Editing Protoavis

{{use dmy dates|date=September 2024}}
{{Short description|Extinct genus of reptiles}}
{{Distinguish|Proavis|Protovis}}
{{Automatic taxobox
| fossil_range = [[Late Triassic]], {{fossil range|210|earliest=216|latest=203}}
| image = Protoavis paratype skeletal.png
| image_caption = ''Protoavis texensis'' [[paratype]] (TTU P 9201)
| image_alt = The fossil of a bird-like animal on a black background. A foot, tail, and upper body are present. The head has a large beak while the arm bones are folded over to look like a bird's wings.
| taxon = Protoavis
| display_parents=2
| type_species = {{extinct}}'''''Protoavis texensis'''''
| type_species_authority = [[Sankar Chatterjee|Chatterjee]], 1991
}}

'''''Protoavis''''' (meaning "first bird") is a [[Nomen dubium|problematic]] [[taxon]] known from fragmentary remains from [[Late Triassic]] [[Norian]] [[Stage (stratigraphy)|stage]] deposits near [[Post, Texas]]. The animal's true classification has been the subject of much controversy, and there are many different interpretations of what the taxon actually is. When it was first described, the fossils were described as being from a primitive [[bird]] which, if the identification is valid, would push back [[Origin of birds|avian origins]] some 60–75 million years.

The original describer of ''Protoavis texensis'', [[Sankar Chatterjee]] of [[Texas Tech University]], interpreted the [[type specimen]] to have come from a single animal, specifically a 35&nbsp;cm tall bird that lived in what is now [[Texas]], [[United States|USA]], around 210 [[Ma (unit)|million years ago]]. Though it existed far earlier than ''[[Archaeopteryx]]'', its skeletal structure is more bird-like. ''Protoavis'' has been reconstructed as a carnivorous bird that had teeth on the tip of its jaws and eyes located at the front of the skull, suggesting a nocturnal or crepuscular lifestyle. Reconstructions usually depict it 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.

However, this description of ''Protoavis'' assumes that ''Protoavis'' has been correctly interpreted as a bird. Many palaeontologists doubt that ''Protoavis'' is a bird, or that all remains assigned to it even come from a single species, because of the circumstances of its discovery and unconvincing avian [[synapomorphy|synapomorphies]] in its fragmentary material. When they were found at the [[Tecovas Formation|Tecovas]] and [[Bull Canyon Formation]]s in the [[Texas panhandle]] in 1973, in a sedimentary strata of a Triassic river delta, the fossils were a jumbled cache of disarticulated bones that may reflect an incident of mass mortality following a [[flash flood]].

==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" />

==Classification and taxonomy==
The [[Taxonomy (biology)|taxonomy]] of ''Protoavis'' is controversial, with very few palaeornithologists considering it to be an early ancestor of modern birds, and most others in the [[Scientific community|palaeontological community]] regard it as a [[Chimera (paleontology)|chimaera]], a mixture of several specimens. American palaeontologist [[Gregory Paul]] suggested that ''Protoavis'' is a [[herrerasaur]].<ref name="DML0540" /> In a paper by [[Phil Currie]] and [[X.J. Zhao]] discussing a [[Endocast|braincase]] of a ''[[Troodon|Troodon formosus]]'', they compared the bird-like characters of ''Troodon'' and ''Protoavis''.<ref name="CurrieZhao93">{{cite journal |last1=Currie |first1=P.J. |last2=Zhao |first2=X-J |year=1993 |title=A new troodontid (Dinosauria, Theropoda) braincase from the Dinosaur Park Formation (Campanian) of Alberta |journal=Canadian Journal of Earth Sciences |volume=30 |issue=10 |pages=2231–2247 |doi=10.1139/e93-194 |bibcode=1993CaJES..30.2231C |url=http://doc.rero.ch/record/14268/files/PAL_E1386.pdf}}</ref> In the paper, they made a number of corrections involving both Chatterjee's and Currie's own misinterpretations of parts of ''Troodon'' cranial anatomy before the particular braincase being described was found.  At least a couple of the corrections (the anterior tympanic recess, and the relatively kinetic quadrate-squamosal contact) made ''Troodon'' more bird-like than Chatterjee made out in his ''Protoavis'' paper, but overall these particular corrections seemed to have little bearing on the avian features of ''Protoavis''.<ref name="CurrieZhao93" /> Currie and Zhao did not explicitly state whether or not they considered ''Protoavis'' to be a theropod, however they suggested that although ''Protoavis'' has characters suggesting avian affinities, most of these are also found in theropod dinosaurs.<ref name="CurrieZhao93" />{{rp|2243}}

