Cretaceous toothed birds evolved from toothless megapodes in the LRT

Today’s heretical dive
into the origin of Cretaceous toothed birds (Fig. 1) brings new insight to a clade that has been traditionally misrepresented as a stem clade, often represented by just two highly derived toothed taxa, Ichthyornis and Hesperornis (Fig. 1). In the large reptile tree (LRT, 1659+ taxa; subset Fig. 3) Cretaceous toothed birds arise from extant toothless Megapodius (Figs. 1, 2; Gaimard 1823). How is this possible?

Toothy jaws from toothless jaws? 
That seems to break some rules. And if the LRT (Fig. 3) is valid, that makes toothed Cretaceous birds crown bird taxa.

Figure 1. Click to enlarge. Toothed birds of the Cretaceous to scale.

Figure 1. Click to enlarge. Toothed birds of the Cretaceous to scale. They are derived from toothless taxa.

Earlier Field et al. 2020
claimed to discover the ‘oldest crown bird‘ fossil when they described Asteriornis (66 mya), a screamer (genus: Chauna) relative. Unfortunately, due to taxon exclusion, Field et al. 2020 did not consider the ostrich sister, Patagopteryx (80 mya), nor did they understand that Juehuaornis (Wang et al. 2015; Early Cretaceous, Aptian, 122mya; Figs. 1, 4) was also a crown bird taxon, the oldest crown bird, derived from Megapodius, the extant mound builder.

One look
(Fig. 1) at the similarity of Megapodius to basal Cretaceous toothed and toothless birds, like Juehuaornis (Figs. 1, 4), makes the relationship obvious. The LRT recovered that relationship based on hundreds of traits and minimized convergence by testing relationships among 1659 taxa.

So, where did those Cretaceous teeth come from?
Megapodius and Juehuaornis both lack teeth. Basalmost toothed taxa had tiny teeth (Fig. 1) Derived toothed taxa had larger teeth. Try to let that sink in. Teeth re-appeared in these Cretaceous birds.

How is that possible? Consider this:
Juehuaornis is smaller than Megapodius. The sternum and keel of Juehuaornis are smaller than in Megapodius. Why is this important? As we learned earlier, at the genesis of many major and minor clades phylogenetic miniaturization (the Lilliput Effect) is present. That’s how gulls become hummingbirds and rauisuchians become dinosaurs. When adults are smaller they mature more quickly and they retain juvenile traits into adulthood. They also develop new traits, in this case, perhaps ontogeny recapitulated phylogeny.

The tooth genes got turned on again,
at first in a minor way… later in a major way.

Figure 2. Click to enlarge. Origin of birds from Archaeopteryx to Megapodius.

Figure 2. Click to enlarge. Origin of birds from Archaeopteryx to Megapodius. Pseudocrypturus is the sister taxon to the kiwi (Apteryx, Fig. 3), the most basal crown birds, but Juehuaornis is known from much older fossils despite being more derived than Megapodius.

How close were Cretaceous toothless taxa,
like Juehuaornis, to toothed Jurassic ancestors, like Archaeopteryx? Depends on how you look at it.

Chronologically
Juehuaornis is from the Aptian, Early Cretaceous, 122 mya. Archaeopteryx is from the Tithonian, Late Jurassic, 150 myaA transitional taxon, Archaeornithura (Fig. 2) is from the Hauterivian, Early Cretaceous, 131 mya, splitting the time difference. Archaeornithura had teeth and lacked a pygostyle, but had a shorter tail than the most derived Archaeopteryx (Fig. 2).

Morphologically
toothless Juehuaornis follows toothless Megapodius (Figs. 1, 3) and is separated from toothy Archaeornithura by at least three taxa (Figs 2, 3). The question I ask is: did the Cretaceous sisters to these toothless taxa have teeth subsequently lost in later generations over the past 140 million years? Or were teeth lost in  Early Cretaceous transitional taxa (represented by late-survivors (Fig. 2)) only to be regained in the toothy extinct clade (Fig. 3)? For now, let’s leave all options open, but toothlessness followed by toothy jaws is the only option currently supported by phylogenetic evidence (Fig. 3).

Figure 2. Subset of the LRT focusing on bird origins. Crown birds and toothed birds are highlighted.

Figure 3. Subset of the LRT focusing on bird origins. Crown birds and toothed birds are highlighted.

This is what happens when you let the cladogram tell you what happened,
rather than gerrymandering the taxa inclusion list and scores to get the results your professors and colleagues will approve and permit publication.

Figure 2. Juehuaornis reconstructed. Note the scale bars. This is a tiny bird.

Figure 4. Juehuaornis reconstructed. Note the scale bars. This is a tiny bird and the oldest known crown bird.

