Drepanolepis, an Early Devonian ‘fork-tail’ fish, enters the LRT

I dreaded this one, fearing its weirdness…
but after a little DGS coloring (Fig. 1) came to realize this tiny furcacaudiforme (Early Devonian fork-tail fish?) was just like another fish already in the large reptile tree (LRT, 1677+ taxa), only shorter and narrower. After analysis the two nested together.

Figure 1. Drepanolepis, traced from Wilson and Caldwell 1998, has a ventral oral cavity and nests with Birkenia in the LRT.

Figure 1. Drepanolepis, traced from Wilson and Caldwell 1998, has a ventral oral cavity and nests with Birkenia in the LRT. I was surprised to see that ventral oral cavity.

Drepanolepis maerssae (Wilson and Caldwell 1993, 1998; Early Devonian; 2cm in length) is a traditional ‘thelodont’ and a member of the Furcacaudiformes (forked tails). In the LRT Drepanolepis is derived from Birkenia (Fig. 2), but with a taller, shorter, more angelfish-like body. They both have a ventral mouth and a hypocercal tail, somewhat elaborated in Drepanolepis with several posterior processes. The gill atrium remains quite large and the nasal extends from the orbit down to the oral cavity, which remains like that of a lancelet, without jaws. Without jaws there is no premaxilla, maxilla quadrate, articular, angular and dentary.

Birkenia is not traditionally considered a thelodont.
All other traditional thelodonts, like Thelodus and Loganiella, have a low, wide morphology. Thelodus has a ventral oral cavity and nests with osteostracans and sturgeons in the LRT. Loganiella has a wide terminal mouth and nests with whale sharks and mantas in the LRT. Drepanolepis and other furcacaudiformes do not nest with these traditional thelodonts in the LRT and should no longer be considered thelodonts.

Figure 2. Birkenia in situ with precursor facial bones labeled. This Middle Silurian taxon is basal to Furcacaudiformes and all other vertebrates.

Figure 2. Birkenia in situ with precursor facial bones labeled. This Middle Silurian taxon is basal to Furcacaudiformes and all other vertebrates.

Birkenia and furcacaudiformes 
bridge the gap between lancelets and gnathostomes. The have the body and bones of a basal fish, but retain a lancelet-like oral cavity that cannot be called a proper mouth. That comes later.

FIgure 1. Birkenia in situ and diagrams.

FIgure 3. Birkenia in situ and diagrams. Note the hypocercal tail as in Drepanolepis (Fig. 1).

By the Early Devonian
fish had evolved to such an extent that some had lobefins (the sarcopterygians) and others had exoskeletons (the placoderms).

Let’s talk about the traditional ‘terminal mouth’ of Furcacauda.
Wilson and Caldwell 1998 restored a terminal mouth on Furcacauda (Fig. 4) but did so by guessing. The skull is missing from the specimen (Fig. 4). No other furcacaudiformes have a terminal mouth (Figs. 5,6). All other furcacaudiformes (Figs. 1,5,6) described and figured by Wilson and Caldwell have an overlooked ventral oral cavity, like that of Birkenia. In addition I rotated one image, that of Sphenonectris (Fig. 6), to bring the dorsal side to the top for proper orientation.

It has been 22 years since Wilson and Caldwell 1998 was published.
Perhaps in the meantime someone else has noticed these issues. If so, let me know and I will promote that citation.

Figure 4. Furcacauda fredholmae specimen in situ along with Wilson and Caldwell 1998 diagram imagining a face and terminal mouth for this taxon. No other sisters have a terminal mouth.

Figure 4. Furcacauda fredholmae specimen in situ along with Wilson and Caldwell 1998 diagram imagining a face and terminal mouth for this taxon. No other sisters have a terminal mouth.

As in lancelets
the oral cavity of Birkenia and furcacaudiformes can never close and is surrounded by oral cirri that work as sand filters.

Figure 5. Pezzopallichthes has a ventral oral cavity (green circle).

Figure 5. Pezzopallichthes has a ventral oral cavity (green circle).

As in Birkenia
precursors to tetrapod skull bones can be found in furcacaudiformes for the first time phylogenetically. Even so, the short, narrow Furcacaudiformes displayed here today are members of a terminal clade with no descendants later than the Devonian. Closer sisters to Birkenia evolved to become basal vertebrates (fish and tetrapods).

