John Ostrom: The man who saved dinosaurs

Saw this on Facebook recently
The following is from an online Yale Alumni Magazine article (link below) by award-winning author, Richard Conniff, July/August 2014.

Preview
“In his book The Riddle of the Dinosaur, science writer John Noble Wilford added that Bakker “was the young Turk whose views could be dismissed by established paleontologists. Ostrom, however, could not be ignored.” Late in 1969, Ostrom took the challenge directly to the North American Paleontological Convention in Chicago, declaring in a speech that there was “impressive, if not compelling” evidence “that many different kinds of ancient reptiles were characterized by mammalian or avian levels of metabolism.” Traditionalists in the audience responded, Bakker later recalled, with “shrieks of horror.” Their dusty museum pieces were threatening to come to life as real animals.”

Figure 1. John Ostrom, from young paleo stud to elderly professorial type.

Figure 1. John Ostrom, as a young paleo stud and as an elder statesman several decades later demonstrating a degree of isometry and allometry during ontogeny.

“Against this false negative, Ostrom laid out the positive evidence, listing more than 20 anatomical similarities between Archaeopteryx and various dinosaurs. It wasn’t just that Ostrom could not be ignored. He was far too thorough and meticulous, and for 30 years too persistent in the face of his critics, for anyone to refute.”

The LRT has been online for only 8 years, so only 22 to go!

“Though one or two holdouts still resist the idea, it is now widely accepted that birds evolved from the group of bipedal theropod dinosaurs”

“The idea that birds are in fact living dinosaurs is so commonplace that the debate has largely turned to the question of why they were the only dinosaurs to survive the mass extinction of 65 million years ago.”

“More significantly, Ostrom lived to see his ideas about the dinosaur origin of birds—and the feathered plumage of dinosaurs—vindicated by a series of remarkable fossils from northeastern China.”

Those should have been unnecessary as Ostrom explains below.

“On Ostrom’s death in 2005, age 77, the Los Angeles Times wrote that he had “almost single-handedly convinced the scientific community that birds are descended from dinosaurs.” “John Ostrom,” the Sunday Times (London) added, “did more than anyone else to make dinosaurs interesting, real, and visceral.”

“When NPR’s All Things Considered marked the occasion by interviewing Ostrom’s first research student, Bob Bakker, the paleontological world held its breath for a moment, recalling the troubled relationship between these two allies in the dinosaur renaissance. But when asked how important Ostrom had been to dinosaur paleontology, Bakker graciously commented: “Nobody was more important.”

In the comments section to the online article,
you can read from Paul Sereno’s epitaph of Ostrom, “He did more than simply point out the great number of similarities between this theropod and the early bird Archaeopteryx. He argued that these similarities were derived. That is, that they were synapomorphies—shared morphology from common ancestry.”

We looked at Ostrom’s frustration with
the slow pace of paleontology earlier. Here it is again.

According to the Hartford Courant (2000), “In 1973, Ostrom broke from the scientific mainstream by reviving a Victorian-era hypothesis (see above) that his colleagues considered far-fetched: Birds, he said, evolved from dinosaurs. And he spent the rest of his career trying to prove it.” With the announcement of the first dinosaurs with feathers from China, Ostrom (then age 73) was in no mood to celebrate. He is quoted as saying, ““I’ve been saying the same damn thing since 1973, `I said, `Look at Archaeopteryx!’” Ostrom was the first scientist to collect physical evidence for the theory. Ostrom provoked a debate that raged for decades. “At first they said, `Oh John, you’re crazy,”’ Ostrom said in 1999.”

On the night Ostrom was to be honored
at the annual convention of the Society of Vertebrate Paleontology, I noticed him walking alone to the proceedings. I took advantage of the coincidence to walk with him. He was gracious enough to allow that. I cannot remember the substance of our conversation. As soon as we got to the building, he was swept up into the celebration as everyone else wanted their own moment with the man who saved dinosaurs.


