Aquatic enoplid nematodes: ancestral to hagfish AND common slugs

Earlier we looked at the many homologies that unite
primitive round worms (= aquatic enoplid nematodes, Fig. 1), with primitive chordates (=  hagfish. Fig. 1).

Now let’s look at overlooked evidence
that unites nematodes and hagfish with… primitive molluscs (= slugs, Figs. 1, 2).

Largely (but not completely) overlooked until now,
nematodes (= amphistomes) could have given rise to both hagfish (chordates, deuterostomes) and slugs (molluscs, protostomes). These three taxa are all long, worm-like, bilaterals with sensory tentacles, rasping retreating mouth parts, and for one reason or another depend on producing slime from their skin.

I say ‘not completely overlooked’
because Clark and Uyeno 2019 portrayed cutaway diagrams of a slug and hagfish to show their ‘convergent’ mouth parts.

Figure 1. Nematodes, hagfish and slugs have so many traits in common, one wonders why they are not related to one another.

Figure 1. Nematodes, hagfish and slugs have so many traits in common, one wonders why they are not related to one another.

With that short list, I could be accused
of “Pulling a Larry Martin” by listing only a few traits. The fact is, these simple, soft-bodied taxa only have a few traits, and they still share these few traits 600 million years after their last common ancestor in the Ediacaran.

Figure 2. A selection of slugs (basal molluscs) to scale.

Figure 2. A selection of slugs (basal molluscs) to scale. Compare to hagfish in figure 1.

Tiny nematodes wriggle through and eat whatever falls on the sea floor.
Slugs slide over and eat whatever falls on the sea floor. Hagfish swim above and eat whatever falls on the sea floor. In the Ediacaran the only food source was the planktonic seafloor and its tiny burrowing and crawling inhabitants.

Side note: Chaetognaths (arrow worms)
(Fig. 3) document yet another clade of swimming nematode descendants with hard mouth parts and fins that evolved by convergence with those of chordates. Notably, on vertically undulating chaetognaths swimming fins appear on the lateral surfaces, distinct from horizontally undulating chordates with vertical fins. Yes, it’s that simple.

Figure 3. Chaetognath (arrow worm) diagram. Note the lateral fins and lateral caudal fin together with the grasping mouth parts.

Figure 3. Chaetognath (arrow worm) diagram. Note the lateral fins and lateral caudal fin together with the grasping mouth parts.

One reference
(Barnes 1980) considered arrow worms deuterostomes. Wikipedia labeled them protostomes, but reported, “Chaetognaths are traditionally classed as deuterostomes by embryologists. Molecular phylogenists, however, consider them to be protostomes. Thomas Cavalier-Smith places them in the protostomes in his Six Kingdom classification. The similarities between chaetognaths and nematodes mentioned above may support the protostome thesis.”

We’ve already seen that nematodes are amphistomes and that gene studies too often recover false positives. So let’s consider those gene studies unreliable. As noted above, visual examination shows chaetognaths to be deuterostomes, whether by convergence or homology.

Try Googling ‘hagfish + slugs’
and you won’t find any prior discussions of this interrelationship in the online academic literature. Any mention of worm-like ancestors for hagfish or any mention of nematode ancestors for molluscs are also rare to absent in the online literature.

Distinct from annelids, arthropods and any other segmented animals,
chordates and molluscs have no body segments.

Traditionally the most primitive mollusc
is the chiton (with eight separate plates of armor) or the heliconelid (with a slightly spiral-shaped shell).

However,
if you start with a flatworm (Platyhelminthes), as you must… then a ribbon worm (Nemertea), as you must… then a round worm (Nematoida), as you must… you’re looking for only minor adjustments to the basic worm shape in both descendants: hagfish and slugs. In this scenario hard mollusc shells are derived traits that evolve after the slug morphology was established. Thus, contra academic tradition naked slugs represent the basal condition in molluscs. They didn’t lose their shells. Slugs never had shells. Those evolved later.

Figure 5. From Peters 1991 a diagram splitting deuterostomates from protostomates.

Figure 4. From Peters 1991 a diagram splitting deuterostomates from protostomates. Now this has to be updated by putting molluscs closer to chordates and nematodes.

