Restoring the little crocodylomorph, Coloradisuchus

In 2017 Martinez, Alcober and Pol introduced a new
small (6cm skull length) crocodylomorph, Coloradisuchus abelini (Figs. 1, 2). The specimen is only known from the bottom half of its small skull + mandibles (Fig. 1). Unique for such a small Late Triassic croc, the nares are confluent at the snout tip, facing anteriorly. The premaxilla/maxilla suture is marked by a large oval fenestra exposing the lower canine in lateral view. This trait is typically found in protosuchids (Fig. 5), but also to a lesser extent in Gracilisuchus (Fig. 3) and Dibothrosuchus (Fig. 2).

Figure 1. Coloradisuchus skull from Martinez, Alcover and Pol 2017. Colors added.

Figure 1. Coloradisuchus skull from Martinez, Alcover and Pol 2017. Colors added. Skull length 6 cm. Restoration according to Dibothrosuchus.

The question is:
where to nest Coloradisuchus?

Figure 2. Dibothrosuchus compared to scale with the much smaller Coloradisuchus.

Figure 2. Early Jurassic Dibothrosuchus compared to scale with the much smaller Triassic Coloradisuchus.

From the abstract:
“Protosuchids are known from the Late Triassic to the Early Cretaceous and form a basal clade of Crocodyliformes. We report here a new protosuchid crocodyliform, Coloradisuchus abelini, gen. et sp. nov., from the middle Norian Los Colorados Formation, La Rioja, northwestern Argentina. Our phylogenetic analysis recovers Coloradisuchus abelini within Protosuchidae, as the sister group of the clade formed by Hemiprotosuchus and two species of Protosuchus (P. richardsoni and P. haughtoni). The new protosuchid C. abelini increases the diversity of crocodyliforms in the Late Triassic and, together with H. leali from the same stratigraphic levels of the Los Colorados Formation, shows that the diversification of basal crocodyliforms was probably faster and/or older than thought previously.”

It is easy to see why the authors assumed Coloradisuchus was a protosuchid, but adding convergent taxa moves it away. On the other hand, distinctly different Hemiprotosuchus (Fig. 4) clearly nests elsewhere.

Figure 5. Gracilisuchus skull updated with new colors.

Figure 3. Gracilisuchus skull updated with new colors. Skull length = 8cm.

Here in the LRT
Hemiprotosuchus nested far from protosuchids, at the base of the Aetosauria (Fig. 4). Protosuchids are terminal taxa also arising form small bipedal ancestors.

Figure 3. Hemiprotosuhus image from Desojo and Ezccura 2016. Colors added. This taxon is derived from Ticinosuchus, basal to aetosaurs.

Figure 4. Hemiprotosuhus image from Desojo and Ezccura 2016. Colors added. This taxon is derived from Ticinosuchus, basal to aetosaurs.

Adding Coloradisuchus
to the large reptile tree (LRT, 1737+ taxa) nests it between the much larger Early Jurassic Dibothrosuchus (Fig. 2) and the similarly-sized Middle Triassic Gracilisuchus (Fig. 3). These taxa also share a fenestra between the naris and antorbital fenestra, though much narrower than in protosuchids and Coloradisuchus. Martinez, Alcober and Pol did not test Dibothrosuchus and Gracilisuchus in their abbreviated cladogram consisting only of protosuchids and putative protosuchids.

Figure 2. Protosuchus skull. The high cranium and low triangular rostrum evidently made Bonaparte 1969 consider Hemiprotosuchus similar enough to Protosuchus.

Figure 5. Protosuchus skull. The high cranium and low triangular rostrum evidently made Bonaparte 1969 consider Hemiprotosuchus similar enough to Protosuchus.

Martinez, Alcobar and Pol note:
“The only known Triassic record of Protosuchidae is Hemiprotosuchus leali, from the upper levels of the middle Norian Los Colorados Formation (Bonaparte, 1971; Kent et al., 2014), and a putative, unnamed protosuchid from thelate Norian–Rhaetian Quebrada del Barro Formation (Martınez et al., 2015), both from northwestern Argentina.” 

