Sciurumimus: a juvenile ornitholestid in the LRT

We looked at tiny,
feathered Sciurumimus albersdoerferi (Germany, Rauhut et al. 2012; BMMS BK 11) and larger bones-only Ornitholestes (North America) earlier as Late Jurassic sisters in the large reptile tree (LRT, 1659+ taxa). After a recent review, these two continue to nest as sisters at the base of the Microraptor (Fig. 3) + Sinornithosaurus clade. So no news here… except now let’s combine the extraordinary size difference between the two and the widely accepted observation that Sciurumimus is a juvenile.

That brings to mind: a juvenile of what?
The LRT indicates a juvenile ornitholestid (Fig. 1). The overall morphologies are strikingly similar and the size difference is appropriate. Other published studies recover other nestings.

Rauhut, et al. 2012
(Suppdata) nested Ornitholestes between ornithomimosaurs and deinonychosaurs, far from Sciurumimus, which Rauhut et al. nested Sciurumimus between an unresolved clade of giant spinosaurs + megalosaurs and giant Monolophosaurus. Like Rauhut et al., the LRT nests also nests Ornitholestes between ornithomimosaurs (+ tyrannosaurs + oviraptors + therizinosaurs) and deinonychosaurs.

Key differences in the LRT include

1. the use of two Compsognathus specimens. The each nest at the base of their own clade, a hypothesis of interrelationships overlooked by Rauhut et al.
2. the inclusion of three Microraptor specimens and two Sinornithosaurus specimens, adults of which are closer in size and morphology to Sciurumimus. This brings to mind the possibility that phylogenetic miniaturization and neotony played a part in the evolution of these bird-mimics. These closely related taxa were omitted by the Rauhut et al. selection process.

Figure 1. Sciurumimus compared to Ornitholestes and Microraptor to scale.

In their study of the wonderfully preserved
anchiornithid, Aurornis, Godefroit et al. nested Sciurumimus between Monolophosaurus + Sinraptor and Zuolong, all more primitive taxa in the LRT. In Godefroit et al. these taxa are far from Ornitholestes, which nested with another small compsognathid, Juravenator. Juravenator nests with equally small, but shorter limbed Sinosauropteryx in the LRT. Evidently few theropod studies agree with one another in the details.

Rauhut et al. 2012 reported,
“Our analysis confirms Sciurumimus as the basalmost known theropod with evidence of feather-like integument.” By contrast, in the LRT, Tawa-like, feathered Sincalliopteryx (Fig. 2) is more primitive, despite its late appearance (Early Cretaceous) in the fossil record.

Figure 2. Late surviving Sinocalliopteryx currently nests basal to Late Triassic Coelophysis, derived from Late Triassic Tawa. It has the most primitive presence of feathers despite its late appearance.

Sinocalliopteryx
currently nests basal to Late Triassic Coelophysis, and was derived from Late Triassic Tawa. In the LRT, Sinocalliopteryx has the most primitive presence of feathers among theropods despite its appearance tens of millions of years later than its phylogenetic genesis.

Figure 3. Microraptor gui (IVPP V 13352) reconstructed from tracings in figure 1. There are no surprises here, except a provisional closer relationship with Compsognathus than with Velociraptor. Microraptor has a large pedal claw two, but it is not quite the killing claw seen in droamaeosaurs.

The Ornitholestes + Sciurumimus + Microraptor + Sinornithosaurus clade
were bird-mimics and bird-mimic ancestors not directly related to birds or bird ancestors in the LRT.

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References
Godefroit P, Cau A, Hu D-Y, Escuillié F, Wu, W and Dyke G 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature. 498 (7454): 359–362.
Rauhut OWM, Foth C, Tischlinger H and Norell MA 2012. Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany. Proceedings of the National Academy of Sciences. 109 (29): 11746–11751.

 

 

Dsungaripterus palate news: Chen et al. 2020

Chen et al. 2020 describe 
a perfectly preserved Dsungaripterus palate (Figs. 1, 2) recovered by Young prior to 1964. This is welcome news! Unfortunately, the presentation of their recent ‘discoveries’ perpetuates a few pterosaur myths.

Figure 1. Dsungaripterus palate from Chen et al. 2020 with colors and diagrams (above) from Peters 2000 added. Note only a vestige remains of the lateral process of the palatine. The extent of the jugal is a guess here. Pink = pterygoid. Blue = palatine. Gold = ectopterygoid.  In Chen et al. the line leading toward the abbreviation pl points to the maxilla.

Chen et al. 2020 cite
Osi et al. 2010, which we looked at earlier here. You might remember, Osi et al. thought they had discovered the true identity of palatal elements, but parenthetically acknowledged that Peters 2000 (Fig. 1) had done so a decade earlier. They did not realize others had also done so over a century before.

Prior to Peters 2000  
and ever since Williston (1902) and continuing through Huene 1914, Wellnhofer (1978, 1991) and Bennett (1991, 2001a,b), the solid palatal plate in pterosaurs had been traditionally considered the palatine. That was the orthodox point-of-view.

Virtually ignored,
Newton (1888), Seeley (1901 and Woodward (1902) reported that the solid palatal plate was an outgrowth of the maxilla, not the palatine. Unfortunately, I did not know those citations when Peters 2000 reported that the palatal plate actually originated from the maxilla. I thought I had discovered something! Rather, I had only confirmed work from a century earlier. Workers: it is important to expand your citation list so future workers will not overlook important papers, be they 20 years old or 120 years old.

