Squamate tooth complexity: Lafuma et al. 2020

Updated July 7, 2020
the LRT moves Meyasaurus, Indrasaurus and Hoyalacerta to the base of the Yabeinosaurus + Sakurasaurus clade within the Scleroglossa and Squamata.

This blogpost builds slowly. 
If you are short of time, drag down to the final paragraphs.

Lafuma et al. 2020 report,
“Complexity increase through cusp addition has dominated the diversification of many mammal groups.”

Be careful with blanket statements like that. What they wrote may be true of pre-mammal cynodonts (adding cusps), but teeth decrease in complexity in the lineage of pangolins, edentates, odontocetes and mysticetes. Carnivores have fewer teeth. So do elephants and manatees.

“However, studies of Mammalia alone don’t allow identification of patterns of tooth complexity conserved throughout vertebrate evolution.”

That sentence needs a re-write. It does not make sense.

“Here, we use morphometric and phylogenetic comparative methods across fossil and extant squamates (“lizards” and snakes) to show they also repeatedly evolved
increasingly complex teeth, but with more flexibility than mammals.”

Starting to sound iffy here knowing that Iguana (Fig. 1) is a basal squamate in the large reptile tree (LRT, 1669+ taxa, subset Fig. 2) and it has complex multi-cusp teeth. In the LRT varanids, sea-going mosasaurs and all legless lizards (including snakes) are all highly derived — and they have simple cones for teeth.

Pet Peeve: The authors don’t discuss lepidosaur pterosaurs that likewise had multi-cusp teeth in the Triassic, and only one cusp or no teeth in derived taxa.

Figure 2. The basalmost tested iguanid, Iguana. Note the resemblance to basalmost scleroglossans.

Figure 2. The basalmost tested iguanid, Iguana, one of the basalmost squamates in the LRT, contra Lafuma et al. who omitted so many outgroup taxa that their cladogram was upside-down.

Lafuma et al. 2020 continue,
“Since the Late Jurassic, six major squamate groups independently evolved multiple-cusped teeth from a single-cusped common ancestor.”

And those six in their phylogenetic order are:

  1. Scincoidea
  2. Polyglyphanodontia
  3. Lacertoidea
  4. Mosasauria
  5. Anguimorpha
  6. Iguania

Sophineta and three members of the Rhynchocephalia are outgroups to Squamata in the Lafuma et al. cladogram. That’s reasonable, but far from complete, and with disastrous consequences (see below).

“Unlike mammals reversals to lower cusp numbers were frequent in squamates, with varied multiple-cusped morphologies in several groups resulting in heterogenous evolutionary rates.”

See above.

The Lafuma et al. 2020 cladogram
lists the following clades of Squamates in this order (LRT order in parentheses).

  1. Gekkota (4th in the LRT and they share an ancestry with Serpentes in the LRT)
  2. Dibamia (last in the LRT, within skinks)
  3. Scincoidea (last in the LRT)
  4. Polyglyphanodontia (third in the LRT)
  5. Lacertoidea (second in the LRT)
  6. Mosasauria (fourth to last in the LRT)
  7. Serpentes (4th and they share an ancestry with Gekkota in the LRT)
  8. Anguimorpha (second to last in the LRT)
  9. Iguania (first in the LRT)

Due to taxon exclusion
the Lafuma et al. 2020 cladogram is inverted (upside-down) compared to the LRT (Fig. 2). As a result, so is their conclusion.

But let’s dig deeper trying to figure out how
this inversion happened. The authors report, “For topology we followed the total evidence phylogeny of Simões et al. – the first work to find agreement between morphological and molecular evidence regarding early squamate evolution.” Take a second look, dear readers. Borrowing a cladogram, taxon exclusion and genomics has given these workers an upside-down topology.

Figure 1.  Subset of the LRT focusing on lepidosaurs and snakes are among the squamates.

Figure 2.  Subset of the LRT from 2019 focusing on lepidosaurs including squamates.

Lafuma et al. 2020 list several hundred more squamate taxa
than the LRT includes, but this is where outgroups become important. Here is a list of missing Protosquamata taxa from the Lafuma et al. taxon list. Adding these taxa would bring much needed polarity to the Lafuma et al. cladogram:

  1. Lacertulus
  2. Schoenesmahl
  3. Fraxinisaura
  4. Hoyalacerta
  5. Indrasaurus
  6. Homoeosaurus
  7. Dalinghosaurus
  8. MFSN 19235
  9. Scandensia
  10. Calanguban
  11. Liushusaurus
  12. Purbicella
  13. Hongshanxi
  14. Euposaurus

But that’s not all… add to that list:
Tetraphodophis, Jucaraseps and Ardeosaurus. These three taxa link Norellius, Eichstaettisaurus and geckos to basal snakes. In the Lafuma cladogram Norellius, Eichstaettisaurus and geckos nest apart from Pontosaurus + Adriosaurus. For some reason, the basalmost gekko in the LRT, Tchingisaurus, nests with the basal amphisbaenan, Sineoamphisbaena in the Lafuma et al. tree. A sister, Sineoscincus, is omitted from the Lafuma et al. tree. Bahndwivici and Yabeinosaurus, nest basal to varanids and mosasaurs in the LRT, but are not listed by Lafuma et al.

If you’re going to report on the order of acquisition of traits,
you have to have your phylogenetic order established correctly. To do that you have to include more outgroup taxa, something that was not done in the Lafuma et al. study. By contrast, the LRT includes outgroup taxa back to Cambrian headless chordates, just to be sure all the bases are covered.


References
Lafuma F, Corfe IJ, Clavel J and Di-Pol N 2020. Multiple evolutionary origins and losses of tooth complexity in squamates. biRxiv preprint: https://doi.org/10.1101/2020.04.15.042796

Kopidodon enters the LRT basal to pangolins

Today
another enigma taxon nests in the LRT.