I should have reported
that Juehuaornis (122 mya) was the oldest known crown bird earlier. I just had to see the toothed birds in phylogenetic order (Fig. 1), making sure they made sense after seeing them listed in the cladogram (Fig. 3).

Add taxa
and your cladograms will be better than most. Create reconstructions to scale and see if your cladograms make sense. When it’s right, it all works out with a gradual accumulation of traits between every node, echoing evolutionary events from deep time. Let me know if this novel hypothesis of interrelationships was published previously anywhere so that citation can be promoted.


References
Gaimard JP 1823. Mémoire sur un nouveau genre de Gallinacés, establi sous le nom de Mégapode. Bulletin General et Universel des Annonces et de Nouvelles Scientifiques 2: 450-451.
Wang R-F, Wang Y and Hu Dong-yu 2015. Discovery of a new ornithuromorph genus, Juehuaornis gen. nov. from Lower Cretaceous of western Liaoning, China. Global Geology 34(1):7-11.

wiki/Megapodius
wiki/Megapode

You heard it here first: Others also doubt the theropod affinities of Oculudentavis

The now famous tiny skull in amber, Oculudentavis, 
(Fig. 1; Xing et al. 2020) continues as a topic of conversation following its online publication in Nature and two previous PH posts here and here.

Figure 1. Oculudentavis in amber much enlarged. See figure 2 for actual size.

Figure 1. Oculudentavis in amber much enlarged.

Several workers have also thrown cold water
on the tiny theropod affinities of Oculudentavis. Oddly, all seem to avoid testing or considering in their arguments the sister taxon in the large reptile tree (LRT): Cosesaurus (Fig. 2). Instead, they report on what Oculudentavis is not. Examples follow:

Dr. Andrea Cau writes in TheropodaBlogspot.com Link here (translated from Italian using Google translate): 

“I believe that the interpretation proposed by Xing et al. (2020) is very problematic. Oculudentavis in fact has numerous anomalous characteristics for a bird and even for a dinosaur. And this makes me doubt that it is classifiable within Dinosauria (and Avialae).

  1. Absence of anti-orbital window. [not true, click here]
  2. Quadrate with large lateral concavity. This character is not typical of dinosaurs, but of lepidosaurs. [that quadrate is twisted, the other is not, the concavity is posterior in vivo]
  3. The maxillary and posterior teeth of the maxilla extend widely below the orbit.
  4. Dentition with pleurodont or acrodont implant.
  5. Very large post-temporal fenestra.
  6. Spoon-shaped sclerotic plates is typical of many scaled lepidosaurs.
  7. Coronoid process that describes a posterodorsal concavity of the jaw reminds more of a lepidosaur than a maniraptor.
  8. Very small size comparable to those of the skulls of many small squamata found in Burmese amber.

“In conclusion, there are too many “lizard” characters in Oculudentavis not to raise the suspicion that this fossil is not a bird at all, let alone a dinosaur, but another type of diapsid, perhaps a scaled lepidosaur, if not possibly a specimen very immature than some other Mesozoic group (for example, a Choristodere). It is well known that many types of reptiles present in the final stage of embryonic development and in the very first moments after hatching a cranial morphology similar to the general one of birds (of in fact, the bird skull is a form of “infantilization” of the classic reptilian skull, extended to the adult).
Unfortunately, the authors, while noting some of the similarities with the squamata, do not test the affinities of Oculudentavis outside Avialae.

“PS: out of curiosity, I tested Oculudentavis in the large Squamata matrix by Gauthier et al. (2012): it turns out to be a stem-Gekkota.”

Note to readers: Neither Gauthier et al. 2012 nor Dr. Cau tested fenestrasaurs, like Cosesaurus… yet another case of taxon exclusion. With regard to phylogenetic age, fenestrasaur tritosaur lepidosaurs, like Oculudentavis, hatch with the proportions of adults (ontogenetic isometry), so the ontogenetic status of this taxon needs further context (e.g. coeval larger adults or smaller hatchlings)/

Update March 14, 2020:
Readwer TG (below) informs me that Cau’s study did include Cosesaurus. My reply follows: “Thank you, Tyler. Good to know. My mistake. Strange that his Oculudentavis has traits more like the distinctively different Sphenodon and Huehuecuetzpalli, when it looks more like Cosesaurus in every regard. Here’s a guess based on experience: neither he nor Gauthier went to Barcelona to see Cosesaurus, and neither did either reference or cite Peters 2000 or the ResearchGate.net update. And Cau probably used the Xing et al. 2020 ink tracing of Oculudentavis rather than the more detailed DGS tracing I produced (or he could have traced himself), since he did not see the tiny antorbital fenestra [or the twisted quadrate]. Just a guess based on 20 years of experience.” 

