The origin and evolution of bats part 4: distance vs. accuracy

Earlier
we looked at bat origins here, here and here from several perspectives. Some of these are now invalid given the following scenario.

Today we’ll take a fresh look at
the behavior and traits of the closest bat relatives in the large reptile tree (LRT, 1233 taxa, subset Fig. 1) and see what they can tell us about bat origins. This is called ‘phylogenetic bracketing‘. In such a thought experiment we can put forth an educated guess regarding an unknown behavior or trait for a unknown taxa (e.g. pre-bats) if all related specimens share similar behaviors and traits inherited from a known or unknown last common ancestor.

We start off with a cladogram
focusing on bat relationships (Fig. 1) and take things one logical step at a time.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

One. Living sister taxa.
The closest tested sister taxa to bats here (Fig. 1) are pangolins and colugos (flying lemurs) in order of increasing distance. The origin of bats and pangolins has remained a traditional enigma. Like the origin of pterosaurs and Longisquama, the surprise is, they are most closely related to each other, despite their current differences.

Two. Ancestral taxa
Th bat/colugo/pangolin clade had its genesis near the original dichotomy of placental mammals, when Carnivora split off from all others. At the next dichotomy the bat/colugo/pangolin clade split off from all others. So this clade is not far from an ancestral clades with living genera. Monodelphis, the short-tailed opossum today restricted to South America, nests just outside of all mammals with a placenta. Nandinia, the African palm civet, is a basal member of the Carnivora, somewhat larger than its Mesozoic forebearers.

Three. Timing for clade origins
The bat/colugo/pangolin clade had its origin in the Early Jurassic based on the more primitive egg-layers, Megazostrodon, Brasilitherium and Kuehneotherium in the Late Triassic and the much more derived arboreal multituberculate/rodent, Megaconus, in the Middle Jurassic. As you can see, Jurassic mammals remain extremely rare, currently represented only by the likes of Megaconus. Others will, no doubt, be discovered in time.

Four. Arboreality (tree niche)
Some bats, colugos and pangolins live in trees, and so do their last common ancestors, short-tailed opossums and African palm civets.

Five. Climbing trees
Bats no longer have to climb trees because they can fly. Colugos and pangolins both climb trees in a series of symmetrical short hops/extended reaches (colugo video, pangolin video), distinct from palm civets and short-tailed opossums, which put forth one hand at a time, like primates do.

Six. Descending trees.
Bats fly between trees. Colugos glide between trees. Pangolins use their prehensile tail to ease themselves down. The African palm civet drops out of trees in play. It also descends tree trunks like a squirrel, head first.

Seven. Nocturnal
Most bats, colugos, pangolins, palm civets and short-tailed opossums prefer to be active at night.

Eight. Omnivorous diet
Some bats eat insects, others prefer nectar or hanging fruit. Colugos prefer leaves, shoots, flowers, sap, and fruit. Pangolins eat ants. Palm civets and short-tailed opossums are omnivorous. African palm civets feed by holding their prey in their hand-like front paws, biting it repeatedly and then once dead, swallowing it whole.

Nine. Extradermal membranes
Colugos and bats both have extradermal membranes to their unguals that extend their glides in the former and enable flapping flying in the latter. Such membranes are lost in living pangolins, but the Early Cretaceous pangolin, Zhangheotherium appears to have scale-lined membranes between the elbows and knees. These were overlooked in the original description. The gliding membrane in colugos is fur-covered and camouflaged dorsally, naked underneath. In bats the flying membrane is naked, translucent and never camouflaged.

Ten. Mobile clavicle, interclavicle and scapula
The basal pangolin, Zhangheotherium, has a mobile clavicle-interclavicle and the large scapula rises above the  dorsal vertebrae, as in bats, but not colugos.

11. Sprawling femora
Zhangeotherium and bats share sprawling hind limbs, distinct from the more erect hind limbs of most limbed mammals.

12. Silent vs. noisy
African palm civets are noisy. Colugos and pangolins are largely silent. Bats are constantly chirping to one another and (micro-bats only) as part of their sonar attack system.

13. Enemies
All current enemies of bats (e.g. birds, snakes) evolved during or after the Late Cretaceous. Jurassic trees might have been a refuge for small early climbing mammals, like colugo, bat and pangolin ancestors. However…the minimally feathered, small theropod dinosaur, Sinosauropteryx, contained the jaws of Zhangheotherium, perhaps caught after descending from the trees or plucked out of lower branches. Certain pterosaurs (e.g. giant anurognathids) might have preyed on arboreal  mammals in the Jurassic, but no evidence of this is yet known.

FIgure x. Calcaneal spur in Zhangheotherium. Not venomous, but perhaps to anchor a uropatagium.

FIgure 2. Calcaneal spur in Zhangheotherium. Not venomous, but perhaps to anchor a uropatagium as in bats.

14. Calcaneal spurs
Hurum et al. 2006 originally considered the small spurs found on the calcaneum of Zhangheotherium (Fig. 2) similar to venom spurs found on the platypus, Ornithorhynchus. Phylogenetic bracketing indicates the closer homolog is with the basal bat, Onychonycteris, which has longer calcaneal spurs framing a trailing uropatagium.

