Tynskya and Messelastur enter the LRT with overlooked bird taxa

Today
two birds enter the LRT, nesting at nodes the experts overlooked. Both were considered closely related members of the clade Messelasturidae. “Initially interpreted as stem-owls, more recent studies have shown that they are actually closely related to modern parrots and are in the same order, Psittaciformes,” according to Wikipedia.

Not true in the LRT.

Backstory #1:
Didunculus, the tooth-billed pigeon (Fig. 1) does not nest in the large reptile tree (LRT, 1807+ taxa) with pigeons or dodos. Instead Didunculus nests with Falco, the falcon, far from pigeons, close to owls, owlets and swifts, something we learned a few years ago.

Figure 2. Figures of the Didunculus skeleton.

Figure 1. Figures of the Didunculus skeleton.

Today’s first bird is
Messelastur (Fig. 2) from the famous middle Eocene Messel pit.

Figure 2. Messelastur skull with colors added.

Figure 2. Messelastur skull with colors added. Note the displaced beak tip and another possible displaced premaxillary bone.

The literature on Messelastur includes:

Peters 1994 (not me) considered Messelastur a member of the Accipitridae (= hawks, eagles, Old World vultures and kin, but not owls). Note the sharp predaceous beak.

Mayr 2005 wrote: “They [Messelasturidae] provide a morphological link between Strigiformes and Falconiformes (diurnal birds of prey), and support the highly disputed falconiform affinities of owls in combining derived tibiotarsus and tarsometatarsus characters of owls with a more plesiomorphic, ‘falcon-’ or ‘hawk-like’, skull morphology.”

Wikipedia 2021 reports, “more recent studies have shown that they are actually closely related to modern parrots and are in the same order, Psittaciformes.” Psittaciformes = parrots (Fig. 3). The Wiki author was citing:

Mayr 2011, who wrote, “If future data strengthen their psittaciform affinities, they not only add a distinctive new taxon to the stem lineage of Psittaciformes, but also show that some stem group Psittaciformes were predatory birds.”

When added to the LRT
Messelastrus nests not with parrots (Fig. 3), but with Didunculus (Fig. 1). Parrots still nest with hoatzins, giant flightless parrots, sparrows and chickens far from hawks, owls and kin.

Figure 3. Skeleton of Ara macao, the scarlet macaw. Note the skeleton has pedal digits 3 and 4 switched.

Figure 3. Skeleton of Ara macao, the scarlet macaw. Note the skeleton has pedal digits 3 and 4 switched.

Backstory #2:
Apus,
the common swift, does not follow tradition and nest with hummingbirds in the LRT. Rather, as we learned several years ago the swift nests with Aegotheles, the owlet, close to owls and other predatory birds.

Figure 2. Apus the common swift is actually a close relative of the falcon and owl, not a hummingbird.

Figure 4. Apus the common swift is actually a close relative of the falcon and owl, not a hummingbird.


Mayr 2000 first described

Tynskya (Fig. 4) an early Eocene Green River bird he considered a link between falcons and owls. In the LRT Tynskya nests with Apus, the swift (Fig. 4), not far from falcons and owls. The skull of Tynskya had huge eyes and a tiny beak, just like Apus, along with hundreds of other aligning traits.

Figure 5. Tynskya in situ and with some parts pulled out for clarity. Apparently the pelvis and backbone are still buried in this ventral view of the torso, dorsal view of the skull after neck torsion.

Figure 5. Tynskya in situ and with some parts pulled out for clarity. Apparently the pelvis and backbone are still buried in this ventral view of the torso, dorsal view of the skull after neck torsion. The ‘x’ marks a broken humerus.The broken sternum is reassembled at lower left.

As you can see,
in both new taxa (above) more closely related taxa were excluded, something the LRT is designed to minimize. Minimizing taxon exclusion will help you nest taxa that display traits convergent with unrelated taxa, like hawks and parrots. Fewer enigmas result, if that’s okay with you. Enigmas and mysteries make paleontology more interesting and intriguing. Unfortunately, the LRT has removed many over the last ten years.