The Messel pit (Eocene) assemblage
has produced some of the most incredible fossils of completely articulated skeletons of birds and mammals, often with feathers and fur. and, in this case (Fig. 1), small round ears.

Figure 1. One of five complete skeletons of Kopiodon known from the middle Eocene Messel pits. A hand, foot and pelvis are layered to extend the fingers and toes for scoring.

Figure 1. One of five complete skeletons of Kopiodon known from the middle Eocene Messel pits. A hand, foot and pelvis are layered to extend the fingers and toes for scoring.

Kopidodon macrognathus (originally Cryptopithecus macrognathus Wittich 1902; Weitzel 1933/4; Tobien 1969; Naturmuseum Senckenberg; 115cm total length; middle Eocene, 47 mya; Figs. 1, 5) is traditionally considered, “a squirrel-like mammal with large canines” and therefore, somewhat of an enigma taxon.

Here
in the large reptile tree (LRT, 1669+ taxa) Kopidodon nests at the at the base of the pangolins, a sister to Chriacus (Fig. 2) + bats. Kopidodon likely had a Late Jurassic genesis based on the presence of scaled Zhangheotherium in the Early Cretacous. The skull of Kopidodon has a convex profile, like that of another pangolin ancestor, Metachromys (Fig. 3). This helps inform the likely profile of Zhangheotherium, preserved ventrally exposed.

Figure 2. Chriacus and Onychonycteris nest as a sister to the undiscovered bat ancestor and a basal bat. Miniaturization was part of the transition. So was enlargement of the manus. It is still a mystery why the transitional form decided to start flapping.

Figure 2. Chriacus and Onychonycteris nest as sisters to the pangolin clade with Kopoidodon at its base.

Pangolins
llike Manis (Fig. 4) are slow-moving, muscular, tree climbing insectivores. Their hair coalesces to form overlapping scales. For protection pangolins are able to roll into a ball.

Figure 2. Pangolin ancestor Metacheiromys skeleton and skull.

Figure 3. Pangolin ancestor Metacheiromys skeleton and skull, less than half the size of Kopidodon.

Kopidon was a late survivor of a primitively fur covered radiation. 
Hair-scales first appear in Zhangheotherium.

Figure 2. Manis, the Chinese Tree Pangolin along with other views of other pangolins

Figure 4. Manis, the Chinese Tree Pangolin along with other views of other pangolins

Kopidodon
had 26-29 (it varies) presacral vertebrae + 3 sacrals. The foreclaws were taller than wide (similar to arboreal mammals) and larger than the hind claws. The feet were plantigrade. The limbs were heavily muscled and designed for slow movement. The tail vertebrae diminished posteriorly to tiny elongate bones. Stomach contents include fruit and seeds.

Figure 3. Kopiodon skull in situ 2x and reconstructed.

Figure 5. Kopiodon skull in situ 2x and reconstructed. Compare to figure 3.

Kopidodon is traditionally considered a member
of the Cimolesta, the Pantolestidae, and the Paroxyclaenidae, but traditional members do not form monophyletic clades in the LRT.

Wikipedia (German version) reports,
The first description of Kopidodon took place in 1933, the taxonomic position was controversial for a long time.” The original name, Cryptopithecus, reflects that uncertainty as it tentatively allied this taxon with primates. The LRT minimizes taxon exclusion problems by including a wide gamut of taxa.

If this is not a novel hypothesis of interrelationships,
let me know of the original citation so I can promote it.


References
Clemens WA and von Koenigswald W 1993. A new skeleton of Kopidodon macrognathus from the Middle Eocene of Messel and the relationship of paroxyclaenids and pantolestids based on postcranial evidence. Kaupia 3, 1993, S. 57–73.
Koenigswald W von 1983. Skelettfunde von Kopidodon (Condylarthra, Mammalia) aus dem mitteleozänen Ölschiefer der Grube Messel bei Darmstadt. N Jb Geol Paläont Abh 167:1–39.
Koenigswald W von 1992. The arboreal Kopidodon, a relative of primitive hoofed mammals. In: Schaal S, Ziegler W (eds) Messel. An insight into the history of life and of the Earth. Clarendon Press, Oxford, pp 233–237.
Tobien H 1969. Kopidodon (Condylarthra, Mammalia) aus dem Mitteleozän (Lutetium) von Messel bei Darmstadt (Hessen). Notizblätter der hessischen Landesanstalt für Bodenforschung 97, 1969, S. 7–37.
Tobien H 1988. Kopidodon (Condylarthra, Mammalia) aus dem Mitteleozän (Lutetium) von Messel bei Darmstadt (Hessen). = Kopidodon (Condylarthra, Mammalia) from the middle Eocene (Lutetian) of Messel near Darmstadt, Hesse. Notizblatt des Hessischen Landesamtes fuer Bodenforschung zu Wiesbaden 97: 7-37.
Weitzel K 1933. Kopidodon macrognathus Wittich, ein Raubtier aus dem Mitteleozän von Messel. Notizblätter des Vereins für Erdkunde der hessischen geologischen Landesanstalt Darmstadt 14, 1933, S. 81–88
Wittich E 1898, 1902. ein Raubtier aus dem Mitteleozän von Messel. Notizblatt des Vereins für. Erdkunde zu Darmstadt (5)14: 81-88.

Greman/wiki/Kopidodon

Taxonomic problems? Go back to the holotype.

Sometimes taxa are mislabeled.
Such is the case with Pholidophorus? radians (Figs. 1–3), a ‘herring-like’ Jurassic (Solnhofen Fm.) fish with ganoid scales, tiny fins and a large forked tail. This specimen (Fig. 1) was identified as Pholidophorus in The Rise of Fishes (Long 1995) and at the Wikipedia entry for Pholidophorus.

Figure 3. Pholidophorus in situ and two skulls attributed to this genus. Compare the one on the left to figure 2. No tested fish in the LRT is closer to Robustichthys than Pholidophorus.

Figure 1. Pholidophorus in situ and two skulls attributed to this genus from Long 1995. Neither diagram matches this specimen, despite overall similarities.

