Elpistostege enters the LRT between fins and fingers

Cloutier et al. 2020 bring us
a new complete specimen of Late Devonian Elpistostege (Fig. 1) along with CT scans of the manus-in-the-lobefin revealing finger buds inside (Fig. 2). Despite these buds, Elpistostege had no elbows (Fig. 2) and was too large (relative to its small posteriorly-oriented fins) to support itself above the substrate. That would come later. Meanwhile it could have wriggled ashore, insured from tipping over by its wide body and low center of gravity.

Figure 1. Elpistostege from Cloutier et al. 2020 in situ, traced and reconstructed.

Figure 1. Elpistostege from Cloutier et al. 2020 in situ, traced and reconstructed.

Cloutier et al. focused on the fingers,
providing an external view and CT scans, colored like a diagram (Fig. 2). I added pastel colors to the four fingers that extend beyond the more numerous nascent metacarpals. Even at this early stage, parallel interphalangeal lines (PILs) can be drawn where phalanges work in sets during extension and flexion.

Figure 2. Elpistostege manus/fin from Cloutier et al. 2020, rotated. Diagram at right with colors and PILs added.

Figure 2. Elpistostege manus/fin from Cloutier et al. 2020, rotated. Diagram at right with colors and PILs added. Only four digits are present primordially.

The skull presents a bit of a tracing challenge
as the rostrum is largely missing here (Fig. 3).

Figure 3. Elpistostege skull from Cloutier et al. 2020 with colors added. Note much of the rostrum is lost.

Figure 3. Elpistostege skull from Cloutier et al. 2020 with colors added. Note much of the rostrum is lost.

The large reptile tree
(LRT, 1658+ taxa, subset Fig. 4) tests more taxa than the traditional cladogram published in Cloutier et al. 2020. They nest Panderichthys as the more basal taxon. In the LRT Panderichthys is more derived (also see Fig. 5). Missing from Cloutier et al. are Spathicephalus (a sister to Tiktaalik) and Koilops, a neotonous form basal to Elpistostege and the rest of the Tiktaalik clade. In the LRT that’s an offshoot clade from the main line of fin to fingers taxa. Trypanognathus has the phylogenetically first known fingers, but that LRT hypothesis of relationships has been overlooked in favor of the multi-digit taxa, Acanthostega and Ichthyostega.

Figure 4a. Subset of the LRT focusing on basal tetrapods. Note the displaced positions of Acanthostega and Ichthyostega.

Figure 4a. Subset of the LRT focusing on basal tetrapods. Note the displaced positions of Acanthostega and Ichthyostega.

Figure 4b. Traditional cladogram produced by Cloutier et al. 2020. Compare to Figure 4a.

Figure 4b. Traditional cladogram produced by Cloutier et al. 2020. Compare to Figure 4a.

Traditional transitional taxa,
like Tiktaalik, Acanthostega and Ichthyostega, are phylogenetically shifting off to the side at various nodes in the LRT. Other taxa that never get talked about (Fig. 4) are more in the main line of tetrapod evolution leading to reptiles. Cloutier et al. seem to be perpetuating the traditional myth that basal tetrapods had more than five fingers (corrected in Fig. 5). The evidence shows that four is the primitive number. We looked at basal tetrapod finger evolution earlier here. and here.

Figure 5. Manus/Fin diagram from Cloutier et al. The phylogenetic order is wrong and Tulerpeton is not related (in the LRT). Greererpeton is substituted. 4 fingers is the primitive number.

Figure 5. Manus/Fin diagram from Cloutier et al. Two frames change every five seconds. The phylogenetic order is wrong and Tulerpeton is not related (in the LRT). Greererpeton is substituted. 4 fingers is the primitive number. Note the shrinking ulnare  in the revised version. Tiktaalik is off the main line of tetrapod evolution.

Elpistostege watsoni (Westoll 1938, Schultze and Arsenault 1985, Cloutier et al. 2020 is another flathead fish transitional to tetrapods, but off toward the Tiktaalik + Spathicephalus clade, derived from Koilops. Some tiny fingerbones are present in the lobefin. This fish is over a meter in length. It is the last taxon in this lineage with an anal fin. The radius continues to be as long as the ulna + ulnare with the intermedium separating them distally.

Figure x. The fin to finger transition in the LRT with the addition of Elpistostege.

Figure x. The fin to finger transition in the LRT with the addition of Elpistostege.

References
Cloutier R, Clement AM, Lee MSY, Noël R, Béchard I, Roy V and Long JA 2020. Elpistostege and the origin of the vertebrate hand. Nature https://doi.org/10.1038/s41586-020-2100-8
Schultze H-P and Arsenault M 1985. The panderichthyid fish Elpistostege: a close relative of tetrapods? Palaeontology 28, 293–309 (1985).
Swartz B 2012. A marine stem-tetrapod from the Devonian of Western North America. PLoS ONE. 7 (3): e33683. doi:10.1371/journal.pone.0033683
Westoll TS 1938. Ancestry of the tetrapods. Nature 141, 127–128 (1938).

wiki/Elpistostege

Sciam.com article on Elpistostege

Short-necked azhdarchids? Probably not.

Naish and Witton 2017 bring their insight
to a short, but giant cervical from a Romanian azhdarchid (Fig. 1 inset). They reported, “we discuss a recently discovered giant azhdarchid neck vertebra referable to Hatzegopteryx from the Maastrichtian Sebes Formation of the Transylvanian Basin, Romania. This vertebra, which we consider a cervical VII, is 240 mm long as preserved and almost as wide. Among azhdarchid cervicals, it is remarkable for the thickness of its cortex (46 mm along its ventral wall) and robust proportions.”

Naish and Witton conclude:
“By comparing its dimensions to other giant azhdarchid cervicals and to the more completely known necks of smaller taxa, we argue that Hatzegopteryx had a proportionally short, stocky neck highly resistant to torsion and compression.”

Figure 2. Quetzalcoatlus has a long cervical 7 and a short cervical 8. Naish and Witton consider the Romanian cervical #7, creating a short neck. But see figure 2.

Figure 2. Quetzalcoatlus has a long cervical 7 and a short cervical 8. Naish and Witton consider the Romanian cervical #7, creating a short neck. But see figure 2. The tall neural spine on cervical 8 is speculative and may be absent.

If the Romanian cervical is similar to cervical 7 of Quetzalcoatlus,
(Fig. 1) then the authors’ extrapolation seems reasonable.

Figure 2. Azhdarcho cervicals 7 and 8 are both short, but the anterior cervicals are elongate.

Figure 2. Azhdarcho cervicals 7 and 8 are both short, but the anterior cervicals are elongate. The Romanian cervical may belong to a similar genus, only larger.

However, if similar to the shorter cervical 7 of Azdarcho,
(Fig. 2) then the authors’ extrapolation can only be considered inconclusive. The rest of the cervicals in Azhdarcho are long and slender, matching those of all other clade members. Azhdarcho comes from Uzbekistan, closer to Romania than Quetzalcoatlus (Fig. 1), which comes from Texas.