PS. Neither Gauthier nor Cau showed their work (e.g. skulls diagrammed with suture interpretations as shown at ReptileEvolution.com links). Therefore we cannot know if or where mistakes were made in their scoring attempts. In a similar fashion, testing revealed a raft of scoring problems with Nesbitt 2011, covered earlier here in the last of a nine-part series. 

Dr. Darren Naish updates his original post in Tetrapod Zoology  
with the following notes:

“A number of experts whose opinions I respect have expressed doubts about the claimed theropod status of the fossil discussed below and have argued that it is more likely a non-dinosaurian reptile, perhaps a drepanosaur or lepidosaur (and maybe even a lizard). I did, of course, consider this sort of thing while writing the article but dismissed my doubts because I assumed that – as a Nature paper – the specimen’s identity was thoroughly checked and re-checked by relevant experts before and during the review process, and that any such doubts had been allayed. At the time of writing, this proposed non-dinosaurian status looks likely and a team of Chinese authors, led by Wang Wei, have just released an article [not linked] arguing for non-dinosaurian status. I don’t know what’s going to happen next, but let’s see. The original, unmodified article follows below the line…”

We can only trust what Dr. Naish reports regarding his private doubts as to the affinities of Oculudentavis. Here he confesses to assuming the ‘opinions’ of ‘relevant experts’ got it right, like all the other journalists who reported on this discovery, rather than testing the hypothesis of Xing et al. 2020, like a good scientist should.

While we’re on the subject of confessing, 
earlier the LRT nested Oculudentavis with Cosesaurus (Fig. 1) despite the former’s much later appearance and derived traits, like the essentially solid palate. I failed to mention the skull of Oculudentavis shares just a few traits with another Late Triassic fenestrasaur, Sharovipteryx (Fig. 1). If Oculudentavis also had a slender neck, like the one in Sharovipteryx, perhaps that was one reason why only the skull was trapped in pine sap, later transformed into amber. Just a guess.

Figure 2. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration.

Figure 2. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration.

Note:
with locked down and elongate coracoids, all members of the clade Fenestrasauria were flapping like flightless pterosaurs. Appearing tens of millions of years after the Middle Triassic genesis of fenestrasaurs, who knows what sort of post-crania tiny Early Cretaceous Oculudentavis may have evolved! Known clade members already vary like Hieronymus Bosch fantasy creatures.

The LRT is a powerful tool for nesting taxa
while minimizing taxon exclusion. And it works fast. Feel free to use it in your own studies.


References
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007.The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Xing L, O’Connor JK,; Schmitz L, Chiappe LM, McKellar RC, Yi Q and Li G 2020. 
Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature. 579 (7798): 245–249.

late arrival:

Wang Wei, Zhiheng Li, Hu Yan, Wang Min, Hongyu Yi & Lu Jing 2020. The “smallest dinosaur in history” in amber may be the biggest mistake in history. Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences: Popular Science News (2020/03/13)
http://ivpp.cas.cn/kxcb/kpdt/202003/t20200313_5514594.html

from B. Creisler’s translated post at dml.cmnh.org:

“Here is the list of problems found by the authors:
Doubts 1. Can the shape of the head prove that it is a bird? 
Doubt 2. Unreasonable Phylogenetic Analysis 
Doubt 3. Birds without antorbital fenestrae? 
Doubt 4. “Birds” with pleurodont teeth? 
Doubt 5. Mysterious quadratojugal bone 
Doubt 6. Scleral bones only found in lizards 
Doubt 7. The bird with the most teeth in history? 
Doubt 8. Body size 
Doubt 9. No feathers? 
Doubt 10. Strange wording and logic chains
We hope that the authors of the paper will respond publicly to these questions as soon as possible. At the same time, it is hoped that the authors of the paper will quickly release the raw data of CT scans, so that other scientists can verify the existing results based on the raw data.”
July Post-Script
Authors retract the paper, according to Nature.

 

Rebuilding Bonnerichthys, a big fish from the Niobrara

Just like a model airplane kit,
Friedman et al. 2010 laid out the parts for the giant toothless Late Cretaceous Niobrara fish, Bonnerichthys gladius (Fig. 1).

The authors considered this big fish
to be a plankton eater from the get-go. The first sentence in their paper reads, “The largest vertebrates—fossil or living—are marine suspension feeders.” Bonnerichthys does have a big mouth and no teeth.

The authors also considered
Bonnerichthys to be a member of the Pachycormidae, of which Pachycormus is a tested taxon in the large reptile tree (LRT, 1649+ taxa).

Figure 1. Bonnerichthys parts from Friedman et al. 2010 and colorized here.

Figure 1. Bonnerichthys parts from Friedman et al. 2010 and colorized here. See figure 2 for a reconstruction.