Figure x. Monodelphis babies in an open pouch. This is how placentals began, slowly evolving from the less open pouch.

Figure 3 Monodelphis babies in an open pouch. This is how placentals began, slowly evolving from the less open pouch.

15. Newborns and mothers
All basal placental mammals give birth to helpless newborns that ride with the mother until mature enough to go out on its own. Monodelphis demonstrates a primitive version of this, protecting its ten young with lateral flaps of skin (Fig. 3). Carnivore mothers make nests for newborns (2-4 for African palm civets), but colugo, bat and pangolin mothers take their one or two babies everywhere they go, like marsupial mothers do. Zhangheotherium might have been fossilized with several newborns. (Fig. 4) and extradermal membranes between elbows and knees, as in bats and colugos. As we know from colugos, these extradermal membranes in basal pangolins (and Chriacus?) likely formed a playpen or nursery for developing young riding beneath their mother during the earliest stages of development.

Figure x. Zhangheotherium showing possible extradermal membranes (green) with keratinous scales (red) and several newborns scattered in the abdominal area, similar to Monodelphis in figure x.

Figure 4. Zhangheotherium showing possible extradermal membranes (light blue and green) with keratinous scales (red) and several newborns scattered in the abdominal area, similar to Monodelphis in figure x. These amorphous blobs with tiny tail bones need further inspection. Some may just be stains and shapes.

16. Curling (flexing the spine)
Mother opossums, palm civets, colugos, bats and pangolins are able to curl their spines so much that the mother’s mouth is able to assist wiggling newborns climb to the abdominal nipples. This curling ability is co-opted by pangolins as they defend themselves by rolling into a tight ball and by bats that catch prey in their tail before curling up to bite the victim as it is brought close to the jaws. Higher mammals lose the ability to curl ventrally in this manner. Humans and other primates have a limited ability to do this. Instead they use their hands. More derived mammals with stiffer backs have more developed newborns.

17. Upside-down vs. right-side up nursery for the young
Colugos may rest right-side up (preferring to hang from below a slightly leaning tree trunk) or upside down hanging by all fours beneath a horizontal branch. When doing so the mother’s extradermal membranes form walls making a protective nursery for the young ones.

By contrast, bats rest up-side down, sometimes hanging by only one locked foot. To fly bats simply release this foot lock, then plummet and start flapping. Bat membranes also provide a protective nursery for their young as they cling to their mothers’ chest and her wings fold over them.

Nowadays pangolins roll into a ball while nursing their young. Later in life, babies ride on the mother’s back and tail when able to do so. Zhangheotherium (Fig. 4) appears to have provided a colugo-like, but scale-lined membrane nursery for several growing babies. The late-surviving pre-bat, Chriacus (Fig. 5), likely did the same, based on phylogenetic bracketing.

18. Claws
Short-tailed opossums and African palm civets use their claws to climb trees and grab prey and fruit, bringing it to the mouth. So do basal primates. Colugos, bats and pangolins use their larger, curved claws principally to hang from trees, though living pangolins have co-opted their large claws to dig out ant and termite nests from trees and underground.

19. Distance vs. accuracy
Colugos leap and turn away from their tree trunk base in order to launch themselves into a glide. Can they do this while hanging beneath a branch? I don’t know. With their long limbs, colugos can just leap (without gliding) across gaps of 5m or more. With limbs extended, they can glide for 136m at 10m/second. Gliding is good for a quick escape from predators, and access to patches of food that are otherwise inaccessible. It does not save them energy to glide, let along climb back to a gliding height.

Bats drop from trees, then fly wherever they please, typically landing upside down on another high branch or cavern roof. The origin of bat flight enabled by flapping hyper-elongated webbed fingers is the key question here, and it is answered by combining all of the above numbered traits.

Before bats could fly Jurassic pre-bats had to climb trees, probably like colugos and pangolins do (see #5 above), before standing bipedally, but upside-down, on a horizontal branch. Why would they do that? To prepare to dive bomb insects on and in the leaf litter below. Here is where sonar became valuable, detecting insects in the leaf litter at night. Here is where the leaf litter became valuable, cushioning the early awkward landings of small dive-bombing pre-bats. Here is where flapping, even with small hands around colugo-like dermal membranes became valuable, at first in panic, then in gradually learning how to better direct the fall to cover the prey below.  (By analogy birds flap their wings vigorously while dropping to slow their descent.)

Upon landing the extended pre-bat nursery membranes ‘put a lid’ on the prey. Then, curling the tooth-line jaws toward the tail and the tail toward the jaws (see #16 above) spelled doom for the captured food item. Over time, larger fingers made better flapping parachutes. Ultimately flapping bats  learned how to hover before diving bombing their prey, like owls do. Later, after further development, bats gained the power and morphology to enable flight, slowly at first, then better and better to escape ground-dwelling predators and avoid having to climb a tree for the next attack. Only later did bats learn to use their sonar and flying skills on flying insects.

So what began as a small pouch, then a larger nursery membrane for bat and colugo infants became a killing zone for bat prey on the ground, another example of co-opting an old trait for a new behavior in derived taxa. Distinct from birds and pterosaurs, which used their nascent flapping behavior to ascend tree trunks to escape predators, create threat displays and slow their descents from branches, bats used their nascent flapping ability only to slow and direct their descent from branches. Distinct from colugos, which glided for distance, bats dropped for accuracy. Distance came later, after flight developed.