===''Protoavis'' is a bird===
{{quote|The most remarkable thing about ''Protoavis'' is that, although it predates ''[[Archaeopteryx]]'' by 75 million years, it is considerably more advanced than ''Archaeopteryx''...''Protoavis'' is more closely related to modern birds than is ''Archaeopteryx''.|[[Sankar Chatterjee]]<ref name="Chatterjee1997" />}}

Sankar Chatterjee and a few other [[Paleornithology|palaeornithologists]] claimed that this material documents a Triassic [[origin of birds]] and the presence of a bird more [[Synapomorphy|advanced]] than ''Archaeopteryx''. Though it existed approximately 75 million years before the oldest known bird, its skeletal structure is allegedly more bird-like.<ref name="Chatterjee1991">Chatterjee, S. (1991). "Cranial anatomy and relationships of a new Triassic bird from Texas." ''Philosophical Transactions of the Royal Society B: Biological Sciences'', '''332''': 277–342. [https://www.jstor.org/stable/55414 HTML abstract] {{Webarchive|url=https://web.archive.org/web/20221002103915/https://www.jstor.org/stable/55414 |date=2 October 2022 }}</ref> ''Protoavis'' has been reconstructed as a carnivorous bird that had teeth on the tip of its jaws and eyes located at the front of the skull, suggesting a nocturnal or crepuscular lifestyle.<ref name="Chatterjee1987">Chatterjee, S. (1987). "Skull of ''Protoavis'' and Early Evolution of Birds." ''Journal of Vertebrate Paleontology'', '''7'''(3)(Suppl.): 14A.</ref> The fossil bones are too badly preserved to allow an estimate of flying ability; although reconstructions usually show feathers, judging from thorough study of the fossil material there is no indication that these were present.<ref name="Paul2002">Paul, G.S. (2002). ''Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds''. Johns Hopkins University Press, Baltimore. {{ISBN|0-8018-6763-0}}</ref><ref name="Witmer2002" >Witmer, L. (2002). "The debate on avian ancestry: phylogeny, function, and fossils." Pp. 3–30 ''in:'' Chiappe, L.M. and Witmer, L.M. (eds), ''Mesozoic birds: Above the heads of dinosaurs''. University of California Press, Berkeley, Calif., USA. {{ISBN|0-520-20094-2}}</ref>

However, this description of ''Protoavis'' assumes that ''Protoavis'' has been correctly interpreted as a bird. Almost all palaeontologists doubt that ''Protoavis'' is a bird, or that all remains assigned to it even come from a single species, because of the circumstances of its discovery and weak avialan [[synapomorphy|synapomorphies]] in its fragmentary material.<ref name="Ostrom1996">{{cite journal |last1=Ostrom |first1=J.H. |year=1996 |title=The questionable validity of ''Protoavis'' |journal=Archaeopteryx |volume=14 |pages=39–42}}</ref><ref>{{cite journal |last1=Nesbitt |first1=Sterling J. |last2=Irmis |first2=Randall B. |last3=Parker |first3=William G. |year=2007 |title=A critical re-evaluation of the Late Triassic dinosaur taxa of North America |journal=Journal of Systematic Palaeontology |volume=5 |issue=2 |pages=209–243 |doi=10.1017/s1477201907002040 |bibcode=2007JSPal...5..209N |s2cid=28782207}}</ref><ref name="Ostromatriassicbird?">{{cite journal |last1=Ostrom |first1=J |year=1987 |title=Protoavis, a Triassic bird? |journal=Archaeopteryx |volume=5 |pages=113–114}}</ref><ref>{{cite journal |last1=Ostrom |first1=J.H. |year=1991 |title=The bird in the bush |journal=[[Nature (journal)|Nature]] |volume=353 |issue=6341 |page=212 |doi=10.1038/353212a0 |bibcode=1991Natur.353..212O |s2cid=4364567 |doi-access=free}}</ref> When they were found at a [[Dockum Group]] quarry in the Texas panhandle in 1984, in a sedimentary stratum of a Triassic river delta, the fossils were a jumbled cache of disarticulated bones reflecting an incident of mass mortality following a flash flood.<ref name="Chatterjee1987" />