Putting the parts back together
using DGS techniques (Fig. 2) Bonnerichthys took on the appearance of the extant arowana (Osteoglossum, Fig. 2 ghosted), a large, extant, tropical fish. Adapted to hunting at the surface, these ‘bony tongues’ are capable of leaving the water to catch prey on branches that overhang slow-moving rivers.

Figure 2. Reconstructed Bonnerichthys plus, at bottom and ghosted, Osteoglossum to scale.

Figure 2. Reconstructed Bonnerichthys plus, at bottom and ghosted, Osteoglossum to scale. These two taxa are a close match in all respects except time. Note the large pectoral fins on both.

Phylogenetic bracketing
indicates Bonnerichthys was a predator with its eyes on prey above the surface of the water, contra Friedman et al. 2010. Osteoglossum was not mentioned in their text, so this may be another case of taxon exclusion.

Figure x. Subset of the LRT focusing on basal vertebrates (= fish).

Figure x. Subset of the LRT focusing on basal vertebrates (= fish).

The post-crania of Bonnerichthys
was not presented, but should be distinct from Pachycormus when found.


References
Friedman M, Shimada K, Martin LD, Everhart MJ, Liston JJ, Maltese A and Triebold M 2010. 100-million-year dynasty of giant planktivorous bony fishes in the Mesozoic seas. Science 327(5968):990-993.

Revisting Protosphyraena (Late Cretaceous)

Revised May 16, 2020
with the addition of Early Jurassic Ohmdenia, a new taxon that attracts enigmatic Protosphyraena to the osteoglossiformes. They all share a spine-like pectoral fin along with matching dorsal and anal fins.

New data on the Late Cretaceous ‘swordfish with teeth’
Protosphyraena nitida (Leidy 1857; Late Cretaceous; 3m; Figs. 1) brings it up for review and reconsideration. It was originally considered a basal baraccuda and traditionally is now considered a member of the Pachycormiformes, but here nests nearby as a sister to coeval Niobrara Ohmdenia, related to the extant arowana, Osteoglossum.

Distinct from Ohmdenia
Protosphyraena had a swordfish-like body, head and tail (Fig. 1).

Figure 1. Skull of Protosphyraena. Colors added to march tetrapod homologies and updated here from previous guesstimates. Comapare to figures 3 and 4.

Figure 1. Skull of Protosphyraena. Colors added to march tetrapod homologies and updated here from previous guesstimates. Comapare to figures 3 and 4.

Like Hybodus,
and most bony fish, the lacrimal + premaxilla + maxilla are essentially fused to the cranium. That added to the confusion.

Figure x. Newly revised fish subset of the LRT

Figure x. Newly revised fish subset of the LRT

The new nesting of Protosphyraena
as a highly derived taxon makes sense. This is a unique taxon leaving no descendants.


References
Leidy J 1857. Remarks on Saurocephalus and its allies. Transactions of the American Philosophical Society. 11: 91–95.

http://reptileevolution.com/polyodon.htm

Acostasaurus enters the LRT

Pérez and Noé 2017 described
a near complete 3D skull, a complete hindlimb and several vertebrae of a eusauropterygian, Acostasaurus (Fig. 1), they considered it a 4-5m long, snort-snouted pliosaur, one of many ‘pliosaurs’ found in Barremian (Early Cretaceous) Columbia. 

Figure 1. Acostasaurus skull from Pérez and Noé 2017, colors added.

Figure 1. Acostasaurus skull from Pérez and Noé 2017, colors added.

Some of those purported Columbian ‘pliosaurs’
turned out to be giant sisters to more basal eusauropterygians in the large reptile tree (LRT, 1430 taxa). You might remember (here) the giant Sachicasaurus nested with Nothosaurus and (here) the very large Bobosaurus nested with the smaller Corosaurus.

In the LRT
Acostasaurus nests with Anningsaura (Fig. 2) apart from the pliosaurs in the LRT.

Figure 6. Anningasaura colorized from an old engraving. No other aquatic taxon has such bizarrely curved teeth. This taxon is closely related to Hauffiosaurus.

Figure 6. Anningasaura colorized from an old engraving. No other aquatic taxon has such bizarrely curved teeth. This taxon is closely related to Hauffiosaurus.

The authors compared Acostasaurus
with Simolestes a taxon not yet added to the LRT. Look for it soon.

Figure 4. Subset of the LRT focusing on Eusauropterygians (pachypleurosaurs, nothosaurs, plesiosaurs and kin).

Figure 4. Subset of the LRT focusing on Eusauropterygians (pachypleurosaurs, nothosaurs, plesiosaurs and kin).


