Archaeornithura: a basal modern bird from 130 mya

Figure 1. Archaeornithura meemannae DGS tracing over aligned plate and counter plate (left). Tracing without fossil at right. Lateral view of post cervical skeleton (with black body outline).

Figure 1. Archaeornithura meemannae DGS tracing over aligned plate and counter plate (left). Tracing without fossil at right. Lateral view of post cervical skeleton (with black body outline). Click to enlarge. Different from a chicken or sparrow: 1. smaller sternum, 2. more gracile ventral pelvis, 3. longer tail and 4. unfused manus bones. The broad and robust sacrum is similar to modern birds.

A recent paper by Wang et al. (2015) brings us the earliest bird of modern aspect, one from the modern Ornithomorpha clade (all living birds), Archaeornitura (Fig. 1). It lived 130 mya in the Early Cretaceous. Two specimens were found. Both had rich feather preservation with primary wing feathers long enough for flight.

Primitive, yet modern
The sternum is small. The ventral pelvis is gracile. The sacrum is large and robust, but not fused together and not fused to the ilium. At least one specimen appears to have retained a long set of tail bones. The coracoids were long and firmly attached to a large sternum, though not nearly as large as in modern flying birds. The fingers were reduced, but unfused. The skull was not well preserved in either specimen. About nine not-very-long cervicals were present. Not much, if any, of a pubic boot in Archaeornithura, but all sister tested sister taxa have one.

Compare the skeleton
of Archaeornithura (Fig. 1) to that of Gallus the chicken (Fig. 2). The chicken, like most modern birds, has a larger, deeper sternum, a larger deeper ventral pelvis, fused fingers and more cervicals.

Figure 1. Gallus the chicken is representative of modern birds. Note the large size of the sternum and ventral pelvis, the fused manual bones, the extended cervical series and the reduced tail

Figure 1. Gallus the chicken is representative of modern birds. Note the large size of the sternum and ventral pelvis, the fused manual bones, the extended cervical series and the reduced tail

So, in pterosaurs and their predecessors 
the pectoral and pelvic girdles came first, the wings developed later. In birds, the wings came first, the pectoral and pelvic girdles took a while to develop.

References
Wang M et al. (7 other authors) 2015. The oldest record of ornithuromorpha from the early cretaceous of China. 6:6987 DOI: 10.1038/ncomms7987

Yi qi and Occam’s razor

Yesterday and earlier we looked at the new dino-bird, Yi qi. This is the third and final note.

Figure 1. Identification errors (in red) on the original Yi qi diagram from Xu et al. 2015.

Figure 1. Identification errors (in red) on the original Yi qi diagram from Xu et al. 2015. LSE = left styliform element. RSE = right styliform element.

To reiterate: 
In Xu et al. (2015) the authors noted a new long bony element in the fore limb of Yi qi (Fig. 1) never before seen on any bird, dinosaur, or archosaur. They labeled the new bone a ‘styliform element’ in accord with similar elements in flying squirrels. Chemical analysis determined that the new bone was indeed bone. This long bone, as long as (or in the opinion of the authors, longer than) any other forelimb element appeared to be attached at one end to the wrist, and at the other end, to nothing else. In certain flying squirrels, the styliform extends laterally to expand the width of the gliding membrane. Xu et al. also compared the unfamiliar bone to similar bones in gliding marsupials, bats and pterosaurs (the pteroid), all of which arise from different parts of the anatomy, frame extradermal membranes and are employed during aerial exercises.

Xu et al. wrote:
“The most striking feature of Yi is the presence of an anomalous, slightly curved, distally tapered, rod-like structure whose length considerably exceeds that of the ulna, associated with each wrist and apparently extending from the ulnar side of the carpus. However, the rod-like bone of the forelimb of Yi is morphologically unlike any normal theropod skeletal element. Indeed, no equivalent of the rod-like bone is known in any other dinosaur even outside Theropoda,” So Yi qi had potentially analogous structures among other tetrapods, but not among birds or other dinosaurs.

The big question is:
was the new bone indeed longer than the ulna? If you trace the elements as they are (Figs. 1, 2), the new bone is not longer than the ulna.

yi-qi-recon1000b

Figure 2. Yi qi tracing of the in situ specimen using DGS method and bones rearranged, also using the DGS method, to form a standing and flying Yi qi specimen. Note the lack of a styliform element, here identified as a left radius and right ulna.

