Sexual selection: a peacock’s tale

Today’s topic began with a YouTube video
featuring Richard Dawkins and Bret Weinstein (click to view). They discussed the peacock’s elaborate plumage with the idea that peahens were choosing the most magnificent displays. Weinstein opined that it may be more difficult for males to survive with such long trains (= tail feathers folded away, extending posteriorly). Thus females were handicapping their male offspring by selecting peacock mating partners with longer and longer more elaborate tail feathers.

According to Wikipedia:
“The function of the peacock’s elaborate train has been debated for over a century. In the 19th century, Charles Darwin found it a puzzle, hard to explain through ordinary natural selection. His later explanation, sexual selection, is widely but not universally accepted. In the 20th century, Amotz Zahavi argued that the train was a handicap, and that males were honestly signalling their fitness in proportion to the splendour of their trains. Despite extensive study, opinions remain divided on the mechanisms involved.”

Figure 3. Peafowl mating. The males stands crouched upon the back and hips of the female.

Figure 1. Peafowl mating. The males stands crouched upon the back and hips of the female.

Phylogenetically,
in the large reptile tree (LRT, 1735+ taxa) peafowl (genus: Pavo) nest with the common chicken (genus: Gallus). Both are terminal taxa.

At the start, I question:

  1. Do peahens always or often or used to pick the most lavish peacock?
  2. Do peacocks actually compete with each other? Or do most of them give up after sizing up the competition?
  3. Do peacocks mate with as many peahens as they can or do they form pair bonds?
  4. In other words, have we examined the situation enough to know?
  5. Were Dawkins and Weinstein just guessing based on end results?
  6. Added after publication, based on a a reader’s comment: What are the differences between domestic and wild peafowl? (If there are any wild peafowl.)

Summarizing earlier studies, Callaway 2011 wrote:
“Size doesn’t always matter for peacocks. Peahens don’t necessarily choose the males with the biggest tails — but small tails are right out.”

Takahashi et al. 2008 concluded,
“our findings indicate that the peacock’s train (1) is not the universal target of female choice, (2) shows small variance among males across populations and (3) based on current physiological knowledge, does not appear to reliably reflect the male condition.”

Yorzinski et al. 2017 write:
“In species where a male trait is only evaluated by one of the sexes, it is often the males that are assessing the trait, suggesting that male traits often evolve initially in the context of male–male competition, and subsequently, in female choice (Berglund et al., 1996; Borgia and Coleman, 2000). 

Like deer antlers or any other tournament species. Meanwhile, what are the peahens doing?

“We know little about how animals selectively direct their attention during mate and rival assessment. Previous work has shown that female peafowl shift their gaze between potential mates and their environment, potentially scanning for predators and other conspecifics while assessing mates. And, when evaluating a mate, peahens selectively direct their attention toward specific display regions of peacocks. In contrast, we do not know how males selectively alter their attention when assessing other males. (Citations deleted).

“We therefore investigated how males direct their attention when they assess potential rivals, using peacocks as a model system.”

“Competition among peacocks is intense as mating success is highly skewed toward a small proportion of successful males. Males compete with each other by displaying their erect trains or walking parallel to other males. If aggression escalates, they chase each other and engage in fights that consist of them jumping and using their spurs Males with longer trains and tarsi establish territories in central locations within leks and engage in more agonistic behaviors with other males. In contrast, males with shorter trains are less likely to establish display territories (Citations deleted).

“it is clear from these sample periods that males spend a significant fraction of their time monitoring their rivals.

“While assessing their competitors, peacocks did not spend very much time looking at females. In fact, they allocated less than 5%

“Further experiments will be necessary to determine how much time males allocate to monitoring females while they are courting them. We found that when males directed their gaze toward females,

Peacocks also devote a significant amount of their daily time budget to preening (Walther, 2003) and directing attention toward themselves could allow them to monitor the condition of their feathers.

“Similar to the results in this study on peacocks, peahens primarily gazed at the lower display regions of males: at their lower trains, body and legs (Yorzinski et al., 2013).”

Here are a few, short ‘peacocks on display’ YouTube videos 
showing the variation in the use of the display behavior or lack thereof.

Callaway 2011 quotes Petrie (of Petrie and Halliday 1994),
“At the end of the day, we will never know what peahens are looking at and how they select their mates. You can’t ask them.”

Figure 2. Peacock flying.

Figure 2. Peacock flying.

One final thought:
Since predators are likely to attack from the rear of the peacock (video #3 above), what a tiger will get is a mouthful or paw-full of feathers, which can detach under sufficient strain, much like the expendable tail of certain lizards. Thus the hypothesis that a long train of feathers is an impediment to survival in an attack may be true only rarely… which is one reason why peacocks are a relatively successful species, all hypothetical doubts aside.


