Basal Tetrapods, slightly revised

Updated June 23, 2017 with the replacement of the cladogram with one containing more recently added taxa.

Figure 4. Subset of the LRT with the addition of Lethiscus as a sister to Oestocephalus, far from the transition between fins and feet. Here the microsaurs are not derived from basal reptiles

Figure 1. Subset of the LRT showing basal tetrapods (amphibians).

After earlier identifying
phylogenetic miniaturization at the bases of several major clades in the large reptile tree (LRT, 969 taxa), I wondered if similar size-related patterns appear in basal tetrapods.

  1. Osteolepis is smaller than Eusthenopteron. Has anyone removed the scales from the fore fins of Osteolepis to see what the bones inside look like?
  2. Ventastaga and Pederpes are successively smaller than Ichthyostega.
  3. Koilops is much smaller than Panderichthys.. 
  4. Eucritta is much smaller than Proterogyrinus, both in overall size and in relative torso length. Eucritta nests at the base of the Seymouriamorpha + Crown Tetrapoda.
Figure 2. Basal tetrapod skulls in dorsal view.

Figure 2. Basal tetrapod skulls in dorsal view. Tetrapoda arise with flattened skulls. Paratetrapoda retain skulls with a circular cross section.

 

Pterodaustro isometric growth series

Tradtional paleontologists think pterosaur babies had a cute short rostrum that became longer with maturity and a large orbit that became smaller with maturity (Fig. 1). This is a growth pattern seen in the more familiar birds, crocs and mammals.

Pterodaustro embryo as falsely imagined in Witton 2013. The actual embryo had a small cranium, small eyes and a very long rostrum.

Figure 1. Pterodaustro embryo as falsely imagined in Witton 2013. The actual embryo had a small cranium, small eyes and a very long rostrum.

Unfortunately
these paleontologists ignore the fossil evidence (Figs 2, 3). These are the data deniers. They see things their own way, no matter what the evidence is. The data from several pterosaur growth series indicates that hatchlings had adult proportions in the skull and post-crania. We’ve seen that earlier with Zhejiangopterus (Fig. 2), Tapejara, Pteranodon, Rhamphorhynchus and others. Still traditional paleontologists ignore this evidence as they continue to insist that small short rostrum pterosaurs are babies of larger long rostrum pterosaurs.

Figure 1. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Figure 2 Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

As readers know,
several pterosaur clades went through a phase of phylogenetic miniaturization, then these small pterosaurs became ancestors for larger clades. Pterosaurs are lepidosaurs and they grow like lepidosaurs do, not like archosaurs do.

Today we’ll look at
the growth series of Pterodaustro (Fig. 1), previously known to yours truly only from adults and embryos. Today we can fill the gaps with some juveniles.

This blog post is meant to help traditional paleontologists get out of their funk.

A recent paper
on the braincase of odd South American Early Cretaceous pterosaur Pterodaustro (Codorniú et al. 2015) pictured three relatively complete skulls from a nesting site (Fig. 1). I scaled the images according to the scale bars then added other available specimens.

Figure 1. Pterodaustro skulls demonstrating an isometric growth series. One juvenile is scaled to the adult length. One adult is scaled to the embryo skull length. There is no short rostrum and large orbit in the younger specimens.

Figure 1. Pterodaustro skulls demonstrating an isometric growth series. One juvenile is scaled to the adult length. One adult is scaled to the embryo skull length. There is no short rostrum and large orbit in the younger specimens. If you can see differences in juvenile skulls vs. adult skulls, please let me know. All these specimens come from the same bone bed.

You can’t tell which skulls are adults or juveniles
without scale bars and/or comparable specimens. As we established earlier, embryos are generally one-eighth (12.5%) the size of the adult. Pterodaustro follows this pattern precisely.  We have adults and 1/8 size embryos and several juveniles of intermediate size.

No DGS was employed in this study.

If you know any traditional paleontologists, 
remind them that the data indicates that pterosaurs matured isometrically, like other  lepidosaurs. Those small, short rostrum specimens, principally from the Late Jurassic Solnhofen Formation, are small adults, transitional from larger ancestors to larger descendants. Tiny pterosaurs experiencing phylogenetic miniaturization(as in birds, mammals, crocs, turtles, basal reptiles, and many other clades) that helped their lineage survive while larger forms perished, Sadly, no tiny pterosaurs are known from the Late Cretaceous when they all became extinct.

