Triassic? No, Eocene Bird Tracks: How to Fix a Mistake in “Nature”

The whole point of this post is to show that sometimes scientists AND referees make mistakes. This one (see below) the authors corrected themselves, likely after catching hell from colleagues for the last 11 years. The referees are probably glad to retain their anonymity.

Figure 1. Bird tracks originally considered Latest Triassic, now considered Eocene, from Argentina.

Figure 1. Bird tracks originally considered Latest Triassic, now considered Eocene, from Argentina.

It all started a decade ago
when Melchor, De Valais and Genise (2002) reported very bird-like tracks in Latest Triassic sediments in Argentina. This was deemed worthy of the academic journal Nature because, if valid, this would have pushed the origin of birds, or bird-like dinosaurs, back from the Latest Jurassic to the Latest Triassic. A very hot topic! Respected paleontologist referees gave this the green light and it was published.

However, recently this paper was retracted.

Here’s the apologetic abstract
from Melchor, De Valais and Genise (2013) 

“Bird-like tracks from northwest Argentina have been reported as being of Late Triassic age. They were attributed to an unknown group of theropods showing some avian characters. However, we believe that these tracks are of Late Eocene age on the basis of a new weighted mean 206Pb/238U date (isotope dilution–thermal ionization mass spectrometry method) on zircons from a tuff bed in the sedimentary succession containing the fossil tracks. In consequence, the mentioned tracks are assigned to birds and its occurrence matches the known fossil record of Aves.”

Hopefully apologies have been accepted worldwide.
These three “came clean” and made their mistake known and I’m sure all three will continue to make important contributions to paleontology.

Some scientists do not accept apologies or corrections. Some rifle through trash for rejected ideas so they can pillory others. Some scientist can not accept their own mistakes. Some scientists reject solutions to problems by labeling them, “highly idiosyncratic (= a mode of behavior or way of thought peculiar to an individual)” just because they have new ideas not preciously considered by others. These are the scientists who are gumming up the works.

There are several papers that have been rejected by referees clinging to the status quo that solve several enigmas and clear up several mysteries using established scientific methods. Several of those rejections from referees who are “gumming up the works” provided the reason for this blog and

Melchor RN, De Valais S and Genise JF 2002. Bird-like fossil footprints from the Late Triassic. Nature 417, 936–938 (2002)
Melchor RN, De Valais S and Genise JF 2013. A late Eocene date for Late Triassic bird tracks. Nature 495, E1–E2 (21 March 2013) doi:10.1038/nature11931

Something about Turkeys on Thanksgiving

Happy Thanksgiving (America).
I encourage my readers, if they have not already done so, to check out My Life as a Turkey online at PBS (Fig. 1, click here). They’re curious, affectionate, loyal and when they hit puberty all hell can break loose. They’re beset by enemies and they learn to control their enemies. They are hit with disease and they mourn their losses. Some are independent. Others, from the same brood, seek touch. Watch them learn to fly, loose their cuteness, play with the mammals and, in the end, go out on their own.

Click to go to online video at PBS/Nature. My Life as a Turkey explores the ontogeny of these little dinosaurs as thoroughly as I've ever seen.

Click to go to online video at PBS/Nature. My Life as a Turkey explores the ontogeny of these little dinosaurs as thoroughly as I’ve ever seen.

Alpine Swifts and Pterosaurs

Alpine Swift (Tachymarptis melba) on the wing for 7 months at a time! Check out that wing shape. Remind you of anything prehistoric?

Alpine Swift (Tachymarptis melba) on the wing for 7 months at a time! Check out that wing shape. Remind you of anything prehistoric?

An interesting NatGeo post on the Alpine Swift (Tachymarptis melba) and its incredible but true 7 months (200 days) on the wing (Liechti et al. 2013) raised my curiosity about what sort of wing must such a bird have?

Turns out to have a very pterosaurian wing (short chord version) in ventral view. Nat Geo reports, Their long wings make them fast and manoeuvrable, allowing them to scythe through the air in search of small insects and other “aerial plankton”.

And why do they fly continuously? Again, Liechti has speculations rather than answers. They may exploit food sources that other birds can’t touch, avoid predators by flying through the night, or stay beyond the reach of parasites like malarial mosquitoes. “These aren’t very convincing,” he admits, “but for sure, there’s a cost to staying in the air, so there must be a benefit.”

Swifts are apodids, famous for their tiny feet (they don’t perch that often). That takes us to the pterosaurs with tiny feet and spindly legs, the ornithocheirids (Fig. 2, 3).

Worth comparing for wing shape and foot size.
Evidently these large pterosaurs were likewise rarely grounded, based on their tiny feet and giant wings, especially compared to other pterosaurs.