References
Callaway E 2011. Size doesn’t always matter for peacocks. Nature 1107 online
Dakin R and Mongomerie R 2011. Peahens prefer peacocks displaying more eyespots, but rarely. Animal Behaviour doi:10.1016/j.anbehav.2011.03.016
Petrie M and Halliday T 1994. Experimental and natural changes in the peacock’s (Pavo cristatus) train can affect mating success. Behavioral Ecology and Sociobiology 35, 213-217.
Takahashi M, Arita H, Hiraiwa-Hasegawa M and Hasegqawa T 2008. Peahens do not prefer peacocks with more elaborate trains. Animal Behaviour 75(4):1209–1219.
Yorzinski JL, Patricelli GL, Bykau S and Platt ML 2017. Selective attention in peacocks during assessment of rival males. Journal of Experimental Biology (2017) 220, 1146-1153 doi:10.1242/jeb.150946

wiki/Indian_peafowl
https://www.nature.com/news/2011/110418/full/news.2011.245.html

Specimen STM 15-15 of Sapeornis under the laser and DGS

Serrano et al. 2020
used Tom Kaye‘s laser-stimulated fluorescence (LSF) device to reveal more feathers on the STM 15-15 specimen of Sapeornis more clearly than in visible light (Fig. 1). All the glue between the reassembled stones also shows up much more clearly. In this specimen the bones are easier to see in visible light. Under LSF everything organic glows: feathers, bones, guts.

Figure 1. Sapeornis specimen STM-1515, in situ, under laser, under DGS.

Figure 1. Sapeornis specimen STM 15-15, in situ, under laser and under DGS. Ventral view. Here bones are easier to see in visible light, feathers under laser.

From the abstract
“Unseen and difficult-to-see soft tissues of fossil birds revealed by laser-stimulated fluorescence (LSF) shed light on their functional morphology. Here we study a well-preserved specimen of the early pygostylian Sapeornis chaoyangensis under LSF and use the newly observed soft-tissue data to refine previous modeling of its aerial performance and to test its proposed thermal soaring capabilities.”

Figure 2. Sapeornis skull specimen STM 1515

Figure 2. Sapeornis skull specimen STM 15-15

From the discussion
“Our study is the first to use the preserved body outline of a fossil bird—as revealed under LSF—to refine its flight modeling.”

Figure 3. Sapeornis skull, specimen STM 1515.

Figure 3. Sapeornis skull reconsructed —  specimen STM 15-15.

An overlay of colors in Photoshop
(Figs. 1, 2 = digital graphic segregation, DGS) also helps each bone stand out from the matrix. Moreover, the color tracings are used to build a reconstruction (Figs. 3, 4) from which it is easier to compare features, point-by-point with other Sapeornis specimens (Fig. 4).

In this way, character scores are backed up
with visual data for referees and readers to quickly judge whether the contours of every bone are valid or not without laboriously examining every score and every centimeter of every in situ specimen. Given the world-wide dispersal of fossils and occasional permission restrictions, DGS tracings just make things easier.

An earlier specimen of Sapeornis
(IVPP V13276; Fig. 4), from a previous post, is grossly similar and larger than STM 15-15. Subtle differences (e.g. toe length, coracoid shape, sternae presence, maxillary tooth presence, etc.) separate the two individuals, perhaps splitting them specifically. Even so, the two humeri are nearly identical in size and shape, despite the overall size differences.

Figure 4. Sapeornis specimen STM 15-15 reconstructed from DGS tracing, figure 1 compared to a more robust specimen with larger feet but an identical humerus.

Figure 4. Sapeornis specimen STM 15-15 reconstructed from DGS tracing, figure 1 compared to a more robust IVPP V13276 specimen with larger feet but an identical humerus.

Sapeornis chaoyangensis (Zhou and Zhang 2002. 2003; Early Cretaceous; IVPP V13276) is a basal ornithurine bird, the clade that gave rise to modern birds. Sapeornis nests in the same clade as Archaeopteryx recurva, the Eichstätt specimen, in the large reptile tree (LRT, 1729+ taxa). The short tail was tipped with a pygostyle and a fan of feathers. The coracoids were oddly wide and relatively short.


References
Serrano FJ, Pittman M, Kaye TG, Wang X, Zheng X and Chiappe LM 2020.
Laser-stimulated fluorescence refines flight modeling of the Early Crettaceous bird Sapeornis. Chapter 13 in Pittman M and Xu X eds. Pennaraptoran theropod dinosaurs. Past progress and new Frontiers. Bulletin of the American Museum of Natural History 440; 353pp. 58 figures, 46 tables.

