. There are short curved ulnae with olecranon processes, and a possible scapula with bent shaft, and the [[Cervical vertebra|cervicals]] have profiles and aspects to their exterior that are very similar to the ''[[Megalancosaurus]]'' cervical series. All the cervicals but the most posterior and axis/atlas have [[hypapophyses]] and those triangular neural spines; all characteristics that have been described in ''Megalancosaurus''.<ref name="DML0748">{{cite mailing list|url=http://dml.cmnh.org/2001Apr/msg00748.html|title=Protoavis & Drepanosauridae (sensu Renesto, 1999)|date=27 April 2001|access-date=2009-08-11|mailing-list=Dinosaur|last=Headden|first=Jaime A.|archive-date=25 May 2021|archive-url=https://web.archive.org/web/20210525134834/http://dml.cmnh.org/2001Apr/msg00748.html|url-status=dead}}</ref><ref group="Note">Specifically, the [[type specimen]] has these features, and they are corroborated in other specimens, including a complete, articulated neck with dorsal series, pectoral girdle, and forelimb.</ref> This suggests that portions of ''Protoavis'' may be drepanosaurid in nature.<ref name="DML0748" />

Chatterjee presents the skull of ''Protoavis'' as complete, although only the caudal aspect of the cranium is represented in the available fossils.<ref name="Ostrom1996" /><ref name="Feduccia1999" /><ref name="Paul2002" /> Chatterjee argues that the temporal region displays a streptostylic [[quadrate bone|quadrate]] with orbital process for attachment of the [[M. protractor pterygoidei et quadrati]], with associated confluence of the orbits with the [[temporal fenestrae]], thus facilitating [[prokinesis]]. He further asserts that the [[Endocast|braincase]] of ''Protoavis'' bears a number of characters seen in [[Ornithurae]], including the structure of the otic capsule, the widespread [[pneumatized bones|pneumatization]] of the braincase elements, a full complement of [[tympanic recesses]], and the presence of an [[epiotic]].

Of this material, only the quadrate and orbital roof, in addition to limited portions of the braincase are preserved with enough fidelity to permit any definitive interpretation.<ref name="Paul2002" /><ref name="Chiappe1995" /> The quadrates of '''TTU P 9200''' and '''TTU P 9201''' are not particularly alike; a fact not easily explained away if the material is conspecific, as Chatterjee insists.<ref name="Paul2002" /> There does not appear to be an orbital process present on either bone, and the modifications of the proximal condyle permitting wide range of motion against the [[squamosal]], are not readily apparent. Furthermore, the [[quadratojugal]] and [[jugal]] appear far more robust in the ''Protoavis'' specimens themselves, than represented by Chatterjee.<ref name="Chatterjee1997" /><ref name="Protoavisearlybirdevo">{{cite journal |last1=Chatterjee |first1=S |year=1999 |title=''Protoavis'' and the early evolution of birds |journal=Palaeontographica A |volume=254 |pages=1–100}}</ref> The size and development of the [[quadratojugal]] seems to contradict Chatterjee's assertion that this bone contacted the quadrate via a highly mobile pin joint.<ref name="Ostrom1996" /><ref name="Paul2002" /><ref name="Chiappe1995" /> These data render the assertion of [[prokinesis]] in the skull of ''Protoavis'' questionable at best, and it seems most [[parsimonious]] to conclude that the specimen displays a conventional [[opisthostylic]] quadrate.

The braincase is where ''Protoavis'' comes close to being as avian as Chatterjee has maintained. The otic capsule is allegedly organized in avian fashion, with three distinct foramina arranged as such: fenestra ovalis, fenestra pseudorotunda, and the caudal tympanic recess, with a bony metotic strut positioned between the fenestra pseudorotunda and caudal tympanic recess.<ref name="Chatterjee1991" /><ref name="Chatterjee1997" /> The claim that the full complement of tympanic recesses seen in [[ornithurines]], are similarly observed in ''Protoavis'' is questionable, as the preservation of the braincase is not adequate to permit concrete observations on the matter.  Chatterjee omits in his 1987 account of the braincase, the presence of a substantial post-temporal fenestra,<ref name="Chatterjee1987" /> which in all [[Aves]] (including ''[[Archaeopteryx]]''), is reduced or absent altogether,<ref name="Paul2002" /><ref name="Currie1995" /> and the lack of a pneumatic sinus on the [[paroccipital]].<ref name="Currie1995" /> Furthermore, the braincase possesses multiple [[character (biology)|character]]s [[symplesiomorphic]] of [[Coelurosauria]], including an expanded cerebellar  auricular fossa, and a vagal canal opening into the occiput.<ref name="Witmer2002" /> What is preserved of the preorbital skull curiously lacks [[apomorphic]] characters to be expected in a specimen, which is allegedly more closely allied to [[Pygostylia]] than is ''Archaeopteryx lithographica''.  Most telling is the complete absence of accessory fenestrae in the [[Antorbital fenestra|antorbital fossa]], leading to maxillary sinuses.<ref name="Paul2002" />