===''Protoavis'' is a chimaera===
{{quote|Except for a few elements, the available material of ''Protoavis'' is extremely fragmentary. Chatterjee's interpretations of certain bones are questionable, and even the association of elements into specimens and then into a single taxon seems difficult to support.|[[Luis Chiappe]]<ref name="Chiappe1995">{{cite journal |last1=Chiappe |first1=L |year=1995 |title=The first 85 million years of avian evolution |journal=Nature |volume=391 |issue=6555 |pages=147–152 |bibcode=1995Natur.378..349C |doi=10.1038/378349a0 |s2cid=4245171}}</ref>}}

[[File:Megalancosaurus skeletal.png|thumb|right|Skeletal diagram of a [[drepanosaurid]], a type of [[Triassic]] reptile that some of the ''Protoavis'' bones may belong to]] 
Chatterjee was convinced that some of these crushed bones belonged to two individuals&nbsp;– one old, one young&nbsp;– of the same species. However, only a few parts were found, primarily a skull and some limb bones which moreover do not well agree in their proportions respective to each other, and this has led many to believe that the ''Protoavis'' fossil is [[Chimera (paleontology)|chimaeric]], made up of more than one organism: the pieces of skull appear like those of a [[coelurosaur]], while the femur and ankle bone catalogued under '''TTU P-9200''' and '''TTU P-9201''' respectively suggest affinities to non-tetanuran theropods<ref>{{cite journal |last1=Nesbitt |first1=Irmis |last2=Parker |year=2007 |title=A critical re-evaluation of the Late Triassic dinosaur taxa of North America |journal=Journal of Systematic Palaeontology |volume=5 |issue=2 |pages=209–243 |doi=10.1017/s1477201907002040 |bibcode=2007JSPal...5..209N |s2cid=28782207}}</ref> and at least some vertebrae are most similar to those of ''[[Megalancosaurus]]'', a drepanosaurid.<ref name="Renesto2000">{{cite journal |last1=Renesto |first1=S |year=2000 |title=Bird-like head on a chameleon body: new specimens of the enigmatic diapsid reptile ''Megalancosaurus'' from the Late Triassic of northern Italy |url=http://dipbsf.uninsubria.it/paleo/mega2000.pdf |journal=Rivista Italiana di Paleontologia e Stratigrafia |volume=106 |pages=157–180 |archive-date=27 July 2020 |access-date=21 April 2008 |archive-url=https://web.archive.org/web/20200727203037/http://dipbsf.uninsubria.it/paleo/mega2000.pdf |url-status=live }}</ref> However, those supposed similarities between the cervicals of ''Protoavis'' and drepanosaurids were the same similarities that Feduccia and Wild (1993) used to argue for an affinity between ''Archaeopteryx'' and drepanosaurids.<ref>{{cite journal |last1=Martz |first1=J. W. |last2=Mueller |first2=B. |last3=Nesbitt |first3=S. J. |last4=Stocker |first4=M. R. |last5=Parker |first5=W. G. |last6=Atanassov |first6=M. |last7=Fraser |first7=N. |last8=Weinbaum |first8=J. |last9=Lehane |first9=J. |year=2013 |title=A taxonomic and biostratigraphic re-evaluation of the Post Quarry vertebrate assemblage from the Cooper Canyon Formation (Dockum Group, Upper Triassic) of southern Garza County, western Texas |journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh |volume=103 |issue=3–4 |pages=339–364 |doi=10.1017/S1755691013000376 |s2cid=129744424}}</ref>