References
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Codorniú L, Paulina-Carabajal A and Gianechini FA 2015.
 Braincase anatomy of Pterodaustro guinazui, pterodactyloid pterosaur from the Lower Cretaceous of Argentina. Journal of Vertebrate Paleontology, DOI:10.1080/02724634.2015.1031340

BPI 2871 has a new sister: Elachistosuchus huenei

Earlier we looked at a tiny basal choristodere, BPI 2871, which was derived from a line of much larger proterosuchids, according to the large reptile tree.

Recently a new PlosOne online paper (Sobral et al. 2015) reintroduces Elachistosuchus huenei (Janensch 1949, Late Triassicm, Norian, Germany; MB.R. 4520 (Museum für Naturkunde Berlin, Berlin, Germany)) with CT scans.

Figure 1. Elachistosuchus (Janensch 1949, Sobral et al. 2015) is a sister to BPI 2871, a basal choristodere.

Figure 1. Elachistosuchus (Janensch 1949, Sobral et al. 2015) is a sister to BPI 2871, a basal choristodere, has been misidentified for over fifty years.The left upper temporal fenestra has been largely closed by crushing here. Like BPI 2871, the nares were located on top of the skull, close to the snout tip. Note the vestige of the antorbital fenestra.

And they don’t know what it is. 
According to Sobral et al, Elachistosuchus could be “an archosauromorph, a lepidosauromorph or a more basal, non-saurian diapsid.” That confusion arises from using outdated matrices with too few generic taxa and too many suprageneric taxa.

Sobral et al. used the matrix from Chen et al. 2014, which nested Elachistosuchus in a polygamy with Choristodera, Prolacerta + Tanystropheus + Macrocnemus, and Trilophosaurus + Rhynchosauria + Archosauriformes. As readers know the large reptile tree found many of these taxa on opposite sides of the reptile cladogram.

Sobral et al. also used the matrix from Ezcurra et al. 2014, which nested Elachistosuchus with the gliding Permian lepidosauriform, Coelurosauravus.

Hmmmm…

Sobral et al. report: 
“These different placements highlight the need of a thorough revision of critical taxa and new character sets used for inferring neodiapsid relationships.” 

Exactly. 
That’s why large reptile tree and reptileevolution.com are here. It’s good to have hundreds of specimen-based taxa for new taxa to nest with. More choice. More accuracy. Complete resolution.

To their credit,
a Sobral et al. analysis nested Elachistosuchus with choristoderes.

Figure 2. Dorsal, lateral and palatal views of BPI 2871 with bones colorized above. Below, reconstructed images of BPI 2871 tracings. It is more complete than illustrated by Gow 1975. Click to enlarge. Note the tiny remnant of the antorbital fenestra. The squamosal has been broken into several parts.

Figure 2. Dorsal, lateral and palatal views of BPI 2871 with bones colorized above. Below, reconstructed images of BPI 2871 tracings. It is more complete than illustrated by Gow 1975. Click to enlarge. Note the tiny remnant of the antorbital fenestra. The squamosal has been broken into several parts. This is a sister to Elachistosuchus.

Among earlier workers
Janensch (1949) considered Elachistosuchus a pseudosuchian archosaur with an antorbital fenestra. Walker (1966 ) considered  Elachistosuchus a rhynchocephalian lepidosaur.

The large reptile tree (now 575 taxa)
finds Elachistosuchus nests firmly as a sister to the BPI 2871 specimen (Fig. 3) that Gow mistakenly attributed to Youngina, but it nests far from Youngina at the base of the large and small choristoderes. And these two taxa are both derived from much larger proterosuchids in yet another case of phylogenetic miniaturization at the genesis of a new clade, in this case the Choristodera.

Elachistosuchus has a larger orbit and a maxilla with a straight, not convex, ventral margin of the maxilla than the BPI 2871 specimen. The former extends the geographic range of the latter, from southern Africa to Germany.

