Coombs et al. 2020 re-study odontocete skull asymmetry

Coombs et al. 2020 described odontocete (toothed whale) skull asymmetry
but did not trace it back to its origins in tenrecs (Fig. 1), as we did here two years ago. Without a valid phylogenetic context, the answers they sought evaded the Coombs team.

Nine years ago
whale skull asymmetry was studied by Fahlke et al. 2011, likewise without including tenrecs.

Figure 1. Skull asymmetry in odontocete whales from Fahlke et al. 2011.

Figure 2. Hemicentetes an extant echolocating tenrec, also has a twisted skull, like its descendants, the odontocete whales.

From the Coombs et al. abstract:
“Unlike most mammals, toothed whale (Odontoceti) skulls lack symmetry in the nasal and facial (nasofacial) region. This asymmetry is hypothesised to relate to echolocation, which may have evolved in the earliest diverging odontocetes.”

Earlier. See figure 1.

“Early cetaceans (whales, dolphins, and porpoises) such as archaeocetes, namely the protocetids and basilosaurids, have asymmetric rostra, but it is unclear when nasofacial asymmetry evolved during the transition from archaeocetes to modern whales.”

Earlier. See figure 1.

“Early ancestors of living whales had little cranial asymmetry and likely were not able to echolocate.”

Incorrect conclusion. Add taxa. See figure 1. And see Gould 1965, who described echolocation in tenrecs.

Figure 1. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.

Figure 2. Odontoceti (toothed whale) origin and evolution from tree shrews to killer whales. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.

Illustrations like these
(Fig 2) can be extremely helpful for ‘seeing’ evolution take place in a series of micro-evolutionary events. Typical of evolution, several lineages go extinct, while one or a few continue to the present day. Here we are lucky enough to have a few flesh and blood tenrecs at the genesis and several odontocetes to compare. This would make a great PhD project.

Coombs et al. 2020
are still not aware that the traditional clade ‘Cetacea’ is no longer valid because odontocete ‘whales’ arise apart from mysticete ‘whales’ in the large reptile tree. Click the links in this paragraph and in the citations below to get more backstory.


References
Coombs EJ, Clavel J, Park T, Churchill M and Goswami A 2020. BMC Biology 18:86 https://doi.org/10.1186/s12915-020-00805-4
Fahlke JM,  Gingerich PD, Welsh RC and Wood AR. 2011. Cranial asymmetry in Eocene archaeocete whales and the evolution of directional hearing in water. PNAS 108 (35) 14545-14548; https://doi.org/10.1073/pnas.1108927108
Gould E 1965. Evidence for Echolocation in the Tenrecidae of Madagascar
Proceedings of the American Philosophical Society 109 (6): 352-360. online here.

https://www.researchgate.net/publication/328388746_The_triple_origin_of_whales

 

Two primitive extant bats enter the LRT

Yesterday we looked at the smallest of the fruit bats (mega bats). Earlier we looked at several micro bats.

Here, at nearly the same size,
Notopteris (Figs. 1, 2( nests in the large reptile tree (LRT, 1671+ taxa, subset Fig. 5) as the most primitive extant megabat due to its long tail and a few other primitive traits.

Figure 1. Notopteris in vivo. Note the microbat proportions and relatively long tail. The wing membrane begins along a dorsal margin, not laterally as in other bats.

Figure 1. Notopteris in vivo. Note the microbat proportions and relatively long tail. The wing membrane begins along a dorsal margin, not laterally as in other bats.

Notopteris macdonaldi (Gray 1859) is the long-tailed fruit bat or Fijian blossom bat. This is the most primitive megabat in the LRT and the only one that retains a long tail. It roosts in large cave colonies only on South Pacific islands. Note the mid-dorsal attachment of the proximal wing membranes, rather than a more lateral attachment. This is a derived trait not shared with other bats.

Figure 2. Notopteris skull and mandible.

Figure 2. Notopteris skull and mandible. Note the primitive skull and derived simple cusp teeth.

The most primitive extant microbat
in the LRT (Figs. 3, 4) is the newly added Rhinopoma, the lesser mouse-tailed bat (Fig. 3). It is similar, to Notopteris (Figs. 1, 2), but with a shorter rostrum and retains primitive multiple cusps on its teeth. Both are cave dwellers.

Figure 3. Rhinopoma is the most primitive extant micro bat in the LRT. Note the long tail, long legs and small feet, all Chriacus-like and Onychonycteris-like primitive traits.

Figure 3. Rhinopoma is the most primitive extant micro bat in the LRT. Note the long tail, long legs and small feet, all Chriacus-like and Onychonycteris-like primitive traits. Note the lateral insertion of the wing membrane on the torso, distinct from Notopteris (Fig. 1).