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

Wulong: a new troodontid, not a microraptor-dromaeosaur

Poust et al. 2020
bring us news of a small, subadult theropod with some interesting traits, Wulong bohaiensis (Early Cretaceous; D2933). They considered the specimen a microraptorine dromaeosaurid.

Figure 1. Wulong in situ, plus the original published diagram.

Figure 1. Wulong in situ, plus the original published diagram. The specimen is somewhat surrounded by a few coprolites = cop.

By contrast, 
the large reptile tree (LRT, 1637+ taxa) nests Wulong among similar, small, long-legged troodontids, between Buitreraptor and Caihong. While this topology differs from that of other workers, the same can be said of nearly every clade in the LRT. That’s why this blog has been self-labeled ‘heretical’.

Figure 2. Wulong skull, original diagram, DGS colors applied to bones and reconstruction based on the DGS tracings.

Figure 2. Wulong skull, original diagram, DGS colors applied to bones and reconstruction based on the DGS tracings.

So, why the different views?
That appears to be due to taxon exclusion. There is no indication in the text that Buitreraptor and Caihong were included in analysisThere is no indication that the authors created a reconstruction, which helps identify bones, their ratios and proportion in crushed taxa like Wulong. More importantly…

Figure 4. Wukong manus DGS tracing and reconstruction. Note the 180º rotation of the manus relative to the radius and ulna.

Figure 4. Wukong manus DGS tracing and reconstruction. Note the 180º rotation of the manus relative to the radius and ulna.

… several taxa converge on birds
and small feathered theropods converge with each other in the LRT. The differences between the clades should not be determined by a few traits (= Pulling a Larry Martin), but here are gleaned after phylogenetic analysis of several hundred traits. As mentioned earlier, you can’t nest a specimen within a clade by a small number of cherry-picked traits because there is so much convergence within the Tetrapoda. Rather, run an analysis and find out which taxon is the last common ancestor of a derived clade. Those, then, are the validated clade members.

Figure 3. Wulong pelvis.

Figure 3. Wulong pelvis.

Figure 4. Wulong pedes, original tracing and reconstruction based on DGS tracings.

Figure 4. Wulong pedes, original tracing and reconstruction based on DGS tracings.

Uniquely
the coracoid is fenestrated in the middle. The ilium includes a prepubis process. Some feathers are preserved.

The authors report,
“Wulong is distinguished by several autapomorphic features and additionally, has many characteristics that distinguish it from its closest well-known relatives. Compared with Tianyuraptor and Zhenyuanlong, Wulong is small and its forelimbs are proportionally long.”

By contrast,
in the LRT Tianyuraptor and Zhenyuanlong are not related to troodontids, microraptorids or dromaoeosaurids. Tianyuraptor and Zhenyuanlong are basal to tyrannosaurids.

References
Poust AW, Gao C-L, Varricchio DJ, Wu J-L and Zhang F-J 2020. A new microraptorine theropod from the Jehol Biota and growth in early dromaeosaurids. The Anatomical Record. American Association for Anatomy. DOI: 10.1002/ar.24343

Another disc-head anurognathid from Jurassic China

Yesterday Yang et al. 2018 presented NJU-57003 (Figs. 1–3), a small anurognathid pterosaur with a great deal of soft tissue preservation, including feather-like filaments, said to be homologous with feathers. That was shown to be invalid by taxon exclusion here.

Today we’ll reconstruct
the crushed skull using DGS and nest this specimen in a cladogram using phylogenetic analysis (Fig. 4) in a few hours. Yang et al. were unable or unwilling to do either, even with firsthand access to the fossil and nine co-authors.

Figure 1. The NJU-57003 specimen and outline drawing, both from Yang et al. 2018. Various membranes and the overlooked sternal complex are colored in here.

Figure 1. The NJU-57003 specimen and outline drawing, both from Yang et al. 2018. Various membranes and the overlooked sternal complex and prepubes are colored in here. Clearly the uropatagia are separated here, as in Sharovipteryx. No wing membrane attaches below the knee.

Overlooked by Yang et al.
the sternal complex is quite large beneath the wide-spread ribs, a trait common to anurognathids. The torso, like the skull, would have been much wider than deep in vivo.

Figure 2. The skull elements of NJU-57003 colored to help alleviate the chaos of the crushed specimen. See figure 3 for the same elements reconstructed.

Figure 2. The skull elements of NJU-57003 colored to help alleviate the chaos of the crushed specimen. I can’t imagine betting able to interpret this skull without segregating each piece with a different color. See figure 3 for the same elements reconstructed with these colors.