<blockquote>"Everywhere one turns; the very fossils ascribed thereto challenge the validity of ''Protoavis''. The most [[Occam's razor|parsimonious]] conclusion to be inferred from these data is that Chatterjee's contentious find is nothing more than a chimera, a morass of long-dead [[archosaur]]s."<ref name="evowiki2004" >EvoWiki (2004). {{usurped|1=[https://web.archive.org/web/20070122195519/http://wiki.cotch.net/wiki.phtml?title=The_Protoavis_controversy Chatterjee's Chimera: A Cold Look at the Protoavis Controversy]}}. Version of 22 January 2007. Retrieved 4 February 2009.</ref></blockquote>

If it really is a single animal and not a chimera, ''Protoavis'' would raise questions about when birds began to diverge from other theropods, if they are a lineage of theropod dinosaurs at all, but until better evidence is produced, the animal's status currently remains uncertain. Furthermore, [[paleobiogeography]] suggests that true birds did not colonize the [[Americas]] until the [[Cretaceous]]; the most primitive undisputed bird-like maniraptorans found to date are all [[Eurasia]]n.<ref name="Ostromatriassicbird?" /> Certainly, the fossils are most parsimoniously attributed to primitive dinosaurian and other reptiles as outlined above. However, coelurosaurs and ceratosaurs are in any case not too distantly related to the ancestors of birds and in some aspects of the skeleton not unlike them, explaining how their fossils could be mistaken as avian. Palaeontologist [[Zhonghe Zhou]] stated:

<blockquote>"[''Protoavis''] has neither been widely accepted nor seriously considered as a Triassic bird ... [Witmer], who has examined the material and is one of the few workers to have seriously considered Chatterjee's proposal, argued that the avian status of ''P. texensis'' is probably not as clear as generally portrayed by Chatterjee, and further recommended minimization of the role that ''Protoavis'' plays in the discussion of avian ancestry."<ref name="Zhou2004">{{cite journal |last1=Zhou |first1=Z |year=2004 |title=The origin and early evolution of birds: discoveries, disputes, and perspectives from fossil evidence |journal=Naturwissenschaften |volume=91 |issue=10 |pages=455–471 |doi=10.1007/s00114-004-0570-4 |pmid=15365634 |bibcode=2004NW.....91..455Z |s2cid=3329625}}</ref></blockquote>

Welman has argued that the [[quadrate bone|quadrate]] of ''Protoavis'' displays [[synapomorphies]] of [[Theropoda]].<ref name="Welam1995">{{cite journal |last1=Welman |first1=J |year=1995 |title=''Euparkeria'' and the origin of birds |journal=South African Journal of Science |volume=91 |pages=533–537 |title-link=Euparkeria}}</ref> Paul has demonstrated the drepanosaur affinities of the cervical vertebrae.  Gauthier & Rowe, and Dingus & Rowe have argued convincingly for identifying the hind limb of ''Protoavis'' as belonging to a [[ceratosaur]]. Feduccia has argued that ''Protoavis'' represents an arboreal "[[Thecodontia|thecodont]]".<ref name="Feduccia1996">Feduccia, A. (1996): ''The Origin and [[Evolution of Birds]]'' (1st ed.). Yale University Press, New Haven.</ref> In a study of early [[ornithischia]]n [[dinosaur]]s, [[Sterling Nesbitt]] and others determined some of the partial remains of ''Protoavis'' to be a non-[[Tetanurae|tetanuran]] [[theropod]].<ref>{{cite journal |last1=Irmis |first1=Randall B. |last2=Parker |first2=William G. |last3=Nesbitt |first3=Sterling J. |last4=Liu |first4=Jun |year=2007 |title=Early ornithischian dinosaurs: the Triassic record |url=http://ist-socrates.berkeley.edu/~irmisr/trornith.pdf |journal=Historical Biology: An International Journal of Paleobiology |volume=19 |issue=1 |pages=3–22 |doi=10.1080/08912960600719988 |bibcode=2007HBio...19....3I |citeseerx=10.1.1.539.8311 |s2cid=11006994 |archive-date=4 March 2016 |access-date=17 February 2010 |archive-url=https://web.archive.org/web/20160304205235/http://ist-socrates.berkeley.edu/~irmisr/trornith.pdf |url-status=dead }}</ref> The entire [[skull]] and neck are considered to be most likely from a [[drepanosaurid]] because the skull and neck are too big compared to the dorsal vertebrae of ''Protoavis''.<ref name="DML0188">{{cite mailing list|url=http://dml.cmnh.org/2001Sep/msg00188.html|title=Protoavis Material, Episode II|date=5 September 2001|access-date=2009-08-11|mailing-list=Dinosaur|last=Marjanovic|first=David|archive-date=4 March 2016|archive-url=https://web.archive.org/web/20160304001146/http://dml.cmnh.org/2001Sep/msg00188.html|url-status=dead}}</ref><ref group="Note">Features present in the remains of ''Protoavis'' that indicate that it is not a bird or more derived than ''[[Archaeopteryx]]'' include:

