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I wonder if the harsh post impact environment selected for small, short lived creatures due to the lower caloric energy requirements, and faster genetic iteration speed respectively. If your environment is particularly hostile with low resources then taking many small bets quickly might be the favored play.

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We have no idea when that transition happened, though, and if it is related to the impact. The time from when these animals lived in the Jurassic to the impact at the end of the Cretaceous is considerably longer than the time from the impact until today, much could have happened inbewteen.

It would be interesting to know what the climate was too. If these animals hibernated or slowed their metabolism during cold periods it would help explain their longevity.

Scotland was around 35 degrees latitude and the Jurassic period was fairly warm compared to now (tropical plants are found up to 60 degrees latitude) so it’s unlikely there was a winter to hibernate through.

However there was significantly more oxygen in the atmosphere back then. There could be a metabolic component related to that since absorbing O2 was probably easier.

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