Naish and Witton suggest,
“This specimen is one of several hinting at greater disparity within Azhdarchidae than previously considered, but is the first to demonstrate such proportional differences within giant taxa.”

Given the anatomy of Azhdarcho,
that conclusion is premature at present. We need to see at least some short anterior cervicals.

Historically, Naish and Witton imagined giant azhdarchids
as world-wide soarers, able to quad launch with folded wings, and terrorizing terrestrial prey like tiny sauropods. All of these fanciful hypotheses have been invalidated, but remain popular with paleoartists.


References
Naish D and Witton MP 2017. Neck biomechanics indicate that giant Transylvanian azhdarchid pterosaurs were short-necked arch predators. PeerJ 5:e2908; DOI 10.7717/peerj.2908

Asteriornis: Oldest crown bird fossil yet discovered? No.

Updated May 19, 2021
with a revised reconstruction of Asteriornis, and the addition of a close relative, the giant flightless goose, Cnemiornis. Click here to see the update.

Taxon exclusion
is the problem here. Still, it’s a wonderful and rare 3D bird fossil.

Figure 1. Asteriornis, a 3D bird fossil from the Latest Cretaceous, now nests with Cnemiornis, a giant flightless goose, in the LRT.
Figure 1. Asteriornis, a 3D bird fossil from the Latest Cretaceous, now nests with Cnemiornis, a giant flightless goose, in the LRT.

Writing in Nature, Field et al. 2020
bring us a new latest Cretaceous bird, Asteriornis (Fig. 1).The authors report, “The fossil represents one of the only well-supported crown birds from the Mesozoic era, and is the first Mesozoic crown bird with well-represented cranial remains.The fossil is between 66.8 and 66.7 million years old—making it the oldest unambiguous crown bird fossil yet discovered.”

The authors note,
“The general appearance of the premaxillary beak resembles that of extant Galliformes, particularly in its gently down-curved tip and delicate construction, with no ossified joints among the rostral components.”

Figure 2. Cnemiornis skull in three views. Compare to latest Cretaceous Asteriornis in figure 3.
Figure 2. Cnemiornis skull in three views. Compare to latest Cretaceous Asteriornis in figure 3.

Among crown birds, (Neornithes)
Asteriornis is old (66 mya), but the hen-sized ostrich sister, Patagopteryx, is older (80 mya), more primitive and was descried earlier (Alvarenga and Bonaparte 1992). Later Chiappe (1996, 2002, 2015) nested Patagopteryx between Enantiornithes and Hesperonis. Patagopteryx was not tested by Field et al. Instead the authors report, “The Mesozoic record of well-supported crown birds is restricted to a single latest Maastrichtian taxon, Vegavis iaai.” In the large reptile tree (LRT, 1657+ taxa then 1861 taxa now; subset Fig. 4), gracile, long-legged Vegavis lies just outside the clade of Crown birds.

Figure 1. The two-toed ostrich (Struthio) nests with the four-toed Patagopteryx, when all relatives have only three toes.
Figure 3. The two-toed ostrich (Struthio) nests with the four-toed Patagopteryx, when all relatives have only three toes.

Field et al. nested Asteriornis 
uncertainly either closer to geese (Anseriformes) or closer to chickens (Galliformes), or at the base of the traditional, but invalid clade, ‘Galloanserae’. The authors report, “The specimen exhibits a previously unseen combination of features that are diagnostic of Galliformes and Anseriformes, which together form the crown clade Galloanserae—one of the most deeply diverging clades of crown birds and the sister group to the hyperdiverse extant clade Neoaves.”

The LRT agrees. The Galliformes do not nest with the Anseriformes.

Figure x. Subset of the LRT focusing on theropods. Asteriornis now nests with Cnemiornis, the giant flightless goose.
Figure 4. Subset of the LRT focusing on theropods. Asteriornis now nests with Cnemiornis, the giant flightless goose.

Chickens and ducks are not related to one another
in LRT (subset, Fig. 4). Chickens are related to grouse, peacocks, sparrows, hoatzins, parrots and other ground-dwelling seed eaters. Ducks and geese arise from long-legged Presybyornis and other long-legged shorebirds. In the LRT, Asteriornis is closer to the newly added giant, flightless goose, Cnemiornis.

Field et al. have too few taxa
in their taxon list. Only one Archaeopteryx is shown in their cladogram, but it was not tested in their analysis where Hesperornithes and Ichthyornis are outgroup taxa. By contrast, in the LRT, both of these toothy taxa are members of the crown group, nesting between toothless ratites and all other toothless birds. Neither the chicken clade nor the duck clade are basal clades in the LRT.

Dr. Kevin Padian (2020) wrote a companion article
explaining the importance of Asteriornis and its relationship to crown birds and stem birds for a broader audience. Padian reports, “Ancient birds are outside the crown group because they lack the structural and physiological features characteristic of living birds. Sometime during the latest Cretaceous, a stem-group lineage of birds evolved that had much higher growth rates than these more basal lineages, and that generally matured within a year or even sooner. These became the crown-group birds.”

Given Dr. Padian’s definitions
several Cretaceous birds, including toothed forms (Fig. 4), qualify as crown group birds because they phylogenetically appear in the LRT after the basalmost extant bird, the kiwi (Apteryx). It only takes one primitive, but extant taxon to define a crown clade.

Dr. Padian also reviews the disagreement
between molecular evidence and the new palaeontological evidence offered by Asteriornis. He reports, “The evidence for Asteriornis reported by Field and colleagues implies that crown-group birds first evolved when the Cretaceous period was nearly over.” That’s not true for many reasons, all based on taxon exclusion.

Field et al. considered Asteriornis unique among known taxa
in exhibiting caudally pointed nasals that overlie the frontals and meet at the midline, and a slightly rounded, unhooked tip of the premaxilla. That first trait appears to be an error. The frontals extend to the premaxilla in Asteriornis. The mesethmoid, the same ‘soft spot’ that creates the casque in Casuarius, the cassowary, may be the source of the confusion.


References
Alvarenga and Bonaparte 1992. A new flightless land bird from the Cretaceous of Patagonia; pp. 51–64 in K. E. Campbell (ed.), Papers in Avian Paleontology, Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County, Science Series 36.
Chiappe LM 1996a. Late Cretaceous birds of southern South America: anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi; pp. 203–244 in G. Arratia (ed.), Contributions of Southern South America to Vertebrate Paleontology, Münchner Geowissenschaftliche Abhandlungen Volume 30.
Chiappe LM 1996. 
Early avian evolution in the southern hemisphere: Fossil record of birds in the Mesozoic of Gondwana. Memoirs of the Queensland Museum 39:533–556.
Chiappe LM 2002. Osteology of the flightless Patagopteryx deferrariisi from the late Cretaceous of Patagonia (Argentina) pp.281–316 in Mesozoic Birds, Above the Heads of Dinosaurs, Chapter: 13, Editors: Chiappe LM and Witmer LM, University of California Press.
Field DJ, Benito J, Chen A, Jagt JWM and Ksepka DT 2020. Late Cretaceous neornithine from Europe illuminates the origins of crown birds. Nature 579:397–401.
Padian K 2020. Poultry through time. Nature online