References

https://pterosaurheresies.wordpress.com/2016/03/16/sometimes-it-takes-the-paleo-crowd-an-epoch-to-accept-new-data/

https://yalealumnimagazine.com/articles/3921-the-man-who-saved-the-dinosaurs?fbclid=IwAR1HMFU7cxeqn-iGd8dtO6nAxsjpERhyTza2AnpkCDz05k9fY3w-63-q4Wc

Shrinking dinosaurs and the evolution of endothermy in birds

A new paper by Rezende et al. 2020
correlate small size with endothermy at the genesis of birds from larger theropod precursors.

A problems arises
due to taxon exclusion at the origin of dinosaurs (Fig. 1) when small size, bipedalism and the genesis of proto-feathers already correlates with endothermy… tens of millions of years before the advent of birds. Rezende et al. apparently decided not to include the genesis of dinosaurs in their study… but should have done so.

Figure 1. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

Figure 1. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

From the abstract:
“The evolution of endothermy represents a major transition in vertebrate history, yet how and why endothermy evolved in birds and mammals remains controversial.”

Controversial? No. Everyone knows the warm-blooded, high-energy tetrapods all had their genesis after phylogenetic miniaturization. We covered that earlier with mammals, dinosaurs and pterosaurs.

“Here, we combine a heat transfer model with theropod body size data to reconstruct the evolution of metabolic rates along the bird stem lineage. Results suggest that a reduction in size constitutes the path of least resistance for endothermy to evolve, maximizing thermal niche expansion while obviating the costs of elevated energy requirements.”

This has been known for decades.

“In this scenario, metabolism would have increased with the miniaturization observed in the Early-Middle Jurassic (~180 to 170 million years ago), resulting in a gradient of metabolic levels in the theropod phylogeny.”

The authors are unaware that phylogenetic miniaturization preceded the origin of dinosaurs in the tiny Middle Triassic taxon PVL 4597 (Figs. 1, 4).

“Whereas basal theropods would exhibit lower metabolic rates, more recent nonavian lineages were likely decent thermoregulators with elevated metabolism. These analyses provide a tentative temporal sequence of the key evolutionary transitions that resulted in the emergence of small, endothermic, feathered flying dinosaurs.”

Seems logical, but as mentioned above, these authors are a few nodes too late. Small endothermic dinosaurs were present in the Late Triassic following PVL 4597.

The Rezende et al. cladogram
(Fig. 2) includes many large to giant theropod dinosaurs and it does not match the large reptile tree (LRT, 1631+ taxa, Fig. 3), which includes more smaller theropods.

Figure 2. Cladogram from Rezende et al. with colors added to show three size classes, under a meter, about a meter, and more than a meter in length.

Figure 2. Cladogram from Rezende et al. with colors added to show three size classes, under a meter, about a meter, and more than a meter in length. Note the transition from large (purple) to medium (green) to little (small). Compare to figure 3 from the LRT.

Figure 4 in Rezende et al.
shows the evolution of ectothermy (240-220mya) to inertial homeothermy (giant taxa, 370kg, 215-190mya) to feathers (190-160mya) to endothermy (180-160mya) to flight (170-160mya).

Taxon inclusion sets can be biased
to present the story you want to tell. In the Rezende et al. cladogram (Fig. 2) a large number of Middle and Late Jurassic giants are included. In the LRT (Fig. 3) small taxa are present throughout the lineage of theropods. Scipionyx (at the base of Jurassic large theropods) is also a small taxon, but workers consider it a juvenile of a medium-sized taxon.

Figure 3. Subset of the LRT focusing on theropods and basal birds. Colors added for large (greater than a meter), medium (about a meter), and small (less than a meter) in length. Compare to figure 2 from Rezende et al. Note the depth of small taxa, some of which give rise to large taxa.

Figure 3. Subset of the LRT focusing on theropods and basal birds. Colors added for large (greater than a meter), medium (about a meter), and small (less than a meter) in length. Compare to figure 2 from Rezende et al. Note the depth of small taxa, some of which give rise to large taxa. Scipionyx at the base of the giant Jurassic theropods, is also a tiny taxon, but is considered a juvenile.

