Globally discordant Isocrinida (Crinoidea) migration confirms asynchronous Marine Mesozoic Revolution

The Marine Mesozoic Revolution (MMR, starting ~200 million years ago) changed the ecological structure of sea floor communities due to increased predation pressure. It was thought to have caused the migration of less mobile invertebrates, such as stalked isocrinid crinoids, into deeper marine environments by the end of the Mesozoic. Recent studies questioned this hypothesis, suggesting the MMR was globally asynchronous. Alternatively, Cenozoic occurrences from Antarctica and South America were described as retrograde reversions to Palaeozoic type communities in cool water. Our results provide conclusive evidence that isocrinid migration from shallow to deep water did not occur at the same time all over the world. The description of a substantial new fauna from Antarctica and Australia, from often-overlooked isolated columnals and articulated crinoids, in addition to the first compilation to our knowledge of Cenozoic Southern Hemisphere isocrinid data, demonstrates a continuous record of shallow marine isocrinids from the Cretaceous-Paleogene to the Eocene/Oligocene boundary.

generally separated and at a slight angle to each other except near lumen. Cirral ossicles are circular.
Remarks: With no characters available for study in the arms, stem characters alone are used.
Shorter internodal lengths of fewer than 10, typically >8 (mostly 7) columnals 7 , except in proximal most part of the stem, suggest all these taxa belong to the Isocrinus subspecies, rather than the Chladocrinus subspecies that has intermodal lengths up to 20 columnals. Unlike Metacrinus, the size of the nodals and internodals is similar. Size of cirrus sockets can also be useful in distinguishing species.  Occurrence: Browns Creek Clay, Eocene, Victoria, Australia Remarks for I. (Isocrinus): These isocrinids are similar in having a small size, pentagonal to pentastellate stem and high columnals. However, there are significant differences in the shape of the latera with species 1 and 3 being much smoother than the highly ornamented species 2, and species 1 and 2 having cirral scars that are much bigger than species 3. The much smaller species 4 has smooth rounded to sub-pentagonal distal columnals with proximal columnals being far more ornamented with well-developed epifacet on the latera. There is insufficient taxonomic information on the 5 th species to attempt further taxonomy.

Metacrinus Carpenter, 1882 12
Description: Cup low and wide. Basals generally large, forming contiguous basal circlet; lower edge with median projection covering interradial edge of uppermost columnals. Typically 7 primibrachials (range: 2 to 11). Arms divided at primibrachials 4 to 7 and further divided 2 more times. Cryptosyzygy between primibrachials 1 and 2; in species with 7 primibrachials also a cryptosyzygy between primibrachials 4 and 5 or primibrachials 5 and 6; in secondibrachitaxis cryptosyzygy between secundibrachials 2 and 3, Br 3 and 4, and more distal parts of the arms. Other brachial articulations muscular. No synarthry. All axillaries follow an oblique muscular articulation. First pinnule on primibrachial 2. Column pentagonal to rounded sub-pentagonal. Columnal facets similar to Isocrinus. Crenulae rather short. 5 to 13 internodals, fewer in proximal part of column. Nodals larger than inter nodals, with 5 rather large, elliptical to circular cirrus sockets facing outward to slightly upward. Cirri long.
Remarks: Although the columnal facets are similar to Isocrinus, Metacrinus has very low internodal heights and unlike Isocrinus the nodals are larger and higher with the cirrus sockets which are deeply set and oval rather than circular. All these taxa have these characters as well as variation in the structure of the articular face.   Articular facet is weakly pentastellate to almost pentagonal to strongly pentalobate. 5-6 marginal crenulae and 3-4 adradial crenulae. Internodal height is long >20 with most preserved examples typically 14-16. Most internodals are smooth, however every 3rd-4th internodal is slightly larger and has an epifacet. This morphology results in an irregular size of the latera.
Most genera with 5 pits arranged radially around apex, forming dorsal star, in large specimens commonly in a depressed area. Some specimens also with shallow, indistinct, lanceolate interradial impressions around aboral pole. Centrodorsal cavity narrow to moderate, 20 to 30 percent of centrodorsal diameter, always surrounded by, or exceptionally fused with, 5 radial pits housing coelomic extensions outside chambered organ and nerve capsule of centrodorsal cavity. Cirrus sockets generally large, with more or less distinct articular tubercles, and in most fossil genera with marginal crenulae. Sockets in 10 columns on small or conical centrodorsals, increasing in number during growth and tending to form 20 columns (obliterated on aboral apex) on hemispherical to discoidal centrodorsals of larger specimens of Glenotremites and Remesimetra. Sockets small in Semiometra, without distinct sculpturing, and closely alternating, without forming columns on a very low discoidal centrodorsal. Rod-shaped basals commonly exposed interradially, with or without subradial cleft. Radials with low exposed surface or concealed; distal margin may be concave, reaching edge of centrodorsal only inter radially. Radial articular facet generally rather low and wide, but in Semiometra high. Muscle fossae distinct, similar in size to interarticular ligament fossae or higher. Radial cavity narrow to wide and funnel shaped. Arms 10, divided at primibrachial 2. Synarthry between primibrachials 1 and 2 and secundibrachials 1 and 2. Syzygy between secundibrachials 3 and 4 and distally at variable intervals. Arms and pinnules aborally rounded, not carinate. Pinnules Radials with low exposed surface, sometimes visible only inter radially or concealed. Radial articular facet rather steep and flat or concave.
Notocrinus Mortensen, 1917, p. 206 23 Diagnosis: after Mortensen 23 Centrodorsal conical or truncated conical. Dorsal star consisting of 5 radial pores surrounding central pore or pit present in juvenile specimens. Cirrus sockets without distinct sculpturing, in 10 columns, or in large specimens crowded, tending to form 20 columns. Aboral apex cirrus-free, pointed or truncated, rugose. Adoral side of centrodorsal with 5 simple, deep radial pits. Cirri stout, rather long. Cirrals rather short and wide; distal cirrals laterally compressed. Rod-shaped basals stout, centrally united, exposed inter radially or concealed. No subradial cleft. Exposed surface of radial low to moderate. Radial articular facet rather steep and wide, not angularly bent or concave. Adoral muscle fossae rather wide, triangular, larger than interarticular ligament fossae; adoral edge wide, with a broad and shallow median embayment. Radial cavity moderate. Arms large. Distal syzygies at interval of 2 to 20. Centrodorsal maximum width about 13-14 mm at the level of radials, height about 8 mm. Cavity 2-3 mm in diameter. Sides of centrodorsal covered by large cirrus sockets (approx. 10-15); sockets not arranged in distinct columns or rows, and are slightly spaced. The exposed radial area of the aboral surface of the centrodorsal tends to be flattened unornamented (naked).
Sockets circular, smooth, no articular ridge, some crenellae, shallow, with a small axial pore.
Cirri not preserved; basals surface flat with distinct dorsal ligament fossa, large, and a distinct ligament pit. Central canal large and sub-circular in outline.