Taxon list used by Field et al. 2020.
Ichthyornis_dispar
Tinamus_robustus
Vegavis_iaai
Chauna_torquata
Anhima_cornuta
Wilaru_tedfordi
Presbyornis_pervetus
Conflicto_antarcticus
Anatalavis_oxfordi
Anseranas_semipalmata
Dendrocygna_eytoni
Cereopsis_novaehollandiae
Anser_caerulescens
Tadorna_tadornoides
Leipoa_ocellata
Megapodius_reinwardt
Megapodius_eremita
Alectura_lathami
Macrocephalon_maleo
Gallus_gallus
Phasianus_colchicus
Coturnix_pectoralis
Acryllium_vulturinum
Crax_rubra
Ortalis_vetula
Dromaius_novaehollandiae
Dinornis_robustus
Struthio_camelus
Lithornis_promiscuus
Lithornis_plebius
Paracathartes_howardae
Burhinus_grallarius
Porphyrio_melanotus
Antigone_rubicunda
Cariama_cristata
Asteriornis_maastrichtensis
Gallinuloides_wyomingensis
Pelagornis_chilensis
Protodontopteryx_ruthae

New ‘Evolution of Feathers’ book already outdated due to taxon exclusion

‘The Evolution of Feathers’
(Foth and Rauhut editors 2020) is a new book the genesis of feathers and the animals that developed them. The following is a brief critique of abstracts from the 12 chapters.

From the introduction
“For years it was generally assumed that the origin of flight was the main driving force for the evolution of feathers.”

Was it really? If promoted by paleontologists that was inappropriate and short-sighted. No birds fly with proto-feathers. Birds don’t get flight feathers first.

“This book is devoted to the origin and evolution of feathers, and highlights the impact of palaeontology on this research field by reviewing a number of spectacular fossil discoveries that document the increasing morphological complexity along the evolutionary path to modern birds. Also featuring chapters on fossil feather colours, feather development and its genetic control, the book offers a timely and comprehensive overview of this popular research topic.”

Foth C 2020.
Introduction to the Morphology, Development, and Ecology of Feathers.
“The origin of feathers goes back deep into the Mesozoic, preceding the origin of flight, and early protofeathers were probably present in the ancestral Tetanurae, Dinosauria, or even Ornithodira.”

Ornithodira‘ is a junior synonym of Reptilia in the large reptile tree (LRT, 1656+ taxa), since it contains Dinosauria + Pterosauria. I mention ‘taxon exclusion’ here because the addition of pertinent taxa separates dinosaurs from pterosaurs.


Lin GW,  Li A and Chuong C-M 2020.
Molecular and Cellular Mechanisms of Feather Development Provide a Basis for the Diverse Evolution of Feather Forms
.

“The important questions include the regional specification of feather tracts, the formation of periodically arranged feather buds and their anterior-posterior orientation, the formation of feather follicles, and the establishment of cyclic regeneration with clustered stem cells and dermal papilla.”


Rauhut OWM and Foth C 2020.
The Origin of Birds: Current Consensus, Controversy, and the Occurrence of Feathers.

“Research in the late 1900s has established that birds are theropod dinosaurs, with the discovery of feather preservation in non-avian theropods being the last decisive evidence for the dinosaur origin of this group.”

Sadly this is so despite the discovery of several Solnhofen theropod birds in the 1800s.

“Birds are part of Paraves, together with such well-known theropod groups as dromaeosaurids and troodontids; Paraves are part of Maniraptora, which furthermore include Oviraptorosauria, Therizinosauria, and Alvarezsauroidea; Maniraptora belong to Maniraptoriformes, which also include Ornithomimosauria; Maniraptoriformes are a subclade of Coelurosauria, to which Tyrannosauroidea and some other basal taxa also belong; Coelurosauria are part of Tetanurae, together with Allosauroidea and Megalosauroidea; finally, Tetanurae are a subclade of Theropoda, which also include Ceratosauria and Coelophysoidea.”

The LRT finds a different tree topology for theropods transitioning to birds and basal birds transitioning to derived birds (Fig. 1). Note how two specimens attributed to Compsognathus are basal taxa in major theropod clades in the LRT. The theropod lineage that led to birds was never larger than Ornitholestes and likely smaller still as more small theropod taxa are added to the LRT.

Figure 4. Subset of the LRT focusing on the theropod-bird transition, distinctly different than in Hartman et al. 2019. Here in a fully resolved cladogram, birds and anchiornithids are monophyletic. Taxon inclusion resolves cladistic issues raised by Hartman et al.

Figure 4. Subset of the LRT focusing on the theropod-bird transition, distinctly different than in Hartman et al. 2019. Here in a fully resolved cladogram, birds and anchiornithids are monophyletic. Taxon inclusion resolves cladistic issues raised by Hartman et al.

Godefroit P et al. (5 co-authors) 2020.
Integumentary Structures in Kulindadromeus zabaikalicus, a Basal Neornithischian Dinosaur from the Jurassic of Siberia.

“Kulindadromeus zabaikalicus, a basal neornithischian dinosaur from the Jurassic of Siberia, preserves diverse integumentary structures, including monofilaments, more complex protofeather structures and scales on its tail and distal parts of its limbs. These exceptionally preserved specimens suggest that integumental features were diversified even in ornithischian dinosaurs and that “protofeather”-like structures were potentially widespread among the entire dinosaur clade.”

The LRT supports this hypothesis.


Xu X 2020.
Filamentous Integuments in Nonavialan Theropods and Their Kin: Advances and Future Perspectives for Understanding the Evolution of Feathers.

“The discovery of Sinosauropteryx in 1996 marks the beginning of a new era in the research on the origin and early evolution of feathers.”

True, but a century behind the discovery of feathered dinosaurs.

“Currently, there are still many issues that continue to be debated or remain unresolved, such as at what point in phylogeny the first feathers originated (e.g., at the base of Avemetatarsalia vs. within Theropoda), etc.”

‘Avemetatarsalia’, like ‘Ornithodira’ (see above) is a junior synonym for Reptilia in the LRT.


Foth et al. (4 co-authors) 2020.
Two of a Feather: A Comparison of the Preserved Integument in the Juvenile Theropod Dinosaurs Sciurumimus and Juravenator from the Kimmeridgian Torleite Formation of Southern Germany.

“Juravenator starki and Sciurumimus albersdoerferi … are preserved with phosphatized soft tissues, including skin and feathers. Both theropods possessed monofilamentous feathers and scaleless skin. In J. starki, short feathers could only be traced in the tail region. The tubercle-like structures, originally described as scales … were reinterpreted as remains of adipocere, maybe indicating the presence of a fat body. S. albersdoerferi was probably entirely plumaged, possessing a filamentous crest on the dorsal edge in the anterior tail section.”

In the LRT Juravenator nests between the large Compsognathus specimen (CN79) and feathered Therizinosauria + Oviraptoria, so it is should have had feathers. In similar fashion, feathered Sciurumimus nests between Ornitholestes and feathered Microraptor (Fig. 2) in the LRT.


Lefävre U, et al. (4 co-authors) 2020.
Feather Evolution in Pennaraptora.