Traditional invertebrate clades:

  1. Bilateria (Flatworms, single digestive opening)
  2. Amphistomia (aquatic nematodes, anus and mouth at the same time)
    1. Protostomia (anus first, mouth second)
      1. Ecdysozoa (segmented invertebrates, tardigrades, arthropods)
      2. Lophotrochozoa (molluscs, annelid worms)
    2. Deuterostomia (mouth first, anus second)
      1. Chordata (hagfish, lancelets, craniates)
      2. Xenambulacraria (hemichordates, echinoderms)

Comment: Annelids should nest with arthropods. Both are elongate and segmented. Velvet worms (Onychophora) are transitional taxa.

Comment: Molluscs are  not segmented. Basal forms (slugs) have sensory tentacles and rasping eversible radula, as in nematodes and hagfish.

Revised invertebrate clades:

  1. Bilateria (Flatworms, single digestive opening)
  2. Amphistomia (aquatic nematodes, anus and mouth at the same time)
    1. Protostomia (anus first, mouth second)
      1. Segmented invertebrates (tardigrades, annelid worms, arthropods)
    2. Deuterostomia (mouth first, anus second)
      1. Chordata (hagfish, lancelets, craniates)
      2. Xenambulacraria (hemichordates, echinoderms)
      3. Chaetognatha (arrow worms) or direct from Amphistomia
    3. Lophotrochozoa (molluscs, with protostome embryos convergent with segmented invertebrates)

Chitin vs. keratin
Chordates have keratin teeth. Molluscs have chitin teeth. Wikipedia reports, “The structure of chitin is comparable to another polysaccharide, cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein keratin. The only other biological matter known to approximate the toughness of keratinized tissue is chitin.”

Chordates and molluscs had a last common ancestor 600 million years ago. Numerous references discuss nematode ‘teeth’, but do not describe them as either chitinous or keratinous. So I don’t know which is the more primitive substance.

This is not the first time that professional systematists
have left ‘low hanging fruit‘ for amateurs to pluck from a long list of traditionally overlooked, ignored and enigma interrelationships. Putting taxa together that have never been put together before is what we should all do to understand our world better. Every so-called enigma taxon is the result of Darwinian evolution and thus did not and can not stand alone. Relatives are out there for all the oddballs. It’s our job to find them.

The hagfish-nematode-slug relationship seems to be a novel hypothesis
of interrelationships. If not, please send a valid citation so I can promote it.

PostScript:
I found this YouTube video of velvet worms, arthropods, Hallucigenia (shown on the screen shot) and other segmented worm-like members of Protostomia. Seems velvet worms also have sensory tentacles and eversible teeth made of chitin (close to keratiin) and spray mucous slime from glands on the side of their head. There’s a deep connection with nematodes here as well.


References
Barnes RD 1980. Invertebrate Zoology 4th ed. Saunders College, Philadelphia 1–1089.
Clark AJ and Uyeno TA 2019. Feeding in jawless fishes. In: Bels V., Whishaw I. (eds) Feeding in Vertebrates. Fascinating Life Sciences. Springer, Cham.
https://doi.org/10.1007/978-3-030-13739-7_7
Peters D 1991. From the Beginning – The story of human evolution. Wm Morrow.

For more informationm:
wiki/Nematode
wiki/Mollusca
wiki/Evolution_of_molluscs
wiki/Chordate
wiki/Hagfish
wiki/Bilateria
wiki/Annelid
wiki/Chiton
wiki/Helcionellid
wiki/Onychophora
wiki/Chaetognatha
wiki/Lophotrochozoa

2020 study on osteostracan swimming omits 1999 study on sturgeon swimming

Osteostracans are primitive and extinct jawless fish
that evolved a variety of head shields (Fig. 1). Some of these head shield shapes were tested for their hydrodynamic properties by Ferrón et al. 2020.

Figure 1. Hemicyclaspis and a variety of other osteostracans in dorsal view created by Ferrón et al. 2020 to test their hydrodynamics.

Figure 1. Hemicyclaspis and a variety of other osteostracans in dorsal view digitally created by Ferrón et al. 2020 to test their hydrodynamics.

In brief:
“Ferron et al. show, using computational fluid dynamics, that early jawless vertebrates were ecologically diversified and had complex hydrodynamic adaptations. These findings challenge the traditional scenario of jaws as the key evolutionary innovation that precipitated the ecological diversification of our ancestors.”