From the Rezende et al. discussion section:
“Two exceptional phenomena are observed during the evolution of birds: a sustained (but not necessarily gradual) miniaturization lasting millions of years and the emergence of endothermy. We argue that these phenomena are mechanistically linked.”

Figure 4. The genesis of the Archosauria embodied in PVL 4597 to scale with a modern archosaur, Cyanocitta, the blue jay.

Figure 4. The genesis of the Archosauria embodied in PVL 4597 to scale with a modern archosaur, Cyanocitta, the blue jay.

Unfortunately,
taxon exclusion invalidates this entire paper. The origin of the clade Archosauria (crocs + dinosaurs) had its genesis in a tiny taxon, PVL 4597 (Figs. 1, 4). That’s where endothermy first evolved. That’s where extradermal membranes (proto-feathers on naked skin) first appeared (more or less retained in both theropods and phytodinosaurs) and later turned into scales on larger dinos.

Birds likely have a higher endothermy
than non-avian theropods, and giant dinosaurs might have had a lower endothermy than smaller dinosaurs, but small theropods with a high endothermy and a bipedal configuration were present throughout the Triassic and Jurassic.

Many times tiny dinosaurs gave rise to
medium, large and giant clades in the LRT. The origin of birds was not the first time dinosaurs became small and endothermic. It was the second time.

If the Rezende et al.  paper sounds familiar, it is.
…and we looked at it earlier here. 


References
Rezende EL, Bacigalupe LD, Nespolo RF and Bozinovic F 2020. Shrinking dinosaurs and the evolution of endothermy in birds. Science Advances 2020:6 eaaw4486 1 January 2020
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.

 

Updated ‘Origin of Dinosaurs and Birds’ YouTube video

When I first posted a video on YouTube
featuring the origin of dinosaurs and birds several years ago, the large reptile tree (LRT, 1611+ taxa) had 500 some taxa and the video featured genera going all the way back to Devonian tetrapods. That far back was unnecessary and became outdated last year with the addition of more tetrapods to the LRT. I will do the same with the other videos as time allows.

And one more thing…
as the late Steve Jobs used to say. The above pterosaur video was updated, as well, to be more concise and informative.

Best regards
and thank you for your readership.

‘When whales walked: Journeys in Deep Time’ from PBS

PBS produced a nearly two hour dive into
various ‘new’ paleo-insights featuring many of paleontology’s rising stars and taxa. They called it, “When whales walked: Journey in Deep Time.” The photography and special effects were excellent. Trailer here.

The first chapter (crocs)
starts in Madagascar caves where Voay, the so-called ‘horned’ crocodile fossils are found (Fig. 1). Dr. Evon Hekkala uses DNA to chart croc evolution. Today only it’s cousin, the Nile crocodile, still lives in Madagascar.  (Surprised that Dr. Chris Brochu (U of Iowa) was not interviewed, since he has done so much work with these crocs.)

Figure 1. Dr. Evon Hekkala shows off a horned crocodile skull found in a Madagascar cave.

Figure 1. Dr. Evon Hekkala shows off a horned crocodile skull found in a Madagascar cave.

Chapter two (pre-crocs)
Dr. Bhart-Anjan Bhullar (Yale) takes us back to the Triassic, “in many ways the Age of Crocodiles”, as he assembles the bones of Poposaurus (Fig. 2). Preview here. Bhullar says, “These animals show us what crocodiles were like at the beginning of their evolution.” That’s close, but not true. Actually Poposaurus was basal to poposaurs and archosaurs (crocs + dinos), so it nests just outside of the croc clade. Junggarsuchus or Pseudhesperosuchus would have made his statement true, but he had Poposaurus in his cabinets at Yale. He also had another specimen, a real Triassic croc.

Figure 1. Revised skull reconstruction for the PEFO specimen. Here the anterior is considered a premaxilla. Those teeth are shaped like triangles, but they are very deeply rooted and exposed very little, which casts doubts on its hypercarnivory.

Figure 2. Revised skull reconstruction for the PEFO specimen. Here the anterior is considered a premaxilla. Those teeth are shaped like triangles, but they are very deeply rooted and exposed very little, which casts doubts on its hypercarnivory.

