After the dinos, tree shrews came down and got big!

During the reign of the dinosaurs
tree shrews, like Ptilocercus (Fig. 1) and Tupaia (Fig. 1), stayed in the trees, evolving into tree-dwelling members of the Carnivora (Genetta, Fig. 1), Volitantia (bats, pangolins and dermopterans), Glires (including multituberculates led by Tupaia) and Primates (Microcebus, Fig. 1) in the large reptile tree (LRT, 1818+ taxa) distinct from all gene studies and all other prior trait studies (due to taxon exclusion). The LRT is the first study that found tree-dwelling Caluromys (Fig. 1), an extant tree shrew-like marsupial, as the proximal outgroup to the Placentalia. Based on chronological bracketing, Caluromys relatives lived in the Early Jurassic.

Figure 1. Mammals at the base of the Placentalia include the outgroup taxon: Caluromys, a basal placental: Genetta, a basal Carnivora: Eupleres, a basal Volitantia: Ptilocercus, a basal Primates: Microcebus, and basal Glires: Tupaia.

Figure 1. Mammals at the base of the Placentalia include the outgroup taxon: Caluromys, a basal placental: Genetta, a basal Carnivora: Eupleres, a basal Volitantia: Ptilocercus, a basal Primates: Microcebus, and basal Glires: Tupaia.

After the Cretaceous some tree shrews became terrestrial.
Leptictids, elephant shrews (Rhynchocyon, Fig. 2 and tenrecs (Tenrec) were phylogenetically among the first of the former tree shrews to become fully terrestrial. They were all small. After the Cretaceous some terrestrial tree shrew descendants began to increase in size. Some became elephants, others horses, still others baleen whales, all following Cope’s Rule.

Figure 7. Rhynchocyon, a living elephant shrew, is a living leptictid.

Figure 2. Rhynchocyon, a living elephant shrew, is a living leptictid and a former tree shrew.

Once established on the ground
and spreading beyond the jungles, the following Early Paleocene terrestrial placentals became cat to tiger size: Onychodectes (Fig. 3), Alcidedorbignya (Fig. 3) and Pantolambda (Fig. 3).

Figure 3. Onychodectes, Alcidedorbignya and Pantolambda are former tree shrews now terrestrial of increasing size in the Early Paleocene.

Figure 3. Onychodectes, Alcidedorbignya and Pantolambda are former tree shrews now terrestrial of increasing size in the Early Paleocene. Note the lost of sharp claws replaced by pre-hooves.

By the late Paleocene
taxa like massive Barylambda showed further increases in size. This taxon was basal to giant glyptodonts and ground sloths, some of which ultimately became smaller and returned to the trees as tree sloths.

Figure 1. Barylambda looks like a large ground sloth for good reason. It is a sister to the direct ancestor and nests at the base of the Xenarthra along with Orycteropus, the aardvark.

Figure 4. Late Paleocene Barylambda looks like a large ground sloth for good reason. It is a sister to the direct ancestor and nests at the base of the Xenarthra along with Orycteropus, the aardvark.

PS… saving the best for last.
Writing this blogpost inevitably brought my gaze back to Fruitafossor (Luo and Wible 2005), a small, Late Jurassic digging mammal with four robust fingers, xenarthran lumbars and single cusp, tubular teeth. When first encountered and based on these traits the LRT mistakenly nested Fruitafossor with edentates for the last four years. That Late Jurassic temporal discontinuity in an otherwise Tertiary clade of edentates required a review and revision of taxon scores for Fuitafossor. That review ultimately re-nested Fruitafossor more plausibly and parimoniously basal to echidnas in the LRT. Fruitafossor is a basal echidna from Colorado. That story comes to you tomorrow.


References
Luo Z-X and Wible JR 2005. A late Jurassic digging mammal and early mammal diversification. Science 308:103–107.

 

 

SVP abstracts – Drepanosaurs are not ‘highly enigmatic’

Britt et al. 2019 bring us a new look
at a 3D drepanosaur.

From the abstract:
“With a bird-like head, mole-like arms, and a “claw” at the end of the tail, derived drepanosaurs (lizard-sized neodiapsids) are highly enigmatic.” 

Not so. The large reptile tree (LRT, 1594 taxa, subset Fig. 2) documents exactly what they are. Paleontologists should stop using the word ‘enigmatic’ when what they really are saying is ‘we haven’t put in the effort.’ And that means the very little effort needed to click on www.ReptileEvolution.com where all candidates for drepanosaur ancestry are considered and tested.

“Multiple 3D skeletons of a new drepanosaur taxon from Utah provides insights into this clade, previously known from flattened skeletons and isolated 3D elements.”

Always good to have, but 2D specimens are still diagnostic, like a photo, rather than a sculpture. You don’t need as many characters as possible to make a taxonomic determination. What you need is a surfeit of taxa.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Figure 1. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale. Drepanosaurs nest at the base of the Lepidoauria. Pink bone is a sesamoid, not an ulna.

