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.

Sciurumimus: a juvenile ornitholestid in the LRT

We looked at tiny,
feathered Sciurumimus albersdoerferi (Germany, Rauhut et al. 2012; BMMS BK 11) and larger bones-only Ornitholestes (North America) earlier as Late Jurassic sisters in the large reptile tree (LRT, 1659+ taxa). After a recent review, these two continue to nest as sisters at the base of the Microraptor (Fig. 3) + Sinornithosaurus clade. So no news here… except now let’s combine the extraordinary size difference between the two and the widely accepted observation that Sciurumimus is a juvenile.

That brings to mind: a juvenile of what?
The LRT indicates a juvenile ornitholestid (Fig. 1). The overall morphologies are strikingly similar and the size difference is appropriate. Other published studies recover other nestings.

Rauhut, et al. 2012
(Suppdata) nested Ornitholestes between ornithomimosaurs and deinonychosaurs, far from Sciurumimus, which Rauhut et al. nested Sciurumimus between an unresolved clade of giant spinosaurs + megalosaurs and giant Monolophosaurus. Like Rauhut et al., the LRT nests also nests Ornitholestes between ornithomimosaurs (+ tyrannosaurs + oviraptors + therizinosaurs) and deinonychosaurs.

Key differences in the LRT include

  1. the use of two Compsognathus specimens. The each nest at the base of their own clade, a hypothesis of interrelationships overlooked by Rauhut et al.
  2. the inclusion of three Microraptor specimens and two Sinornithosaurus specimens, adults of which are closer in size and morphology to Sciurumimus. This brings to mind the possibility that phylogenetic miniaturization and neotony played a part in the evolution of these bird-mimics. These closely related taxa were omitted by the Rauhut et al. selection process.
Figure 1. Sciurumimus compared to Ornitholestes and Microraptor to scale.

Figure 1. Sciurumimus compared to Ornitholestes and Microraptor to scale.

In their study of the wonderfully preserved
anchiornithid, Aurornis, Godefroit et al. nested Sciurumimus between Monolophosaurus + Sinraptor and Zuolong, all more primitive taxa in the LRT. In Godefroit et al. these taxa are far from Ornitholestes, which nested with another small compsognathid, Juravenator. Juravenator nests with equally small, but shorter limbed Sinosauropteryx in the LRT. Evidently few theropod studies agree with one another in the details.

Rauhut et al. 2012 reported,
“Our analysis confirms Sciurumimus as the basalmost known theropod with evidence of feather-like integument.” By contrast, in the LRT, Tawa-like, feathered Sincalliopteryx (Fig. 2) is more primitive, despite its late appearance (Early Cretaceous) in the fossil record.

Figure 4. Sinocalliopteryx currently nests as a provisional sister to Deinocheirus, awaiting the discovery of transitional sister taxa.

Figure 2. Late surviving Sinocalliopteryx currently nests basal to Late Triassic Coelophysis, derived from Late Triassic Tawa. It has the most primitive presence of feathers despite its late appearance.

Sinocalliopteryx
currently nests basal to Late Triassic Coelophysis, and was derived from Late Triassic Tawa. In the LRT, Sinocalliopteryx has the most primitive presence of feathers among theropods despite its appearance tens of millions of years later than its phylogenetic genesis.

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 3. 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.

The Ornitholestes + Sciurumimus + Microraptor + Sinornithosaurus clade
were bird-mimics and bird-mimic ancestors not directly related to birds or bird ancestors in the LRT.


References
Godefroit P, Cau A, Hu D-Y, Escuillié F, Wu, W and Dyke G 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature. 498 (7454): 359–362.
Rauhut OWM, Foth C, Tischlinger H and Norell MA 2012.
 Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany. Proceedings of the National Academy of Sciences. 109 (29): 11746–11751.

 

 

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

 

Phylogenetic miniaturization in Theropoda: two hypotheses

Lee, Cau, Naish and Dyke 2014
described the ‘sustained miniaturization…in the dinosaurian ancestors of birds’ starting with an unspecified basal tetanuran (Earliest Jurassic, 190mya) at 163kg, then evolving to a basal neotetanuran at 46kg, followed by a basal coelurosaurian at 27kg, a basal maniraptoran at 10kg, a basal parades at 3.3kg, and a basal bird at 1kg. We first looked at that theropod-bird evolution paper earlier here.

A distinctly different theropod tree topology
is found in the large reptile tree (LRT, 1315 taxa). More theropods have been added since 2014 (subset Fig. 1). Here small (goose-sized) theropods (in hot pink) arise from late (Early Cretaceous) survivors of Late Triassic radiations (based on the presence of Coelophysis as a derived taxon in an early clade, derived from a sister to Sinocalliopteryx, which was fully feathered with filaments in the fossil). So feather filaments were present in theropods from at least this point forward, with scales/placodes replacing filaments in very large taxa.

Figure 1. Subset of the LRT focusing on basal theropods. Pink area are more or less goose-sized and smaller taxa.

Figure 1. Subset of the LRT focusing on basal theropods. Pink areas are more or less goose-sized and smaller taxa leading to birds and following Tawa and Sinocalliopteryx. Smaller theropods evolve to become large and giant theropods several times by convergence here.