Both probably look like juvenile proterosuchids (whenever they are discovered, we can compare them). Phylogenetic miniaturization often takes juvenile traits and sizes and makes them adult traits and sizes to start new clades.

Janensch thought Elachistosuchus had an antorbital fenestra. As in BPI 2871, that is the vestige of the antorbital fenestra found in ancestors and lost in descendants.

Contra the title of the Sobral et al. paper
Elachistosuchus huenei has nothing to do with the origin of ‘Sauria.’

Sauria definition: “.Any of various vertebrates of the group Sauria, which includes most of the diapsids, such as the dinosaurs, lizards, snakes, crocodilians, and birds. Sauria was formerly a suborder consisting ofthe lizards” Rather, Elachistosuchus is a basal choristodere and a derived proterosuchid according to the large reptile tree. Based on the current definition of ‘Sauria’ ‘Sauria’ is synonymous with ‘Amniota’ which is a junior synonym for ‘Reptilia’ because the last common ancestor of lizards and dinosaurs is the basalmost reptile/amniote, Gephyrostegus bohemicus.

The reason why Sobral et al. were confused
with regard to their blurred nesting of Elachistosuchus is due to taxon exclusion. BPI 2871 is a rarely studied taxon and was not included in their analyses. Moreover, traditional paleontologists are not sure what choristoderes are. They don’t recognize them as being derived proterosuchids. And to make matters worse, traditional paleontologists prefer to think of Proterosuchus specimens as members of an ontogenetic series, when they should consider them as a phylogenetic series.

Figure 4. This is where Elachistosuchus nests, next to BPI 2871, at the base of the Choristodera.

Figure 3. This is where Elachistosuchus nests, next to BPI 2871, at the base of the Choristodera. Click to see the complete reptile cladogram.

The large reptile tree (Fig. 3) has proven itself time and again to solve paleontological problems in the reptile family tree. It is unfortunate that it has been rejected for publication so many times. If published, it can be use.

A MacClade file is available on request.

References
Chen X, Motani R, Cheng L, Jiang D, Rieppel O. 2014. The enigmatic marine reptile Nanchangosaurus from the Lower Triassic of Hubei, China and the phylogenetic affinities of Hupehsuchia. PLoS ONE. 2014; 9: e102361. doi: 10.1371/journal.pone.0102361 PMID: 25014493
Ezcurra MD, Scheyer TM, Butler RJ 2014. The origin and early evolution of Sauria: reassessing the Permian saurian fossil record and the timing of the crocodile-lizard divergence. PLoS ONE. 2014; 9: e89165. doi: 10.1371/journal.pone.0089165 PMID: 24586565
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Janensch W 1949. Ein neues Reptil aus dem Keuper von Halberstadt. N Jb Mineral Geol Palaeont B. 1949:225–242.
Sobral G, Sues H-D & Müller J 2015. Anatomy of the Enigmatic Reptile Elachistosuchus huenei Janensch, 1949 (Reptilia: Diapsida) from the Upper Triassic of Germany and Its Relevance for the Origin of Sauria. PLoS ONE 10(9): e0135114. doi:10.1371/journal.pone.0135114
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0135114
Walker AD 1966. Elachistosuchus, a Triassic rhynchocephalian from Germany. Nature. 1966; 211: 583–585.

wiki/Elachistosuchus

BPI 2871 – Now it is the oldest known choristodere

Updated July 5, 2015 with a lateral and occipital views of BPI 2871 and few text changes.

Earlier we looked at some of the earliest known Choristoderes recognized by traditional paleontologists. According to Wikipedia, Choristoderes are difficult to nest.Cladistshave placed them between basal diapsids and basal archosauromorphs, but the phylogenetic position of Choristodera is still uncertain. It has also been proposed that they represent basal lepidosauromorphs. Most recently, workers have placed Choristodera within Archosauromorpha.”

Figure 1. The sister to Doswellia, the BPI2871 specimen of Youngina.

Figure 1.  BPI 2871 specimen attributed to Youngina slightly modified from Gow 1975.