It’s easy to make errors here
The right radius is incomplete and splintered (Figs. 1-3) so that it looks like a radius and ulna. The distal right radius is lost beyond the edge of the matrix. The right so-called ‘styliform element’ extends beyond the elbow and was presumed to also extend beyond the end of the matrix. However, taken ‘as is’ the two so-called ‘styliform elements’ are actually similar in length to each other and similar to the virtually complete left ulna.

Taphonomic churning
Evidently the elements were churned prior to burial with medial digits of the left hand now lateral and the right foot high kicking like a Rockette. Thus Padian’s comment, “Yi qi’s body is not preserved below the ribcage, so reconstructions of the pelvis, hindlimbs and tail must be conjectured from what is known of other scansoriopterygids,” is incorrect or an oversight (see Figs. 1, 2).

Figure 3. Right ulna (former styliform process) of Yi traced using DGS techniques. See Figure 4 for comparison to Epidendrosaurus.

Figure 3. Right ulna (former styliform process, amber color here) of Yi traced using DGS techniques. See Figure 5 for comparison to Epidendrosaurus. The newly identified ulna was flipped prior to burial so that the thicker proximal end is now closer to the lost wrist. The radius (pink and purple) is cracked lengthwise with toothy ridges marking the break. This gave the impression of a radius and ulna, but no intact radius and ulna have tooth-like cracks and ridges. This is a shattered hollow bone. 

On the left forelimb,
the left so-called ‘radius’ (Figs. 1, 4) is barely present. The left so-called ‘styliform element’ gives the erroneous impression of continuing beneath the left humerus. It does not.

Figure 3. Closeup of the former 'styliform element' here identified as a radius in Yi qi.

Figure 4. Closeup of the former ‘styliform element’ here identified as a left radius in Yi qi.

The authors never considered the possibility
that the ulna and radius could have been splintered during crushing prior to burial. Both forearm elements are as hollow as long bones from other dino-birds. And they have been subject to torsion and churning prior to burial. In this scenario the purported left ‘radius’ (Fig. 4) is simply a splinter of the ulna, separated during axial torsion. Similarly, the purported right ‘ulna’ is a splinter of the right radius (Fig. 3).

In this hypothesis
the curved right ‘styliform element’ is in reality an ulna and the straighter left ‘styliform element’ is a radius. As preserved the new radius and ulna are about the same length and similar in diameter to their counterparts. In birds and sister taxa, like Epidendrosaurus (Fig. 5), the radius is typically straighter than the ulna. And the ulna tapers distally.

In the Xu et al. 2015 Supplemental Data,
the ‘styliform element’ lengths each have an asterisk associated with them: 133.5* and 91.3* mm. The ulna likewise has an asterisk measurement, 88.5* mm. The length of the radius was not estimated or shown. The authors note: “* indicates estimated value; the preserved length of the right styliform element is 91.3 mm, but taphonomic information and morphological comparisons between the right and left styliform elements lead us to estimate that the total length of the styliform element is 133.5 mm.” In this case, they overestimated. Perhaps a more precise tracing would have been helpful.

Occam’s razor
As everyone knows, “The principle states that among competing hypotheses that predict equally well, the one with the fewest assumptions should be selected.” Xu et al. struggled with the identity of the odd long bones in Yi qi. Unfortunately they did not select the identity with the fewest assumptions (and autapomorphies). Instead they made headlines around the globe and more than a few eyebrows rise with the invention of a new styliform element, which is really just a misidentified common fore arm element.

In this case
the left ‘styliform element’ articulates with the wrist because the left radius likewise articulates with the wrist. That the distal end no longer articulates with the elbow can be ascribed to taphonomic torsion prior to burial.

The right radius still articulates with the humerus, but the right ulna has flipped lengthwise, such that the narrow distal end (Fig. 4) is now proximal, far behind the elbow. While more difficult to visualize how this may have happened, this bone flip also must be the product of taphonomic churning prior to burial. Perhaps it goes along with the high kick of the foot. Comparisons to the articulated specimen of Epidendrosaurus (Fig. 4) are instructive here. The ulna shapes are virtually identical.

Figure 4. Right ulna of Yi (former 'styliform element') compared to right ulna of Epidendrosaurus.

Figure 5. Right ulna of Yi (former ‘styliform element’) compared to right ulna of Epidendrosaurus.