===Post-cranial anatomy===
The post-cranial remains are as badly preserved, or worse, than the cranial elements, and their interpretation by Chatterjee<ref name="Chatterjee1997" /> are in many cases unsubstantiated or speculative. Of the postcranial skeleton, Chatterjee has isolated the axial skeleton as displaying a suite of avian characters, including [[heterocoelous]] centra, [[hypapophyses]] and reduction of the neural spines. First and foremost, the preservation quality of the vertebrae is poor. While the centra are modified, they do not appear to be truly heterocoelous.<ref name="Paul2002" /> The presence of incipient hypapophyses in and of itself might be considered indicative of avian affinity, but their poor development and presence on vertebrae otherwise thoroughly non-avian, is most parsimoniously regarded as mild convergence until further material should be brought to light. The reduction of the neural spines is questionable.

Curiously, [[Gregory Paul]] has noted that the cervicals of ''Protoavis'' and [[drepanosaurs]] are astonishingly similar, such they are hardly distinguishable from one another.<ref name="Paul2002" />{{rp|Fig. 10.7Ba}} Considering the modification of the drepanosaur neck for the purposes of snap-action predation, it becomes more likely that superficial similarities in the cervicals of both taxa are in fact only convergent with [[Aves]].<ref name="Paul2002" /> Chatterjee does not identify the remaining vertebrae as particularly avian in their osteology.<ref name="Chatterjee1997" />

====Pectoral girdle====
The pectoral girdle is discussed by Chatterjee as being highly [[Synapomorphy|derived]] in ''Protoavis'', displaying synapomorphies of avialans more derived than ''Archaeopteryx'', including the presence of a [[hypocleidium]]-bearing [[furcula]], and a hypertrophied, [[carinate]] [[sternum]]. Chatterjee's interpretation of the fossils identified as such in his reviews of the ''Protoavis'' material<ref name="Chatterjee1997" /> are open to question due to the preservation quality of the elements and as of this time, it is not clear whether either character was in fact present in ''Protoavis''.<ref name="Chiappe1995" /> The [[glenoid]] appears to be oriented dorsolaterally permitting a wide range of humeral movement. Chatterjee implies that this is a highly derived trait which allies ''Protoavis'' to [[Aves]],<ref name="Chatterjee1997" /> but why this should be so is not clearly discussed in the descriptions of the animal. In and of itself, the orientation of the [[glenoid]] is not a sufficient basis for placing ''Protoavis'' within [[Aves]]. The scapular blade is far broader than illustrated by Chatterjee in his 1997 account,<ref name="Chatterjee1997" /> and not particularly avian in its gross form.<ref name="Paul2002" /> The [[coracoid]], identified by Chatterjee as strut-like and retroverted, is, like the supposed furcula and sternum, too poorly preserved to permit accurate identification. Moreover, the original spatial relationship of the alleged coracoid to the scapula is entirely unknown.<ref name="Ostrom1996" /><ref name="Paul2002" /> [[Uncinate processes of ribs|Uncinate processes]] and sternal ribs are missing.

====Pelvic girdle====
Chatterjee asserts that the pelvic girdle is apomorphic comparative to archaic birds and displays a retroverted [[pubis (bone)|pubis]], fusion of the [[ischium]] and [[ilium (bone)|ilium]], an [[antitrochanter]], and the presence of a [[renal fossa]]. The pubis does appear to display [[Pubis (bone)#Dinosaurs|opisthopuby]], although this has yet to be verified. The alleged fusion of the ischium and ilium into an ilioischiadic plate is currently not substantiated by the fossils at hand, despite Chatterjee's auspicious illustration to the contrary in ''The Rise of Birds''.<ref name="Feduccia1999" /><ref name="Paul2002" /><ref name="PadianChiappe98" /> At this time the pelvic girdle is not sufficiently well preserved to ascertain whether or not a renal fossa was present, although as no known avian from the [[Mesozoic]] displays a renal fossa, it is not clear why ''Protoavis'' should, even if it is more derived than ''Archaeopteryx''.<ref name="Witmer2002" /> Similarly, it is unclear if the alleged antitrochanter has been correctly identified as such.

====Arms and legs====
The [[manus (zoology)|manus]] and [[Carpal bones|carpus]] are among the few areas of the ''Protoavis'' material which are well preserved, and they are astonishingly non-avian. The distal carpals, while long, are in no way similar to those observed in the [[urvogel]] or other archaic birds. There is no semilunate element, and the structure of the radiale and ulnare would have limited the flexibility of the wrist joint.<ref name="Paul2002" /><ref name="Chatterjee1997" /> The manus is not tridactyl, and metacarpal V is present. In even the most basal avialian, ''Archaeopteryx'', there is no vestige of the fifth metacarpal and its presence in ''Protoavis'' seems incongruous with the claim that it is a bird, let alone one more derived than ''[[Archaeopteryx]]''.