Figure 2. Germanodactylus and the Dsungaripteridae. Contra Chen et al. , azhdarchids are not related.

Longtime readers may remember a wide gamut of dozens
of pterosaur and pterosaur ancestor palates (example Fig. 3) illustrated here, and in nine blogposts that followed, so pterosaur palate data has been online for several years.

The diagram illustration by Chen et al. 2020
(Fig. 1) uses the old-fashioned method of identifying bones, with lines leading from somewhere on the bones to outlying abbreviations. No indication of borders or sutures is provided. All the bones in their Dsungaripterus palate appear fused, despite remnants of borders visible in closer view (Fig. 1). More workers are using colors lately because they impart more data.

From the Chen et al. abstract:
“Among the unique features is a lateral process of the pterygoid divided into two parts: an anterior thin, parabolic arc shaped element that separates the secondary subtemporal and the subtemporal fenestrae, followed by a dorsoventrally flattened portion that is directed inside the sub temporal fenestrae.”

Actually there is no lateral process of the pterygoid divided in two parts. The anterior part is the ectopterygoid often fused to the palatine (= ectopalatine) in most, but not all pterosaurs (Fig. 1; exception: the dorygnathid specimen in Osi et al. remained unfused). The posterior portion is a new outgrowth of the pterygoid. Such a lateral ‘split’ is also found in Pteranodon (Fig. 2) and related sharp-rostrum pterosaur taxa.

From the Chen et al. abstract:
“Among all pterosaurs where the palate is known, the posterior configuration of the palate of D. weii is similar to some azhdarchoids, which is consistent with the suggested phylogenetic position of the Dsungaripteridae as closely related to the Azhdarchoidea.”

Actually dsungaripterids nest between germanodactylids and tapejarids (Fig. 2) in the large pterosaur tree (LPT), far from azhdarchids. A traditional error here perpetuated by taxon exclusion nests azhdarchids with tapejarids in the invalid clade (as currently defined) Azhdarchoidea. When more taxa are included in analysis, azhdarchids arise from tiny dorygnathids.

Figure 3. The palates of several Tapejaridae and Pteranodontidae, both evolving from Germananodactylus. Note the yellow tooth at the tip of each sharp premaxilla here.

From the Chen et al. abstract:
“Furthermore, we identify symmetrical grooves on the lateral surface of the upper and lower jaws, that likely represent the impression of the edge of a keratinous sheath that would cover the upturned toothless rostrum during foraging activity, most likely consisting of hard elements, as has been previously assumed.”

Actually those ‘toothless’ jaws are tipped with large, procumbent single teeth. Check them for dentine and enamel. That’s what makes the tips of the jaws so sharp and resistant to abrasion (more resistant than bone), evident on older specimens (Fig. 4) with blunt tooth tips. Sometimes these teeth fall out. These teeth have roots. And they have a phylogenetic history traceable back to germanodactylids and earlier scaphognathids.

Figure 4. Dsungaripterus single teeth at the tips of the jaws. Phylogenetically these began with Germanodactylus (Fig. 4). The groove (gr) is the premaxilla-maxilla suture.

PS
That ‘groove’ (gr) in figure 4 is the premaxilla-maxilla suture, as noted by Young 1964 and Chen et al. 2020. In such cases, it is a better practice to label a suture as a suture, not a groove.

It’s always good to see new specimens,
but the presentation must be up-to-date. Too many pterosaur workers are perpetuating old myths. Color your bones and expand your taxon list. That will clarify most issues.

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References
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodonand Systematics of the Pterodactyloidea. [Volumes I and II]. – Ph.D. thesis, University of Kansas [Published by University Microfilms International/ProQuest].
Bennett SC 2001a, b. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I and 2. General description of osteology. – Palaeontographica, Abteilung A, 260: 1-153.
Chen et al. (7 co-authors) 2020. New anatomical information on Dsungaripterus weii Young, 1964 with focus on the palatal region. PeerJ 8:e8741 DOI 10.7717/peerj.8741
Newton ET 1888. On the skull, brain and auditory organ of a new species of pterosaurian (Scaphognathus Purdoni) from the Upper Lias near Whitby, Yorkshire. Philosphoical Transaction of the Royal Society, London 179: 503-537.
Osi A, Prondvai E, Frey E and Pohl B 2010. New Interpretation of the Palate of Pterosaurs. The Anatomical Record 293: 243-258.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Seeley HG 1901. Dragons of the air. An account of extinct flying reptiles. – London, Methuen: 1-240.
Wellnhofer P 1978. Pterosauria. Handbuch der Paläoherpetologie, Teil 19.– Stuttgart, Gustav Fischer Verlag: 1-82.
Wellnhofer P 1991. The Illustrated Encyclopedia of Pterosaurs. London, Salamander Books, Limited: 1-192.
Williston SW 1902. On the skull of Nyctodactylus, an Upper Cretaceous pterodactyl. Journal of Geology 10:520–531.
Woodward AS 1902. On two skulls of Ornithosaurian Rhamphorhynchus. Annals of the Magazine Natural History 9:1.
Young CC 1964. On a new pterosaurian from Sinkiang, China. Vertebrata PalAsiatica 8: 221-256.

wiki/Dsungaripterus

https://pterosaurheresies.wordpress.com/2012/03/10/the-evolution-of-the-pterosaur-palate-part-1/

Finding two more sacral impressions in Lagosuchus

With fragile, damaged fossils like
Lagosuchus talampayensis (Romer 1971; PULR 09; Late Triassic; Fig. 1), sometimes the fossilized bones alone tell only part of the story.