References
Mayr G 2000a. A new raptor-like bird from the Lower Eocene of North America and Europe. Senckenbergiana lethaea 80:59–65.
Mayr G 2005. The postcranial osteology and phylogenetic position of the Middle Eocene Messelastur gratulator Peters, 1994—a morphological link between owls (Strigiformes) and falconiform birds? Journal of Vertebrate Paleontology 25(3):635–645.
Mayr G 2011. Well-preserved new skeleton of the Middle Eocene Messelastur substantiates sister group relationship between Messelasturidae and Halcyornithidae (Aves, ? Pan-Psittaciformes). Journal of Systematic Palaeontology 9(1):159-171.
Peters DS 1994. Messelastur gratulator n. gen. n. spec., ein Greifvogel aus der Grube Messel (Aves: Accipitridae). Courier Forschungsinstitut Senckenberg 170:3–9.

wiki/Accipitridae
wiki/Didunculus
wiki/Tooth-billed_pigeon

The juvenile enantiornithine STM-34-1 nests with Chiappeavis in the LRT

In a paper on Early Cretaceous fossilized feather molting,
O’Connor et al. 2020 presented several specimens, among them an unnamed juvenile STM-34-1 (Figs. 1–3). The specimen originally appeared in part in Zheng et al. 2012 in their study on sternum ontogeny. O’Connor was a co-author then, too.

Figure 1. STM-34-1 in situ along with select elements.

Figure 1. STM-34-1 in situ along with select elements.

Note the shorter forelimb
and longer hind limb in the juvenile, which has no tail feathers preserved as well as those elsewhere on the body and limbs. Birds, like other archosaurs, develop allometrically, changing in shape as they mature. By contrast, pterosaurs, like other lepidosaurs, develop isometrically, not changing in shape as they mature, contra traditional thinking.

Figure 2. STM-34-1 skull in situ and reconstructed.

Figure 2. STM-34-1 skull in situ and reconstructed.

STM 34-1 is from
Liutiaogou, Ningcheng, Chifeng, Inner Mongolia, Lower Cretaceous.

Chiappeavis is from 
Jianchang, Liaoning Province, northeastern China. Jiufotang Formation, Lower Cretaceous

Figure 3. Chiappeavis, Pengornis and STM-34-1 to scale.

Figure 3. Chiappeavis, Pengornis and STM-34-1 to scale.

Added to
the large reptile tree (LRT, 1785+ taxa, subset Fig. 4) STM-34-1 nested with Chiappeavis (Fig. 3).

Figure 4. Subset of the LRT focusing on the bird clade, Enantiornithes.

Figure 4. Subset of the LRT focusing on the bird clade, Enantiornithes.

A phylogenetic analysis that tested STM 34-1
was not presented by O’Connor et al. 2020, nor by Zheng et al. 2012.


References
O’Connor JK, Falk A, Wang M and Zheng X-T 2020.
 First report of immature feathers in juvenile enantiornithines from the Early Cretaceous Jehol avifauna. Vertebrata PalAsiatica 58(1):24–44. DOI: 10.19615/j.cnki.1000-3118.190823
Zheng XT, Wang XL, O’Connor JK et al., 2012. Insight into the early evolution of the avian sternum from juvenile enantiornithines. Nat Commun, 3: 1–8.

wki/Chiappeavis

An even larger genetic study of extant birds in Nature

Feng et al. 2020 bring us
yet another genomic study of extant birds, this time with a circular cladogram so dense it makes no attempt to list the 10,135 bird taxa in this study by dozens of authors.

This was my reply on the study,
copied from the Comments section on the Nature website. The asterisk and double asterisk are how the chicken* and finch** are located on the dense cladogram (their figure 1).

How can one test the validity of genomic studies like this one? Earlier testing by Prum et al. 2015 nested flamingoes (Phoenicopterus) with dissimilar grebes (Aechmophorus) and yardbirds/chickens (Gallus) with dissimilar geese (Anser). Three of these four are not named in the present cladogram which lists and illustrates only a few sample genera. Among these, the genomically distant separation of the phenomically similar finch**, parrot (Agapornis) and chicken* duplicate what was discovered earlier in the Prum et al. 2015 study. Genomic deep time studies too often produce false positives that separate similar taxa and lump dissimilar taxa. By comparison, phenomic studies, like the one online at: http://reptileevolution.com lump similar taxa and separate dissimilar taxa, modeling evolutionary events while including fossil taxa.