Remember the fall need not be far at first. Conifers can have very low branches and leaf litter can be a soft cushion for a mouse-sized mammal. Graduating slowly to higher branches provides bats a wider ‘field-of-view’ for their slowly developing sonar, and more time to develop flapping. Bat hind limbs are not long or heavily muscled. They are not good at leaping, like colugos.

Fruit eating bats could not have developed until flowering and fruit-bearing trees developed, later in the Cretaceous. The LRT and the fossil record indicates that fruit-eating bats are derived relative to smaller insect-eating bats. So sonar-emitting apparently was lost in fruit-eating bats, rather than never a part of their lineage. The great variation now seen in sonar-emitting bat morphology was likely developed during and after the Cretaceous, based on the current fossil record. I think we’ll find fully volant fossil bats in the Cretaceous someday.

I happened upon this idea while watching a pigeon descend from a roofline to a balcony beneath it and wondered if accuracy was more important for bats, while distance was more important for colugos. That distinction seems to be the key driver in both clades. In any case, it is important that any proposed scenario be viable at every point during the gradual evolution of new traits and behaviors. In this case, developing flapping forelimbs had to originate with a bipedal configuration, even it inverted. Developing sonar had to originate from simply listening to nocturnal insects and other small prey rustling in the leaf litter, not far below, gradually getting better in those families that randomly had slightly better skills once dive-bombing and trapping became the method for predation.

20. Bat ontogeny
Recapitulates this phylogenetic scenario. The fingers elongate last. 

21. Solitary vs. communal
Colugos and pangolins are solitary. So are African palm civets except when food is plentiful. Bats are communal, whether nesting in trees or caves. According to Kerth 2008, “Variable dispersal patterns, complex olfactory and acoustic communication, flexible context-related interactions, striking cooperative behaviors, and cryptic colony structures in the form of fission-fusion systems have been documented. tropical bats often form groups year-round, whereas sociality in temperate-zone species is sometimes restricted to certain times of the year. In most species, females form so-called maternity colonies to rear their young communally, whereas males are solitary, form groups of their own, or join female groups. In only a few species are both sexes solitary, meeting only to mate.”

Kerth concludes, “None of the three factors that I identify as important for the evolution of sociality in bats (ecological constraints, physiological demands, and demographic traits) can fully explain the frequency and diversity of group living in bats.”

Figure 1. Basal placentals at two scales, all arising from a Middle Jurassic sister to Monodelphis, based on the Earliest Cretaceous appearance of Zhangheotherium, in the lineage of pangolins.

Figure 5. Basal placentals at two scales, all arising from a Middle Jurassic sister to Monodelphis, based on the Earliest Cretaceous appearance of Zhangheotherium, in the lineage of pangolins..

22. Soles of the feet oriented opposite to those of most mammals
Distinct from most mammals, the knees of bats are splayed laterally, which should extend the toes laterally. However, the ankle is rotated another 90º producing a foot in which the soles are ventral during flight and while hanging. In the case of long-legged fish-eating bats, the feet help bring captured fish back to the mouth.

FIgure 1. Wondering if Chriacus had an inverted stance and dermopteran membranes? Comparisons to Onychonycteris and Pteropus.

FIgure 6. Wondering if Chriacus had an inverted stance and dermopteran membranes? Comparisons to Onychonycteris and Pteropus are shown. Yes, the knees are straight in derived fruit bats, bent in Onychonycteris and micro bats. The uropatagia are spread while inverted and while flying. Chriacus appears to be a much larger and much later-surviving version of much smaller Jurassic pre-bats. The membranes are conjectural and may have been lost in this large specimen, but it illustrates the possibility of a dive bombing taxon that covered prey like a casserole lid.

Why do bats hang upside down?
Without a phylogenetic or deep-time perspective, the following video is the best answer current bat workers can provide:

Bats are not using their wings to cool off.
A recent heat wave killed many fruit bats. They fell dead out of the trees (see below). None were creating a cooling breeze with their wings or extending their wings in a cooling fashion, like elephants sometimes do. Microbats that live in caves never have this problem.

Bat wings notes:

  1. Finger flexibility during flight varies greatly in bats.
  2. The flight stroke is otherwise bird-like with elbows raised above the back, nearly meeting at the midline, for maximum power at low airspeed, or less so for cruising at higher airspeeds.
  3. The large fingers do nothing else but push air for thrust and lift. They are not extended to cool the bat, nor do they extend or flash during courtship.
  4. Bat fingers hyper flex at the wrist to tuck away the flight membrane and reduce its surface area when not in use, as in pterosaurs and birds. When flexed they do little but envelope the bat and its clinging young.