We’ve seen phylogenetic miniaturization before
attending the genesis of new clades in turtle origins, pterosaur origins, derived pterosaur origins, dinosaur origins, archosauriform origins, reptile origins, mammal origins, snake origins, squamate origins and I’m forgetting a few.

Given that the basalmost archosaur,
PVL 4597, is also goose-sized or smaller, it is possible that small undiscovered theropods were present throughout the Mesozoic, giving rise to larger taxa in the Herrersaurus, Tawa, Zuolong and the Coelophysis clades in the early part of the Age of Dinosaurs. 

References
Lee MSY, Cau A, Naish D and Dyke GJ 2014. Sustained miniaturization and anatomicial innovation in the dinosaurian ancestors of birds. Science 345(6196):562–566.

Anchiornis or not? And what about Pedopenna?

Xu et al. 2009
described a new genus, Anchiornis huxleyi IVPP V14378 (the holotype), along with LPM-B00169A, BMNHC PH828 as referred specimens), from the Late Jurassic of China. Two of these (Fig. 1) were added to the large reptile tree (LRT, 1315 taxa, subset Fig. 2). They nest in the LRT in the clade traditionally considered Troodontidae, between Velociraptor and Archaeopteryx. (Note other traditional troodontids, like Sinornithoides and Sauronithoides, do not nest in this pre-bird clade, but within the Haplocheirus clade.

Last year
a paper by Pei et al. 2017 described “new specimens of Anchiornis huxleyi. Two of these (Fig. 1) were also added to the LRT (subset in Fig. 2).

Figure 1. Four specimens attributed to Anchiornis. Two of these nest apart from two others (see figure 2).

Figure 1. Four specimens attributed to Anchiornis along with two others related to Anchiornis, but given different names. Two of these Anchiornis specimen nest apart from two others (see figure 2).

In the LRT
only two of the four tested Anchiornis specimens nested together (one was the holotype). That means the two other specimens were originally mislabeled. Moreover, a specimen attributed to a separate genus, Jinfengopteryx, nests with the holotype of Anchiornis and a referred specimen.

So do a few of the referred specimens need to be renamed? Perhaps so. Beyond the distinctly different skulls (Fig. 1), various aspects of the post-crania are also divergent.

Figure 2. Cladogram of taxa surrounding four specimens attributed to Anchiornis, which do not nest together in the LRT.

Figure 2. Cladogram of taxa surrounding four specimens attributed to Anchiornis, which do not nest together in the LRT. The holotype is the IVPP specimen in a darker tone and white arrowhead.

Pedopenna daohugouensis
(Xu and Zhang 2005; IVPP V 12721, Fig. 3) is a fossil theropod foot with long stiff feathers from the Middle or Late Jurassic, 164mya.

According to Wikipedeia
“Pedopenna was originally classified as a paravian, the group of maniraptoran dinosaurs that includes both deinonychosaurs and avialans (the lineage including modern birds), but some scientists have classified it as a true avialan more closely related to modern birds than to deinonychosaurs.”

Figure 1. Pedopenna in situ. Very little is known of this specimen.

Figure 3. Pedopenna in situ. The large alphanumerics are original. The color is added here. Very little is known of this specimen, but clearly long feathers arise from the metatarsus.

The first step
in figuring out what Pedopenna is, is to create a clear reconstruction (Fig. 4). Only then will we be able to score the pedal elements in the LRT.

Figure 2. Pedopenna in situ and reconstructed using DGS techniques.

Figure 4. Pedopenna in situ and reconstructed using DGS techniques.

Surprisingly,
and despite the relatively few pedal traits, the LRT is able to nest Pedopenna between and among the several Anchiornis specimens (Fig. 5). Specifically it nests between the holotype IVPP specimen and the LPM specimen. So is Pedopenna really Anchiornis? Or do all these taxa, other than the holotype, need their own generic names?

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

Figure 5. Where feathers on the foot are preserved on the LRT.

Earlier we looked at the development of foot feathers to aid in stability in pre-birds and other bird-like taxa just learning to flap and fly, convergent with uropatagia in pre-volant pterosaur ancestors.

A note to Anchiornis workers:
Try to test all your specimens in a phylogenetic analysis for confirmation, refutation or modification of the above recovery. Pei et al. considered all the specimens conspecific. They are not conspecific, as one look at their skulls alone (Fig. 1) will tell the casual observer.

References
Pei R, Li Q-G, Meng Q-J, Norell MA and Gao K-Q 2017. New specimens of Anchiornis huxleyi (Theropoda: Paraves) from the Late Jurassic of Northeastern China. Bulletin of the American Museum of Natural History 411:66pp.
Xu X, Zhao Q, Norell M, Sullivan C, Hone D, Erickson G, Wang X, Han F and Guo Y 2009. A new feathered maniraptoran dinosaur fossil that fills a morphological gap in avian origin. Chinese Science Bulletin 54 (3): 430–435. doi:10.1007/s11434-009-0009-6
Xu X and Zhang F 2005. A new maniraptoran dinosaur from China with long feathers on the metatarsus. Naturwissenschaften. 92 (4): 173–177. doi:10.1007/s00114-004-0604-y.

wiki/Pedopenna

 

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