References
Padian K. 2015. Paleontology: Dinosaur up in the air. Nature (2015) doi:10.1038/nature14392
Xu X, Zheng X-T, Sullivan C, Wang X-L, Xing l, Wang Y, Zhang X-M, O’Connor JK, Zhang F-C and Pan Y-H 2015.
 A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings.Nature (advance online publication)
doi:10.1038/nature14423

No styliform element on Yi qi. That’s just a displaced radius and ulna.

Modified May 3, 2015 with the new identification of the curved ‘styliform element’, as the ulna, not the radius. 

Error alert
Apparently all the fuss and PR over the new batwing dino/bird Yi qi  is based on an error of bone identification. Both antebrachia on the specimen were splintered during crushing. The splinters were misidentified as slender radii. The purported ‘styliform elements’ (Xu et al. 2015) that gave Yi qi such an odd appearance are actually a displaced right radius and left ulna. The pictures below tell the story (Figs. 1-3).

Figure 1. Identification errors (in red) on the original Yi qi diagram from Xu et al. 2015.

Figure 1. Identification errors (in red) on the original Yi qi diagram from Xu et al. 2015.

The digits
were also mislabeled following the pattern in Limusaurus, which we touched on earlier.

The long scapula identified by Xu et al.
appears instead to be a pair of opposing elongate coracoids. Long coracoids make Yi qi a flapper, not a glider, weak though it may have been.

Figure 2. The Yi qi fossil plate and counter plates. Counterplates above and flipped to match plate.

Figure 2. The Yi qi fossil plate and counter plates. Counterplates above and flipped to match plate. Click to enlarge.

Only a few elements
appear on the counter plate (Fig. 2) that are not present on the plate. Putting them together in Photoshop and painting the bones using the methodology of DGS helped sort out the data (Fig. 3).

Figure 3. Closeup of the former 'styliform element' here identified as a radius in Yi qi.

Figure 3. Closeup of the former ‘styliform element’ here identified as a radius in Yi qi. Click to enlarge. Bone splinters led to earlier misidentification.

Reports say
the Xu et al. team struggled for several months to come to grips with this large, never-before-seen bone, the so-called ‘styliform element’. Evidently the left ulna splinters looked enough like a radius that they discounted the possibility that the odd bone was indeed the radius, likewise splintered. Note the odd orientation of the left manus (Fig. 3) in which the lateral digits are medial. The observed membrane may have been the propatagium. Or it could have simply trailed the wing like other bird membranes do. Remember, birds have no scales, as we learned earlier. Birds have naked skin with some feathers later transforming to scales on their legs with few exceptions (like owls).

Figure 4. Yi qi tracing of the in situ specimen using DGS method and bones rearranged, also using the DGS method, to form a standing and flying Yi qi specimen. Note the lack of a styliform element, here identified as a displaced radius and ulna.

Figure 4. Yi qi tracing of the in situ specimen using DGS method and bones rearranged, also using the DGS method, to form a standing and flying Yi qi specimen. Note the lack of a styliform element, here identified as a displaced radius and ulna.

Reconstructions (Fig 4) are also part of the DGS process, making sure that all bones fit together and also match those of closely related taxa (Fig. 5). Odd autapomorphies, like a styliform element, are immediately suspect, but odd autapomorphies do occasionally occur.,, apparently not this time.

Figure 4. Right ulna of Yi (former 'styliform element') compared to right ulna of Epidendrosaurus.

Figure 4. Right ulna of Yi (former ‘styliform element’) compared to right ulna of Epidendrosaurus. Click to enlarge.

DGS has gotten a bad rap.
This is just another example where, without seeing the fossil, a contribution to identification and understanding can be made. Maybe now would be a good time to take down some of those anti-DGS websites and blogposts out there.

References
Padian K. 2015. Paleontology: Dinosaur up in the air. Nature (2015) doi:10.1038/nature14392
Xu X, Zheng X-T, Sullivan C, Wang X-L, Xing l, Wang Y, Zhang X-M, O’Connor JK, Zhang F-C and Pan Y-H 2015.
 A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings.Nature (advance online publication)
doi:10.1038/nature14423

 

Yi Qi (‘strange wing’) new bat-like dinosaur/bird

It’s May 2, 2015 and I’m going to let this blogpost stand unaltered, but please see May 2 for notes that the so-called styliform process is really just a displaced radius.