References
Gómez Pérez M and Noè LF 2017. Cranial anatomy of a new pliosaurid Acostasaurus pavachoquensis from the Lower Cretaceous of Colombia, South America. Palaeontographica Abteilung A. 310 (1–2): 5–42. doi:10.1127/pala/2017/0068.

wiki/Acostasaurus

Mesozoic mammals: Two views

Smith 2011 reported,
at the beginning of the Eocene, 55mya, “the diversity of certain mammal groups exploded.” These modern mammals”, according to Smith, ‘ consist of rodents, lagomorphs, perissodactyls, artiodactyls, cetaceans, primates, carnivorans and bats. Although these eight groups represent 83% of the extant mammal species diversity, their ancestors are still unknown. A short overview of the knowledge and recent progress on this research is here presented on the basis of Belgian studies and expeditions, especially in India and China.’

Contra the claims of Smith 2011
in the large reptile tree (LRT, 1354 taxa, subsets Figs. 2–4) prototherians are known from the late Triassic (Fig. 1). Both metatherians and eutherians are known from the Middle Jurassic. Many non-mammal cynodonts survived throughout the Mesozoic. In addition, the ancestors of every included taxon are known back to Devonian tetrapods.

Noteworthy facts after an LRT review (Fig. 1):

  1. All known and tested Mesozoic mammals (Fig. 1) are either small arboreal taxa or small burrowing taxa (out of sight of marauding theropods).
  2. All Mesozoic monotremes are more primitive than Ornithorhynchus and Tachyglossus (both extant).
  3. All Mesozoic marsupials are more primitive than or include Vintana (Late Cretaceous).
  4. All Mesozoic placentals are more primitive than Onychodectes (Paleocene).
Figure 1. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

Figure 1. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

Given those parameters
we are able to rethink which mammals were coeval with dinosaurs back on phylogenetic bracketing (= if derived taxa are present, primitive taxa must have been present, too).

Smith reports, “The earliest known mammals are about as old as the earliest dinosaurs and appeared in the fossil record during the late Trias around two hundred and twenty million years ago with genera such as Sinoconodon (pre-mammal in the LRT), Morganucodon (basal therian in the LRT) and Hadrocodium (basal therian in the LRT). However, the earliest placental mammals (Eutheria) were not known before the Early Cretaceous. Eomaia scansoria (not eutherian in the LRT) from the Barremian of Liaoning Province, China is the oldest definite placental and is dated from a hundred and thirty million years ago.”

Mesozoic Prototherians

  1. All included fossil taxa are Mesozoic. Two others are extant (Fig. 2).
Figure 2. Mesozoic prototherians + Megazostrodon, the last common ancestor of all mammals. Only two taxa (gray) are post-Cretaceous.

Figure 2. Mesozoic prototherians + Megazostrodon, the last common ancestor of all mammals. Only two taxa (gray) are post-Cretaceous.

Mesozoic Metatherians (Marsupials)

  1. Derived Vincelestes is Early Cretaceous, which means Monodelphis and Chironectes were present in the Jurassic.
  2. Derived Didelphodon is Late Cretaceous, which means sisters to Thylacinus through Borhyaena were also present in the Mesozoic.
  3. Derived Vintana is Late Cretaceous, which means sisters to herbivorous marsupials were also present in the Mesozoic.
Figure 3. Mesozoic metatherians (in black), later taxa in gray. Whenever derived taxa are present in the Mesozoic (up to the Late Cretaceous) then ancestral taxa, or their sisters, were also present in the Mesozoic. Didelphis is extant, but probably unchanged since the Late Jurassic/Early Cretaceous.

Figure 3. Mesozoic metatherians (in black), later taxa in gray. Whenever derived taxa are present in the Mesozoic (up to the Late Cretaceous) then ancestral taxa, or their sisters, were also present in the Mesozoic. Didelphis is extant, but probably unchanged since the Late Jurassic/Early Cretaceous.

Mesozoic Eutherians (= Placentals)

  1. Rarely are placental mammals identified from the Mesozoic, because many are not considered placentals.
  2. Placentals (in the LRT) are remarkably rare in the Mesozoic, but sprinkled throughout the cladogram, such that all taxa more primitive than the most derived Mesozoic taxon (Anagale and derived members of the clade Glires, Fig. 4, at present a number of multituberculates) must have had Mesozoic sisters (Carnivora, Volitantia, basal Glires). 
Figure 4. Mesozoic euthrerians (placentals, in black). Later taxa in light gray. All taxa more primitive than Mesozoic taxa were likely also present in the Jurassic and Cretaceous. None appear after Onychodectes. Madagascar separated from Africa 165-135 mya, deep into the Cretaceous with a population of tenrecs attached. No rafting was necessary. 

Figure 4. Mesozoic euthrerians (placentals, in black). Later taxa in light gray. All taxa more primitive than Mesozoic taxa were likely also present in the Jurassic and Cretaceous. None appear after Onychodectes. Madagascar separated from Africa 165-135 mya, deep into the Cretaceous with a population of tenrecs attached. No rafting was necessary.

