Bat carpus (wrist) issues

The bat wrist (carpus)
is interesting. And I’d like to know more about it than I do.

Figure 1. Bat carpus compared to that of the basal bat Onychonycteris, and two other mammals, Home and Ptilocercus.

Figure 1. Bat carpus compared to that of the basal bat Onychonycteris, and two other mammals, Home and Ptilocercus. The pink bone is the pisiform. Some carpals appear to fuse in certain taxa. Note that in Homo and Ptilocercus the carpals are locked together, but rotate as a unit proximally. That is not the case with bats, which appear to have mobility within the carpals, not at the proximal articulation with the radius and ulna. On Onychonycteris digit 1 is preserved below the other digits and so is hidden in this graphic.

The wrist bones 
of Homo and Ptilocercus are pretty well locked in as a unit, but a sliding joint permits movement (rotation in two axes) at the radius and ulna.

Bats appear to be different,
perhaps due to their ability of completely fold their hands (wings) against their antebrachia (radius + ulna or forearm), in the manner of birds and pterosaurs, in the plane of the wing.  Above (Fig. 1) I have attempted to identify homologous bones. Please advise if any mistakes were made.

In the basal bat,
Onychonycteris, the carpal bones were not locked into place. This could be a taphonomic issue with elements drifting. Or perhaps it represents an early stage in bat carpus evolution. Or both.

In the only bat carpus illustration
I could find (genus unknown), the proximal carpals appear to be fixed to the ulna and radius. The distal carpal elements appear to be loose. The metacarpals appear to overlap like Japanese fan struts. I don’t see the same proximal metacarpal expansion in the basal bat Onychonycteris.

Since bat wing claws are still present
on all of the fingers of Onychonycteris and with wrist rotation in the plane of the wing, the claws would still have been oriented toward the palmar side and thus could be used. Or if not used, this orientation of the fingers and claws provides clues to those of ancestral bats with smaller hands not yet used for flying that might have been likewise rotated 180 degrees while oriented ventrally on tree trunks and other vertical substrates.

Too bad we have no postcrania of Protictis.

I have asked for,
but have not yet received, the pdf for Greene 2005 listed below. I’m sure there will be more to say on this subject when that pdf comes in.

References
Greene WE Jr. 2005. The development of the carpal bones in the bat. Journal of Morphology 89(3):409-422. Article first published online: 6 FEB 2005 DOI: 10.1002/jmor.1050890303

 

Synapsid evolution – then and now

With the addition of more taxa,
the lineage of synapsids (including mammals) is filling up nicely — and a little differently than what was once thought. In 1982 TS Kemp produced this image (Fig. 1).

Figure 1. Synapsid evolution according to TS Kemp 1982.

Figure 1. Synapsid evolution according to TS Kemp 1982.

The large reptile tree confirms many of these nestings, adds a few taxa, and subtracts Casea, which now nests with Milleretta and kin (Fig. 2).

Figure 2. The TS Kemp figure modified to reflect changes recovered by the large reptile tree. Casea is removed. It is not related to the rest of these taxa but nests with Milleretta. Therapsids appeared near the Haptodus node with Cutleria. Therapsids thereafter split into anomodonts and the rest of the clade.

Figure 2. The TS Kemp figure modified to reflect changes recovered by the large reptile tree. Casea is removed. It is not related to the rest of these taxa but nests with Milleretta. Therapsids appeared near the Haptodus node with Cutleria. Therapsids thereafter split into anomodonts and the rest of the clade.

Every cladogram
is built, more or less, from past efforts. Sometimes this can be a problem when the root cladogram has unrecognized problems.

Kemp (1982) produced his family tree (Fig. 1) without the aid of phylogenetic software and prior to the discovery of several key taxa.  He was building on past work by Romer and Price (1940) and others before them. The large reptile tree also builds upon early work.

More links for synapsid family trees at reptileevolution.com here, here, and here.

References
Kemp TS 1982. Mammal-Like Reptiles and the Origin of Mammals.  Academic Press: London. 363 pp.
Romer AS and Price LW 1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.

Origin of bats 2

One of the most popular blogposts here, year after year, has been the post on bat origins back in 2011. Nothing has changed since then except for the fact that I have added a few bats and kin to the large reptile tree (Fig. 1, subset).

Figure 1. A few bats and kin have been added to the large reptile tree. Surprisingly enough traits are present to resolve their relationships without getting into too many dental traits.

Figure 1. A few bats and kin have been added to the large reptile tree. Surprisingly enough traits are present to resolve their relationships without getting into too many dental traits.

And here (Fig. 2), for good measure are Chriacus and Onychonycteris, a bat ancestor candidate and a basal bat respectively, according to the large reptile tree.

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 nests as a sister to the undiscovered bat ancestor. Onychonycteris was 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. Click to enlarge.

 

Phylogenetic miniaturization contributed to bat origins. The teeth became better adapted to insect eating. The larger scapulae and clavicles anchored larger muscles. The ulna became reduced relative to the radius and fused to it. The hands became enlarged. Membranes spanned the forelimbs and hind limbs. This is the only flapper that did not have an obvious bipedal phase.

