Entelognathus: revisions

Updated Nov 21, 2019
with new bone identities for Entelognathus.

Yesterday we looked at Entelognathus (Figs. 1-3; Zhu et al. 2013), a Silurian placoderm transitional to bony fish. That was my first placoderm and I made some errors that have since been corrected. Those errors were corrected when I realized the frontal (pineal in placoderms and Cheirolepis) originated as a tiny median (purple) triangle that included the pineal opening. I was also confused by the splitting of the parietal in Osteolepis, which I thought gave rise to the parietal/postparietal split, but instead that is an autapomorphy arising only in certain Osteolepis specimens. Further confusion comes from the fusion of bones, the splitting of bones and the different names given to the same bone in Silurian to Devonian taxa. Because of this, today and today only I will call the bones by the colors provided by Zhu et al. A key to their various names is provided (Fig. 1).

I was also surprised
to see that Zhu et al. 2013 found no trace of a purple/orange division in Entelognathus (Fig. 1f). This is odd for a transitional taxon, but still possible. Worth looking into. Equally odd, Zhu et al. did not color the purple bone consistently (Fig. 1).

The pineal opening drift
from the purple to the orange bones attends the lengthening of the rostrum and perhaps the brain and olfactory regions. The purple bone invades the paired orange bones and at the posterior tip of the parietal is the pineal opening. So the purple bone more or less delivers the pineal opening more or less in the middle of the orange bones.

Figure 1. From Zhu et al. 2013 SuppData showing placoderm and other basal vertebrate skull roofs. Note: Entelognathus is the only taxon without frontals, which I found in the photos of the fossil, figure 2.

Figure 1. From Zhu et al. 2013 SuppData showing placoderm and other basal vertebrate skull roofs. Note: Entelognathus is the only taxon without a frontal/parietal split, which I found in the photos of the fossil, figure 2 and corrected at the tip of the long arrow.

I traced bone sutures on photos of the specimen
and found that purple/orange division. So now Entelognathus has a complete set of skull roofing bones from the nasal to the frontal to the parietal and post parietal. I may have even seen where the yellow green intertemporal splits from the orange parietal.

Figure 2. The placoderm, Entelognathus, is widely considered the outgroup to the crossopterygians, the stem tetrapods. Compare the skull bones to those of Polypterus (Fig. 1) and Tinirau (Fig. 3). The posterior is unknown.

Figure 2. The placoderm, Entelognathus, is widely considered the outgroup to the crossopterygians, the stem tetrapods. Compare the skull bones to those of Polypterus (Fig. 1) and Tinirau (Fig. 3). The posterior is unknown.

I hope to never do another fish.
But happy that I was able to resolve some earlier questions and move on. Feelings aside, mistakes that go on unnoticed are worse than mistakes you, or others, find and correct.

Figure 1. Entelognathus drawings from Zhu et al. 2013, with colors and homologous tetrapod bone. abbreviations added.

Figure e. Entelognathus drawings from Zhu et al. 2013, with colors and homologous tetrapod bone. abbreviations added. Corrected from an earlier version.

References
Zhu M, Yu X-B, Ahlberg PE, Choo B and 8 others 2013. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature. 502:188–193.

Cheirolepis fossil images
wiki/Cheirolepis
wiki/Eusthenopteron
wiki/Entelognathus

 

Placoderm Entelognathus skull bones re-identified with tetrapod homologies

Updated Nov 21, 2019
with new bone identities for Entelognathus.

Barford 2013 wrote: 
“It may be hard to see, but you seem to share a family resemblance with Entelognathus primordialis. The fish, which lived 419 million years ago in an area that is now part of China, is the earliest known species with a modern jaw.” Here (Fig. 1) one can identify a complete set of homologous tetrapod skull bones understood by the original authors, who identified the bones with traditional placoderm names. (Ala, placoderms, bony fish and sacropterygians, including tetrapods, have different names for the same bone). And they made a mistake or two along the way, none of which negate their conclusions, but cement them.

I never thought I’d be featuring any placoderm fish in this blog
or in ReptileEvolution.com, but Entelognathus, as everyone already knows — and I just learned, is something very special. A major discovery. And this was my first day studying placoderms.

Barford 2013 reported, “Palaeontologists have traditionally believed that the fishes’ features bore no relation to ours. They assumed that the placoderm face was lost to evolutionary history, and most thought that the last common ancestor of living jawed vertebrates had no distinct jawbones — that it was similar to a shark, with a skeleton made mostly of cartilage and at most a covering of little bony plates. The theory went that the bony fishes evolved later, independently developing large facial bones and inventing the ‘modern’ jaw. Such fishes went on to dominate the seas and ultimately gave rise to land vertebrates. [Entelognathus] has what looks like a bony fish’s jaw, even though it is older than the earliest known sharks and bony fishes.”