“Here, we present a concise review of the plumage evolution within pennaraptora, the most inclusive clade containing Oviraptorosauria and Paraves.”

In the LRT this clade is a junior synonym for Compsognathidae.

“The feather-like structures in non-eumaniraptoran paravians were obviously not adapted for flight.”

In the LRT the bird mimics, Microraptor  (Fig. 2) and Rahonavis are non-eumaniraptors.

“However, Microraptor and maybe some of its relatives preserve large pennaceous feathers along the limbs and tail, similar in morphology and organization to those in modern birds, so that they could have functioned in active flight or passive gliding.”

So the authors want it both ways? Microraptor (Fig. 2) and Sinornithosaurus both have elongate locked-down coracoids, so they were flapping, convergent with birds.

Figure 2. Microraptor gui (IVPP V 13352) reconstructed from tracings in figure 1. There are no surprises here, except a provisional closer relationship with Compsognathus than with Velociraptor. Microraptor has a large pedal claw two, but it is not quite the killing claw seen in droamaeosaurs.

Figure 2. Microraptor gui (IVPP V 13352) reconstructed from tracings in figure 1. There are no surprises here, except a provisional closer relationship with Compsognathus than with Velociraptor. Microraptor has a large pedal claw two, but it is not quite the killing claw seen in droamaeosaurs.

Longrich NR, Tischlinger H and Foth 2020.
The Feathers of the Jurassic Urvogel Archaeopteryx.

“The Jurassic stem bird Archaeopteryx is an iconic transitional fossil, with an intermediate morphology combining features of non-avian dinosaurs and crown Aves.:”

Of the 13 Solnhofen specimens attributed to Archaeopteryx, no two are alike in the LRT. These authors put all 13 into a taxonomic wastebasket by not giving most of them a different genus.

“The hindlimbs bear large, vaned feathers as in Microraptor and Anchiornis. Feather morphology and arrangement in Archaeopteryx are consistent with lift-generating function, and the wing loading and aspect ratio are comparable to modern birds, consistent with gliding and perhaps flapping flight. The plumage of Archaeopteryx is intermediate between Anchiornis and more derived Pygostylia, suggesting a degree of flight ability intermediate between the two.”

In the LRT the pygostyle developed several times by convergence.


O’Connor J 2020. The Plumage of Basal Birds.
“Basal pygostylians show disparate tail plumages that are reflected by differences in pygostyle morphology.”

Pygostylia is not monophyletic in the LRT (see above).


Foth C 2020. A Morphological Review of the Enigmatic Elongated Tail Feathers of Stem Birds.
“Several stem birds, such as Confuciusornithidae and Enantiornithes, were characterized by the possession of one or two pairs of conspicuous, elongated tail feathers with a unique morphology, so-called rhachis-dominated racket plumes. As the rhachis-dominated racket plumes combine different morphologies that are apparent among modern feather types, this extinct morphotype does in fact not show any aberrant morphological novelties, but rather fall into the morphological and developmental spectrum of modern feathers.”


Smithwick  F and Vinther J 2020. Palaeocolour: A History and State of the Art.
“From the overturning of the paradigm that lithified bacteria were responsible for vertebrate integumentary preservation to the development of analytical techniques used to probe pigment preservation, we review the origins and development of the field of palaeocolour.”


Campione NE, Barrett  PM and Evans DC 2020. On the Ancestry of Feathers in Mesozoic Dinosaurs.
“Over the last two decades, the dinosaur fossil record has revealed much about the nature of their epidermal structures. These data challenged long-standing hypotheses of widespread reptile-like scalation in dinosaurs and provided additional evidence that supported the deeply nested position of birds within the clade. Ancestral state reconstructions demonstrate that irrespective of the preferred phylogenetic framework, the ancestral pterosaur condition or whether any one major dinosaur lineage had a Late Triassic-feathered representative, support values for a filamentous/feathered dinosaur ancestor are low.”

This contradicts Godefroit et al. from the same volume (see above). Phylogenetically pterosaurs have nothing to do with dinosaurs. Pterosaur ancestors (clade Fenestrasauria) developed morphologically different plumes and filaments by convergence.

If you want to see what the first feathers on the earliest naked dinosaurs looked like, the best clues come from embryo birds (Fig. 3). The outgroup for Dinosauria, the PVL 4597 specimen mistakenly attributed to Gracilisuchus, had parasagittal dorsal scutes lost thereafter in basal dinosaurs, like Herrerasaurus, but retained in basal bipedal crocodylomorphs, like Gracilisuchus and Scleromochlus.

Figure 2. Primordial feathers on the back of a 10-day-old chick embryo.

Figure 3. Primordial feathers on the back of a 10-day-old chick embryo. Ontogeny recapitulates phylogeny in this pre-hatchling theropod.

The Solnhofen Archipelago was the Galapagos Islands of its day,
breeding at least 13 different Archaeopteryx-grade basal bird types, only one of which, Jurapteryx (the Eichstätt specimen, Fig. 4), gave rise to the one clade of birds that survives and flourishes today. If not for that single evolutionary variation, we would be surprised to see feathered theropods in the fossil record.

Figure 3. The Eichstätt specimen, Jurapteryx recurva, nests with the living ostrich, Struthio, presently in the LRT.

Figure 4. The Eichstätt specimen, Jurapteryx recurva, nests with the living ostrich, Struthio, presently in the LRT. It is the only lineage of Solnhofen birds still flying.

The following earlier posts may prove helpful
for those interested in the genesis and loss of feathers.

  1. when-did-t-rex-lose-its-feathers/
  2. hindlimb-feathers-useful-as-brood-covers/
  3. what-makes-a-bird-a-bird-everyone-knows-its-not-feathers-any-more/
  4. the-genesis-of-feathers-tied-to-the-genesis-of-bipedalism-in-dinosaurs/
  5. the-origin-of-feathers-and-hair-part-3-feathers/

References
Foth C and Rauhut OWM (editors) 2020. The Evolution of Feathers: From Their Origin to the Present. Series: Fascinating Life Sciences, Year: 2020. Springer, Cham
Print ISBN: 978-3-030-27222-7 Online ISBN: 978-3-030-27223-4
DOI: https://doi.org/10.1007/978-3-030-27223-4

Hyomandibular evolution + Introducing the postsquamosal

Revised July 19, 2020
with new bone identities given to several lobefin fish, correcting the mistakes of Thomson 1966.

The hyomandbular is the largest bone
in the entire body of the basal ray-finned fish Trachinocephalus (Fig. 1). Over time and phylogeny it evolves to become the smallest bone in the human body, the stapes (Fig. 3), one of the ultra tiny sound-conducting bones of the middle ear.

Along the way,
the large reptile tree (LRT, 1656+ taxa) presents a new (and heretical) lineage of tetrapod ancestry, distinct from the traditional one that includes Ichthyostega and Acanthostega. Today we go below the surface and formally introduce ‘the lineup.’

Figure 1. Hyomandibular evolution from the first dichotomy of bony fish to Gephyrostegus. The hyomandibular evolves to become the stapes. Note the hyomandibula contact with the intertemporal, quadrate and pterygoid, sometimes fused to these bones. The hyomandibular is poorly ossified in Onychodus, so it restored here. Note how the maxilla splits to produce the quadratojugal.