Only in phenomic (trait-based) studies can one produce a cladogram in which all related taxa document a gradual accumulation of derived traits modeling actual events. If one is concerned about convergence, adding taxa to phenomic studies overcomes that problem.

Genomic studies have lumped bats with whales (Laurasiatheria) and golden moles with elephants (Afrotheria). Workers have to wake up to the sad fact that genetic studies work in criminal investigations, but not in cladograms.”


References
Feng et al. (dozens of co-authors) 2020. Dense sampling of bird diversity increases power of comparative genomics. Nature 587:252–257.

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

Shedding new light (literally!) on Jianianhualong: Li et al. 2020

Li et al. 2020 used various frequencies of light
and spectroscope technology on the holotype bones and feathers of Jianianhualong (Figs. 1, 2; Early Cretaceous, Xu et al. 2020, DLXH 1218) to identify specific elements in the matrix and specimen.

From the abstract:
“Here, we carried out a large-area micro-X-Ray fluorescence (micro-XRF) analysis on the holotypic specimen of Jianianhualong tengi via a Brucker M6 Jetstream mobile XRF scanner.”

Figure 2. Jianianhualong, Serikornis and Jurapteryx to scale.

Figure 1a. Jianianhualong, Serikornis and Jurapteryx to scale.

Figure 1. Jianianhualong tengi in situ. This is the largest among the early birds, a fact overlooked by the Xu et al. 2017. Think of Jianianhualong as a giant Archaeopteryx!

Figure 1b. Jianianhualong tengi in situ. This is the largest among the early birds, a fact overlooked by the Xu et al. 2017. Think of Jianianhualong as a giant Archaeopteryx!

From the abstract:
“Jianianhualong tengi is a key taxon for understanding the evolution of pennaceous feathers as well as troodontid theropods, and it is known by only the holotype, which was recovered from the Lower Cretaceous Yixian Formation of western Liaoning, China.” 

What they didn’t do is to rerun their phylogenetic analysis with more taxa (Fig. 2).

What they didn’t do is to create a reconstruction, perhaps using DGS to precisely trace and segregate the bones to rebuild the skeleton (Figs. 1, 3, 4).

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

Figure x. Subset of the LRT focusing on birds and their ancestors. Jianianhualong nests within Aves (five taxa from the bottom).

By contrast,
in the large reptile tree (LRT, 1730+ taxa) Jianianhualong nests within Aves (five taxa from the bottom of Fig. 2) even though it was clearly not volant due to its much larger size and smaller forelimbs. Close relatives include Archaeopteryx (= Jurapteryx) recurva (= Eichstätt specimen, Fig. 3) and the privately held #11 specimen of Archaeopteryx.

The authors think Jianianhualong is a troodontid.
According to Wikipedia“A number of characteristics allow Jianianhualong to be identified as a member of the Troodontidae. These include:

  1. the long forward-projecting branch and flange of the lacrimal bone; [✓]
  2. the foramina on the nasal bone; [?]
  3. the smooth transition between the eye socket and the backward-projecting branch of the frontal bone; [✓]
  4. the ridge on the forward-projecting branch of the jugal bone; [✓]
  5. the triangular dentary bearing a widening groove; [✓]
  6. the robust forward-projecting branch of the surangular bone; [✓]
  7. the relatively large number of unevenly-distributed teeth; [✓]
  8. the flattened chevrons with blunt forward projections and bifurcated backward projections; [✓]
  9. and the broad and flat “pubic apron” formed by the pubic bones.” [?]
Figure 3. The Eichstätt specimen, Jurapteryx recurva, nests with the living ostrich, Struthio, presently in the LRT.

Figure 2. The Eichstätt specimen, Jurapteryx recurva, nests with the living ostrich, Struthio, presently in the LRT.

Professor Larry Martin would be so proud!
Why? Because the Wikipedia author (above) is using a list of traits to support an hypothesis of interrelationships rather than using a cladogram to support that hypothesis.  Checkmarks [✓] indicate traits Jurapteryx shares. Question marks [?] indicate traits not shown in Jianianhualong or Jurapteryx. Or did I miss something?