According to Wikipedia
Entelognathus
 primordialis
 (Zhu et al. 2013; Late Ludlow, Silurian, 419 mya; IVPP V18620) “is a genus of placoderm fish with dermal marginal jaw bones (premaxilla,
maxilla and dentary), features previously restricted to Osteichthyes (bony fish).”

More than that,
all of the skull bones find homologies in tetrapods and bony fish (Figs. 1, 2) when certain bones are correctly identified or homologized. It just takes a few colors here and there to make it all clear.

Figure 2. The placoderm, Entelognathus, is widely considered the outgroup to the crossopterygians, the stem tetrapods. Compare the skull bones to those of Polypterus (Fig. 1) and Tinirau (Fig. 3). The posterior is unknown.

Figure 1. The placoderm, Entelognathus, is widely considered the outgroup to the crossopterygians, the stem tetrapods. Compare the skull bones to those of Polypterus (Fig. 1) and Tinirau (Fig. 3). The posterior is unknown.

All of the bones in the skull of Entelognathus
find homologies with those in Cheirolepis (Whiteaves 1881; Fig. 2) and also with tetrapods. Entelognathus lived 59 million years before the appearance of tetrapods like Ichthyostega. and is someday going to be a part of the story behind those Middle Devonian footprints.

Here new labels and colors
repair original errors and indicate tetrapod homologies in Entelognathus (Zhu et al. 2013).

  1. Three purported sclerotic bones are circumorbital bones (prefrontal, postfrontal, jugal)
  2. The purported jugal is the dorsal half of the maxilla before these bones fused.
  3. The purported quadratojugal is the posterior of the maxilla
  4. The rostral is the nasal
  5. The triangular frontal was overlooked
  6. The pineal plate is a pair of parietals
  7. The central plate is a pair of postparietals
  8. The marginal plate is the supratemporal
  9. The anterior paranuchal plate is the tabular
  10. The opercular is the quadratojugal
Figure 2. Cheirolepis skull (left) with skull bones colorized as in Osteolepis (right) and Enteognathus, figure 1. Colors make bone identification much easier. Note the post opercular bone differences between Osteolepis and Cheirolepis indicating separate and convergent derivation, based on present data.

Figure 2. Cheirolepis skull (left) with skull bones colorized as in Osteolepis (right) and Enteognathus, figure 1. Colors make bone identification much easier. Note the post opercular bone differences between Osteolepis and Cheirolepis indicating separate and convergent derivation, based on present data.

On the subject of nomenclature
Zhu et al. 2013 (SuppData) list the various names given to fish skull bones and their homologies in other fish clades. Some of the more confusing include:

  1. The parietal in sarcopterygians is the frontal in actinopterygians and the preorbital in placoderms.
  2. The postparietal in sarcopterygians is the parietal in actinopterygians and the central in placoderms.
  3. The supratemporal in sarcopterygians is the intertemporal in actinopterygians and the marginal in placoderms.
  4. The tabular in sarcopterygians is the supratemporal in actinopterygians and the anterior paranuchal in placoderms.
  5. And there are others…

Where is the authority that can fix this problem?
But if we fix it, then what? Then all prior literature will have to be translated. Either way, we’re hosed. Maybe we should just colorize homologous bones and leave it at that, as Zhu et al. did in their SuppData.

Entelognathus precedes Cheirolepis by 29 million years.
Preopercular and opercular bones do not appear in Entelognathus, but are present in Cheirolepis. So they are new bones in osteichythys.

The ‘al’ bone in Entelognathus (Fig. 1) is the cleithrum, supporting the pectoral fin.

The split (spiracle) between the skull roofing bones (intertemporal. supratemporal, tabular) and cheek bone (squamosal) do not appear in Entelognathus, but do so in Cheirolepis.

Sclerotic rings are not necessary in such small and well-protected eyes as in Entelognathus and if present, would have been very tiny and fragile.

Comparisons of the circumorbital bones in Entelognathus and Cheirolepis are strikingly similar down to the small post-orbit depression in the jugal in Entelognathus that becomes a notch in Cheirolepis.

Comparisons of the postopercular bones
of Cheirolepis and Osteolepis (Fig. 2) show little to no homology, suggesting a possible separate but convergent derivation.

Note some skull bones
later split apart at the median, while others fuse together. It’s their shapes and locations that identify them. “The large hexagonal central plate seems to have a single ossification centre, whereas most placoderms have paired centrals,” reports Zhu et al, making a case in point. A pineal opening is not present in the pineal plate (fused parietals) of Enteleognathus. This is further evidence that the pineal opening migrated from the frontals to the parietals over tens of millions of years. More on that tomorrow.