Figure 1. Hyomandibular evolution from the first dichotomy of bony fish to Gephyrostegus. The hyomandibular evolves to become the stapes. Note the hyomandibula contact with the intertemporal, quadrate and pterygoid, sometimes fused to these bones. The hyomandibular is poorly ossified in Onychodus, so it restored here. Note how the maxilla splits to produce the quadratojugal.

Some bones are relabeled
from the diagram found in Thomson 1966 (modified in Fig. 2), who presented several layers of skull bones (cranial, palatal and dermal) in the the Permian megalichthyid rhipidistian fish, Ectosteorhachis, a late-survivor of an earlier (Mid-Devonian) radiation that ultimately produced tetrapods and humans. Thomson mislabeled the dentary as a maxilla (mx) in his diagram, but all other labels are traditional.

In most fish 
the hyomandibular is roofed over by the otherwise unremarkable intertemporal, which anchors it dorsally.

That brings up a problem in Thomson’s diagram
(Fig. 2). To remedy that problem, here the dorsal rim of the traditional palatoquadrate is relabeled as the hyomandibular fused to the pterygoid and other palatal elements. Second, the labeled hyomandibular (h) is now the preopercular. Third, the traditional preopercular (pop) requires a new name: the postsquamosal. It is not homologous with the preopercular of teleost fish.

The disappearance of the traditional preopercular
Trachinocephalus (Fig. 1) retains a traditional preopercular. Pteronisculus (Fig. 1) has a postsquamosal and lacks a traditional preopercular on the surface. Cheirolepis (Fig. 1) lacks both. The squamosal and postsquamosal appear to be fused or else the tiny postsquamosal is overwhelmed by the advancing squamosal. The traditional rhipidistians have a postsquamosal. The tetrapods (Fig. 1) lack a postsquamosal.

The more derived traditional transitional tetrapods,
Acanthostega and Ichthyostega, have a postsquamosal, but this appears as a reversal, a neotonous trait. These two are secondarily more aquatic than their ancestor, Ossinodus.

Figure 2. Ectosteorhachis skull from Thomson 1966 with layers to show the brain case and palatoquadrate. Some bones are relabeled in the revised view.

Figure 2. Ectosteorhachis skull from Thomson 1966 with layers to show the brain case and palatoquadrate. Some bones are relabeled in the revised view.

The hyomandibular decreases in size
in most later tetrapods (Fig. 3), where it continues to shrink into the auditory channel where it is then known as the stapes.

At the same time, the intertemporal
disappears or fuses to nearby skull bones in several derived basal tetrapods and basal reptiles, all by convergence.

Figure 4. Evolution of the tetrapod mandible and ear bones leading to humans.

Figure 4. Evolution of the tetrapod mandible and ear bones leading to humans in lateral and medial views, first printed in From The Beginning, the Story of Human Evolution (Peters 1991), colors added here.

The quadratojugal first appears in the tetrapod lineage
in Gogonasus (Fig. 1) after the elongate maxilla of Onychodus splits in two.

Finally,
sharks also have a palatoquadrate, but it is composed of a fused lacrimal, jugal and squamosal with a tooth-bearing premaxilla and maxilla fused to the ventral rim. The pseudo- or plesio-palatoquadrate illustrated by Thomson 1966 in Ectosteorhachis and other rhipidistians,is not homologous and is comprised of different bones. 


References
Thomson KS 1966. The evolution of the tetrapod middle ear in the rhipidistian-amphibian transition. American Zoologist 6:379–397.

Did Oculudentavis have an antorbital fenestra?

Some say: Yes.
Others say: No.

You decide. 
Here are two CT scans (Figs. 1, 2), one from the left and the other from the right with overlays interpretating skull sutures, enlarged from the previous presentation.

Figure 1. CT scan from Xing et al. 2020, colors added to show antorbital fenestra. Note the wrinkling of the maxilla reacting to the twisting of the tiny, fragile skull during taphonomy.

Figure 1. CT scan from Xing et al. 2020, colors added to show antorbital fenestra. Note the wrinkling of the maxilla (green) reacting to the twisting of the tiny, fragile skull during taphonomy.

Now, perhaps, you can see the difficulty
in determining whether or not an antorbital fenestra was present in Oculudentavis. DGS makes things easier by segregating bones with color. All interpretations are up for discussion. I hope you’ll agree, DGS overlays facilitate such discussions better than line tracings do.

Figure 1. CT scan of Oculudentavis from Xing et al. 2020, colors added. Antorbital fenestra here is mailer than in Cosesaurus, but still visible.

Figure 2. CT scan of Oculudentavis from Xing et al. 2020, colors added. Antorbital fenestra here is mailer than in Cosesaurus, but still visible.

The antorbital fenestra
in Cosesaurus (Fig. 3) and Oculudentavis (Figs. 1, 2) is only one trait among many linking these basal members of the Fenestrasauria with derived members in the Pterosauria. No single trait is ‘key’. Between the Middle Triassic (Cosesaurus) and the Early Cretaceous (Oculudentavis) the antorbital fenestra could have grown larger, as it did in pterosaurs, or disappear entirely. It’s only one trait. No one trait is that important in a phylogenetic analysis that includes 238 traits.

Figure 2. Cosesaurus nasal crest (in yellow).

Figure 3. Cosesaurus nasal crest (in yellow).

Some workers doubt
that Cosesaurus (Fig. 3) had an antorbital fenestra. Again, you decide. The large reptile tree  (LRT, 1656+ taxa) nests Cosesaurus basal to pterosaurs and other fenestrasaurs.

Final thought:
With cosesaurs in the Early Cretaceous, it might seem possible to spawn a second origin for pterosaur-like flyers… but that never happened. Only in the Middle Triassic were genes and environs in lock-step with one another to produce basal pterosaurs.


References
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Ellenberger P 1978. L’Origine des Oiseaux. Historique et méthodes nouvelles. Les problémes des Archaeornithes. La venue au jour de Cosesaurus aviceps (Muschelkalk supérieur) in Aspects Modernes des Recherches sur l’Evolution. In Bons, J. (ed.) Compt Ren. Coll. Montpellier 12-16 Sept. 1977. Vol. 1. Montpellier, Mém. Trav. Ecole Prat. Hautes Etudes, De l’Institut de Montpellier 4: 89-117.
Ellenberger P 1993. Cosesaurus aviceps . Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330
Sanz JL and López-Martinez N 1984. The prolacertid lepidosaurian Cosesaurus aviceps Ellenberger & Villalta, a claimed ‘protoavian’ from the Middle Triassic of Spain. Géobios 17: 747-753.
Xing L, O’Connor JK,; Schmitz L, Chiappe LM, McKellar RC, Yi Q and Li G 2020. Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature. 579 (7798): 245–249.

wiki/Oculudentavis
wiki/Cosesaurus

The LRT vs. The Rise of Fishes (Long 1995)

Figure 1. The Rise of Fishes 1995 book by fish expert John Long.