It is still a mystery what evolutionary events spanned these two taxa. All we have is Protictis (Fig. 3) a taxon known form skulls and teeth. The rest has to be imagined.

Bat ancestor

Figure 1. Bat Ancestor Protictis, known from three skulls/teeth of varying sizes. 

 

A re-reconstruction of Rauisuchus

A recent paper by Lautenschlager and Rauhut (2015) provided a reconstruction (Fig. 1)of the first known rauisuchid, Rauisuchus (von Huene 1942). I thought they provided it with something of a roller-coaster backbone, unlike that of more completely known rauisuchians. So, I moved the bones around on top of an established skeleton of Saurosuchus, which is another closely related rauisuchian of the same size (Fig. 1). Just a hypothesis based on a bauplan.

Figure 1. Rauisuchus reconstructed according to the baulplan of Saurosuchus (above) and as originally reconstructed (below).

Figure 1. Rauisuchus reconstructed according to the baulplan of Saurosuchus (above) and as originally reconstructed (below). Click to enlarge

Otherwise the paper is quite good with excellent photos.

References
Lautenschlager S and Rauhut OWM 2015. Osteology of Rauisuchus tiradentes from the Late Triassic (Carnian) Santa Maria Formation of Brazil, and its implications for rauisuchid anatomy and phylogeny. Zoological Journal of the Linnean Society 173:55-91.
von Huene F 1942. Die fossilen Reptilien des südamerikanischen Gondwanalandes. Ergebnisse der Sauriergrabung in Südbrasilien 1928/29. München: C.H. Beck’sche Verlagsbuchhandlung.

Subset cladogram of extant taxa only

The large reptile tree is anchored on about 450 extinct taxa. However, more than a few (39) extant taxa are now included. Today we’ll simply delete all the extinct taxa and see what sort of tree we recover. This will demonstrate what changes to the tree topology occur without extinct taxa, and note how parts of it kind of resemble the latest DNA studies.

Figure 1. Cladogram of extant taxa, a subset of the large reptile tree that does not quite retain the original topology.Here turtles nest with archosaurs (in the absence of about 450 other taxa.

Figure 1. Cladogram of extant taxa, a subset of the large reptile tree that does not quite retain the original topology.Here turtles nest with archosaurs (in the absence of about 450 other taxa. Loss of resolution here is due to taxon exclusion. For instance, without Megazostrodon, the mammals lack resolution.

Rana the frog nests at the base, perhaps because it is now listed first among the taxa. Or perhaps because it is indeed primitive. Not sure, but if there are no objections?

There is loss of resolution
at the base of the Amniota, where three clades branch off: 1) mammals, 2) turtles and archosaurs and 3) lepidosaurs. This largely matches certain DNA studies, by the way, that nest turtles with archosaurs. Interesting solution to that old problem…

Within the Lepidosauromorpha (sans the turtles)
the clades largely match the large reptile tree. Sphenodontians split from Squamates and Iguania branches off from Scerloglossa thereafter.

Here (Fig. 1) the geckos are separated from the snakes. Instead, amphisbaenids nest with snakes. These ‘odd bedfellows’ appear due to taxon exclusion and loss of limbs.

Here 510 total taxa are reduced to 39, an exclusion of 92 percent. Like other smaller, more focused studies, this one demonstrates the problems they have and, by inference, the value of adding prehistoric taxa. That’s where the transitions are to be found.

The original tree topology is not quite retained.
Turtles transfer from lepidosauromorphs to archosauromorphs. The legless taxa nest together. This tree also nearly echoes DNA studies that have mammals branching off first in the absence of about a dozen taxa that precede synapsids in the large reptile tree.

Word of Warning
No one in their right mind would ever consider turtles the sister taxon to birds and crocs… Yet here they are. Sisterhood varies based on taxon inclusion. This situation is analogous to those that nest pterosaurs with archosaurs and archosauriformes and other such odd nestings.

By the way
I made comments to the recent Reeder et al. morphology + molecules study of squamates here. In short they did not include enough extinct taxa and did not recognize the large number of lepidosaurs that nest between Sphenodontia and Squamata, some of which nest as proximal basal taxa to the Squamata. Without them, the base of their tree did not have the correct roots and so the initial branching also suffered.

 

Nesting turtles with pterosaurs redux 2011-2015

For those who don’t read the ‘Letters to the Editor’,
a recent comment on sister taxa inspired me to revisit the old experiment that nested pterosaurs and turtles together as a result of taxon exclusion, which you can review here.

By default nestings
can be interesting and silly. The point behind nesting pterosaurs with turtles back then was to examine the folly behind nesting pterosaurs with archosaurs — only possible due to a similar taxon exclusion that’s been going on for at least fifteen years now, following the publication of a phylogenetic analysis that nested pterosaurs with fenestrasaurs (Peters 2000) and has been ignored ever since.