The images in the diagrams above
(Fig. 1) are indeed variations on Pholidophorus (Fig. 4). However, the specimens in the photographs (Figs. 1–3) nest with Elops, the ladyfish (or tenpounder) in the large reptile tree (LRT, 1668+ taxa) on the other branch of bony fish.

Figure 2. Another specimen of Pholidophorus? radians

Figure 2. Another specimen attributed to Pholidophorus? radians

Figure 3. DGS tracing of Pholidophorus? radians along with a reconstruction moving the crushed bones to their invivo positions.

Figure 3. DGS tracing of Pholidophorus? radians along with a reconstruction moving the crushed bones to their invivo positions.

Yesterday
I found the Pholidophorus latiusculus holotype in the literature (Arratia 2013; Late Triassic; Fig. 4). The LRT recovered it apart from the Solnhofen (Late Jurassic) specimen identified as Pholidophorus in Long 1995 and Wikipedia.

The Late Triassic holotype of Pholidophorus
nests with Osteoglossum, the extant arrowana of South America and spiny-finned Bonnerichthys, from the Niobrara Sea of the Cretaceous. All likely had their genesis in the Late Silurian based on their close-to-the-base phylogenetic node.

Figure 4. Pholidophorus holotype from Arratia 2013, overlay drawing from Agassiz 1845.

Figure 4. Pholidophorus holotype from Arratia 2013, overlay drawing from Agassiz 1832.

It is easy to see how later specimens
were allied with the holotype, but this turns out to be yet another case of convergence. A wide gamut phylogenetic analysis that minimizes taxon exclusion minimizes phylogenetic errors like this one. Earlier I made the mistake of combining the data from the diagram (Fig. 1) and the photo (Fig. 2) creating a chimaera. Best to just find the holotype and work from that.


References
Agassiz L 1832. Untersuchungen über die fossilen Fische der Lias-Formation. Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefaktenkunde, 3, 139–149.
Arratia G 2013. Morphology, taxonomy, and phylogeny of Triassic pholidophorid fishes (Acinopterygii, Teleostei). Journal of Vertebrate Paleontology 33:sup1:1–138.
Sallan LC 2012. Tetrapod-like axial regionalization in an early ray-finned fish. Proceedings of the Royal Society B 279:3264–3271.

wiki/Pholidophorus

Livyatan (originally Leviathan) enters the LRT

Lambert et al. 2010 made a ‘big splash’
when they introduced a giant ‘raptorial’ odontocete, Leviathan melvillei (Fig. 1). Distinct from a similarly-sized sperm whale (Physeter), Leviathan has a shorter rostrum and retained giant teeth on the maxilla. It also had a preoccupied name, so it was later renamed Livyatan.

Figure 1. Leviathan diagram from Lambert et al. 2010 and colored here.

Figure 1. Livyatan diagram from Lambert et al. 2010 and colored here.

Size:
The skull of Livyatan was fifty percent larger skull than the largest sauropterygians, similar in size to the skull of the largest ichthyosaurs, 3/4 the length of the skull of the largest odontocete, Physeter, but with much larger teeth.

Phylogeny
In the large reptile tree (LRT, 1666+ taxa), Livyatan is transitional between several extinct archaeocetes and all extant odontocetes of which Physeter and Tursiops  are the most primitive. The dolphin smile famously worn by Tursiops had its genesis in Livyatan (Fig.1) and was lost in long-jawed Physeter.

One question:
The lateral extent of the premaxilla in the Lambert et al. diagram (Fig. 1) is different in dorsal, lateral and palatal views.


References
Lambert O et al. (6 co-authors) 2010. The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru. Nature 466:105–108.

wiki/Livyatan (Leviathan)
wiki/Physeter

Any major gaps left in the vertebrate family tree?

Not in the LRT.
While new vertebrate taxa are being published every week, categorically none of these are completely new and unheard of. New taxa are all falling into or between established clades.

There are no large gaps or weird enigmas
in the vertebrate fossil record, according to the the large reptile (LRT, 1663+ taxa). We know where turtles, catfish, snakes, whales and pterosaurs came from. Sure, I’d like to find someone report a short-fingered bat in the Cretaceous (Fig. 1), but that won’t come as a surprise when it happens. We already have the bookend taxa for that discovery.

Figure 1. Subset of the LRT focusing on the clade of colugos, pangolins and bats.

Figure 1. Subset of the LRT focusing on the clade of colugos, pangolins and bats.

Now only microevolution separates one taxon from another
and one clade from another. Every taxon in the LRT has sisters and ancestors back to Cambrian chordates. All sisters are more or less visually similar to one another.

Now all we have to do
is to continue slipping new taxa between established taxon pairs already in the LRT.

The only issue that remains is one that may always remain…
We don’t have, nor will we ever have, transitional fossils from the genesis of every transition (Fig. 1). Most of these are lost to time, or were never fossilized. What we do have are later-to-extant representatives of these transitions. And that’s okay.

That’s where systematics and taxonomy stands in Spring 2020.
The hard work is done. Fossil and extant taxa nest together. Taxon exclusion has been minimized in the LRT due to its wide gamut.

Unfortunately, paleo moves at a snail’s pace,
so there are still workers who cling to invalid hypotheses like pterosaur are archosaurs, caseids are pelycosaurs, or reptiles began with Hylonomus. Vancleavea is still on several archosauriform taxon lists. Multituberculates are still considered egg-laying mammals.

All of this nonsense
can stop now. Just add taxa. The LRT provides a suggestion list.

Run your own tests
to validate the LRT or invalidate it. Don’t trust it. Test it. Just make sure your observations are insightful and true, your reconstructions (show your work!) minimize freehand influences, and your taxon list is wide enough to include all possible candidates. Then share it with us when you have something to present.

A good scientist
attempts to falsify his own and other conclusions. To that end, scoring changes and reevaluations have been a part of the LRT since its inception nearly a decade ago.

