''Palaeoechinastacus australianus'' is a species of

freshwater crayfish Crayfish are freshwater crustaceans belonging to the clade Astacidea, which also contains lobsters. In some locations, they are also known as crawfish, craydids, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, rock lobsters, mu ...

known from

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

fossils from

Victoria, Australia Victoria is a state in southeastern Australia. It is the second-smallest state with a land area of , the second most populated state (after New South Wales) with a population of over 6.5 million, and the most densely populated state in Au ...

Specimens and stratigraphy

''Palaeoechinastacus'' is known from one partial body fossil, which is the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

, and has been deposited in the

National Museum of Victoria National may refer to: Common uses * Nation or country ** Nationality – a ''national'' is a person who is subject to a nation, regardless of whether the person has full rights as a citizen Places in the United States * National, Maryland, ce ...

Melbourne Melbourne ( ; Boonwurrung/Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a met ...

as lot number NMV-P186041. Two specimens, each showing a single

chela Chela may refer to: * ''Chela'' (fish), a genus of small minnow-type fish in the Cyprinid family * Chela (organ), a pincer-like organ terminating certain limbs of some arthropods such as crabs * Chela (meteorite), a meteorite fall of 1988 in Tan ...

(claw) were deposited as lots NMV-P186042 and NMV-P186009, but are not part of the

type series In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...

, and are therefore considered to be "hypotypes". The body fossils were collected in 1987 and 1989, but it is not known exactly who found them. In addition, a number of

trace fossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

s of burrow-like structures were found in a similar geological setting, and may be related to ''Palaeoechinastacus''.

Holotype

The holotype was collected at

Dinosaur Cove The Dinosaur Cove in Victoria, Australia is a fossil-bearing site in the south-east of the continent where the Otway Ranges meet the sea to the west of Cape Otway, adjacent to Great Otway National Park (''map''). The inaccessible ocean-front clif ...

on the Victoria coast from "a fine-grained lithic sandstone" of the Otway Group. The rocks are thought to have formed from a river channel, and date from the

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...

age of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

period. Despite some damage from a rock saw, the specimen comprises most of an abdomen, including the

telson The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...

and one

uropod Uropods are posterior appendages found on a wide variety of crustaceans. They typically have functions in locomotion. Definition Uropods are often defined as the appendages of the last body segment of a crustacean. An alternative definition sugge ...

, and parts of four

pereiopod The decapod (crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various g ...

s. The

somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide in ...

s of the abdomen overlap, and bear a few small spines. The entire abdomen is about long, including the telson, implying a total length of around .

Hypotypes

Two disjointed claws were collected from the same horizon as the holotype. It is not clear that they came from the same animal as the holotype. The two isolated chelae also differ from each other, although this could be due to

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

ontogenetic Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the st ...

differences rather than differences between species.

Trace fossils

Trace fossils resembling those made by crayfish were found near Marengo in sandstones of

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

age. Similar trace fossils from freshwater environments have previously been linked specifically to crayfish, and other potential creators, such as

lungfish Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...

, are not considered likely in this case, because of the form of the burrows.

Ecology

A the time ''Palaeoechinastacus'' was alive, the Otway and Gippsland basins of Australia were at high latitudes. On the basis of

palaeobotany Paleobotany, which is also spelled as palaeobotany, is the branch of botany dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments (paleogeogr ...

and

geochemistry Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the e ...

, the annual mean

air temperature Atmospheric temperature is a measure of temperature at different levels of the Earth's atmosphere. It is governed by many factors, including insolation, incoming solar radiation, humidity and altitude. When discussing surface air temperature, the ...

would have been in the range .

Significance

''Palaeoechinastacus'' is the earliest body fossil from the family

Parastacidae The Parastacidae are the family of freshwater crayfish found in the Southern Hemisphere. The family is a classic Gondwana-distributed taxon, with extant members in South America, Madagascar, Australia, New Zealand, and New Guinea, and extinct ta ...

, and the earliest crayfish from

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

. The only earlier pieces of evidence of crayfish in the southern hemisphere are the trace fossils from Marengo, and some trace fossils from

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

, dating from the

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

to the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

. This accords with the modern distribution of crayfish, which are most abundant in temperate regions, and live in the tropics chiefly in cooler, montane environments.

References

* {{Taxonbar, from=Q7126408 Parastacidae Early Cretaceous crustaceans Monotypic arthropod genera Cretaceous arthropods of Australia Early Cretaceous animals of Australia Albian genera Cretaceous Australia Fossils of Australia