Figure 1. Lagosuchus in situ from Agnolin and Ezcurra 2019 preserves impressions of two additional sacrals. The length of the two ilia alone strongly suggest the presence of four sacrals or two very reinforced sacrals, a la Herrerasaurus, which was not the case here.

When bones disappear through taphonomy,
sometimes they leave impressions of their past presence providing workers subtle data that can be used for scoring in phylogenetic analysis, unless overlooked.

Figure 2. Marasuchus lilloensis (above) and Lagosuchus talampayensis (below) compared. The radius and ulna are longer in Marasuchus. The hind limbs are more robust in Lagosuchus. The length of the torso in Lagosuchus is based on the insitu placement of the pectoral girdle and forelimb, which may have drifted during taphonomy.

These two bipedal archosaur taxa
(Fig. 2) are similar, but the large reptile tree recovered them in distinct clades. The LRT nests Marasuchus with basal theropod Dinosaurs. Lagosuchus nests with Saltopus and other basal bipedal crocodylomorphs. These novel nestings were recovered due to including taxa overlooked by traditional studies.

Lagosuchus sister taxa in the LRT,
also have four sacrals. That fact provided the impetus for the present study searching for additional sacral impressions in high resolution photos from Agnolin and Ezcurra 2019.

As mentioned earlier,
a review of taxa tested within the Crocodylomorpha, like this one (Fig. 1), has resulted in several revisions to the croc subset of the LRT. The work is exciting, necessary and in progress. Results will be announced when they are known.

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References
Agnolin FL and  Ezcurra MD 2019.The validity of Lagosuchus talampayensis Romer, 1971 (Archosauria, Dinosauriformes), from the Late Triassic of Argentina. Breviora. 565 (1): 1–21.
Rauhut OMW and Hungerbühler A 2000. A review of European Triassic theropods. Gaia, 15: 75-88. 
Romer AS 1971. The Chañares (Argentina) Triassic reptile fauna. X. Two new but incompletely known long-limbed pseudosuchians. Breviora. 378: 1–10.
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna. XV. Further remains of the thecodonts Lagerpeton and Lagosuchus. Breviora. 394: 1–7.
Sereno PC and Arcucci AB 1994. Dinosaurian precursors from the Middle Triassic of Argentina: Marasuchus lilloensis, gen. nov. Journal of Vertebrate Paleontology. 14 (1): 53–73.

wiki/Saltopus
wiki/Lagosuchus

 

Erpetosuchus now nests outside of the Archosauria + Poposauria in the LRT

Based on its uniquely inset tooth row
(Figs. 1–3) Erpetosuchus (Newton 1894; Late Carnian, Late Triassic) has been a traditional enigma taxon.

Figure 1. Erpetosuchus in several views. Here the post-crania of Parringtonia is added.

According to Wikipedia,
“The relationship of Erpetosuchus to other archosaurs is uncertain. In 2000 and 2002, it was considered a close relative of the group Crocodylomorpha, which includes living crocodylians and many extinct relatives. However, this relationship was questioned in a 2012 analysis that found the phylogenetic placement of Erpetosuchus to be very uncertain.”

“Benton and Walker (2002) found the same sister-group relationship and proposed the name Bathyotica for the clade containing Erpetosuchus and Crocodylomorpha.”

“Nesbitt and Butler (2012) included Erpetosuchus within a more comprehensive phylogenetic analysis and found it to group with the archosaur Parringtonia (Fig. 1) from the Middle Triassic of Tanzania. Both were part of the clade Erpetosuchidae. Nesbitt and Butler did not find support for the sister-group relationship between Erpetosuchus and Crocodylomorpha. Instead, erpetosuchids formed a polytomy or unresolved evolutionary relationship at the base of Archosauria along with several other groups. It could take many positions within Archosauria, but none were as a sister taxon of Crocodylomorpha.”

Figure 2. Erpetosuchus, Tarjadia, Parringtonia now nest with Decurisuchus outside of the Archosauria + Poposauria. Note the extreme anterior lean of the quadrate and quadratojugal here, convergent with crocodyliformes.

A recent review of the Crocodylomorpha
subset of the large reptile tree (LRT, 1660+ taxa; Fig. 4) knocked Erpetosuchus out of the Crocodylomorpha and out of the Archosauria. Erpetosuchus and other members assigned to the Erpetosuchidae (Pagosvenator, Parringtonia, Tarjadia (Figs. 2-3), but not the basal marine crocodile Dyoplax, at least not yet) now nest with Decuriasuchus (Figs. 2–3) in the LRT. This clade nests between Rauisuchia and Poposauria + Archosauria (Fig. 4).

Figure 3. Erpetosuchus and kin illustrated to scale. Parringtonia + Tarjadia + Erpetosuchus now nest with Decuriasuchus basal to Poposaurs + Archosauria.

The small size of Erpetosuchus
(Fig. 3) is a derived trait, following several much larger ancestors. Alas, as far as we know, Erpetosuchus was a terminal taxon, leaving no descendants.

Figure 4. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Why was Erpetosuchus traditionally considered ‘crocodile-like’?
The extreme anterior lean of the quadrate and quadratojugal are typical crocodile traits shared by convergence with members of the clade Erpetosuchidae (including Decuriasuchus).

Eagle-eyed readers may note
a few other changes in the Crocodylomorpha subset of the LRT (Fig. 4). We’ll deal with these in future blogposts.