Thank you
for your readership, your suggestions and your criticisms.

Straight out of Star Wars: Satyrichthys, the armored sea robin

One of the strangest fish in the sea
is the armored sea robin, Satyrichthys (Fig. 1). Based on phylogenetic bracketing, that’s the palatine + lacrimal + jugal + postorbital creating a face mask of bony armor. Ancestral taxa, like the sea robin, Prionotus (Fig. 4) and the thread fin, Polydactylus (Fig. 3), have progressively smaller circumorbital bones.

Figure1. Satyrichthys skull with DGS applied and overall diagrams.

Figure 1. Satyrichthys skull with DGS applied and overall diagrams. That preoperculum spike is shared with Prioonotus (Fig. 5).

The Satyrichthys skull
(Fig. 1) looks strikingly like a Star Wars Legion T-47 Airspeeder (Fig. 2) IMHO. In paleontology, we call this an unrelated ‘convergence.’

Figure 2. Star Wars air speeder model.

Figure 2. Star Wars air speeder model.

Satyrichthys rieffeli (originally Peristethus rieffeli Kaup 1859, 1873; Kawai T 2013; Fig. 1) is the extant armored sea robin with massively developed external palatine + lacrimal + jugal + postorbital extending far anterior to the small, weak, mouth.

Phylogenetically that face-mask started off innocently enough
as a circumoribital ring (palatine + lacrimal + jugal + postorbital) with a slight bump to the front on Polydactylus (Fig. 3). That ring evolved to cover more and more of the face (e.g. Prionotus, Fig. 4) until it became an all enclosing mask, as in Satyrichthys (Fig. 1).

Figure 3. Primitive Polydactylus skull has only a small, fused circumorbital ring.

Figure 3. Primitive Polydactylus skull has only a small, fused circumorbital ring. The former lacrimal is here the palatine given comparisons to outgroup Seriola zonata (Fig. 5). 

Polydactylus oxtonemus (Girard 1858; up to 23cm, some species up to 2m; Fig. 3) is the extant Atlantic threadfin. A perciforme (perch family), here Polydactylus (above) is also a shallows-dwelling relative of the sea robin Prionotus (below). Note the five thread-like rays/feelers anterior to the pectoral fin arising from the coracoid. These drag along the sea floor sensing prey. A second dorsal fin and forked tail distinguish this taxon from its sisters.

Figure 1. The sea-robin, Prionotus, has a more extensive circumorbital ring/face-mask.

Figure 4. The sea-robin, Prionotus, has a more extensive circumorbital ring/face-mask. The palatine here may instead by relegated to just the ventral rim of the naris if the lacrimal extends anteriorly, as in Satyrichthys.

Prionotus evolans (Linneaus 1766; 40cm; Fig. 4 is the extant striped sea robin, a scorpionfish that uses a set of finger-like flexible spines (homologous with the thread fin fins (Fig. 2) of its large pectoral fin to walk on the seafloor. With a long straight snout, it looks more like it’s barracuda-like relatives, but descends from a last common ancestor, the banded rudderfish, Seriola zonata (Fig. 5). We looked at missing cheekbones in the banded rudder fish earlier here.

Figure 1. Gregory 1933 did not illustrate a jugal and lacrimal for Seriola zonata, but the cladogram indicates they should be there. We find them in the photo.

Figure 5. Gregory 1933 did not illustrate a jugal and lacrimal for Seriola zonata, but the cladogram indicates they should be there. We find them in the photo. Note the anteriorly projecting palatine retained in derived taxa like Satyrichthys.

The phylogenetic connection of rudder fish, threadfins and sea robins
appears to be a novel hypothesis of interrelationships. If you know of a prior citation, please let me know so I can promote it.


References
Girard CF 1858. Notes upon various new genera and new species of fishes, in the museum of the Smithsonian Institution, and collected in connection with the United States and Mexican boundary survey: Major William Emory, Commissioner. Proceedings of the Academy of Natural Sciences of Philadelphia. 10: 167-171.
Kaup JJ 1859. Description of a new species of fish, Peristethus rieffeli. Proceedings of the Zoological Society of London, 1859, 103–107, 8 pl.
Kaup JJ 1873. Über die Familie Triglidae nebst einigen Worten über die Classification. Archiv für Naturgeschichte, 39, 71–93.
Kawai T 2013. Revision of the peristediid genus Satyrichthys (Actinopterygii: Teleostei) with the description of a new species, S. milleri sp. nov. Zootaxa, 3635 (4): 419–438.
Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Linneaus C von 1766. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio duodecima, reformata. pp. 1–532. Holmiæ. (Salvius)
Sulak KJ 1975. The systematics and biology of Bathypterois (Pisces, Chlorophthalmidae) with a revised classification of benthic mystophiform fishes. University of Miami Press, 398 pp. also:  Galathea Report. 1977; 14:49pp.

wiki/Polydactylus
wiki/Flying_gurnard
wiki/Triglidae-SeaRobin

How primitive are megapodes?

Earlier the large reptile tree (LRT, 1663+ taxa) nested megapodes (like Megapodius) at a more primitive node than any other living bird, except the kiwi (Apteryx) and ratites, like (like Struthio). You might remember, a toothed bird clade restricted to the Early and Late Cretaceous was derived from toothless Crypturus (Fig. 1) in the LRT.

Figure 1. Megapodius is the extant bird nesting at the base of all neognathae (all living birds except ratites).

Figure 1. Megapodius is the extant bird nesting at the base of all neognathae (all living birds except ratites). And it looks like a basal bird, not too this… not too that.

With that in mind
and hoping to understand the reemergence of previously lost teeth in Early Cretaceous birds, I checked out Clark 1960, who reported on megapode embryology.