The problem is,
various authors add taxa to the Troodontidae that don’t belong there in the LRT, as we learned earlier here. The LRT; subset Fig. x) recovers Jiaianhualong as the largest known member of the Sapeornis/Jurapteryx clade of birds. Several flightless birds are in this clade. These could be confused with troodontids for that reason. In the LRT the clade Troodontidae include Sinornithoides + Sauronithoides their LCA and all derived taxa. None of these are direct bird ancestors.

Getting back to chemistry
“The bone in Jianianhualong is, as expected rich in calcium and phosphorus, corresponding mineralogically to apatite. The regions where feather remains can be observed show an enrichment and correlation pattern of several elements including manganese, titanium, nickel and copper.”

FIgure 2. GIF animation of the skull of Jianianhualong showing original tracing in line art and colorized bones (DGS) used to create a reconstruction (Fig. 3).

FIgure 3. GIF animation of the skull of Jianianhualong showing original tracing in line art and colorized bones (DGS) used to create a reconstruction (Fig. 3).

Jianianhualong is a troodontid-like bird,
not a bird-like troodontid. Note the odd scapula shape, like that in Sapeornis. Note the retrovered pedal digit 1, showing this taxon was derived from perching birds. The tall naris and long tibia are autapomorphies.

Xu et al. 2014 made a headline out of
the asymmetric feathers found with Jianianhualong. In the present context, Jianianhualong is derived from volant ancestors. So asymmetry is expected, not exceptional. This is the earliest known large flightless bird, not an example of the invalid hypothesis of ‘mosaic’ evolution.

Figure 3. Reconstruction of the skull of Jianianhualong based on DGS tracings in figure 2.

Figure 4. Reconstruction of the skull of Jianianhualong based on DGS tracings in figure 2.

Liaoningventor curriei (Shen et al. 2017; DNHM D3012; Early Cretaceous) was also originally described as a non-avian troodontid, but nests with Jianianhualong as a flightless bird.


References
Li J, et al. (8 co-authors 2020. Micro-XRF study of the troodontid dinosaur Jianianhualong tengi reveals new biological and taphonomical signals. bioRxiv 2020.09.07.285833 (preprint) PDF doi: https://doi.org/10.1101/2020.09.07.285833
https://www.biorxiv.org/content/10.1101/2020.09.07.285833v1
Shen C-Z, Zhao B, Gao C-L, Lü J-C and Kundrat 2017. A New Troodontid Dinosaur (Liaoningvenator curriei gen. et sp. nov.) from the Early Cretaceous Yixian Formation in Western Liaoning Province. Acta Geoscientica Sinica 38(3):359-371.
Xu X, Currie P, Pittman M, Xing L, Meng QW-J, Lü J-C, Hu D and Yu C-Y 2017. Mosaic evolution in an asymmetrically feathered troodontid dinosaur with transitional features. Nature Communications DOI: 10.1038/ncomms14972.

wiki/Sapeornis
wiki/Jianianhualong
wiki/Liaoningvenator

“Pulling a Larry Martin” with basal bird pectorals and hands

This is a cautionary tale
The following blog reminds all workers to score the entire specimen if possible, and to score as many more-or-less-complete specimens as possible. Why?

It is of vital importance to use as much data as possible
when scoring each taxon in a phylogenetic analysis to remove any trace of attraction by convergence that happens when just using bits and pieces of cherry-picked taxa.

From Pittman et al. 2020,
“Generally during early avian evolution, the furcula, coracoid, and sternum become more craniocaudally elongate, while the manual digits become reduced and fusion between the metacarpals increases.” 

Not true. In a valid phylogenetic context (Figs. 1–3), like the wide gamut large reptile tree (LRT, 1729+ taxa; subsets Figs. 2, 3), some taxa developed birdy traits quickly while others dawdled or reversed. In this way some bones demonstrated convergence with other less related clades. With this in mind, start with a valid unbiased topology, then let the taxa tell their own story. Avoid the temptation of an easy diagram. Do the necessary work.

