More details on Parahesperornis

Bell and Chiappe 2020
provide additional insight and valuable photos of Parahesperornis alexi (Martin 1984; Fig. 1; Late Cretaceous ~90 mya) a smaller sister/ancestor to Hesperornis (Fig. 1) with more plesiomorphic traits.

Figure 1. Parahesperornis (from Bell and Chiappe 2020) compared to Hesperornis (Marsh 1890) to scale and not to scale. Here the glenoid to tail tip lengths are the same. Everything is exaggerated in Hesperornis.

Figure 1. Parahesperornis (from Bell and Chiappe 2020) compared to Hesperornis (Marsh 1890) to scale and not to scale. Everything is exaggerated in the derived taxon, Hesperornis.

Backstory
According to Bell and Chiappe, “The Hesperornithiformes constitute the first known avian lineage to secondarily lose flight in exchange for the evolution of a highly derived foot-propelled diving lifestyle, thus representing the first lineage of truly aquatic birds. First unearthed in the 19th century, and today known from numerous Late Cretaceous (Cenomanian-Maastrichtian) sites distributed across the northern hemisphere, these toothed birds have become icons of early avian evolution.”

Figure 2. Hesperornis cladogram from Bell and Chiappe 2020. Compare to LRT results in figure x.

Figure 2. Hesperornis cladogram from Bell and Chiappe 2020. Compare to LRT results in figure 3 where more taxa are tested and nested. Gansus should be closer to Hesperornis. Many taxa are omitted between Archaeopteryx and Asparavis here.

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

Figure 3. Click to enlarge. Toothed birds of the Cretaceous to scale. Compare to figure 2. See the difference when more taxa are added.

Cladistics
Bell and Chiappe and the Large Reptile Tree (LRT, 1694+ taxa, illustrated in figure 3) are in broad agreement regarding the phylogenetic nesting of Parahesperornis (Fig. 2). Unfortunately, Bell and Chiappe don’t include enough taxa to understand the nesting of toothed birds within the clade of toothless birds, as recovered by the LRT (Fig. 3).

And what the heck 
are Gallus, the chicken, and Anas, the duck, doing in figure 2 nesting together? They are not related to one another in the LRT, but… (and here’s the key)… absent ANY pertinent transitional taxa, figure 2 is actually correct, a match with the LRT. Taxon exclusion delivers this oversimplified and misinforming cladogram (Fig. 2). More taxa, not more characters, makes a cladogram more and more accurate.


References
Bell A and Chiappe LM 2020. Anatomy of Parahesperornis: Evolutionary Mosaicism
in the Cretaceous Hesperornithiformes (Aves). Life 2020, 10, 62; doi:10.3390/life10050062
Marsh, OC 1880. Odontornithes, a Monograph on the Extinct Toothed Birds of North America. Government Printing Office, Washington DC.
Martin L 1984. A new Hesperornithid and the relationships of the Mesozoic birds. Transactions of the Kansas Academy of Science 87:141-150.

wiki/Hesperornis

Plesiosaur necks: not so flexible after all

With a neck WAAAYYY longer than half the total length
elasmosaurs, like Albertonectes (Figs. 1, 2), have been traditionally referred to as ‘a snake threaded through a sea turtle’ (going back to the Buckland lectures 1832, full story online here). Snakes have no trouble swimming, but so far, paleontologists have not considered the long, minimally flexible neck of elasmosaurs a propulsive organ, as in sea snakes. That might change a little today.

Figure 1. A weak attempt at making sine waves in the neck of Albertonectes.

Figure 1. A weak attempt at making sea snake-like sine waves in the neck of Albertonectes. Note the minimum of bending through effort. Relaxation realigned the neck.

Earlier a vertical configuration was suggested
to explain the weird and extreme morphology of elasmosaurs, entering fish and squid schools from below, distinct from all other oceanic predators. While the flippers were powerful propulsive organs for long distance, when it came to fine tuning while hovering, perhaps the increasingly longer (Fig. 2), snake-like necks helped some. It also moved the bulky flapping torso further from the mouth, so the school of fish would be less and less  likely to notice the intruder in the middle.