To set the stage, Clark wrote,
Young birds are exceedingly precocious, being able to fly on the day of hatching and feeding actively only a few days after hatching.” He then referenced Portmann (1938, 1951, 1955) who listed several reptile-like characters of megapodes:

  1. no egg tooth (megapodes hatch by kicking their way out of the shell. The ‘egg tooth’ of chickens temporarily appears on the top of the beak, not the rim);
  2. lack of down feathers in embryos or nestlings;
  3. lack of parental care;
  4. primitive method of incubation (by solar heat, fermentation, vulcanism);
  5. long incubation period (8 weeks for Leipoa);
  6. large number of eggs laid;
  7. slow growth to adult size (especially for Alectura);
  8. primitive structure of the brain;
  9. eggs usually not turned and yet hatch relatively successfully;

Clark added to Portmann’s #9
a general lack of movement of the embryo until just before hatching. This may be related to the use of fermentation as a heat source for incubation. Clark notes,
the presence of aerobic bacteria should presumably greatly deplete the available oxygen supply.” Moving embryos might have suffocated for lack of oxygen. Clark also noted: relatively large yolks, as in reptiles.

I never found a tooth thread
connecting Late Jurassic teeth in stem birds to the reemergence of teeth in Early Cretaceous crown birds (Fig. 2) following Apteryx, ratites and megapodes. Even so, every other trait indicated a transition. The above authors further support the extreme primitive nature of megapodes. Ratites no longer bury their eggs. Kiwis dig burrows.

Figure 1. Click to enlarge. Toothed birds of the Cretaceous to scale.

Figure 1. Click to enlarge. Toothed birds of the Cretaceous to scale.

In the post-cladistic era
Dekker and Brom 1992 wrote, “Among megapodes, four different incubation-strategies may be distinguished:

  1. mound-building,
  2. burrow-nesting between decaying roots of trees,
  3. burrow-nesting at volcanically heated soils, and
  4. burrow-nesting at sun-exposed beaches.”

Dekker and Brom employed a cladogram
originally published by Cracraft and Mindell (1989), which mistakenly nested megapodes with galliforms (chickens and kin) due to taxon exclusion. Dekker and Brom wrote, We conclude that similarities shared with reptiles and kiwis are due to convergence.” That traditional nesting is not confirmed by the LRT due to taxon exclusion. Burying and burrowing are primitive, but give no clue as to how Early Cretaceous birds redeveloped small teeth at first, large teeth later. Neither does megapode embryology. Perhaps that’s why this novel hypothesis of interrelationships has never appeared elsewhere. 


References
Clark GA Jr. 1960. Notes on the embryology and evolution of the megapodes (Aves: Galliformes). Postilla 45:1–7.
Cracraft J and Mindell DP 1989. The early history of modern birds: a comparison of molecular and morphological evidence.— In: B. Fernholm, K. Bremer & H . Jörnvall, eds. The Hierarchy of Life: Molecules and Morphology in Phylogenetic Analysis: 389-403. Amsterdam, New York, Oxford.
Dekker RWRJ and Brom TG 1992. Megapode phylogeny and the interpretation of the incubation strategies. xxx 19–31.  Zoologische Verhandelingen  278(2): 19–31.
Portmann A 1938.
Beitrage zur Kenntnis der postembryonalen Entwick- lung der Vogel. Rev. Suisse Zool., 45: 273-348.
Portmann A 1951. Ontogenesetypus und Cerebralisation in der Evolution der Vogel und Sauger. Rev. Suisse Zool., 58: 427-434.
Portmann A 1955. Die postembryonale Entwicklung der Vogel als Evolu- tionsproblem. Acta XI Congr. Int. Orn., 1954. Pp. 138-151.

Gogosardina: the genesis of the squamosal

Choo, Long and Trinajstic 2009 brought us
a small, Late Devonian actinopterygian, Gogosardina coatesi (Figs. 1, 2; holotype WAM 07.12.2) known from four crushed and incomplete specimens. One contains conodont elements lodged among the branchial arches.

Figure 1. Gogosardina from Choo, Long and Trinajstic 2009 shown at full size if shown on a typical 72dpi computer monitor.

Figure 1. Gogosardina from Choo, Long and Trinajstic 2009 shown at full size if shown on a typical 72dpi computer monitor. Gray areas indicate missing bones on skull.

Here
(Fig. 2) a few skull bones are relabeled according to their tetrapod homologs, as in all taxa entered into the large reptile tree (LRT, 1663+ taxa). The skull is nearly identical to coeval and similarly-size Mimipiscis with slightly rotated premaxilla, a straighter anterior maxilla, a higher naris and only a partial ‘razor back’ ridge anterior to the dorsal fin. The skull is proportionally larger as well. Both have a large pineal opening between the frontals (yes, the frontals), distinct from almost all fish. The excurrent naris is confluent with the orbit. This entire clade lacks postparietals.

Figure 2. Gogosardina soul from Choo, Long and Trinajstic 2009. New labels in red. The intertemporal anchors the large hyomandibular in all fish.

Figure 2. Gogosardina soul from Choo, Long and Trinajstic 2009. New labels in red. The intertemporal anchors the large hyomandibular in all fish.

Choo, Long and Trinajstic considered Gogosardina to be
a stem actinopterygian. No cladogram of relationships was published then. Wikipedia lists Gogosardina among the Palaeonisciformes (Hay 1902). In the LRT Gogosardina nests between Cheirolepis and Mimipiscis, all basal to the extant anchovy, Engraulis., which is not traditionally considered to be a paleonisciform.

Figure 3. Pteronisculus shows how the jugal splits to form a jugal and squamosal, a bone that will ultimately take over for the preopercular.

Figure 3. Pteronisculus shows how the jugal splits to form a jugal and squamosal, a bone that will ultimately take over for the preopercular in this clade.

Clade member, Pteronisculus
(Fig. 3) splits the jugal into four parts. The posterior two become the single squamosal in Strunius (Fig. 4), Onychodus (Fig. 5) and all later lobefins and ultimately tetrapods.

Figure 5. Strunius shows the next step in the enlargement of the squmosal and the two bones making up the preopercular.

Figure 4. Strunius shows the next step in the enlargement of the squmosal and the two bones making up the preopercular.

