Dendromaia: Not mother + juvenile… just roommates

Updated December 26
with new tracings of the small den-mate now nesting as a juvenile Varanosaurus in the LRT.

Figure 1. The large and small Dendromaia specimens in part and counterpart, traced using DGS methods.

Figure 1. The large and small Dendromaia specimens in part and counterpart, traced using DGS methods.

Dendromaia unamakiensis made big news
this week by with headlines like:

  1. 305-Million-Year-Old Fossil Shows Parent Caring for Its Offspring
  2. 300m-year-old fossil is early sign of creatures caring for their young
  3. New Fossil Shows Parental Care Is At Least 300 Million Years Old

That’s the paleo PR machine at work.

Figure 2. Partial reconstructions of the two specimens found together in figure 1.

Figure 2. Partial reconstructions of the two specimens found together in figure 1. The LRT separates these taxa phylogenetically, so the large one is not the parent of the small one, contra Maddin et al. 2020.

when both the little one and the big one were added to the large reptile tree (LRT, 1625+ taxa), only the little one nested near where Maddin, Mann and Hebert 2020 recovered it. They were using a taxon list that excluded too many taxa in comparison to the LRT.

Figure 3. Reconstruction of the small den mate based on DGS tracings in figure 1.

Figure 3. Skull of the small specimen. In the LRT it nests with Heleosaurus within the Protodiapsida, a clade not recognized by Maddin et al. due to taxon exclusion.

From the Maddin et al. abstract:
“Here we report on a fossil synapsid, Dendromaia unamakiensis gen. et sp. nov., from the Carboniferous period of Nova Scotia that displays evidence of parental care—approximately 40 million years earlier than the previous earliest record based on a varanopid from the Guadalupian (middle Permian) period of South Africa. The specimen, consisting of an adult and associated conspecific juvenile, is also identified as a varanopid suggesting parental care is more deeply rooted within this clade and evolved very close to the origin of Synapsida and Amniota in general. This specimen adds to growing evidence that parental care was more widespread among Palaeozoic synapsids than previously thought and further provides data permitting the identification of potential ontogeny-dependent traits within varanopids, the implications of which impact recent competing hypotheses of the phylogenetic affinities of the group.”

The Maddin et al. cladogram
did not test both specimens separately. The Maddin et al. results nested Dendromaia with the poorly preserved Pyozia near the base of their Varanopidae.

The small specimen
The LRT nested the small specimen (Fig. 1) with Heleosaurus, sharing some traits with sister Mesenosaurus. These nest with other protodiapsids apart from Varanops and the Varanopidae in the clade Synapsida. Protodiapsids and synapsids are both derived from a sister to Vaughnictis their last common ancestor in the LRT.

The large specimen
The LRT nested the large skull-less specimen with several skull+pecs and skull-only taxa (Delorhynchus, Microleter and Acleistorhinus) close to the turtle mimics Eunotosaurus and Eorhynchochelys, which preserve post-crania.

these two roommates are not conspecific parent and young, but distinctly different genera sharing a space. The larger one likely dug the tunnel. The smaller one likely found safe harbor under the thigh of the large one, a robust herbivore based on phylogenetic bracketing.

Maddin et al. might have come to the same conclusion if they had tested the two taxa separately… just to be sure their assertion was confirmed phylogenetically… and added enough taxa to recover a correct tree topology. That’s what the LRT is here for.

Maddin HC, Mann A and Hebert B 2020. Varanopid from the Carboniferous of Nova Scotia reveals evidence of parental care in amniotes. Nature ecology & evolution 4:50–56.

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