Figure 2. The ornithocheirid pterosaur, Arthurdactylus. Note the tiny size of its feet.

Figure 2. The ornithocheirid pterosaur, Arthurdactylus. Note the tiny size of its feet and the huge wings. Like a swift, this pterosaur could have slept while on the wing. The spindly fingers were no good for grappling tree trunks.

Awkward on the ground.
Graceful in the air. This is the reason why the ornithocheirid humerus is so much larger than the femur – not the forelimb launch hypothesis! They put everything into their wings, which transport them to food. Their legs simply enable them to walk out of their eggs.

Figure 2. Arthurdactylus in dorsal view while flying. Note the knife-like wing shape,  that could be maneuvered, like that of a sail plane or swift.

Figure 2. Arthurdactylus in dorsal view while flying. Note the knife-like wing shape, that could be maneuvered, like that of a sail plane or swift. Wings back = less drag, greater speed.

Basically the pterosaur wing in ornithocheirds is a tapering cone, with a large diameter proximally and a tiny diameter distally. This has proved to be a very strong structure from outstretched traffic lights to fishing rods.

Outstretched to swept back
As in swifts, the wings of pterosaurs could have maneuvered in flight from strictly lateral to backswept. Each configuration has their own use, advantage and disadvantage.

Liechti, Witvliet, Weber & Bachler 2013. First evidence of a 200-day non-stop flight in a bird. Nature Communications.

The unexpected bipedal/marine connection

Several times in the evolution of reptiles bipedal forms have phylogenetically preceded marine forms. Yes, marine forms. It’s bizarre, but true.

Here’s the list, more or less. Did I miss any?

Huehuecuetzpalli (bipedal capable) > Dinocephalosaurus (marine)
Huehuecuetzpalli, a small speedy lizard with short fore limbs and long hind limbs evolves to become Dinocephalosaurus, a giant long-necked sit-and-wait predator via Macrocnemus, something in between.

Langobardisaurus (biped) > Tanystropheus (marine)
Langobardisaurus, a small long-necked strider evolves to become Tanystropheus, a giant stand-and-wait marine predator.

Eudibamus (biped) > Claudiosaurus (marine)
Eudibamus, a small lizard-like diapsid with a long neck and long hind limbs evolves to become Claudiosaurus, a long-necked marine undulating marine predator of tiny prey. Thereafter descendants evolve to become ichthyosaurs and plesiosaurs.

Varanus (biped while fighting) > Mosasaurus (marine)
Okay, so only certain varanids only go bipedal when fighting, even so mosasaurs are giant and marine.

Scleromochlus & Terrestrisuchus (bipeds) > Metriorhynchus (marine)
Scerlomochlus, and Terrestrisuchus, tiny long-legged basal crocs evolve to become large short-paddled marine crocs, like

Storks (biped) > Penguins (marine)
Flying bipeds evolve to fly underwater.

Australopithecines (biped) > Humans (Homo, marine capable)
(grassland roamers evolve to become able to swim)

Evidently it all comes down to 
Conscious control of breathing — if you want to become a marine animal you have to hold your breath.

Not sure what the bipedal connection is with reptiles, because lots of marine reptiles never had a bipedal phase. I just wanted to throw the idea out there.

More on Humans:
Anthropologist Elaine Morgan on TED talks about the origin of bipedal humans from aquatic apes here. Step-by-step: Apes all walk bipedally when they cross streams. For insulation humans have fat migration to a subdermal position, that’s why obesity is possible for humans, not for apes. The nostrils open ventrally, keeping water out by air pressue in humans. Ape nostrils don’t keep out water, except for the proboscis monkey (the most aquatic of primates).  Ability to speak comes by way of the conscious control of their breath, according to Morgan.

Late Cretaceous pterosaurs, penguins, storks and falcons

A 2006 paper (Slack et al.) on earliest Paleocene penguin (Waimanu manneringi) fossils finds sheds light on early bird diversification and possible decline of the pterosaurs (reduction to only large taxa).

Penguins and storks
According to Slack et al., penguins and storks nest together closer than loons and albatross + petrel. And they must have diversified at 67.1 mya, prior to the K/T extinction.

Falcons and pterosaurs
An earlier diversification, 77.2 mya marked the splitting of the falconiformes from the sea birds (including the above listed taxa). That means falcons or protofalcons were soaring over Late Cretaceous skies. Noting trends for ever larger pterosaurs and the absence  smaller pterosaurs in the Late Cretaceous, the authors report, “Kim et al. (2003) offer the interpretation that pterosaurs might have fed on small birds—equally plausible to us, however, is that the raptors (Falconiformes) could have preyed on young pterosaurs.”

Never heard that one before. Of course, if a predator eats all of its prey, the predator also dies. So, improbable, but interesting.