Figure 3. Click to enlarge. Albertonectes reconstructed. This 11 m elasmosaur is the longest thusfar recorded. This may be the breathing pose, swallowing air, then submerging the neck. When horizontal the air could be passed back to the lungs, as hypothesized for Dinocephalosaurus.

Figure 2. Click to enlarge. Albertonectes reconstructed. This 11 m elasmosaur is the longest thusfar recorded. This may be the breathing pose, swallowing air, then submerging the neck. When horizontal the air could be passed back to the lungs, as hypothesized for Dinocephalosaurus.

By contrast, Noe, Taylor and Gomez-Perez 2017 reported,
Based on the anatomy of the articular faces of contiguous cervical vertebral centra, neural arches, and cervical ribs, the plesiosaur neck was mainly adapted for ventral bending, with dorsal, lateral and rotational movements all relatively restricted. A new model is proposed for the plesiosaur bauplan, comprising the head as a filter, straining, sieve feeding or sediment raking apparatus, mounted on a neck which acted as a stiff but ventrally flexible feeding tube, attached to the body which acted as a highly mobile feeding platform.”

“The neck increased drag due to its form and large surface area, but was also potentially part of an integrated locomotor system, for instance affecting steering (as it lies in front of the locomotor apparatus) and because the rear of the neck acted as anchorage for musculature from the anterior limb girdles. Hence, any explanation of neck function should consider both slow speed locomotion and more rapid movement during respiration, feeding and predator avoidance.”

Their study looked at
Muraenosaurus (Figs. 3, 4), Cryptoclidus and Tricleidus (none if these yet in the LRT) as exemplars of long-necked plesiosaurians. All are related to one another, not to elasmosaurs. Noe, Taylor and Gomez-Perez presented a history of plesiosaur neck interpretation and presented their own interpretation (ventral flexion, Fig. 5). Given that comprehensive review, apparently no prior workers envisioned a sea-snake analog for the long neck of elasmosaurs, nor have any envisioned a vertical feeding orientation.

Figure 2. Muraenosaurus in dorsal and lateral views. Compare to figure 1.

Figure 2. Muraenosaurus in dorsal and lateral views. Compare to figure 1.

Rather than a flexible ball-and-socket joint
between cervicals, each plesiosaur vertebra consisted of a spool-shaped centrum with flat or slightly concave articular surfaces (Fig. 4). Most cervical centra are wider than deep. according to Noe, Taylor and Gomez-Perez, but that is largely due to a dorsal indentation for the neural spine. Cervicals preserved in situ indicate no intervening cartilage between centra. So, think of plesiosaur centra as Incan wall stones. There are no spaces between either. This compaction between vertebrae greatly restricts movement between individual cervicals and restricts cervical movement overall. Even so, even half a degree per centrum magnified by 76 cervicals can add up (Fig. 1) permitting some movement. Short, L-shaped cervical ribs are fused to each centrum.Their distal processes do not articulate with one another, but hypothetical ligaments extending from anteroposteriorly-oriented distal tips may have done so.

Figure 5. Muraenosaurus cervical sections from Noe et al. 2017 alongside a ghosted diagram of a complete Muraenosaurus neck.

Figure 4. Muraenosaurus cervical sections from Noe et al. 2017 alongside a ghosted diagram of a complete Muraenosaurus neck. The space between centra can be compared to the space between Incan wall stones. In other words: none. That is not shown in the ghosted reconstruction.

Noe, Taylor and Gomez-Perez conclude,
The consistent presence of numerous cervical segments that lack bony stiffening adaptations, however, is also strong evidence that flexibility was an important functional element in plesiosaur necks (Evans 1993), and gives the potential for a considerable range of movement in the living animal (cf. Zarnik 1925–1926).” The authors compare plesiosaurs to stiff-necked tanystropheids (with only 12 cervicals) to emphasize their point. They overlooked the tight articulations of each centrum with its neighbors. 

