Bishops enters the LRT

Figure 1. The dentary of Bishops compared to its Late Cretaceous sister, Asioryctes, which has fewer and larger premolars.

Figure 1. The dentary of Early Cretaceous Bishops (1.5cm long) compared to its Late Cretaceous sister, Asioryctes, which has fewer and larger premolars and one more molar.

The genus Bishops whitmorei
(Rich et al. 2001; Early Cretaceous, Australia; Fig.1) is represented by a small mandible with a high coronoid process, six premolars and only three molars. In the LRT it nests basal to the much larger carnivorous marsupials (= creodonts), starting with the wolf-sized Arctocyon. It is a sister to Asioryctes (Fig. 1) which is basal to the herbivorous marsupials of Australia.

What makes this important?
It is the only tiny creodont known. All others are dog to wolf-sized. Cenozoic descendants of Bishops include the following carnivorous marsupials: Thylacinus, Thylacosmilus, Borhyaena, Hyaenodon and Vincelestes.

References
Rich TH, Flannery TF, Trusler P. Kool L, van Klaveren NA and Vickers-Rich P 2001. A second tribosphenic mammal from the Mesozoic of Australia. Records of the Queen Victoria Museum 110: 1-9.

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The many faces (and bodies) attributed to Camarasaurus

The genus Camarasaurus is known from several species
These display differences in the shapes of their skulls and post-crania (Fig. 1). Distinct from the bipedal or tripodal Diplodocus we looked at yesterday, the general build of this genus suggests it did not rise from all fours. Rather elevation of the great neck enabled high browsing, though not as high as its sister in the LRT, Brachiosaurus

Figure 1. Camarasaurus AMNH 567.

Figure 1. Camarasaurus lentus AMNH 567. Compare to shorter legged SMA 0002 specimen in figure 2.

Once considered a Camarasaurus,
the short-limbed, big pelvis Cathetosaurus (Fig. 2) is certainly related, but distinct from the other camarasaurs.

Figure 2. The SMA0002 specimen attributed to Camarasaurus.

Figure 2. The SMA0002 specimen attributed to Camarasaurus an/or Cathetosaurus. Note the robust elements and short distal limbs.

Not only are the bodies distinct,
so are the skulls (Fig. 3) assigned to this genus.

Figure 3. Several skulls attributed to Camarasaurus to scale. SMA 0002 is the short-limbed Cathetosaurus. Brachiosaurus appears to be a derived camarasaur.

Figure 3. Several skulls attributed to Camarasaurus to scale. SMA 0002 is the short-limbed Cathetosaurus. Brachiosaurus appears to be a derived camarasaur. We’re looking at the inside of the mandible in the DINO 2580 specimen.

As in many genera
for which several specimens are known, it is always a good idea to start with just one rather complete specimen in phylogenetic analysis. Add others as your interest grows.

References
Gilmore CW 1925. A nearly complete articulated skeleton of Camarasaurus, a saurischian dinosaur from the Dinosaur National Monument, Utah. Memoirs of the Carnegie Museum 10:347-384.
Madsen JH Jr, McIntosh JS, and Berman DS 1995. Skull and atlas-axis complex of the Upper Jurassic sauropod Camarasaurus Cope (Reptilia: Saurischia). Bulletin of Carnegie Museum of Natural History 31:1-115.
McIntosh JS, Miles  CA, Cloward KC and Parker JR 1996. A new nearly complete skeleton of CamarasaurusBulletin of the Gunma Museum of Natural History 1:1-87.
McIntosh JS, Miller WE, Stadtman KL and Gillette DD 1996. The osteology of Camarasaurus lewisi (Jensen, 1988). Brigham Young University Geology Studies 41:73-115.
Tschopp E, Wings O, Frauenfelder T, and Brinkmann W 2015. Articulated bone sets of manus and pedes of Camarasaurus (Sauropoda, Dinosauria). Palaeontologia Electronica 18.2.44A: 1-65.

Diplodocus joins the LRT

There are several ways to measure the tallest dinosaur.
One way is to let the long sauropods, like Diplodocus carnegii (Fig. 1; Marsh 1878; Late Jurassic; 25-32 m long), stand on their hind limbs, like their prosaurod ancestors, balanced by a very long narrow whiplash tail of up to 80 vertebrae. While the neck could not be elevated much beyond horizontal (relative to the dorsal vertebrae), by standing on its hind limbs the torso + neck could be elevated.

Figure 1. Diplodocus standing in a typical feeding posture, as in its prosauropod ancestors.

Figure 1. Diplodocus standing in a typical feeding posture, as in its prosauropod ancestors. Diplodocus could potentially increase its feeding height up to about 11m

Wikipedia reports,
“No skull has ever been found that can be confidently said to belong to Diplodocus, though skulls of other diplodocids closely related to Diplodocus are well known.”