Back in the day (July 2011) with 360 taxa,
when all other taxa were removed from the lepidosauromorph side of the large reptile treeProganochelys, the turtle, nested with MPUM6009, the pterosaur at the base of the Sauropterygia. That’s bizarre, but interesting and hopefully enlightening by analogy to the achosaur-link question.

Today,with 508 taxa,
and deleting all other lepidosauromorphs, the pterosaur now nests between Cathayornis and Struthio, the ostrich, + Gallus, the chicken. The turtle now nests with the frogs, between Doleserpeton and Gerobatrachus + Rana.

Hmm. Let’s fix that.
Let’s delete the amphibians and add the basal lizard Huehuecuetzpalli and guess what happens?

The three lepidosauromorphs:
the turtle, the lizard and the pterosaur, all nest together again in their own clade at the base of the Sauropterygia… in other words, nowhere near dinos, pre-dinos, parasuchians, Lagerpeton or Marasuchus. Delete Huehuecuetzpalli and Proganochelys nests with the turtle-like placodont, Henodus, as you might imagine, while the basal pterosaur bounces back to the birds. So one taxon in-between the turtle and pterosaur were needed this time to glue them together in a single clade and to trump the attraction of other candidate sisters.

Bottom line:
by including more and more taxa the large reptile tree provides more and more nesting sites, and thus the large reptile tree minimizes unwanted ‘by default’ nestings. Up to now other workers have been relying an tradition and paradigm for their taxon lists, and many of those traditions have been tested (and falsified) at reptileevolution.com. When workers base their smaller, more focused studies on a larger umbrella study, they will have greater success and greater confidence that their cladogram is a good one = with no ‘by default’ nestings.

At the nothosaur/plesiosaur node

A cover story and rapid communication in the latest Journal of Vertebrate Paleontology features Wangosaurus (Ma et al. 2015, Fig. 1), a long-necked, short-faced sauropterygian with short fingers and toes.

[Unfortunately, Wangosaurus in the urban dictionary is “a complete jackass.”] But let’s concentrate on the fossil, which is virtually complete and wonderfully preserved.

Figure 1. Wangosaurus. Click to enlarge.

Figure 1. Wangosaurus. Click to enlarge. Note the short fingers and toes.

Sister taxa
In the Ma et al paper, Wangosaurus nested as a sister Yungisaurus (Figs. 2, 3) and both were considered pistosaurids, the clade transitional between nothosaurs and plesiosaurs, despite their morphological differences.

Figure 2. The Ma et al. tree that nested Wangosaurus with Yungisaurus as a pistosaurid. Colors were added. Yellow = enaliosauria in the large reptile tree. Blue = protorosaurs + archosauriformes. Pink = lepidosauromorphs.

Figure 2. The Ma et al. tree that nested Wangosaurus with Yungisaurus as a pistosaurid. Colors were added. Yellow = enaliosauria in the large reptile tree. Blue = protorosaurs + archosauriformes. Pink = lepidosauromorphs.

In the large reptile tree (subset Fig. 4), Yungisaurus also nests between Pistosaurus and Plesiosaurus, but Wangosaurus nests in a much more basal node, between nothosaurs and Simosaurus, still close to the nesting in the Ma et al. paper (Fig. 2).

Figure 3. Yungisaurus in situ and closeups of the skull and flippers.

Figure 3. Yungisaurus in situ and closeups of the skull and flippers. This is a much larger sauropterygian with longer toes transformed into flippers. Interesting to see the rear flippers larger than the forelimbs. So does that tell us something about their swimming technique?  

The Ma et al. tree is based on earlier work by Jiang et al. (2014 – featuring the basal placodont Majianshanosaurus), which is an updated version of Neenan et al. (2013). Note the differences in the skulls of Wangosaurus and Yungisaurus. Those don’t look like close relatives to me and their scores confirm those suspicions.

 

Figure 4. The enaliosaur/marine reptile subset of the large reptile tree. Note there are intervening taxa here between Wangosaurus and Youngisaurus.

Figure 4. The enaliosaur/marine reptile subset of the large reptile tree. Note there are intervening taxa here between Wangosaurus and Youngisaurus.

The Ma et al. tree employs suprageneric taxa (always a problem). You’ll note that turtles and lepidosauriformes are the proximal outgroup taxa to sauropterygians here. That is not supported by the large reptile tree. I also find it odd that the marine reptiles Claudiosaurus and Hovasaurus nest so far from the rest of their natural clade in the Ma et al. tree, and separate from one another.

References
Cheng Y-N,  Sato T, Wu X-C and Li C 2006. First complete pistosaurid from the Triassic of China. Journal of Vertebrate Paleontology 6(2):501-504.
Ma L-T, Jiang D-Y, Rieppel O, Motani R and Tintori A 2015.
A new pistosaurid (Reptilia, Sauropterygia) from the late Landinian Xingyi marine reptile level, southwestern China. Journal of Vertebrate Paleontology 35(1): e881832.