From a historical perspective, Noe, Taylor and Gomez-Perez report, 
“Previous workers have considered the degree of neck flexibility in plesiosaurs to range from: extreme mobility (Hawkins 1840; Zarnik 1925–1926; Welles 1943; Welles and Bump 1949), including the ability to arch the neck like a swan (Conybeare 1824; Andrews 1910; Brown 1981b); through relative inflexibility (Hutchinson 1897; Williston 1914; North 1933; Shuler 1950; Storrs 1997); to almost complete rigidity (Buckland 1836; Watson 1924, 1951; Cruickshank and Fordyce 2002; Figs. 3, 9); although some of this variation in interpretation may be due to differences between the species studied (Watson 1924, 1951).”

Clearly some of these workers were right and others were wrong.
But which ones? Zoe, Taylor and Gomez-Perez conclude, to their credit, “Overall, the range of movement available to the plesiosaur neck was strictly limited.”

Figure 7. Illustration from Noe, Taylor and Perez-Gomez showing their view of plesiosaur feeding and escape configurations.

Figure 5. Illustration from Noe, Taylor and Perez-Gomez showing their view of plesiosaur feeding and escape configurations. Usually paleo illustrations are more anatomically accurate than this.

Elasmosaurs were morphologically different than anything else in the sea. 
And they became more and more different as time went by (Fig. 2). So, something was working better and better as evolution selected for more extreme neck lengths.

Once again, let’s broaden our scope and look at the environs,
including coeval predators. All of these were robust, fast, streamlined, short-neck predators that swam horizontally preceding an attack from outside in. All of this is the opposite of elasmosaurs who hypothetically loitered below schools of fish unobtrusively rising to slip only their head in from below with minimum turbulence in order to remove fish or squid at leisure from the inside out.

Plesiosaur respiration at the surface
had to take place horizontally due to air pressure constraints. Alternatively, elasmosaurs could have gulped air, then assumed a horizontal or diving orientation to let the air bubble travel back through their long neck back or up to their lungs. With such tiny nostrils, gulping air seems more reasonable than narial inhalation.

Exhalation could have been more leisurely
and might have involved producing a ‘bubble net’ from stale air stored in the long trachea and released through the tiny nares. Extant baleen whales sometimes produce a bubble net to herd fish and plankton as they rise to feed on them. Perhaps elasmosaurs did the same, again based on their vertical orientation.

Fins at all four corners
Noe, Taylor and Gomez-Perez report, “With limbs at the four corners of the body, plesiosaurs could potentially produce vectored thrust from different limbs, to provide fine control of movement in all directions, and around all axes. This is more useful in slow swimming or hovering animals than simple shark-like control fins, which require movement in order to generate a current over the control surfaces.” Exactly. Unfortunately, these authors did not consider plesiosaurs to have a vertical orientation. Instead they focused on the ability of the neck to flex ventrally from a horizontal orientation.

Stomach stones
Noe, Taylor and Gomez-Perez report, “Swimming efficiency was further impaired by the mass of the neck, and the stomach stones commonly preserved in plesiosaurs. This stone ballast was probably needed to establish trim control and longitudinal stability to enable the animal to swim slowly horizontally and to hover, especially when diving in shallow water when the animal was positively buoyant.” The other explanation is that stomach stones helped weight the body below the more buoyant neck (filled with stagnant air), again supporting a vertical orientation when not swimming to other locations.


References
Noe LF, Taylor MA and Gomez-Perez M 2017. An integrated approach to understanding the role of the long neck in plesiosaurs. Acta Palaeontologica Polonica 62 (1): 137–162.

Mononykus and Shuvuuia: Cretaceous tickbirds

Traditionally
the small, but extremely robust hand claws of Mononykus and Shuvuuia (Figs. 1, 2) were considered digging tools. If so, their forelimbs would have been distinctly different from the digging forelimbs of all other fossorial tetrapods based on size alone, not to mention the rest of the bird-like morphology that does nothing to support a digging hypothesis.

Figure 1. Forelimb of Mononykus. Large deltopectoral crest pulls humerus toward the sternum like a clasp.

