Figure 1.
Paleogeographic reconstruction for the late Aptian with the position of ODP site 1049 (Blake Nose).
Thick lines denote paleo-coastlines, grey areas represent emerged land (modified from ref. [51]).
Figure 2.
Key echinoderm plates from the early Cretaceous of Blake Nose (ODP site 1049) with corresponding plates of Recent relatives.
A: Ophiolimna sp. (Ophiacanthidae), lateral arm plate (LAP), Blake Nose (GZG.INV.78777). B: Ophiolimna bairdi (Lyman) (Ophiacanthidae), LAP, Recent, North Atlantic. C: Ophiohelinae gen. nov. (Ophiacanthidae), LAP (GZG.INV.78778), Blake Nose. D: Ophiotholia spathifer (Lyman) (Ophiacanthidae), LAP, Recent, Japan. E: Ophiohelinae gen. nov. (Ophiacanthidae), parasol spine (GZG.INV.78779), Blake Nose. F: Ophiotholia spathifer (Lyman) (Ophiacanthidae), parasol spine, Recent, Japan. G: Ophioleuce sp. (Ophioleucinae), LAP (GZG.INV.78780), Blake Nose. H: Ophioleuce seminudum Koehler (Ophioleucinae), LAP, Recent, Pacific. I: Ophiomusium sp. (Ophiolepididae), LAP (a: external, b: internal) (GZG.INV.78781), Blake Nose. J: Ophiomusium lymani (Wyville-Thomson) (Ophiolepididae), LAP (a: external, b: internal), Recent, North Atlantic. K: Benthopectinidae gen. nov., ambulacral (GZG.INV.78782), Blake Nose. L: Pectinaster filholi Perrier (Benthopectinidae), ambulacral, Recent, Atlantic. M: Benthopectinidae gen. nov., adambulacral (GZG.INV.78783), Blake Nose. N: Pectinaster filholi Perrier (Benthopectinidae), adambulacral, Recent, North Atlantic. O: Laetmogonidae gen. nov., body wall ossicle (lower side) (GZG.INV.45613), Blake Nose. P: Laetmogone olivacea Théel (Laetmogonidae), body wall ossicle (lower side), Recent, North Atlantic. Q: Hemisphaeranthos sp. (Myriotrochidae), body wall ossicle (upper side) (GZG.INV.45634), Blake Nose. R: Myriotrochus rinkii Steenstrup (Myriotrochidae), body wall ossicle, Recent, North Atlantic. S: (?)Myriotrochus sp. (Myriotrochidae), radial calcareous ring element (inner side) (GZG.INV.45623), Blake Nose. T: Myriotrochus rinkii Steenstrup (Myriotrochidae), radial calcareous ring element (inner side), Recent, North Atlantic. Scale bars equal 100 µm.
Figure 3.
Additional diagnostic skeletal components of the echinoderm groups from the Aptian-earliest Albian (Early Cretaceous) of Blake Nose (ODP Site 1049).
A: Ophiacanthidae gen. et sp. nov., lateral arm plate (GZG.INV.78784). B: Ophiologimus sp. nov. (Ophiacanthidae), lateral arm plate (GZG.INV.78785). C: Ophiologimus sp. nov. (Ophiacanthidae), lateral arm plate (GZG.INV.78786). D: Ophiacantha sp. nov. (Ophiacanthidae), lateral arm plate (GZG.INV.78787). E: Balanocrinus sp. (Isocrinidae), columnal (GZG.INV.78788). F: Bathycrinus? sp. (Bathycrinidae), holdfast (GZG.INV.78789). G: Bathycrinus? sp. (Bathycrinidae), second primibrachial (GZG.INV.78790). H: echinothurioid ambulacral plate (GZG.INV.78791). I: echinothurioid? spine (GZG.INV.78792). J: diadematoid spine (GZG.INV.78793). K-L: Histocidaridae gen. et sp. indet., adoral spine fragments (GZG.INV.78794–78795). M: holasteroid ambulacral plate (GZG.INV.78796). N: holasteroid spine fragment (GZG.INV.78797). O: holasteroid spine fragment (GZG.INV.78798). P: Jumaraina sp. (Chiridotidae) body wall ossicle (upper side) (GZG.INV.78799). Scale bars equal 100 µm.
Figure 4.
Relative abundances of the most common ophiuroid families in present-day middle and lower bathyal settings, in comparison with the middle to lower bathyal ophiuroid assemblages from the upper Aptian–lowermost Albian of Blake Nose (ODP site 1049).
Relative family-level abundances of the Blake Nose ophiuroid assemblage were inferred from lateral arm plate counts, assuming that the number of lateral arm plates serves as an approximation for the number of individuals.
Figure 5.
Quantitative assessment of the Blake Nose ophiuroid assemblage.
A: Detrended Correspondence Analysis (DCA) of modern ophiuroid assemblages in comparison with the Blake Nose ophiuroid fauna and Cretaceous shelf assemblages. The Blake Nose assemblage plots within the modern lower bathyal communities, and strongly differs from modern shallow-water communities and Cretaceous shelf assemblages, challenging the possibility of repeated deep-sea recolonization from shelf depths in the Cretaceous. The analysis is based on the relative abundances of all 17 extant ophiuroid families minus the Ophiuridae, which are abundant at all depths (see Table 1 for abundance data). B: Linear correlation between DCA scores (axis 1) and LOG depth. The relationship is very strong (r = −0.80, adjusted r-square = 0.64). The probability of such strong correlation occurring by chance is virtually zero (4.8899E−29). When the score of the Blake Nose fauna is projected onto this relationship, it would be assigned a depth of 1,486 m (1,218–1,864 m) (uncertainty based on 95% confidence interval for regression line). Remarkably, this is exactly within the range of paleodepth reconstructions for this site [13], [16]. This means the fauna is similar to present-day lower bathyal assemblages to such degree that even the faunal composition versus depth relationship appears to have remained the same.
Figure 6.
Position of the Blake Nose deep-sea echinoderm assemblage in the context of the events assumed to have triggered major reorganizations of the deep-sea fauna [4]–[6].
Table 1.
Ophiuroid lateral arm plate counts of the Blake Nose samples.
Table 2.
Ophiuroid lateral arm plate counts of Cretaceous shallow-water assemblages.