Figure 1. Avian furcula aviation from Pittman et al. 2020 and repaired based on LRT results. Let your software decide based on the whole specimen. Convergence is rampant as you can see here.

Figure 1. Avian furcula aviation from Pittman et al. 2020 and repaired based on LRT results. Let your software decide based on the whole specimen. Convergence is rampant as you can see here.

Due to taxon exclusion
Pittman et al. mixed up the order of the pectoral girdles + hands of basal birds (Fig. 1), hoping to tell the story they wanted to tell: gradual evolution. Not only did they skip about a dozen pertinent taxa, they got the order wrong by eyeballing a few traits on cherry-picked taxa.

With more taxa, as in the LRT,
(Figs. 2, 3) the girdles and limbs are phylogenetically re-ordered here (Fig. 1, layer 2 with colors). If Pittman et al. wanted to show gradual evolution, they needed to first establish a valid tree topology by adding more taxa. Instead, by cherry-picking certain traits to show gradual evolution, Pittman et al. were “Pulling a Larry Martin“, putting individual traits on cherry-picked taxa ahead of an entire suite of traits and a wide gamut of taxa.

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999 = Coelurosauria 1914. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

Figure 2. Subset of the LRT focusing on bird origins. Crown birds and toothed birds are highlighted.

Figure 3. Subset of the LRT focusing on bird origins. Crown birds and toothed birds are highlighted. Figure 2 is slightly more up-to-date, but includes fewer extant birds.

When the phylogenetic order is corrected
based on unbiased results recovered by the LRT (subsets Figs. 2, 3), what seemed to Pittman et al. a gradual transitional series is here revealed to be an example or two of convergence. Note the similarly elongate coracoids on the enantiornithine Parabohaiornis and the unrelated ornithurine, Yanornis (Fig. 1`), derived from an Early Cretaceous sister to a living taxon, Megapodius.

Time after time paleontologists cherry-pick taxa.
That has to stop. Add more taxa and let the software decide the tree topology. Similarly, don’t rely on parts alone (Fig. 1) to illustrate hypotheses, unless they represent taxa already nesting together based on all of their parts and a wide gamut of taxa. Body parts, like hands and girdles, can converge, as they do here.

Figure 3. Mammal tooth evolution alongside odontocete tooth evolution, reversing the earlier addition of cusps.

Figure 4. Mammal tooth evolution alongside odontocete tooth evolution, reversing the earlier addition of cusps.

On a similar note, basal mammal workers
have put too much reliance on tooth traits. Unfortunately, sometimes that’s all they have. If so, what should they do? They should build a tree topology based on complete or more nearly complete specimens. THEN fit it in those tooth and mandible taxa once the tree topology is established in a broader sense, as in the LRT. Earlier (Fig. 4) you saw how odontocete and archaeocete traits brilliantly document a step-by-step reversal to a simple cone shape, like those of basal pelycosaurs. The addition, subtraction and modification of tooth cusps in mammals occurred much more widely than shown by this one example.


References
Pittman M, O’Connor J, Field DJ, Turner AH, Ma W, Makovicky P and Xu X 2020.
Pennaraptoran Systematics. Chapter 1 from Pittman M and Xu X eds. 2020. Pennaraptoran theropod dinosaurs. Past progress and new Frontiers. Bulletin of the American Museum of Natural History 440; 353pp. 58 figures, 46 tables.

https://pterosaurheresies.wordpress.com/2020/08/23/pennaraptora-avoid-this-junior-synonym/

More details on Parahesperornis

Bell and Chiappe 2020
provide additional insight and valuable photos of Parahesperornis alexi (Martin 1984; Fig. 1; Late Cretaceous ~90 mya) a smaller sister/ancestor to Hesperornis (Fig. 1) with more plesiomorphic traits.

Figure 1. Parahesperornis (from Bell and Chiappe 2020) compared to Hesperornis (Marsh 1890) to scale and not to scale. Here the glenoid to tail tip lengths are the same. Everything is exaggerated in Hesperornis.

Figure 1. Parahesperornis (from Bell and Chiappe 2020) compared to Hesperornis (Marsh 1890) to scale and not to scale. Everything is exaggerated in the derived taxon, Hesperornis.