# The cranium appears to lack accessory fenestrae enclosed within the antorbital fossa, leading to auxiliary maxillary sinuses.
# The braincase displays a large post-temporal [[foramen]].
# A pneumatopore leading to a pneumatic sinus is not present on the [[paroccipital process]].
# The quadrate lacks an orbital process, doubled proximal condyle, and pin-joint with the [[quadratojugal]].
# The vertebral centra are only mildly [[heterocoelous]].
# Uncinate processes and sternal ribs absent.
# [[Carpal bones|Carpus]] lacks a semilunate element.
# [[Carpometacarpus]] absent.
# Fifth metacarpal retained.
# Manus not tridactyl.
# Thumb is not medially divergent.
# [[Tibiotarsus]] absent.
# [[Pygostyle]] absent, tail elongate.</ref>

===In discussions of evolution===
Scientists such as Alan Feduccia have cited ''Protoavis'' in an attempt to refute the hypothesis that birds evolved from dinosaurs.<ref name="Feduccia1999">Feduccia, A. (1999). ''The Origin and Evolution of Birds'' (2nd ed.). Yale University Press, New Haven. {{ISBN|0-300-07861-7}}</ref> However, some scientists have claimed the only consequence would be to push the point of bird divergence further back in time.<ref name="evowiki2004" /> At the time when such claims were originally made, the affiliation of birds and maniraptoran theropods which today is well-supported and generally accepted by most ornithologists was much more contentious; most [[Mesozoic]] birds have only been discovered since then. Chatterjee himself has since used ''Protoavis'' to support a close relationship between dinosaurs and birds.<ref name="Chatterjee1997" >Chatterjee, S. (1997). ''The Rise of Birds: 225 Million Years of Evolution''. Johns Hopkins University Press, Baltimore. {{ISBN|0-8018-5615-9}}</ref>

<blockquote>"As there remains no compelling data to support the avian status of ''Protoavis'' or taxonomic validity thereof, it seems mystifying that the matter should be so contentious. The author very much agrees with Chiappe in arguing that at present, ''Protoavis'' is irrelevant to the phylogenetic reconstruction of Aves. While further material from the Dockum beds may vindicate this peculiar archosaur, for the time being, the case for ''Protoavis'' is non-existent."<ref name="evowiki2004"  /></blockquote>

===Phylogenetic implications===
It has been argued that if valid, ''Protoavis'' will represent the death knell to the [[theropod]] descent of birds.<ref name="Feduccia1999" /><ref>{{cite journal |last1=Martin |first1=L |year=1988 |title=Review of: ''The Origin of Birds and the Evolution of Flight'', K. Padian (ed) |journal=Auk |volume=105 |issue=3 |pages=596–597 |jstor=4087470}}</ref><ref>Tarsitano, S. (1991). ''Archaeopteryx'': Quo vadis? In: Schultze, H. P. and Trueb, L. (eds.), ''Origins of the Higher Groups of Tetrapods'', 319–332.</ref><ref>{{cite journal |last1=Bock |first1=W |year=1997 |title=Review of: ''The Origin and Evolution of Birds'', by A. Feduccia |journal=Auk |volume=114 |issue=3 |pages=531–534 |doi=10.2307/4089261 |jstor=4089261 |doi-access=free}}</ref> Palaeontologists counter that if valid, ''Protoavis'' in no way falsifies the [[theropod]] [[origin of birds]].<ref name="Paul2002" /><ref name="Chatterjee1997" /> The very fact that Chatterjee used his putative bird to defend [[theropod]] origins for birds seems to contradict the argument of [[Alan Feduccia]] that a true bird from the [[Triassic]] would bring about the collapse of the [[theropod]] "dogma".