Continuing….
Bhullar next showed us a tiny ‘sphenosuchian’, nearly complete and nicknamed ‘little foot’ and cf. DromicosuchusYPM VP 57103). Originally it was discovered atop Popoposaurus.

Figure 3. The so-called 'little foot' specimen found with Poposaurus in Utah. YPM-VP-57103

Figure 3. The so-called ‘little foot’ specimen found with Poposaurus in Utah. YPM-VP-57103

Then Bhullar pulled a Larry Martin,
describing unique shared characters, rather than deciding what a croc is after phylogenetic analysis. We looked at YPM-VP-57103 earlier here.

Unfortunately,
Bhullar next held up a Euparkeria fossil and told viewers this specimen does not belong in the ancestry of crocs. That may be correct or incorrect depending on how you read it. According to the large reptile tree (LRT, 1546 taxa) Euparkeria nests so far back in the ancestry of crocs, it is too early to be a crocodylomorph.

Figure 3. YPM VP 057 103 reconstructed using color tracings from figures 1 and 2 in two scales. The smaller one shows the tail attached.

Figure 4. YPM VP 057 103 reconstructed using color tracings from figures 1 and 2 in two scales. The smaller one shows the tail attached.

Chapter three (another croc)
Dr. Diego Pol (AMNH) presented a Jurassic notosuchid with a short snout and  large eyes on the side (not on the top). Pol discussed the variety of crocodylomorphs, but showed very few.

Chapter four (birds)
Dr. Julia Clarke (U of Texas) discussed birds and mentioned, “They can dive so deep into waters that light cannot reach.” Hmmm. Never heard that before. Clarke repeated the tradition based on genomic studies that half the total number of birds are passerines (song birds). By contrast, in the LRT sparrows (genus: Passer) give rise only to hoatzins, parrots and moas.

The PBS narrator noted that birds evolved from dinosaurs, then asked the silly question, “How could something so huge and heavy evolve into something so light?” According to the LRT, dinosaur taxa in the bird lineage were never huge, never heavy. Rather many basal small taxa gave rise to larger taxa—including moas and elephant birds, which are huge and heavy birds, as everyone knows. I just pulled a Larry Martin.

Chapter five (more birds)
Dr. Jacques Gauthier (Yale) said “Deinonychus altered everything we know about dinosaurs and birds” and that’s one of the major embarrassments according to Dr. John Ostrom, Gauthier’s mentor.  Gauthier mentions the first feathers were for warmth. Actually that was secondary. Warmth only happens when lots of feathers spread into a thick coat around the body. Gauthier describes the flight stroke of birds as they lift their forelimbs over the back, which is “very weird for tetrapods.” Gauthier makes no mention of Ken Dial‘s work or the elongation and locking down of the coracoids that enable a flight stroke in pterosaurs and birds.

Chapter six (more birds)
Dr. Jingmai O’Connor (USC, IVPP) describes dinosaurs buried in volcanic ash. Specimens document every stage of the dino–bird transition as they once lived side-by-side. She shows and discusses Caudipteryx, Jeholornis and Confuciusornis. O’Connor said an abbreviated tail evolved many times in dinosaurs and birds. You heard that here first, following a paper on pygostyles by O’Connor.

Chapter seven (more birds)
Dr. Erich Jarvis (The Rockefeller U) studies bird brains, learned behavior, and bird song evolution. The PBS narrator asks, “We all want to know is the bird family tree correct?” Jarvis says, he trusts genes to infer relatedness, and “most people trust DNA.” The LRT shows that “most people” are wrong. Jarvis thinks that “just a handful survived the (Cretaceous) mass extinction: shorebirds. ducks, geese, ostriches, emus.” This quietly omits one of the most highly derived bird clades, penguins in the Paleocene.

Chapter eight (whales)
Dr. Mark Uhen (George Mason U) mentioned that Charles Darwin suggested something like a bear could become a mysticete, then described a history of fossil whale discovery beginning with Basilosaurus, first thought to be a giant sea serpent.