Figure 6. Sphenonectris with facial bones colored. Here the oral elements are displaced. The orbit is close to the anterior margin as in Drepanolepis (Fig. 1).

Figure 6. Sphenonectris with facial bones colored. Here the oral elements are displaced. The orbit is close to the anterior margin as in Drepanolepis (Fig. 1).

We looked at Birkenia
and the origin of dermal facial bones from splintery scales earlier here. using similar DGS methods.


References
Traquair RH 1898. Report on fossils fishes. Summary of Progress of the Geological Survey of the United Kingdom for 1897: 72-76.
Wilson MVH and Caldwell MW 1993. New Silurian and Devonian fork-tailed ‘thelodonts’ are jawless vertebrates with stomachs and deep bodies. Nature. 361 (6411): 442–444.
Wilson MVH and Caldwell MW 1998. 
The Furcacaudiformes, a new order of jawless vertebrates with thelodont scales, based on articulated Silurian and Devonian fossils from northern Canada. Journal of Vertebrate Paleontology 18 (1): 10-29.

wiki/Thelodus
wiki/Birkenia
wiki/Drepanolepis
wiki/Furcacaudiformes

Dialipina: an overlooked coelacanth (clade: Actinistia)

Early Devonian Dialipina
(Figs. 2, 4,5) has been described as, ‘the oldest known actinopterygian’, Clement et al. 2018 nested Dialipina as the outgroup to the stem bony fish on their cladogram (Fig. 1). It was orignally considered a palaeonisciform, like Cheirolepis.

Figure x. This is a traditional cladogram, from Clement et al. 2018, lacking appropriate outgroup taxa.

Figure 1. This is a traditional cladogram, from Clement et al. 2018, lacking appropriate outgroup taxa. Dialipina is the outgroup here. Latimeria is not listed here.

Prior authors have missed the many traits shared between this taxon and the extant coelacanth, Latimeria, (Fig. 3) perhaps because Dialipina fossils did not readily display distinct pectoral and pelvic lobe fins. The lobes are present (Figs. 4, 5), just not distinct. No one misses the coelacanth-like tail. Nor do they miss the muscular dorsal and anal fins.

Wikipedia does not list Dialipina in their list of coelacanths (clade: Actinistia).

Figure 2. Dialipina skull in situ and reconstructed.

Figure 2. Dialipina skull in situ and reconstructed. The slender lacrimal, maxilla and jugal fuse in Latimeria (Fig. 3).

The  traditional view of bony fish systematics (Fig. 1):
“Osteichthyans comprise two divisions, each containing over 32,000 living species : Sarcopterygii (lobe-finned fishes and tetrapods) and Actinopterygii (ray-finned fishes).”

The LRT view of bony fish systematics (Fig. 6):
lobefins arose from fish without lobe-fins in the Late Silurian, documented by Dialipina in the Early Devonian.

Figure 4. Latimeria updated. Note the fusion of the jugal, lacrimal and toothless maxilla into one bone. Compare to Dialipina in figure 2.

Figure 3. Latimeria updated. Note the fusion of the jugal, lacrimal and toothless maxilla into one bone. Compare to Dialipina in figure 2.

Dialipina salgueiroensis (D. markae Schultze 1968; Schultze 1992; Schultze and Cumbaa 2001; Early Devonian. 420 mya) is the earliest known bony fish known from a complete skeleton. It is a sister to the extant coelacanth, Latimeria.

Figure 3. Dialipina overall in situ. Two specimens. Note the very Latimeria-like tail, and the lobe portion of the lobefins were overlooked in prior studies.

Figure 4. Dialipina overall in situ. Two specimens. Note the very Latimeria-like tail, and the lobe portion of the lobefins were overlooked in prior studies.

Latimeria chalumnae (Smithi 1939) is the extant coelocanth, a slow-swimming deep-water fish. The fins arise from long lobes. The postorbital is large. The supratemporal is absent. The maxilla is fused to the jugal and lacrimal. M maxillary teeth are absent.

Figure 6. Dialpina in situ.

Figure 5. Dialpina in situ with DGS applied. This small Early Devonian lobefin was not recognized as one, despite so many traits shared with Latimeria

Giles et al. 2015 reported,
“Dialipina was originally diagnosed as a actinopterygian based on scale morphology (Schultze, 1968), but more recent analyses have resolved it either as an stem actinopterygian (Giles et al., 2015bSchultze and Cumbaa, 2001) or stem osteichthyan (Choo et al., 2017Friedman and Brazeau, 2010Giles et al., 2015cLu et al., 2016aQiao et al., 2016).”

