Editing Onychophora (section)

=== Insights on decay and fossilization ===
[[File:Onychophora Decay Timeline.png|left|thumb|400x400px|Feature decay timeline. Yellow means "pristine", orange means "decaying", red means "some or all lost"]]
Due to being soft-bodied, onychophorans need excellent conditions to [[Fossil|fossilize]]. However, even when this happens, their fossils can be subject to [[taphonomic bias]]. Experiments were done with modern velvet worms to analyze their decomposition in various [[Saline water|saline solutions]].<ref name=":5">{{Cite journal |last1=Murdock |first1=Duncan JE |last2=Gabbott |first2=Sarah E. |last3=Mayer |first3=Georg |last4=Purnell |first4=Mark A. |date=2014-11-29 |title=Decay of velvet worms (Onychophora), and bias in the fossil record of lobopodians |journal=BMC Evolutionary Biology |volume=14 |issue=1 |pages=222 |doi=10.1186/s12862-014-0222-z |doi-access=free |issn=1471-2148 |pmc=4266977 |pmid=25472836|bibcode=2014BMCEE..14..222M }}</ref> The study also investigated whether they experienced something called [[stemward slippage]]. In this phenomenon, animals are falsely categorized as more primitive due to the decay of certain features.<ref name=":5" />

The researchers found that different features [[Decomposition|decayed]] at significantly different rates.<ref name=":5" /> [[Salinity]] and time of [[Moulting|moult]] had little effect on decay, and the way things decomposed remained the same for different species (though it could happen at different speeds).<ref name=":5" /> Before any degradation, velvet worms flex into a S, U, or circular shape. Most flexing happens in the first 24 hours, but the process can continue for around two more days.<ref name=":5" /> In the early stages of decay, the [[epidermis]] and outer cuticle separate, causing a bloated appearance. The elongates while increasing in width by around 10–30%. The [[Limb (anatomy)|limbs]] do the same, increasing in length and width by around 10–25%.<ref name=":5" /> Around the same time, the internal organs begin to degrade. This eventually culminates in the [[Gastrointestinal tract|gut]] rupturing, destroying the other organs.<ref name=":5" /> In later stages of decay, the body cuticle shrinks close to its original size. A similar trend was found with the limbs, but it was just short of being statistically significant.<ref name=":5" /> It's around this time that many external features begin to deteriorate. These include the [[Dermal papillae (Onychophora)|dermal papillae]], leg rings, [[anus]], [[gonopore]], [[Antenna (zoology)|antenna]], slime papillae, and eventually [[Eye|eyes]]. Interestingly, the dermal papillae on the trunk disappear faster than those on the limbs.<ref name=":5" /> Even as decay progresses, the body is still recognizable. This stops once the outer cuticle finally ruptures. After that, the animal’s anatomy is extremely difficult to interpret. At this stage, the only identifiable features would be the [[Chitin|chitinous]] jaws and claws.<ref name=":5" />

Onychophorans are unlikely to experience any [[stemward slippage]] since their defining features (jaws, feet, and slime papillae) are generally decay-resistant.<ref name=":5" /> However, [[decomposition]] has a significant impact on fossil anatomy. For starters, the preserved body outline is probably somewhat inaccurate, as this gets bloated in the decay process. A similar thing happens with the [[Limb (anatomy)|limbs]], so this needs to be accounted for when analyzing locomotion and/or leg length.<ref name=":5" /> While fossilized onychophorans can appear to display [[Patterns in nature|patterning]], these aren't true to life. [[Biological pigment|pigment granules]] are one of the first things to degrade and can easily move around in the body.<ref name=":5" /> Another finding is that characters such as [[Internal organ|internal organs]] or the [[Pseudocoelom|body cavity]] are highly unlikely to fossilize. If these appear preserved in a fossil, they should be treated with skepticism, especially if they’re [[Mineralization (biology)|unmineralized]].<ref name=":5" /> When it comes to placement of the [[mouth]], even moderate decay makes it hard to tell if it's at the front or underside of the head.<ref name=":5" /> Additionally, [[Fossil|fossils]] that lack decay-resistant features probably lacked them in life. This is even more plausible if the fossil preserves decay-prone features, as their presence indicates a better level of preservation. For example, an onychophoran (or related animal) with [[Eye|eyes]] but no claws likely never had them.<ref name=":5" />