Dr. Philip Gingerich (U Michigan) was highlighted for his discoveries in 1975, but even he made the mistake of assuming whale monophyly and descent from artiodactyls (a primitive deer). The LRT recovers at least two origins for extant whales where tenrecs nest basal to odontocetes and desmostylians nest basal to mysticetes. Gingerich discovered Pakicetus in Pakistan, which was once close to Madagascar, where tenrecs are found today.

At the Museum of Natural History in Paris, Dr. Christian De Muizon shows off the complete reconstruction of the Pakicetus skeleton, surprisingly an ancient relative of modern day whales.

Figure 5. At the Museum of Natural History in Paris, Dr. Christian De Muizon shows off the complete reconstruction of the Pakicetus skeleton, surprisingly an ancient relative of modern day whales.

Chapter nine (more whales)
Dr. Christian De Muizon (Muséum National d’Histoire Naturelle, Paris, Fig. 5) shows off a complete skeleton of Pakicetus, saying, “It looks like a dog with a long snout and webbed feet,” ignoring the fact that it looks more like a big tenrec and tenrecs echolocate.

Dr. Carlos Peredo (George Mason U) says baleen whales and toothed whales had their split early within cetacea (30 mya), in the descendants of Dorudon. By contrast, in the LRT the odontocete/mysticete split was much earlier, in the Jurassic. when tree shrews diversified.

Chapter ten (elephants)
Something about elephant tracks and extinction. Interesting to watch, but not much to comment about.

Indrasaurus and Microraptor: the inside story

O’Connor et al. 2019 report on
a small pre-squamate lizard, Indrasaurus wangi (Fig. 1; STM5-32), ingested just before the untimely death of its feathered predator, Microraptor (Fig. 3, STM5-32). Both were added to the large reptile tree (LRT, 1542 taxa). O’Connor et al. note, “This is the fourth specimen of Microraptor described with ingested remains preserved in the abdominal cavity, with enantiornithine birds, mammals, and fish previously documented.”

Figure 1. Indrasaurus reconstructed.

Figure 1. Indrasaurus reconstructed. Sister taxa do not have an antorbital fenestra, so the one that appears here is suspect, but possible.

From their abstract:
“Phylogenetic analysis suggests Indrasaurus wangi gen. et sp. nov. is a basal scleroglossan closely related to the slightly older Liushusaurus. Comparison of ingested remains preserved across Paraves suggests that dromaeosaurids retained the plesiomorphic condition in which ingested prey were fully digested, rather than egested, as has been demonstrated was the case in the probable troodontid Anchiornis.”

In the LRT Liushusaurus is an outgroup taxon to the Squamata, a clade defined by extant taxa. Liushusaurus nests six nodes apart from Indrasaurus.

FIgure 3. Hoyalacerta in situ nests close to Indrasaurus in the LRT. Note the similarly long torso and short, small limbs.

Figure 2. Hoyalacerta in situ nests close to Indrasaurus in the LRT. Note the similarly long torso and short, small limbs.

O’Connor et al. remarked,
“Phylogenetic relationships in fossil squamates are difficult to determine with currently available matrices. Given the uncertainty regarding squamate relationships at this time, we do not find it unusual that our results add to the current disparity.” O’Connor et al. did not realize the clade Protosquamata enclosed the clade Squamata. The LRT was the first to recover this clade and another previously overlooked lepidosaur clade, the Tritosauria, nesting between Sphenodontia and Squamata.

Figure 2. Indrasaurus and Microraptor to scale.

Figure 3. Indrasaurus and Microraptor to scale. Despite what appear to be jaw tips, those are separated dentaries an the skull is preserved in dorsal view, lacking premaxillae and nasals.

In the LRT,
Indrasaurus (STM5-32) nests close to the coeval Hoyalacerta (Fig. 2) in the Protosquamata, a more primitive clade than Squamata that includes Squamata and otherwise no extant taxa. O’Connor et al. are mistaken, according to the LRT, when they consider Indrasaurus a scleroglossan squamate.

Antorbital fenestra?
Indrasaurus sister taxa do not have an antorbital fenestra, so the one that appears here (Fg. 1) is suspect, but possible.