Backstory
According to Bell and Chiappe, “The Hesperornithiformes constitute the first known avian lineage to secondarily lose flight in exchange for the evolution of a highly derived foot-propelled diving lifestyle, thus representing the first lineage of truly aquatic birds. First unearthed in the 19th century, and today known from numerous Late Cretaceous (Cenomanian-Maastrichtian) sites distributed across the northern hemisphere, these toothed birds have become icons of early avian evolution.”

Figure 2. Hesperornis cladogram from Bell and Chiappe 2020. Compare to LRT results in figure x.

Figure 2. Hesperornis cladogram from Bell and Chiappe 2020. Compare to LRT results in figure 3 where more taxa are tested and nested. Gansus should be closer to Hesperornis. Many taxa are omitted between Archaeopteryx and Asparavis here.

Figure 1. Click to enlarge. Toothed birds of the Cretaceous to scale.

Figure 3. Click to enlarge. Toothed birds of the Cretaceous to scale. Compare to figure 2. See the difference when more taxa are added.

Cladistics
Bell and Chiappe and the Large Reptile Tree (LRT, 1694+ taxa, illustrated in figure 3) are in broad agreement regarding the phylogenetic nesting of Parahesperornis (Fig. 2). Unfortunately, Bell and Chiappe don’t include enough taxa to understand the nesting of toothed birds within the clade of toothless birds, as recovered by the LRT (Fig. 3).

And what the heck 
are Gallus, the chicken, and Anas, the duck, doing in figure 2 nesting together? They are not related to one another in the LRT, but… (and here’s the key)… absent ANY pertinent transitional taxa, figure 2 is actually correct, a match with the LRT. Taxon exclusion delivers this oversimplified and misinforming cladogram (Fig. 2). More taxa, not more characters, makes a cladogram more and more accurate.


References
Bell A and Chiappe LM 2020. Anatomy of Parahesperornis: Evolutionary Mosaicism
in the Cretaceous Hesperornithiformes (Aves). Life 2020, 10, 62; doi:10.3390/life10050062
Marsh, OC 1880. Odontornithes, a Monograph on the Extinct Toothed Birds of North America. Government Printing Office, Washington DC.
Martin L 1984. A new Hesperornithid and the relationships of the Mesozoic birds. Transactions of the Kansas Academy of Science 87:141-150.

wiki/Hesperornis

Asteriornis: Oldest crown bird fossil yet discovered? No.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

SVP abstracts – Ichthyornis and the origin of extant birds

Benito et al. 2019 dive into bird phylogeny
with a study of the Late Cretaceous toothed bird, Ichthyornis (Fig. 1).

Figure 1. Skull of Ichthyornis in 3 views from Field et al. 2018 and overall skeleton.

Figure 1. Skull of Ichthyornis in 3 views from Field et al. 2018 and overall skeleton.

From their abstract
“The origin of crown birds is poorly understood

By contrast, in the large reptile tree (LRT, 1592 taxa) the origin of crown birds is well understood back to Silurian jawless fish. Ichthyornis is a member of the clade of crown birds in the LRT, not an ancestor to it.

“…and the study of their early evolution must incorporate data from their closest relatives among Mesozoic stem birds. The postcranial morphology of the Late Cretaceous toothed bird Ichthyornis dispar may be more representative of the ancestral condition of crown birds than that of any other known Mesozoic avialan, and its study has crucial implications for understanding morphological evolution prior to the great radiation of the avian crown group.”

By contrast, in the LRT Vegavis (Latest Cretaceous) is basal to all extant birds including Mesozoic toothed birds like Icthyornis. It was a late survivor from an earlier genesis.

“Here we present high resolution scans of new, exquisitely preserved three dimensional specimens of Ichthyornis from the Late Cretaceous of Kansas. These correspond to a partial skeleton from a single individual, more complete and in better condition than the classic material known since the 19th Century. The new material includes a complete sternum and shoulder girdle with evidence of extensive pneumatization. This new skeleton shows certain morphological differences from the classic material, including the absence of some previously proposed autapomorphies of I. dispar. Thus, the new material may represent a previously unknown species, or it could indicate that morphological variation within I. dispar was greater than previously appreciated.”