Remarks: Glenotremites tends to have a flat 'button shaped' centrodorsals. Unlike most
Glenotremites, this species tends to be larger and has a flattened unornamented aboral surface. Remarks: This species is slightly smaller than those examined from the Cretaceous. However, it still has the distinctive conical shape with a rugose aboral surface typical of the genus, but the arrangement of the cirrus sockets is more regular than other members of the genus.

Supplementary Note 2: Geological Settings
The subsequent section summarises the geological setting of the above described crinoids, with the current interpretation of the environment of deposition. Herein shallow water is defined as occurring on the inner shelf or shallower.

Environment: Shallow marine delta
The contact at the base of the Sobral Formation has been dated at 65.5 Ma 25 . The Sobral Formation was deposited in the Paleocene, and shows an overall coarsening-upward, regressive trend reflecting eastward progradation of a marine delta 26 Sobral Fm has been interpreted as a shallow water unit, deposited by the filling of the James Ross Basin by progradation of a delta, with sediments originating from the Antarctic Peninsula 26 . This occurred in a wave dominated tide influenced system (Ineson pers comm).

Environment: Very shallow marine
The Paleocene Cross Valley Formation, is a valley infill deposit, which cuts into the lower Paleocene Sobral Fm and older beds 29,30

. A Late Paleocene age for the upper Cross Valley
Formation was suggested based on dinoflagellates and pollen 31,32 . Three "allomembers" are distinguished 1,27 ; the crinoid specimens were collected from the base of allomember C.
Allomember A is dominated by volcanic clasts, conglomerates and glauconitic sandstones.
This lower part of the formation has been interpreted as a lahar deposit 33 . Allomember B consists of sandstones with charred wood and leaf imprints, interpreted as deposited in an estuary with tidal influence 1 . Allomember C consists of sandstones and shales, some of which contain a fauna of oysters, fish teeth, sharks, gastropods and also a penguin that was described by Tambussi et al. 29 . Tambussi et al. 29 mention crinoids from this allomember but, until now, no specimens have as yet been described from this unit. Other beds contain plant imprints 1,27 .
Deposition is thought to have occurred in a very shallow marine environment with a potential decrease in sea level, followed by a transgression 27 .

Environment: Shallow marine (within the photic zone)
The Cardabia Formation, originally known as the "Cardabia Group", was reduced to formation status by Hocking et al. 34 , and the constituent "formations" to member status. Named Tortachilla Limestone is a yellow-brown, green and grey bioclastic autochthonous limestone, which grades from the base upwards from bryozoan sands rich in limonite grains into a hard, richly fossiliferous bryozoan limestone, which becomes partly glauconitic towards the top 42 .
The colour also grades from the base to the top from brownish to pinkish-white. The top of the formation is a recrystallized limestone with quartz grains and limonite pellets 43 50 . This species is of the consueta group, and tends to typify outer shelf or deep-water assemblages (cf. 50 Clay are discussed in detail by Shafik 57 . Assemblages from the base of the formation include two key species, the nannofossil Isthmolithus recurvus and the foraminifera Acarinina