Miscellaneous notes:

  1. Zhangheotherium was originally considered a symmetrodont mammal, but its teeth seems to converge with archaeocete whales in this regard. The reappearance of a more primitive symmetrodont molar shape is here considered an atavism in the evolution of toothlessness in both certain odontocetes and pangolins by convergence.
  2. The uncoiled cochlea of highly derived Zhangheotherium and multituberculates, has been traditionally considered a trait that nests these taxa in more basal branches of the mammal family tree. Here, in the LRT, these traits appear to be neotonous or atavistic developments that, taken alone, tend to confuse systematics. No traits should ever be taken alone to determine systematics. That would be ‘pulling a Larry Martin.’
  3. The initial splitting up of Pangaea in the Early Jurassic gave the previously dry climate a more lush, subtropical parade of cycads, conifers, ginkgoes and tree ferns. So there were plenty of standing and fallen trees for early mammals to gambol upon, learning how to climb and leap. The forest floor was likely cushioned with a carpet of leaves and fronds to absorb accidental falls and hunger-driven dive bombs mediated by fluttering pre-wings and large membranes co-opted for eventual flight.

References
Byrnes, Libby, Lim & Spence. 2011. Gliding saves time but not energy in Malayan colugos. Journal of Experimental Biology http://dx.doi.org/10.1242/jeb.052993
Hurum JH, Luo Z-X and Kielan-Jaworowska Z 2006. Were mammals originally venomous? Acta Palaeontologica Polonica 51(1): 1–11.
Kerth G 2008. Causes and Consequences of Sociality in Bats. BioScience, Volume 58, Issue 8, 1 September 2008, Pages 737–746, https://doi.org/10.1641/B580810
Online here.

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New(?) mammal at the Eutheria-Metatheria split

Bi et al. 2018 bring us a small Virginia opossum from the early Cretaceous
“Molecular estimates of the divergence of placental and marsupial mammals and their broader clades (Eutheria and Metatheria, respectively) fall primarily in the Jurassic period. Supporting these estimates, Juramaia, the oldest purported eutherian is from the early Late Jurassic (160 million years ago) of northeastern China. Sinodelphys, the oldest purported metatherianâis from the same geographic area but is 35 million years younger, from the Jehol biota. Here we report a new Jehol eutherian, Ambolestes zhoui, with a nearly complete skeleton that preserves anatomical details that are unknown from contemporaneous mammals, including the ectotympanic and hyoid apparatus. This new fossil demonstrates that Sinodelphys is a eutherian, and that postcranial differences between Sinodelphys and the Jehol eutherian Eomaia, previously thought to indicate separate invasions of a scansorial niche by eutherians and metatherians, are instead variations among the early members of the placental lineage. The oldest known metatherians are now not from eastern Asia but are 110 million years old from western North America, which produces a 50-million-year ghost lineage for Metatheria.”

Figure 1. Ambolestes tracing from Bi et al. 2018.

Figure 1. Ambolestes tracing from Bi et al. 2018. plate and counter plate. Note the scale bar. This taxon is one third the size of the extant opossum. Apparently and oddly no unguals were preserved.

In the large reptile tree (LRT, 1131 taxa) the new fossil at the Metatheria/ Eutheria split is phylogenetically identical to and therefore congeneric with Didelphis, the Virginia opossum. So, this is pre-marsupial in a clade at the base of the marsupial/placental split. There are also a series of pre-placentals, some of which are extant and retain a reduced pouch, like Monodelphis.

Figure 2. Ambolestes skull in situ with DGS applied.

Figure 2. Ambolestes skull in situ with DGS applied.

Ambolestes zhoui gen. & sp. nov. (Bi et al. 2016, 126 mya; 25cm in length) is is one third the size of the extant opossum, but otherwise nearly identical based on tested traits. In the LRT Didelphis nests with Ambolestes and they nest with Eomaia and Agilodocodon as the last common ancestors to Metatheria and Eutheria. Bi said in an interview, “Ambolestes zhoui is an early member of the placental lineage. It also carries mixed features both placentals and marsupials”. In the LRT, Ambolestes is exactly as much in the placental lineage (Fig. 4) as Didelphis is… and Didelphis has a pouch. Both have prepubic (epipubic) bones.

Since Ambulestes is congeneric with Didelphis,
you heard it hear first when the LRT nested Didelphis as the last common ancestor of Metatheria and Eutheria. Good to see confirmation.

Figure 3. Ambolestes skull reconstructed. Jaw tips restored.

Figure 3. Ambolestes skull reconstructed. Jaw tips restored. Lower last molar appears to be just erupting. No retroartcular process is apparent here, which sometimes happens with Didelphis (Mohamed 2018)

The Pittsburgh Post-Gazette reported,
“The well-preserved new mammal, an ancient furry creature most similar to a modern tree shrew, is named Ambolestes zhoui.” Actually Ambolestes was a little less exotic than that.

“John Wible, curator of mammals at the Carnegie Museum of Natural History, became involved in the project about two years ago.As soon as I saw the photographs of the fossil I was like, ‘Oh my God this is amazing,’ ” he said. “It was amazingly complete. Right off the bat I saw there were skeletal parts of the body that were not known of other animals of that time period.”

But if Dr. Wible happened upon a certain type of roadkill
or went out after midnight with a flashlight he would have seen a living version of the Early Cretaceous fossil. Rather than, “this is amazing” he could have said, “we could have predicted this.”

Figure 7. Subset of the LRT focusing on basal live-bearing mammals.

Figure 4. Subset of the LRT focusing on basal live-bearing mammals.