Figure 2. Diplodocus skull animation. Note the short chin and voluminous throat.

Figure 2. Diplodocus skull (USNM 2672, CM 11161) animation. Note the short chin and voluminous throat.

The peg-like teeth of Diplodocus
were smaller and fewer than in other sauropods. And the skull was smaller with nares placed higher on the skull. Evidently diplodocids could only handle smaller needles and leaves from conifer trees matching their height. Wikipedia reports, “Unilateral branch stripping is the most likely feeding behavior of Diplodocus.”

Figure 4. Subset of the LRT focusing on the Phytodinosauria. Three sauropods are added here.

Figure 4. Subset of the LRT focusing on the Phytodinosauria. Three sauropods are added here.

We know of junior diplodocids
(Fig. 5), half the skull length but with relatively larger eyes. Cute!

Figure 5. A small Diplodocus skull to scale with an adult one.

Figure 5. A small Diplodocus skull to scale with an adult one.

References
Marsh OC 1878. Principal characters of American Jurassic dinosaurs. Part I. American Journal of Science. 3: 411–416.

 

At last! Some sauropods enter the LRT.

Overlooked no longer: the clade Sauropoda.
Learning about clade members now for the first time. Three have been added to the large reptile tree (LRT, 1291 taxa): Diplodocus, Camarasaurus and Brachiosaurus (Figs. 1, 4).

Figure 1. Several sauropod skulls to scale with DGS colors on the bones. Here are Shunosaurus, Camarasaurus, Brachiosaurus and Diplodocus.

Figure 1. Several sauropod skulls to scale with DGS colors on the bones. Here are Shunosaurus, Camarasaurus, Brachiosaurus and Diplodocus.

Note:
the antorbital fossa is absent in derived taxa.

Figure 2. Family of Brachiosaurus illustration from A Dinosaur Year 1989.

Figure 2. Family of Brachiosaurus illustration from A Dinosaur Year 1989 (flipped left to right). The original illustration hangs on the wall behind my computer monitor.

Note 2:
The palate of sauropods shows an increasing space allotted to the internal nares. That makes sense given the increased volumes of air passing in and out of the nares of these increasingly gigantic dinosaurs — a volume that has to be several times the volume of the dead air in that long sauropod throat.

Figure 3. Sauropodiform and sauropod palates, Yizhousaurus, Diplodocus, Camarasaurus and Brachiosaurus. The choanae (internal nares) get bigger in sauropods.

Figure 3. Sauropodiform and sauropod palates, Yizhousaurus, Diplodocus, Camarasaurus and Brachiosaurus. The choanae (internal nares) get bigger in derived sauropods.

Other sauropod traits:

  1. Fingers reduced to single phalanx stubs below semi-tubular metatarsals. Only digit 1 retains an ungual and tracks show it was retroverted, dorsal side down, saving the point, oriented medially to posteriorly (Fig. 4).
  2. External nares dorsal with fragile to absent premaxillary ascending process (Fig. 1).
Figure 5. Reconstructions of manus and pes of Camarasaurus SMA0002 from Tschopp et al.

Figure 4. Reconstructions of manus and pes of Camarasaurus SMA0002 from Tschopp et al. 2015.

The LRT
divided dinosaurs into theropods and phytodinosaurs in 2011. Sauropodomorpha is a phytodinosaur clade, the sister clade of the clade Ornithischia (Fig. 5). Currently 5 taxa within the Phytodinosauria precede this split.

Figure 4. Subset of the LRT focusing on the Phytodinosauria. Three sauropods are added here.

Figure 4. Subset of the LRT focusing on the Phytodinosauria. Three sauropods are added here.

More
on each of these sauropods will come shortly.

References
Tschopp E, Wings O, Frauenfelder T, and Brinkmann W 2015. Articulated bone sets of manus and pedes of Camarasaurus (Sauropoda, Dinosauria). Palaeontologia Electronica 18.2.44A: 1-65.

Triassic origin of scales, scutes, hair, etc. as biting fly barriers?

During the Middle to Late Triassic

  1. Mammals developed fur/hair.
  2. Aetosaurs developed plates and horns beyond the earlier paired dorsal scutes.
  3. Crocodylomorphs developed large scales beyond the earlier paired dorsal scutes.
  4. Dinosaurs lost those paired scutes and developed placodes and quills. Ultimately these became scales and feathers.
  5. Turtles developed hard scales over a carapace and plastron.
  6. Lepidosaurs developed small scales.
  7. Pterosaurs and their Late Triassic sisters developed pycnofibers

All of these developed on the soft, naked skin
(think of a plucked chicken) that was a universal covering for Carboniferous and Permian tetrapods (Early forms retained large ventral scales inherited from finned ancestors, but these were lost by the Permian).