The big news today is the announcement of a new Chinese dinosaur/bird, Yi Qi, with a long wrist bone that extended into soft membranes trailing the forelimb, likely to extend them like a bat wing (Fig. 1).

Two possible reconstructions were offered (Fig. 1). I offer below a new reconstruction that does not have the forelimbs overextended at the elbow and shoulders.

Figure 1. Above: the two Yi Qi reconstructions offered by Xu et al. Below: a little bend at the elbows, as in bats, birds and pterosaurs, probably replicates the wing a little bit better.

Figure 1. Above: the two Yi Qi reconstructions offered by Xu et al. Below: a little bend at the elbows, as in bats, birds and pterosaurs, probably replicates the wing a little bit better and adds strength. Also the feet are tucked under, as in birds. Click to enlarge.

From the Xu et al. abstract:
“Most surprisingly, Yi has a long rod-like bone extending from each wrist, and patches of membranous tissue preserved between the rod-like bones and the manual digits. Analogous features are unknown in any dinosaur but occur in various flying and gliding tetrapods, suggesting the intriguing possibility that Yi had membranous aerodynamic surfaces totally different from the archetypal feathered wings of birds and their closest relatives.” 

References
Xu X, Zheng X-T, Sullivan C, Wang X-L, Xing l, Wang Y, Zhang X-M, O’Connor JK, Zhang F-C and Pan Y-H 2015. A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings.Nature (advance online publication)
doi:10.1038/nature14423

Notes on Limusaurus (Dinosauria, Theropoda) and its odd little hand

Figure 1. Limusaurus in situ. The associated croc has been painted red here.

Figure 1. Limusaurus in situ. The associated croc has been painted red here. Their marriage was legal in only 16 states.  : )

Limusaurus inextricabilis (Xu et al. 2009; earliest Late Jurassic, Oxfordian; 1.7m in est. length; IVPP V 15923; Figs. 1, 2) is an herbivorous theropod with very tiny arms and hands in the lineage of proto-birds. Coincidentally, Limusaurus was buried next to the skeleton of a tiny Jurassic croc (in red above). Pol and Rauhut (2012) nested Limusaurus with Elaphrosaurus and Spinotropheus. Those taxa have not been added yet to the large reptile tree where Limusaurus nests between Sinocalliopteryx and Aurornis. Limusaurus shares a ventral pelvis, but not long arms and large hands with these bird-like taxa. Like birds, Limusaurus has a pair of sternae. The coracoids appear to be transitional between disc-like and stem-like.

Figure 2. Limusaurus reconstructed. Both hands are shown and colorized. Digit 1= purple. Digit 2= pink. Digit 3 = Green. Digit 0=pale yellow. Digit 0 goes back to basal tetrapods, like Ichthyostega, and only appear here due to the vestigial nature of the manus in which it matured at an embryologically immature state compared to sister taxa.

Figure 2. Limusaurus reconstructed. Both hands are shown and colorized. Digit 1= purple. Digit 2= pink. Digit 3 = Green. Digit 0=pale yellow. Digit 0 goes back to basal tetrapods, like Ichthyostega, and only appear here due to the vestigial nature of the manus in which it matured at an embryologically immature state compared to sister taxa.

Limusaurus is notable for two main reasons:

  1. It is an herbivorous theropod from the earliest Late Jurassic
  2. It has four fingers when all sister taxa have three. This fact has added credence and confusion to the chick embryo digit identification issue we looked at earlier here

It’s well worth looking at both sides of this extra finger issue:
From the Xu et al. abstract: “Theropods have traditionally been assumed to have lost manual digits from the lateral side inward, which differs from the bilateral reduction pattern seen in other tetrapod groups. This unusual reduction pattern is clearly present in basal theropods, and has also been inferred in non-avian tetanurans based on identification of their three digits as the medial ones of the hand (I-II-III). This contradicts the many developmental studies indicating II-III-IV identities for the three manual digits of the only extant tetanurans, the birds. Here we report a new basal ceratosaur from the Oxfordian stage of the Jurassic period of China (156–161 million years ago), representing the first known Asian ceratosaur and the only known beaked, herbivorous Jurassic theropod. Most significantly, this taxon possesses a strongly reduced manual digit I, documenting a complex pattern of digital reduction within the Theropoda. Comparisons among theropod hands show that the three manual digits of basal tetanurans are similar in many metacarpal features to digits II-III-IV, but in phalangeal features to digits I-II-III, of more basal theropods. Given II-III-IV identities in avians, the simplest interpretation is that these identities were shared by all tetanurans. The transition to tetanurans involved complex changes in the hand including a shift in digit identities, with ceratosaurs displaying an intermediate condition.”

