Current Biology Vol 23 No 19 R860

comprehensive cell cycle controlling before palaeontologists could piece machinery. Anomalocaridids together the unusual anatomy of the MTOCs are also studied in other anomalocaridids. They are completely fungi, e.g. Aspergillus nidulans, Allison C. Daley soft bodied animals, lacking bones or Ustilago maydis and Ashbya gossypii. hard shells, but their frontal appendages Much less is known about the What are anomalocaridids? Imagine and circular mouthparts were about as composition of these MTOCs. you’re a small crab-like creature hard as a fingernail and so are found living on the ocean floor: you’re just fossilized on their own much more often Is the SPB equivalent to the minding your own business, when than as part of full body specimens. centrosome? Although sharing no suddenly you’re in the shadow of a The first anomalocaridid fossils were structural similarity, the yeast SPB is huge animal gliding through the water found in 1892 near the Burgess Shale, the functional equivalent of animal above you, its body flattened with and consisted of isolated frontal cells’ centrosomes. Whereas the wide swim flaps, huge limbs with appendages of Anomalocaris, which centriole-less SPBs are situated in sharp claws and a circular toothey were then thought to be the body of a the NE during mitosis (fungi have mouth; and it’s looking at you with shrimp. Soon after, strange fossils in mostly a closed mitosis) to organize its two large insect-like eyes. You are the form of a ring of plates with sharp the mitotic spindle, the centrosome, about to become the next meal of an teeth were found and interpreted which consists of a pair of cylindrical anomalocaridid! These animals are to be a jellyfish. Actually, they were centrioles surrounded by the the Earth’s oldest super predators. anomalocaridid mouthparts (Figure 1). pericentriolar material, is associated Now extinct, the anomalocaridids Other specimens were discovered and with the NE in interphase and then were found in marine environments thought to be sponges, sea cucumbers, becomes released with nuclear worldwide in Cambrian and Early and various early arthropods, before envelope breakdown in early mitosis Ordovician times, about 520 to 480 it was revealed in 1985 that all these when the centrosome establishes million years ago. They originated fossils were actually different parts the mitotic spindle. Despite these during a rapid burst of evolution called of the anomalocaridid body. All structural differences, a small set of the Cambrian Explosion, when most anomalocaridids have a flattened components of the yeast SPB and the major animal phyla first appeared in a and segmented body with a series of vertebrate centrosome are conserved, relatively short period of time. wide swim flaps, and a head bearing reflecting ancestral functions in a pair of spiney frontal appendages, duplication and MT organization. How do we know all that? The fossil circular plated mouthparts and a pair of record of the Cambrian Explosion multifaceted eyes on stalks (Figure 1). What can we learn from SPBs? SPBs is exquisite, because special local have proven to be as good a model conditions allowed soft tissues to How many different types of for addressing how a cell restricts the be preserved, meaning that whole anomalocaridids were there? duplication of the MTOC to one event bodies can be seen with skin, eyes, Recent research has revealed that the per cell cycle as they are for studying gills and internal organs fully intact. anomalocaridids were highly diverse MT nucleation. Furthermore, SPBs These fossils are flattened carbon and distributed worldwide. There are explain to us how cells can fulfil many impressions in dark shaley rock (Figure at least seven different genera and 13 diverging processes with a limited set 1). Localities yielding this type of fossil species of anomalocaridids known of protagonists. are known as ‘Konservat Lagerstätten’, from Canada, China, Australia, the USA, the most famous of which is the Greenland and Morocco. The group is Where can I find out more? Burgess Shale in the Canadian Rocky named after Anomalocaris canadensis, Adams, I.R., and Kilmartin, J.V. (1999). Localization Mountains. It took decades of collecting the first anomalocaridid ever found, of core spindle pole body (SPB) components during SPB duplication in Saccharomyces cerevisiae. J. Cell Biol. 145, 809–823. Bullitt, E., Rout, M.P., Kilmartin, J.V., and Akey, C.W. (1997). The yeast spindle pole body is assembled around a central crystal of Spc42p. Cell 89, 1077–1086. Jaspersen, S.L., and Winey, M. (2004). The budding yeast spindle pole body: structure, duplication, and function. Annu. Rev. Cell Dev. Biol. 20, 1–28. Knop, M., Pereira, G., Schiebel E. (1999). 10 mm Microtubule organization by the budding yeast spindle pole body. Biol. Cell 91, 291–304. Lim, H.H., Zhang, T., and Surana, U. (2009). Regulation of centrosome separation in yeast and vertebrates: common threads. Trends Cell Biol. 19, 325–333. Pereira, G., and Schiebel, E. (2001). The role of the yeast spindle pole body and the mammalian centrosome in regulating late mitotic events. Curr. Opin. Cell Biol. 13, 762–769. 10 mm

Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Figure 1. Anomalocaridids from the Burgess Shale. Im Neuenheimer Feld 282, 69120 Heidelberg, Top left: Mouthparts of Peytoia. Bottom left: Full body specimen of Anomalocaris with Germany. complete frontal appendage (arrow). Photos courtesy of Jean-Bernard Caron. Top right: Full E-mail: [email protected] body specimen of Hurdia. Bottom right: Model of Peytoia by E. Horn. Magazine R861 from the Burgess Shale in Canada (Figure 1). Anomalocaris is found at Priapulida most Cambrian fossil lagerstätten. Tardigrada The Burgess Shale has yielded a wide Onychophora variety of anomalocaridids, including Lobopodians the highly abundant Hurdia, which is characterised by an enigmatic large Opabinia carapace that extended forward from Stem group Anomalocaris arthropoda its head and appeared to be empty Peytoia (Figure 1). The function of this structure Hurdia remains unknown. The Chengjiang Biota Anomalocaridids Leanchoilia in China has yielded several beautifully preserved whole body specimens of Chelicerata and Eurypterida anomalocaridids, but at most other Trilobita Cambrian localities only fragments of Crown group anomalocaridids are known. Even still, arthropoda Hexapoda these fragments can reveal important Crustacea morphological details not seen Myriapoda elsewhere, such as at the Emu Bay Shale in Australia where exceptional Current Biology preservation of the eyes revealed that they were composed of over Figure 2. Tree of arthropod relationships. Anomalocaridids are found in the stem lineage leading to crown group Arthropoda. Drawings 16,000 tiny lenses. For over a century, by M. Streng. anomalocaridids were thought to be exclusively Cambrian in age, until the shrimp. The eyes of Anomalocaris are identified morphological differences in recent discovery of giant anomalocaridid made up of thousands of tiny lenses, the appendages and mouthparts of the fossils in the Ordovician of Morocco just like the eye of a fly. Thus, we can anomalocaridids, and suggested that revealed that they had survived much determine that Anomalocaris and other different taxa ate different diets. Some longer than previously thought. anomalocaridids were stem lineage anomalocaridids like Anomalocaris members of the phylum Arthropoda, have long appendages with short How big were they? Anomalocaridids which today includes spiders, crabs, spikey spines (Figure 1), perfect were the largest swimming animals in millipedes, centipedes and insects. As for grasping prey off the sea floor, the Cambrian seas. The majority of taxa arthropod ancestors, understanding while others like Hurdia have short ranged from 30 cm to 60 cm in length, the complex morphology of the appendages with long slender spines but some were over a metre long. That’s anomalocaridids has given us insight that could have made a crude net for pretty big when you think that most into the evolution of key arthropod filtering smaller prey items out of the other animals alive at that time were traits, such as segmentation, biramous water column or seafloor sediment only a few centimetres in length and limbs, and cephalic shields. (Figure 1). Anomalocaridids were lived on or in the sea floor. undoubtedly important in Cambrian What did they eat? Their highly- marine ecosystems. Okay, so that’s what they looked toothed mouthparts and the sharp like, but what were they? At first, the claws on their frontal appendages Where can I find out more? Chen, J., Ramsköld, L., and Zhou, G.Q. (1994). anomalocaridids and other oddities suggest that the anomalocaridids were Evidence for monophyly and arthropod affinity from the Cambrian Explosion were active predators. They were probably of Cambrian giant predators. Science 264, considered so weird that they could agile swimmers, as indicated by the 1304–1308. Collins, D. (1996). The “evolution” of Anomalocaris only be dead-end experiments in hydrodynamic shape of their flattened and its classification in the arthropod class animal form. However, parts of their body with wide swim flaps, and their Dinocarida (nov) and order Radiodonta (nov). J. Pal. 70, 280–293. bodies are actually very similar to those highly developed eyes suggest they Daley, A.C. and Budd, G.E. (2010). New of animals alive today. If a fossil is had good visual acuity for locating anomalocaridid appendages from the Burgess similar to a particular group of living prey items. With all these armaments, Shale, Canada. Palaeontology 53, 721–738. Daley, A.C., Budd, G.E., Caron, J.-B., Edgecombe, animals but doesn’t quite have all of coupled with their large body size, the G.D. and Collins, D. (2009). The Burgess Shale the defining characteristics, we place anomalocaridids were surely highly anomalocaridid Hurdia and its significance for early euarthropod evolution. Science 323, it in the ‘stem lineage’ or ancestral line mobile and very deadly predators. 1597–1600. of that animal phylum. When we do Anomalocaris had long been thought Paterson, J.R., García-Bellido, D.C., Lee, M.S.Y., this with many fossils, placing them to be a ferocious trilobite predator, Brock, G.A., Jago, J.B., and Edgecombe, G.D. (2011). Acute vision in the giant Cambrian in order on a stem lineage, it allows because there were few other known predator Anomalocaris and the origin of us to piece together the evolutionary Cambrian animals large enough compound eyes. Nature 480, 237–240. Whittington, H.B. and Briggs, D.E.G. (1985). The history of how modern animal body to have produced supposed bite largest Cambrian animal, Anomalocaris, plans were assembled (Figure 2). For marks in trilobite exoskeletons and Burgess Shale, British Columbia. Philos. T. example, the spiney frontal limbs large coprolites containing trilobite Roy. Soc. B., 309, 569-609. of Anomalocaris are jointed and fragments. However, the feasibility of Department of Zoology, University of made up of hard segments joined the soft-bodied Anomalocaris being Oxford, South Parks Road, Oxford, OX1 together by thin membranes — just able to tear apart mineralized trilobites 3PS, UK. like the appendages of crabs or has been questioned. Recent work has E-mail: [email protected]