==Discovery and history==
{{quote|Smushed and mashed and broken.|[[Jacques Gauthier]] informally describing the [[holotype]] specimen.<ref>Shipman, P. (1998). ''Taking Wing: Archaeopteryx and the Evolution of Bird Flight''. Simon & Schuster, New York.</ref>}}

[[Archosaur]] discoveries are comparatively abundant in Texas, and have been recovered in some quantity since [[Edward Drinker Cope|E. D. Cope]] worked the redbeds of the panhandle over a century ago.<ref>{{cite journal |last1=Cope |first1=E. D. |author-link=Edward Drinker Cope |year=1892 |title=A contribution to the vertebrate paleontology of Texas |journal=Proceedings of the American Philosophical Society |volume=30 |pages=123–131 |title-link=vertebrate paleontology}}</ref> The [[holotype]] specimen of ''Protoavis'' ('''TTU P 9200'''), the [[paratype]] ('''TTU P 9201'''), and all referred materials,<ref group="Note">Chatterjee (1995) describes these ''Protoavis'' specimens in addition to the description of the skeletons referred to '''TTU P 9200''' and '''TTU P 9201'''. They are:

*(TTU P 9350-9355) six dorsal vertebrae (6–10 mm)
*(TTU P 9356-9359) four caudal vertebrae (8–9 mm)
*(TTU P 9360) coracoid(?) (14 mm)
*(TTU P 9361) sternum(?) (25 mm)
*(TTU P 9362) humerus (~80 mm)
*(TTU P 9263) humerus
*(TTU P 9364) partial mandible
*(TTU P 9365) humerus
*(TTU P 9370) femur (~58 mm)
*(TTU P 9372) femur
*(TTU P 9373) femur
*(TTU P 9374) tibia
*(TTU P 9375-9380) phalanges
</ref> were discovered in the [[Dockum Group]], from the panhandle of Texas. The Dockum dates from the [[Carnian]] through the early [[Norian]], in the terminal [[Triassic]] and is composed of four units of decreasing age: the [[Santa Rose Formation]], the [[Tecovas Formation]], the [[Trujillo Formation]], the [[Cooper Canyon Formation]], and the [[Bull Canyon Formation]].<ref name="Chatterjee1997" /><ref>Lehman, T. (1994). The saga of the Dockum Group and the case of the Texas/New Mexico boundary fault. Summarized in ''The Rise of Birds: 225 Million Years of Evolution'', Chatterjee (1997).</ref> Many skeletal elements and partial elements of ''Protoavis'' were collected from the [[Post (Miller) Quarry]] of the Bull Canyon Formation in the 1980s and other specimens referred to ''Protoavis'' were collected from the underlying [[Kirkpatrick Quarry]] of the Tecovas Formation.<ref name="Protoavisearlybirdevo" /> The specimens altogether consists of a partial [[skull]] and postcranial remains belonging to possibly several large individuals.<ref name="Chatterjee1991" /><ref name="Chatterjee1997" /> The bones were completely freed of the surrounding matrix, and some were heavily reconstructed and the identification of some of the elements have been questioned by other [[Paleornithology|palaeornithologists]] and [[Paleontology|palaeontologists]].