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

With Hemiprotosuchus now nesting with coeval aetosaurs,
Coloradisuchus in the Triassic nests temporally and phylogenetically apart from other protosuchids. Unfortunately, due to preservation issues (Fig.1), relatively few traits can be scored for Coloradisuchus. Even so, moving Coloradisuchus to the protosuchid lineage adds five steps. That may change with further study or better data. Let’s keep working on this one.


References
Martinez RN, Alcober OA and Pol D 2017. A new protosuchid crocodyliform (Pseudosuchia, Crocodylomorpha) from the Norian Los Colorados Formation, northwestern Argentina. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1491047.

 

Beg tse: restoring missing neoceratopsian parts

Yu et al. 2020 bring us
a mostly complete and articulated 3D skull of a new neoceratopsian, Beg tse (Fig. 1; Mid- Cretaceous, Mongolia). Here some restoration, based on comparison to a phylogenetic sister Auroraceratops (Fig. 2), helps us understand the extent of the missing parts of this neoceratopsian.

Figure 1. Most of the skull of the new neoceratopsian, Beg tse. Colors added.

Figure 1. Most of the skull of the new neoceratopsian, Beg tse. Colors added.

Sereno 2005 defined Neoceratopsia as:
The most inclusive clade (Fig. 3) including Triceratops horridus, but not Psittacosaurus mongoliensis.

Figure 2. Beg tse nests with Auroraceratops in the LRT.

Figure 2. Beg tse nests with Auroraceratops in the LRT.

Yu et al. considered
Beg tse the most basal neoceratopsian currently known. That does not quite agree with the results recovered by the LRT (subset Fig. 3). Other taxa (Leptoceratops (Fig. 4), Auroraceratops) also nest in this node.

Figure 3. Subset of the LRT focusing on Ornithischia with the addition of Beg tse.

Figure 3. Subset of the LRT focusing on Ornithischia with the addition of Beg tse.

Figure 1. Leptoceratops in situ 2x. This taxon resolves the headless and head only node at the base of the ceratopsians in the LRT.

Figure 4. Leptoceratops in situ 2x. This taxon resolves the headless and head only node at the base of the ceratopsians in the LRT.

Since Stenopelix (Fig. 5) is almost quadrupedal,
phylogenetic bracketing indicates that Beg tse and Aurorceratops were likely bipeds, like Psittacosaurus (Fig. 5) and Leptoceratops (Fig. 4).

Figure 1. Stenopelix reconstructed in lateral and dorsal views to scale with Psittacosaurus. The curved ischium and short tail with short chevrons allies Stenopelix with ceratopsians.

Figure 5. Stenopelix reconstructed in lateral and dorsal views to scale with Psittacosaurus. The curved ischium and short tail with short chevrons allies Stenopelix with ceratopsians.

References
Yu C, Prieto-Marquez A, Chinzorig T, Badamkhatan Z and Norell M 2020. A neoceratopsian dinosaur from the early Cretaceous of Mongolia and the early evolution of ceratopsia. Nature Communications Biology 3:499 | https://doi.org/10.1038/s42003-020-01222-7 http://www.nature.com/commsbio

wiki/Beg_tse

Restoring the skull of the basal bat, Onychonycteris

Short one today,
more ‘show’ than ‘tell’ as one picture and a caption pretty much tell the tale.

Figure 1. Onychonycteris is known from an articulated but crushed bottom half of the skull. Uncrushing it and giving it a suitable top half (Myzopoda) provides a restoration with some possibility of resemblance to theo original.

Figure 1. Onychonycteris is known from an articulated but crushed bottom half of the skull. Uncrushing it and giving it a suitable top half (Myzopoda) provides a restoration with some possibility of resemblance to theo original. Images from Simmons et al. 2010. The skull could have been less crushed than imagined here, so may have been proportionately shorter. The hole in the braincase of Myzopoda (above) may be a surgical opening to remove brain tissue. If natural, I do not know what it is.