Good to have these new data.

Figure 3. Subset of the LRT focusing on early birds, including Ichthyornis.

Figure 2. Subset of the LRT focusing on early birds, including Ichthyornis.

Benito et al. continue:
“Phylogenetic analyses incorporating our new morphological data corroborate recent results and recover a grade of predominantly marine taxa close to the origin of crown birds. I. dispar is recovered stemward of Hesperornithes and Iaceornis marshi, which is recovered as the sister taxon to all crown birds. Additional information on the crownward-most portion of the avian stem group will help confirm these results and provide critical information on the ancestral ecology of the crown bird radiation.”
I don’t know if Benito et al. employed all the taxa shown here (Fig. 2) in this subset of the LRT, but you can see Ichthyornis nests in the LRT within the clade of extant/crown birds. Here Ichthyornis is a highly derived member of its own small clade of toothed birds, within extant birds between megapodes and seriemas. Other taxa closer to the main line of Cretaceous bird evolution would probably make a better model for studies like this.

References
Benito J et al. 2019. New Ichthyornis specimens: shedding new light on modern bird origins. Journal of Vertebrate Paleontology abstracts.

The snakebird lacks external nares, breathes through its mouth

Figure 1. Skull of Anhinga rufa, an Old World relative of the New World Anhinga anhinga. Note the expansion of the maxilla (or overlying horny tissue) nearly obscuring the naris and antorbital fenestra. Compare to the loon in figure 3.

Figure 1. Skull of Anhinga rufa, an Old World relative of the New World Anhinga anhinga. Note the expansion of the maxilla (or overlying horny tissue) nearly obscuring the naris and antorbital fenestra. Compare to the loon in figure 2.

Anhinga anhinga (Linneaus 1766; 89cm) is the extant snakebird, which swims underwater and stabs its fish prey with its sharp beak, striking like a snake. It breathes only through the mouth as the bones and other hard tissues around the nostrils are overgrown. The feathers do not shed water, so some time is spent drying the feathers prior to flying. Snakebirds are related to grebes (genus: Aechmophorus) and loons (genus: Gavia, Fig. 2).

Figure 2. Skull of the common loon (Gavia stellata) showing the primitive state, with large external nares and antorbital fenestra.

Figure 2. Skull of the common loon (Gavia stellata) showing the primitive state, with large external nares and antorbital fenestra.

The large number and length of cervical vertebrae
in snakebirds (Fig. 3) is more or less matched only by flamingoes (genus: Phoenicopterus) by convergence.

Figure 3. Anhinga anhinga skeleton. Note the large number of cervical vertebrae. These enable the snake-like darting of the sharp skull while attacking prey underwater.

Figure 3. Anhinga anhinga skeleton. Note the large number of cervical vertebrae. These enable the snake-like darting of the sharp skull while attacking prey underwater.

Hackett et al. 2008 nested loons with penguins.
While close, the large reptile tree (LRT, 1562 taxa) nests loons + grebes derived from terns (genus: Thalasseus) and sisters to kingfishers (genus: Megaceryle) + jabirus (genus: Jabiru) and murres (genus: Uria) + penguins (genus: Aptenodytes). Among these taxa, only Jabiru experiences a reversal in having such long, stork-like legs, a primitive trait for extant birds.

Figure 1. The rostrum of Spinosaurus. Note the maxilla rising to close off the elongate naris into a reduced anterior and posterior opening.

Figure 4. The rostrum of Spinosaurus. Note the maxilla rising to close off the elongate naris into a reduced anterior and posterior opening.

Footnote:
Another aquatic dinosaur taxon that expanded its maxilla to shut off its nostrils was Spinosaurus (Fig. 4) as we learned earlier here.


References
Hackett S et al. 2008. A phylogenetic study of birds reveals their evolutionary history. Science 320:1763–1768.
Kennedy M et al. 2019. Sorting out the Snakebirds: The species status, phylogeny, and biogeography of the Darters (Aves: Anhingidae). Journal of Zoological Systematics and Evolutionary Research (advance online publication)
doi: https://doi.org/10.1111/jzs.12299 https://onlinelibrary.wiley.com/doi/10.1111/jzs.12299