Barford 2013 concludes
“There remains a chance that E. primordialis evolved its jaw independently from the bony fish, so that we did not inherit it, and the resemblance is an illusion.” I don’t agree with this conclusion. The evidence for homology elsewhere overwhelms any competing hypotheses.

Friedman and Brazeau (2013) also comment on this discovery.
First, Entelognathus alwaybranches outside the radiation of living jawed vertebrates, meaning that key components othe osteichthyan face are no longer unique innovations of that group. Second, acanthodians — that pivotal assortment of extinct shark-like fishes — are shifted, en masse, tthe branch containing the cartilaginous fishes. This triggers a cascade of implications. If all acanthodians are early cartilaginous fishes, then their shark-like features are not generalities of jawed vertebrates, but specializations of the cartilaginous-fish branch. The most recent common ancestor of jawed vertebrates was thus probably clad in bonarmor othe sort common to both placoderms anbony fishes. This inversion of a classic scenario in vertebrate evolution raises an obvious question: how did we get it so wrong?”

In summary
Even when someone gets it right, some of the details may still be correctable – and the present corrections do not overturn the conclusion, but support it. As usual, I have not seen the fossil firsthand. I have not added Entelognathus to the LRT. I simply make comparisons to published figures of Cheirolepis, which was one source of the earlier problems I had, no hopefully settled.

Thanks to David M.
for directing me to the Entelognathus paper. : – )

Please let me know
if someone else has drawn the same insight in the last 4 years since the publication of Zhu et al. 2013. If so, I am unaware of it.

References
Barford E 2013. Ancient fish face shows roots of modern jaw. Nature News. online here.
Friedman M and Brazeau 2013. A jaw-dropping fossil fish. Nature 502:175-177. online here.
Whiteaves JF 1881. On some remarkable fossil fishes from the Devonian rocks of Scaumenac Bay, in the Province of Quebec. Annals and Magazine of Natural History. 8: 159–162.
Zhu M, Yu X-B, Ahlberg PE, Choo B and 8 others 2013. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature. 502:188–193.

wiki/Cheirolepis
wiki/Entelognathus

Prorastomus/Pezosiren: when sirenians still had legs

Nothing heretical today.
We haven’t looked at any sirenians yet. And this one adds one more taxon to the LRT.

Figure 1. Prorastomus is a pro-sirenian with legs. All four feet remain unknown.

Figure 1. Prorastomus (or is this Pezosiren) is a pro-sirenian with legs. All four feet remain unknown. Elements from Pezosiren are also shown.

Prorastomus sirenoides (Owen 1855; Middle Eocene, 40 mya; 1.5m in length; Fig. 1) and Pezosiren are basal sirenians with four legs, a short tail and more teeth. They nest with the recenly extinct dugong, Dusisiren, in the large reptile tree (LRT, 1006 taxa).

Figure 2. Sirenian skulls, including Dusisiren, Prorastomus, and Eotheroides.

Figure 2. Sirenian skulls, including Dusisiren, Prorastomus, and Eotheroides. Note the loss of many teeth in Dusisiren.

Compared to its phylogenetic predecessor,
Moeritherium, Prorastomus/Pezosiren demonstrates the reduction in sacral vertebrae, the reduction in the cranial crest and the enlargement of the tail (what little is known). Pezosiren portelli (Domning 2001) is a related genus

According to Domning 2001
“Modern seacows (manatees and dugongs; Mammalia, Sirenia) are completely aquatic, with flipperlike forelimbs and no hindlimbs. Here I describe Eocene fossils from Jamaica that represent nearly the entire skeleton of a new genus and species of sirenian—the most primitive for which extensive postcranial remains are known. This animal was fully capable of locomotion on land, with four well-developed legs, a multivertebral sacrum, and a strong sacroiliac articulation that could support the weight of the body out of water as in land mammals. Aquatic adaptations show, however, that it probably spent most of its time in the water. Its intermediate form thus illustrates the evolutionary transition between terrestrial and aquatic life. Similar to contemporary primitive cetaceans3, it probably swam by spinal extension with simultaneous pelvic paddling, unlike later sirenians and cetaceans, which lost the hindlimbs and enlarged the tail to serve as the main propulsive organ. Together with fossils of later sirenians elsewhere in the world, these new specimens document one of the most marked examples of morphological evolution in the vertebrate fossil record.”