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

Figure 6. Updated subset of the LRT, focusing on basal vertebrates = fish. Here Dalipina nests with Latimeria closer to the bottom of this diagram than to the top.

Giles et al. 2015 reported, 
“The phylogeny of Silurian and Devonian (443–358 million years (Myr) ago) fishes remains the foremost problem in the study of the origin of modern gnathostomes (jawed vertebrates).” According to the LRT, the foremost problem of Giles et al. only exists due to taxon exclusion.d


References
Clement AM et al. 2018. Neurocranial anatomy of an enigmatic Early Devonian fish sheds light on early osteichthyan evolution. Evolutinary Biology online here. eLife 2018; 7:e34349 DOI: 10.7554/eLife.34349
Giles S, Friedma M and Brazeau MD 2015. Osteichthyan-like cranial conditions in an Early Devonian stem gnathostome. Nature, 520 (7545): 82–85.
Lund R and Lund W 1984. New genera and species of coelacanths from the Bear Gulch Limestone (Lower Carboniferous) of Montana (U.S.A.). Geobios. 17 (2): 237–244.
Schultze H-P 1968. Palaeoniscoidea-Schuppen aus dem Unterdevon Australiens und Kanadas und aus dem Mitteldevon Spitzbergens. Bulletin of the British Museum (Natural History) 16: 343–376.
Schultze H-P 1973. Crossopterygier mi heterozerker Schwanzfloss aus dem Oberdevon Kanadas, nebst einer Beschreibung von Onychodontida-Resten aus dem Middledevon Spaniens und aus dem Karbon der USA. Palaeontograhica A 143:188–208.
Schultze H-P 1992. Early Devonian actinopterygians (Osteichthyes, Pisces) from Siberia. Pp. 233–242 in Mark-Kurik, E.: Fossil Fishes as Living Animals. Academy of Sciences of Estonia.
Schultze H-P, and  Cumbaa SL 2001. Dialipina and the characters of basal actinopterygians, p. 315–332. In: Major Events in Early Vertebrate Evolution: Palaeontology, Phylogeny and Development. Ahlberg PE (ed.). Systematics Association Special Volume 61, Taylor and Francis, London.

Finding Our First Fish

wiki/Dialipina
wiki/Latimeria
wiki/Miguashaia

wiki/Actinistia
wiki/Coelocanth

‘The most radical revision of early actinopterygian evolution since the late 1980s’

Coates 2017, describing Giles et al. 2017 in Nature,
reported, “This is the most radical revision of early actinopterygian evolution since the late 1980s: it offers new data, evolutionary trees and timescales, and provides newly populated stem lineages where none existed before for polypterids and the Actinopterygii as a whole.”

Giles et al. 2017 report,
“Polypterids (bichirs and ropefish) represent the earliest-diverging lineage of living actinopterygians…. Here we show that scanilepiforms, a widely distributed radiation from the Triassic period (around 252–201 million years ago), are stem polypterids

One of the scanilepiforms (= stem polypterids) key to the Giles et al. cladogram is Middle Triassic Fukangichthys (Fig.1). Giles et al. hypothesize it shares more traits with extant Polypterus (Fig. 4) than to Early Triassic Pteronisculus (Fig. 2).

Figure 1. Middle Triassic Fukangicthys from Su 1978, Xu et al. 2014; Giles et al. 2018) is not a basal fish taxon in the LRT.

Figure 1. Middle Triassic Fukangicthys from Su 1978, Xu et al. 2014; Giles et al. 2018) is not a basal fish taxon in the LRT.

Radical is one thing… but is the Giles et al. cladogram correct?
With more outgroup taxa the large reptile tree (LRT, 1673+ taxa) nests derived polypterids with derived lungfish. More primitive scanilepiforms, like Fukangichthys, nest with more primitive Pteronisculus and other Triassic fish. Both have tall narrow oval morphologies distinct from the low wide shape of Polypterus and lungfish. That’s just for starters.

Figure 2. Pteronisculus nests with Fukangichthys in the LRT apart from Polypterus.

Figure 2. Pteronisculus nests with Fukangichthys in the LRT apart from Polypterus.