The Post-Gazette also reported, 
“The fossil was not allowed to leave China, said Mr. Wible, noting that this is the first paper he’s published where he’s been unable to actually hold the fossil, though he hopes to see it in person in the next few years. Instead, he relied on detailed photographs and scanned images.”

Figure 4. Didelphis, the extant opossum, a sister to the smaller Ambolestes

Figure 5. Didelphis, the extant opossum, a larger sister to the smaller and 126 million years older Ambolestes.

Now it’s important to remember 
that tooth traits can converge and reverse. Think about archaeocetes (pre-whales), which have three cusps all in a row, like cynodont. Consider odontocetes, which have simple cones, like basal reptiles. Thus, tooth only taxa must be treated separately from skeletal taxa and cladograms must be based on skeletal traits, not tooth traits, which can be dangerous based on the issues that arise from the Bi et al. cladgoram (Fig. 6).

Take another look at taxa listed in Bi et al. 2018
Maelestes, when tested with more taxa, nests at the base of the tenrec/odontoete clade. Necrolestes nests with the golden mole, Chrysochloris, a basal member of Glires. Zhangeotherium is a basal pangolin. They (Bi et al. and other basal mammal workers) are going to have to expand their taxon lists to include at least all the mammals that don’t have hooves, and that includes a few that do have quasi-hooves, like the descendants of Maelestes.

FIgure 8. Cladogram published in Bi et al. 2018 with colors added to show taxa appearing elsewhere in the LRT. As you can see, this is a mess, likely created by too much emphasis on teeth traits, which converge and reverse.

FIgure 6. Cladogram published in Bi et al. 2018 with colors added to show taxa appearing elsewhere in the LRT. As you can see, this is a mess, likely created by too much emphasis on teeth traits, which converge and reverse. Treeshrew-like Maelestes, when tested with more taxa, nests at the base of the tenrec/odontoete clade. Necrolestes nests with the golden mole, Chrysochloris, a basal member of Glires. Zhangeotherium is a basal pangolin.

References
Bi S-B, Zheng X-T, X, Wang X-L, Cignetti N-E, Yang SL and Wible JR 2018.
An Early Cretaceous eutherian and the placental/marsupial dichotomy. Nature (advance online publication) DOI: https://doi.org/10.1038/s41586-018-0210-3
https://www.nature.com/articles/s41586-018-0210-3
Mohamed R. 2018. Anatomical and radiographic study on the skull and mandible of the common opossum (Didelphis marsupialis Linneaus, 1758 (in the Caribbean). Veterinary Sciences 5(44) 10 pp. doi:10.3390/vetsci5020044

https://carnegiemnh.org/press/new-mammal-fossil-provides-insights-on-early-placental-mammal-evolution/

 

Cifelliodon: new echidna ancestor from the Early Cretaceous of Utah

This one seemed pretty obvious from the first impression,
but failed to make the same impression on the original authors (Huttenlocker et al., 2018).

Usually mammal teeth are found without a skull.
Huttenlocker et al., 2018 found a skull largely without teeth (most don’t erupt beyond the rim of the very few alveoli), certainly a derived trait for mammals. And this is one more way tetrapods became toothless. They named their new taxon, Cifelliodon wahkarmoosuch (Fig. 1).

Figure 1. Early Cretaceous Cifelliodon is ancestral to the living echidna, Tachyglossus according to the LRT. The lack of teeth here led to toothlessness in living echidnas. The skull of Tachyglossus is largely fused together, lacks teeth and retains only a tiny lateral temporal fenestra (because the jaws don't move much in this anteater. Compared to Cifelliodon the braincase is greatly expanded, the lateral arches are expanded and the two elements fuse, unlike most mammals.

Figure 1. Early Cretaceous Cifelliodon is ancestral to the living echidna, Tachyglossus according to the LRT. The reduced number and size of teeth here led to toothlessness in the living echidna. The skull of Tachyglossus retains only a tiny lateral temporal fenestra (because the jaws don’t move much in this anteater. Compared to Cifelliodon the braincase is greatly expanded, the lateral arches are expanded and the two elements fuse, unlike most mammals.

According to Wikipedia:
“Cifelliodon is an extinct genus of haramiyid mammal from the Lower Cretaceous of North America. It is a mammaliaform, and is one of the latest surviving haramiyids yet known, belonging to the family Hahnodontidae. Its discovery led to the proposal to remove hahnodontids from the larger well-known group, the multituberculates.”

As usual the LRT recovered a different nesting.

Figure 2. Cifelliodon skull in three views, plus DGS, plus the original drawing, which is not very accurate.

Figure 2. Cifelliodon skull in three views, plus DGS, plus the original drawing, which is not very accurate. A mandible is restored here.

Figure 3. Subset of the LRT focusing on Monotremes, now including Cifelliodon.

Figure 3. Subset of the LRT focusing on Monotremes, now including Cifelliodon.

Here
in the large reptile tree (LRT, 1233 taxa) Cifelliodon wahkarmoosuch from the Early Cretaceous of Utah nests strongly with Tachyglossus (Figs. 1, 4, 5), one of the extant egg-laying echidnas, currently restricted to Australia and surrounding islands. Tachyglossus was tested in the (Huttenlocker et al. analysis of basal mammal relationships, but the two taxa did not nest together.