The [[type material]] was collected from mudstone deposits in June 1973 and initially identified as a juvenile ''[[Coelophysis|Coelophysis bauri]]''.<ref name="Chatterjee1997" /> The level of the Dockum group from which the ''Protoavis'' material was recovered, was most likely deposited in a deltaic river system. The bone bed excavated by [[Sankar Chatterjee]] and his students of Texas Tech University, in which ''Protoavis'' was discovered, likely reflects an incident of [[Mortality plate|mass mortality]] following a flash flood.<ref name="Chatterjee1997" /><ref>{{cite journal |last1=Lehman |first1=T. |last2=Chatterjee |first2=S. |last3=Schnable |first3=J. |year=1992 |title=The Cooper Canyon Formation (Late Triassic) of western Texas |journal=Texas Journal of Science |volume=44 |pages=349–355}}</ref> Chatterjee, who first described ''Protoavis'', has assigned the binomial ''Protoavis texensis'' ("first bird from Texas") to the small cache of bones, allegedly conspecific. He interpreted the [[type specimen]] to have come from a single animal, specifically a 35&nbsp;cm tall bird that lived in what is now [[Texas]], [[United States|USA]], between 225 and 210 million years ago.

Due to the nature of the bones being jumbled into sandstone nodules, and completely disarticulated, it has been suggested that ''Protoavis'' was reworked from later sediments.<ref>{{cite mailing list|url=http://dml.cmnh.org/1997Oct/msg00534.html|title=Re: Protoavis?|date=18 October 1997|access-date=2009-08-11|mailing-list=Dinosaur|last=Woolf|first=Jonathon|archive-date=24 May 2021|archive-url=https://web.archive.org/web/20210524153053/http://dml.cmnh.org/1997Oct/msg00534.html|url-status=dead}}</ref> However, a basic stratigraphic principle, the "[[principle of inclusions]]", is a special case of the principle of cross-cutting relationships. It states that rock has to exist before it can be included in other [[sedimentary rock]]. Reworking is the process of weathering fossils or rock containing fossils out of rocks already present, transporting them, and redepositing them in sediments which are later [[Rock (geology)|lithified]] as new sedimentary rocks. Since the [[Jurassic]] rocks occurred after the Triassic sediments of the Dockum Group, they could not have been reworked into the Dockum sediments as inclusions.<ref name="DML0540">{{cite mailing list|url=http://dml.cmnh.org/1997Oct/msg00540.html|title=Re: Protoavis?|date=18 October 1997|access-date=2009-08-11|mailing-list=Dinosaur|last=Wagner|first=Jonathan R.|archive-date=25 May 2021|archive-url=https://web.archive.org/web/20210525210305/http://dml.cmnh.org/1997Oct/msg00540.html|url-status=dead}}</ref>

==Palaeoenvironment==
The inferred [[Paleoclimatology|palaeoclimate]] of the [[Dockum Group]] would have been subtropical and governed by a distinct dry/wet season pattern, with the latter marked by monsoonal rains.<ref name="Chatterjee1997" /> The botanical evidence indicates that the area was densely forested, and the abundance of both [[invertebrate]] and [[vertebrate]] material from the site suggests that the locale was in general richly populated by a wide variety of species.<ref name="Chatterjee1997" /><ref>Ash, S. R. 1972. Upper Triassic Dockum flora of eastern New Mexico and Texas. In ''New Mexico Geological Society Guide Book'', 124–128.</ref> [[Dinosaur]]s were still fairly rare in the Dockum group, and only some [[Ceratosauria|ceratosaurs]] and other [[Basal (phylogenetics)|basal]] forms are well documented.<ref name="Chatterjee1997" /><ref>{{cite journal |last1=Chatterjee |first1=S |year=1984 |title=A new ornithischian dinosaur from the Triassic of North America |journal=Naturwissenschaften |volume=71 |issue=12 |pages=630–631 |doi=10.1007/bf00377897 |bibcode=1984NW.....71..630C |s2cid=6993997}}</ref><ref>{{cite journal |last1=Chatterjee |first1=S |year=1993 |title=''Shuvosaurus'', a new theropod |journal=National Geographic Research and Exploration |volume=9 |pages=476–491 |title-link=Shuvosaurus}}</ref> The principal [[carnivore]]s of the locale would have been [[Poposauridae|poposaurids]] such as ''[[Postosuchus]]'', a species well represented in the Triassic redbeds of Texas.<ref name="Chatterjee1997" /> Other archaic [[archosaur]]s, such as [[Rhynchosauria|rhynchosaurs]] and [[Aetosauria|aetosaurs]], were also fairly common.