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References
Benton MJ and Walker AD 2002. Erpetosuchus, a crocodile-like basal archosaur from the Late Triassic of Elgin, Scotland, Zoological Journal of the Linnean Society 136:25-47.
Nesbitt SJ and Butler RJ 2012. Redescription of the archosaur Parringtonia gracilis from the Middle Triassic Manda beds of Tanzania, and the antiquity of Erpetosuchidae. Geological Magazine: 1. doi:10.1017/S0016756812000362
Nesbitt SJ, Stocker MR, Parke WGr, Wood TA, Sidor CA and Angielczy KD 2018. The braincase and endocast of Parringtonia gracilis, a Middle Triassic suchian (Archosaur: Pseudosuchia) Journal of Vertebrate Paleontology 37, Memoir 17: Vertebrate and Climatic Evolution in the Triassic Rift Basins of Tanzania and Zambia.
Newton TE 1894. Reptiles from the Elgin Sandstone—Description of two new genera. Philosophical Transactions of the Royal Society of London, B, 185:573–607.

wiki/Tarjadia
wiki/Parringtonia
wiki/Erpetosuchus

http://reptileevolution.com/decuriasuchus.htm

New basal tapejarid with broken wings needs specimen number, citation

Updated April 1, 2020
The specimen number is SMA 0154 / 02. Kind readers reported the location of this specimen: Sauriermuseum, Aathal, Switzerland. I can now reveal the phylogenetic nesting of this specimen is between Sinopterus and Tapejara. I know of no citation yet.

Figure 1. Complete basal tapejarid without identification. Please provide a museum number or citation if possible.

This image above (Fig. 1) appears on the website,
“Tapejaraluv.weebly.com” under the headline “The Tapejara,” created by Jordyn Rosen and Teya Good. There are no ‘contact us‘ or ‘comments‘ links on their website and all attempts at finding them elsewhere on the ‘net don’t seem to be leading to any Tapejara fans. 

I will forego posting any more information on this specimen
pending the acquisition of a citation or museum number on the chance that it is currently under study and awaiting publication. Even so, it has been added to the large pterosaur tree (LPT) as the 243rd taxon, but not yet posted online.

Revisiting the origin and living relatives of spiny sharks (Acanthodii)

In today’s somewhat lengthy post
there’s going to be a set-up (so you can see traditional thinking)
and a take-down (so you can see what happens when you add taxa).

According to Wikipedia:
“Acanthodii or acanthodians (sometimes called spiny sharks) is an extinct paraphyletic class of teleostome fish, sharing features with both bony fish and cartilaginous fish. In form they resembled sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteans (gars, bowfins). They represent several independent phylogenetic branches of fishes leading to the still extant Chondrichthyes.”

“Although not sharks or cartilaginous fish, acanthodians did, in fact, have a cartilaginous skeleton, but their fins had a wide, bony base and were reinforced on their anterior margin with a dentine spine.”

“The earliest unequivocal acanthodian fossils date from the beginning of the Silurian Period, some 50 million years before the first sharks appeared. Spiny sharks died out in Permian times (250 Million years ago).”

Figure 1. Cladogram from Burrow et al. 2016 (colors and labels added here) showing the origin of Acanthodii from Placodermi using only Silurian and Devonian taxa. Compare to figure 3, which includes extant taxa.

More from Wikipedia:
“Davis et al. (2012) found acanthodians to be split among the two major clades Osteichthyes (bony fish) and Chondrichthyes (cartilaginous fish).”

“Burrow et al. 2016 (Fig. 1 above) provides vindication by finding chondrichthyans (sharks + ratfish) to be nested among Acanthodii, most closely related to Doliodus (Fig. 5) and Tamiobatis (Paleozoid shark based on multi cusp teeth). A 2017 study of Doliodus morphology points out that it appears to display a mosaic of shark and acanthodian features, making it a transitional fossil and further reinforcing this idea”. 

By contrast,
the LRT found Doliodus (Fig. 5) nested with xenacanthid ‘sharks’ basal to bony fish, far from spiny sharks.

Figure x. Updated subset of the LRT, focusing on basal vertebrates = fish.

After adding more taxa, like the spiny shark,
Climatius (Fig. 3, ), and a long list of extant taxa in the large reptile tree (LRT, subset Fig. 2) the tree topology in figure 1 changes greatly.

Distinct from Burrow et al. 2016

1. Sharks and ratfish are not derived from spiny sharks, but are derived from the most primitive fish with simple transverse jaws, like Rhincodon.
2. Placoderms and pre-lobefin fish (like Cheirolepis) are not basal to spiny sharks, but are related through a last common ancestor in Bonnerichthys (Figs. 3, 4).
3. Spiny sharks arise from Silurian sisters to extant taxa, like lizard fish (Trachinocephalus, and arowana (Osteoglossum Fig. 3) in the newly recovered clade of short-face fish (clade: Breviops) distinct from fish with the orbit set further back on the skull (at least initially, the long-face fish (clade: Longiops) that starts with the bowfin (Amia).
4. Spiny sharks give rise to Triassic Perleidus and extant featherbacks (Notopterus, Fig. 3), both of which have traditional ray-fin fins, though Notopterus pelvic fins remain tiny spines.

Figure 3. Acanthodians, their ancestors and sometimes extant sisters. Presently tested spiny sharks are all quite tiny as adults. Larger ones are known.