Unfortunately Huttenlocker et al., 2018
experienced taxon exclusion problems that nested Cifelliodon with the distinctly different wombat Vintana and those two with the distinctly different multituberculates all more primitive than monotremes.

To their credit
Huttenlocker et al. linked this North American taxon with others from Gondwana which includes Australia, which broke off 99 mya, 40 million years after the appearance of Cifelliodon in Utah. In an interview for USC, Huttenlocker reported, “Most of the fossil record of early mammal relatives is based on teeth. Cifelliodon is unique in that it is one of the only near-complete skulls of a mammal relative from the basal Cretaceous of North America and is the only fossil of early mammal relatives from this time interval in Utah.”

“The fact that the skull looked so primitive compared to other known mammal groups from the Cretaceous made figuring out its relationships extremely difficult. It shows some unique dietary specializations that are seen in only a handful of groups that lived during the age of dinosaurs. Ultimately, the structure of the preserved molars showed clear similarities to some neglected fossil teeth from Northern Africa. So we think that Cifelliodon represents an archaic offshoot whose relatives may have dispersed into the southern continents and became fairly successful during the Cretaceous.”

Figure 3. Tachyglossus skeleton, manus and x-rays. Note the perforated pelvis.

Figure 4. Tachyglossus skeleton, manus and x-rays.

The skull of Tachyglossus
retains only a tiny lateral temporal fenestra (because the jaws don’t move much in this anteater. Compared to Cifelliodon the braincase is greatly expanded, the lateral arches are expanded and the two elements fuse, unlike most mammals.

Figure 1. The echidna (genus: Tachyglossus) in life. This slow-moving spine-covered anteater has digging claws.

Figure 5. The echidna (genus: Tachyglossus) in life. This slow-moving spine-covered anteater has digging claws. Many of the derived traits seen here developed during the last 100 million years since Cifelliodon.

 

References
Huttenlocker AD, Grossnickle DM, Kirkland JI, Schultz JA and Luo Z-X 2018. Late-surviving stem mammal links the lowermost Cretaceous of North America and Gondwana. Nature Letters  Link to Nature

wiki/Cifelliodon

https://news.usc.edu/143411/why-you-should-care-about-this-130-million-year-old-fossil/

Anhanguera animation at the NHM (London)

This one started off with so much promise
as the animators at the National History Museum (NHM) in London assembled their version of the ornithocheirid pterosaur, Anhanguera, bipedally (Fig. 1), as you’ll see when you click on the video under ‘References’.

Figure 1. Animated by the NHM, Anhanguera is bipedal and flapping its literally oversize wings.

Figure 1. Animated by the NHM, Anhanguera is bipedal and flapping its literally oversize wings standing on oversize feet with an undersized skull and hyperextended elbows and unbalanced stance.

Unfortunately there were some morphology issues (compared in Fig. 2):

  1. wings too long
  2. sternal complex missing
  3. gastralia missing (but rarely preserved in ornithocheirids)
  4. feet way too big
  5. skull too small
  6. tail too short
  7. not sprawling
  8. free fingers too big
  9. wing fingers should tucked tight against elbows (in the same plane)
  10. one extra cervical
  11. anterbrachia too short and gracile
  12. elbows overextended (in Fig. 1)
  13. too much weight put on forelimbs, center of balance (wing root) should be over the toes
  14. Prepubes are extremely rare in ornithocheirds, but when present they are tiny, putter-shaped and oriented ventrally in line with the bent femora, not anteriorly
Figure 2. NHM Anhanguera compared to skeletal image from ReptileEvolution.com.

Figure 2. NHM Anhanguera compared to skeletal image from ReptileEvolution.com. There are at least 10 inaccuracies here. See text for list.

Also unfortunately, the video quickly devolved
to the invalid and dangerous quad launch, when (doggone it!) it was all set up to do a more correct and  much safer bird-like launch. The laws of physics and biomechanics are ignored here, but at least David Attenborough narrates.

Figure 3. NHM Anhanguera quad launch select frames.

Figure 3. NHM Anhanguera quad launch select frames. The laws of physics and the limitations of biomechanics are ignored here.

Attempts to convince readers and workers
that the quad-launch hypothesis cheats morphology and physics (as recounted here and at links therein) have so far failed. But I’m not giving up. So, if anyone has a connection to the NHM in London, please make this post available to alert them of their accidental foray into wishful thinking and inaccurate morphology.

References
National History Museum (NHM) in London

Mystery solved: Thylacoleo is a giant sugar glider…

no doubt, a little too big to glide…
and Thylacoleo (Fig. 2) is looking even less carnivorous in phylogenetic bracketing.

Sugar gliders
(Fig. 1) are phalangers (Fig. 6), a marsupial clade nesting between kangaroos and wombats (Fig. 5).

Figure 1. Petaurus breviceps skeleton in two views, plus a skull with mandible, lacking in the skeleton.

Figure 1. Sugar glider, Petaurus breviceps, skeleton in two views, plus a skull with mandible, lacking in the skeleton.

Adding the marsupial sugar glider,
Petaurus (Figs. 1, 3), and the cuscus, Phalanger (Fig. 6), to the large reptile tree (LRT, 1231 taxa) resolves a decades-old phylogenetic problem because Petaurus, the sugar glider, nests as a sister to Thylacoleo, the marsupial lion (Figs. 2, 4). Phalanger, the cuscus, nests as their last common ancestor, which has been suggested earlier.