In Onychodus
(Fig. 5) the squamosal is beginning to take over the preopercular (= postsquamosal). Thereafter the postsquamosal is a vestige until it disappears in most tetrapods, only to reappear in a few basal tetrapods undergoing reversals.

Figure 1. Onychodus is typical of most fish having dual external nares strictly for olfactory sensing. Gill covers are part of the respiratory apparatus.

Figure 5. Onychodus continues the enlargement of the squamosal and the reduction of the preopercular (post squamosal) in our tetrapod lineage.

Wikipedia reports,
“The Palaeonisciformes (Hay 1902) are an extinct order of early ray-finned fishes (Actinopterygii) which began in the Late Silurian and ended in the Late Cretaceous. It is not a natural group, but is instead a paraphyletic assemblage of the early members of several ray-finned fish lineages.”

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

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

With regard to anchovies, Wikipedia reports, 
Clupeiformes (Goodrich 1909) is the order of ray-finned fish that includes the herring family, Clupeidae, and the anchovy family, Engraulidae.” 

The LRT nests few traditional clupeiformes,
but the wolf herring, Chirocentrus, nests elsewhere (at a more basal node, along with toothy Trachinocephalus) apart from the anchovy, Engraulis. So this seems to be a paraphyletic clade based on these two disparate taxa.

Putting related taxa in phylogenetic order
helps us visualize the less dramatic processes of evolution that no one ever talks about, like the origin of the squamosal. which ultimately creates the dentary-squamosal jaw joint in mammals and humans.


References
Choo B, Long JA and Trinajstic K 2009. A new genus and species of basal actinopterygian fish from the Upper Devonian Gogo formation of Western Australia. Acta Zoologica (Stockholm) 90 (Supp 1):194–210.

wiki/Gogosardina (not online yet)
wiki/Palaeonisciformes
wiki/Clupeiformes

Can volant fossil vertebrates inspire mechanical design?

Martin-Silverstone, Habib and Hone 2020 review volant fossil taxa,
in their hope to “synthesise key elements to provide an overview of those cases where fossil flyers might provide new insights for applied sciences.”

Caveat
readers should note, these authors have been responsible for some of the current pterosaur myth-making (e.g. pterosaur quadrupedal catapult launch) in the academic literature. (To see the entire list, enter the keywords “Silverstone”, “Habib” or “Hone” in the white box above).

Even so, let’s start with a fresh slate
and see what they have to say.

The authors report,
“Soaring is a form of passive flight (though as with gliding, is often a behaviour of powered fliers) which involves using external sources of lift.”

“Change ‘often’ to ‘always’. Soaring only comes to those who have excelled at powered flight earlier. Soaring is the next step for the highest, longest-range flyers.

“Unique fossil-only bauplans have also been described, such as the nonavialan dinosaurs Yi qi and Ambopteryx.” 

Not unique. Misinterpreted, as detailed here. Both Yi qi and Ambopteryx are derived from specific Late Jurassic Solnhofen birds (specimens traditionally assigned to Archaeopteryx), in the large reptile tree (LRT, 1663+ taxa) which makes them avialan dinosaurs. The proper phylogenetic context must be the foundation.

On the same subject, later in their text, “the recently discovered Yi and Ambopteryx show a melange of features – notably an enlarged wrist bone supporting an apparently small membranous wing, but also a flight surface composed of feathers.” This is a myth. That ‘wrist bone’ is either a radius or an ulna, depending on which wing is under consideration as corrected and detailed here.

Figure 1. Above: freehand image from Martin-Silverstone 2020 of Quetzalcoatlus northropi wing. Pink arrows call out errors. Below: Traced image of Q. sp. wing.

Figure 1. Above: freehand image from Martin-Silverstone 2020 of Quetzalcoatlus northropi wing (based on the humerus shape). Pink arrows call out errors. Below: Traced image of Q. sp. wing after firsthand examination in the Wann Langston lab where the fossils were kept years ago.

Credit where due:
In the authors’ illustration of the pterosaur wing (Fig. 1), they correctly located the pteroid on the radiale, but incorrectly placed the medial carpal there, too. Free fingers 1–3 are too large and appear to be on top of one another, with their palmar surfaces facing anteriorly, following Bennett (2008, Fig. 2). In reality the palmar surfaces faced ventrally in flight with only metatarsal 3 attached to the wing finger, as in all other tetrapods (Fig. 2). That makes the free fingers point laterally while quadurpedal, as ichnites show. The wing membrane illustration (above) mistakenly extends to the hind limbs. This is the myth of the bat-wing pterosaur promoted by several Bristol professors.

Ironically,
the authors chose a flightless pterosaur, Quetzalcoatlus, to model their volant wing.

Pterosaur hand dorsal view

Figure 2. Pterosaur hands, dorsal view, the two opposing hypotheses.

Continuing onward to the bottom of their Figure 1
(Fig. 3 below), the authors mislabeled the left and right wings in this dorsal view (with scapulae indicating the dorsal side) of the BSP 1937 I 18 specimen of Pterodactylus.

Figure 2. This is Figure 1B of Martin-Silverstone et al. 2020 where they mislabel the left and right wings of BSP 1937 I 18. Colors added to show the extent of the wing membrane. See figure 4 for an animation of a similar fossil.

Figure 2. This is Figure 1B of Martin-Silverstone et al. 2020 where they mislabel the left and right wings of BSP 1937 I 18. The authors labeled this specimen “Aerodactylus”, but it nests in the midst of several Pterodactylus specimen.  Colors added to show the extent of the wing membrane. See figure 4 for an animation of a similar fossil. I did not color the uropatagia behind each knee. You can see those plainly here.

The lower arrow pointing to the ‘membrane’
(‘m‘ in Fig. 2) just barely points to the trailing edge of the membrane, just missing the space behind the elbow, where, as Peters (2002) showed (and see Fig. 4) the wing membrane stretched only between the elbow and wing tip, contra Martin-Silverstone, et al. (Fig. 1). The upper arrow points to the biceps (light red), not the propatagium membrane (yellow).