Not according to the large reptile tree (LRT, 1741+ taxa; subset Fig. x). That diversification followed the genesis of jaws and pelvic fins (Chondrosteus (Fig. 4) and descendants, (Fig. 1) and accelerated with the genesis of marginal teeth (Polyodon  and descendants, Figs. 5).

Figure x. Subset of the LRT focusing on fish.

Figure x. Subset of the LRT focusing on fish.

Ferron et al. report, 
“the extinct jawless ‘‘ostracoderms’’ are interpreted as cumbersome deposit feeders lacking key apomorphies of jawed vertebrates including multiple pairs of appendages and an epicercal tail, as well as jaws. This popular scenario belies the challenge of constraining the biology of ostracoderms that lack living analogs, traditionally compromising attempts to derive functional interpretations of their morphology.”

Accoding to the LRT (Fig. x) ostracoderms have living homologs (and analogs), sturgeons (Figs. 2, 3), a clade of extant fish omitted by Ferrón et al. 2020. Traditionally sturgeons are considered much more derived ray-fin fish, not living osteostracans. Taxon exclusion, like this, is a common problem in paleontology.

Figure 1. Top to bottom: Thelodus a soft jawless fish with a ventral oral opening and gill slits, perhaps a hint of diamond-shaped armor laterally. Hemicyclaspis, adds extensive armor. Acipenser, a sturgeon with a protrusible tube for a mouth and reduced armor.

Figure 2. Top to bottom: Thelodus a soft jawless fish with a ventral oral opening and gill slits, perhaps a hint of diamond-shaped armor laterally. Hemicyclaspis, adds extensive armor. Acipenser, a sturgeon with a protrusible tube for a mouth and reduced armor homologous with that of the osteostracan, Hemicyclaspis.

Ferron et al. report,
“We analyzed the functional morphological diversity of the Silurian-Devonian Osteostraci, the jawless sister group to all jawed vertebrates, which cover all the morphological grades exhibited by ostracoderms, including forms that entirely lack paired appendages and others that possess just a single (pectoral) pair.”

Due to taxon exclusion,
Ferrón et al. wrote: “These results suggest different hydrofoil functions among osteostracan headshield morphologies, compatible with ecological diversification and undermining the traditional view that jawless stem-gnathostomes were ecologically constrained with the origin of jaws as the key innovation that precipitated the ecological diversification of the group.”

Ferron et al. did not realize that 
living sturgeons are derived ostracoderms and stem gnathostomes, according to the LRT. Sturgeons also come in a variety of sizes and shapes. Rather than creating computer graphics of osteostracoderms alone, the Ferron team could have started with actual sturgeons in actual water over actual lake beds… or cited Wilga and Lauder 1999 (Fig. 3).

Figure 2. Sturgeon swimming in a test tank from Wilga and Lauder 1999.

Figure 3. Sturgeon swimming in a test tank from Wilga and Lauder 1999. Note pectoral fin in middle image has posterior edge elevated.

According to the LRT,
(subset Fig. x) ostracoderms are sturgeon ancestors. Sturgeons gave rise to jawed fish (gnathostomes) like Chondrosteus (Fig. 4) and THAT’s where the present diversity of fishes arises.

Wilga and Lauder 1999 reported,
“In the plesiomorphic pectoral fin condition, exemplified by sturgeon, pectoral fins extend laterally from the body in a generally horizontalorientation, have been assumed to generate lift to balance lift forces and moments produced by the heterocercal tail, and are not oscillated to generate propulsive force. Three-dimensional kinematic analysis showed that during steady horizontal swimming the pectoral fins are oriented with a negative angle of attack predicted to generate no significant lift.”

But note (Fig. 3) the entire sturgeon is a lifting body with a flat underside and convex dorsal surface. So the negative angle of attack of the pectoral fins balances the natural hydrodynamic lifting forces. Note the similar overall  body shapes of sturgeons and the osteostracn, Hemicyclaspis (Figs. 1, 2), along with similar pectoral fins capable of rising posteriorly, like airplane elevators (fgi. 3).

Wilga and Lauder 1999 continue:
“The orientation of the pectoral fins estimated by a two-dimensional analysis alone is greatly in error and may have contributed to previous suggestions that the pectoral fins are oriented to generate lift.”

See:But note” above. Same answer here.