===Taphonomy===
Both the [[holotype]] and [[paratype]] were recovered from disparate locations, both disarticulated and unassociated. Consequently, spatial relationships are impossible to determine.<ref name="Ostrom1996" /><ref name="Feduccia1999" /><ref name="Ostromatriassicbird?" /> No record of the original orientation of the material even as recovered, exists. Further material assigned to the [[taxon]] has been recovered in isolation with no apparent spatial relationships to each other, and their referral to ''Protoavis'' is difficult to support.

Not only were the remains recovered disarticulated and unassociated, there are morphometric differences in the various components of the [[holotype]] and [[paratype]]. For instance, the scapulae and coracoids are heavily reduced, to the point that association with the axial skeleton is extremely difficult to support. Juvenile [[ontogeny]] cannot be invoked credibly to explain this discrepancy.<ref name="Paul2002" /> Furthermore, the degree of morphometric variation in the holotype and paratype seems incongruent with the component material representing a conspecific assemblage of bones.<ref name="Paul2002" />

The fossils themselves display significant postmortem damage, and are in some cases so badly crushed and distorted at the hand of geological processes, that accurate interpretation thereof is impossible.<ref name="Ostrom1996" /><ref name="Feduccia1999" /><ref name="Paul2002" /><ref name="Chiappe1995" /><ref name="Currie1995">{{cite journal |last1=Currie |first1=P |year=1995 |title=New information on the anatomy and relationships of ''Dromaeosaurus albertensis'' |journal=Journal of Vertebrate Paleontology |volume=15 |issue=3 |pages=576–591 |doi=10.1080/02724634.1995.10011250}}</ref><ref name="PadianChiappe98">{{cite journal |last1=Padian |first1=K. |last2=Chiappe |first2=L. |year=1998 |title=The origin and evolution of birds |doi=10.1111/j.1469-185x.1997.tb00024.x |journal=Biological Reviews |volume=73 |pages=1–42 |s2cid=86007060 |url=http://doc.rero.ch/record/16121/files/PAL_E3214.pdf |archive-date=10 April 2023 |access-date=23 January 2023 |archive-url=https://web.archive.org/web/20230410121553/http://doc.rero.ch/record/16121/files/PAL_E3214.pdf |url-status=live }}</ref><ref>Paul, G.S. (1988): ''Predatory Dinosaurs of the World''. Simon & Schuster, New York.</ref><ref>Witmer, L. (1991): Perspectives on avian origins. ''In:'' Schultze, H.-P. & Trueb, L. (eds.): ''Origins of the Higher Groups of Tetrapods'': 427–466.</ref><ref>{{cite journal |last1=Sanz |display-authors=etal |year=1998 |title=Living with dinosaurs |doi=10.1038/29916 |journal=Nature |volume=393 |issue=6680 |pages=32–33 |bibcode=1998Natur.393...32S |s2cid=5480705}}</ref>

In his definitive analysis of the material, ''The Rise of Birds'' (1997),<ref name="Chatterjee1997" /> Chatterjee failed to illustrate the ''Protoavis'' fossils via pictures or sketches of the fossils proper, and instead offered artistic reconstructions. For this, Chatterjee has been criticized.<ref name="Feduccia1999" />

==See also==
*[[Proavis]]
*[[Origin of birds]]
*[[Origin of avian flight]]
*[[Feathered dinosaurs]]
*[[Temporal paradox (paleontology)]]

==Notes==
{{Reflist|group=Note|colwidth=30em}}

==References==
{{Reflist|2}}

==External links==
* [http://www.fossilwiki.org/index.php?title=Protoavis ''Protoavis'']{{dead link|date=February 2025|bot=medic}}{{cbignore|bot=medic}} at the Fossil Wiki, upon which this article is adapted from.
{{Eureptilia|state=autocollapse}}
{{Theropoda|N.|state=autocollapse}}
{{Taxonbar|from=Q284477}}

[[Category:Controversial taxa]]
[[Category:Fossil taxa described in 1991]]
[[Category:Late Triassic archosaurs of North America]]
[[Category:Nomina dubia]]
[[Category:Paleontological chimeras]]
[[Category:Prehistoric reptile genera]]