Figure 1. The Rise of Fishes 1995 book by fish expert John Long.

The majority of data sources
for fish here and in ReptileEvolution.com come from the excellent ink drawings of WK Gregory 1933 and the excellent photos of John Long 1995 in his book, ‘The Rise of Fishes’ (Fig. 1). Newer editions of the book are out there, but I don’t have them. Long’s own updates may erase some of the issues raised here. 

Long 1995 writes:
“The first osteichthyans are very poorly known from fossils, represented by a few scales and a mere fragments of bone. The oldest articulated remains, showing what their bodies and heads were like, are about 400 million years old.”

The LRT demonstrates
restricting phylogenetic fish taxa to just Silurian and Devonian fossils is unnecessary and restrictive. There are plenty of extant, yet still primitive, taxa one can plug into any fish phylogenetic analysis, like the large reptile tree (LRT, 1656+ taxa), for one. Without fossils the LRT can recreate the fish ‘tree of life’ starting with lancelets, then sturgeons, then sharks, and ending with sea horses, anglerfish and tetrapods.

Long includes sturgeons in the clade of bony fish (Osteichthyes)
despite his notes that sturgeon skeletons retain large amount of cartilage and much of the external armor is bone. In the LRT jawless armored Osteostraci are basal to sturgeons prior to the evolution of terminal jaws.

Long “pulls a Larry Martin”
when he states, “Osteichyan fishes are characterized by having a well-ossified internal bony skeleton” then backtracks by noting, “although the earliest fossil forms show the least degree of ossification of the vertebrae and internal bones.”

By contrast,
in the LRT only the last common ancestor of all extant bony fish (sans sturgeons and paddle bills) determines clade membership, despite the presence or absence to certain ‘key’ traits, like a bony internal skeleton.

Figure x. Subset of the LRT focusing on fish.

Figure x. Subset of the LRT focusing on fish.

The LRT confirms Long’s 1995 fish cladogram
with regard to nesting jawless fish (Agnatha) basal to jawed fish (Gnathostomata), naturally.

In Long 1995, Osteostraci
is the proximal outgroup to the Gnathostomata.

In the LRT, a member of the Osteostraci is basal to tube-mouth sturgeons in the LRT. Members of the Thelodonti are basal to Gnathostomata in the LRT.

In Long 1995, the basal dichotomy in Gnathostomata
splits Placodermi from Acanthodii. Those two are not related in the LRT.

In the LRT basal Gnathostomata splits taxa with transverse toothless jaws (LoganelliaRhincodon + Manta) from taxa with U-shaped toothy jaws (Falcatus) in the LRT. No suprageneric taxa are employed (exception: Reptilia, Lepidosauromorpha, Archosauromorpha).

In Long 1995, Silurian Placodermi give rise to 
“protosharks”, then Cladoselache, then Holcephalomorpha (ratfish) and Neoselachii (true sharks)

In the LRT, Placodermi include and give rise to catfish, all derived from Cheirodus/Amphicentrum. In the LRT, the second great dichotomy splits ratfish + sharks apart from xenacanthid ‘sharks‘, hybodontid ‘sharks‘ and Pachycormus.

In Long 1995, Silurian Acanthodii give rise to
Lophosteiformes (known only from ornate epidermal scales) and Actinopterygii (ray-finned fish)

In the LRT, Acanthodii are not primitive, but arise from ray-fin fish like the Cretaceous, bony-finned Bonnerichthys and the extant Osteoglossum.

Cause for concern
This major time gap between known fossils and phylogenic first appearance is cause for concern on the one hand, and a call to action on the other. At present it does not make sense that placoderms and acanthodians (spiny sharks) are present in the Silurian while intervening and more primitive taxa in the LRT are no yet known from the Silurian… and yet, we’ve seen this before with Jurassic multituberculates preceding more basal members of the placental clades, Glires, Carnivora and Primates.

Phenomic phylogenetic analyses, like the LRT, deliver
the gradual accumulation of derived traits that support evolutionary theory. Missing Silurian taxa will have to be discovered whenever someone discovers them.

On the other hand,
Long 1995 makes no attempt to provide any generic last common ancestors with jaws for Acanthodii + Placoderm, nor does he spell out any gradual accumulations of derived traits at transitional points, not does he employ more than a token number of generic or specific taxa in his cladogram. Suprageneric taxa are often a problem in taxonomy, as noted earlier. They can be too easily cherry-picked.

Figure 1. Early Devoniann Mesacanthus in situ. This 3 cm fish is a typical acanthodian here traced using DGS methods and reconstructed. Distinct from other spiny sharks, this one lacks large cheek plates, as in the extant Notopterus (Fig. 3).

Figure 2. Early Devoniann Mesacanthus in situ. This 3 cm fish is a typical acanthodian here traced using DGS methods and reconstructed. Distinct from other spiny sharks, this one lacks large cheek plates, as in the extant Notopterus (Fig. 3).

So, are placoderms and acanthodians ‘bony fish’?
In the LRT: yes, despite having less than fully ossified internal skeletons. That could be a retained primitive trait or a reversal in both cases. Both are derived from taxa in which the external scales are robust, providing support to the body, allowing the skeleton to degenerate. As for that heterocercal tail in acanthodians (Fig. 2) and placoderms… based on the evidence, that is a primitive trait, not a reversal. Intervening taxa, like extant Trachinocephalus, appear to have independently evolved a diphycercal tail and bony skeleton, which their Silurian direct ancestors probably lacked.

Cherry picking traits,
even ‘important’ traits, is ‘Pulling a Larry Martin‘, something the wise professor taught us not to do. Find your clades using specific or generic taxa tested against 200+ traits to find that last common ancestor, no matter the ‘key’ traits that tickle your fancy.


References
Gregory WK 1933. Fish skulls. A study of the evolution of natural mechanisms. American Philosophical Society 23(2) 1–481.
Long JA 1995.
The Rise of Fishes. Johns Hopkins University Press. Baltimore and London.

 

You heard it here first: Others also doubt the theropod affinities of Oculudentavis

The now famous tiny skull in amber, Oculudentavis, 
(Fig. 1; Xing et al. 2020) continues as a topic of conversation following its online publication in Nature and two previous PH posts here and here.

Figure 1. Oculudentavis in amber much enlarged. See figure 2 for actual size.

Figure 1. Oculudentavis in amber much enlarged.

Several workers have also thrown cold water
on the tiny theropod affinities of Oculudentavis. Oddly, all seem to avoid testing or considering in their arguments the sister taxon in the large reptile tree (LRT): Cosesaurus (Fig. 2). Instead, they report on what Oculudentavis is not. Examples follow:

Dr. Andrea Cau writes in TheropodaBlogspot.com Link here (translated from Italian using Google translate): 

“I believe that the interpretation proposed by Xing et al. (2020) is very problematic. Oculudentavis in fact has numerous anomalous characteristics for a bird and even for a dinosaur. And this makes me doubt that it is classifiable within Dinosauria (and Avialae).