Re: osteostracoderms Ferrón et al. reported:
“Combined electromyographic and kinematic data showed that the posterior half of the pectoral fin is actively moved as a flap to reorient the head and body to initiate rising and sinking movements.”

As shown by Wilga and Lauder (Fig. 3).

Ferrón et al. continue:
“During steady locomotion, the pectoral fins generate no lift and the positive body angle to the flow is used both to generate lift and to balance moments around the center of mass.”

As shown by Wilga and Lauder (Fig. 3).

Ferrón et al. continue:
“To initiate rising or sinking, the posterior portion of the pectoral fins is actively moved ventrally or dorsally, respectively, initiating a starting vortex that, in turn, induces a pitching moment reorienting the body in the flow to body angle initiated by the pectoral fins serve as the primary means by which moments are balanced.”

As shown earlier by Wilga and Lauder (Fig. 3). Wilga and Laude 1999 were not cited by Ferrón et al. 2020. Chondrosteus is also missing,

Not only did Chondrosteus have real jaws (still without teeth),
the rostrum was raised from ventral to middle, making it more of a bullet shape with a more circular cross-section with a narrower transversely rounder belly). These traits helped make Chondrosteus a better open water swimmer, like many living sharks and paddlefish, freeing it from seeking buried prey. Chondrosteus (Fig. 4) also increases the size of the pelvic fins for added hydrodynamic control and the lower lobe of the caudal fin was larger, more like the heterocercal upper lobe (Fig. 2).  These traits continue in the paddlefish, Polyodon (Fig. 5).

Figure 1. Chondrosteus animation (2 frames) in situ and reconstructed in lateral view. This is the transitional taxon linking sturgeons to bony fish + sharks.

Figure 4. Chondrosteus animation (2 frames) in situ and reconstructed in lateral view. This is the transitional taxon linking sturgeons to bony fish + sharks.

Figure 4. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo.

Figure 5. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo. Note the large size of the pelvic fins.

Chondrosteus descendants
like Loganellia, Manta and Rhincodon (Fig. 6), returned to a flattend skull and body shape, but with an anterior toothless mouth and an open-water swimming pattern.

Figure 11.  Manta compared to Thelodus (Loganellia) and Rhincodon. All three have a terminal mouth essentially straight across, between the lateral eyes, distinct from most fish. Note the lack of teeth. 

Figure 6.  Manta compared to Thelodus (Loganellia) and Rhincodon. All three have a terminal mouth essentially straight across, between the lateral eyes, distinct from most fish. Note the lack of teeth.

Other Chondrosteus descendants
include free-swimming, circular, cross-section, predatory Gregorius and its descendants, the bony fish. This clade splits from similar free-swimming, circular, cross-section Hybodus and its descendants, the cartilaginous fish (sharks + ratfish). Thereafter both clades produced some bottom dweller feeders with flattened ventral surfaces ( e.g. sawfish, Panderichthys). These taxa can be considered reversals.


References
Ferrón HG, Martinez-Perez C, Rahman IA, Selles de Lucas V, Botella H and Donoghue PCJ 2020. Computational Fluid Dynamics Suggests Ecological Diversification among Stem-Gnathostomes. Current Biology 30:1–6.
Wilga CD and Lauder GV 1999. Locomotion in sturgeon: Function of the pectoral fins. The Journal of Experimental Biology 202, 2413–2432.

wiki/Sturgeon
wiki/Osteostraci

Publicity

Mud-slurping chinless ancestors had all the moves

Olympian Michael Phelps and the aquatic ape hypothesis

According to Wikipedia (abridged)
“The aquatic ape hypothesis (AAH) is the idea that the ancestors of modern humans were more aquatic. The hypothesis in its present form was proposed in 1960 by Alister Hardy. Though ignored or derided by the majority of workers, a few suggest in the last five million years humans became dependent on essential fatty acids and iodine, which are found in abundance in sea resources. Efficient function of the human brain requires these nutrients. The “aquatic ape” proposal is more popular with the lay public than with scientists.”

FIgure 1. Michael Phelps, gold medal winner in Olympic swimming, compared to Ardipithecus skeleton.

FIgure 1. GIF movie of Michael Phelps, gold medal winner in Olympic swimming, compared to Ardipithecus skeleton, not to scale.