Another error in the Giles et al. 2017 study
was subjectively and arbitrarily choosing outgroup taxa (the placoderms Dicksonosteus and Entelognathus) rather than expanding the taxon list and letting software choose valid bony fish outgroups. That’s what the LRT does (Fig. 3) going back to Cambrian chordates.

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

Figure 3. Updated subset of the LRT, focusing on basal vertebrates = fish.

Giles et al. 2017
are unaware of the bask dichotomy splitting bony fish, and that placoderms and spiny sharks nest within one of those clades. Polypterus and other lungfish nest close to tetrapodomorphs.

Figure 1. The Nile bichir (Polypterus), skull, skeleton and bones colorized for ease of comparison. Compare to the placoderm, Entelognathus, (Fig. 2) and the stem tetrapod Tinirau (Fig. 3).

Figure 4. The Nile bichir (Polypterus), skull, skeleton and bones colorized for ease of comparison.

For their basalmost bony fish,
Giles et al. nest Dialipina (Early Devonian). By contrast the LRT nests Dialpina in a much more derived node, with the extant coelacanth, Latimeria, which it greatly resembles. We’ll look at that nesting tomorrow, but the links above will give the anxious reader a sneak preview.

Contra Coates 2017,
the LRT has become the most radical revision of early actinopterygian evolution since the late 1980s. If you come across a more radical one, or one that includes more outgroup taxa complete with reconstructions (to check scoring accuracy), let me know and I will promote that citation.


References
Coates M. 2017. 
Plenty of fish in the tree. Nature 549:167–169.
Giles S, Xu G-H, Near TJ and Friedman 2017.
Early members of ‘living fossil’ lineage imply later origin of modern ray-finned fishes. Nature 549:265–268.
Xu G-H and Gao K-Q 2011. A new scanilepiformfrom the Lower Triassic of northern Gansu Province, China, and phylogenetic relationship of non-teleostean Actinopterygii. Zoological Journal of the Linnean Society 161:595–612.

Fish cladogram: Cambrian period to the present day

When one layers established time periods
over the fish portion of the large reptile tree (LRT, 1673+ taxa; Fig. 1) the surprising length of certain ghost lineages and the ability of several clades to survive several hundred million years becomes apparent.

Figure 1. Subset of the LRT focusing on basal vertebrates (= fish). Colors indicate time periods. This chart documents the lack of fossils for several clades and genera in the Silurian and Devonian.

Figure 1. Subset of the LRT focusing on basal vertebrates (= fish). Colors indicate time periods. This chart documents the lack of fossils for several clades and genera in the Silurian and Devonian.

The antiquity of Silurian members in the highly derived lungfish clade
(Guiyu and Psarolepis) helps one understand the coeval Silurian appearances of so-called primitive fish, like acanthdians and placoderms (Entelognathus). Traditional cladograms assumed early taxa must be more primitive, not realizing that phylogenetic analysis indicates a vast undiscovered radiation of taxa in the Silurian (Fig. 1). Most of these are still waiting to be discovered.

What do Silurian and Early Devonian fossil fish in the LRT have in common?
Many were flat bottom dwellers with small eyes.

By contrast, coeval spiny sharks had large eyes and were free-swimmers. Even so they lost their flexible fin rays, they lost large teeth, they kept a large mouth, and they had vestigial skeletons. Such traits are associated today with slow-moving deep sea fish.

So known Silurian fish were not open sea visual predators with great swimming skills. Their ecological absence must have a reason. I wonder if such taxa were gobbled up before they could drift to muddy or silty anoxic regions of the sea floor where they could wait undisturbed to be buried for fossilization? Even a few exceptions are lacking. Very puzzling…

According to Google:
“In North America geologic activity over the last 417 million years has removed or covered up most Silurian rocks. Well-preserved fossils from Silurian reefs can be found in the Great Lake States of Minnesota, Wisconsin, Michigan, and Illinois.” So Silurian exposures are comparatively rare.

How do left column fish differ from right column (Fig. 1) fish?
As a general rule (allowing for many exceptions) left column fish do not appear to be the fast, open water swimmers seen in the majority of primitive right column fish in the Silurian and Devonian. It is noteworthy that not one taxon in the right column has a Silurian through Permian representative. I will add them as they come to my attention. It is also noteworthy that the left column has very few living representatives. I count nine.