  1. Absence of anti-orbital window. [not true, click here]
  2. Quadrate with large lateral concavity. This character is not typical of dinosaurs, but of lepidosaurs. [that quadrate is twisted, the other is not, the concavity is posterior in vivo]
  3. The maxillary and posterior teeth of the maxilla extend widely below the orbit.
  4. Dentition with pleurodont or acrodont implant.
  5. Very large post-temporal fenestra.
  6. Spoon-shaped sclerotic plates is typical of many scaled lepidosaurs.
  7. Coronoid process that describes a posterodorsal concavity of the jaw reminds more of a lepidosaur than a maniraptor.
  8. Very small size comparable to those of the skulls of many small squamata found in Burmese amber.

“In conclusion, there are too many “lizard” characters in Oculudentavis not to raise the suspicion that this fossil is not a bird at all, let alone a dinosaur, but another type of diapsid, perhaps a scaled lepidosaur, if not possibly a specimen very immature than some other Mesozoic group (for example, a Choristodere). It is well known that many types of reptiles present in the final stage of embryonic development and in the very first moments after hatching a cranial morphology similar to the general one of birds (of in fact, the bird skull is a form of “infantilization” of the classic reptilian skull, extended to the adult).
Unfortunately, the authors, while noting some of the similarities with the squamata, do not test the affinities of Oculudentavis outside Avialae.

“PS: out of curiosity, I tested Oculudentavis in the large Squamata matrix by Gauthier et al. (2012): it turns out to be a stem-Gekkota.”

Note to readers: Neither Gauthier et al. 2012 nor Dr. Cau tested fenestrasaurs, like Cosesaurus… yet another case of taxon exclusion. With regard to phylogenetic age, fenestrasaur tritosaur lepidosaurs, like Oculudentavis, hatch with the proportions of adults (ontogenetic isometry), so the ontogenetic status of this taxon needs further context (e.g. coeval larger adults or smaller hatchlings)/

Update March 14, 2020:
Readwer TG (below) informs me that Cau’s study did include Cosesaurus. My reply follows: “Thank you, Tyler. Good to know. My mistake. Strange that his Oculudentavis has traits more like the distinctively different Sphenodon and Huehuecuetzpalli, when it looks more like Cosesaurus in every regard. Here’s a guess based on experience: neither he nor Gauthier went to Barcelona to see Cosesaurus, and neither did either reference or cite Peters 2000 or the ResearchGate.net update. And Cau probably used the Xing et al. 2020 ink tracing of Oculudentavis rather than the more detailed DGS tracing I produced (or he could have traced himself), since he did not see the tiny antorbital fenestra [or the twisted quadrate]. Just a guess based on 20 years of experience.” 

PS. Neither Gauthier nor Cau showed their work (e.g. skulls diagrammed with suture interpretations as shown at ReptileEvolution.com links). Therefore we cannot know if or where mistakes were made in their scoring attempts. In a similar fashion, testing revealed a raft of scoring problems with Nesbitt 2011, covered earlier here in the last of a nine-part series. 

Dr. Darren Naish updates his original post in Tetrapod Zoology  
with the following notes:

“A number of experts whose opinions I respect have expressed doubts about the claimed theropod status of the fossil discussed below and have argued that it is more likely a non-dinosaurian reptile, perhaps a drepanosaur or lepidosaur (and maybe even a lizard). I did, of course, consider this sort of thing while writing the article but dismissed my doubts because I assumed that – as a Nature paper – the specimen’s identity was thoroughly checked and re-checked by relevant experts before and during the review process, and that any such doubts had been allayed. At the time of writing, this proposed non-dinosaurian status looks likely and a team of Chinese authors, led by Wang Wei, have just released an article [not linked] arguing for non-dinosaurian status. I don’t know what’s going to happen next, but let’s see. The original, unmodified article follows below the line…”

We can only trust what Dr. Naish reports regarding his private doubts as to the affinities of Oculudentavis. Here he confesses to assuming the ‘opinions’ of ‘relevant experts’ got it right, like all the other journalists who reported on this discovery, rather than testing the hypothesis of Xing et al. 2020, like a good scientist should.

While we’re on the subject of confessing, 
earlier the LRT nested Oculudentavis with Cosesaurus (Fig. 1) despite the former’s much later appearance and derived traits, like the essentially solid palate. I failed to mention the skull of Oculudentavis shares just a few traits with another Late Triassic fenestrasaur, Sharovipteryx (Fig. 1). If Oculudentavis also had a slender neck, like the one in Sharovipteryx, perhaps that was one reason why only the skull was trapped in pine sap, later transformed into amber. Just a guess.

Figure 2. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration.

Figure 2. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration.

Note:
with locked down and elongate coracoids, all members of the clade Fenestrasauria were flapping like flightless pterosaurs. Appearing tens of millions of years after the Middle Triassic genesis of fenestrasaurs, who knows what sort of post-crania tiny Early Cretaceous Oculudentavis may have evolved! Known clade members already vary like Hieronymus Bosch fantasy creatures.

The LRT is a powerful tool for nesting taxa
while minimizing taxon exclusion. And it works fast. Feel free to use it in your own studies.


References
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007.The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Xing L, O’Connor JK,; Schmitz L, Chiappe LM, McKellar RC, Yi Q and Li G 2020. 
Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature. 579 (7798): 245–249.

late arrival:

Wang Wei, Zhiheng Li, Hu Yan, Wang Min, Hongyu Yi & Lu Jing 2020. The “smallest dinosaur in history” in amber may be the biggest mistake in history. Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences: Popular Science News (2020/03/13)
http://ivpp.cas.cn/kxcb/kpdt/202003/t20200313_5514594.html

from B. Creisler’s translated post at dml.cmnh.org:

“Here is the list of problems found by the authors:
Doubts 1. Can the shape of the head prove that it is a bird? 
Doubt 2. Unreasonable Phylogenetic Analysis 
Doubt 3. Birds without antorbital fenestrae? 
Doubt 4. “Birds” with pleurodont teeth? 
Doubt 5. Mysterious quadratojugal bone 
Doubt 6. Scleral bones only found in lizards 
Doubt 7. The bird with the most teeth in history? 
Doubt 8. Body size 
Doubt 9. No feathers? 
Doubt 10. Strange wording and logic chains
We hope that the authors of the paper will respond publicly to these questions as soon as possible. At the same time, it is hoped that the authors of the paper will quickly release the raw data of CT scans, so that other scientists can verify the existing results based on the raw data.”
July Post-Script
Authors retract the paper, according to Nature.

 

Oculudentavis: First 3D skull of pterosaur precursor discovered with skin!!!

That could have been the spectacular headline
circulating ’round the world now about Oculudentavis (Fig. 1, Xing et al. 2020), the tiny (1.4cm) skull found in Early Cretaceous Burmese amber.

Figure 1. Oculudentavis in amber much enlarged. See figure 2 for actual size.

Figure 1. Oculudentavis in amber much enlarged. See figure 2 for actual size.

Smallest Mesozoic dinosaur skull discovered”
is also pretty exciting, but it’s not true, as noted in yesterday’s post.

Figure 1. Cosesaurus insitu. No bones are present. This is a natural mold that includes an amorphous blob, a jellyfish, that trapped one foot of this unique specimen.