References
Domning DP 2001. The earliest known fully quadrupedal sirenians. Nature. 413 (6856): 625–627. online.
Owen R 1855.
 On the fossil skull of a mammal (Prorastomus sirenoïdes, Owen) from the island of Jamaica. The Quarterly Journal of the Geological Society of London 11:541-543.
Self-Sullivan C 2006. Evolution of the Sirenia.

wiki/Dusisiren
wiki/Prorastomus
wiki/Evolution_of_sirenians
wiki/Pezosiren

Liaoningosaurus: perhaps not an ankylosaur

This one goes back several years… with several updates!
Xu, Wang and You 2001 described what they thought was a juvenile ankylosaur, Liaoningosaurus paradoxes (Early Cretaceous, Yixian Formation) featuring “a large bony plate (somewhat shell-like) shielding the abdomen.” They tested it against only 13 other taxa and nested it outside the nodosaurs and outside the ankylosaurs…with no taxa between it and Stegosaurus.

Figure 1. Several specimens of Liaoningosaurus crushed flat plus a lateral view based on original holotype tracings.

Figure 1. Several specimens of Liaoningosaurus crushed flat plus a lateral view based on original holotype tracings.Note the lizard-like sprawling limbs in situ, a product of taphonomic crushing. Like all dinos, this one also had vertical limbs. Only a few small osteoderms are identified.

Xu et al. report:
“Diagnosis. An ankylosaurian that differs in having: shell-like ventral armour, trapezoidal sternum with slender and distally pointed posterolateral process and short medial articular margin, and pes more than twice as long as manus.”

Perhaps Xu et al. focused on ankylosaurs and nodosaurs
because all the specimens of Liaoningosaurus I have seen in publications or online (Fig. 1) have been crushed flat, with ribs spread out like ankylosaur ribs. Moreover, the pelvis was very wide, with limbs beneath the ilia, like those in ankylosaurs.

A closer look
(Fig. 1) reveals the ribs would have enclosed a deeper chest, not a wider one, though not as relatively deep as in Stegosaurus. Other more primitive stegosaurs likewise had a shorter, rounder torso cross-section.

Note,
the limbs are preserved sprawling, like those of the horned lizard, Phrynosoma. No dinosaur had sprawling limbs, so it’s okay to bring in both the limbs and the ribs (Fig. 1).

Finally,
basal stegosaurs also have a very broad pelvis with limbs rotating beneath the ilium. Considering how closely ankylosaurs and stegosaurs match each other in so many traits, it is a tribute to the LRT that it recovers them in separate clades, separated by bipedal agile taxa like Lesothosaurus and Heterodontosaurus. It is unlikely that ankylosaurs ever reared up on their hind limbs, but stegosaurs appear to be able to do this.

Osteoderms are rare in Liaoningosaurus,
which is odd for an armored ankylosaur.

Ankylosaur teeth and stegosaur teeth greatly resemble one another and also resemble Liaoningosaurus teeth (Fig. 1), despite the great difference in size.

There are five digits on the manus
in Liaoningosaurus (Fig. 1) and metacarpal #5 is as long as #4. Unfortunately, ankylosaurs and kin in the LRT lack a preserved manus, but a look through the Princeton Field Guide to Dinosaurs (Paul 2010) finds no similar ankylosaur manus.

Arbour et al. 2014 report, “Examination of the holotype of Liaoningosaurus paradoxus, IVPP V12566, indicates that the ventral “plastron” is better interpreted as epidermal scales, because the broken edges do not reveal any bony histology.” Readers will note that the odd ventral plate (closeup in Fig. 2) does not appear in other Liaoningosaurus specimens (Fig. 1), but they are exposed dorsally.

Figure 2. Liaoningosaurus ventral patch. Note the scales.

Figure 2. Liaoningosaurus ventral patch. Note the scales.

The large reptile tree (LRT, 1005 taxa) includes several more ornithischian taxa, though fewer taxa with armor. In the LRT Liaoningosaurus nests between Scutellosaurus and Stegosaurus, several nodes away from the other armored ornithischians, Minmi and Scelidosaurus. No skull traits were tested in Liaoningosaurus due to the low resolution of the available images.

The armored ornithischians (stegosaurs and ankyosaurs) are so similar
to one another they are traditionally nested in one clade: Thyreophora. By contrast, the LRT separates ankylosaurs from stegosaurs. Here the few hind limb traits that separate Liaoningosaurus from Scelidosaurus and/or Minmi and ally it with Scutellosaurus and/or Stegosaurus include the following:

  1. Tibia/femur ratio not less than 1:1
  2. Fibula not appressed to tibia
  3. Fibula diameter not > half tibia diameter
  4. Metatarsus not compact
  5. Metatarsal 1 < half metatarsal 3
  6. Metatarsal 1 not > half metatarsal 4
  7. Metatarsals 2 and 3 align beyond p1.1
  8. Pedal 4 length <  metatarsal 4

Perhaps better imagery
of the skull and other parts will add to or modify this list and nesting.