Rhinopoma hardwickei (Gray 1831) is the extant lesser mouse-tailed bat, an insectivore found from North Africa to India. The tail is 3/4 free and no calcar is present on the heel. The legs are long and the feet are small.

Figure 4. Rhinopoma skull from Digimorph.org and used with permission.

Figure 4. Rhinopoma skull from Digimorph.org and used with permission. Note the prominent ear bones (yellow) in this echolocating microbat.

Simmons et al. 1984 looked at echolocation in Rhinopoma.
They concluded, “Except for duration these signals are relatively inflexible and suggestive of a primitive kind of echolocation in which only one dimension is changed to achieve qualities which most other species of bats obtain by changing a variety of signal dimensions simultaneously.”

Nelson and Hamilton Smith 1982 looked at echolocation in Notopteris.
They concluded, “Some field experiments… showed these flying foxes were unable to avoid obstacles in complete darkness or when blindfolded, but were able to do so in very dim light. No audible or ultrasonic sounds that could be used in echolocation were detected during their flight.”

Holland et al. 2004 looked at echolocation in the megabat Rousettus.
They reported, “Rousettus aegyptiacus Geoffroy 1810 is a member of the only genus of Megachiropteran bats to use vocal echolocation, but the structure of its brief, click-like signal is poorly described.Rousettus aegyptiacus Geoffroy 1810 is a member of the only genus of Megachiropteran bats to use vocal echolocation, but the structure of its brief, click-like signal is poorly described. However, the low energy content of the signals and short duration should make returning echoes difficult to detect. The performance of R. aegyptiacus in obstacle avoidance experiments using echolocation therefore remains something of a conundrum.”

Simmons and Geisler 1998 looked at echolocation in Icaronycteris.
They reported, “We propose that flight evolved before echolocation, and that the first bats used vision for orientation in their arboreal/aerial environment. The evolution of flight was followed by the origin of low-duty-cycle laryngeal echolocation in early members of the microchiropteran lineage. This system was most likely simple at first, permitting orientation and obstacle detection but not detection or tracking of airborne prey.”

Veselka et al. 2010 concluded that Onychonycteris finneyi may have been capable of echolocation. in reply, Simmons et al. 2010 argued that Onychonycteris finneyi was probably not an echolocating bat.

Echolocation seems to have been convergently acquired
in microbats and Rousettus.

Figure 1. Subset of the LRT focusing on the resurrected clade Volitantia, including dermopterans, pangolins, bats and their extinct kin.

Figure 5. Subset of the LRT focusing on the resurrected clade Volitantia, including dermopterans, pangolins, bats and their extinct kin.

Basal bats in the LRT have more plesiomorphic traits overall,
like small ears, simple nose, long legs, long tail and small feet, all Chriacus-like (Fig. 6) traits. This is what we should expect when any cladogram models micro-evolutionary changes.

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 6. 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.

We looked at the origin of bats from Chriacus-like ancestors
earlier here, here and at earlier links therein. These posts are –by far– the most popular posts at this PterosaurHeresies.

To summarize one of those posts
hanging pre-bats simply listened for the sounds of prey in leaf litter below, then pounced from above. Parachuting with flapping evolved into helicoptering then that evolved into flight to return to the branch the bat fell from. Larger hands and extradermal membranes would have increasingly aided entrapment at the moment of impact. Even larger hands and extradermal membranes would have increasingly helped helicoptering while falling. Smaller size and weight (Fig. 6) was co-opted to aid these behaviors. Echolocation seems to have evolved in bats seeking aerial prey and co-opted to live in caves in complete darkness.


References
Gray JE 1831. Description of some new genera and species of bats. The Zoological Miscellany, 1: 37-38.
Gray GR 1859.
 The annals and magazine of Natural History, Zoology, Botany and Geology 3. Series IV: 4859.
Holland RA, Waters DA and Rayner JMV 2004. Echolocation signal structure in the megachiropteran bat Rousettus aegyptiacus Geoffroy 1810. Journal of Experimental Biology 207:4361–4369.
Nelson JE and Hamilton-Smith E 1982. Some observations on Notopteris macdonaldi (Chiroptera: Pteropodidae) in Australian Mammal Society 5: 247–252.
Simmons JA, Kick SA and Lawrence BD 1984. Echolocation and hearing in the mouse-tailed bat, Rhinopoma hardwickei: acoustic evolution of echolocation in bats. Journal of Comparative Physiology A 154: 347–356.
Simmons NB and Geisler JH 1998. Phylogenetic relationships of Icaronycteris, Archaeonycteris, Hassianycteris, and Palaeochiropteryx to extant bat lineages, with comments on the evolution of echolocation. Bulletin of the American Museum of Natural History 235.
Simmons NB, Seymour KL, Habersetzer J and Gunnell GF 2010. Inferring echolation in ancient bats. Nature 466: E8.
Veselka et al. (8 co-authors) 2010. A bony connection signals larygenal echolocation in bats.Nature 463: 939–942.