Figure 1. Forelimb of Mononykus. Large deltopectoral crest pulls humerus toward the sternum like a clasp.

Maybe there’s another answer.
For a moment, let’s not focus on Mononykus and Shuvuuia. Let’s broaden our view to see what related taxa are doing with their forelimbs. Let’s see if phylogenetic bracketing and environment can provide clues to the Mononykus forelimb mystery.

Figure 1. Shuvuuia and Mononykus to scale in various poses. The odd digit 1 forelimb claws appear to be retained for clasping medial cylinders, like tree trunks. The forelimb is very strong. Perhaps these taxa rest vertically and run horizontally. Click to enlarge.

Figure 2. Shuvuuia and Mononykus to scale in various poses. The odd digit 1 forelimb claws appear to be retained for clasping medial cylinders, like tree trunks and dinosaur backs. The forelimb is very strong. Click to enlarge.

Outgroup taxa
include Haplocheirus (Fig. 3) and, more distantly, Velociraptor (Fig. 3). These two have forelimbs more typical of theropods with three digits and digit 2 longer than 1. Both come with a reputation and ability to jump on large dinosaurs (Fig. 4).

That’s similar to
what extant tickbirds (oxpeckers) do to large African mammals (Fig. 4), though not with the intention of ripping into their flesh with a wicked pedal digit 2.

Figure 1. Haplocheirus sollers traced from several photos. This specimen is 15 million years older than Archaeopteryx and tens of million years older than dromaeosaurs and alvarezsarids. Click to enlarge. Note the robust pedal digit 2 and manual digit 1.Haplocheirus sollers (Choiniere et al. 2010 Late Jurassic, 150 mya, 2m long) is a a theropod dinosaur from the Jurassic that nests at the base of the alvarezsaurids (including Mononykus and Shuvuuia) and also basal to the Cretaceous dromaeosaurids (including Velociraptor), ~and~ basal to Jurassic proto-birds (including Aurornis, Fig. 2).

Figure 3. Haplocheirus sollers traced from several photos. This specimen is 15 million years older than Archaeopteryx and tens of million years older than dromaeosaurs and alvarezsarids. Click to enlarge. Note the robust pedal digit 2 and manual digit 1.Haplocheirus sollers (Choiniere et al. 2010 Late Jurassic, 150 mya, 2m long) is a a theropod dinosaur from the Jurassic that nests at the base of the alvarezsaurids (including Mononykus and Shuvuuia) and also basal to the Cretaceous dromaeosaurids (including Velociraptor), ~and~ basal to Jurassic proto-birds (including Aurornis, Fig. 2).

In modern day Africa
tickbirds are often seen happily perching atop rhinos and other larger mammals (Fig. 5), cleaning them of parasites and riding them like passengers on a bus… yet always able to fly away or jump off and run away.

To scale with other dinosaurs of their time and place
(Fig. 3) it becomes clear that alvarezsaurids and Mononykus were relatively about the size of tickbirds and able to do the same job (plucking off parasitic insects) for their mutual benefit.

Figure 3. Giant Deinocheirus, a contemporary of Mononykus, might have served as the host and dining room for a series of ever smaller and more specialized parasite eaters.

Figure 4. Giant Deinocheirus, a contemporary of Mononykus, might have served as the host and dining room for a series of ever smaller and more specialized parasite eaters.

Clearly Mononykus and Shuvuuia are highly specialized
taxa leaving no descendants. In the large reptile tree (LRT, 1692+ taxa) these alvarezsaurids evolve from larger theropods like Hapolocheirus. As the ancestors of Mononoykus and Shuvuuia grew smaller, so did their forelimbs, pelvis, killer toe and teeth. These tiny theropods became more and more specialized for their insect-plucking, hitchhiking niche. As they became phylogenetically-miniaturized, smaller alvarezsaurids were able to hitch rides on smaller and smaller dinosaurs.

Figure 3. Tickbirds sitting atop a pair of rhinos, perhaps a modern analog for mononykids.