The addition of a basal ankylosaur
with these traits would nudge Liaoningosaurus toward the ankylosaurs. In the LRT ankylosaurs were derived from large, armored, lumbering Scelidosaurus. By contrast, the stegosaurs were derived from small, agile Lesothosaurus and Scutellosaurus. So finding a small armored dinosaur with the above list of traits, even if it is a juvenile, should suggest taking a close look at its stegosaur affinities, despite the initial appearance of a wide round horned-lizard-like torso.

PS
Ji et al. 2016 found fish within the torso (but not restricted to the gut) of a Liaoningosaurus suggesting a fish diet, rather than an herbivorous one.

PPS
Xu et al. 2001 reported, “Liaoningosaurus has an unusual combination of characters and it might (for example) represent a third ankylosaur lineage.” Perhaps one closer to stegosaurs. Xu et al. 2001 also report, “all manual and pedal unguals claw-shaped.” At present the manual unguals do not appear to be claw-shaped, with the the exception of #3, as in stegosaurs… AND as in ankylosaurs.

References
Xu X, Wang XL and You HL 2001. A juvenile ankylosaur from China. Naturwissenschaften 88:297. doi:10.1007/s001140100233
Ji Q, Wu X, Cheng Y, Ten F, Wang X and Ji Y 2016. Fish-hunting ankylosaurs (Dinosauria, Ornithischia) from the Cretaceous of China. Journal of Geology, 40(2).
Thompson RS, Parish JC, Maidment SCR and Barrett PM 2011. Phylogeny of the ankylosaurian dinosaurs (Ornithischia: Thyreophora). Journal of Systematic Palaeontology. 10 (2): 301–312. doi:10.1080/14772019.2011.569091
Arbour VM, Burns ME, Bell PR and Currie PJ 2014. Epidermal and dermal integumentary structures of ankylosaurian dinosaurs. Journal of Morphology, 275(1): 39-50. doi:10.1002/jmor.20194

wiki/Liaoningosaurus

In honor of Mother’s Day…

We have a pregnant
plesiosaur (Fig. 1; O’Keefe and Chiappe 2011; LACM 129639; Late Cretaceous, 78 mya)…

Figure 1 Pregnant Polycotylus (LACM 129639) from O'Keefe and Chiappe 2011.

Figure 1 Pregnant Polycotylus (LACM 129639) from O’Keefe and Chiappe 2011.

and a pregnant primate (Fig. 2) very dear to my heart.

Figure 2. My daughter Stephanie one week before giving birth to grandson James (nickname: Jet).

Figure 2. My daughter Stephanie one week before giving birth to grandson James (nickname: Jet) and about three years ago.

Being a mom goes way, way back
In our lineage, first cells stuck together, flagella out (Fig. 3). Then four cells stuck together. Then eight. Ultimately hundreds stuck together creating a sphere, or blastula. And little blastulas formed inside until they were large enough to break free.

Figure 3. Blastula from the book, "From the Beginning" by Peters 1991.

Figure 3. Blastula from the book, “From the Beginning” by Peters 1991.

Plesiosaurs and primates capable of understanding prehistory
followed shortly thereafter. The basics of being a mother haven’t really changed much in the last few billion years.

References
O’Keefe FR and Chiappe LM 2011. Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia). Science. 333 (6044): 870–873. doi:10.1126/science.1205689.
Peters D 1991. From the beginning – the story of human evolution. Little Brown. 128 pp. Online here.

wiki/Polycotylus

Vintana and the vain search for the clades Allotheria and Gondwanatheria

Figure 1. Vintana as originally illustrated. I added colors to certain bones. Note the high angle of the ventral maxilla and the deep premaxilla. Lateral view reduced to scale with other views.

Figure 1. Vintana as originally illustrated. I added colors to certain bones. Note the high angle of the ventral maxilla and the deep premaxilla. Lateral view reduced to scale with other views.

Earlier we looked at Vintana (Fig. 1, Krause et al. 2014a, b). To Krause et al. Vintana represented the first specimen in the clades Allotheria and Gondwanatheria to be known from more than teeth and minimal skull material.

To Krause et al. 
Allotheria included Multituberculata and nested between the clade Eutriconodonta (including Repenomamus and Jeholodens) and the clade Trechnotheria (including the spalacotheres Maotherium and Akidolestes) and Cronopio, Henkelotherium, Juramaia, Eomaia, Eutheria and Metatheria.

Taxon exclusion issues
The large reptile tree (LRT, 1005 taxa) did not recover the above clades or relationships. Alotheria does not appear in the LRT.