According to the AustraliaMuseum website
“Most palaeontologists think that the ancestors of thylacoleonids were herbivores, an unusual occurrence since most carnivores evolved from other carnivorous lineages. One proposal suggests that thylacoleonids evolved from a possum ancestor (Phalangeroidea) based on dental formula, the skull of the cuscus Phalanger, and on a phalangerid-like musculature. Alternatively, evidence from certain skull features may show that thylacoleonids branched off the vombatiform line, the lineage that includes wombats and koalas.”

In the LRT,
wombats and koalas are now sister taxa to the cuscus clade. Without the sugar glider and the cuscus, the marsupial lion earlier nested with the wombat, Vombatus.

Just to be clear,
Phalanger is not an ancestor to Didelphis, the Virginia opossum, in the LRT, even though the Australian Museum called it a ‘possum ancestor.’

Figure 2. Thylacoleo skeleton compared to Petaurus skeleton to scale.

Figure 2. Thylacoleo skeleton compared to Petaurus skeleton to scale.

Long thought to be a super predator, 
in the midst of a clade of gentle wombat-like herbivores, Thylacoleo had, for its size, the strongest bite of any mammal, living or extinct, despite having tiny upper canines. This linking with sugar gliders further erodes the carnivorous hypothesis. 

Figure 3. Skulls of the genus Petaurus with many more teeth than in Thylacoleo, but in the same general pattern. Note the lower third premolar and its similarity to the same tooth in Thylacoleo.

Figure 3. Skulls of the genus Petaurus with many more teeth than in Thylacoleo, but in the same general pattern. Note the lower third premolar and its similarity to the same tooth in Thylacoleo. The big organe tooth at the tip of the dentary is the canine. The lower incisors are absent.

Arboreal or not?
Wikipedia reports, “The claws [of Thylacoleo] were well-suited to securing prey and for climbing trees.” And now we know how that came to be. Petaurus, despite its arboreal abilities, does not have a divergent thumb, like the one found in Thylacoleo.

Dentary canines
traditionally considered large, rodent-like incisors due to their placement, the anterior-most (medial-most) dentary teeth are actually canines. The incisors and their alveoli have disappeared. This can only be traced via phylogeny (see Arctocyon and Didelphis). The ancestrally small lower incisors are gone, replaced with ancestrally large large lower canines that meet medially like typical incisors. Notably, the lower canines maintain their traditional placement relationship to the upper canines (Fig. 6).

Even more interesting,
some marsupial taxa that experience a phylogenetic miniaturization, like Eurygenium (basal to Toxodon) the incisors reappear and the canines are not much larger than the incisors. That’s called a reversal or an atavism.

Figure 4. Thylacoleo skull. Many times larger than Petaurus, with fewer larger teeth, this is a giant sugar glider.

Figure 4. Thylacoleo skull. Many times larger than Petaurus, with fewer larger teeth, this is a giant sugar glider. The large orange tooth is the lower canine. The upper canine is a vestige. 

Size
Thylacoleo was 71 cm tall at the shoulder, about 114-150cm long from head to tail tip, about the size of a jaguar.

Petaurus is 40cm long to the tail tip, about the size of a ‘flying’ squirrel. Loose folds of skin spanning the fore and hind limbs to the wrists and ankles are used to extend glides from tree to tree, or up to 140m. The diet includes sweet fruits and vegetables.

The sugar glider in vivo.

Figure 5. The sugar glider, Petaurus, in vivo. Note the wrinkled fur between the fore and hind limb. That’s the gliding membrane.

Petaurus species
According to Wikipedia, “There are six species, sugar glidersquirrel glidermahogany glidernorthern glideryellow-bellied glider and Biak glider, and are native to Australia or New Guinea.” Whichever one is closest to Thylacoleo has not been tested or determined.

Figure 2. Thylacoleo skeleton compared to Petaurus skeleton to scale.

Figure 5. Subset of the LRT focusing on Marsupialia, Metatheria and then nesting of Thylacoleo.

Petaurus breviceps (Waterhouse 1839; Early Miocene to present; up to 30cm) is the extant sugar glider, a nocturnal squirrel-like marsupial able to climb trees and glide with furry membranes between the fore and hind limbs. An opposable toe is present on each hind foot. Sharp claws tip every digit.

Phalanger orientalis (Pallas 1766; 34 cm in length) is a nocturnal arboreal folivore marsupial known as thte Northern common cuscus. Commonly considered a ‘possum’ the cuscus nests between wombats and kangaroos, basal to sugar gliders and marsupial lions.

Figure 6. The cuscus (genus: Phalanger orientalis) nests with Petaurus and Thylacoleo in the LRT.

Figure 6. The cuscus (genus: Phalanger orientalis) nests with Petaurus and Thylacoleo in the LRT. Those anterior dentary teeth look like incisors, but phylogenetically are actually canines.