Click to animate. This is the Vienna specimen of Pterodactylus, which preserves twin uropatagia behind the knees.

Figure 4. This is the Vienna specimen of Pterodactylus, which preserves soft tissue membranes as in Fig. 3.

The authors labeled the BSP 1937 I 18 pterosaur, ‘Aerodactylus‘.
According to Wikipedia, “Aerodactylus is a dubious pterosaur genus containing a single species, Aerodactylus scolopaciceps, previously regarded as a species of Pterodactylus.”

In the large pterosaur tree (LPT) the BSP 1937 I 18 specimen nests between several other Pterodactylus specimens.

The authors report, 
“It is therefore the evolution of more extreme vane asymmetry, rather than slight asymmetry, that was critical to avian flight.”

According to the LRT, it is the elongation of locked down corticoids (and the clavicle in bats because they lack a coracoid) marks the genesis of flapping, which is more critical to avian flight.

The authors report, 
“The largest pterosaurs reached in excess of 10 m in wingspan, 250 kg in weight, and had skulls perhaps 3 m long, vastly exceeding any other known flying animal in size and weight.”

Actually the largest pterosaurs, like the largest birds, were flightless, as shown earlier here.

With regard to pterosaur wing membranes, the authors report, 
“All fossils that have relevant portions preserved and undistorted show the membrane attaching to the lower leg or ankle.” 

Actually, none of them do, including their Figure 1 (Fig. 2 above). The authors referenced Elgin, Hone and Frey 2011, another botched paper discussed earlier here. You might remember, the authors employed a fictional “shrinkage” to explain away all the fossils that did no fit their preconception, but all matched the observations in Peters 2002.

The authors report,
“Mechanical considerations indicate that pterosaur wings must have had a concave posterior margin to avoid aeroelastic instability.”

Why guess, hope and assume when you can observe? The aktinofibrils are there to avoid aeroelastic instability.

The authors report, 
“Proper tensioning of membrane wings in pterosaurs would have been impossible with a convex posterior margin, because of the single-spar construction.”

Tension between the elbow and wing tip (Peters 2002) is supported by fossil evidence (Figs. 2, 3).

The authors report,
“It has been suggested that the largest pterosaurs were secondarily flightless, but more recent work suggests that the maximum launch-capable body mass for pterosaurs may have been high, owing to the high maximum lift coefficient of their wings and their potential for quadrupedal launch.”

This is Habib’s claim based on imagined and falsified ‘evidence’ argued here. Habib’s hypothesis was based on an imagined elastic catapult potential in the wing knuckle pressed against the ground, but pterosaurs never do this according to track evidence. Click here to see the doctored evidence presented by Habib 2008.

The authors also cite the PhD thesis of C. Palmer, University of Bristol 2016. One of his first assignments as a PhD (October 2016 ) must have been to place an seeking a student, to investigate the effectiveness of the quadrupedal launch [of pterosaurs] and by comparing it with the bipedal launch of birds, test if it was one of the factors that enabled pterosaurs to become much larger than any bird, extant or extinct.” You can read more about that advert here.

Wait a minute… since that quad launch hypothesis was a subject in Palmer’s PhD dissertation (according to the Martin-Silverstone, et al. citation, why was he advertising for someone else with less experience to take on this task? Let’s remember, students and PhD candidates have the least experience in the field. Most of the myth-making in pterosaurs comes out of universities in Southern England, evidently where students have to produce what their professors demand, or fail.

Please note: In the advert the Bristol bunch were not testing the hypothetical quad launch of pteros against the hypothetical bipedal launch of pteros. For them, quad launch was/is ‘a given’ that must be proved, despite the danger to the pterosaur, the criticism from colleagues and the lack of evidence.

At this point,
I’m only halfway through the paper. The rest we’ll save for later, if necessary. For now, some concluding remarks.

The authors stated their goal in lofty language, 
“A robust understanding of the origin of flight and the evolution of morphologies related to flight performance provides critical context for the constraints and optimisation of biological traits that can inspire mechanical design.”

The problem is, the authors have collected and presented invalid data. They have avoided putting the origin of bats, birds and pterosaurs into their proper phylogenetic context by showing the origin of flapping. How can the authors hope to emulate a pterosaur mechanically if they are freehand designing their own fictional pterosaur (Fig.1) and not looking carefully at specimens under their nose (Fig.2)? A scientist should always be trying to falsify a claim. I don’t see that here. By ignoring the literature (and the evidence) that falsifies a claim, these three authors are not acting like scientists.

With regard to mechanical pterosaurs,
the Stanford pterosaur project did not fair as well as simpler ornithopter designs.

The famous MacCready mechanical flying pterosaur
(Figs. 5, 6), was ostensibly modeled on the smaller Quetzalcoatlus specimen (Figs. 5, 6), but MacCready extended the wingspan to make his model fly. For a discussion on mechanical pterosaurs, it’s a little strange that the keyword, “MacCready” yields no results in their PDF.

Figure 5. The Macready flying model compared to Q. sp. Perhaps it has always been overlooked that the neck proportions were changed and heavy mechanical motors and batteries filled the torso.

Figure 5. The Macready flying model compared to Q. sp. Perhaps it has always been overlooked that the neck proportions were changed, even though the body included the weight of the motor, batteries, radio and controls. The wingspan is longer on the flying model than on the real genus.

We looked at arguments against
the hypothesis of giant volant pterosaurs here. The first thing that pterosaurs do when they give up flying is to shorten the distal wing phalanges, a fact overlooked by Martin-Silverstone, Habib and Hone. The keyword, “vestigial” does not appear in their PDF. The keyword, “distal” appears, but not in regards to pterosaur wing phalanges.

Figure 6. Paul MacCready's flying pterosaur model had longer wings than Q. sp., with its vestigial distal wing phalanges. Here the model and its inspiration are shown to the same length.