  1. Multituberculata, Henkelotherium and Maotherium nest within Glires (rats and rabbits and kin) in the LRT.
  2. Repenomamus and Jeholodens nest within the pre-mammalian trityllodontid cynodonts in the LRT.
  3. Akidolestes nests within basal Mammalia, close to Ornithorhynchus in the LRT.
  4. Cronopio and Juramaia nest within basal Mammalia between Megazostrodon and Didelphis in the LRT.
  5. Eomaia nests at the base of the Metatheria in the LRT.
  6. Vintana nests with Interatherium among the derived Metatheria (marsupials), with wombats, like Vombatus and Toxodon in the LRT.

Despite a paper in Nature
and a memoir of 222 pages in the Journal of Vertebrate Paleontology; despite CT scans and firsthand examination with electron microscopes; despite being examined and described by many of the biggest name and heavy hitters in paleontology… Krause et al. never understood that Vintana was just a derived wombat, evidently due to taxon exclusion problems.

Figure 3. Interatherium does not nest with notoungulates or other purported interotheres. Rather cat-sized Interatherium nests with wombats, between Vombatus and the giant Toxodon.

Figure 2. Interatherium does not nest with notoungulates or other purported interotheres. Rather cat-sized Interatherium nests with wombats,with Vintana,  between Vombatus and the giant Toxodon

The large reptile tree now includes
1005 taxa, all candidates for sisterhood with every added taxon. Despite the large gamut of 74 taxa employed by Krause et al. they did not include the best candidates for Vintana sisterhood. Perhaps the fault lies in the reliance of prior studies and paradigms. Perhaps the fault lies in the over reliance by Krause et al. and other mammal workers, on dental traits. Perhaps the fault lies in the absence of pertinent sisters to the above-named taxa, including Interatheriium for Vintana.

In any case
Vintana does not stand alone as the only taxon in its clade represented by skull material. Based on its sisterhood with Interatherium, we have  pretty good idea what its mandibles and post-crania looked like. Yes, Vintana is weird. But Interatherium is also weird in the same way, just not as weird.

The LRT has dismantled and invalidated
several other clades, too, Ornithodira and Parareptilia among them.

References
Krause DW, Hoffmann S, Wible JR, Kirk EC, and several other authors 2014a. First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism. Nature. online. doi:10.1038/nature13922. ISSN 1476-4687.
Krause DW et al. 2014b. Vintana sertichi (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology Memoir 14. 222pp.

wiki/Vintana
pterosaur heresies – Vintana

Animated chronology of basal tetrapods

An animated color-coded cladogram
(Fig. 1, subset of the large reptile tree) of basal tetrapods demonstrates a great Devonian radiation prior to the multiple convergent reduction in digit numbers that typify most tetrapods. And perhaps suggests a multiple origination for land-living tetrapods (i.e. metoposaurs and eryopids appear to have had different basal tetrapod ancestors than frogs and reptiles).

  1. Late Devonian – deep blue
  2. Early Carboniferous – light green
  3. Late Carboniferous – deep green
  4. Early Permain – light orange
  5. Late Permian – dark orange (brown)
  6. Early Triassic – pink
  7. Late Triassic – red
  8. Jurassic – cyan
  9. Post-Jurassic to extant – black
Figure 1. Subset of the LRT focusing on basal tetrapods.

Figure 1. Subset of the LRT focusing on basal tetrapods. Six frames change every 2 seconds. 

The cladogram also supports
the reptilian identification of Tulerpeton giving rise to the large number and radiation of Viséan (early Carboniferous) and later reptiles.

Note also
the radiation of derived legless microsaurs also from the Viséan (340 mya).

What you don’t see in this cladogram
are the many short ghost lineages of basal and other taxa implied by the presence of derived taxa known from earlier sediments. Of course, this is due to the somewhat random and certainly rare preservation and excavation of vertebrate fossils.

Even so
the general order of appearance of taxa in the cladogram seems to be correlated to phylogenetic relationships. Exceptions arise due to the random nature of fossil discovery. Give us another 200 years and see how the tree fills out!

Here, once again,
colorizing the taxa and putting them into an animated cladogram increases global understanding of basal tetrapod interrelationships that cannot be communicated in traditional print media.

The tail feathers of Chiappeavis. The coracoid of Jianianhualong.

An exercise in DGS today
(digital graphic segregation, Fig. 1). It’s okay to increase the contrast in a fossil photo. That’s not considered ‘manipulating’ the data, but enhancing it, like using a magnifying glass of a colored filter.

Figure 1. GIF animation of the a photograph of the tail of Chiappeavis from O'Connor et al. 2016. Original tracing is included in this series.