Traditional cladograms
put more emphasis on time and exclude extant taxa. That’s why traditional cladograms often nest spiny sharks and placoderms near the base of the basal vertebrates, prior to sharks and bony fish. And they attempt to add tube-feeding sturgeons somewhere in the middle of bony fish. In the LRT taxon exclusion is minimized and more natural evolutionary patterns are recovered based on phenomics (traits).

Some previously unrecognized relationships recovered by the LRT include:

  1. The wide radiation of clades in the Silurian.
  2. Devonian taxa take us rapidly to tetrapods, documented by Middle Devonian tracks
  3. Note the proximity of Silurian lobefins to Viséan (Early Carboniferous) tetrapods, including reptiles.
  4. Note the unbalanced fossil record with regard to the major dichotomy splitting bony fish
  5. Proamia is known from the Devonian while a sister taxon, Amia, is known from extant taxa, separated by 360 million years. This is the closest we get to a right column fish fossil in the Silurian or Devonian.
  6. The time span between tiny Silurian Loganiella and giant extant sisters Rhincodon + Manta is about 430 million years.
  7. A similar time span splits Hemicyclaspis from living sturgeons.
  8. A longer time span (~500 my) splits Branchiostoma from its Cambrian precursors.
  9. When comparing the LRT to traditional cladograms, check to make sure they have similar outgroup taxa. Too often taxon exclusion is an unaddressed issue in those papers, which make them fitting subjects for the next few blogposts.

Cautionary note:
The choosing of fish taxa for the LRT has not been random, but was made on the basis of availability and possible importance. At present the fossil record is skewed toward left column fish prior to the Permian. As more taxa are discovered and added, the subjective second reason will hopefully pale to become less of a factor.

 

Restoring the skull of the basal bat, Onychonycteris

Short one today,
more ‘show’ than ‘tell’ as one picture and a caption pretty much tell the tale.

Figure 1. Onychonycteris is known from an articulated but crushed bottom half of the skull. Uncrushing it and giving it a suitable top half (Myzopoda) provides a restoration with some possibility of resemblance to theo original.

Figure 1. Onychonycteris is known from an articulated but crushed bottom half of the skull. Uncrushing it and giving it a suitable top half (Myzopoda) provides a restoration with some possibility of resemblance to theo original. Images from Simmons et al. 2010. The skull could have been less crushed than imagined here, so may have been proportionately shorter. The hole in the braincase of Myzopoda (above) may be a surgical opening to remove brain tissue. If natural, I do not know what it is.

And a cladogram
for phylogenetic context (Fig. 2).

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

Figure 2. Subset of the LRT focusing on the resurrected clade Volitantia, including dermopterans, pangolins, bats and their extinct kin.

Onychonycteris finneyi (Simmons, Seymour, Habersetze and Gunnell 2008) Eocene (~52mya), ~27 cm in length, is the most primitive known bat. It retained unguals (claws) on all five digits, a primitive trait not shared with other bats. Derived from a sister to ChriacusOnychonycteris phylogenetically preceded IcaronycterisMyotis and Pteropus in the LRT (subset Fig. 2).

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 3. 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.

Onychonycteris is smaller than Chriacus,
but the preserved portions of the skull and teeth are similar in proportion and morphology (Fig. 3). So… perhaps the proportions of the missing portion of the Chriacus skull are similar (fig. 1). More fossils will tell.

Veselka et al. 2010
concluded that O. finneyi may have been capable of echolocation.

By contrast, Simmons et al. 2010
argued that O. finneyi was probably not an echolocating bat.


References
Simmon NB, Seymour KL, Habersetzer J, Gunnell GF 2008. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature 451 (7180): 818–21. doi:10.1038/nature06549. PMID 18270539.
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/Onychonycteris

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

The ‘smallest megabat’, Balionycteris, enters the LRT

Yesterday we looked at how bats are able to
cling inverted to broad cave walls and narrow branches with their twisted feet.

Today we add
Balionycteris (Fig. 2), the ‘smallest megabat’ to the large reptile tree (LRT, 1670+ taxa, subset Fig. 1).

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

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

Not surprisingly
Balionycteris nests basal to two larger megabats (= fruit bats = flying foxes), Pteropus and Rousetta in the LRT. The megabat clade nests between two micro bats, extinct Icaronycteris and extant Rhinopoma, both of which have a long Chriacus-type free tail. Balionycteris does not share this trait, so I searched for a megabat with a long tail.