The above represents what a robust cladogram is capable of,
helping workers determine the likelihood of certain clades appearing in certain strata, before their discovery therein, based on their genesis, not their widest radiation or eventual reduction and extinction. In other words, we might expect sisters to basal primates, like adapids and lemurs, to be present in the Mesozoic, but not sisters to apes and hominids. We should expect sisters to all tree shrews and rodents to be recovered in Mesozoic strata. We should expect to see sisters to Caluromys, Vulpavus and other small arboreal therians/carnivorans in Mesozoic strata, but not cat, dog and bear sisters.

References
Smith T 2011. Contribution of Asia to the evolution and paleobiogeography of the earliest modern mammals. Bulletin des séances- Académie royale des sciences d’outre-mer. Meded. Zitt. K. Acad. Overzeese Wet.57: 293-305

SVP 2018: Placentals in the Cretaceous

Halliday et al. 2018
wonder about “the traditional lack of Cretaceous placental fossils when results from diverse dating analyses favor a Cretaceous origin of Placentalia.”

Unfortunately
they use an outdated cladogram that includes the following invalid clades (superorders) that Halliday et al. surmise should be present in Cretaceous sediments:

  1. Atlantogenata = Afrotheria + Xenarthra (elephants and anteaters in one clade?)
  2. Laurasiatheria = shrews, pangolins, bats, whales, carnivorans and ungulates (whales and bats in the same clade?)
  3. Euarchontoglires = rodents, lagomorphs, tree shrews, colugos and primates (lacking only carnivores, these are basal eutherians

Together these three clades
comprise the entirety of extant Eutheria (placental mammals). All of the above clades are extant. Where are the extinct clades, like Multituberculata?

By contrast,
the large reptile tree  (LRT, 1313 taxa) recovers Middle and Late Jurassic placentals (multituberculate rodents) along with several Early Cretaceous taxa, like the pangolin ancestor, Zhangheotherium (Fig. 1). So “the traditional lack of Cretaceous placental fossils” has been updated in the LRT.

Figure 1. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

Figure 1. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

Halliday et al. conclude: “The lack of definitive Cretaceous placental mammals may therefore be explained by high predicted morphological similarity among stem and basal crown eutherians, providing an avenue for partially reconciling the fossil record and molecular divergence estimates in Placentalia.”

No.
Taxon exclusion has given Halliday et al. an outdated tree topology. There is plenty of evidence for Mesozoic placentals in the LRT. Adding taxa provides every included taxon new opportunities to nest more parsimoniously. A good starter list can be found here (LRT subset Fig. 2). Many taxa from this list are candidates for discovery in the Mesozoic based on the discovery of multituberculates in the Mesozoic.

Figure 3. Subset of the LRT, focusing on basal Eutheria and Heterocephalus. Aqua taxa are arboreal. Tan taxa are terrestrial. Blue taxa are aquatic.

Figure 3. Subset of the LRT, focusing on basal Eutheria and Heterocephalus. Aqua taxa are arboreal. Tan taxa are terrestrial. Blue taxa are aquatic.

References
Halliday TJ et al. (5 co-authors) 2018. Delayed increase in morphological rates of evolution after the origin of the placental mammal crown group. SVP abstracts.

Mammal taxa: origin times

A few days ago, we looked at a revised and expanded cladogram of the Mammalia based on skeletal traits (distinct from and contra to a cladogram based on DNA). Today we add chronology to the cladogram to indicate the first appearance of various mammals and estimate the origin of the various clades (Fig. 1).

Note that derived taxa
that chronologically precede more primitive taxa indicate that primitive taxa had their genesis and radiation earlier than the first appearance of fossil specimens, which always represent rare findings usually during wide radiations that increase the chance the specimen will fossilize in the past and be found in the present day.

Looking at time of mammal taxa origin categories:

Figure 1. Cladogram with time notes for the Mammalia (subset of the LRT).

Figure 1. Cladogram with time notes for the Mammalia (subset of the LRT).

Some notes:

  1. Both prototheres and basal therians were present (and probably widespread) in the Late Triassic.
  2. Derived prototheres appear in the Late Triassic, suggesting an earlier (Middle Triassic?) origin for Mammalia and an earlier (Middle Triassic?) split between Prototheria and Theria.
  3. Both fossorial metatherians and basal arboreal eutherians were present (and probably widespread) in the Late Jurassic. These were small taxa, out of the gaze of ruling dinosaurs.
  4. Large derived eutherians eolved immediately following the K-T boundary in the Paleocene and radiated throughout the Tertiary.
  5. A large fraction of prototherians, metatherians and eutherians are known only from extant taxa, some of which are rare and restricted, not widespread.
  6. Multituberculates and kin are derived placentals close to rodents by homology, not convergence.