Gow 1975
considered the skull-only fossil, BPI 2871 (Bernard Price Institute, Fig. 1) a specimen of Youngina, despite its Late Triassic appearance (all other Youngina are Late Permian). For years his drawing (Fig. 1) was the only data I had for this specimen. Recently, and after several years of waiting, a requested image (Fig. 2) from the BPI was emailed and it clarified my understanding of this vaguely-croc-like basal archosauriform — perhaps without an antorbital fenestra — or perhaps this is one of the last taxa in the choristodere lineage to have a vestige antorbital fenestra, as it appears.

Figure 2. Dorsal, lateral and palatal views of BPI 2871 with bones colorized above. Below, reconstructed images of BPI 2871 tracings. It is more complete than illustrated by Gow 1975. Click to enlarge. Note the tiny remnant of the antorbital fenestra. The squamosal has been broken into several parts.

Figure 2. Dorsal, lateral and palatal views of BPI 2871 with bones colorized above. Below, reconstructed images of BPI 2871 tracings. It is more complete than illustrated by Gow 1975. Click to enlarge. Note the tiny remnant of the antorbital fenestra. The squamosal has been broken into several parts.

The new image
of BPI 2871 (Fig. 2) indicates that the skull is more complete than illustrated by Gow 1975. With this new data added to the matrix of the large reptile tree (Fig. 3) the nesting of BPI 2871 shifts it closer to the base of the Choristodera, evidently making it the oldest known member in the Late Triassic (210 mya).

Figure 3. Subset of the large reptile tree focusing on the pararchosauriformes and the Choristodera.

Figure 3. Subset of the large reptile tree focusing on the pararchosauriformes and the Choristodera.

BPI 2871 is distinctly different
in chronology and morphology from Y. capensis, a fact overlooked or ignored by Gow who considered it another specimen of Youngina capensis. Like Bennett (1995, 1996, 2014) Gow was a lumper.

Tiny
BPI 2871 apparently lost the antorbital fenestra (requested lateral views are on the way, I am told). An absent antorbital fenestra is the reason why choristoderes have been difficult to nest in the reptile family tree. In the large reptile tree I simply popped in the traits and let the software recover the nesting. And it all makes sense. Note the resemblance of tiny BPI 2871 to the much larger Chanaresuchus, a related taxon. Like ancestral proterosuchids, BPI 2871 retains an overhanging snout and a shorter mandible. This specimen also retains postparietals.

Phylogenetic miniaturization
We keep meeting phylogenetic miniaturization at the base of novel clades and the same holds true for BPI 2871 and the Choristodera. Predecessor and successor taxa are both much larger.

Doswellia
and a rather large specimen of Proterosuchus (SAM PK-K 10603, early to Middle Triassic) also nest at the base of the Choristodera. Both retain an antorbital fenestra, rather feeble in the case of Doswellia (late Triassic).

Phylogeny
With all the new data BPI 2871 shifted one node over toward the choristoderes. This proves that inaccurate data, in the form of a simple drawing (Fig. 1), can still carry a large amount of data, that in this case, rather accurately places this taxon on the large reptile tree. More data refines that nesting.

References
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.

wiki/Youngina
wiki/Choristodera

 

 

Adelosaurus: transitional between Claudiosaurus and Atopodentatus

Another roadkill fossil gets nested
Adelosaurus huxleyi (Hancock and Howse 1870, Evans 1988, Figs. 1, 2) was originally considered to be a small protorosaur distinct from Protorosaurus (Watson 1914). It is the poster child for roadkill fossils, spread out on a plate and lacking a skull. Evans (1988) reported, “In the absence of the skull and ankle, classification remains tentative. The skeleton seems immature.” Otherwise there’s not much out there on Adelosaurus.

Phylogenetic analysis brings new insight
as Adelosaurus now nests between Claudiosaurus germaini (Carroll 1981, Late Permian) and the odd new kid on the block (not known to anyone before last year), Atopodentataus unicus (Cheng et al. 2014, early Middle Triassic).

Figure 1. Adelosaurus, a genuine roadkill fossil from the Late Permian together with a reconstruction of same. Note the dorsal expansion of the clavicle, and the robust scapulocoracoid.

Figure 1. Adelosaurus, a genuine roadkill fossil from the Late Permian together with a reconstruction of same. Note the dorsal expansion of the clavicle, and the robust scapulocoracoid.