There were a long list of authors (see below) that agreed with the above, some of whom have come to our attention earlier for publishing various errors, along with their otherwise excellent work.

Unfortunately the Xu et al. abstract ignores the fact that basal tetrapods, like Acanthostega, had an additional digit medial to digit #1 (we’ll call this digit #0). Therefore digit #0 is part of the phylogenetic history of all tetrapods, despite the fact that it is almost never expressed in tetrapod adults, only embryos. Digit #0 is expressed in Limusaurus, in which the hand is a small vestige relative to those of sister taxa. Like other vestiges the hand of Limusaurus did not continue to develop normally as a hatchling and into adulthood. Rather the hand retained a shape found at a certain embryological stage, a stage that included digit #0.  That’s why the big metacarpal (in purple) has the morphology of metacarpal 1 in sister taxa (Fig. 3) and metacarpal #0 continues the shape of metacarpal #1 in cross section. In most tetrapods digit #0 is fused to metacarpal #0 or otherwise disappears before birth or hatching.

Figure 3. The manus of several theropods including Limusaurus. Here digit 1 is purple, digit 2 is pink and digit 3 is green. Note the presence of digit 0 in this vestigial hand, a holdover from basal tetrapods that has not been correctly identified by Xu et al. and others.

Figure 3. The manus of several theropods including Limusaurus. Here digit 1 is purple, digit 2 is pink and digit 3 is green. Note the presence of digit 0 in this vestigial hand, a holdover from basal tetrapods that has not been correctly identified by Xu et al. and others. Click to enlarge.

That’s why otherwise you only see digit #0 in embryos. Thus there is no “phase shift” of digit identity. There is only loss, fusion or absorption of digit #0, a factor missed by earlier workers.

References
Xu X, Clark JM. Mo J, Choiniere J, Forster CA, Erickson GM, Hone DWE, Sullivan C, Eberth DA, Nesbitt S, Zhao Q, Hernandez R, Jia C-K, Han F-L. and Guo Y 2009. A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature, 459(18): 940–944.

Analyses and random notes on Chilesaurus from the media

Still big news, Chilesaurus was originally considered (Novas et al. 2015) a ‘bizarre’ theropod, but nests at the base of all ornithischians in the large reptile tree.

Figure 1. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria.

Figure 1. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria.

Prior hylogenetic analyses
Novas et al. tested Chilesaurus into four different data matrixes with samplings focused on basal dinosauriforms (Nesbitt et al.7), basal sauropodomorphs (Otero & Pol) and basal theropods (Carrano et al.; a modified version of Smith et al.). Some were modified by the addition and removal of characters and taxa. Ultimately, none agreed with one another in the nesting of ChilesaurusThat’s a red flag. 

The results of the four analyses
did agreed in the position of Chilesaurus as a tetanuran theropod (but that’s a very large clade, and done so in the absence of its true sister taxa, see below). According to Novas et al, “Features supporting the theropodan position of Chilesaurus include: pleurocoelous cervical and cranial dorsal vertebrae; hypapophyses on ‘pectoral’ vertebrae; preacetabular wing of ilium dorsoventrally expanded; femoral fourth trochanter semicircular; and tibia distally expanded and with lateral malleolus extending strongly laterally. Tetanuran characteristics present in Chilesaurus are: scapular blade elongate and strap-like; distal carpal semilunate; and manual digit III reduced.”

Novas et al. found this combination of derived Coelurosaurian and Prosauropod-like traits specifically recalls the plant-eating Laurasian therizinosaurs, nevertheless, this set of general characteristics contrasts with the 18 derived features absent in Chilesaurus that are usually recognized as uniting therizinosaurs with derived coelurosaurs.

Furthermore, under constrained suboptimal topologies, 11 additional steps are necessary to force the position of Chilesaurus as a therizinosaur. This set of anatomical distinctions implies a phylogenetic position for Chilesaurus outside Therizinosauria, Maniraptora and Coelurosauria.