Placoderms are not extinct
They exist today as catfish. Spiny sharks are not extinct. They exist today as anchovies (Engraulis) and featherbacks (Notopterus, Figs. 3, 4) in the LRT, where taxon exclusion recovers novel hypotheses of interrelationships. Spiny shark sisters don’t have spines for fins. Using a single trait, even one like ‘spines for fins’, would be “Pulling a Larry Martin.” IN order to be a spiny shark sister, a taxon just has to nest closer to spiny sharks than any other included taxon. In your own analyses, include more taxa and the transition from one to another will become more and more gradual and apparent.

Figure 4. Acanthodian skulls, plus those of ancestors and related taxa. Notopterus is a living featherback. Engraulis is a living anchovy.

Acanthodes bronni (Anonymous 1880; Early Permian 290 mya; 20cm; Fig. 4) is the latest occurring acanthodian, the largest and has the most ossified braincase. Davis et al. mislabeled the hyomandibular as a giant quadrate and the preopercular as the mislabeled hyomandibular (Fig. 4). Acanthodes is toothless and presumed to have been a filter feeder. No extra spines or fins are present. Other species can reach 41cm.

Reports that acanthodians are the last common ancestors
of sharks and bony fish (e.g. Friedman and Brazeau 2010, Davis, Finarelli and Coates 2012) are not supported by the LRT.

Figure 5. Doliodus skull and pectoral region with lateral reconstruction at right. Note the narrow pectoral region relative to the wide spread occiput. Apparently this fish had a narrower body than head.

Doliodus (Fig. 5) has similar spiny fins,
but nests elsewhere in the LRT, with Xenacanthus. Catfish (e.g. Clarias) often have spines anterior to their pectoral fins, but are not related to spiny sharks. the giant Cretaceous predator, Xiphactinus, bundles fin rays into a spine, but is not related to spiny sharks. Yet another Cretaceous giant, Bonnericthys, (Figs. 3, 4) likewise bundles fin rays into a spine, and is basal to spiny sharks.,

Remember this as you finish reading:
Presently some (not all) spiny sharks appear earlier  in the fossil record (early Silurian) than do many precursor taxa in the LRT, some of which wait to appear until the Late Carboniferous, Jurassic and Cretaeous. Others are only known as extant taxa. Loganellia, the tiny primitive whale shark sister, is also from the Early Silurian, 444 mya.  Guiyu, a basal lobefin (Fig. 6), and Psarolepis are from the Late Silurian. So every taxon in the LRT preceding Guiyu and Psarolepis will someday be found somewhere in Silurian strata.

Figure 6. Guiyu in situ, DGS colors added here and used to create the flatter, wider reconstruction with paddles preserved.

Fossilization is rare.
Finding a fossil-bearing locality of the right age is also rare. So it is wise not to put too much exclusionary weight on chronology (as in Fig. 1 above). Keep adding taxa and the puzzle of evolution will ultimately become a coherent picture. The gaps keep getting smaller as enigma taxa, like the spiny sharks, are better understood in a phylogenetic context, using extinct AND extant taxa.

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References
Anonymous 1880. Royal Physical Society of Edinburgh. Proceedings of the Royal Physical Society of Edinburgh. V: 115.
Baron MG 2015. An investigation of the genus Mesacanthus (Chordata: Acanthodii) from the Orcadian Basin and Midland Valley areas of Northern and Central Scotland using traditional morphometrics. PeerJ. 3: e1331. doi:10.7717/peerj.1331
Brazeau M 2009. The braincase and jaws of a Devonian ‘acanthodian’ and modern
gnathostome origins. Nature 457, 305–308.
Burrow C, den Blaauwen J, Newman M and Davidson R 2016. The diplacanthid fishes (Acanthodii, Diplacanthiformes, Diplacanthidae) from the Middle Devonian of Scotland. Palaeontologia Electronica 19 (1): Article number 19.1.10A.
Davis SP, Finarelli JA and Coates MI 2012. Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes. Nature 486:247–250.
Egerton P de MG 1860. Report of the British Association for Science for 1859.
Transactions of the Sections. 116.
Friedman M and Brazeau 2010. A reappraisal of the origin and basal radiation of the Osteichthyes. Journal of Vertebrate Paleontology 30(1):36–56.
Miller RF, Cloutier R and Turner S 2003. The oldest articulated chondrichthyan from the Early Devonian period. Nature 435:501–504.
Newman M and Davidson B 2010. Early Devonian fish from the Midland Valley of Scotland. National Palaentological Congress London 14–15.
Traquair RH 1888. Notes on the nomenclature of the Fishes of the Old Red Sandstone of Great Britain. Geol. Magazine (3)5:507–517.
Woodward AS 1892. On the Lower Devonian fish-fauna of Campbellton, New Brunswick.. Geol. Mag. 9, 1–6.

wiki/Acanthodii
wiki/Ischnacanthus
wiki/Mesacanthus
wiki/Acanthodes
wiki/Climatius

 

In memoriam: Professor Jennifer Clack

If you never met her,
here’s your second chance, via YouTube videos.

This week marks the passing of Professor Jennifer Clack (1947-2020),
a renown specialist in Devonian tetrapods, especially Acanthostega (Fig. 1). In the above 4-minute YouTube video from 2017, Clack introduces her concept that the first tetrapods, like her discovery of Acanthostega, had more than five manual digits. This is confirmed by Middle Devonian tetrapod tracks (Fig. 3) with more than five digits.