wiki/Notopteris

wiki/Rhinopoma

Torsioned odontocete skulls go back to tenrecs

Today two blogposts are published
because they relate strongly to one another. Shortly there will be a post on Monodon, the narwhal, which introduced me to whale skull asymmetry, which I then researched and found the following study from 2011.

Figure 1. Skull asymmetry in odontocete whales from Fahlke et al. 2011.

Figure 1. Skull asymmetry in odontocete whales from Fahlke et al. 2011.

A paper by Fahlke et al. 2011 reported,
“Eocene archaeocete whales gave rise to all modern toothed and baleen whales (Odontoceti and Mysticeti) during or near the Eocene-Oligocene transition. Odontocetes have asymmetrical skulls, with asymmetry linked to high-frequency sound production and echolocation.” 

This is not true
when more taxa are added to a phylogenetic analysis looking at whales. Archaeocetes are not basal to baleen whales (Mysticeti) in the LRT.

Figure 1. Skull asymmetry in odontocete whales from Fahlke et al. 2011.

Figure 2. Hemicentetes an extant echolocating tenrec, also has a twisted skull, like its descendants, the odontocete whales. The direction is opposite in this image. Could be a result of the scanning technique (mirroring the image) or a real trait.

Fahlke et al. did not look at tenrecs,
which nest basal to archaeocetes and pakicetids in the large reptile tree (LRT, 1187 taxa). Hemicentetes (Fig. 2) echolocates (Gould 1965) and travels in pods — and it has a torsioned skull (Fig. 2). Baleen whales (mysticetes) had a separate ancestry with desmostylians, apart from archaeocetes.

A torsioned skull further cements tenrecs to archaeocetes and odontocetes. Fahlke et al. did not look at desmostylians either.

Taxa basal to tenrecs
in the LRT, like the elephant shrew, Rhynchocyon, do not have a torsioned skull. So that trait originated with a sister to Hemicentetes.

In an interview, Fahlke reported, 
“This means that the initial asymmetry in whales is not related to echolocation,” said Fahlke, who is working with Philip Gingerich, an internationally recognized authority on whale evolution, at the U-M Museum of Paleontology.

Oh, yes, asymmetry is related to echolocation!
Expand that taxon list to tenrecs, read Gould (1965) and everything will fall into place. The origin of echolocation in the ancestors of whales goes back to the mid-Cretaceous, based on the separation of Madagascar (where tenrecs live) from Pakistan and India (where whale ancestors like the tenrec, Indohyus) are found.

Fahlke’s backstory from the U. of Michigan webpage:
“The actual skull on which the model was based was noticeably asymmetrical, but Fahlke and colleagues at first dismissed the irregularity.

“We thought, like everybody else before us, that this might have happened during burial and fossilization,” Fahlke said. “Under pressure from sediments, fossils oftentimes deform.” To correct for the deformation, coauthor Aaron Wood, a former U-M postdoctoral researcher who is now at the University of Florida, straightened out the skull in the digital model. But when Fahlke began working with the “corrected” model, the jaws just didn’t fit together right. Frustrated, she stared at a cast of the actual skull, puzzling over the problem.

“Finally it dawned on me: Maybe archaeocete skulls really were asymmetrical,” Fahlke said. She didn’t have to go far to explore that idea; the U-M Museum of Paleontology houses one of the world’s largest and most complete archaeocete fossil collections. Fahlke began examining archaeocete skulls, and to her astonishment, “they all showed the same kind of asymmetry?a leftward bend when you look at them from the top down,” she said.”

References
Fahlke JM,  Gingerich PD, Welsh RC and Wood AR. 2011. Cranial asymmetry in Eocene archaeocete whales and the evolution of directional hearing in water. PNAS 108 (35) 14545-14548; https://doi.org/10.1073/pnas.1108927108
Gould E 1965. Evidence for Echolocation in the Tenrecidae of Madagascar
Proceedings of the American Philosophical Society 109 (6): 352-360. online here.

https://pterosaurheresies.wordpress.com/2016/07/23/tenrecs-and-echolocation/

U of Michigan story on the Fahlke team’s discovery here