Systematic paleontology

Celliformidae Genise, 2000

Cellicalichnus krausei Genise and Sarzetti isp. nov. urn:lsid:zoobank.org:act:5D4BE8A7-D32E-4B57-89CA-663E7A601E6B

Etymology. Dedicated to the discoverer of the first specimen, our colleague and friend J. Marcelo Krause.

Type material. Museo Paleontológico Egidio Feruglio, Trelew, Chubut, Argentina; MPEF-IC 4600 (holotype), the longest specimen collected, removed from the matrix and preserved in full relief (Figs 1B and 3A). MPEF-IC 4601 (paratype), the second-longest nest showing a lateral tunnel, removed from the matrix and preserved in full relief (Fig 3B). MPEF-IC 4602 (paratype), the first specimen found, preserved in full relief in the rock matrix (Fig 1A). All from the Castillo Formation, Tronador canyon, Chubut, Argentina.

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larger image TIFF original image Download: Fig 3. Type material and the most complete specimens of Cellicalichnus krausei isp. nov. (A) Holotype (MPEF-IC 4600). (B) Paratype (MPEF-IC 4601). (C) Fragment of a nest showing a lateral tunnel at a right angle (arrow, MPEF-IC 4625). (D) Fragment of a nest showing cells and scars (MPEF-IC 4610). Note the sessile cells in all cases. Scale bars are 5 cm. https://doi.org/10.1371/journal.pone.0227789.g003

Other material. A total of 15 remains of nests and 9 samples of isolated cells and tunnels (MPEF-IC 4603–4626) from the Castillo Formation, Tronador canyon, Chubut, Argentina.

Diagnosis. Specimens of Cellicalichnus composed of irregularly distributed, mostly in a plane, tear-shaped, sub-horizontal cells attached directly to inclined shafts, which rarely branch at nearly right angles. The presence of an opposite pair or whorls of cells is occasional. The diameter of shafts is similar to slightly larger than those of cells. Cells show smooth linings and passive fill.

Comments. It is an intermediate morphology between C. dakotensis and C. chubutensis. The former shows vertical main tunnels and short horizontal ones with opposite pairs of cells and the latter shows the cells arranged in dense whorls. Both the opposite pairs and the whorls of cells are occasionally present in C. krausei, only in small parts of the tunnels.

Description. The longest nest (MPEF-IC 4600) is composed of a tunnel that penetrates the substrate at an angle of 35o showing a bend that divides it in a proximal section, 17 cm long, and a distal one, 35 cm long, the latter at an angle of 140o with the previous one (Figs 1B and 3A). The tunnel is 12 mm wide and 9 mm high. Horizontal cells are distributed mostly in a plane along both sections. Besides the 18 cells preserved in the 52 cm tunnel, there are scars of 13 more cells. They are more grouped at the bottom of the tunnel. No whorl of cells is present and only two pairs of opposite cells are recorded. The other most complete nests show similar features. One of the paratypes (MPEF-IC 4601) is composed of a tunnel that penetrates the substrate at an angle of 60o showing a bend that divides it in a proximal section, 14 cm long, and a distal one, 17 cm long, the latter at an angle of 100o with the previous one. It preserves 38 cells and 7 scars. Most of the cells are distributed in the same plane, particularly in the proximal section, whereas some cells from the deeper section are located in other planes forming a few whorls (Fig 3B). The secondary tunnel, 5 cm long, 10 mm wide, and 9 mm high, branching at a right angle from the distal part of the main tunnel, preserves 3 cells in the same plane and a scar in another one. Most cells are sub-horizontal with their rears slightly inclined downwards. The proximal and distal sections of the main tunnel and the entire secondary tunnel show an inclination of about 60o. The other paratype (MPEF-IC 4602) is a short (84 mm) portion of a sloping tunnel preserving 3 cells and 2 scars on one side and 5 scars on the other, where a short (65 mm) lateral tunnel bearing two cell scars arise (Fig 1A). The main tunnel is 11 mm wide and 9–8 mm high, whereas the lateral one is 9–6 mm wide. The specimen MPEF-IC 4625 is a straight tunnel, 14 cm long, preserving 23 cells and scars of another two ones, connected to a short, 8 cm long, lateral tunnel at a right angle, preserving 6 cells (Fig 3C). The main tunnel is 13 mm wide and 10 mm high and penetrates the substrate at an angle of 30o. In the main tunnel, the cells are irregularly distributed. Most of them are in the same plane, whereas others are in different planes but without forming whorls. In the lateral tunnel, which branches at a right angle from the main one, the preserved cells are mostly distributed in a single plane. Most cells of the entire nest are sub-horizontal, but a few ones, in other planes, are more inclined. The specimen MPEF-IC 4607 is a tunnel, 96 mm long, preserving the external casts of 5 cells and a secondary tunnel, 55 mm long, with another cell. The main and lateral tunnels are 8–7 mm wide. The specimen MPEF-IC 4624 is a remnant of a nest, which shows a straight and sloping tunnel, 16 cm long, 12 mm wide, and 11 mm high, preserving 17 cells distributed in the same plane, some of them in opposite pairs. The remaining fragments of nests (MPEF-IC 4605–4606, 4608–12, 4615–16, 4618, 4623–24) are tunnels, 215–42 mm long, which preserve 10–1 cells and show the same characters as the more complete nests described above (Fig 3D). Some of them are preserved as full relief casts, whereas others are preserved as external casts in the matrix. Other samples correspond to fragments of tunnels without cells, and isolated cells (MPEF-IC 4603–4, 4613–14, 4617, 4619–22). Taking into account the most complete cells, isolated or connected to tunnels, they are tear-shaped, 24–19 mm long (n = 154), 11–9 mm wide (n = 161), 10–7 mm high (n = 171) and the neck is 8–5 mm in diameter (n = 173).