We don’t have the nasal bones
for Ardipithecus. So it is possible that they were not flat, but arched, as in humans. And in humans, the ventral opening of the nostrils prevents water from entering the air passage whenever underwater.

Figure 4. Ardipithecus is a transitional taxon between Pronconsul and Homo.

Figure 4. Ardipithecus is a transitional taxon between Pronconsul and Homo. We don’t have the nasal bones for Ardipithecus (in gray), so they could have arched to create a protruding nose with ventral nostrils.

Hardy argued aquatic adaptations in humans include:

  1. lack of body hair
  2. subcutaneous fat (but captive apes have levels similar to humans.
  3. location of the trachea in the throat rather than the nasal cavity
  4. the human propensity for front-facing copulation
  5. tears and eccrine sweating
  6. bipedalism as an aid to wading
  7. tool use evolved out of the use of rocks to crack open shellfish
  8. selection for wading, swimming and diving in procurement of aquatic food distinct from the jungle niche leading to chimps.

So what does Olympian Michael Phillips have to do with Ardipithecus?

  1. Both have a wider ‘wingspan’ than height.
  2. Both have a long trunk and relatively short legs.

Admittedly,
this is just ‘cocktail-chatter,’ and will probably always be ‘cocktail-chatter.’

FIgure 2. Primate cladogram with the addition of Pan, Gorilla, Ardipithecus and Indri. The topology of the LRT did not change with these additions.

FIgure 2. Primate cladogram with the addition of Aegyptopithecus, Pan, Gorilla, Ardipithecus and Indri. The topology of the LRT did not change with these additions.

The addition of the five primates, Indri, Aegyptopithecus, Pan, Gorilla and Ardipithecus to the large reptile tree (LRT, 1172 taxa, subset Fig. 2) recovers nothing controversial and does not change the LRT topology of the primates.

References
Hardy A 1960. Was Man More Aquatic in the Past? New Scientist 7(174):642–645.

wiki/Aquatic_ape_hypothesis

 

Added November 10, 2020
The following link to a Joe Rogan podcast

features author, Kermit Pattison talking for two hours about Ardipithecus in his book ‘Fossil Men: The Quest for Oldest Skeleton and the Origins of Humankind’.

Neoparadoxia swimming animation

The origin of the Mysticeti
Earlier we nested baleen whales with desmostylians like Neoparadoxia (Fig. 1; Barnes 2013). 

Figure 1. GIF animation of the Neoparadoxia (original image from Barnes 2013). It seems illogical that the tiny tail of a desmostylian like this would ever become the giant tail of a mysticete, while the giant hind limbs disappear into the torso, but phylogenetic analysis recovers just such a scenario. Many long-jawed desmostylians are known from cranial material only and these are likely to be those that had large tails and smaller hind limbs.

Figure 1. GIF animation of the Neoparadoxia (original image from Barnes 2013). It seems unlikely that the tiny tail of a desmostylian like this would ever become the giant tail of a mysticete, while the giant hind limbs disappear into the torso, but phylogenetic analysis recovers just such a scenario. Many long-jawed desmostylians are known from cranial material only and these are likely to be those that had large tails and smaller hind limbs.

Recovered by phylogenetic analysis
The large reptile tree (LRT 1040 taxa) nests desmostylians as proximal outgroups to the mysticetes. Mysticeti, like the gray whale Eschrichtius robustus (Fig. 2)have a large robust tail and no visible hind limbs. That’s just the opposite of what you find in what little we know of known desmostylians (Fig. 1). Noteworthy: we don’t know the tail length in several of the long-jawed desmostylians, the ones most like mysticetes. This is when you have to put away traditional biases and let the cladogram truly be your guide.

Figure 6. Eschrichtius-robustus, the gray whale is the most basal mysticete tested in the LRT with a skull similar to Desmotylus and Beheomotops.

Figure 2. Eschrichtius-robustus, the gray whale is the most basal mysticete tested in the LRT with a skull similar to Desmotylus and Beheomotops. The sacrals here are orange and the robust tail follows to the right. 

In similar fashion
pterosaur workers have been looking in vain for a long manus reptile as the proximal ancestor to the Pterosauria, overlooking taxa with small forelimbs like Cosesaurus, Sharovipteryx and LongisquamaAll this time, they did not realize the elongation of the forelimb elements to various degrees was the LAST transformation that occurred in the known outgroups to the Pterosauria (Peters 2002). You, too, will make discoveries like this when you put away traditional biases, expand your taxon list and let the cladogram be your guide.