As in other disc/flathead anurognathids
the palatal processes of the maxilla (red in Figs. 2, 3) radiate across the light-weight palate.  Yang et al. mislabeled these struts the ‘palatine’ (Fig. 1) following in the error-filled footsteps of other pterosaur workers who did not put forth the effort to figure things out.

The skull
is likewise supported by relatively few and very narrow struts. Contra Yang et al. 2018, who once again, mistakenly identify the toothy maxilla as an scleral ring (Fig. 1), the actual scleral rings (Figs. 2, 3) are complete and smaller within a large squarish orbit bounded ventrally by a deep jugal.

Figure 3. The skull of NJU-57003 reconstructed in animated layers for clarity. This is something the print media just cannot do as well. All elements are similar to those found earlier in other anurognathids.

Figure 3. The skull of NJU-57003 reconstructed in animated layers for clarity. This is something the print media just cannot do as well. All elements are similar to those found earlier in other anurognathids. Note the eyes, as in ALL pterosaurs, are in the back half of the skull.

Discodactylus megasterna (Yang et al. 2018; Middle-Late Jurassic, Yanlio biota, 165-160mya; NJU-57003) is a complete skeleton of a disc-skull anurognathid with soft tissue related to Vesperopterylus. The sternal complex is quite large to match the wider than tall torso. Distinct from other anurognathids, m4.1 does not reach the elbow when folded.

Figure 4. Subset of the LPT nesting Discodactylus with Vesperopterylus within the Anurognathidae.

Figure 4. Subset of the LPT nesting Discodactylus with Vesperopterylus within the Anurognathidae.

This specimen was introduced without a name
in a paper that incorrectly linked pterosaur filaments to dinosaur feathers (Yang et al. 2018), rather than with their true ancestor/relatives, the filamentous fenestrasaurs, Sharovipteryx and Longisquama, taxa omitted in Yang et al. and all workers listed below. Details here. The authors were unable to score traits for the skull and did not mention Vesperopterylus in their text.

Apparently the same artist
who originally traced the skull of Jeholopterus in 2003 (Fig. 5) also traced the present specimen (Fig. 1) with the same level of disinterest and inaccuracy. Compare the original image (Fig. 5 left) to a DGS image (Fig. 5 right). 

Figure 5. The original 2003 tracing of Jeholopterus (upper left) was inaccurate, uninformed and uninformative despite first hand access compared to the more informative and informed tracing created using DGS methods.

Why did these anurognathids have such long filaments?
Owls use similar fluffy feathers to silence their passage through air, first discussed earlier here.

The pterosaur experts weigh in the-scientist.com/news:
“I would challenge nearly all their interpretations of the structures. They are not hairs at all, but structural fibers found inside the wings of pterosaurs, also known aktinofibrils,” says pterosaur researcher David Unwin at the University of Leicester in the UK who was not part of the study. “They discovered lots of hair-like structures, but [don’t report any] wing fibers. I find that problematic.” Unwin suspects these fibers are likely to be present but have been mislabeled as feathers.  

This is a very important discovery,” says Kevin Padian, a palaeontologist at the University of California, Berkeley, “because it shows that integumentary [skin] filaments evolved in both dinosaurs and pterosaurs. That’s not surprising because they are sister groups, but it is good to know.”  

Padian draws attention to the pycnofibers’ “hair-like structure” as illustrating that they served as insulation. This is yet another characteristic of dinosaur and pterosaurs, along with high growth rate, pointing to their common ancestor as warm blooded.  “I wish the illustrations in the paper were better, but there is no reason to doubt them,” he adds.

Dr. Padian knows better.
He’s keeping the family secret by not mentioning fenestrasaurs (Peters 2000).

“The thing that is cool is that it bolsters the idea that pterosaurs and dinosaurs are sister taxa, if they are correct in interpreting these structures as a type of feather,” writes paleobiologist David Martill of the University of Plymouth in the UK, in an email. 

Dr. Martill knows better.
He’s keeping the family secret by not mentioning fenestrasaurs.

The specimens described in the paper are very interesting, agrees Chris Bennett, a palaeontologist at Fort Hays State University in Kansas, but in an emailed comment he describes the interpretation of the structures as problematic. “The authors’ characterization of the integumentary structures as ‘feather-like’ is inappropriate and unfortunate,” he writes. Some of the structures look like they could be from fraying or other decomposition, rather than feathers. Bennett adds that filamentous structures for insulation and sensation are fairly common, from hairy spiders to caterpillars to furry moths. “It seems to me to be premature to use filamentous integumentary structures to support a close phylogenetic relationship between pterosaurs and dinosaurs,” says Bennett. 