Thylacoleo carnifex (Owen 1859; Pliocene-Pleistocene; 1.14 m long) was a giant sugar glider like Petaurus. Thylacoleo had the strongest bite of any mammal with the largest, sharpest molars of any mammal. It had fewer but larger teeth than Petaurus. The manus included retractable claws. The pes had a very large heel bone (calcaneum). This supposedly carnivorous ‘marsupial lion’ nests with herbivores. Pedal digit 1 likely had a phalanx and claw, but it has not been shown.

References
Goldingay RL 1989. The behavioral ecology of the gliding marsupial, Petaurus australis. Research Online. University of Wollongong Thesis Collection. PDF
Owen R 1859. On the fossil mammals of Australia. Part II. Description of a mutilated skull of the large marsupial carnivore (Thylacoleo carnifex Owen), from a calcareous conglomerate stratum, eighty miles S. W. of Melbourne, Victoria. Philosophical Transactions of the Royal Society 149, 309-322. 
Waterhouse GR 1838. Observations on certain modifications observed in the dentition of the Flying Opossums (the genus Petaurus of authors). Proceedings of the Zoological Society of London. 4: 149–153.

wiki/Petaurus
wiki/Thylacoleo
https://australianmuseum.net.au/thylacoleo-carnifex

Armadillosuchus: another small herbivorous croc

Marinho and Carvalho 2009
brought us a new, small, crocodyliform from the Late Cretaceous of South America, Armadillosuchus (Fig. 1).

Oddly,
the nares are not mentioned in the text, nor labeled in the published figure (Fig. 1). Where are they?

Figure 1. Armadillosuchus skull in dorsal view and lateral view. A second specimen preserves teeth. Reconstruction below aligns the ventral maxilla with the quadrate, as in all sister taxa.

Figure 1. Armadillosuchus skull in dorsal view and lateral view. A second specimen preserves teeth. Reconstruction below aligns the ventral maxilla with the quadrate, as in all sister taxa. Where are the nares? They are not mentioned in the text.

Armadillosuchus arrudai (Marinho and Carvalho 2009; Late Cretaceous; est. 2m in length) was an herbivorous and armored crocodylomorph from South America. It nests with Mariliasuchus (above) in the LRT. Both have giant premaxillary teeth. The naris is reduced to a tiny hole facing anteriorly. The rostrum may have been more horizontal than originally reconstructed as all sister taxa line up the quadrate with the ventral maxilla (Fig. 1 bottom figure). These are members of the Ziphosuchia.

Figure 1. Mariliasuchus skull in several views. Note the premaxillaery fangs and the short blunt remainder of the teeth.

Figure 2. Mariliasuchus skull in several views. Note the premaxillaery fangs and the short blunt remainder of the teeth. The nares are very tiny and anteriorly oriented. Note the alignment of the quadrate with the ventral rim of the maxilla together with the rostrum vs. forehead angle, as in the new lateral view of Armadillosuchus (Fig. 1).

The nares of Armadillosuchus
are best found by phylogenetic bracketing based on the nares found in its sister taxon Mariliasuchus (Fig. 2).

Figure 2. Subset of the LRT focusing on Crocodylomorpha (basal Archosauria) including Armadillosuchus.

Figure 2. Subset of the LRT focusing on Crocodylomorpha (basal Archosauria) including Armadillosuchus.

Key to understanding the origin of the clade Dinosauria
is to understand the proximal outgroup taxa, the bipedal basal Crocodylomorpha, which no prior studies include (though some include Lewisuchus).

Images of complete skeletons of Armadillosuchus
are online, photographed from museum mounts. I have not found academic data for anything more than is figured above. The rest may be restored. Let me know of any citations I have missed.

References
Marinho T S and Carvalho, IS 2009. An armadillo-like sphagesaurid crocodyliform from the Late Cretaceous of Brazil. Journal of South American Earth Sciences. 27 (1): 36–41.

wiki/Mariliasuchus
wiki/Armadillosuchus

The curassow (genus: Mitu/Crax) another chicken cousin

Mitu tuberosum aka Crax turberosa (Linneaus 1758, Spix 1825; 85 cm) is the extant razor-billed curassow, a pheasant-like galliform from the Amazon. Only two eggs are laid per year. Precocious young are feathered and mobile after hatching. Omnivorous. Sexes are similar.

Figure 1. Crax tuberosa skeleton and invivo. This basal neognath bird prefers to walk than fly.

Figure 1. The curassow, Mitu tuberosum/Crax tuberosa, skeleton and invivo. This basal neognath bird prefers to walk than fly.

In the large reptile tree (LRT, 1127 taxa) the curassow (genus Mitu or Crax) nests with the Early Cretaceous bird, Eogranivora, and this clade nests with the chicken (Gallus) and the peafowl (Pavo).

Figure 1. Crax tuberosa skull in three views.

Figure 2. The curassow, Crax tuberosa, skull in three views. Note the slender postorbital (yellow) descending from the robust postfrontal (orange).

The helmeted curassow (genus: Pauxi pauxi) has a casque convergent with the cassowary (Casuarius).

References
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
von Spix JBR 1825. Avium species novae, quas in itinere per Brasiliam annis MDCCXVII – MDCCCXX […] collegit et descripsit. Franc. Seraph. Hübschmann, Monachii [Munich], 1, [VII], 90 pp., 91 pls.

wiki/Crax
wiki/Mitu
wiki/Razor-billed_curassow