Figure 6. Paul MacCready’s flying pterosaur model had longer wings than Q. sp., with its vestigial distal wing phalanges. Here the model and its inspiration are shown to the same length.

Once again, and true to Professor Bennett’s curse,
“You will not be published, and if you are published, you will not be cited,” my published papers on the origin of pterosaurs from fenestrasaurs (Peters 2000), the origin and shape of pterosaur wings (Peters 2002), and the origin and orientation of the pteroid (Peters 2009) were not cited by these authors. As good scientists they should have cited these papers, discussed the presented data, constructed arguments, and most importantly, attempted to falsify their own hypotheses with faithful and precise observations unsullied by invented excuses (‘shrinkage’). Only when they get their pterosaurs right will they have a good basis for discussing mechanical equivalents. And please cite the work of inventor Paul MacCready.

PS
Citation #76 in Martin-Siverstone, et al. (Zakaria et al. 20160 discusses several mechanical aspects of pterosaurs. They copied the bad pterosaur bauplan from Elgin, Hone and Frey 2011 (Fig. 7) then provided an optimized wing plan with a narrower chord from their studies (Fig. 8) that more closely matched the actual wing shape of pterosaurs in Peters (2002).

Problems with the Elgin, Hone and Frey (2011) pterosaur wing model with corrections proposed by Peters (2002).

Figure 7. Above problems with the Elgin, Hone and Frey (2011) pterosaur wing model with corrections proposed by Peters (2002).

All I can say is,
it’s a topsy-turvy world out there where bad data rules the day.

Figure 8. When Zanzaria et al. 2016 used math to model the optimum pterosaur wing, they found a narrow chord, as in figure 7, worked better.

Figure 8. When Zanzaria et al. 2016 used math to model the optimum pterosaur wing, they found a narrow chord (red), as in figure 7, worked better than the ‘actual shape’ actually invented by Elgin, Hone and Frey 2011 wing (black).

Added a few days later:
From the Scientific American article that promoted four-fingered tenrec tracks as Crayssac pterosaur tracks: “Elizabeth Martin-Silverstone, a pterosaur expert at the University of Bristol in England, who did not take part in the work, says the fossil is the ‘final nail in the coffin of the idea that basal pterosaurs were awkward and clumsily walking around—and definitely of the idea that early pterosaurs might have been bipedal.” Not only did they walk on all fours, “but they moved around quickly and with style,’ she adds.” Martin-Silverstone is not using critical thinking. Four fingers and anteriorly-oriented manus tracks invalidated these as possible pterosaur tracks. Many pterosaurs and their fenestrasaur tritosaur lepidosaur ancestors were bipeds. See keyword “Rotodactylus” in the white box above.

References
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E Buffetaut and DWE Hone eds., Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Habib M 2008. Comparative evidence for quadrupedal launch in pterosaurs. Pp. 161-168 in Buffetaut E, and DWE Hone, eds. Wellnhofer Pterosaur Meeting: Zitteliana B28
Mazin J-M, Billon-Bruyat J-P and Padian K 2009. First record of a pterosaur landing trackway. Proceedings of the Royal Society B doi: 10.1098/rspb.2009.1161 online paper
Martin-Silverstone E, Habib MB and Hone DWE 2020. Volant fossil vertebrates: Potential for bio(-)inspired flight technology. Trends in Ecology & Evolution (advance online publication) doi: https://doi.org/10.1016/j.tree.2020.03.005
https://www.sciencedirect.com/science/article/abs/pii/S016953472030080X
Palmer C 2011. Flight in slowmotion: aerodynamics of the pterosaur wing. Proc. R. Soc. Lond. B Biol. Sci. 278, 1881–1885.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Prondvai E and Hone DWE 2009. New models for the wing extension in pterosaurs. Historical Biology DOI: 10.1080/08912960902859334
Sharov AG 1971. New flying reptiles fro the Mesozoic of Kazakhstan and Kirghizia. Trudy of the Paleontological Institute, Akademia Nauk, USSR, Moscow, 130: 104–113 [in Russian].
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.
Zakaria MY. et al. 2016. Design optimization of flapping ornithopters: the pterosaur replica in forward flight. J. Aircraft 53: 48–59
Zittel KA 1882. Über Flugsaurier aus dem lithographischen Schiefer Bayerns. Palaeontographica 29: 7-80.

http://reptileevolution.com/pterosaur-wings.htm
http://reptileevolution.com/pterosaur-wings2.htm

In Memorium: paleontologist Robert L. Carroll

Figure 1. Robert L. Carroll in his younger days.

Figure 1. Robert L. Carroll in his younger days.

Robert L. ‘Bob’ Carroll (1938-2020):
a warm-hearted, kind, and knowledgeable professor, always eager to answer a question.

Earlier, we looked at the impact of his major work from 1988, the textbook ‘Vertebrate Paleontology.’ That ‘must-have’ volume was a prime resource for many students and professors for decades. Some considered it ‘The Bible’ of our profession.

We all enter science to make a contribution. Carroll made his in small and large ways, not only by describing and illustrating many of his own discoveries, but by working with others to bring them all together between book covers in the pre-cladistic era. His work will remain on our library shelves. ReptileEvolution.com was built on that foundation and stands on the shoulders of this giant.


References
Use key word “Carroll” to see the index of all the taxa RL Carroll helped describe and covered in this blogpost.

A few days later this link goes into detail on RL Carroll’s career.

Headline: “Vertebrate palaeontologist who recognized and described the oldest known ancestor of all reptiles birds and mammals; the origins of terrestrial vertebrates, the origin of various amphibians such as frogs and salamanders.” 

Subhead: “Any high-school kid can go out and make fossil discoveries.”

Caveat: Some of those hypotheses have been superseded by more recent discoveries (e.g. “Hylonomus lyelli, shown here, is the oldest known reptile (315 million years)”… “Another paleontological mystery: where did turtles come from? Nobody knows.”)