 |
| Paradoryphoribius chronocaribbeus Mapalo, Robin, Boudinot, Ortega-Hernández & Barden, 2021 Illustration: Holly Sullivan. |
Abstract
Tardigrades are a diverse group of charismatic microscopic invertebrates that are best known for their ability to survive extreme conditions. Despite their long evolutionary history and global distribution in both aquatic and terrestrial environments, the tardigrade fossil record is exceedingly sparse. Molecular clocks estimate that tardigrades diverged from other panarthropod lineages before the Cambrian, but only two definitive crown-group representatives have been described to date, both from Cretaceous fossil deposits in North America. Here, we report a third fossil tardigrade from Miocene age Dominican amber. Paradoryphoribius chronocaribbeus gen. et sp. nov. is the first unambiguous fossil representative of the diverse superfamily Isohypsibioidea, as well as the first tardigrade fossil described from the Cenozoic. We propose that the patchy tardigrade fossil record can be explained by the preferential preservation of these microinvertebrates as amber inclusions, coupled with the scarcity of fossiliferous amber deposits before the Cretaceous.
Keywords: Paradoryphoribius, Miocene, invertebrate palaeontology, Eutardigrada
 |
| Phylogenetic and temporal summary of the tardigrade fossil record. (a) Simplified tardigrade phylogeny following topology from recent molecular analyses; node ages correspond with mean molecular divergence estimates of Regier et al. [2004]. The position of the undescribed ‘Orsten’ tardigrade as sister to all extant tardigrades reflects the putative stem-group hypotheses recently summarized by Guidetti & Bertolani [2018]. (b) Eutardigrade fossil record. (1) Paradoryphoribius chronocaribbeus gen. et sp. nov. from Miocene age Dominican amber. (2) Beorn leggi from Campanian age Grassy Lake Canadian amber. Horizontal dotted line indicates uncertainty in the ordinal-level placement. (3) Milnesium swolenskyi from Turonian age Raritan amber from New Jersey. (4) ‘Orsten’ tardigrade from the middle Cambrian Kuonamka Formation in Siberia. |
 |
| Artistic reconstruction of Paradoryphoribius chronocaribbeus gen. et sp. nov. Illustration: Holly Sullivan. |
Systematic palaeontology
Phylum Tardigrada Doyère, 1840
Class Eutardigrada Richters, 1926
Order Parachela Schuster, Nelson, Grigarick and Christenberry, 1980
Superfamily Isohypsibioidea Sands, McInnes, Marley, Goodal-Copestake, Convey and Linse, 2008
Genus Paradoryphoribius gen. nov.
(Three letter acronym: Pdo.).
Etymology: owing to the close resemblance (para-) to the extant genus Doryphoribius [Gąsiorek, et al. 2019].
Diagnosis: tardigrade with Isohypsibius-type claws (i.e. the basal section and secondary branch form a right angle) with the claw pairs slightly different in shape and size. Accessory points present but not clearly visible. Cuticular bar present between claws of the fourth pair of legs. Pseudolunules absent. Bucco-pharyngeal apparatus consists of a rigid buccal tube with a ventral lamina (ventral apophysis) for the apophyses of the stylet muscle insertion (AISM). No dorsal AISM observed. Pharyngeal apophyses and one thin macroplacoid present, but microplacoids appear absent. Cuticle smooth. Cuticular gibbosities (i.e. cuticular protuberances) may be present.
Differential diagnosis: by the presence of Isohypsibius-type claws and ventral lamina, the new genus is morphologically similar to Doryphoribius but differs in the presence of a single thin macroplacoid instead of separated granular-shaped macroplacoids present in Doryphoribius.
Paradoryphoribius chronocaribbeus sp. nov.
Etymology: from the Greek ‘chrono’ (khronos)—meaning time—in reference to the age of the fossil taxon and ‘caribbeus’ reflecting the region of the type locality.
Type locality: Dominican Republic mined from La Cumbre; amber from this region dates to the Miocene, with an approximate age of 16 Ma.
Marc A. Mapalo, Ninon Robin, Brendon E. Boudinot, Javier Ortega-Hernández and Phillip Barden. 2021. A Tardigrade in Dominican Amber. Proc. R. Soc. B. 20211760. DOI: 10.1098/rspb.2021.1760
“Once-in-a generation” tardigrade fossil discovery reveals new species in 16-million-year-old amber
Researchers announce just the third-ever tardigrade fossil on record, offering a glimpse into the history of the cryptic micro-animal that has survived five mass extinction events over its 500 million years on Earth.