Figure 1. GIF animation of the a photograph of the tail of Chiappeavis from O’Connor et al. 2016. Original tracing is included in this series. Photoshop was used to increase contrast.

Chiappeavis magnapremaxillo (O’Connor et al. 2016, Early Cretaceous; Figs. 1-2) is a basal enantiornithine bird with a pygostyle. The short tail was tipped with a fan of feathers. The forelimbs were relatively larger than in related taxa.

Figure 2. Chiappeavis with a shorter premaxillary ascending process and no metatarsal 5. Some small changes make big differences. Pengornis is shown to scale.

Figure 2. Chiappeavis with a shorter premaxillary ascending process and no metatarsal 5. Some small changes make big differences. Pengornis is shown to scale. The elongate corticoids were not scored in the LRT matrix.

Error amended.
Earlier I nested Chiappeavis between the Eichstaett specimen of Archaeopteryx recurva and Jianianhualong, the large troodontid-like, flightless bird of the Early Cretaceous. Then a red flag appeared. The problem was: short-tailed Chiappeavis did not belong between two long-tailed taxa. That has been repaired in the large reptile tree (LRT) and Chiappeavis has been nested appropriately as it was originally nested by O’Connor et al., with Pengornis (Fig. 2). And now there is no intervening short-tailed taxon between the small Archaeopteryx and the large Jianianhualong, both with long tails.

Figure 3. Jianianhualong and Archaeopteryx recurva to scale.

Figure 3. Jianianhualong and Archaeopteryx recurva to scale. Both are birds. Jianianhualong is the earliest known large flightless bird, and it retained asymmetrical flight feathers.

The first Big Bird
was Jianianhualong. Larger than its closest kin and definitely flightless, Jianianhualong retained asymmetrical flight feathers. It also had a coracoid nearly identical to that found in Sapeornis (Fig. 4). Jianianhualong had a reduced vestige of the large perching pedal digit 1 found in basal volant birds.

Two specimens attributed to Sapeornis, that nest together in the LRT. IVPPP V13276 is larger and more robust. DNHM-F3078 has a juvenile bone texture. Gao et al 2012 considered these two conspecific.

Figure 4. Two specimens attributed to Sapeornis, that nest together in the LRT. IVPPP V13276 is larger and more robust. DNHM-F3078 has a juvenile bone texture. Gao et al 2012 considered these two conspecific.

The cladogram of birds
has been updated with the addition of taxa (Fig. 5).

Figure 5. Subset of the LRT focusing on the bird cladogram.

Figure 5. Subset of the LRT focusing on the bird cladogram.

References|
O’Connor JK, Wang X-L, Zheng X-T, Hu H, Zhang X-M and Zhou Z 2016.
An Enantiornithine with a Fan-Shaped Tail, and the Evolution of the Rectricial Complex in Early Birds.Current Biology (advance online publication) DOI: http://dx.doi.org/10.1016/j.cub.2015.11.036

Lambdotherium: not a basal brontothere — it’s another pig relative!

Earlier a putative stem brontothere, Danjiangia, was re-nested with basal artiodactyls in the large reptile tree (LRT, 1005 taxa).

Here another putative stem brontothere,
Lambdotherium (Cope 1880, Mader 1998; Eocene, 50mya; Fig. 1) likewise moves away from the basal brontothere, Eotitanops. In the LRT  Lambdotherium nests with Ancodus (Fig. 2), another basal artiodactyl close to extant pigs.

Figure 1. Lambdotherium traditionally nests with the basal brontothere, Eotitanops, but here nests with Ancodus, a basal artiodactyl.

Figure 1. Lambdotherium traditionally nests with the basal brontothere, Eotitanops (ghosted here), but here nests with Ancodus, a basal artiodactyl. Brontotheres have a very tall naris. Pigs do not. 

I don’t know of any post-crania
for Lambdotherium. Note that Ancodus (Fig. 2), like Eotitanops, has a pentadatyl manus. Lambdotherium was traditionally considered a brontothere based on its teeth. The LRT employs relatively few dental traits. And maybe some specimens need to be reexamined. The very high arch of the Lambdotherium squamosal, among many other traits, is more similar to pig-like taxa, than to basal brontotheres, which here nest closer to rhinos, than to horses, contra the Wikipedia report on brontotheres.

Distinct from both rhinos and horses,
brontotheres have four toes on the forefeet. All are derived from a sister to Hyrachyus, which likewise has four toes.

Figure 1. Ancodus nests as a more derived sister to Sus and it retains digit 1 on the manus and pes.

Figure 2. Ancodus nests as a more derived sister to Sus and it retains digit 1 on the manus and pes.