As you might remember
the origin of the Odontoceti (toothed whales) started with swimming tenrecs like Leptictidium (Fig. 3) and its close relative Pakicetus, both with a very long tail and large feet.

Figure 1. Leptictidium is known as a hopper. Here it nests with whales. Combine the two and when Lepticitidium jumps in the water, it continues hopping. That long, long tail is homologous to the long, long tail in Zeuglodon.

Figure 1. Leptictidium is known as a hopper. Here it nests with whales. Combine the two and when Lepticitidium jumps in the water, it continues hopping. That long, long tail is homologous to the long, long tail in Zeuglodon.

References
Barnes LG 2013. A new genus and species of Late Miocene Paleoparadoxiid (Mammalia, Desmostylia) from California. Contributions in Science 521:51-114.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.

A living whale ancestor you can hold in the palm of your hand

I was as surprised to see this develop, as I’m sure you will be.
Adding the land whale Maiacetus inuus (Gingerich et al. 2009, Eocene ~47 mya, 2.6 m in length; Fig. 1) to the large reptile tree (Fig. 3) nested it at the base of the current Afrothere/herbivore clade along with the tenrec, Hemicentetes (Fig. 2). The resemblance is remarkable, despite the difference in size. And this sets the earliest origin of whales on a slightly different tangent with, I’m sure you’ll agree, much better support.

Figure 1. Maiacetus is a basal whale with legs and it is also a giant tenrec. Compare to Hemicentes in figure 2 and remember that another tenrec, Limnogale, has a long tail.

Figure 1. Maiacetus is a basal whale with legs and it is also a giant tenrec. Compare to Hemicentes in figure 2 and remember that another tenrec, Limnogale, has a long tail, webbed feet and a semiaquatic niche.

Tenrecs have been traditionally associated with
a list of mammals of African origin: golden moleselephant shrews,  aardvarks (Orycteropus), hyraxes (Procavia), elephants (Elephas), and sea cows, as they are here (Fig. 3) as well.

Whales have been traditionally associated with
artiodactyls, as they are here (Fig. 2) as well. The hippopotamus is considered their closest living relative based on DNA data. The present data appears to invalidate the hippo connection. We’ll see what happens when the hippo is added to the large reptile tree, but it does not look promising. Not sure if tenrecs were included in the whale DNA analysis study. If not, that was an oversight.

Figure 2. The short-tailed tenrec, Hemicentetes. Other than size and tail length, this taxon shares a long list of traits with the basal whale, Maiacetus in figure 1.

Figure 2. The short-tailed tenrec, Hemicentetes. Other than size and tail length, this taxon shares a long list of traits with the basal whale, Maiacetus in figure 1. This has not been recognized previously. Skeleton image used with permission from Digimorph.org.

The tenrec Hemicentetes
(Fig. 2) shares more traits with Maiacetus than any other taxon listed. And vice versa, of course. They nest as sisters.

Another very rare tenrec,
Limnogale (29-35cm) has a long thick tail, webbed feet and a semiaquatic lifetyle. That probably seals the deal. Limnogale is nocturnal, so it is using senses underwater we can only surmise from the whale relationship. This needs more study, but Limnogale is hard to catch! And it is very rare. Click here for an image and data on Limnogale. I want more data on that tenrec, but it has not been well studied or sent to digimorph.org yet.

Figure 3. The mammals updated with the addition of a basal whale, Maiacetus, and an aardvark Orycteropus.

Figure 3. The mammals updated with the addition of a basal whale, Maiacetus, and an aardvark Orycteropus.

While Limnogale has the 
wet look and aquatic niche we are looking for in a whale ancestor. another Madagascar tenrec, Hemicentetes has skeletal data (Fig. 2) that enables comparison, but has a spiny coat (Fig. 4) like a hedgehog. Sometimes in evolution, you have to play the cards (data) you are dealt,

About tenrecs
Not typical of placental mammals, a cloaca remains present, rather than a separate anus and urogenital opening and tenrecs lack a scrotum. That shows how primitive they are. Living whales also lack a scrotum, but have separate anal and genital openings, perhaps by convergence with most other mammals. Tenrecs are omnivorous. Most tenrecs are nocturnal and have poor eyesight, but their whiskers are sensitive. Distinct from whales, tenrecs tend to have 20-32 young. Some species are social.