Figure 1. Acanthostega does not have much of a neck. Note the narrow torso, taller than wide, distinct from lobefin fish that phylogenetically led to basal tetrapods, like Trypanognathus in figure 4.

But not
according to the large reptile tree (LRT) which recovers Acanthostega as a terminal taxon, not a transitional one, far from the main line of tetrapod origins. Four digits are found in Panderichthys, Greererpeton and many other basal tetrapods, as we learned earlier here, here and here. More than five digits are found in only a few derived taxa, including the stem reptile, Tulerpeton, far from the origin of digits.

A more complete and technical account
of basal tetrapod traits is provided by Clack in this 20-minute YouTube lecture video from 2016 (above).

It may be that Clack only saw evolutionary progress
without considering the possibility of evolutionary reversal, as happens when taxa return to a more aquatic niche from a less aquatic niche, reducing the importance of their digits and limbs. In the above video, Clack does not provide a phylogenetic analysis, like the LRT (subset Fig. 2) that includes more primitive, but late-surviving basal tetrapods, all of which follow the pattern of a wider than deep torso, as in ancestral fish with embedded arm bones in their lobefins. Rather, she concentrates on individual traits, which while valuable, set her up for ‘Pulling a Larry Martin‘, rather than concentrating efforts on determining a phylogeny that minimizes taxon exclusion and lets the software determine (= mirror) evolutionary events, as the LRT does while minimizing taxon inclusion bias.

Figure 2. Subset of the LRT focusing on basal tetrapods. Note the displaced positions of Acanthostega and Ichthyostega.

Only after a phylogeny is documented and validated
can one then discuss the various traits and their uses by the creature that possessed them.

Lest we forget
the first tetrapod tracks (Fig. 1, Niedźwiedzki et al. 2010) predate fossil tetrapods, including Acanthostega, by 20 to 30 million years, as we looked at here. And even they had more than five toes. Thus the phylogenetic origin of tetrapods goes back even further. The early Devonian must have provided quite a few niches for such rapid evolution to take place.

Figure 3. Best Devonian Valentia track with various overlays.

We need to look more closely at
Trypanognathus (Fig. 4; latest Carboniferous), which is the most primitive, but by far not the earliest, taxon in the LRT to document fingers and limbs, rather than lobe fins. Note the anterior eyes, wide flat skull and body, and primitive sprawling limbs. Can someone count the fingers and toes on this specimen? I find no more than four digits. Some may be hiding here.

Figure 4. Trypanognathus in situ, colorized to bring out ribs and limbs is the most primitive, but not the earliest taxon with limbs and toes, not lobe fins.

We’ve seen the chronology of several fossil finds
at odds with their phylogeny in the LRT (e.g. multituberculates, bats, Gregorius). That keeps it interesting, but only a wide gamut phylogenetic analysis based on traits will deliver a valid tree topology. As time goes by and more discoveries are made the competing hypotheses will someday converge.

Figure 5. Silvanerpeton from the Upper Viséan (331 mya) is the outgroup taxon for Gephyrostegus and the Amniota.

And one more thing,
Clack 1994 described Silvanerpeton (Fig. 5, Viséan, 335 mya) first as an anthrcosauroid and later (Ruta and Clack 2006) as a stem tetrapod, all without recovering it as the basalmost reptile, as shown in the LRT. Adding taxa, creating a wider gamut phylogenetic analysis, would have brought even more fame to this well-respected paleontologist.

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References
Clack JA 1994. Silvanerpeton miripedes, a new anthracosauroid from the Visean of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 84 (for 1993), 369–76.
Niedźwiedzki G, Szrek P, Narkiewicz K, Narkiewicz M and Ahlberg PE 2010. Tetrapod trackways from the early Middle Devonian period of Poland Nature 463, 43-48. doi:10.1038/nature08623
Ruta M and Clack, JA 2006 A review of Silvanerpeton miripedes, a stem amniote from the Lower Carboniferous of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences, 97, 31-63.

https://www.zoo.cam.ac.uk/news/professor-jenny-clack-frs-1947-2020

http://www.theclacks.org.uk/jac/Biography.html

https://www.pbs.org/wgbh/nova/link/clack.html
(make sure to click on the parts 2-4 links therein)

 

Cretaceous toothed birds evolved from toothless megapodes in the LRT

Today’s heretical dive
into the origin of Cretaceous toothed birds (Fig. 1) brings new insight to a clade that has been traditionally misrepresented as a stem clade, often represented by just two highly derived toothed taxa, Ichthyornis and Hesperornis (Fig. 1). In the large reptile tree (LRT, 1659+ taxa; subset Fig. 3) Cretaceous toothed birds arise from extant toothless Megapodius (Figs. 1, 2; Gaimard 1823). How is this possible?

Toothy jaws from toothless jaws? 
That seems to break some rules. And if the LRT (Fig. 3) is valid, that makes toothed Cretaceous birds crown bird taxa.

Figure 1. Click to enlarge. Toothed birds of the Cretaceous to scale. They are derived from toothless taxa.

Earlier Field et al. 2020
claimed to discover the ‘oldest crown bird‘ fossil when they described Asteriornis (66 mya), a screamer (genus: Chauna) relative. Unfortunately, due to taxon exclusion, Field et al. 2020 did not consider the ostrich sister, Patagopteryx (80 mya), nor did they understand that Juehuaornis (Wang et al. 2015; Early Cretaceous, Aptian, 122mya; Figs. 1, 4) was also a crown bird taxon, the oldest crown bird, derived from Megapodius, the extant mound builder.