References
Cope ED 1880. The bad lands of the Wind River and their fauna. The American Naturalist 14(10):745-748.
Mader BJ 1998. Brontotheriidae. In Janis CM, Scott KM, and Jacobs LL (eds.), Evolution of Tertiary Mammals of North America 1:525-536.
Mihlbachler MC 2004. Phylogenetic Systematics of the Brontotheriidae (Mammalia, Perissodactyla). PhD dissertation. Columbia University. p. 757.
Mihlbachler MC 2008. Species taxonomy, phylogeny and biogeography of teh Brontotheriidae (Mammalia: Perissodactyla). Bulletin of the American Museum of Natural History 311:475pp.

wiki/Eotitanops
wiki/Lambdotherium

Jianianhualong: not a bird-like troodontid — it’s a troodontid-like bird

Revised May 11, 2017 with new nesting for Chiappeavis. 

Once again, taxon exclusion issues arise
Colleagues, we have to let the taxa nest themselves. Don’t restrict your inclusion sets to the short list of taxa you prefer! In the Jianianhualong paper a long list of candidate taxa were excluded, including its actual proximal sisters (Fig. 6). And they missed the other big headline that should have attended this new taxon. See below.

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

Xu et al. 2017
bring us a new genus of theropod dinosaur with feathers, Jianianhualong tengi (DLXH 1218; Yixian Formation, Early Cretaceous; Fig. 1). They nested their new find in an unresolved clade including the non-bird troodontid, Sinornithoides (Fig. 5). Notably they did not resolve Solnhofen birds (Archaeopteryx’ specimens), troodontids and dromaeosaurids. That should have been a red flag that more effort was needed to weed out bad scores in their matrix. Maybe a reconstruction would have helped? (Fig. 3).

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 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).

Here
in the large reptile tree (LRT, 1004 taxa) Jianianhualong tengi nests strongly with sapeornithid birds, despite its long bony tail, short forelimbs and large size, all atavistic traits retained in this one of the first flightless birds and certainly one of the first large flightless birds. This aspect was overlooked by Xu et al. 2017 as they mistakenly considered this a feathered non-bird troodontid. It is a bird. A big flightless bird.

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

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

If you think the long tail of Jianianhualong is an issue…
Archaeopteryx recurva (the Eichstaett specimen) nests with Jianianhualong and it has a long bony tail, too.

Figure 4. Colorizing the bones of Jianianhualong helps separate them from other elements on the matrix.

Figure 4. Colorizing the bones of Jianianhualong helps separate them from other elements on the matrix better than simply dropping a two letter abbreviation somewhere on the bone.

If you think the large size of Jianianhualong is an issue…
think of it like an early ostrich, flightless with no sternum, a giant Archaeopteryx in the Early Cretaceous, running from more primitive dinosaur-eating theropods.

Figure 5. The Xu et al. cladogram that nests Jianianhualong with troodontids. Note the loss of resolution at important nodes. Compare to the LRT in figure 6.

Figure 5. The Xu et al. cladogram that nests Jianianhualong with troodontids. Note the loss of resolution at important nodes. Compare to the LRT in figure 6. The LRT is fully resolved with more taxa.

Unfortunately
Xu et al. did not test taxa that actually nest closer to Jianianhualong, using an antiquated matrix with only two Solnhofen birds. Xu et al. report, “The discovery of Jianianhualong provides direct evidence for the presence of pennaceous feathers in an unquestionable troodontid theropod.” Since all birds are troodontids in the LRT this statement is true. However, Xu et al. were not thinking that birds arose from troodontids (Fig. 5), so this became a surprising discovery for them. As in so many other cases discussed herein, character traits come as no surprise when the taxon in question is correctly nested.

Fgure 6. Subset of the LRT focusing on birds and their immediate ancestors. Note the nesting of Jianianhualong with Sapeornis.

Fgure 6. Subset of the LRT focusing on birds and their immediate ancestors. Note the nesting of Jianianhualong with Sapeornis.

I just add taxa
and the software/cladogram does the rest. No initial bias. Reconstructions help. So does colorizing the bone. In this case, at least, working from the photo with DGS was more instructive and better able to demonstrate observations to others than traditional firsthand access labeled with small two-letter abbreviations.

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 (Figs. 1, 6). So, asymmetry is not exceptional, but expected. Xu et al. reported, “Most significantly, the taxon has the earliest known asymmetrical troodontid feathers, suggesting that feather asymmetry was ancestral to Paraves.” The entire statement is false under the present hypothesis of interrelationships.

The unfortunate return of ‘modular evolution.”
Xu et al cite references to the concept of ‘modular (mosaic) evolution‘ which is based on invalid phylogeny. Please avoid ‘modular evolution’. That’s not how evolution works in the real world.

References
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.