The first step in understanding any roadkill, even if the only data is a crude drawing, is to rearrange the parts into its in vivo position, realizing that mistakes can be corrected later, following Steve Jobs guidelines.

Figure 2. Adelosaurus (middle) nests between Claudiosaurus (top) and Atopodentatus (bottom), all at the base of the Enaliosauria. Click to enlarge.

Figure 2. Adelosaurus (middle) nests between Claudiosaurus (top) and Atopodentatus (bottom), all at the base of the Enaliosauria. Click to enlarge.

Adelosaurus has a pectoral girdle, manus and carpus nearly identical to those of Claudiosaurus (Fig. 2). Digit 4 of the manus lacks two phalanges, unlike Claudiosaurus, but that’s an odd trait found  in Atopodentatus. The clavicle of Adelosaurus is interesting. Evidently it doesn’t have a broad medial portion. No sister taxa do either. That’s the dorsal portion, nearly identical to those odd clavicles in an Atopodentatus sister, Largocephalosaurus. Atopodentatus has standard straight clavicles, or so it appears. Adelosaurus is also the most basal taxon with a curved humerus, an enaliosaur trait.

Ultimately Adelosaurus is the ‘small plain brown sparrow’ from which all the odd and wonderful variations within the Enaliosauria appear. So it needs to appear in all future phylogenetic studies that employ member clades.

References
Cheng L, Chen XH,Shang QH and Wu XC 2014. A new marine reptile from the Triassic of China, with a highly specialized feeding adaptation. Natur
Carroll RL 1981. Plesiosaur ancestors from the Upper Permian of Madagascar. Philosophical Transactions of the Royal Society London B 293: 315-383.
Currie PJ 1981. Hovasaurus bolei, an aquatic eosuchian from the Upper Permian of Madagascar. Palaeontologica Africana, 24: 99-163.
Evans 1988. The Upper Permian reptile Adelosaurus from Durham. Palaeontology 31(4): 957-964. online pdf
Hancock A and Howse R 1870. On Protorosaurus speneri von Meyer, and a new species, Protorosaurus huxleyi, from the Marl Slate of Middridge, Durham. Quarterly Journal of the geological Society of London 26, 565-572.
Watson DMS 1914. Broomia perplexa gen. et. sp. nov., a fossil reptile from South Africa. Proceedings of the Zoological Society, London 1914:995-1010

 

wiki/Claudiosaurus

Leptosaurus: another transitional taxon between Rhynchocephalia and Rhynchosauria

Leptosaurus, a very small rhynchoceplian basal to Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Azendohsaurus, Mesosuchus and rhynchosaurs on the other. Teeth are not fused to the jaws. Astragalus not fused to the calcaneum. Note the very tiny pectoral girdle. Preserved in ventrolateral view, the nares are not visible, so perhaps they were dorsal as in rhynchosaurs.

Leptosaurus, a very small rhynchoceplian basal to Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Mesosuchus and rhynchosaurs on the other. Teeth are not fused to the jaws. Astragalus not fused to the calcaneum. Note the very tiny pectoral girdle. Preserved in ventrolateral view, the nares are not visible, so perhaps they were dorsal as in rhynchosaurs.

Leptosaurus pulchellus (Fitzinger 1837, Zittel 1887, Renesto and Viohl 1997; aka: Kallimodon Cocude & Michel, 1963) SCHA 40 Late Jurassic, Tithonian Stage, Germany,
155.7 to 150.8 Ma.

Holotype: Leptosaurus neptunicus Fitzinger 1837.

Rhynchocephalians are generally not so small, but this one is, likely yet another case of miniaturization at the base or transition to a major clade. In this case the SCHA 40 specimen attributed to Leptosaurus (I haven’t seen the holotype) is basal to the much larger Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Mesosuchus. Priosphenodon and rhynchosaurs on the other.

The large reptile tree (still not updated) keeps adding transitional taxa without changing the tree topology. That’s a measure of its strength. And more taxa using the same number of characters keeps dropping that character/taxon ratio.

References
Renesto S and Viohl G 1997. A sphenodontid (Reptilia, Diapsida) from the late Kimmeridgian of Schamhaupten (Southern Franconian Alb, Bavaria, Germany). Archaeopteryx 15:27-46.