All of these extradermal structures have one thing in common.
They separated and/or protected the animal’s naked skin from the environment, one way or another. They developed by convergence. Dhouailly 2009 and other workers discussed the chemical similarities of the keratin found in these dermal structures. 

The question is:
What was different about the Triassic environment that was not present in earlier Carboniferous and Permian environments? We can 
eliminate heat, cold, UV rays, rain, aridity, etc. as possible reasons for the development of insulator structures because those factors had always been present. So what was new in the Triassic that affected all terrestrial tetrapods?

Flies and their biting, piercing kin.
“The earliest definitive flies known from the mid-Triassic of France, approximately 230 Ma (Krzemiski and Krzeminska, 2003)” according to Blagoderov, Grimaldi and Fraser 2007. The order Diptera (flies, mosquitos and kin) tend to land on large tetrapods for food, blood, etc. Scales, scutes, hair, feathers, etc. all separate flying insects from the naked skin of Triassic terrestrial tetrapods. Williams et al. 2006 even found mosquito repellents in frog skin. It is notable that, except for armored placodonts and mosasaurus (derived varanid lepidosaurs), aquatic and marine tetrapods also had naked skin with the thalattosaur, Vancleavea, a notable sermi-terrestrial exception. Is that because they had aquatic antecedents in the Triassic that were never affected by flying insects?

It’s not just the insect bite that drives this evolution,
it’s the appearance of new vectors for the rapid spread of disease that drives this evolution.

Interesting coincidence.
If this is not the case, this will take further study.

Figure 1. Lacertulus, a basal squamate from the Late Permian

Figure 1. Lacertulus, a basal squamate from the Late Permian

Carroll and Thompson 1982 report
on the Late Permian lepidosaur, Lacertulus (Fig. 1), “No scales dermal or epidermal are evident in the specimen.”

From the Dhouailly 2009 abstract:
“I suggest that the alpha-keratinized hairs from living synapsids may have evolved from the hypothetical glandular integument of the first amniotes, which may have presented similarities with common day terrestrial amphibians.

Concerning feathers, they may have evolved independently of squamate scales, each originating from the hypothetical roughened beta-keratinized integument of the first sauropsids. The avian overlapping scales, which cover the feet in some bird species, may have developed later in evolution, being secondarily derived from feathers.” Not realized by Dhouailly, the purported clade ‘Sauropsida’ is paraphyletic and a junior synonym for Amniota and Reptilia in the LRT.

Earlier we looked at the first appearances
of hair, quills, pycnofibers and hard scales in a three-part series here, here and here

Exceptionally, humans are terrestrial tetrapods
that have lost most of their hair, more or less returning to the primitive naked state. And yes, flies and mosquitos do bother humans. It is the price we pay for the benefits of naked skin. Clothing helps provide a barrier.

Remember:
Just because an idea is proposed and a hypothesis is advanced doesn’t make it so. In science ideas have to be confirmed or refuted following their first appearance. If anyone has data concerning scales or other dermal structures in Carboniferous or Permian taxa, please make us aware of those.

References
Blagoderov V, Grimaldi D and Fraser NC 2007. How Time Flies for Flies: Diverse Diptera from the Triassic of Virginia and Early Radiation of the Order. American Museum Novitates 3572:1-39. DOI: 10.1206/0003-0082(2007)509[1:HTFFFD]2.0.CO;2
Carroll RL and Thompson P 1982.
A bipedal lizardlike reptile from the Karroo. Journal of Palaeontology 56:1-10.
Dhouailly D 2009.
A new scenario for the evolutionary origin of hair, feather, and avian scales Journal of Anatomy 214(4): 587–606. doi: 10.1111/j.1469-7580.2008.01041.x
Krzeminnski, W., and E. Krzeminska. 2003. Triassic Diptera: descriptions, revisions and phylogenetic relations. Acta Zoologica Cracoviensia (suppl.) 46: 153–184.
Maderson PFA and Alibardi L 2000.
The Development of the Sauropsid Integument: A Contribution to the Problem of the Origin and Evolution of Feathers. American Zoologist 40:513–529.
Rohdendorf BB, Oldroyd H and Ball GE 1974. The Historical Development of Diptera. The University of Alberta Press, Edmonton, Canada. ISBN 0-88864-003-X.
Williams CR, Smith BPC, Best SM and Tyler MJ 2006.
Mosquito repellents in frog skin. Biol Lett. 2006 Jun 22; 2(2): 242–245. doi: 10.1098/rsbl.2006.0448

‘Origin of avian flight’ needs a phylogenetic underpinning

Segre and Banet 2018
discuss the origin of avian flight like a parent trying to stop a fight among siblings. They’re off base, working without a phylogenetic underpinning. You’ll see what I mean.