Such a bat exists in the long-tailed fruit bat (Notopteris macdonaldi ). As expected, it nests at the base of the megabits in the LRT. More on this transitional taxon soon.

Figure 5. Balionycteris hanging from both sides of a slender branch by laterally-twisted feet.

Figure 2. Balionycteris hanging from both sides of a slender branch by laterally-twisted feet.

Balionycteris maculatus (originally Cynopterus Thomas 1893; Matschie 1899; 5-6cm in length) is the extant spotted-winged fruit bat, the smallest megabat and (for one day, yesterday) the most primitive one in the LRT (details above). It can be readily distinguished from other small species of Pteropodidae by a single pair of lower incisors, 2 pairs of upper molars, and by characteristic pale spots on wing membranes, particularly on digit joints.

Figure 2. Balionycteris skull. Note the short rostrum, as in related micro bats.

Figure 3. Balionycteris skull. Note the short rostrum, as in related micro bats.

Like microbats, 
Balionycteris has short, broad wings and highly maneuverable flight. Balionycteris inhabits small cavities, but rarely cave entrances, and roosts singly, or in small groups. Note the premolars and molars have reduced cusps, convergent with edentates, whales, pangolins and other placental mammals.


References
Matschie P 1899. Die Fledermäuse der Berliner Museums für Naturkunde. 1. Megachiroptera 72: 80.
Thomas O 1893. On some new Bornean mammalia. Ann. Nag. Nat. Hist., S.6 (65):341-347.

wiki/Pteropus
wiki/Archaeopteropus
wiki/Rousettus
wiki/Balionycteris

How bat feet turn laterally, then upside-down

Bats are inverted bipeds.
They hang by branches and cave walls by their feet. While inverted, bat forelimbs are folded away until needed for flight. The hind limbs frame membranes linking the laterally oriented legs to the medial tail. We looked at the origin of bats from non-volant ancestors earlier here, here and at several earlier links therein (also see Fig. 3).

Figure 1. Hind limbs and closeup of ankle of Cynopterus, an extant micro bat, from Digimorph.org. Colors and diagram elements added here.

Figure 1. Hind limbs and closeup of ankle of Cynopterus, an extant micro bat, from Digimorph.org. Colors and diagram elements added here. Unlike most mammals, the knees are often above the hips in bats.

Bat experts know this, but it  comes as news to me.
A closer examination of bat hindquarters (Fig. 1) reveals two axial twists that add up to a ~180º rotated hind limb for the micro bat Cynopterus. The ankle is capable of additional rotation.

  1. The acetabulum axially rotates ~90º from ventrolateral to dorsolateral.
  2. The femur axially rotates so the distal end is ~90º rotated from the proximal head (Fig. 2).
  3. The tarsal centralia also rotate upon the tibiale (Fig. 1).
Figure 2. Bat femur animated to show untwisted typical mammal orientation of femoral head.

Figure 2. Two views of a bat femur animated to show typical untwisted orientation of femoral head as found in most mammals.

Axial torsion in proximal bones ultimately produces a pes
that is dorsal side up in flight in derived extant bats. Based on these twists, bat knees appear to bend backwards compared to other mammals.

Figure 3. The basal bat, Onychonycteris.

Figure 3. The basal bat, Onychonycteris. The feet are smaller and the hind limbs are more gracile primitively, like those of the bat precursor, Chriacus in figure 3.

In the transitional basal bat
Onychonycteris, the hind limb appears to be laterally oriented with long gracile hind limbs and the dorsal side of the tiny pes likewise oriented laterally. If you think such tiny feet seem less capable of inverted clinging compared to the relatively big feet of Cynopterus (Fig. 1), you’re being observant. But long legs and small feet are primitive for bats. So is inverted bipedal hanging. What you’re seeing is a transitional phase.

Figure 1. Hypothetical bat ancestors arising from a sister to Chriacus, which may be a large late survivor of a smaller common ancestor.

Figure 4. Hypothetical bat ancestors arising from a sister to Chriacus, which may be a large late survivor of a smaller common ancestor. Imagine stem bat 3 and Onychonycteris pinching the branch they hang from with long legs acting like pliers, an idea that did not occur to me years ago when this was illustrated.

Rather than clinging to the same side of the twig (or cave wall)
the long legs and small feet of Onychonycteris acted more like tongs or pliers, pinching both sides of a branch medially between them. We also see this in primitive micro bats, like long-tailed Rhinopoma and primitive megabats, like Balionycteris (Fig. 5).