The rest of the abstract
describes the drepanosaur as a scratch-digger with an elongate naris and a hook tail capable of striking a tripod pose. They do not consider the ancestry or clade to which drepanosaurs belong, but consider them common and worldwide in distribution during the Late Triassic.

Figure 1. Subset of the LRT focusing on the Lepidosauria. Now the drepanosaur clade lumps with the rhynchocephalians in the crown group. Extant lepidosaurs are in gray.

Figure 1. Subset of the LRT focusing on the Lepidosauria. Now the drepanosaur clade lumps with the rhynchocephalians in the crown group. Extant lepidosaurs are in gray.

The title of this abstract 
may be the longest one I have ever read. See below.


References
Britt B et al. 2019. Still stranger things: MicroCT imaging of 3D drepanosaur skulls and skeletons (Saints & Sinners quarrry, Late Triassic, Eolian/Interdunal nugget formation) reveals bizarre and novel morphologies including a beak combined with transversely wide teeth, sauropod-like pneumatic dorsal vertebrae, a chevron that articulates with the pelvis and tripodal adaptations. Journal of Vertebrate Paleontology abstracts.

Naked, horned and pocket gophers

Figure 1. Subset of the LRT focusing on the rabbit/rodent and kin clade where gophers nest with hedgehogs.

Figure 1. Subset of the LRT focusing on the rabbit/rodent and kin clade where gophers nest with hedgehogs.

In the large reptile tree (LRT, 1258 taxa, Fig. 1) the naked mole rat (genus: Heterocephalus, Fig. 2) nests with the hedgehog clade, one node off from the mouse/rat/clade. So the naked mole rat should be the  naked mole gopher.

Figure 1. The naked mole rat, Heterocephalus is closer to hedgehogs than to rats.

Figure 2. The naked mole rat, Heterocephalus is closer to hedgehogs than to rats.

Heterocephalus glaber (Rüppell 1842-5; 8-10cm) is the extant naked mole rat. It has a cold-blooded metabolism, lives underground, and can move backwards as fast as forward. Not the claws, but the teeth (protruding outside the lips) are used for digging. Heterocephalus is essentially hairless, lives in a colony dominated by a queen and may live up to 32 years in a low oxygen environment, or several times longer than related taxa.

Figure 2. Naked mole rat (Heterocephalus) skull in several view. The mandibles are disarticulated here, but the glenoid appears to be reduced to absent, providing great mobility to the jaws.

Figure 2. Naked mole rat (Heterocephalus) skull in several view. The mandibles are disarticulated here, but the glenoid appears to be reduced to absent, providing great mobility to the jaws.

Ceratogaulus hatcheri is the extinct horned gopher (Fig. 3). It nests with the naked mole rat in the LRT (Fig. 1).

Figure 3. Ceratogaulus, the extinct horned gopher

Figure 3. Ceratogaulus, the extinct horned gopher

Thomomys bottae (Figs. 4, 5) is the extant pocket gopher, another rodent nesting with hedgehogs.

Figure 4. Skull of Thomomys, the extant pocket gopher.

Figure 4. Skull of Thomomys, the extant pocket gopher. No large retroarticular process here.

These taxa look like rodents
but they nest with hedgehogs. So do we expand our concept of rodents (lumping)? Or make new clades (splitting)?

Figure 5. Skeleton of Thomomys, the pocket gopher.

Figure 5. Skeleton of Thomomys, the pocket gopher.

 

Rodentia is characterized by a single pair of continuously growing incisors in each of the jaws, as opposed to rabbits, which have two incisors.

Glires (Latin glīrēsdormice) is a clade consisting of rodents and lagomorphs (rabbits, hares, and pikas). In the LRT many more clades of small mammals nest with rabbits and rodents.

Euarchontoglires (synonymous with Supraprimates) is a clade of mammals, the living members of which belong to one of the five following groups: rodentslagomorphstreeshrewscolugos and primates. In the LRT rodents nest with primates, but not colugos.

References
Rüppell E 1842-5. Säugethiere aus der Ordnung der Nager, beobachtet im nordöstlichen Africa. Museum Senckenbergianum: Abhandlungen aus dem Gebiete der beschreibenden Naturgeschichte. 3: 99–101.

wiki/Hedgehogs
wiki/Erinaceus
wiki/Echinops
wiki/Naked_mole-rat

https://blogs.scientificamerican.com/tetrapod-zoology/african-mole-rats-so-much-more-than-just-the-naked-mole-rat/

Rats! – (or where Mickey Mouse diverged from Walt Disney)

Updated January 3, 2019, seven years and about 1000+ taxa later.

We don’t talk about mammals much,
but as reptiles they (we) do qualify as subjects to be covered by ReptileEvolution.com.

A new online study by Wu et al. (2012) finds evidence for a post-Cretaceous origin for rodents. Rodents (everything from porcupines and guinea pigs to squirrels, mice and multituberculates) are related to rabbits (lagomorphs).

The Wu et al 2012 study on rodents and their post-Cretaceous appearance.