Ornithischians were considered:
Novas et al. report, “Apart from typically saurischian and theropodan characters, Chilesaurus also shows several potential apomorphies of ornithischians or subclades thereof. Unfortunately, very few basal ornithischians are currently known from good materials. The data matrix of Nesbitt et al. 2009 includes Scutellosaurus, Lesothosaurus, Eocursor, Heterodontosaurus and Pisanosaurus, and thus provides as good a taxon. This matrix discards that Chilesaurus is an ornithischian.”

As noted above,
none of the Novas analyses included the basal ornithischians, Daemonosaurus and Jeholosaurus. By excluding these taxa Novas et al. were comparing apples to oranges, something that happens far too often in paleontology as noted tar too many times in this blog.

Figure 3. Cladogram of basal dinosaurs. Note that Chilesaurus nests near the base of the Phytodinosauria and at the base of the Ornithischia, both far from the Theropoda.

Figure 1. Cladogram of basal dinosaurs. Note that Chilesaurus nests near the base of the Phytodinosauria and at the base of the Ornithischia, both far from the Theropoda.

Quotes from the PR machine:
I thought it interesting to run through some quotes from the various online news stories carried today on this new find. When you read this, keep the new phylogenetic nesting in mind and it will clarify the mysteries raised.

NBC News: “Scientists have unearthed fossils of a strange dinosaur in southern Chile that boasts such an unusual combination of traits that they are comparing it to a platypus, that oddball egg-laying, duckbilled mammal from Australia…  it ate only plants with a beak and leaf-shaped teeth, scientists said on Monday. …Its skull and neck resembled those of primitive long-necked dinosaurs, and its vertebrae those of primitive meat-eating theropods. It had robust arms, but just two blunt fingers on each hand. It was bipedal, but its wide, four-toed feet were unlike the slender, three-toed feet of most theropods. And it had a bird-like pelvis.”

“Chilesaurus constitutes one of the most bizarre dinosaurs ever found,” said paleontologist Fernando Novas. “No other dinosaurs exhibit such a combination or mixture of features.”

America Aljazeera: “Four nearly complete skeletons and dozens of bones from other individuals were found, making Chilesaurus one of the best-understood Jurassic Southern Hemisphere dinosaurs. It belongs to a previously unknown dinosaur lineage,” University of Birmingham paleontologist Martín Ezcurra said.

Brian Switek writing for Smithsonian: “In the place where Diego discovered it, there are more bones of Chilesaurus than any other creature. This is odd. In most environments of about the same age, the most common dinosaurs are beaky little herbivores that belonged to a very different lineage of dinosaurs called ornithischians. Here, for some reason, a theropod came to dominate instead.

“This is a really unusual beastie, a bit of a dinosaur Frankenstein,” says paleontologist Lindsay Zanno of the North Carolina Museum of Natural Sciences.

Reuters: “It belongs to a previously unknown dinosaur lineage,” University of Birmingham paleontologist Martín Ezcurra said. “Convergent evolution’ is a process in which two unrelated species or groups acquire similar characteristics from living in similar environments or having a similar behavior,” like the wings of a bat and a bird, Ezcurra added. “In the case of ‘mosaic convergent evolution,’ different parts of the body resemble those of other unrelated species, such as in the case of the platypus and Chilesaurus.”

Sydney Morning Herald: “Chilesaurus can be considered a ‘platypus’ dinosaur because different parts of its body resemble those of other dinosaur groups due to mosaic convergent evolution,” study author Martín Ezcurra of the University of Birmingham said in a statement. “In this process, a region or regions of an organism resemble others of unrelated species because of a similar mode of life and evolutionary pressures. Chilesaurus provides a good example of how evolution works in deep time and it is one of the most interesting cases of convergent evolution documented in the history of life”

EurkaAlert (the Global Source for Scientific News): “Chilesaurus represents one of the most extreme cases of mosaic convergent evolution recorded in the history of life. For example, the teeth of Chilesaurus are very similar to those of primitive long-neck dinosaurs because they were selected over millions of years as a result of a similar diet between these two lineages of dinosaurs.” 

Novas et al. writing in Nature: “Early theropod evolution is currently interpreted as the diversification of various carnivorous and cursorial taxa, whereas the acquisition of herbivorism, together with the secondary loss of cursorial adaptations, occurred much later among advanced coelurosaurian theropods12. A new, bizarre herbivorous basal tetanuran from the Upper Jurassic of Chile challenges this conception.”