Figure 5. Balionycteris hanging from both sides of a slender branch by laterally-twisted feet.

Figure 5. Balionycteris, the smallest megabat, hanging from both sides of a slender branch by laterally-twisted small feet.

Is there any new process on the bat pelvis that facilitates such adduction?
Yes. The pubis often develops a bump or rod, a prepubic process, analogous to the prepubis in pterosaurs. This process anchors muscles of femoral adduction.

Colugos and pangolins
also hang inverted from branches like that, with feet on both sides of a supporting branch.

The outgroup to bats in the LRT,
Chriacus, (Fig. 4) does not preserve evidence of long bone axial torsion (the mid-portion of the femur is not preserved). The acetabulum does not open dorsally.

Hanging upside-down
is something nearly all small arboreal mammals (e.g. squirrels, tree shrews, monkeys, tree opossums) can do facilitated by a flexible ankle that ensures the claws attach to the bark at any angle. Only bats and their immediate ancestors had such a firm toe grip while inverted they no longer needed their hands to grip. That freed the forelimbs to evolve into infant nurseries and parachute-like wings, not quite like those of birds and pterosaurs (Fig. 5), which were bipedal the conventional way: right side-up.

Figure 6. Click to enlarge. The origin of the pterosaur wing and the migration of the pteroid and preaxial carpal. A. Sphenodon. B. Huehuecuetzpalli. C. Cosesaurus. D. Sharovipteryx. E. Longisquama. F-H. Bergamodactylus.

The axial rotation of long limb bones is rare in tetrapods,
but it also can be seen in metacarpal 4 of Sharovipteryx, Longisquama and basal pterosaurs like Late Triassic Bergamodactylus (Fig. 6). That twist facilitates wing (finger 4) folding in the lateral plane of the wing (Peters 2002) rather than against the palm as in other tetrapods, including bats. Apparently the storage of long wings was just as important as the evolution of the long wings themselves in all volant tetrapods.


References
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Simmon NB, Seymour KL, Habersetzer J, Gunnell GF 2008. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature 451 (7180): 818–21. doi:10.1038/nature06549. PMID 18270539.

wiki/Onychonycteris

 

Perhaps Tulerpeton had only 5 fingers (and five toes)

Let’s get right to it.
Tulerpeton (Fig. 1) was originally described with six fingers. If not six fingers, where did that sixth finger come from?

The other hand.
Specifically, the tip of finger 4 from the left hand (Fig. 1) provides a suitable match.  The left hand is otherwise buried in the matrix beneath the well-exposed right hand.

Figure 1. Tulerpeton manus with digit 6 re-identified as the top of digit 4 from the other hand.

Figure 1. Tulerpeton manus with digit 6 re-identified as the top of digit 4 from the other hand. The drawing at left is the in situ presentation. The diagram at right is the traditional six-finger interpretation. The manus in the middle represents the new hypothesis of digit identity.

Tulerpeton sisters in the LRT
don’t have a digit 6. So, maybe the original description was a mistake.

Likewise, the pes of Tulerpeton
was also originally described with six digits (Fig. 2). However, a new interpretation first discussed here indicated only five toes were present. That sixth digit was created to fill a perceived space produced by broken and displaced phalanges.

Figure 1. Tulerpeton pes reconstruction options using published images of the in situ fossil.

Figure 2. Tulerpeton pes reconstruction options using published images of the in situ fossil.

References
Coates MI and Ruta M 2001 2002. Fins to limbs: What the fossils say. Evolution & Development 4(5): 390–401.
Lebedev OA 1984. The first find of a Devonian tetrapod in USSR. Doklady Akad. Navk. SSSR. 278: 1407–1413.
Lebedev OA and Clack JA 1993. Upper Devonian tetrapods from Andreyeva, Tula Region, Russia. Paleontology36: 721-734.
Lebedev OA and Coates MI 1995. postcranial skeleton of the Devonian tetrapod Tulerpeton curtum Lebedev. Zoological Journal of the Linnean Society. 114 (3): 307–348.
Mondéjar-Fernandez J, Clément G and Sanchez S 2014. New insights into the scales of the Devonian tetrapods Tulerpeton curtum Lebedeve, 1984. Journal of Vertebrate Paleontology 34:1454-1459.

wiki/Tulerpeton