FIgure 6. Ornitholestes nests as a sister to Sciurumimus, between Compsognathus and Microraptor.

FIgure 4. Ornitholestes nests as a sister to Sciurumimus, between Compsognathus and Microraptor.

The STM5-32 specimen of Microraptor (Fig. 3) nests as the basalmost tested Microraptor derived from a sister to Sciurumimus and Ornitholestes (Fig. 4), convergent with and distinct from pre-bird clades. Traditional cladograms, like the recently published Hartman et al. 2019, do not associate these three taxa apart from birds. O’Connor et al. consider Microraptor to be a dromaeosaurid. The LRT rejects that hypothesis of interrelationships.

Three Microraptor species
Since the three tested Microraptors nest apart from one another with high Bootstrap scores, two need to be given new specific names, not lumped under Microraptor zhaoianus, as O’Connor et al. do.

Was Microraptor volant?
O’Connor et al. consider all specimens of Microraptor to be volant (capable of flight). The short, nearly disc-like shape of the coracoid (Fig. 2) argues against this, despite the presence of large feathers in this genus. The key difference between Late Jurassic birds and pre-bird anchiornithids is the elongation of the locked-down coracoid, which marks the genesis of flapping in pterosaurs and birds. Like their ancestor, Ornitholestes, Microraptor had small, disc-like coracoids that slid like those of most tetrapods with coracoids. Based on the elongation and locking down of coracoids, evidently flapping occurred before forelimb elongation in pterosaurs, afterwards in basalmost birds, like the basal Archaeopteryx specimens. Microraptor was a glider at best, not a flapper, which requires locked-down elongate coracoids.

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.

I am in the heretical minority
when I say giant azhdarchids and small microraptors were not capable of flight. I report from the evidence, not the feeling, the authority or tradition.


References
O’Connor et al. (six co-authors) 2019. Microraptor with ingested lizard suggests non-specialized digestive function. Current Biology 29, 1–7. https://doi.org/10.1016/j.cub.2019.06.020

UV light vs. LCA (last common ancestor) approach to flapping flight in birds

Schwarz et al. 2019
employed ultraviolet (UV) light to report, “In contrast to previous studies, we show that most of the vertebral column of the Berlin Archaeopteryx possesses intraosseous pneumaticity, and that pneumatic structures also extend beyond the anterior thoracic vertebrae in other specimens of Archaeopteryx. With a minimum Pneumaticity Index (PI) of 0.39, Archaeopteryx had a much more lightweight skeleton than has been previously reported, comprising an air sac-driven respiratory system with the potential for a bird-like, high-performance metabolism.

“The neural spines of the 16th to 22nd presacral vertebrae in the Berlin Archaeopteryx are bridged by interspinal ossifications, and form a rigid notarium-like structure similar to the condition seen in modern birds. this reinforced vertebral column, combined with the extensive development of air sacs, suggests that Archaeopteryx was capable of flapping its wings for cursorial and/or aerial locomotion.”

Schwarz et al. did not perform a phylogenetic analysis
nor did they mention anything about the elongate locked down coracoid present on this specimen. In the large reptile tree (LRT, 1445 taxa, subset Fig. 1) the Berlin specimen of Archaeopteryx (MB.Av.101) nests at the base of all flapping birds, including the Enantiornithes, the first clade to split off. As in the amniotic egg issue, the last common ancestor is where you find the genesis of traits common to all descendant taxa. So, Schwarz et al. are correct: the Berlin specimen is indeed close to the origin of flapping flight.

Figure 3. Subset of the LRT focusing on basal birds and pre-bird theropods. Note many of the various Solnhofen birds nest apart from one another and the Daiting specimen nests outside the birds (Aves).

Figure 1. Subset of the LRT focusing on basal birds and pre-bird theropods. Note many of the various Solnhofen birds nest apart from one another and the Daiting specimen nests outside the birds (Aves). The Berlin Archaoepteryx is the last common ancestor of all flapping birds.