Dr. Bennett knows better.
He’s keeping the family secret by not mentioning fenestrasaurs.

Benton stands by his conclusion that pterosaurs wore plumage. Asked about the suggestion that the feathers could be wing fibers, he writes in an email, “Actinofibrils occur only in the wing membranes, whereas the structures we describe occur sparsely on the wings, but primarily over the rest of the body.”

Dr. Benton knows better.
He’s keeping the family secret by not mentioning fenestrasaurs. More details here.

References
Bennett SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoological Journal of the Linnean Society 118:261-308.
Hone DWE and Benton MJ 2007.
An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2009.
Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Peters D 2000. 
A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Yang et al. (8 co-authors) 2018. Pterosaur integumentary structures with complex feather-like branching. Nature ecology & evolution doi:10.1038/s41559-018-0728-7

 

SVP 2018: Ancestral dinosaur integument

Holtz 2018 tackles the question:
What sort of dermal covering did basal dinosaurs, like Herrerasaurus have? Naked skin (Fig. 1)? Scales? Dorsal osteoderms? Pre-feather filaments? Or combinations thereof?

We looked at this question
earlier. In the poultry section of grocery stores chickens are nude and have no scales.

Holtz concludes,
“In some of these analyses, the more likely ancestral status for Dinosauria or Ornithoscelida was recovered as filamentous. However, the fact that the basal relationships are indeed poorly resolved at present requires an acceptance of ambiguity for the integumentary condition of the original dinosaur.”

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

Figure 1. Primordial feathers on the back of a 10-day-old chick embryo. Ontogeny sometimes recapitulates phylogeny. Perhaps this embryo provides just such a clue.

In the non-ambiguous
large reptile tree (LRT,  1315 taxa) the ancestral state (based on phylogenetic bracketing) is nudity with filaments and dorsal osteoderms transformed into subcutaneous spine tables that disappear shortly thereafter. Given that Holtz did not recover a clade Phytodinosauria, he is not likely to have included basal bipedal crocs as proximal outgroups, as recovered in the LRT.

Figue 1. A new reconstruction of the basal bipedal croc, Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The posterior dorsals are deeper than the anterior ones.

Figue 1. A new reconstruction of the basal bipedal croc, Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The posterior dorsals are deeper than the anterior ones.

References
Holtz TR 2018. Integumentary status: It’s complicated: phylogenetic sedimentary, and biological impediments to resolving the ancestral integument of Mesozoic Dinosauria. SVP abstracts.

SVP 2018: Hindlimb feathers useful as brood covers in oviraptorids?

Hopp and Orsen 2018
bring a novel and well documented hypothesis to light: “Here we present evidence gleaned from our studies of a number of fossils that possess hind-limb feathers, as well as two examples of nesting Citipati. Two well preserved individuals sitting on nests with large egg clutches (IGM-100/979, IGM-100/1004) clearly demonstrate a lack of complete coverage of the eggs by the animals’ bodies and limbs. We previously showed that pennaceous feathers would have aided the coverage of eggs near the ulna and manus. We also noted a deficiency of egg coverage at the rear quarters laterally adjacent to the pelvis and tail. Here we demonstrate how pennaceous feathers, recently described on the tibiae and tarsi of several non-flying theropods and some primitive birds as well, could have served very effectively to cover eggs in these rear quarter positions.”

FIgure 1. From Zheng et al. 2013 showing the maximum extent of hind leg feathers in Anchiornis.

FIgure 1. From Zheng et al. 2013 showing the maximum extent of hind leg feathers in Anchiornis. Pedopenna nests with Anchiornis.

Excellent hypothesis. But…
Zheng et al. 2013 also studied this problem. They wrote, “parallel pennaceous feathers are preserved along the distal half of the tibiotarsus and nearly the whole length of the metatarsus in each hindlimb [of Sapeornis]. The feathers are nearly perpendicular to the tibiotarsus and metatarsus in orientation and form a planar surface as in some basal deinonychosaurs with large leg feathers.”

Zheng et al. 2013 also report similar leg and/or foot feathers are found in
“Basal deinonychosaurians (= Microraptor), the basal avialan Epidexipteryx, Sapeornis, confuciusornithids, and enantiornithines. In these taxa, the femoral and crural feathers are large, and in most cases they are pennaceous feathers that have curved rachises and extend nearly perpendicular to the limbs to form a planar surface.”