And a cladogram
for phylogenetic context (Fig. 2).

Figure 1. Subset of the LRT focusing on the resurrected clade Volitantia, including dermopterans, pangolins, bats and their extinct kin.

Figure 2. Subset of the LRT focusing on the resurrected clade Volitantia, including dermopterans, pangolins, bats and their extinct kin.

Onychonycteris finneyi (Simmons, Seymour, Habersetze and Gunnell 2008) Eocene (~52mya), ~27 cm in length, is the most primitive known bat. It retained unguals (claws) on all five digits, a primitive trait not shared with other bats. Derived from a sister to ChriacusOnychonycteris phylogenetically preceded IcaronycterisMyotis and Pteropus in the LRT (subset Fig. 2).

Figure 2. Chriacus and Onychonycteris nest as a sister to the undiscovered bat ancestor and a basal bat. Miniaturization was part of the transition. So was enlargement of the manus. It is still a mystery why the transitional form decided to start flapping.

Figure 3. Chriacus and Onychonycteris nest as a sister to the undiscovered bat ancestor and a basal bat. Miniaturization was part of the transition. So was enlargement of the manus. It is still a mystery why the transitional form decided to start flapping.

Onychonycteris is smaller than Chriacus,
but the preserved portions of the skull and teeth are similar in proportion and morphology (Fig. 3). So… perhaps the proportions of the missing portion of the Chriacus skull are similar (fig. 1). More fossils will tell.

Veselka et al. 2010
concluded that O. finneyi may have been capable of echolocation.

By contrast, Simmons et al. 2010
argued that O. finneyi was probably not an echolocating bat.


References
Simmon NB, Seymour KL, Habersetzer J, Gunnell GF 2008. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature 451 (7180): 818–21. doi:10.1038/nature06549. PMID 18270539.
Simmons NB, Seymour KL, Habersetzer J and Gunnell GF 2010. Inferring echolation in ancient bats. Nature 466: E8.
Veselka et al. (8 co-authors) 2010. A bony connection signals larygenal echolocation in bats.Nature 463: 939–942.

wiki/Onychonycteris

Variations on a Cutleria Restoration

Crushed fossils missing some of the middle/connecting bones give paleontologists several options for restoration. Case in point: Cutleria (Figs. 1, 2) a very basal therapsid. We looked at this specimen/taxon earlier here and here.

Figure 1. Cutleria restoration version 1, straight maxilla.

Figure 1. Cutleria restoration version 1, straight maxilla. Click to enlarge.

The first restoration aligns the ventral maxilla in a straight line. Note the very deep reflected lamina on the angular, sharply angled from the dentary.

Figure 2. Cutleria restoration version 2, convex maxilla.

Figure 2. Cutleria restoration version 2, convex maxilla. Click to enlarge.

The second restoration (Fig. 2) is the more conservative (more like the in situ fossil) producing a deeper, ventrally convex maxilla. Note the reflected lamina of the angular is not so deep here. In both cases the mandible needs to mate to the maxilla, so it changes in each case, enabled by the mid-length break.

Which one is more correct?

Factors to consider:

  1. Ancestral taxa (like Haptodus and Ophiacodon) have a shallow reflected lamina.
  2. Descendant taxa (like Biarmosuchus) have a deeper reflected lamina; but then
  3. Other descendant taxa (like Stenocybus) have a shallow reflected lamina.
  4. Descendant taxa (like Haptodus and Ophiacodon) have a convex maxilla.
  5. Descendant taxa (like Biarmosuchus have a less convex to straight maxilla.
  6. Other descendant taxa (like Stenocybus, dromasaurs, dicynodonts and other therapsids) have a convex maxilla.
  7. Version 2 requires less bone movement.
  8. Version 1 requires less ‘putty’ to fill in holes left by missing bones. The puzzle pieces fit tighter.
  9. The strong posterior lean of the lateral temporal fenestra is not present in either ancestral or descendant taxa and it probably reflects the angle of the mandible adductor.

Your opinion or insights would be appreciated.