As noted
earlier, Chilesaurus is not bizarre, convergent or enigmatic in the large reptile tree. Rather it nests at the base of the Ornithischia, close to the base of the Sauropodomorpha, together nesting near the base of the Phytodinosauria and derived from Eoraptor, Pampadromaeus and kin.

Together with Jeholosaurus, Chilesaurus provides a rare glimpse into the genesis of the ornithischian beak and pelvis, something paleontologists have been looking for for decades. This long-sought relationship was completely overlooked by the original authors. AND this is one of the holy grails of paleontology… sadly passed by due to taxon exclusion.

Gotta work on that…

References
Novas FE, Salgado, Suárez LM, Agnolín FL, Ezcurra MND, Chimento NSR.,de la Cruz R, Isasi MP, Vargas AO, Rubilar-Rogers D. 2015. An enigmatic plant-eating theropod from the Late Jurassic period of Chile. Nature. doi:10.1038/nature14307

Chilesaurus, new dinosaur: not so ‘enigmatic’ after all…

Chilesaurus diegosuarezi (Novas et al. 2015; Late Jurassic, 150 mya, Fig. 1) is the current media darling. Described as an ‘enigmatic’ and ‘bizarre’ theropod, Chilesaurus was nested  with Velociraptor, Tawa and kin, and Elaphrosaurus using various prior cladograms in the supplementary data. So that’s an issue (no internal agreement).

Several articulated specimens are known at distinct ontogenetic stages.

Unfortunately taxon exclusion raises its ugly head again…
The large reptile tree nests Chilesaurus outside of the Theropoda, near the base of the Phytodinosauria, at the base of the Ornithischia and at the base of the clade that also includes Daemonosaurus and Jeholosaurus (Fig. 1), two taxa that were unfortunately ignored by the Novas et al. study. Hate to see that happen yet again.

Figure 1. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria.

Figure 1. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria to scale.

Figure 2. Look familiar? Here are the pelves of Jeholosaurus and Chilesaurus compared.  As discussed earlier, this is how the ornithischian pelvis evolved from that of Eoraptor and basal saurorpodomorpha.

Figure 2. Look familiar? Here are the pelves of Jeholosaurus and Chilesaurus compared. As discussed earlier, this is how the ornithischian pelvis evolved from that of Eoraptor and basal saurorpodomorpha..

Folks,
Chilesaurus is not bizarre.

It is simply a descendant from an unknown Late Triassic transitional taxon at the base of the Ornithischia, a hypothesis overlooked by Novas et al. Chilesaurus is not a theropod, but a phytodinosaur (Fig. 3). The fact that fossils of Chilesaurus were found much later than the original split is not a cause for concern. That happens all the time.

Pelvis  changes
Along with Jeholosaurus, Chilesaurus demonstrates the changes that were happening to the dinosaurian pelvis at the genesis of the ornithischian pelvis. As a plant eater, Chilesaurus and kin were expanding their gut volume to digest less digestible plant matter.

Manus and tooth changes
The hands of Chilesaurus are not as primitive and plesiomorphic as might be hoped, but then Chilesaurus is a descendent of that Late Triassic transitional taxon, appearing tens of millions of years after the split. Things evolve! While the teeth remain large and robust, Chilesaurus had flat teeth, rather than the pointed ones of its Triassic sister, Daemonosaurus or its Cretaceous sister, Jeholosaurus.

Figure 3. Cladogram of basal dinosaurs. Note that Chilesaurus nests near the base of the Phytodinosauria and at the base of the Ornithischia, both far from the Theropoda.

Figure 3. Cladogram of basal dinosaurs. Note that Chilesaurus nests near the base of the Phytodinosauria and at the base of the Ornithischia, both far from the Theropoda.

Clues
to the largely missing post-crania of Daemonosaurus are provided by its sister Chilesaurus.

Now let’s talk about the PR barrage
This is where the science reporters separate themselves from the scientists. All those who reported without testing the results of Novas et al. … you may have to do some backtracking.

References
Novas FE, Salgado, Suárez LM, Agnolín FL, Ezcurra MND, Chimento NSR.,de la Cruz R, Isasi MP, Vargas AO, Rubilar-Rogers D. 2015. An enigmatic plant-eating theropod from the Late Jurassic period of Chile. Nature. doi:10.1038/nature14307