The distribution of foot feathers
in theropods in the large reptile tree (LRT, subset Fig. 2) is shown in blue (cyan). Few included taxa preserve feathers. The question is: do foot feathers appear, then disappear, then reappear? Or do all intervening taxa have foot feathers?

Figure 3. Where feathers on the foot are preserved on the LRT.

Figure 2. Where feathers on the foot are preserved on the LRT.

Back to the brooding question:
Citipati is an oviraptorid and oviraptorids are outside of the occurrences of foot feathers in theropods in the LRT. Note: all specimens with foot feathers are a magnitude smaller than oviraptorids. Hopp and Orsen do not differentiate (in their abstract, I did not see their presentation) between tibial feathers and foot feathers. Citipati nests outside of the current phylogenetic bracket for foot feathers. Tibial feathers have a much wider distribution in fossils. Tibial feathers are more likely to be present in Citipati, but note: tibial and foot feathers are not present in Caudipteryx (Fig. 3) an oviraptorid sister in the LRT .

Figure 3. Caudipteryx preserves forelimb and tail feathers, but no leg or foot feathers. It nests with oviraptorids in the LRT.

Figure 3. Caudipteryx preserves forelimb and tail feathers, but no leg or foot feathers. It nests with oviraptorids in the LRT.

Back to the question of pennaceous hind limb feathers in pre-birds:
Here’s one answer, perhaps convergent with the presence of large uropatagia in flapping, but non-volant fenestrasaurs (like Cosesaurus Fig. 4). And look at the long legs and large uropatagia of the basalmost pterosaur, Bergamodactylus (Fig. 4)! It was just learning how to flap and fly and could use a little aerodynamic help in keeping steady.

When pre-birds, like Anchiornis,
and other convergent theropods, like Microraptor, first experimented with flapping and leaving the ground, they were necessarily new at it, not perfect at coordinated symmetrical flapping. Perhaps pre-birds used a bit of aerodynamic stabilization in the form of hind limb feathers as they phylogenetically became better and better at flapping, then flying. Tibial and foot feathers may have provided that aerodynamic stability, acting like vertical stabilizers in most airplanes. Exceptionally, present-day flying wing-type airplanes no longer require a vertical stabilizer because computers assist the pilot in controlling the aircraft, just as modern birds control flight without vertical stabilizers. That’s because modern birds with unfeathered feet have established neural networks not present or only tentatively present in pre-birds.

Figure 1. Bergamodactylus compared to Cosesaurus. Hypothetical hatchling also shown.

Figure 4. Bergamodactylus compared to Cosesaurus. Hypothetical hatchling also shown. Look at those large uropatagia. Those are for stability in this student pilot, not yet as coordinated as in later, more derived pterosaurs.

References
Hopp TP and Orsen MJ 2018. Evidence that ‘four-winged’ paravian dinosaurs may have used hindlimb feathers for brooding.” SVP abstracts.
Hu D, Hou L, Zhang L and Xu X 2009. A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus. Nature 461(7264):640-3. doi: 10.1038/nature08322.
Longrich N 2006. Structure and function of hindlimb feathers in Archaeopteryx lithographica. Paleobiology 32 (3), 417-431
Xu X and Zhang F 2005. A new maniraptoran dinosaur from China with long feathers on the metatarsus. Naturwissenschaften. 92(4): 173–177.
Zhang F-C and Zhou Z-H 2004. Palaeontology: Leg feathers in an Early Cretaceous bird. Nature 431, 925(2004). doi:10.1038/431925a
Zheng X-T et al. 2013. Hind wings in basal birds and the evolution of leg feathers. Science 339:1309-1312. DOI: 10.1126/science.1228753

When did T-rex lose its feathers?

There will be two answers here:
1) phylogenetically; and 2) ontogenetically as Bell et al. 2017 discuss changing ideas regarding the integument of tyrannosauroids.

Tradtional taxon exclusion
has given the Bell et al. team a different ancestry of tyrannosaurs than in the large reptile tree (LRT, 1307 taxa). Even so, Early Cretaceous taxa are the last to preserve feathers or filaments in the large and giant members of this clade.

A few facts before we get started:

  1. Mid-sized Early Cretaceous Yutyrannus (from the allosaur clade, Fig. 1) has filaments
  2. Giant Late Cretaceous Tyrannosaurus (a tyrannosauroid, Fig. 1) has scales preserved in small patches and no filaments preserved (Fig. 2).
  3. Small-sized Zhenyuanlong (a stem tyrannosaur, Fig. 2) has flight and contour feathers, but no elongate coracoids for flapping
  4. Bell et al. include Yutyrannus in the ancestry of tyrannosaurs and ignore Zhenyuanlong.
  5. Plucked poultry reveals naked skin, except around the feet
  6. Large dinosaurs of all types also lose their feathers phylogenetically
Figure 1. Late Cretaceous Tyrannosaurus, which has scales, to scale with Early Cretaceous allosaurid, Yutyrannus, which has filaments.

