Overview: The Fendouzhe Trench Expedition
During the TS29-3 cruise (7 February to 18 March 2023) aboard the R/V Tan Suo Yi Hao, the full-ocean-depth HOV Fendouzhe conducted 32 surveys along the trench axis, spanning over 1,200 km from western to central and southeastern regions.
The estimated trench-floor area is about 14,400 km².
The HOV video survey had a field of view of about 5 m width, calibrated using 10-cm laser scale points. Each transect was 2.4–5.5 km long (4.3 km average), totaling 127.72 km, yielding a surveyed area of about 0.64 km².
Whale-Fall Sample Collection and Processing
Whale-fall fossil samples were collected using the submersible's hydraulically powered manipulator arms and stored in geological baskets. Bones in the sulfophilic stage were kept in the biobox.
Associated free-living fauna (gastropods, squat lobsters, brittle stars) were collected using a slurp sampler. Upon retrieval, specimens were sorted, fixed, and registered.
- For taxonomy: Specimens preserved in 10% formalin or 75% ethanol.
- For molecular analysis: Specimens preserved in -80°C freezers.
Examination of Fauna and Chemosymbionts
Morphological identification used published literature on deep-sea macrobenthos from whale falls, cold seeps, and hydrothermal vents.
For molecular examination, tissues (up to 0.5 cm³) underwent DNA extraction, library preparation, and metagenomic sequencing (DNBSEQ-T10, 2×150 bp paired-end, ~50 Gb). Assembled contigs were searched against the MetaCOXI database for 16S rRNA and COI sequences. 18S and 28S rRNA genes were predicted using rRNA_HMM.
Microbiome analyses for three bivalves yielded metagenome-assembled genomes (MAGs) from gill tissues, binned and annotated using GTDB-tk v2.4.0 against GTDB R220. Dominant symbiont MAGs are listed by relative abundance.
Density Assessments
Density assessments for macro- and megafauna were performed using HOV high-definition video, with scale from two parallel laser pointers (10 cm apart). Each whale-fall community was measured by species, including the bone region (dominated by Osedax) and surrounding sediment (dominated by jellyfish or tubeworms).
- For three smaller whale falls (WF1, WF2, WF4): Total individuals were counted.
- For two larger falls (WF3, WF5): 16 or 6 quadrats (each 4 dm²) were randomly selected and counted; average and maximum densities were analyzed.
Sr Isotopic Dating of Whale Fossils
Sr isotopic dating was performed on 25 fossil bone specimens at Nanjing FocuMS Technology Co. Ltd. and eight at the Radiogenic Isotope Facility, University of Queensland. Samples (~0.1 g) were digested in nitric acid.
Sr separation used two-step column chemistry (HCl on Bio-Rad AG50W-X8 resin, then Milli-Q water on Sr-specific resin) or the protocol from ref. 56. Sr-isotope ratios were determined using Nu Plasma MC-ICP-MS.
Raw data were corrected for exponential mass fractionation (normalized to ⁸⁶Sr/⁸⁸Sr = 0.1194). Instrumental drift corrected using SRM 987. Accuracy monitored using USGS reference materials (BCR-2, BHVO-2, EN-1).
Best-fit ages were calculated from mean isotopic ratios using the seawater ⁸⁷Sr/⁸⁶Sr curve of ref. 24.
Phylogenetic Analysis
Phylogenetic relationships of Perucetus diamantinae sp. nov. with other Ziphiidae were investigated using PAUP v4.0a169, using the same morphological data matrix and assumptions as ref. 60, with an additional character:
Antorbital notch narrow, V- or U-shaped (0) vs. deep and broad, bordered posterolaterally by an anteroventrolaterally expanded antorbital process (1) (derived state in Pterocetus benguelae and P. diamantinae).
Homoplastic characters were downweighted using the method of ref. 61. Results are presented in Extended Data Fig. 6.
Reporting Summary
Further information on research design is available in the Nature Portfolio Reporting Summary.