Figure 4. The spiny tenrec Hemicentetes with a Digimorph skull overprinted. Until skeletal data on Limnogale comes in, this short tail tenrec will have to do.

Figure 4. The spiny tenrec Hemicentetes with a Digimorph skull overprinted. Until skeletal data on Limnogale comes in, this short tail tenrec will have to do. That foramen below the orbit is retained in some basal land whales.

That little foramen
below the orbit of Hemicentetes (Fig. 4) is also found in basal whales like Dorudon (Fig. 5). Not sure what it is or was used for. That’s another paper to be written by some future grad student.

Figure 5. Dorudon skull featuring the foramina below the orbit, similar to the one in the tenrec, Hemicentetes in figure 4.

Figure 5. Dorudon skull featuring the foramen below the orbit, similar to the one in the tenrec, Hemicentetes in figure 4.

For whale ancestors 
you might like tenrecs (Fig. 6) more than hippos. The snout is long and narrow. The teeth are similar to those of whales both in pattern and size. With that long otter-like tail on Limnogale, and flexible spine on Hemicentetes, at this point we can only imagine that swimming tenrecs swim in a fashion more similar to whales than any sort of hippo could ever manage. The chest cavity is large. The feet are flat and have not developed hooves or lost digits. The tenrec/whale case may be one more instance where DNA has let us down.

Figure 6. Tenrecs now nest as sisters to whales in the large reptile tree. Here are a few other extinct land whales to scale.

Figure 6. Tenrecs now nest as sisters to whales in the large reptile tree. Here are a few other extinct land whales to scale. They are all giant aquatic tenrecs. 

This discovery made my day.
Giant aquatic tenrecs add support to this continuing study and the validity of the large reptile tree at www.ReptileEvolution.com.

This is further evidence
that you don’t have to have the fossil in front of you to add to the present body of knowledge in evolution and paleontology, despite the vocal majority that says otherwise. That restrictive paradigm has to change.

References
Gingerich PD, Ul-Haq M, von Koenigswald W, Sanders WJ, Smith BH, Zalmout IS 2009. New protocetid whale from the middle eocene of pakistan: birth on land, precocial development, and sexual dimorphism. PLoS ONE 4 (2): e4366. doi:10.1371/journal.pone.0004366

New ichthyosaur family tree by Ji et al. 2015

A recent paper on ichthyosaur systematics
(Ji et al. 2015, Fig. 1) adds newly discovered taxa and the tree is getting nice and big.

Unfortunately,
at the base of their cladogram Ji et al. place a distinctly different proximal outgroup for ichthyosaurs than what was recovered in the large reptile tree (subset shown in Fig. 1, click to enlarge). They appear to be guessing. Apparently they are not sure how ichthyosaurs are related to other reptiles.

Here 
proximal outgroup taxa for ichthyosaurs include Wumengosaurus, Thaisaurus and Xinminosaurus (in ascending order) not Thadeosaurus. These large reptile tree taxa demonstrate a gradual accumulation of basal ichthyosaur traits. The Ji et al taxa, HovasaurusClaudiosaurus and Thadeosaurus do not. In the large reptile tree these three are basal younginiformes, related, yes, but much more distantly related to ichthyosaurs.

Figure 1. Ichthyosaur family trees compared. Left: subset of the large reptile tree. Right: from Ji et al. 2015. Note the lack of correct outgroups in the Ji et al study. They have no idea which taxa are proximal ancestors.

Figure 1. Click to enlarge. Ichthyosaur family trees compared. Left: subset of the large reptile tree. Right: from Ji et al. 2015. Note the lack of correct outgroups in the Ji et al study. They have no idea which taxa are proximal ancestors. Yellow are taxa found in both trees.

Figure 1. Subset of the LRT focusing on the clade Ichthyosauria.

Figure 1. Subset of the LRT focusing on the clade Ichthyosauria updated November 4, 2018 with a shift of the Hupehsuchidae closer to the base of the Ichthyosauria.

So, as an experiment, 
we’ll delete the large reptile tree proximal outgroup taxa in order to match more closely the Ji et al taxon list. What is recovered now?