Figure 1. Late Cretaceous Tyrannosaurus, which has scales, to scale with Early Cretaceous allosaurid, Yutyrannus, which has feather-like filaments. This is the largest theropod, so far, to have such filaments.

Bell et al. report
“Recent evidence for feathers in theropods has led to speculations that the largest
tyrannosaurids, including Tyrannosaurus rex, were extensively feathered. We describe fossil integument from Tyrannosaurus and other tyrannosaurids (Albertosaurus, Daspletosaurus, Gorgosaurus and Tarbosaurus), confirming that these large-bodied forms possessed scaly, reptilian-like skin. These new findings demonstrate that extensive feather
coverings observed in some early tyrannosauroids were lost by the Albian, basal to Tyrannosauridae. This loss is unrelated to palaeoclimate but possibly tied to the evolution of gigantism, although other mechanisms exist.”

And they conclude,
“Gigantism (i.e. increased body mass) affords greater heat retention: a thermodynamic by-product of the square-cube law and linked to reductions in hair in large modern terrestrial mammals.”

Figure 2. Tyrannosaurus (without feathers) to scale and directly compared to Zhenyuanlong (with feathers).

Figure 2. Tyrannosaurus (without feathers) to scale and directly compared to Zhenyuanlong (with feathers). Integument patches shown from Bell et al. 2017. Note the reduction of the forelimbs and hind limbs as tyrannosaurs grow in size phylogenetically. For those who don’t like the LRT phylogeny, this GIF animation shows just how similar tiny Zhenyuanlong and Tyrannosaurus really are.

A modern analogy: small furry hyrax ~ large naked elephant
Just as baby elephants can have a bit more vestigial hair than their parents do, baby giant theropods might have had more vestigial filaments. And considering the small patches of scales found for giant theropods so far, small patches of vestigial filaments might still have been present elsewhere, perhaps trailing the forelimbs, for instance. We just don’t know yet.

Figure 4. The small furry hyrax is in the lineage of the large naked elephant, analogous to small feathery theropods and large naked theropods. The fingers and incisors already show similarities.

Figure 4. The small furry hyrax is in the lineage of the large naked elephant, analogous to small feathery theropods and large naked theropods. The fingers and teeth already show similarities here.

The authors discuss hatchling tyrannosaurs
as they report, “Finally, the presence of epidermal scales in a large adult individual does not rule out the possibility that younger individuals possessed feathers—a developmental switchover that, to our knowledge, would be unprecedented at any rate.” No birds have more feathers as hatchlings than as adults.

What are tyrannosaur scales? And did birds lose their scales?
According to bird studies (Dhouailly 2009) theropod scales may be [phylogenetically] derived from feathers. (Remember chickens and other birds are naked underneath.) Scales and scutes can develop at any place and at any time from naked skin. Consider the ankylosaurs, as an extreme example. Naked and/or furry skin can develop from scales. Consider the scaly tail of the opossum ancestral to the tail of a hamster or lemur, as examples.

Figure 1. Zhenyuanlong compared to scale with the foot of T-rex and a another overall view of T-rex to a similar overall length.

Figure 1. Zhenyuanlong compared to scale with the foot of T-rex and a another overall view of T-rex to a similar overall length.

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.

This topic was inspired by the following video on YouTube:

References
Bell PR, Campione NE, Persons WS, Currie PJ, Larson PL, Tanke DH, Bakker RT 2017. Tyrannosauroid integument reveals confllcting patterns of gigantism and feather evolution. Biology Letters 13: 20170092. http://dx.doi.org/10.1098/rsbl.2017.0092
Dhouailly D 2009. A new scenario for the evolutionary origin of hair, feather, and avian scales. Journal of Anatomy 214:587-606.

the-origin-of-feathers-and-hair-part-3-feathers/

What are birds-of-paradise?

Lophorina superba
is a black and cyan male superb bird-of-paradise (BoP) with an incredible feather display during mating rituals (Figs. 1, 2).

My question is: What are birds-of-paradise?
Where do they nest in the large reptile tree (LRT, 1283 taxa)?

Wikipedia reports:
Lophorina (and all other birds-of-paradise) nests within the family Paradisaeidae within the order Passeriformes which means, close to Passer the sparrow, which nests between chickens and parrots in the LRT. One catch: Wikipedia reports: the family Paradisaeidae nests most closely with crows and jays, which are not closely related to the seed-eating chickens, sparrows and parrots in the LRT.

