Let’s try to identify that mammal foot inside the fossil Microraptor

Just ran this data
(Fig 1) for the Mesozoic mammal swallowed by a Microraptor specimen (IVPP V 12330) for which only a slightly disassembled foot was left in the gut as evidence of that meal.

PAUP recovered an identity
based on pedal traits only (Fig 2). The specimen is a primitive Mesozoic monotreme.

The authors of the original paper
Hone et al 2022, reported, “The foot exhibits the mammalian synapomorphies of having a well-defined trochlea on the astragalus, an elongate calcanei, and no more than three phalanges per digit.”

“The digits are slender, similar to Eomaia or Sinodelphys, although the phalanges are not as elongate as in these two taxa.” The authors go on to further describe the pedal elements without creating a reconstruction or adding their data to a mammal cladogram.

That’s where DGS (Fig 2) and the LRT step in.

The mammal foot nested
among the Mesozoic monotremes in the LRT, creating a loss of resolution in that clade due to its incomplete skeleton and complete lack of skull data. Plus some Mesozoic monotremes do not preserved foot data.

Sinodelphys is one of those primitive Mesozoic monotremes in the LRT. So Hone et al. did well in their comparative anatomy.

PILs
Parallel Interphalangeal Lines or PILs were introduced in Peters 2000 as an aid in determining plantigrady vs digitigrady in fossil pterosaur pedes by aligning or misaligning the three sets of interphalangeal flex/extend lines (Fig 2). In counterpoint, flippers have to be stiff, so the PILs are always misaligned. Terrestrial animals have to extend and flex their digits in sets, which is why PILs can help in certain situations, like this one (Fig 2).

Hone, Sullivan and Benett 2009 thought
the concept might ‘hinge on too many assumptions.’ …Did you get their little joke?

The authors wrote, “the hinge lines, as conceived by Peters (2000a) can often be superimposed on 2-D drawings of tetrapod mani or pedes but have little to no value as a tool in paleontological research. The rules given for constructing the lines are so permissive as to be almost arbitrary, and the putative supporting evidence from ichnology for the widespread occurrence of hinge lines is obviated by preservational problems and variability in the relationship between soft tissue pads and underlying skeletal structures. IP hinge lines have functional significance only in rare cases, and cannot be reliably utilised to predict autopodial postures of extinct animals or to infer the proportions of missing phalanges or metapodials. and cannot be reliably utilised to predict autopodial postures of extinct animals or to infer the proportions of missing phalanges or metapodials. We would therefore strongly advise against the use of hinge lines as a guide to functional analysis, a source of phylogenetic information or a basis for identifying trackmakers in the ichnological record.”

Cleary, and once again, the authors were bent on disparaging a new hypothesis.
Please note in line # one their use of the word, ‘often.”

Historical Biology was kind enough
to allow me to rebut the Hone, Sullivan and Bennett 2009 diatribe. Today, only one sentence from that Peters 2010 rebuttal is enough: “Considering their negative stance, it is disconcerting how often Hone et al. (2009) concede that hinge lines are valid.”

Remember, “when you step on their toes, you will get a bloody nose” – but only if there is no chance you will ever referee one of their manuscripts. Academics never say such things to one another = i.e. those who are in the queue to referee manuscripts. Thus, this sort of bad behavior may be how they relieve the many pressures they endure in Academia: by punching down = to criticize someone who is in a less powerful position.

This is the world we independent researchers live in. And that’s okay.
Just make sure all your work and all your words follow the scientific method.

Only by taking the road less traveled will you ever be able to discover something that others pass by, overlook or consider to ‘have little to no value as a tool in paleontological research.’

Here’s a link to Dr David Hone’s views on ‘unnecessary phylogenies’.
https://archosaurmusings.wordpress.com/2026/03/20/unnecessary-phylogenies/

References
Hone DWE, Sullivan C and Bennett SC 2009. Interpreting the autopodia of tetrapods: interphalangeal lines hinge on too many assumptions. Historical Biology, 21(1–2), 67–77. https://doi.org/10.1080/08912960903154503
Hone DW, Dececchi TA, Sullivan C, Xu X. and Larsson HC 2022. “Generalist diet of Microraptor zhaoianus included mammals”. Journal of Vertebrate Paleontology. 43 (e2144337). e2144337. 
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods Ichnos, 7: 11-41.
Peters D 2010. In defence of parallel interphalangeal lines Historical Biology iFirst article, 2010, 1–6 DOI: 10.1080/08912961003663500

Source: https://pterosaurheresies.wordpress.com/2026/05/27/lets-try-to-identify-that-mammal-foot-inside-the-fossil-microraptor/