 

‘The Dawn of Mammals’ YouTube video illuminates systematic problems

Sorry, looks like video was yanked off of YouTube.

Part of this YouTube video (see below, click to view)
pits DNA paleontolgist, Dr. Olaf Bininda-Emonds (U. Oldenburg), against bone trait paleontologist, Dr. John Wible (Carnegie Museum of Natural History) in their common and contrasting search for basal placental mammals. Both realize that DNA cladograms do not replicate bone cladograms and DNA cannot be utilized with ancient fossils.

Dr. Bininda-Emonds, used molecular clocks
in living taxa to hypothetically split marsupials from placentals about 160 mya ago (Late Jurassic).

By contrast, Dr. Wible reports (28:53),
“Our study supported the traditional view that there were no fossils living during the Cretaceous [that] were members of the placental group itself. There were only ancestors of the placentals living.” (unscripted verbatim)

The impulse for this argument
came from the discovery of Maelestes (Wible et al. 2007a,b; 28:30 on the video) from the Late Cretaceous (75 mya). Dr. Wible’s paper nested Maelestes with the pre-placental, Asiorcytes, another tree-shrew-like mammal from the Late Cretaceous.

The large reptile tree
 (subset in Fig. 2) nests the first known placental mammals at the 160 mya mark, matching the DNA predictions of Dr. Bininda-Emonds et al. A long list of taxa, including Maelestes, nest in the Jurassic and Cretaceous, contra Wible et al. Only more complete taxa are tested in the LRT and dental traits are not emphasized.

Figure 2. Mesozoic time line showing the first appearances of several fossil mammals and the clades they belong to. Many, if not most of the listed taxa are late survivors of earlier radiations, sometimes much earlier radiations. Monodelphis and Didelphis are extant animals that originated in the Early Jurassic at the latest. Note also the large gaps over tens of millions of years, highlighting the rarity of fossil bearing locales.

Figure 2. Mesozoic time line showing the first appearances of several fossil mammals and the clades they belong to. Many, if not most of the listed taxa are late survivors of earlier radiations, sometimes much earlier radiations. Monodelphis and Didelphis are extant animals that originated in the Early Jurassic at the latest. Note also the large gaps over tens of millions of years, highlighting the rarity of fossil bearing locales.

In the video Dr. Wible says, “Many modern groups, according to the molecular clock analysis, actually are, they should be, present in the Cretaceous fossil record. We can’t find them.” Actually Dr. Wible already found them, but does not recognize them for what they are. That’s a common problem in paleontology, largely due to taxon exclusion, that we’ve seen before here, here, here and here. And in dozens of other mislabeled clades, like multituberculates.

The Bininda-Edmonds et al. paper reports,
“Here we construct, date and analyse a species-level phylogeny of nearly all extant Mammalia to bring a new perspective to this question. Our analyses of how extant lineages accumulated through time show that net per-lineage diversification rates barely changed across the Cretaceous/Tertiary boundary. Instead, these rates spiked significantly with the origins of the currently recognized placental superorders and orders approximately 93 million years ago, before falling and remaining low until accelerating again throughout the Eocene and Oligocene epochs. Our results show that the phylogenetic ‘fuses’ leading to the explosion of extant placental orders are not only very much longer than suspected previously, but also challenge the hypothesis that the end-Cretaceous mass extinction event had a major, direct influence on the diversification of today’s mammals.”

The LRT agrees with the timing indicated by the DNA analysis
Placentals are indeed found in the LRT Cretaceous and Jurassic fossil record (Fig. 2). They were not recognized by traditional workers using smaller taxon lists, for what they were. The LRT minimizes taxon exclusion and so solves many paleo problems with an unbiased and wide gamut approach currently unmatched in the paleo literature. Extant birds have a similar deep time record based on a few recent finds.

Perhaps overlooked
there are currently large gaps spanning tens of millions of years, highlighting the rarity of fossil bearing locales. All Mesozoic mammals are rare.

The DNA tree
of the Bininda-Emonds team correctly splits monotremes from therians, but incorrectly nests ‘Afrotherians‘ with Xenarthrans at the base of all mammals followed by moles + shrews, bats + carnivores + hoofed mammals + whales, followed by primates and rodents. As anyone can see, this is a very mixed up order, placing small arboreal taxa in derived positions and stiff-backed elephants and in in basal nodes. This DNA analysis is not validated by the LRT.

To its credit, basal mammals in the LRT
greatly resemble their marsupial ancestors. Then derived mammals become generally larger, with derived tooth patterns, stiffer dorsal/lumbar areas and longer pregnancies with more developed (precocious) young.