Pallichnidae Genise, 2004

Fictovichnus sciuttoi Genise et al., 2007

Examined material. Forty-eight specimens from Cerro Colorado de Galveniz hill (MPEF-IC 4627–4674) and thirty seven specimens from Tronador canyon (MPEF-IC 4675–4711), all from the Castillo Formation of Chubut, Argentina.

Description. Ellipsoid to ovoid chambers mostly preserved as internal casts horizontally to sub-horizontally oriented in the paleosol (Fig 4). The diagnostic helical surface composed of fine to rough ridges is present in 26% of the specimens (Fig 4B and 4C), whereas the diagnostic flat oval area is present in 21% of the specimens (Fig 4D). Specimens are 42–15 mm long (n = 42), 20–6 mm wide (n = 76), and 17–6 mm high (n = 67). A total of 79% of the specimens shows a flattened outline (Fig 4A).

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larger image TIFF original image Download: Fig 4. Other insect trace fossils found along with the bee nests in the Castillo Formation. Fictovichnus sciuttoi (A–D). (A) Lateral view of a specimen showing the flattened outline (MPEF-IC 4669). (B) Specimen preserving a helical surface morphology composed of fine ridges (arrow, MPEF-IC 4698). (C) Specimen showing rough ridges (arrow, MPEF-IC 4700). (D) Specimen with a flat oval area in one extreme (arrow, MPEF-IC 4683). Pallisphaera puertai isp. nov.(E–H). (E) Holotype in the matrix showing the casts of pellets (arrow, MPEF-IC 4712). (F) Paratype in the matrix showing the casts of pellets (arrow, MPEF-IC 4713). (G) Wall of a specimen attached to the matrix (MPEF-IC 4725). Note the pellets (arrow). (H) Specimen with an emergence hole (arrow, MPEF-IC 4718). Pallisphaera piriforme isp. nov. (I–K). (I) Holotype showing pellets and the lateral protuberance (MPEF-IC 4732). Note the piriform shape and the tight constriction between the two spheroids (arrow). (J) Ovoid specimen (MPEF-IC 4734, paratype). (K) Longitudinal section of a specimen showing cylindrical pellets (arrows, MPEF-IC 4824). Scale bars are 10 mm. https://doi.org/10.1371/journal.pone.0227789.g004

Coprinisphaeridae Genise, 2004

Pallisphaera Genise igen. nov. urn:lsid:zoobank.org:act:88DE2197-EFA2-447E-B31B-FFE2A50A65C7

Etymology. Derived from the Greek palla meaning ball, and sphaira meaning sphere. The combination refers to a sphere whose wall is composed of little balls (pellets).

Type ichnospecies. Pallisphaera puertai isp. nov.