From the Segre and Banet abstract
“Few topics in evolutionary biology have been as controversial as the debate over the origin of avian flight. Although significant progress has been made in understanding how dinosaurs acquired flight, the debate remains mired in historical perspectives that prevent progress. We would like to renew the call to set aside the arboreal / cursorial debate and to draw attention to the common ground shared by both sides. To this end, we propose the following starting points:

  1. Paravian dinosaurs were bipedal, with decoupled but complementary hindlimb and forelimb locomotion.
  2. They had feathers on their body, their wings and in many cases their legs, that were probably highly plastic and multi-functional.
  3. Paravians inhabited complex, three-dimensional environments that required proficiency in a variety of behaviours to negotiate.
  4. Once the incipient wing form existed, asymmetric and symmetric flapping and possibly static wing postures served a variety of aerodynamic purposes that enhanced fitness.

Taken together, these tenets conjure an exciting portrait of a dynamic organism adept at navigating through a complex environment with its versatile, incipient wings.”

Unfortunately,
Segre and Banet fail to mention the elongate coracoids that mark the genesis of flapping, and the origin of birds starting with the most primitive Solnhofen bird, the Thermopolis specimen attributed to Archaeopteryx. They would have known this if they had performed a phylogenetic analysis, which is the most important factor in determining in-groups and out-groups.

Missing the most basic point by skipping the phylogenetic analysis
The first bird is the last common ancestor of all birds. That’s it. That’s all. No matter what it looks like. Or what it has. And that taxon is… the Thermopolis specimen attributed to Archaeopteryx.

Pygostyles don’t matter.
Pygostyles appeared several times by convergence.

Wings don’t matter.
Unrelated Microraptor had wings.

The Thermopolis specimen
happens to have longer coracoids. So that’s a clue that the earliest birds were flapping, not gliding, from the beginning. This trait appearing at this node represents the origin, however tentative, of avian flight.

References
Segre PS and Banet AI 2018. The origin of avian flight: finding common ground. Biological Journal of the Linnean Society, bly116 (advance online publication) doi: https://doi.org/10.1093/biolinnean/bly116

Giant rat (Coryphomys), giant squirrel (Ratufa) and giant capybara (Josephoartigasia)

Another short one today.
The images say it all.

Figure 1. The giant rat (genus: Coryphomys) compared to an extant rat of typical size.

Figure 1. The giant rat (genus: Coryphomys) compared to an extant rat of typical size.

Some rodents grew really big
(by comparison to their modern counterparts). We have a giant rat (genus: Coryphomys, Fig. 1) and a giant capybara (genus: Josephoartigasia, Fig. 2; Rinderknecht & Blanco 2008), the size of a cow. The largest living rodent is the capybara (genus: Hydrochoerus). One might say it is the size of a pig with a skull larger than a human skull.

Figure 9. Josephoartigasia monesi dwarfs the largest extant rodent, Hydrochoerus, the capybara.

Figure 2. Josephoartigasia monesi dwarfs the largest extant rodent, Hydrochoerus, the capybara. That skull is 53cm long.

The giant squirrel,
Ratufa (Fig. 3; extant) at 36 cm snout/vent length is the size of a small dog.

Figure 2. Ratufa, giant Indian squirrel skeleton and in vivo image. Note the large, cat-like claws and compare them to the smaller claws on all related taxa.

Figure 2. Ratufa, giant Indian squirrel skeleton and in vivo image. Note the large, cat-like claws and compare them to the smaller claws on all related taxa.

References
Aplin et al. 2010. Quaternary Murid Rodents of Timor Part I: New Material of Coryphomys buehleri Schaub, 1937, and Description of a Second Species of the Genus. Bulletin of the American Museum of Natural History, 2010; 3411 DOI: 10.1206/692.1
Aplin KP and Helgen KM 2010. Quaternary murid rodents of Timor part I: new material of Coryphomys buehleri Schaub, 1937, and description of a second species of the genus. Bulletin of the American Museum of Natural History. 341: 1–80. doi:10.1206/692.1
Braun J, Mares M, Coyner B and Van Den Bussche R 2010. New species of Akodon (Rodentia: Cricetidae: Sigmodontinae) from central Argentina. Journal of Mammalogy, 91 (2), 387-400 DOI: 10.1644/09-MAMM-A-048.1
CSIRO Australia. Archaeologists discover biggest rat that ever lived: Weight of about 6 kilograms (over 13 lb). ScienceDaily. ScienceDaily, 26 July 2010.
Rinderknecht A, Blanco RE 2008. “The largest fossil rodent”. Proceedings of the Royal Society B. 275 (1637): 923–8.

https://en.wikipedia.org/wiki/Josephoartigasia_monesi