  1. Hovasaurus, Claudiosaurus and Thadeosaurus now nest together in an outgroup clade.
  2. Hupehsuchus + Xinminosaurus, Grippia and (Utatsusaurus + (Shastasaurus  pacificus + Shastasaurus alexandrae) now form clades at the base of the Ichythyosauria.
  3. Then Chaohusaurus nests at the base of the rest of the Ichthyosauria with the same topology as the subset of the large reptile tree.

A few differences between the two topologies without deletions…
Note the morphological mismatches in the Ji et al. topology not found in the large reptile tree.

  1. In the large reptile tree Chaohusaurus nests between two similar taxa, Parvinatator and Besanosaurus. In the Ji et al. tree Chaohusaurus nests between the mismatched and odd Hupehsuchus and a clade of basal ichthyosaurs as the basalmost ichthyosaur, even though it has a derived ichthyosaur shape and traits.
  2. In the large reptile tree the derived, but still Triassic, Cymbospondylus petrinus nests between its contemporary, Mixosaurus and several other giant serpentine ichthyosaurs. All have a depressed cranium with a central ridge. The unrelated flat-headed C. buchseri nests elsewhere with similar deep-bodied, high-crested Shonisaurus popularis. By contrast, in the Ji et al. tree C. piscosus (= petrinus) and C. buchseri nest together with the very primitive, very small, Xinminosaurus, which does not have such a depressed cranium with a central crest.
  3. Ji et al. have a clade of Shastasauridae that includes only shastasaurs. In the large reptile tree, that clade also includes the odd little hupehsuchids and demonstrates how these little toothless enigmas evolved from larger forbearers. Ji et al. provided several skull reconstructions. Perhaps a few more would help to resolve the distinct topologies.

Those are the major issues.
The rest can be swept up later. I’d like to see the authors either expand their own taxon list or work off the large reptile tree to confidently establish a series of outgroup taxa for the Ichthyosauria that actually demonstrate a gradual accumulation of character traits, instead of doing what they did. Then we might have closer correspondence in tree topology. And we’re going to have to figure out Cymbospondylus… is it derived? or primitive?

References
Ji C, Jiang D-Y,  Motani R, Rieppel O, Hao -C & Sun Z-Y 2015. Phylogeny of the Ichthyopterygia incorporating recent discoveries from South China, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2015.1025956

Pterosaurs and Their Webbed Feet

In some pterosaurs, basal forms primarily, the metatarsals were appressed to one another. In many other clades the metatarsals separated distally, spreading the bases of the toes apart from one another. Between the toes of all pterosaurs (in which soft tissues like this are preserved) there is webbing, like duck feet. Toe webbing in pterosaurs goes back at least as far as Sharovipteryx. Toe webbing most often appears in Pterodactylus (Figs. 1, 2) and Rhamphorhynchus.

Pterosaur toe webbing on the Vienna specimen of Pterodactylus.

Figure 1. Pterosaur toe webbing on the Vienna specimen of Pterodactylus from Wellnhofer (1991).

Toe webbing on the Frey and Tischlinger private specimen of Pterodactylus.

Figure 2. Click to enlarge. Toe webbing on the Frey and Tischlinger private specimen of Pterodactylus.

Was toe webbing present on all pterosaurs?
It’s hard to tell whether webbing was present on more pterosaurs without better preservation over a wider range of taxa. Anurognathus had webbing, but apparently PAL 3830 did not. At present, toe webbing is less common than wing membrane preservation, but some of that is due to the angle of preservation, as in Sordes, in which webbing cannot be ascertained due to the medial view exposure.

Dorsal view of flying pterosaur.

Figure 3. Dorsal view of n42 (BSPG 1911 I 31) in flight position. The dorsal side of the foot would have pointed laterally. The curve of the toes would have produced a vertical stabilizer with lateral lift if the toes were webbed. Such lateral lift would have extended the legs without so much of the effort to do so, counteracting the natural drag forces on the leading edge working to flex the knee during flight.

Useful for?
Swimming (paddling the feet) and flying (establishing an aerodynamic surface that lifts the foot dorsally (laterally in flight, Fig. 3) while the uropatagium provides lift to the entire hind limb.

References
Wellnhofer P 1991. The Illustrated Encyclopedia of Pterosaurs. London, Salamander Books, Limited: 1-192.