Given three cladograms of placental relationships,
none of them identical, how does one choose which one is more accurate? Here’s my suggestion: look at each sister at each node and see where you best find a gradual accumulation of derived traits, without exception. And look at outgroups leading to basal members of the in group.

Some readers are still having a hard time realizing
that someone without direct access to fossils and without a PhD is able to recover a more highly resolved cladogram that features gradual changes between every set of sister taxa than trees published over the last ten years in the academic literature. I agree. This should not be taking place. This is not what I expected to find when I started this 7-year project. One tends to trust authority. It’s been an eye-opening journey. In nearly all tested studies overlooking relevant taxa continues to be the number one shortcoming. The LRT minimizes that issue. The number two problem is blind faith in DNA results. The number three problem is an apparent refusal to examine phylogenetic results to weed out mismatched recovered sister taxa.

The video spends also some time with Zhangheotherium,
which we looked at earlier here and here. The interviewed workers talk about the ankle spur, but as a venom injector, as in the duckbill, Ornithorhynchus, not as a membrane frame, like a calcar bone, as in bats.

The video considers Repenomamus a large Early Cretaceous mammal
but the LRT nests Repenomamus as a late-surviving synapsid pre-mammal, derived from a sister to Pachygenelus, as we learned earlier here.

PS. As touched on earlier,
many basal arboreal mammals were experimenting with gliding (e.g. Volaticotherium and Maiopatagaium), but only one clade, bats, experimented with flapping. This was, perhaps not coincidentally, during the Middle to Late Jurassic (Oxordian, 160 mya). Remember, these gliding membranes were all extensions of the infant nursery membrane found in colugos and other volatantians, not far from the basalmost placental, Monodelphis.

References
Bininda-Emonds ORP, et al., (9 co-authors) 2007. The delayed rise of present-day mammals. Nature 446(7135):507-512.
Wible JR, Rougier GW, Novacel MJ and Asher RJ 2007a. The eutherian mammal Maelestes gobiensis from the Late Cretaceous of Mongolia and the phylogeny of Cretaceous Eutheria. Bulletin of the American Museum of Natural History 327:1–123.
Wible JR, Rougier GW, Novacek MJ and Asher RJ 2007b. Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary.” Nature, 447: 1003-1006.

What is a limpkin? (genus: Aramus)

Figure 1. The limpkin (Aramus guarauna) is a basal member of the x family.

Figure 1. The limpkin (Aramus guarauna) is a long-legged, wading basal member of the x family.

Aramus guarauna (Linneaus 1766) is the extant limpkin. It is often considerd transitional between rails and cranes. In the large reptile tree (1121 taxa) the limpkin nests basal to seagulls and hummingbirds, plovers and crowned cranes, common cranes and stilts, terns and loons, kingfishers and jabirus, murres and penguins.

Figure 1. Skeleton of the limp kin (Aramus), traditionally nests within the crane and rail order Gruiformes.

Figure 2. Skeleton of the limpkin (Aramus), traditionally nests within the crane and rail order Gruiformes. In the LRT rails are not closely related, so Gruiformes should no longer include rails.

Extant limpkins eat snails.
Primitive limpkins like Aramournis  probably had a more diverse diet. It is known from a distal tarsus.

Traditional rails
like the corn crake (Crex) and the coot (Fulica) are much more basal birds that give rise to chickens, sparrows and parrots. Adding Rallus, the Virginia rail, to the LRT nests it between Aramus and the rest of the clade, which, phylogenetically makes hummingbirds, terns and penguins variations on the rail theme and Rallus at least a Middle Cretaceous taxon radiation.

Figure 4. Virginia rail alongside the rail clade in the LRT.

Figure 4. Virginia rail alongside the rail clade in the LRT.

Congeneric specimens of Aramus
are found in the Miocene, but more derived penguins are found in the Paleocene, pointing to a mid-Cretaceous radiation of this clade.

Limpkins are derived from Cretaceous sisters to
hamerkops (Scopus) and stone curlews (Burhinus), both long-legged taxa. By the evidence shown in the crown bird subset of the LRT (Fig. 4), long legs, like those shown by Aramus, the limpkin, are basal traits. The retention of hatchling short legs occurred several times by convergence, sometimes during the Cretaceous. See the earlier post on post K-T non-arboreal birds. 

Figure 4. Subset of the LRT focusing on the crown bird clade. Brown taxa are all long-legged. Neotony produces the smaller, shorter-legged, arboreal taxa.

Figure 4. Subset of the LRT focusing on the crown bird clade. Brown taxa are all long-legged. Neotony produces the smaller, shorter-legged, arboreal taxa.

References
Linneaus C von 1766. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio duodecima, reformata. pp. 1–532. Holmiæ. (Salvius)

wiki/Aramus_limpkin