It’s not the reinforced vertebral column
that determines if a bird (or pterosaur) flaps or not. It’s the elongation of an immobile coracoid these two flapping clades share in common at the genesis of this behavior.

Distinctlively different
due to lacking a coracoid, bats employ the hyper-elongation of the clavicle to do the same thing by convergence.

Figure 1. Generic freehand Archaeopteryx (Berlin specimen) from Schwarz et al. 2019, retraced from Wellnhofer 2008 compared to bone-by-bone tracing for ReptileEvolution.com.

Figure 2. Generic freehand Archaeopteryx (Berlin specimen) from Schwarz et al. 2019, retraced from Wellnhofer 2008 compared to bone-by-bone tracing for ReptileEvolution.com. Wellnhofer’s drawing appears to be a generic Archaeopteryx. Tracings of all specimens show no two are alike.

One more thing…
if possible, don’t freehand your reconstructions (Fig. 2) and don’t redraw freehand reconstructions from Wellnhofer 2008 ~ especially if you’re going to go through all the trouble of extracting more precise data on a fossil than has been recovered before. Do your own more precise bone tracings and reconstructions!


References
Schwarz D, Kundrat M, Tischlinger H, Dyke G and Carney RM 2019. Ultraviolet light illuminates the avian nature of the Berlin Archaeopteryx skeleton. Nature.com
Wellnhofer P 2008. Archaeopteryx. Der Urvogel von Solnhofen. (Verlag Dr. Friedrich Pfeil, München), pp. 256.

New view on ‘Paravians’: Agnolin et al. 2019

Agnolin et al. 2019 produced
a new view of early bird and pre-bird relationships. They write, “We here present a review of the taxonomic composition and main anatomical characteristics of those theropod families closely related with early birds, with the aim of analyzing and discussing the main competing hypotheses pertaining to avian origins. We reject the postulated troodontid affinities of anchiornithines, and the dromaeosaurid affinities of microraptorians and unenlagiids, and instead place these groups as successive sister taxa to Avialae.”

By contrast
in the large reptile tree (LRT, 1401 taxa; subset Fig. 1) some troodontids are basal to anchiornithines, which are basal to avians. Other traditional troodontids are not basal to birds and pre-birds.

Agnolin et al. report, “Regarding character evolution, we found that: (1) the presence of an ossified sternum goes hand in hand with that of ossified uncinate processes; (2) the presence of foldable forelimbs in basal archosaurs indicates widespread distribution of this trait among reptiles, contradicting previous proposals that forelimb folding driven by propatagial and associated tendons was exclusive to the avian lineage; (3) in basal paravians and avialans (e.g., Archaeopteryx, Anchiornis) the wings are relatively large and wide, with relatively short rectricial feathers, a rounded alar contour, and a convex leading margin. These taxa exhibit restricted forelimb folding capability with respect to more derived birds, their hands being preserved at angles of flexion (with respect to the radius/ulna) of no less than 90. In more derived birds, however, the rectrices are notably elongate and the angle between the hand and forearm is much less than 90, indicating not only increased forelimb folding capability but also an increased variety of wingbeat movements during flight. Because of the strong similarities in pectoral girdle configuration between ratites and basal avialans and paravians, it is possible to infer that the main forelimb movements were similar in all these taxa, lacking the complex dorsoventral wing excursion characteristic of living neognathans.”

Unfortunately
Agnolin et al. presented a cladogram that was largely unresolved. According to the LRT that loss of resolution can be attributed to one thing: exclusion of taxa. Key taxa missing from the Agnolin et al. tree include:

  1. Compsognathus (both species)
  2. Ornitholestes
  3. The other ten or so ‘Archaeopteryx’ specimens

With the addition of these key taxa theropods (including pre-birds and birds) become completely resolved in the LRT (subset Fig. 1).

Figure 1. More taxa, updated tree, new clade names.

Figure 1. More taxa, updated tree, new clade names, from an earlier blog post.

References
Agnolin FL et al. (4 co-authors) 2019. Paravian phylogeny and the dinosaur-bird transition: an overview. Frontiers in Earth Science 6:252.
doi: 10.3389/feart.2018.00252