''Timorebestia koprii'' is an extinct species of

stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

chaetognath The Chaetognatha or chaetognaths (meaning ''bristle-jaws'') are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms, they are mostly pelagic; however about 20% of the known species ...

(arrow worm relative) that lived about 520 million years ago, in the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

. Its fossils are known from the

Sirius Passet Sirius Passet is a Cambrian Lagerstätte in Peary Land, Greenland. The Sirius Passet Lagerstätte was named after the Slædepatruljen Sirius, Sirius sledge patrol that operates in North Greenland. It comprises six places in Nansen Land, on the eas ...

Lagerstätte A Fossil-Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that preserves an exceptionally high amount of palaeontological information. ''Konzentrat-Lagerstätten'' preserv ...

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

, and it was first described in 2024.

Description

''Timorebestia'' has a wide body marginally surrounded by continuous rayed fins: a pair of lateral fins and a rounded

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

. The anterior region is a short head, bearing a pair of antennae as long as half of the body length. The mouth opened below the head, with internal jaw apparatus consisting paired subtriangular elements, blunt anterior elements, and an unpaired anterior, possibly ventral or basal plate. Rows of longitudinal and transverse muscles surround the wide trunk region. The digestive tract terminates at the base of caudal fin. It also has a pair of well-defined ventral

ganglia A ganglion (: ganglia) is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there a ...

that identifies it as a chaetognath, but was probably more basal to modern arrow worms than ''

Amiskwia ''Amiskwia'' is a genus of soft-bodied marine animals known from fossils of the Middle Cambrian Lagerstätten both in the Burgess Shale in British Columbia, Canada and the Maotianshan shales of Yunnan Province, China. It is interpreted as a membe ...

''.

As of January 2024, 13 known specimens have been assigned to this species, ranging from 2.2 cm to more than 20 cm in body length (the largest specimen had a body length of ~206 mm in addition to 92-mm-long antennae).

Paleoecology

Compared to extant chaetognaths, which are

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

ic and rarely grow beyond 10 cm, ''Timorebestia'' was much larger, up to 20 cm (30 cm when antennae included), and occupied a higher

trophic level The trophic level of an organism is the position it occupies in a food web. Within a food web, a food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the ...

. This suggests that back in the Cambrian, chaetognaths constituted an important group of

nektonic Nekton or necton (from the ) is any aquatic organism that can actively and persistently propel itself through a water column (i.e. swimming) without touching the bottom. Nektons generally have powerful tails and appendages (e.g. fins, pleopods ...

predators Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...

alongside various

panarthropod Panarthropoda is a clade comprising the greatest diversity of animal groups. It contains the extant phyla Arthropoda (Euarthropoda), Tardigrada (water bears) and Onychophora (velvet worms), although the precise relationships among these remained ...

groups like the

radiodonts Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and were used for a variety ...

. It lived alongside other nektonic

fauna such as ''

Kerygmachela ''Kerygmachela kierkegaardi'' is a Kerygmachelidae, kerygmachelid Lobopodia#Gilled lobopodians, gilled lobopodian from the Cambrian Stage 3 aged Sirius Passet Lagerstätte in northern Greenland. Its anatomy strongly suggests that it, along with i ...

'', ''

Kiisortoqia ''Kiisortoqia soperi'' is an extinct species of arthropod from the Early Cambrian Sirius Passet Lagerstätte in Greenland. While it had a superficially trilobite-like bodyform, it also possessed large frontal appendages similar to those of radiod ...

'', ''

Pauloterminus ''Pauloterminus'' is an extinct genus of bivalved arthropod known from Early Cambrian (about 520 to 516 million years ago) Sirius Passet locality of northern Greenland. It is tentatively classified under the family Waptiidae. The genus only has ...

'', ''

Isoxys ''Isoxys'' (meaning "equal surfaces") is a genus of extinct bivalved Cambrian arthropod; the various species of which are thought to have been freely swimming predators. It had a pair of large spherical eyes (which are the most commonly preserve ...

'' and so on. Some specimens with gut contents suggest it prey on the small and abundant arthropod ''Isoxys volucris''. ''Timorebestia'' is thought to be one of the earliest examples of an

apex predator An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the hig ...

Phylogeny

The following

dendrogram A dendrogram is a diagram representing a Tree (graph theory), tree graph. This diagrammatic representation is frequently used in different contexts: * in hierarchical clustering, it illustrates the arrangement of the clusters produced by ...

shows the evolutionary relationships of ''Timorebestia'' as in Park et al. 2024. :A yet-undescribed chaetognath, as of January 2024, from

Etymology

The genus name is derived from the Latin words ''timor'' (fear) and ''bestia'' (beast) which translates to "fear-causing beast". The species name is derived from the Korea Polar Research Institute (KOPRI), who has helped with the expeditions to the lagerstätte.

References

{{Taxonbar, from=Q124134810 Chaetognatha Cambrian invertebrates Sirius Passet fossils Fossil taxa described in 2024