Kim CB, Huh M, Cheong CS, Lockley MG and Chang HW 2003. Age of the pterosaur and web-footed bird tracks associated with dinosaur footprints from South Korea. Island Arc 12:125–131.
Slack KE, Jones CM, Ando T Harrison GL, Fordyce RE Arnason U and  Penny D 2006. Early Penguin Fossils, Plus Mitochondrial Genomes, Calibrate Avian Evolution. Mol. Biol. Evol. 23(6):1144–1155.

How Birds Got Their Wings

A recent article, “How Birds Got Their Wings,” also here, here and here describe work by Dececchi and Larsson (2013) that noted scaling of forelimb vs hind limb took a big turn with Archaeopteryx and kin (Fig. 1). They note, as forelimbs lengthened, they became long enough to serve as an airfoil, allowing for the evolution of powered flight. Shorter legs would have aided in reducing drag during flight — the reason modern birds tuck their legs as they fly — and also in perching and moving about on small branches in trees.

That’s all well and good, but its not the key. It’s one step following the key.
The key is flapping. That’s a behavior that definitely leads to flight. Having long forelimbs vs. hind limbs is also found in primates, chalicotheres and sloths. They don’t fly. Even the “flying lemur” Cynocephalus had long arms. All it can do is glide because it doesn’t flap.

Figure 2. Cosesaurus running and flapping - slow.

Figure 1. Click to animate. Cosesaurus running and flapping – slow.

The key to flapping is a locked down coracoid.
As we learned earlier with Cosesaurus (Fig. 1), a locked down coracoid is one thing pterosaurs and birds share. Cosesaurus had fibers trailing its forelimbs (Ellenberger 1993, Peters 2011) but its forelimbs were too short to fly. Nevertheless, it could flap because it had a locked down coracoid. And that was a secondary sexual trait (behavior) that led to more of the same in three distinct directions in Sharovipteryx, Longisquama and basal pterosaurs.

Taxa in the lineage of birds.

Figure 2. Taxa in the lineage of birds. From top to bottom: Tawa, Juravenator, Sinocalliopteryx, Archaeopteryx, Cathayornis, Sinornithes plus enlarged skulls. Note the coracoid becomes taller and fixed in Archaeopteryx.

Other dinosaurs
with long forelimbs and a tall, narrow, locked down coracoid include oviraptorids, dromaeosaurids, alvarezaurs and birds all taxa that phylogenetically follow Archaeopteryx.

And bats?
They have a locked down tall clavicle that serves the same function. We don’t know when they started flapping because the closest known fossils of prebats are all skull material only.

Dececchi TA and,  Larsson HCE 2013. Body and Limb Size Dissociation at the Origin of Birds: Uncoupling Allometric Constraints Across a Macroevolutionary Transition. Evolution 67(9):2741 DOI:10.1111/evo.12150

What?? No feathers on velociraptors?

Figure 1. Inside cover illustration spread for "Raptors, the Nastiest Dinosaurs" by Don Lessem, illustrated by David Peters. Don asked for a "no feathers dinosaur" so that's what he got. Don't blame the artist. I tried to persuade. Utahraptor is the big dromaeosaur here.

Figure 1. Inside cover illustration spread for “Raptors, the Nastiest Dinosaurs” by Don Lessem (1996), illustrated by yours truly, David Peters. Don asked for a “no feathers dinosaur” so that’s what he got. Don’t blame the artist. I tried to dissuade. Utahraptor is the big dromaeosaur here.

This post was inspired
by a blog and Flickerstream I ran across here and here that bemoaned the fact that my 1996 dromaeosaurids / velociraptors (Fig. 1) in “Raptors – The Nastiest Dinosaurs” did not have feathers, but did have propatagia.

Guys, I tried to add feathers, as I had done several years earlier (1989) to my own velociraptors in Gallery of Dinosaurs (Fig. 2). However, author Don Lessem insisted that no feathers appear in his book. I tried to dissuade, but was vetoed. After all, he is the author. And that was then. I’m sure Dino Don has come around to new thinking since then.

See how difficult it is to promote a new idea supported by data? Even an expert like Don Lessem balked back in 1995-6.

Figure 2. Feathered Deinonychus from A Gallery of Dinosaurs by David Peters.

Figure 2. Feathered Deinonychus from A Gallery of Dinosaurs by yours truly, David Peters. (1989). Click to enlarge.

So, there is a backstory,
as there is with other controversial aspects of my work. At present the backstory and trashed ideas are not as important as the current work. Science marches on and new data keeps coming in. So let’s stay with the current wave. If you see any other problems with my  tracings or identifications, please let me know of those issues.

These are kids books, not academic journals!
“A Gallery of Dinosaurs” is online here.