The Wu et al 2012 study on rodents and their post-Cretaceous appearance.

How are they all related? 
Near (but not at) the base of the primates is an interesting set of taxa known as tree shrews, like Tupaia (Raffles 1821, Fig. 1). Essentially they are basal rodents/rabbits/multituberculates.

Tupaia, the large tree shrew,

Figure 1. Tupaia, the large tree shrew, a living taxon close to the base of rabbits and rodents with origins in the Paleocene, just following the Cretaceous. Click to learn more.

The most common tree shrew, Tupaia was found to be basal to the equally arboreal and highly derived Plesiadapis (Fig. 3) and terrestrial rabbits, and rodents, like the porcupine. It’s worthwhile to see the porcupine skull and how close it resembles that of Plesiadapis.

Plesiadapis

Figure 3. Plesiadapis, formerly considered a basal primate, is here considered a basal arboreal lagomorph (rabbit ancestor).

The other arboreal tree shrew, 
Ptilocercus, is basal to Tupaia, derived from basal primates and carnivores.

Ptilocercus, pen-tailed tree shrew

Figure 2. Ptilocercus, pen-tailed tree shrew, a living relative to the ancestor of bats and colugos.

Based on the nesting of multituberculates
all these tree shrews, rodents and rabbits had their origin in the Jurassic, not the Paleocene (contra Wu et al. 2012.

References
Wu S, Wu W, Zhang Z, Ye J, Ni X, Sun J, Edwards SV, Meng J and Organ CL 2012. Molecular and Paleontological Evidence for a Post-Cretaceous Origin of Rodents. PLoS ONE 7(10): e46445. doi:10.1371/journal.pone.0046445
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0046445

Pterosaur Tree Clingers and Non-Clingers

While we know of bipedal and quadrupedal pterosaur tracks left in soft mud and sand, we will never have traces of pterosaurs clinging to trees. Nevertheless, certain pterosaurs have provided clues that they did so, or could have done so, while others could not.

Four pterosaur hands with fingers of various sizes.

Figure 1. From left to right the pterosaurs MPUM 6009, Dorygnathus, Pterodaustro and Nyctosaurus, all to the same relative metacarpus length demonstrating the relative size of the free fingers. Those with larger free fingers were more adapted to cling to trees.

Tree Clinging in Pterosaurs
Tree clinging goes back to LongisquamaCosesaurus and perhaps even Huehuecuetzpalli and Lacertulus, basal tritosaur lizards that had tendril-like hind toes, like a modern Iguana. Unlike Iguana, Huehuecuetzpalli and Lacertulus had relatively smaller hands, fingers and finger claws. A quick look at the modern glider, Draco, can be instructive on this point. Giant claws may not be necessary, but long tendril-like fingers seem to help.

The pterosaur ancestor Longisquama had relatively enormous fingers tipped with trenchant claws and a bipedal body plan. So it clung to trees in a different fashion than a typical lizard — and more like a telephone lineman (or a lemur) with feet planted beneath the hips, the belly elevated off the trunk, the arms extended and the fingers wrapped around the trunk, claws dug in. Finger 4 was rotated axially and posteriorly at the carpus. Despite its great length, finger 4 was no longer involved with tree clinging, as demonstrated by the discontinuous PILs (described here).

Like their Lizard Forebearers
Early pterosaurs, like MPUM 6009 (Fig. 1) and Dorygnathus (Fig. 1) had relatively long fingers tipped with trenchant, bark-stabbing claws.  Primitively their metacarpals and fingers increased in length from 1 to 4. In Dorygnathus metacarpal 2 and 3 were subequal.

Derived Pterosaur Hands
In certain later pterosaurs the metacarpals would appear in different proportions.  Pterodaustro (Fig. 1) had relatively tiny fingers on metacarpals in which mc 1 was longer than mc2, which was longer than mc3. Digit 2 was subequal to 3 and no manual ungual was deeper than its penultimate phalanx.

A series of Nyctosaurus specimens demonstrate the reduction of all three fingers in that genus, culminating in the UNSM93000 specimen which had useless wire-like vestiges.

Needlessly Controversial
In the present supposedly “heretical” configuration the forearm was unable to pronate or supinate, thus the palmar side of the fingers faced ventrally in flight and medially with wings folded (Peters 2002). This controversy was blogged about earlier. The key here is the palmar sides of the fingers facing medially with wings folded so pterosaurs could grapple parasagittal tree trunks between their opposing hands, much like the early bird, Archaeopteryx, which had similarly elongated fingers and a forearm similarly unable to pronate and supinate. Other scientists proposed finger configurations that were permanently supinated (i.e. Bennett 2008), but these did not allow tree clinging.

Questions
Azhdarchids, even large ones, had robust fingers with deep claws. Were they found in trees? Or only on the ground?

Jeholopterus had extremely long, curved hand claws, built like surgeon’s needles. These look to be ideal for stabbing and clinging to dinosaur hide. Were these clues to its vampire lifestyle?

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E Buffetaut and DWE Hone eds., Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.