One look
(Fig. 1) at the similarity of Megapodius to basal Cretaceous toothed and toothless birds, like Juehuaornis (Figs. 1, 4), makes the relationship obvious. The LRT recovered that relationship based on hundreds of traits and minimized convergence by testing relationships among 1659 taxa.

So, where did those Cretaceous teeth come from?
Megapodius and Juehuaornis both lack teeth. Basalmost toothed taxa had tiny teeth (Fig. 1) Derived toothed taxa had larger teeth. Try to let that sink in. Teeth re-appeared in these Cretaceous birds.

How is that possible? Consider this:
Juehuaornis is smaller than Megapodius. The sternum and keel of Juehuaornis are smaller than in Megapodius. Why is this important? As we learned earlier, at the genesis of many major and minor clades phylogenetic miniaturization (the Lilliput Effect) is present. That’s how gulls become hummingbirds and rauisuchians become dinosaurs. When adults are smaller they mature more quickly and they retain juvenile traits into adulthood. They also develop new traits, in this case, perhaps ontogeny recapitulated phylogeny.

The tooth genes got turned on again,
at first in a minor way… later in a major way.

Figure 2. Click to enlarge. Origin of birds from Archaeopteryx to Megapodius. Pseudocrypturus is the sister taxon to the kiwi (Apteryx, Fig. 3), the most basal crown birds, but Juehuaornis is known from much older fossils despite being more derived than Megapodius.

How close were Cretaceous toothless taxa,
like Juehuaornis, to toothed Jurassic ancestors, like Archaeopteryx? Depends on how you look at it.

Chronologically
Juehuaornis is from the Aptian, Early Cretaceous, 122 mya. Archaeopteryx is from the Tithonian, Late Jurassic, 150 mya. A transitional taxon, Archaeornithura (Fig. 2) is from the Hauterivian, Early Cretaceous, 131 mya, splitting the time difference. Archaeornithura had teeth and lacked a pygostyle, but had a shorter tail than the most derived Archaeopteryx (Fig. 2).

Morphologically
toothless Juehuaornis follows toothless Megapodius (Figs. 1, 3) and is separated from toothy Archaeornithura by at least three taxa (Figs 2, 3). The question I ask is: did the Cretaceous sisters to these toothless taxa have teeth subsequently lost in later generations over the past 140 million years? Or were teeth lost in  Early Cretaceous transitional taxa (represented by late-survivors (Fig. 2)) only to be regained in the toothy extinct clade (Fig. 3)? For now, let’s leave all options open, but toothlessness followed by toothy jaws is the only option currently supported by phylogenetic evidence (Fig. 3).

Figure 3. Subset of the LRT focusing on bird origins. Crown birds and toothed birds are highlighted.

This is what happens when you let the cladogram tell you what happened,
rather than gerrymandering the taxa inclusion list and scores to get the results your professors and colleagues will approve and permit publication.

Figure 4. Juehuaornis reconstructed. Note the scale bars. This is a tiny bird and the oldest known crown bird.

I should have reported
that Juehuaornis (122 mya) was the oldest known crown bird earlier. I just had to see the toothed birds in phylogenetic order (Fig. 1), making sure they made sense after seeing them listed in the cladogram (Fig. 3).

Add taxa
and your cladograms will be better than most. Create reconstructions to scale and see if your cladograms make sense. When it’s right, it all works out with a gradual accumulation of traits between every node, echoing evolutionary events from deep time. Let me know if this novel hypothesis of interrelationships was published previously anywhere so that citation can be promoted.

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References
Gaimard JP 1823. Mémoire sur un nouveau genre de Gallinacés, establi sous le nom de Mégapode. Bulletin General et Universel des Annonces et de Nouvelles Scientifiques 2: 450-451.
Wang R-F, Wang Y and Hu Dong-yu 2015. Discovery of a new ornithuromorph genus, Juehuaornis gen. nov. from Lower Cretaceous of western Liaoning, China. Global Geology 34(1):7-11.

wiki/Megapodius
wiki/Megapode

Colobops: back to Rhynchocephalia

Scheyer et al. 2020 revisit
Colobops noviportensis (unnamed in Sues and Baird 1993; Pritchard et al. 2018; Late Triassic; YPM VPPU 18835; Fig. 1) a tiny 2.5cm long skull originally considered a ‘pan-archosaur’. Using µCT scans, Pritchard et al. scored Colobops and nested it at the base of the Rhynchosauria. Pritchard et al. wrote: “Colobops noviportensis reveals extraordinary disparity of the feeding apparatus in small-bodied early Mesozoic diapsids, and a suite of morphologies, functionally related to a powerful bite, unknown in any small-bodied diapsid.”

You heard it here first in 2018. Colobops is a rhynchocephalian.

Figure 1. Colobops as originally presented and slightly restored.

That same week in 2018,
Colobops was added to the large reptile tree (LRT, now 1659+ taxa, then 1085 taxa) where it nested as a sister to the morphologically similar and size similar basal rhynchocephalian, Marmoretta (Fig. 2; Evans 1991). You can read about that nesting here.

Figure 2. Marmoretta, a basal rhynchocephalian in the lineage of pleurosaurs

This week,
Scheyer et al. nested Colobops with Sphenodon (Fig. 3), a basal extant rhynchocephalian. Sadly, the authors again omitted Marmoretta (Fig. 2).