Figure 2. Male Lophorina niedda in various stages of its mating ritual.

Figure 2. Male Lophorina superba in various stages of its mating ritual from Scholes and Laman 2018.

Evidently the skeletons of birds-of-paradise
are not as highly prized as are the feathers. So, due to a lack of skeletal data for Lophorina
the LRT nested another bird-of-paradise, Semioptera wallacii (Fig. 3), based on skull data only, within the cuckoo clade between Menura, the lyrebird (Fig. 6), and Geococcyx, the roadrunner. Distinct from these two taxa, birds-of-paradise have shorter legs, which usually results from neotony (chicks of long-legged taxa generally have short legs).

FIgure 3. Skull of Semioptera wallacii has basic cuckoo clade features.

FIgure 3. Skull of Semioptera wallacii has basic cuckoo clade features.

Semioptera shares with Lophorina
a set of breast shields and that ventrally concave beak. Not sure yet how any other BoPs are related to one another yet. If you have access to BoP skeletons, please send the citations or images.

As we learned
earlier, few of these bird relationships (Fig. 4) match genomic studies, which have been favored in recent years over skeletal studies. For instance, using DNA Prum et al. 2015 nested the lyrebird, Menura, at the base of a clade of bowerbirds, then crows + Lophorina (BoPs), and finally thrushes and sparrows. So results are not confirmed. Adding BoP and other taxa, as they become available, will help paint a better picture of evolution here.

Figure 4. Semioptera, the bird-of-paradise, nests in the cuckoo clade between the lyrebird, Menura, and the roadrunner, Geococcyx.

Figure 4. Semioptera, the bird-of-paradise, nests in the cuckoo clade between the lyrebird, Menura, and the roadrunner, Geococcyx, not with sparrows, crows or jays (Passer, Corvus or Cyanocitta) in the LRT.

If you’ve not had your fill of dancing BoPs,
here’s a link to a YouTube video you might like:

The Darwinian thing is…
these males do not choose to act or look like they do. A long line of ancestors made that decision for them when they acted and looked that way (or thereabouts) and successfully mated with the females that, in reality, did all the choosing during these rituals.

Figure 6. The lyrebird, Menura, nests close to the one BoP in the LRT.

Figure 6. The lyrebird, Menura, nests close to the one BoP in the LRT.

References
Scholes E and Laman TG 2018. Distinctive courtship phenotype of the Vogelkop Superb Bird-of-Paradise Lophorina niedda Mayr, 1930 confirms new species status. PeerJ. 6:e4621: e4621. doi:10.7717/peerj.4621

birdsofparadiseproject.org

The 11th Archaeopteryx: closer to Sapeornis

Figure 1. The 11th specimen attributed to Archaeopteryx in situ. See figure 2 for a reconstruction. This specimen remains in private hands without a museum number.

Figure 1. The 11th specimen attributed to Archaeopteryx in situ. See figure 2 for a reconstruction. This specimen remains in private hands without a museum number. Note all the soft tissue feathers preserved here.

Archaeopteryx number 11
(Figs. 1, 2) has no museum number and is in private hands, but Foth et al. 2014 published a description in Nature. These authors unfortunately considered this specimen just another Archaeopteryx, but one well supplied with feather impressions. In the large reptile tree (LRT, subset Fig. 3) this Solnhofen bird nests at the base of the node that produced two specimens of Sapeornis, a clade convergent with Euronithes in having a pygostyle.  The 11th specimen is complete and articulated, but lacks a large part of the cranium.

Figure 2. Most of the complete Solnhofen birds, including Archaeopteryx and the eleventh specimen to scale.

Figure 2. Most of the complete Solnhofen birds, including Archaeopteryx and the eleventh specimen to scale.

Foth et al. 2014 do not mention
the lack of a sternum. Sapeornis likewise lacks a sternum even though more primitive taxa have one.

Figure 4. The eleventh Archaeopteryx nests with Sapeornis.

Figure 4. The eleventh Archaeopteryx nests with Sapeornis.

At first glance
this appears to be an ordinary Archaeopteryx. However, when you put the dividers on the bones you find that it differs in subtle ways from the holotype and is more similar to Sapeornis and its sisters. As I mentioned yesterday, it would be a good thing for all early bird workers to start considering the Solnhofen birds individual genera, not a single genus. It’s just a lazy habit we have to overcome.

References
Foth C, Tischlinger H and Rauhut OWM 2014. New specimen of Archaeopteryx provides insights into the evolution.of pennaceous feathers. Nature 511:79–83.DOI: 10.1038/nature13467