Diagnosis. Spherical to sub-spherical or pear-shaped to ovoid chambers, which are surrounded by a discrete wall composed of smooth, rounded to rhomboid pellets.

Comments. It differs from Coprinisphaera because of the wall composed of pellets and the lack of an egg chamber and from Castrichnus because of the lack of concentric rings in the internal surface of the pellets and the rounded to meniscate pellets in the filling of the chambers.

Pallisphaera puertai Genise isp. nov. urn:lsid:zoobank.org:act:65DC8879-8022-470B-81E8-3DD1AF030ABA

Etymology. Dedicated to the discoverer of the first specimen and friend, Pablo Puerta.

Type material. MPEF-IC 4712 (holotype), a specimen in the matrix showing the casts of pellets in the filling (Fig 4E). MPEF-IC 4713 (paratype), another specimen similar to the holotype (Fig 4F). Both from the Castillo Formation, Cerro Colorado de Galveniz, Chubut, Argentina.

Other material. Fourteen specimens from Cerro Colorado de Galveniz hill (MPEF-IC 4714–4727) and four from Tronador canyon (MPEF-IC 4728–4731), all from the Castillo Formation of Chubut, Argentina.

Diagnosis. Spherical to sub-spherical Pallisphaera showing the wall composed of small rhomboid pellets in some cases arranged in rows parallel to the equator.

Description. Specimens are mostly preserved as spheroidal casts showing the concave casts of pellets on their surface, and separated by a thin space from the matrix that represents the wall (Fig 4E and 4F). When the wall is preserved, it is composed of rhomboid pellets (Fig 4G). The equatorial diameter is 17–10 mm (n = 17), but in some cases the outline is somewhat elliptical, being one of the axes about 1 mm larger than the other. The height is 16–10 mm (n = 10). All specimens in which it was possible to measure wide and height (n = 8) show a flattened outline, representing the height 70–90% of the width. The wall itself or the space representing it is 1–2 mm thick (n = 10). Rhomboid pellets, 2 x 1 mm, are oriented with the long axis parallel to the equator. One specimen shows on top a rounded hole, 8–9 mm in diameter, which would be compatible with an emergence hole (Fig 4H). Infillings are structureless.

Pallisphaera piriforme Genise isp. nov. urn:lsid:zoobank.org:act:CA30C2D1-92A4-46BB-914E-5F71D5A07FD0

Etymology. After its pear-shaped shape.

Type material. MPEF-IC 4732 (holotype), a complete specimen showing pellets and protuberance (Fig 4I). MPEF-IC 4733–34 (paratypes), two specimens similar to the holotype (Fig 4J). All from the Castillo Formation, Tronador canyon, Chubut, Argentina.

Other material. One hundred and ninety-three specimens from the Castillo Formation, Tronador canyon, Chubut, Argentina (MPEF-IC 4735–4927).

Diagnosis. Pear-shaped to ovoid Pallisphaera showing the wall composed of adjacent rounded to elliptical, small pellets. Specimens are vertically oriented with the thinner end facing down. Some specimens may show a lateral protuberance near the top.

Description. Specimens in situ look like inverted drops composed of two attached spheroids of different sizes. The smaller one faces down. In the more piriform specimens, the constriction between the two spheroids is tighter (Fig 4I), whereas in the ovoid ones the constriction is gentle (Fig 4J). The height is 25–13 mm (n = 140), but half of the specimens is 21–18 mm high. The equatorial diameter of the larger sphere (upper part) is 17–9 mm (n = 174), but half of the specimens is 14–13 wide. The equatorial diameter of the smaller sphere (lower part) is 12–6 mm (n = 150), but 60% of the specimens are 10–9 mm wide. The wall is 3–1.5 mm thick (n = 68) and the pellets are 2–1 mm large (n = 50). In a few specimens, the lateral outline shows an undulated pattern (Fig 4I). Pellets are cylindrical in longitudinal section, which is observable in broken and weathered walls (Fig 4K). In a few specimens, the pellets seem to be arranged in diagonal rows. About 35% of the specimens show a sub-cylindrical to rounded lateral protuberance near the top, 8–3 mm wide and 5–2 mm high (n = 16). In four specimens the wall shows a rounded discontinuity on top suggesting an emergence hole. Infillings are structureless.