Figure 2. Middle Triassic Cosesaurus insitu. No bones are present. This is a natural mold that includes an amorphous blob, a jellyfish, that trapped one foot of this unique specimen.

Why was the Middle Triassic sister taxon Cosesaurus
(Ellenberger and DeVillalta 1974; Fig. 2) not on the radar of Oculudentavis authors Xing et al. 2020?

You can thank
the current crop of pterosaur experts who have ignored and omitted this taxon and others (Peters 2000a, b, 2002, 2007, 2009; Fig. 3) for the last twenty years in their unprofessional efforts to retain an invalidated hypothetical relationship of pterosaurs to unspecified archosaurs, dinosaurs, phytosaurs, erythrosuchids or basal bipedal crocodylomorphs like Scleromochlus, depending on which author you study. Dr. John Ostrom remarked on the snails’ pace of paleontology as it slowly came to accept the dinosaurian origin of birds in the 1980s that was clearly documented in the 1870s. It also took a long time to raise the dragging tails of dinosaurs in museum mounts, despite the lack of drag marks in dinosaur tracks.

Worse yet,
those workers are adversely influencing the next generation of pterosaur artists and experts.

The lineage of pterosaurs recovered from the large reptile tree. Huehuecuetzpalli. Cosesaurus. Longisquama. MPUM 6009.

Figure 3. The lineage of pterosaurs recovered from the large reptile tree. Huehuecuetzpalli. Cosesaurus. Longisquama. MPUM 6009 (now Bergamodactylus). Oculudentavis is a late-surviving sister to Cosesaurus.

It comes down to taxon exclusion, as usual.
Between 1974 and 2000 it used to be by accident or oversight. Now and for the last two decades, taxon exclusion has been part of the plan. We discussed this problem earlier here.

Yesterday Oculudentavis became
the 1656th taxon added to the large reptile tree (LRT).

PS
Four pterosaur precursors preserve skin/filaments/extradermal membranes or impressions of same, but all are crushed specimens.


References
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Peters D 2000a. 
Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330
Xing L, O’Connor JK,; Schmitz L, Chiappe LM, McKellar RC, Yi Q and Li G 2020. Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature. 579 (7798): 245–249.

wiki/Oculudentavis

Cosesaurus_aviceps_Sharovipteryx_mirabilis_and_Longisquama_insignis_Reinterpreted

 

Oculudentavis: not a tiny bird or dinosaur. It’s a tiny cosesaur lepidosaur.

Figure 1. Oculudentavis in amber much enlarged. See figure 2 for actual size.

Figure 1. Oculudentavis in amber much enlarged from Xing et al. 2020. See figure 2 for actual size.

I never thought the tiny Middle Triassic pterosaur ancestor, Cosesaurus
(Fig. 2, 4) would ever be joined by an Early Cretaceous sister taxon that was even smaller. Yesterday the impossible happened when the editors of Nature published a description of tiny Oculudentavis (Xing et al. 2020; Figs. 1, 2; Early Cretaceous, 99 mya; 1.4cm skull), which the authors mistakenly considered a basal bird with teeth and the smallest Mesozoic dinosaur.

Figure 2. CT scans of Oculudentavis from Xing et al. 2020 and colored here, plus a comparison of Cosesaurus to scale.

Figure 2. CT scans of Oculudentavis from Xing et al. 2020 and colored here, plus a comparison of Cosesaurus to scale.

Taxon exclusion
Unfortunately the authors did not test Oculudentavis with Cosesaurus, a fenestrasaur, tritosaur lepidosaur… a taxon far from dinosaurs. When Oculudentavis was added to the large reptile tree (LRT) as the 1656th taxon, the tree length was 20291.

As a test
I forced Oculudentavis over to the London specimen of Archaeopteryx, which Xing et al. recovered as a sister, and the LRT bumped up to 20324, a mere 33 steps more despite the huge phylogenetic distance.

I’ve said it before,
convergence is rampant in the tetrapod family tree.

To that point, it should be remembered,
the original describers of Cosesaurus (Ellenberger and de Villalta 1974) mistakenly considered it a Middle Triassic stem bird.

In contrast,
Peters (2000) recovered Cosesaurus and kin with pterosaurs using four previously published phylogenetic analyses. Later, with more taxa, Peters (2007) recovered pterosaurs and kin with the lepidosaur Huehuecuetzpalli (Fig. 3). In addition, ResearchGate.net holds an unpublished manuscript and figures redescribing Cosesaurus and kin much more accurately. The pterosaur referees did not want that manuscript published, having ignored the earlier ones for so long.

Figure 3. Oculudentavis added to the LRT.

Figure 3. Oculudentavis added to the LRT with previously untested  tritosaur lepidosaurs.

Ironically
Xing et al. noted in tiny Oculudentavis lepidosaur-like sclerotic (eyeball) bones and acrodont to pleurodont teeth extending below the orbit, as in modern lizards. Even with these clues, they did not add lepidosaurs to their analysis. They assumed from the start they had a tiny dinosaur-bird (with lepidosaur traits).

Figure 2. Cosesaurus running and flapping - slow.

Figure 4. Cosesaurus running and flapping. If you want to know what the Oculudentaivis post-crania looks like, this is the closest known sister taxon, slightly smaller than full scale.

Distinct from Cosesaurus,
(Fig. 2) the palate of Oculudentavis is solid below the rostrum. The antorbital fenestra is reduced. Damage to the skull displaced one ectopterygoid to the mid palate and broke the jugal. The post-crania remains unknown, but Cosesaurus (Fig. 4) is the most similar taxon.

From the Xing et al. 2020 abstract:
“Here we describe an exceptionally well-preserved and diminutive bird-like skull that documents a new species, which we name Oculudentavis khaungraae gen. et sp. nov. The find appears to represent the smallest known dinosaur of the Mesozoic era, rivalling the bee hummingbird (Mellisuga helenae)—the smallest living bird—in size. The O. khaungraae specimen preserves features that hint at miniaturization constraints, including a unique pattern of cranial fusion and an autapomorphic ocular morphology9 that resembles the eyes of lizards. The conically arranged scleral ossicles define a small pupil, indicative of diurnal activity. The size and morphology of this species suggest a previously unknown bauplan, and a previously undetected ecology.”

The authors saw lepidosaur traits not found in basal birds/tiny dinosaurs.
Rather than seeking and testing more parsimonious sister taxa elsewhere, the authors chose to follow their initial bias and described their find as an odd sort of tiny bird.

In a similar fashion
just a few days ago Hone et al. 2020 did much the same as they mistakenly described a large pteryodactylid, Luchibang, as a small istiodactylid, following their initial bias.

The LRT provides a wide gamut of 1656 taxa 
to test your next new taxon. Don’t make the same mistake as the above authors by assuming your odd little something is something it isn’t.


References
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007.The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Xing L, O’Connor JK,; Schmitz L, Chiappe LM, McKellar RC, Yi Q and Li G 2020. 
Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature. 579 (7798): 245–249.

Thanks to Dr. O’Connor for sending a PDF of the Nature paper. 

wiki/Oculudentavis
www.researchgate.net