Chatterjee claims that the [[humerus]] of ''Protoavis'' is "remarkably avian",<ref name="Chatterjee1997" />{{rp|53}} but as in all matters with the fossils referred to this taxon, accurate identification of the elaborate trochanters, ridges, etc., attributed to the [[humerus]] by Chatterjee is impossible at this time. The expanded distal condyles, which appear to be present in the [[humerus]] of ''Protoavis'' and enlarged [[deltopectoral crest]] (a ridge for the attachment of chest and shoulder muscles), are congruent with the morphology of [[ceratosaur]] humeri, as is the apparent presence of a distal brachial depression.<ref name="Dinosauriaceratosauria">Gauthier, J. & Rowe, T. (1990). Ceratosauria. In ''The Dinosauria'', Dodson ''et al'' (eds.).</ref>

The [[femur]] of ''Protoavis'' is astonishingly similar to non-tetanurans, namely coelophysoids. The proximal [[femur]] displays a trochanteric shelf caudal to the lesser and greater trochanters, a feature distinguishing non-tetanurans theropods from Tetanurae.<ref name="Rowe1989">{{cite journal |last1=Rowe |first1=T |year=1989 |title=A new species of the theropod dinosaur Syntarsus from the Early Jurassic Kayenta Formation of Arizona |journal=[[Journal of Vertebrate Paleontology]] |volume=9 |issue=2 |pages=125–136 |doi=10.1080/02724634.1989.10011748 |bibcode=1989JVPal...9..125R}}</ref> Further similarities between the proximal [[humerus]] of ''Protoavis'' and that of non-tetanuran theropods are found in the shared presence of an enlarged obturator ridge, whose morphology in ''Protoavis'' is again, uncannily like that observed in robust basal theropods, e.g., ''[[Megapnosaurus|"Syntarus" kayentakatae]]''.<ref name="Rowe1989" /> The resemblance between the [[femur]] of ''Protoavis'' and that of a non-tetanuran theropod becomes ever more pronounced at the distal end of the bone. Both share a [[crista tibiofibularis groove]], a feature of a non-tetanuran theropod separating the medial and lateral condyles.<ref name="Chatterjee1997" /><ref name="Rowe1989" />

The [[tibia]] of ''Protoavis'' allegedly possesses both a lateral and cranial cnemial crest, though the validity of this claim is subject to question due to the preservation quality of the material.  The [[fibula]] is continuous to the astragalocalcaneal unit. A [[tibiotarsus]] is absent, unusual considering Chatterjee's claims for the [[pygostylia]]n affinity of ''Protoavis'', as is a [[tarsometatarsus]].<ref name="Paul2002" /><ref>Dingus, L. & Rowe, T. (1998): ''The Mistaken Extinction: [[Dinosaur Evolution]] and the [[Origin of Birds]]''. W. H. Freeman & Company, New York.</ref> The ascending process of the [[talus bone|astragalus]] is reduced, a character entirely incongruous with a highly derived status for ''Protoavis''. Curiously, such abbreviation of the ascending process is found in [[Ceratosauria|ceratosaurs]], and in its general osteology, the ''Protoavis'' [[tarsus (skeleton)|tarsus]] and [[pes (zoology)|pes]], is quite similar to those of non-tetanuran theropods. Chatterjee's restoration of the [[hallux]] as reversed is nothing more than speculation, as the original spatial relationships of the pedal elements are impossible to ascertain at this time.<ref name="Paul2002" />

====Quill knobs====
Reconstructions usually depict ''Protoavis'' with feathers, as Chatterjee originally interpreted structures on the arm to be [[quill knob]]s, the attachment point for flight feathers found in some modern birds and non-avian dinosaurs. However, re-evaluation of the fossil material by subsequent authors such as Lawrence Witmer have been inconclusive regarding whether or not these structures are actual quill knobs.<ref name="Paul2002" />

In his 1997 account, Chatterjee infers the presence of [[feather]]s from alleged quill knobs on the badly smashed [[ulna]] and metacarpals III and IV, and infers the presence of [[remige]]s from such structures (though he does caution that this is uncertain).<ref name="Chatterjee1997" /> As is the case with the alleged quill knobs on the [[ulna]], the metacarpal structures appear to be attributable to post-mortem damage.<ref name="Paul2002" /> Moreover, the thumb, unlike the case in all birds, is not medially divergent. Considering how poorly preserved the [[ulna]] is, it is entirely premature to make any definitive conclusions as to the presence of quill knobs until such time as more adequate material becomes available. Upon further examination of the material no structures were isolated that could be deemed as [[homology (biology)|homologous]] to remigial papillae.<ref name="Witmer2002" />