Sues and Baird 1993 first described this specimen
without naming it and without a phylogenetic analysis, as a member of the Sphenodontia (Williston 1925), a junior synonym for Rhynchocephalia (Gunther 1867).

Marmoretta oxoniensis (Evans 1991, Waldman and Evans 1994; Middle/Late Jurassic, ~2.5 cm skull length; Fig. 2), orginally considered a sister of kuehneosaurs, drepanosaurs and lepidosaurs. Here in the LRT, Marmoretta nests between Megachirella and Gephyrosaurus + the rest of the Rhynchochephalia. Two specimens are known with distinct proportions in the skull roof.

Figure 3. Sphenodon, the extant tuatara, is close to Colobops, but Marmoretta is closer.

The LRT minimizes taxon exclusion
because it includes such a wide gamut of taxa, from Cambrian chordates to humans. The Colobops information has been online for the past two years. Colleagues, please use it. Don’t ‘choose’ taxa you think might be pertinent. Let the LRT provide you a long list of validated taxa competing to be the sister to your new discovery.

Final note: 
In the LRT (since 2011) even rhynchosaurs are lepidosaurs. Just add pertinent taxa and your tree will recover the same topology. Traditional paleontologists are taking their time getting around to testing this well-supported hypothesis of interrelationships.

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References
Evans SE 1991. A new lizard−like reptile (Diapsida: Lepidosauromorpha) from the Middle Jurassic of Oxfordshire. Zoological Journal of the Linnean Society 103:391-412.
Pritchard AC, Gauthier JA, Hanson M, Bever GS and Bhullar B-AS 2018. A tiny Triassic saurian from Connecticut and the early evolution of the diapsid feeding apparatus. Nature Communications open access DOI: 10.1038/s41467-018-03508-1
Scheyer TM, Spiekman SNF, Sues H-D, Ezcurra MD, Butler RJ and Jones MEH 2020. Colobops: a juvenile rhynchocephalian reptile (Lepidosauromorpha), not a diminutive archosauromorph with an unusually strong bite. Royal Society Open Science 7:192179.
http://dx.doi.org/10.1098/rsos.192179
Sues H-D and Baird D 1993. A Skull of a Sphenodontian Lepidosaur from the New Haven Arkose (Upper Triassic: Norian) of Connecticut. Journal of Vertebrate Paleontology. 13 (3): 370–372.
Waldman M and Evans SE 1994. Lepidosauromorph reptiles from the Middle Jurassic of Skye. Zoological Journal of the Linnean Society 112:135-150.

wiki/Marmoretta
wiki/Colobops

https://pterosaurheresies.wordpress.com/2018/03/25/colobops-and-taxon-exclusion-issues/

Elgin and Hone 2020 document two large Solnhofen pterosaur wings

Two large, disassociated,
but strongly similar Solnhofen pterosaur wings, SMNK 6990 (Fig. 1) and MB.R.559.1 (Fig. 2) were described in detail by Elgin and Hone 2020. Unfortunately they did so without a phylogenetic analysis and therefore presented no firm hypothesis of interrelationships.

Figure 1. The SMNK 6990 wing from Elgin and Hone 2020. Contrast was raised from the original photo. Metacarpal 1 is actually mc3. Reconstruction in figure 3.

In the SMNK 6990 specimen
(Fig. 1) Elgin and Hone 2020 mistakenly flipped metacarpals 1-3  then wondered why 2 and 3 were reduced.

In the MBR.5991.1 specimen
Elgin and Hone 2020 overlooked the three free fingers.

Figure 2. MB.R.5991.1 specimen as originally published, then a higher contrast image and color tracing including three overlooked free fingers and a radius.

In their conclusion,
Elgin and Hone first guessed, then gave up trying to figure out what sort of wings these were when they reported, “a placement within either the Ctenochasmatoidea or Dsungaripteridae appears most likely… further differentiation is impossible.”

Figure 3. Luchibang, Pterodactylus longicollum and the two new Solnhofen wings to scale. The latter two are nearly identical.

In counterpoint,
testing against all 242 taxa already in the large pterosaur tree (LPT, where nothing is impossible) both new Solnhofen wing specimens nested with the largest pterodactylids, including, ironically, Luchibang (Fig. 3), which just this month Dr. Hone mistook for an ornithocheirid with weird proportions.

Alas, and with regret,
these two authors have a long history of making similar mistakes and overlooking details despite having firsthand access. Those low batting averages were covered earlier here, here, here, here, here and here. Not sure why referees keep accepting such work for publication. In the end it just has to be cleaned up.

Contra the authors’ title,
the traditional clade ‘Pterodactyloidea’ becomes a grade with four convergent appearances, when more taxa are added. Traditional paleontologists have been loathe to do this in their own cladograms. This hypothesis of interrelationships has been in the literature for the last 13 years (Peters 2007) and online in the LPT for the last ten. 

Keeping the blinders on
is what pterosaur workers seem to continue to be doing. The next generation of workers (Elgin and Hone among them) seems to be stuck in the same quagmire. Not sure why this is so. Astronomers and physicists are always testing each others’ observations and hypotheses. They are always inviting ideas. In the end, they seem to speak with one voice. Why can’t we be like that?

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References
Elgin RA and Hone DWE 2020. A review of two large Jurassic pterodactyloid specimens
from the Solnhofen of southern Germany. Palaeontologia Electronica, 23(1):a13. https://doi.org/10.26879/741
palaeo-electronica.org/content/2020/2976-solnhofen-pterodactyloids
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.