Figure 5. Tickbirds (oxpeckers) sitting atop a pair of rhinos, perhaps a modern analog for mononykids.

So the little adducting forelimbs of Mononykus and Shuvuuia
acted like little hair clips, keeping these little dinosaurs attached to the skin and feathers of their hosts. That’s really all they were good for. Not flying. Not flapping. Not digging. Not display. Just mighty adduction. Those tiny forelimbs with big thumbs were perfect for clipping to giant host dinosaurs. The long legs of Mononykus would have been just long enough to walk through high feathers, like a human walks through tall grass. Or to run and hop on one new dinosaur after another. Active and highly coordinated, alvarezsaurids would have had the same agility as modern birds when they cavort on tree branches, tree trunks and rhino backs, all without using their ‘hands.’

This may be a novel hypothesis.
If not, please provide a citation so I can promote it.

Added a day later in response to the above promise:
Thank you, Tyler. From the abstract: “I propose that bizarre structures may have served to defend against parasitic dorsal attacks from riding dromaeosaurs. Frequent dismounts from large living dinosaurs may explain the origin of feathers, gliding and avian flight.”

Fraser G 2014. “Bizarre Structures” Point to Dromaeosaurs as Parasites and a New Theory for the Origin of Avian Flight. The Journal of Paleontological Sciences: JPS.C.2014.01 PDF

In counterpoint, Fraser was postulating the origin of larger wings and feathers for dismounting dromaeosaurs. He also discussed the origin of frills, plates and spikes on large host herbivores to dissuade dromaesaurs from mounting in the first place. Unfortunately, nowhere does he discuss the alvarerzsaurids or Mononykus and the development of its bizarre tiny forelimbs. Evidently they were not on his ‘radar’. Even so, thank you for bringing this paper to my attention. A good read!

A few more data points and citations:

Velociraptor mongoliensis (Osborn 1924; Late Cretaceous, 75 mya; 6.8m long) The tail was long and stiffened with elongate chevrons and zygapophyses. The deep pubis was oriented posteriorly with a large pubic ‘boot’.

Haplocheirus sollers (Choiniere et al. 2010 Late Jurassic, 150 mya, 2m long) The tail was not stiffened with elongate accessory processes.

Mononykus olecranus (Perle et al, 1993; Late Cretaceous ~70 mya, 1 m in length) Only digit I remained full size on the stunted hand. The proximal ulna (the elbow)  was enlarged. The pubis was shorter and lacked a pubic boot.

Shuvuuia deserti (Chiappe, Norell and Clark 1998, Late Cretaceous) was smaller and retained digits 2 and 3 as vestiges.

Halszkaraptor escuilliei (Cau et al. 2017; Late Cretaceous) was originally considered an aquatic dromaeosaur related to Mahakala, but here nests with Shuvuuia. A distinctly different manual digit 3 was the longest, but the gracile thumb retained the largest claw. The hands did not act like hair clips.


References
Cau A, et al. 2017. Synchrotron scanning reveals amphibious ecomorphology in a new clade of bird-like dinosaurs. Nature. doi:10.1038/nature24679
Chiappe LM, Norell MA and Clark JM 1998. The skull of a relative of the stem-group bird Mononykus. Nature, 392(6673): 275-278.
Choiniere JN, Xu X, Clark JM, Forster CA, Guo Y, Han F 2010. A basal alvarezsauroid theropod from the Early Late Jurassic of Xinjiang, China. Science 327 (5965): 571–574. Perle A, Norell MA, Chiappe LM and Clark JM 1993. Flightless bird from the Cretaceous of Mongolia. Nature 362:623-626.
Perle A, Chiappe LM, Rinchen B, Clark JM and Norell 1994. Skeletal Morphology of Mononykus olecranus (Theropoda: Avialae) from the Late Cretaceous of Mongolia. American Museum Novitates 3105:1-29.

wiki/Mononykus
wiki/Halszkaraptor
wiki/Shuvuuia

Here’s the blogpost that inspired this one.

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.”

 

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 (Maelestes 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.